BR112020021939B1 - POLAR MONOMER GRAFTED POLYPROPYLENE RESIN, METHOD FOR PREPARING A GRAFTED POLYPROPYLENE RESIN, PELLETS OR ARTICLES, COMPOSITE MATERIALS, COATING FILM MATERIALS AND BINDING MATERIALS AND USE OF THE GRAFTED POLYPROPYLENE RESIN - Google Patents

Abstract

POLAR MONOMER-GRAFTED POLYPROPYLENE RESIN, METHOD FOR PREPARING A GRAFTED POLYPROPYLENE RESIN, PELLETS OR ARTICLES, COMPOSITE MATERIALS, COATING FILM MATERIALS AND BINDING MATERIALS, AND USE OF THE GRAFTED POLYPROPYLENE RESIN. The present invention relates to the field of polypropylene graft modification, and provides a polar monomer-grafted polypropylene resin, a method of preparing the same and an application thereof. The grafted polypropylene resin according to the present invention is prepared by a grafting reaction of a polar monomer capable of absorbing microwaves so as to raise its temperature in a microwave field to more than 200°C and a solid polypropylene resin using microwave irradiation without adding an initiator. According to the present invention, the polar grafted polypropylene resin that does not contain initiator residues and does not have a significant reduction in molecular weight compared with a resin before grafting is obtained. The preparation process of the present invention is simple, easy to operate, simple in production device, low in cost, and easy for industrialization.

Description

Field of invention

[0001] The present invention relates to the technical field of polypropylene graft modification, in particular to a polar monomer grafted polypropylene resin, and a method of preparing the same and applications thereof, as well as pellets, articles, composite materials, coatable film materials, and binding materials prepared from the grafted polypropylene resin.

Background of the invention

[0002] Polypropylene is a general polymer material with a wide range of uses and has excellent physical and mechanical properties. However, due to its non-polarity and low surface energy property, polypropylene has poor compatibility with most polymer fillers, is not easily wettable and adhered, and has poor printing and coating properties, and when bonded with polar materials, it also cannot obtain materials with good performance. Therefore, some methods are needed to improve the polarity of polypropylene. A common method is to graft polar monomers such as maleic anhydride onto the polypropylene backbone to increase its polarity. The graft modification methods mainly include the solvent method, the melting method and the solid phase method.

[0003] The solvent method achieves a relatively high grafting ratio, and the temperature during the reaction process is relatively low. However, the organic solvent is generally toluene or xylene, so it is quite complicated in post-treatment, high in cost, and poor in environmental friendliness, and has been gradually abandoned in industrial production.

[0004] The melt grafting method is currently the most reasonable method and is suitable for industrialized production. For example, Chinese patent application CN104804143 A reports that a maleic anhydride grafted polypropylene with a high grafting ratio and no significant decrease in molecular weight compared with the raw polypropylene material was obtained by using a twin screw extruder having an aspect ratio greater than 48:1 and adding to a blending solution of styrene and an initiator at multiple positions in different sections of the extruder barrel. US patent 6,228,948B1 reported that with different process parameters and conditions in various sections of the twin screw extruder, polypropylene and maleic anhydride were added to the extruder, and after they were melted, an initiator was added, and maleic anhydride was reacted and grafted onto the polypropylene molecular chain, thus the polypropylene having a grafting ratio above 2% and having good general properties was obtained. Chinese patent application CN102924661A reported that the use of auxiliary monomers could increase the grafting ratio of polypropylene and inhibit the degradation of polypropylene, and at the same time, a new initiator was used to reduce the irritating odor of maleic anhydride grafted polypropylene, and this initiator could also increase the grafting reaction rate and the copolymerization degree with the auxiliary monomers, thus to obtain a maleic anhydride grafted polypropylene having a high grafting ratio and low irritating odor.

[0005] However, the β-chain scission reaction during the melt grafting of polypropylene is an inevitable side reaction during the grafting process. Therefore, the melt index of the maleic anhydride-grafted polypropylene product prepared by the melt grafting method is usually very high, that is, the molecular weight is greatly reduced, which will cause the mechanical properties of the polypropylene product to deteriorate. Therefore, the main problem facing the melt grafting method is how to obtain a sufficiently high grafting ratio of maleic anhydride while maintaining the mechanical properties of the polypropylene matrix, that is, keeping the molecular weight substantially unchanged, so that when blended with other materials, the final overall mechanical properties of the material will not be affected. The traditional solid phase method refers to the graft copolymerization reaction carried out by mixing polypropylene with monomers, initiators, tensides, etc. The reaction temperature is low (100 to 140°C), and polypropylene (having a melting point of about 164 to 171°C) is still in the form of solid particles at the reaction temperature. Therefore, this method is called the solid phase grafting method. In the solid phase method, the reaction proceeds on an exposed polypropylene surface. Chinese patent application CN1283642 A describes a process for preparing a solid phase graft copolymer of polypropylene and three monomers and applications thereof, wherein polypropylene, an initiator and three monomers were charged into a reactor in proportions, and xylene tensides were added for the solid phase grafting reaction under a nitrogen atmosphere. Chinese patent application CN103102455A describes a method for grafting polypropylene, wherein polypropylene, an organic acid (or salt) and a surfactant were added to a stirred reactor, and an initiator was added after the reaction temperature was reached, thereby performing the solid phase grafting reaction, wherein the initiator was wax-encapsulated peroxide microcapsules. Chinese patent application CN1704436A describes a process for preparing continuous solid phase grafting of polypropylene and a device thereof. US patent application 5,585,435 A describes a production method for modifying solid phase grafting of polypropylene in a fluidized bed. Both of these techniques achieve a high grafting ratio by improving the contact efficiency of the reactants and initiators.

[0006] The existing polypropylene graft modification methods all have the following shortcomings: graft modification indicates a decrease in molecular weight, there are monomers left in the products, initiators need to be used in the modification process, the products have odors or special equipment is needed, etc. Due to the wide applications of polar polypropylene and the great market demand, a grafted polypropylene that is economical, simple in preparation method and does not have the above shortcomings has become an urgent problem to be solved. In order to solve the above problem, the present invention is proposed.

Description

[0007] The object of the present invention is the provision of a polar monomer grafted polypropylene resin prepared by microwave initiation and a preparation method thereof, which do not have the deficiencies of existing grafted polypropylene resins and polypropylene graft modification methods. The grafted polypropylene resin product has no initiator residues, has a molecular weight that is not significantly reduced after grafting, and involves a greatly reduced b-chain scission reaction during its preparation process.

[0008] Another object of the present invention is the provision of a polar monomer grafted polypropylene resin, which can achieve a relatively high grafting ratio.

[0009] Another object of the present invention is the provision of a polar monomer grafted polypropylene resin that does not contain residual unreacted monomers or auxiliary graft monomers.

[0010] Another object of the present invention is the provision of a method for preparing a polar grafted polypropylene resin, which is simple in process, easy to operate, simple in production equipment, low cost and can be easily industrialized.

[0011] According to the present invention, it was unexpectedly discovered that the above object was achieved by utilizing selective microwave heating properties and the grafting reaction of polar monomers, which are capable of absorbing microwaves so as to increase their temperature in the microwave field to more than 200°C, and a solid polypropylene resin under microwave irradiation without adding an initiator.

[0012] Thus, in a first aspect, the present invention provides a polypropylene resin grafted with polar monomer, wherein the grafted polypropylene resin does not contain initiator residues, and the polar monomers are capable of absorbing microwaves so as to increase their temperature in the microwave field to greater than 200°C.

[0013] The term “microwave” as used herein refers to electromagnetic waves having a frequency of 300 MHz-300GHz.

[0014] The term “polar monomer” as used herein refers to monomers containing oxygen, sulfur, nitrogen, halogen and other heteroatoms, or substituents thereof. The polar monomers that can be used in the present invention are capable of absorbing microwaves so as to increase their temperature in the microwave field to more than 200°C.

[0015] The polar monomers that can be used can be determined by the following measurement method:

[0016] The polar monomers are loaded into a 10 ml glass vial until the volume of the polar monomers accounts for 2/3 of the volume of the glass vial. Then, a thermocoupler is inserted into the glass vial loaded with the polar monomers, the glass vial together with the thermocoupler is placed in a microwave oven, the microwave is turned on, the temperature of the polar monomer under microwave irradiation is tested, and the polar monomers with the temperature exceeding 200°C under any power and time period can be used as the polar monomers in the present invention. Specifically, for example, under the condition of irradiation with a microwave having a power of 700 W for 30 minutes, the polar monomers tested to have a temperature increased to more than 200°C can be used in the present invention.

[0017] For example, the polar monomer may be selected from those polar monomers containing a carbon-carbon double bond, for example, those polar monomers containing a heteroatom selected from the group consisting of oxygen, sulfur, nitrogen, and halogen, and combinations thereof or a substituent thereof, and containing a carbon-carbon double bond.

[0018] Preferably, the polar monomer may be selected from the group consisting of organic acids, organic acid derivatives (such as anhydrides, esters, salts) and combinations thereof, preferably selected from the group consisting of maleic anhydrides, maleic anhydride derivatives, (meth)acrylic acids, (meth)acrylic acid derivatives (such as glycidyl methacrylate), vinyl acetate, alkenyl sulfonic acids and derivatives thereof, p-styryl formic acid, p-styryl acetic acid, itaconic acid, oleic acid, arachidonic acid and combinations thereof and salt forms thereof. (Meth)acrylic acids include acrylic acids, methacrylic acids and mixtures thereof.

[0019] The polar monomer is preferably one or more selected from the group consisting of maleic anhydride, maleic anhydride derivative, (meth)acrylic acids, (meth)acrylic acid derivatives (such as glycidyl methacrylate) and vinyl acetates, preferably maleic anhydride, maleic anhydride derivatives, (meth)acrylic acids, (meth)acrylic acid derivatives, and most preferably maleic anhydride, and salt forms thereof.

[0020] As used herein, the term “initiator” refers to a substance commonly used in the art to initiate the polymerization reaction (including grafting reaction) of monomers, such as free radical initiators, including peroxide initiators, azo initiators, and Redox initiators, etc. Peroxide initiators can in turn be divided into organic peroxide initiators (such as dicumyl peroxide) and inorganic peroxide initiators.

[0021] In the grafted polypropylene resin according to the present invention, the grafting ratio may be 0.01%-8%, preferably 0.01%-6%. There are side groups of polar monomers on the main chain of polypropylene molecules, such as side groups of an organic acid or salt thereof. The grafting ratio of the side groups of an organic acid may be 0.01%-8%, preferably 0.01%-6%, more preferably 0.01%-3%, and most preferably 0.01%-1.2%. For an organic acid salt grafted polypropylene resin, there are side groups of the organic acid salt on the main chain of the polypropylene molecules, and the grafting ratio of the side groups of the organic acid salt can be 0.01%-8%, preferably 0.01%-6%, more preferably 0.01%-3%, and most preferably 0.01%-1.2%.

[0022] The side groups of the organic acid salt may comprise at least one selected from the group consisting of the side groups of maleic anhydrides, side groups of maleic anhydride derivatives, side groups of (meth)acrylic acids, side groups of (meth)acrylic acid derivatives (such as glycidyl methacrylate side groups), and side groups of vinyl acetates after formation of the salt.

[0023] Here, the grafting ratio of the polar monomers is characterized by infrared spectroscopy.

[0024] The water contact angle value of the grafted polypropylene resin according to the present invention may be less than 90°, preferably less than 65°, as measured on a film prepared from the grafted polypropylene resin by a solution method. For example, for an organic acid-grafted polypropylene resin, after a film is formed by a solution method, the water contact angle value of the side of the film containing the organic acid groups is less than 90°, preferably less than 65°. For an organic acid salt-grafted polypropylene resin, after a film is formed by the solution method, the water contact angle value of the side of the film containing the organic acid salt groups is less than 90°, preferably 50°-0°, and more preferably 0°.

[0025] Here, the water contact angle is measured by the following method: the grafted polypropylene resin is prepared into a film by the solution method, and the side of the obtained film containing the side groups of the polar monomers is measured for the water contact angle with a water contact angle measuring instrument.

[0026] The melt index of the grafted polypropylene resin according to the present invention is preferably less than or equal to the melt index of the polypropylene resin as the grafting base, that is to say, its melt index is less than or equal to the melt index of the raw material per se before grafting the polypropylene resin. In the process of preparing the polar monomer grafted polypropylene resin of the present invention, the β-chain scission reaction of the polypropylene is controlled, the phenomenon of decrease in the molecular weight of the polypropylene will not occur, and the melt index of the grafted polypropylene can be kept consistent with that of the raw material polypropylene or even decreased.

[0027] Here, the melt index is measured according to the GB/T3682-2000 standard.

[0028] The term “polypropylene” or “polypropylene resin” as used herein includes homopolymers and copolymers of propylene and mixtures thereof.

[0029] The polypropylene resin used as the graft base may be selected from the group consisting of propylene homopolymers and propylene copolymers and mixtures thereof, preferably propylene random copolymers. For example, the comonomer in the propylene random copolymer may be selected from the group consisting of ethylene, α-olefins other than propylene, and combinations thereof, preferably ethylene, C4, C5, C6 to C8 α-olefins, and combinations thereof. More preferably, the propylene random copolymer comprises only ethylene or an α-olefin other than propylene as the comonomer.

[0030] The polypropylene resin as the graft base may also be an impact polypropylene resin, which comprises a rubber phase in addition to a propylene homopolymer. The rubber phase may be a copolymer formed by propylene and at least one selected from the group consisting of ethylene and α-olefins, preferably ethylene, α-olefins C4, C5, C6 to C8 as the comonomer. Preferably, the rubber phase of the impact polypropylene resin is formed by polymerizing propylene and ethylene or an α-olefin in addition to propylene.

[0031] The polypropylene resin used as the graft base may be in a solid form including powders, pellets or articles, preferably polypropylene powders obtained by polymerization using a spherical catalyst.

[0032] Method for preparing a polar monomer grafted polypropylene resin.

[0033] In a second aspect, the present invention further provides a method for preparing a polar monomer grafted polypropylene resin according to the present invention, comprising the step of subjecting the polar monomer and the solid polypropylene resin to a grafting reaction under microwave irradiation without the addition of an initiator. During the grafting reaction, it is also possible not to use auxiliary grafting monomers.

[0034] In the method of the present invention, the amount of the polar monomer may be 0.1-10 wt%, preferably 1-8 wt% based on the weight of the solid polypropylene resin used as the raw material.

[0035] The polar monomer may be in liquid form or in solution form. If the polar monomer itself is liquid at room temperature, the polar monomer alone may be used; in other cases, the polar monomer may be dissolved in a solvent to obtain a solution for use. The solvent may be at least one selected from the group consisting of organic solvents such as alcohols, ketones, esters, and water, preferably acetone or ethanol.

[0036] The solid polypropylene resin as the graft base can be used in the form of powders, pellets or articles.

[0037] Specifically, the method may comprise the following steps: (1) sufficiently mixing the polar monomer with the solid polypropylene resin; and (2) subjecting the mixture obtained in step (1) to microwave irradiation, preferably under an inert gas atmosphere.

[0038] In step (1), the polar monomer and the solid polypropylene resin can be sufficiently mixed under vacuum. For example, the solid polypropylene resin can be sufficiently mixed with the polar monomer solution under vacuum. The vacuum more than sufficiently facilitates the mixing of polar monomer and polypropylene resin, especially for the polypropylene resin with pores, it promotes the entry of the graft monomer into the pores of the polypropylene resin and is more favorable for the grafting reaction.

[0039] In step (2), the inert gas may be one or more selected from the group consisting of nitrogen, helium and argon.

[0040] If the polar monomer is in the form of a solution dissolved in a solvent, the mixture obtained in step (1) is dried to remove the solvent before step (2).

[0041] If desired, the irradiated mixture obtained in step (2) is washed to remove unreacted polar monomers and dried. The solvent used for washing may be at least one selected from the group consisting of organic solvents, such as alcohols, ketones and esters, and water, and is preferably water.

[0042] More specifically, the method of the present invention may comprise the steps of: (1’) dissolving the polar monomer in a solvent to obtain a solution of the polar monomer; (1) mixing the solid polypropylene resin with the solution of the polar monomer obtained in step (1’) sufficiently, followed by drying treatment; (2) subjecting the mixture obtained in step (1) to microwave irradiation, preferably under an inert gas atmosphere; (3) washing the irradiated mixture obtained in step (2) with a solvent to remove unreacted polar monomer, and carrying out drying treatment to obtain a polar monomer-grafted polypropylene resin. The solvents in step (1’) above and step (3) may be at least one selected from the group consisting of water and organic solvents, and the two of them may be the same or different from each other.

[0043] The amount of the solvent used in step (1’) above only needs to be capable of dissolving the polar monomer to form a solution, preferably the amount of the polar monomer solution obtained is such that the solid polypropylene resin used as the raw material can be completely immersed so as to facilitate sufficient mixing of the two. Generally, the weight ratio of the polar monomer to the solvent can be in the range of (0.1-100):100, preferably (0.5-50):100, and more preferably (1-30):100.

[0044] Furthermore, the method of the present invention may further comprise step (4) on the basis of the above steps: - subjecting the product obtained in step (3), optionally with addition of an additive, to melt pelletization by extrusion, to obtain pellets of the grafted polypropylene resin, to obtain pellets of the grafted polypropylene resin.

[0045] In the method according to the present invention, the solid polypropylene resin as the raw material is preferably free of an antioxidant. The solid polypropylene resin in step (1) is preferably a polypropylene resin such as powders without the addition of an antioxidant. Generally, the raw material polypropylene resin in the prior art comprises a certain antioxidant, which is added during the extrusion melt pelletizing of the polypropylene powder obtained after the polymerization reaction. The solid polypropylene resin or powder in the present invention is preferably a polypropylene resin or powder which is obtained by polymerization and has not been subjected to extrusion melt pelletizing. At this period, the solid resin or powder is free of an antioxidant. Antioxidants tend to consume free radicals in the subsequent grafting modification, so the use of the polypropylene resin without the addition of an antioxidant achieves better grafting effect.

[0046] The solid polypropylene resin used in the method according to the present invention may be at least one of several common types of solid or powdered polypropylene resins in the prior art, such as homopolymerized polypropylenes, random copolymerized polypropylenes, and impact copolymerized polypropylenes.

[0047] The polymerization process of the solid polypropylene resin in the present invention is known in the art. The solid polypropylene resin of the present invention is preferably a polypropylene powder obtained by polymerization using a spherical catalyst. The particles of the polypropylene powder obtained by polymerization by a spherical catalyst are spherical and the particles have many pores on the surface. Therefore, such a polypropylene powder has a large specific surface area and a large contact area with the polar monomer, which helps to obtain a grafting product having a larger grafting ratio.

[0048] When the polypropylene resin of the present invention is a random copolymerized polypropylene, the comonomer of the random copolymerized polypropylene comprises at least one of ethylene or α-olefin comonomer other than propylene; preferably ethylene, C4 α-olefin, C5 α-olefin, and C6 α-olefin to C8 α-olefin, more preferably ethylene, 1-butene, 1-heptene, 1-hexene, and 1-octene, and even more preferably, ethylene and C4 α-olefin, even more preferably ethylene and 1-butene, most preferably ethylene. The comonomer may comprise a mixture of the above ethylene and/or α-olefin comonomers other than propylene, preferably ethylene alone or an α-olefin monomer, in a more preferred embodiment the random copolymerized propylene comprises propylene and ethylene alone.

[0049] When the solid polypropylene resin of the present invention is impact copolymerized polypropylene, the impact copolymerized polypropylene comprises a rubber phase in addition to a propylene homopolymer. The rubber phase is formed by the polymerization of propylene and a comonomer. The comonomer is at least one of ethylene or α-olefin other than propylene, preferably ethylene, C4 α-olefin, C5 α-olefin, and C6 α-olefin to C8 α-olefin, more preferably ethylene, 1-butene, 1-heptene, 1-hexene, and 1-octene, even more preferably ethylene and C4 α-olefin, even more preferably ethylene and 1-butene, and most preferably ethylene. The rubber phase of the impact copolymerized polypropylene is preferably formed by polymerization of propylene and ethylene or an α-olefin in addition to propylene; in a more preferred embodiment, the rubber phase only comprises a copolymer of propylene and ethylene.

[0050] The polar monomers that can be used in step (1) are as described above.

[0051] In step (1), various mixing methods known in the prior art can be used to sufficiently mix the polar monomer and the solid polypropylene resin, and it is preferably to use common stirring methods and stirring equipment. Among others, the stirring equipment can be conventional stirring device such as magnetic stirring device and mechanical stirring device.

[0052] Drying in step (1) above may use various conventional drying methods known in the art, including, but not limited to, for example, blast drying, room temperature drying, and the like. The preferred drying temperature is a temperature at which the polypropylene does not melt, for example, not more than 160°C.

[0053] The irradiation powder of the microwave irradiation in step (2) may be 100w-2000w, preferably 500-1000w, and more preferably 600w-800w; the irradiation time may be 1s-120min, preferably 1min-30min, and more preferably 3min-10min. The microwave irradiation may be carried out by using various microwave reactors existing in the prior art.

[0054] The inert gas in step (2) may comprise one or more of nitrogen, helium, and argon, preferably nitrogen.

[0055] The solvent in step (3) may comprise at least one of alcohols, ketones, esters and water, preferably water.

[0056] In step (3), washing of the irradiated mixture is not particularly limited, as long as residual polar monomers (such as organic acid) can be removed, and common washing methods can be used. For example, after microwave irradiation, at a high temperature, the solvent having a volume exceeding the solid polypropylene resin is immediately used for soaking for a certain period of time (such as 5-15 minutes), and then redundant solvent or water is removed by a filtering device; soaking and filtering are repeated multiple times (such as 2-6 times), thus a clean solid polypropylene resin is obtained. Drying in step (3) is the same as that in step (1), and various conventional drying methods in the prior art can be used, including but not limited to jet drying, room temperature drying, and the like. The preferred drying temperature is a temperature at which polypropylene does not melt, for example, not more than 160°C.

[0057] For melt extrusion pelletizing in step (4), a melt extrusion equipment common in plastic processing is used to pass the polar monomer grafted polypropylene resin through the conventional melt extrusion equipment for melt extrusion pelletizing to thereby obtain polar monomer grafted polypropylene resin pellets. The useful additives are those commonly used in the field of rubber and plastic processing, such as antioxidants, plasticizers, lubricants, release agents (calcium stearate), etc.

[0058] In the preparation process, the mixing temperatures of the materials is a common processing temperature for the polypropylene resin and is selected within the range that not only ensures the complete melting of the polypropylene resin, but also does not cause its decomposition. In addition, according to the processing requirements, common auxiliaries for polypropylene, such as antioxidants and plasticizers, can be added in a common amount to the polar monomer grafted polypropylene resin.

[0059] The method for preparing an organic acid salt grafted polypropylene resin.

[0060] In order to prepare an organic acid grafted polypropylene resin, an organic acid or its derivative (such as anhydride or ester) and a solid polypropylene resin (such as powders) can be subjected to microwave irradiation for grafting reaction to obtain a grafted product, then the grafted product is reacted with a base (such as hydroxide). The term “organic acid grafted polypropylene” or “organic acid grafted solid polypropylene resin” herein includes polypropylenes or solid polypropylene resins with an organic acid or its anhydride or ester.

[0061] Preferably, an organic acid grafted polypropylene powder and an aqueous solution of a base are sufficiently mixed to react under vacuum, and optionally a solvent is used for washing to remove unreacted base and drying treatment is carried out, to thereby obtain an organic acid salt grafted polypropylene resin.

[0062] The base may be a hydroxide, preferably selected from the group consisting of ammonia and metal hydroxides such as sodium hydroxide, potassium hydroxide, barium hydroxide, lithium hydroxide, strontium hydroxide, calcium hydroxide, iron hydroxide, and ferrous hydroxide, zinc hydroxide, magnesium hydroxide, cobalt hydroxide, gold hydroxide, aluminum hydroxide, copper hydroxide, beryllium hydroxide, and rare earth hydroxide, and preferably is selected from the group consisting of sodium hydroxide, potassium hydroxide, barium hydroxide, lithium hydroxide, strontium hydroxide, calcium hydroxide, and combinations thereof.

[0063] Specifically, the method for preparing an organic acid salt grafted polypropylene resin may comprise the following steps: (1’) dissolving an organic acid or its derivative monomer in a solvent to obtain a solution of the organic acid or its derivative monomer, and dissolving a base (such as a hydroxide) in a solvent (such as water) to obtain an alkaline solution (preferably an aqueous solution); (1) sufficiently mixing a solid polypropylene resin (such as powder) with the solution of the organic acid or its derivative monomer obtained in step (1’), and then performing drying treatment; (2) subjecting the mixture obtained in step (1) to microwave irradiation, preferably under an inert gas atmosphere; (3) washing the irradiated mixture obtained in step (2) with a solvent to remove unreacted organic acid or its derivative monomer, and performing drying treatment to obtain a solid organic acid grafted polypropylene resin; (4) sufficiently mixing the organic acid-grafted solid polypropylene resin obtained in step (3) with the alkali solution prepared in step (1’) under vacuum to react; (5) washing the reaction mixture obtained in step (4) with a solvent to remove the base that has not been reacted with the organic acid-grafted solid polypropylene resin, and carrying out drying treatment to obtain an organic acid salt-grafted solid polypropylene resin.

[0064] The above solvent is at least one of the group consisting of water and organic solvents, and among the solvents in step (1’), step (3), and step (5), at least two are the same or they are all different from each other.

[0065] The hydroxide in step (1’) may be one or more of the group consisting of ammonia and metal hydroxides, preferably sodium hydroxide, potassium hydroxide, barium hydroxide, lithium hydroxide, strontium hydroxide, calcium hydroxide, iron hydroxide, ferrous hydroxide, zinc hydroxide, magnesium hydroxide, cobalt hydroxide, gold hydroxide, aluminum hydroxide, copper hydroxide, beryllium hydroxide, and rare earth hydroxide, more preferably sodium hydroxide, potassium hydroxide, barium hydroxide, lithium hydroxide, strontium hydroxide, calcium hydroxide, and most preferably sodium hydroxide, potassium hydroxide, and calcium hydroxide. Sodium hydroxide is most preferred.

[0066] The amount of solvent used for the organic acid or its derived monomer in step (1’) is as described above for the solvent for the polar monomer.

[0067] The amount of the solvent (preferably water) used to dissolve a base in step (1’) is only required to be capable of dissolving the base, such as hydroxide, to form a solution. Preferably, the amount of the alkaline solution obtained is such that the solid polypropylene resin grafted with organic acid can be completely immersed, so as to be more favorable for sufficient mixing and reacting of the two. Generally, the weight ratio of the solvent (preferably water) to the base (such as hydroxide) can be (0.1-100):100, preferably (0.5-50):100, more preferably (1-30):100. The amount of the base (such as hydroxide) can be 0.1-10% by weight, preferably 1-8% by weight, based on the weight of the raw material polypropylene resin used.

[0068] In this method, the drying treatment in step (1), step (3) and step (5) may adopt various conventional drying methods in the state of the art including, but not limited to, air jet drying, room temperature drying and the like. The preferred drying temperature is a temperature at which polypropylene does not melt, for example, not more than 160°C.

[0069] In step (4), various mixing methods in the prior art can be used to sufficiently mix the organic acid-grafted solid polypropylene resin and the alkali solution, preferably, common stirring ways and common stirring equipment are used. Among others, the stirring equipment can be conventional stirring device such as magnetic stirring device and mechanical stirring device.

[0070] In step (4), the alkali solution and the organic acid grafted solid polypropylene resin are sufficiently mixed and reacted at the same time. There is no special requirement for the reaction time, as long as the reaction proceeds sufficiently. Generally, after the addition of the alkali solution is completed, mixing is further carried out and at the same time, the reaction proceeds for a period of time, for example, 1-20 minutes, preferably 2-8 minutes. The reaction temperature and pressure are not limited and are generally normal temperature and normal pressure.

[0071] The solvent in step (5) is the same as or different from the solvent in step (3), and includes at least one of alcohol, ketone, esters, and water, preferably water. In step (5), washing of the reaction mixture after the mixing reaction is not particularly limited, as long as the residual base can be removed, and a common washing method can be used. For example, the solvent having a volume exceeding the solid polypropylene resin (such as polypropylene powder) is used for immersion for a certain period of time (such as 5-15 minutes) at a high temperature immediately after microwave irradiation, and then the redundant solvent or water is removed by a filtering device; the immersion and filtering are repeated multiple times (such as 2-6 times), thereby obtaining a clean solid polypropylene resin.

[0072] The method further preferably comprises subjecting the powder obtained in the above step (5), optionally with addition of an additive, to melt extrusion pelletizing to obtain organic acid salt grafted polypropylene resin pellets. Here, for melt extrusion pelletizing, a melt extrusion equipment common in plastic processing is used to pass the organic acid salt grafted polypropylene powder through the conventional melt extrusion equipment for melt extrusion pelletizing, and thereby prepare organic acid salt grafted polypropylene resin pellets. The additives used are those commonly used in the rubber field and plastic processing field, such as antioxidants, plasticizers, lubricants, release agents (calcium stearate), etc.

[0073] In the preparation process, the mixing temperature of the materials is a common processing temperature for polypropylene resin, and is selected within the range that not only ensures the complete melting of the polypropylene resin, but also does not cause its decomposition. In addition, according to the processing needs, common auxiliaries for polypropylene, such as antioxidants and plasticizers, can be added in a common amount to the organic acid salt grafted polypropylene powder.

[0074] Preparation method using an inorganic microwave absorbing medium.

[0075] In one embodiment of the preparation method according to the present invention, an inorganic microwave absorbing medium may be used.

[0076] An inorganic microwave absorbing medium may be added prior to microwave irradiation. The amount of the inorganic microwave absorbing medium may be 0.1-10% by weight, preferably 1-8% by weight, based on the weight of the solid polypropylene resin.

[0077] As the inorganic microwave absorbing medium, various inorganic substances in the prior art, which can absorb microwaves, can be used. For example, the inorganic microwave absorbing medium can be selected from the group consisting of metal hydroxides, preferably potassium hydroxide, barium hydroxide, sodium hydroxide, lithium hydroxide, strontium hydroxide, calcium hydroxide, iron hydroxide, ferrous hydroxide, zinc hydroxide, magnesium hydroxide, cobalt hydroxide, gold hydroxide, aluminum hydroxide, copper hydroxide, beryllium hydroxide, and rare earth hydroxide; metal salts, preferably ammonium nitrate, potassium nitrate, sodium nitrate, barium nitrate, calcium nitrate, magnesium nitrate, aluminum nitrate, manganese nitrate, zinc nitrate, iron nitrate, ferrous nitrate, copper nitrate, silver nitrate, ammonium chloride, potassium chloride, sodium chloride, barium chloride, calcium chloride, magnesium chloride, aluminum chloride, manganese chloride, zinc chloride, iron chloride, ferrous chloride, copper chloride, ammonium sulfate, potassium sulfate, sodium sulfate, calcium sulfate, ferrous sulfate, copper sulfate, silver sulfate, ammonium carbonate, potassium carbonate, sodium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, potassium dihydrogen phosphate, barium titanates, strontium titanates, and copper-calcium titanates, metal oxides, preferably ferric oxide, and ferric oxide ferroferric; graphite materials, preferably carbon black, graphite powder, graphene oxide and its reduction products (the reducing agent being, for example, ascorbic acid), graphene, carbon nanotubes, and activated carbon; ferroelectric materials, electrolysis stone, chalcopyrite, and combinations thereof.

[0078] A polar monomer (optionally dissolved in a solvent), an inorganic microwave absorbing medium (optionally dissolved or dispersed in a solvent) and a solid polypropylene resin may be sufficiently mixed prior to microwave irradiation. Two of the polar monomers, the inorganic microwave absorbing medium and the solid polypropylene resin may be mixed first, and then mixed with the remainder, or the three may be mixed together. The mixing process is preferably carried out under vacuum condition.

[0079] The mixing process can be carried out by various mixing methods commonly used in the prior art, and by common stirring ways and stirring equipment such as mechanical mixing stirrer, centrifugal mixer and magnetic mixing stirrer, so that the polar monomer is sufficiently dissolved in the solvent, the microwave absorption medium can be sufficiently and stably dissolved or dispersed in the solvent, and the mixed substances are sufficiently mixed.

[0080] In one embodiment, the polypropylene resin is first mixed with a polar monomer optionally dissolved in a solvent, and then the resulting mixture is mixed with an inorganic microwave absorbing medium optionally dissolved or dispersed in a solvent.

[0081] The solvent used to dissolve the polar monomer and the solvent used to dissolve or disperse the inorganic microwave absorption medium may be the same or different and are preferably selected from the group consisting of water and organic solvents (such as alcohol, ketones, esters). The solvent used to dissolve the polar monomer may be at least one selected from the group consisting of alcohols, ketones, esters and water, preferably acetone or ethanol. The solvent used to dissolve or disperse the inorganic microwave absorption medium may be at least one selected from the group consisting of alcohols, ketones, esters and water, preferably water.

[0082] The amount of the solvent used to dissolve or disperse the microwave absorption medium only needs to be able to dissolve the microwave absorption medium to form a microwave absorption medium solution, or to disperse the microwave absorption medium sufficiently and uniformly. Preferably, the amount of the microwave absorption medium solution or dispersion as obtained can be completely immersed in the mixture of the polar monomer and the polypropylene resin, so as to be more convenient for sufficient mixing and reaction of the three. Generally, the weight ratio of the solvent to the microwave absorption medium in the microwave absorption medium solution or dispersion can be (0.1-100):100, preferably (0.5-50):100, more preferably (1-30):100.

[0083] In order to ensure that the microwave absorption medium can form a stable and sufficiently dispersed dispersion with the solvent, a common surfactant in the prior art can be added to the dispersion of the microwave absorption medium. Generally, surfactants such as polyoxyethylene type and polyol type can be used, and the amount is generally 0.1-100% by weight of the inorganic microwave absorption medium.

[0084] Preferably, the drying treatment may be carried out after the above mixing to remove the solvent in the mixture prior to microwave irradiation. The microwave absorbing medium may be removed by washing with a solvent after grafting by irradiation. The solvent for washing is at least one selected from the group consisting of water and organic solvents, preferably at least one selected from the group consisting of alcohols, ketones, esters and water, and preferably water.

Additional products and applications

[0085] In a third aspect of the present invention, the present invention further provides pellets or articles, which are obtained from the grafted polypropylene resin according to the present invention, optionally with addition of an additive, through melt extrusion pelletizing or an additional molding process. The useful additive are those commonly used in rubber and plastic processing field, such as antioxidants, plasticizers, lubricants, mold release agents (calcium stearate), etc.

[0086] In a fourth aspect of the present invention, the present invention provides composite materials, coatable film materials and bonding materials, which can be obtained by mixing the grafted polypropylene resin of the present invention with other polymers. The composite material is, for example, an inorganic substance-filled polyolefin composite material and a glass fiber reinforced polyolefin composite material.

[0087] In a fifth aspect of the present invention, the present invention further provides the use of grafted polypropylene resin of the present invention for modifying plastics.

[0088] The polar monomer grafted polypropylene resin of the present invention can be widely used in plastic modification including but not limited to mixing the polar monomer grafted polypropylene resin (pellets or powders) with other polymers to prepare composite materials, coatable film materials and bonding materials, etc. Specifically, in plastic modification, the polar monomer grafted polypropylene resin of the present invention can be used as a compatibilizer when polypropylene is bonded and combined with other polymers; for example, in materials such as inorganic substance filled polyolefin composite materials, glass fiber reinforced polyolefin composite materials, coatable film materials and bonding materials, and can improve the interfacial interaction between the inorganic materials or other components and the polypropylene resin, so that the resulting material has excellent overall properties and can be applied in automobiles, tools, and construction engineering and other fields.

[0089] In the present invention, by utilizing the selective microwave heating feature, the polar monomer and the solid polypropylene resin are subjected to a grafting reaction using microwave irradiation without the addition of an initiator, so as to prepare a polar monomer-grafted polypropylene resin without initiator residue and without significant reduction in molecular weight. Without being bound by any theory, the applicant believes that the solid polypropylene resin (such as powder) is microwave transparent in a microwave medium (it absorbs little or no microwaves under microwave irradiation, so it does not generate heat under microwave irradiation), while the polar monomer used in the present invention can absorb microwaves, so that its temperature in the microwave field increases by 200°C, and so that an increased temperature can cause dehydrogenation of the tertiary carbon atom in the polypropylene molecular chain near the polar monomer to thereby generate free radicals, and so that the free radicals further initiate the reaction of the monomer to thereby graft onto the polypropylene chain; the increased temperature is close to the melting point of polypropylene and will not lead to chain scission of polypropylene, thus leading to the grafting reaction but not to the chain scission reaction of polypropylene; The said microwave grafting reaction can greatly avoid the β-chain scission reaction of polypropylene during melt grafting, does not reduce the molecular weight of polypropylene, and maintains excellent mechanical properties of the articles. Since no initiator is added in the method of the present invention, the grafted polypropylene resin as obtained will not comprise any initiator residue, thereby avoiding the side effects of the initiator residue on the properties and subsequent processing of the product, and further avoid the large amount of polypropylene β-chain scission reactions caused by the addition of an initiator, as well as the resulting increase in the melt index of polypropylene and the corresponding decrease in molecular weight, and avoid the possible competition between the grafting reaction and the self-polymerization reaction under the circumstance of the addition of an initiator, thereby increasing the grafting ratio.

[0090] In the case of an organic acid grafted polypropylene, further reacting it with a base (such as a metal hydroxide) can convert the organic acid grafted polypropylene into an organic acid salt grafted polypropylene, which will further improve the polarity of the grafted polypropylene.

[0091] In the preferred case of adding a microwave absorbing medium, the grafting ratio of the polar monomer can be increased. Due to the selective heating of the microwaves, the inorganic microwave absorbing medium is heated so that its temperature is increased in the microwave medium, thereby promoting the rapid increase of the temperature of the polar monomer to near above 200°C, and thus more effectively starting the grafting reaction without occurrence of the chain scission reaction, so that an efficient grafting reaction can be carried out in a short period of time and a polar polypropylene having a relatively high grafting ratio can be obtained.

[0092] In addition, since in the preferred case, no auxiliary grafting monomer is added and the unreacted polar monomer and base (such as hydroxide) can be completely removed, it is possibly possible to obtain a grafted polypropylene having a high polarity without significant decrease in molecular weight, without residual monomer, without initiator residue, and without color and odor.

[0093] The preparation process of the present invention is simple, easy to operate, simple in production equipment, low in cost and easy to be industrialized.

Description of drawings

[0094] Figure 1 shows the infrared spectrum of the maleic anhydride-grafted polypropylene samples prepared in Examples 1 and 2 according to the present invention, wherein curve a is the curve of a pure polypropylene powder, curve b is the curve of the maleic anhydride-grafted polypropylene obtained after microwave irradiation for 3 minutes in Example 1, and curve c is the curve of the maleic anhydride-grafted polypropylene obtained after microwave irradiation for 5 minutes in Example 2.

[0095] For organic acid grafted polypropylene, the monomer is grafted into the polypropylene molecular chain in the form of anhydride. After washing with water, part of the anhydride groups are open rings within the acid, and part of them are still anhydride. It can be seen from Figure 1 that the polypropylene samples after completing the entire grafting have both anhydride groups and carboxylic acid groups, and the extension of microwave time helps to increase the grafting ratio.

[0096] Figure 2 shows the infrared spectrum of the organic acid salt grafted polypropylene samples prepared in Examples S1 and S2 according to the present invention, wherein curve a is the curve of a pure polypropylene powder, curve b is the curve of the organic acid salt grafted polypropylene obtained after microwave irradiation for 3 minutes in Example S1, and curve c is the curve of the organic acid salt grafted polypropylene after microwave irradiation for 5 minutes in Examples S2.

[0097] For the polypropylene grafted with organic acid salt, there is only one acid salt peak. That is to say, due to this time, the anhydride or acid grafted to the polypropylene molecular chain are all salted out and can become the acid salt peak. It can be seen from the infrared spectrum of Figure 2 that the grafted polypropylene samples after completing the grafting and reaction with all the hydroxide having carboxylic acid groups, and the extension of microwave time helps to increase the grafting ratio.

Examples

[0098] In the following, the present invention is further illustrated with reference to examples. However, the scope of protection of the invention is not intended to be limited by these examples, while the scope of the present invention is represented in the appended claims.

[0099] The experimental data in the examples and comparative examples were determined with the following instruments and measurement equipment and methods: (1) The melt index of the resin in the examples and comparative examples was determined with reference to the GB/T3682-2000 standard. (2) The instrument for measuring the water contact angle in the examples and comparative examples: German EASYDROP contact angle tester.

[0100] The method for preparing samples for measuring the contact angle of the resin was as follows: 4g of the resin was dissolved in 40ml of xylene (AR analytical reagent), the resin was sufficiently dissolved in xylene at 120°C; then the xylene solution of the resin was poured into a watch glass having a diameter of 100mm for film preparation, the watch glass was placed in an oven at 110°C to sufficiently evaporate the solvent to obtain a resin film sample; then the resin film sample was sufficiently washed in ethanol and air dried to obtain a sample for measuring the contact angle of the resin. The sample underwent phase separation during film preparation by a solution method. The dispersed phase was the side containing the polar monomer (organic acid or organic acid salt), and the other side was only polypropylene. The side containing the polar monomer side group of the obtained contact angle measurement sample was subjected to water contact angle measurement using the above-mentioned water contact angle tester. (3) The grafting ratio of the polar monomer (organic acid or organic acid salt) in the examples and comparative examples was characterized by infrared microscopy as follows:

[0101] First, a standard curve was established. The mixed samples of high temperature resistant dodecenyl succinic anhydride (DDSA) and the pure polypropylene resin in different ratios were used as standard samples, the infrared absorption peak area at 1818-1755 cm-1 (the peak peak was at about 1782 cm-1) of the carbonyl group (C=O group) of the anhydride in dodecenyl succinic anhydride and the absorption area at 484-435 cm-1 (the peak peak was at about 460 cm-1) of the internal standard peak of polypropylene were determined, and by plotting the ratio of them two against the content of maleic anhydride, a standard curve of the grafting ratio of maleic anhydride in the grafted polypropylene could be obtained.

[0102] The specific process for testing the grafting ratio of a grafted sample was as follows: A. For the microwave grafted samples used in the examples and comparative examples, since deionized water was used to sufficiently remove the unreacted MAH monomer after the grafting was completed, it was only necessary to press the samples into a transparent film having a thickness of about 100μm on a flat vulcanizer (a temperature of 200°C), then the characteristic absorption peak was measured with an infrared spectrometer (model: Nicolet iS50, Nicolet Company), and then the grafting ratio was calculated by the above standard curve. B. For the samples grafted with a melting method in the comparative examples, the test procedure was as follows: about 1g of the grafted polypropylene sample obtained in the comparative examples was weighed, placed in 20ml of xylene, heated until completely dissolved, and then immediately poured into 150ml of acetone, the unreacted small molecules and monomers that were not grafted onto the polypropylene molecules were dissolved in acetone, and the isolated white flakes were pure grafted substances. They were filtered, dried, and then pressed into a transparent film having a thickness of about 100μm on a flat vulcanizer (a temperature of 200°C), the characteristic absorption peak was determined with an infrared spectrometer, and then the grafting ratio was calculated from the above standard curve. The grafting ratio of the organic acid salt grafted polypropylene of the present invention may be equal to the grafting ratio of the organic acid grafted polypropylene obtained in the step of grafting the polypropylene with the organic acid. (4) The microwave reactor used: SINEO-multifunctional microwave synthesis and extraction instrument, model: UWave-2000.

[0103] The raw materials used in the examples and comparative examples and their manufacturers are as follows:

[0104] Homopolymerized polypropylene powder (Zhenhai Refining & Chemical Company M60, MI=60g/10min, obtained by polymerization with a spherical catalyst), Random copolymerized polypropylene powder (Zhenhai Refining & Chemical Company M60ET, MI=60g/10min, obtained by polymerization with a spherical catalyst), Impact copolymerized polypropylene powder (Zhenhai Refining & Chemical Company M30RH, MI=30g/10min, obtained by polymerization with a spherical catalyst), maleic anhydride (Xilong Scientific Co., Ltd.), acrylic acid (Sinopharm Chemical Reagent Co., Ltd.), methacrylic acid (Sinopharm Chemical Reagent Co., Ltd.), sodium chloride (Sinopharm Chemical Reagent Co., Ltd.), graphene oxide (Nanjing Jicang Nano Technology Co., Ltd.), ascorbic acid (J&K Scientific Ltd.), sodium hydroxide (Xilong Scientific Co., Ltd.), potassium hydroxide (Xilong Scientific Co., Ltd.), calcium hydroxide (Xilong Scientific Co., Ltd.), acetone (Xilong Scientific Co., Ltd.), dicumyl peroxide (Tianjin Guangfu Fine Chemical Research Institute), antioxidant 1010 (BASF), antioxidant 168 (BASF), and calcium stearate (Tianjin Jinke Fine Chemical Research Institute).

Example 1

[0105] On the basis of 100 parts by mass of a homopolymerized polypropylene powder, maleic anhydride (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain an acetone solution of maleic anhydride; the acetone solution of maleic anhydride was added to the polypropylene powder with mechanical stirring under vacuum and mixed sufficiently, then the mixture was dried (dried in a jet drying oven at 80°C). The dried polypropylene/maleic anhydride mixture powder after drying was irradiated with a microwave (power 700W) for 3 minutes under a nitrogen atmosphere; After completing the microwave irradiation, the powder was immersed in deionized water for 10 minutes, and the deionized water was replaced, which was repeated 3 times to ensure the removal of maleic anhydride monomers that were not involved in the grafting reaction, and then the powder was placed in a jet drying oven at 80°C for drying. Finally, the powder and 0.1 part by mass (based on 100 parts by mass of homopolymerized polypropylene powder) of antioxidant 1010, 0.1 part by mass of antioxidant 168, and 0.1 part by mass of calcium stearate were extrusion melted and pelletized in a twin-screw extruder, the temperature of the extruder feeding section was 190-200°C, the temperature of the mixing section was 200-210°C, and the temperature of the head was 190-220°C. After extrusion and pelletizing, the melt index, contact angle and grafting ratio were tested, and the test results are shown in Table 1.

Example 1’

[0106] Based on 100 parts by mass of a homopolymerized polypropylene powder, maleic anhydride (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain a maleic anhydride acetone solution; sodium chloride (3 parts by mass) was dissolved in deionized water (50 parts by mass) to obtain a sodium chloride aqueous solution; the maleic anhydride acetone solution was added to the polypropylene powder with mechanical stirring under vacuum and mixed sufficiently, then the mixture was dried (dried in a jet drying oven at 80°C). The dry polypropylene/maleic anhydride blend powder was mixed sufficiently with the sodium chloride aqueous solution, then the mixture was dried (dried in a jet drying oven at 80°C); The dried polypropylene/maleic anhydride/sodium chloride blend powder after drying was irradiated with a microwave (power 700W) for 2 minutes under a nitrogen atmosphere; after completing the microwave irradiation, the powder was immersed in deionized water for 10 minutes, and the deionized water was replaced, which was repeated 3 times to ensure the removal of maleic anhydride and sodium chloride monomers that were not involved in the grafting reaction, and then the powder was replaced in a jet drying oven at 80°C for drying. Finally, the powder and 0.1 part by mass (based on 100 parts by mass of homopolymerized polypropylene powder) of antioxidant 1010, 0.1 part by mass of antioxidant 168, and 0.1 part by mass of calcium stearate were melt extruded and pelletized in a twin-screw extruder, the temperature of the extruder feeding section was 190-200°C, the temperature of the mixing section was 200-210°C, and the temperature of the head was 190-200°C. After extrusion and pelletizing, the melt index, contact angle, and grafting ratio were tested, and the test results are shown in Table 1.

Example 1”

[0107] Except that the dry powder of polypropylene/maleic anhydride/sodium chloride blend after drying was irradiated with a microwave (power 700W) for 3 minutes under a nitrogen atmosphere, the rest was the same as that of Example 1’. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 1

[0108] On the basis of 100 parts by mass of a homopolymerized polypropylene powder (the same as in Example 1), maleic anhydride (5 parts by mass) and dicumyl peroxide (0.005 part by mass) were dissolved in acetone (50 parts by mass) to obtain an acetone solution of maleic anhydride; the acetone solution of maleic anhydride was added to the polypropylene powder with mechanical stirring under vacuum and sufficiently mixed, then the mixture was dried (dried in a jet drying oven at 80°C). The dried polypropylene/maleic anhydride mixture powder after drying was irradiated with a microwave (power 700W) for 3 minutes under a nitrogen atmosphere; After completing the microwave irradiation, the powder was immersed in deionized water for 10 minutes, and the deionized water was replaced, which was repeated 3 times to ensure the removal of maleic anhydride monomers that were not involved in the grafting reaction, and then the powder was placed in a jet drying oven at 80°C for drying. Finally, the powder and 0.1 mass part of antioxidant 1010, 0.1 mass part of antioxidant 168, and 0.1 mass part of calcium stearate were melt extruded and pelletized in a twin-screw extruder, the temperature of the extruder feeding section was 190-200°C, the temperature of the mixing section was 200-210°C, and the head temperature was 190-200°C. After extrusion and pelletizing, the melt index, contact angle and grafting ratio were tested, and the test results are shown in Table 1.

Example 2

[0109] Except that the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 2

[0110] Except that the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Comparative Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Example 3

[0111] Except that the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 3

[0112] Except that the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Comparative Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Example 4

[0113] Except that the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 10 minutes under a nitrogen atmosphere, the rest were the same as those of Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 4

[0114] Except that the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 10 minutes under a nitrogen atmosphere, the rest were the same as those of Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 5

[0115] Based on 100 parts by mass of a homopolymerized polypropylene powder (the same as in Example 1), dicumyl peroxide (0.005 part by mass) was dissolved in acetone (20 parts by mass) to obtain an initiator solution; maleic anhydride (5 parts by mass) and the polypropylene powder were subjected to solid-phase dry mixing with a stirring blade in a metal mug, and during the mixing process, the well-dissolved peroxide initiator solution was added. Finally, the well-mixed reactants and 0.1 mass part of antioxidant 1010, 0.1 mass part of antioxidant 168, and 0.1 mass part of calcium stearate were melt extruded and pelletized in a twin-screw extruder. The temperature of the extruder feeding section was 190-200°C, the temperature of the mixing section was 200-210°C, and the head temperature was 190-200°C. After extrusion and pelletizing, the melt index, contact angle, and grafting ratio were tested, and the test results are shown in Table 1.

Example 5

[0116] Except that maleic anhydride (1 part by mass) was dissolved in acetone (50 parts by mass) to obtain a maleic anhydride acetone solution, and the dry powder of polypropylene/maleic anhydride blend after drying, was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Example 1. The sample was tested for melting index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 6

[0117] Except that maleic anhydride (1 part by mass) was dissolved in acetone (50 parts by mass) to obtain a maleic anhydride acetone solution, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Comparative Example 1. The sample was tested for melting index, contact angle and grafting ratio, and the test results are shown in Table 1.

Example 6

[0118] Except that maleic anhydride (8 parts by mass) was dissolved in acetone (50 parts by mass) to obtain a maleic anhydride acetone solution, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Example 1. The sample was tested for melting index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 7

[0119] Except that maleic anhydride (8 parts by mass) was dissolved in acetone (50 parts by mass) to obtain a maleic anhydride acetone solution, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those in Comparative Example 1. The sample was tested for melting index, contact angle and grafting ratio, and the test results are shown in Table 1.

Example 7

[0120] Except that maleic anhydride (10 parts by mass) was dissolved in acetone (50 parts by mass) to obtain a maleic anhydride acetone solution, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Example 1. The sample was tested for melting index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 8

[0121] Except that maleic anhydride (10 parts by mass) was dissolved in acetone (50 parts by mass) to obtain a maleic anhydride acetone solution, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Comparative Example 1. The sample was tested for melting index, contact angle and grafting ratio, and the test results are shown in Table 1.

Example 8

[0122] Except that acrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain an acrylic acid acetone solution, and the dry powder of polypropylene/acrylic acid blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 9

[0123] Except that acrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain an acrylic acid acetone solution, and the dry powder of polypropylene/acrylic acid blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Comparative Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Example 9

[0124] Except that acrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain an acrylic acid acetone solution, and the dry powder of polypropylene/acrylic acid blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 10

[0125] Except that acrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain an acrylic acid acetone solution, and the dry powder of polypropylene/acrylic acid blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Comparative Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Example 10

[0126] Except that methacrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain a methacrylic acid acetone solution, and the dry powder of polypropylene/methacrylic acid blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 11

[0127] Except that methacrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain a methacrylic acid acetone solution, and the dry powder of polypropylene/methacrylic acid blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those in Comparative Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Example 11

[0128] Except that based on 100 parts by mass of a copolymerized polypropylene powder, the dry powder of the polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest was the same as that in Example 1. The sample was tested for melting index, contact angle and grafting ratio, and the test results are shown in Table 1.

Example 11’

[0129] Except that based on 100 parts by mass of an impact copolymerized polypropylene powder, graphene oxide (0.5 part by mass) and ascorbic acid (0.5 part by mass) were dissolved in deionized water (50 parts by mass) to obtain an aqueous solution of graphene oxide; the dry powder of the polypropylene/maleic anhydride mixture after drying was sufficiently mixed with the aqueous solution of the graphene oxide, then the mixture was dried (dried in a jet drying oven at 80°C); and the polypropylene/maleic anhydride/graphene oxide blend powder after drying was irradiated with a microwave (power 700W) for 1 minute under a nitrogen atmosphere, the rest was the same as that of Example 1. The sample was tested for melting index, contact angle and grafting ratio, and the test results are shown in Table 1. Example 11”

[0130] Except that the dry powder of polypropylene/maleic anhydride/graphene oxide blend after drying was irradiated with a microwave (power 700W) for 2 minutes under a nitrogen atmosphere, the rest was the same as that of Example 1’. The sample was tested for melting index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 12

[0131] Except that based on 100 parts by mass of an impact copolymerized polypropylene powder, the dry powder of the polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest was the same as that of Comparative Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Example 12

[0132] Except that on the basis of 100 parts by mass of an impact copolymerized polypropylene powder, acrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain an acrylic acid acetone solution, and the dry polypropylene/acrylic acid blend powder after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest was the same as that of Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 13

[0133] Except that on the basis of 100 parts by mass of an impact copolymerized polypropylene powder, acrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain an acrylic acid acetone solution, and the dry polypropylene/acrylic acid blend powder after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest was the same as that of Comparative Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Example 13

[0134] Except that based on 100 parts by mass of a random copolymerized polypropylene powder, the dry powder of the polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest was the same as that of Example 1. The sample was tested for melting index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 14

[0135] Except that based on 100 parts by mass of a random copolymerized polypropylene powder, the dry powder of the polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest was the same as that of Comparative Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Example 14

[0136] Except that on the basis of 100 parts by mass of a random copolymerized polypropylene powder, acrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain an acrylic acid acetone solution, and the dry polypropylene/acrylic acid blend powder after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest was the same as that of Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1.

Comparative Example 15

[0137] Except that on the basis of 100 parts by mass of a random copolymerized polypropylene powder, acrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain an acrylic acid acetone solution, and the dry polypropylene/acrylic acid blend powder after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest was the same as that of Comparative Example 1. The sample was tested for melt index, contact angle and grafting ratio, and the test results are shown in Table 1. Table 1

[0138] It can be seen from Table 1 that the examples of the present invention involve grafted propylene under microwave irradiation without the addition of an initiator which has a grafting ratio higher than that of the comparative examples of polypropylene grafted by melt blending with the addition of an initiator, and the melt index of the polypropylene after grafting does not increase, that is, the molecular weight does not decrease. Clearly, the chain scission phenomenon of the main chain of the polar monomer grafted polypropylene resins obtained in the examples of the present invention was controlled, thereby ensuring that the mechanical properties of the resins were not damaged. In addition, it can be seen that in the comparative examples involving grafting by microwave irradiation with the addition of a peroxide, even under the condition of grafting with microwave irradiation, the melt index of the polypropylene increased sharply due to the addition of peroxide; and due to the completion between the grafting reaction and the self-polymerization reaction, with the same microwave irradiation time, the grafting ratio of the samples obtained without the addition of a peroxide was always greater than that of the samples obtained with the addition of a peroxide. The higher the grafting ratio was, the lower the contact angle after film formation was. The grafted polypropylenes according to the present invention were changed from the non-hydrophilicity (contact angle greater than 90°C) of the polypropylene raw material to hydrophilicity.

[0139] In addition, it can be seen that in the case of further adding an inorganic microwave-absorbing medium, the grafting ratio of the grafted polypropylene could be further increased and the water contact angle and melting index could be decreased. Furthermore, compared with the case where no inorganic microwave-absorbing medium was added, the use of an inorganic microwave-absorbing medium could achieve the grafted polypropylene resins having similar properties in a shorter microwave irradiation time, thereby improving the production efficiency.

Example S1

[0140] Based on 100 parts by mass of a homopolymerized polypropylene powder, maleic anhydride (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain a maleic anhydride acetone solution; sodium hydroxide (5 parts by mass) was dissolved in deionized water (50 parts by mass) to obtain a sodium hydroxide aqueous solution; the maleic anhydride acetone solution was added to the polypropylene powder with mechanical stirring under vacuum and sufficiently mixed, then the mixture was dried (dried in a jet drying oven at 80°C). The dried polypropylene/maleic anhydride blend powder after drying was irradiated with a microwave (power 700W) for 3 minutes under a nitrogen atmosphere. After the microwave irradiation was completed, the powder was immersed in deionized water for 10 minutes, and the deionized water was replaced. This was repeated 3 times to ensure the removal of maleic anhydride monomers that were not involved in the grafting reaction. Then the powder was placed in a jet drying oven at 80°C for drying. The sodium hydroxide aqueous solution was added to the dried maleic anhydride-grafted polypropylene powder with stirring under vacuum, and mixed sufficiently. After adding the sodium hydroxide aqueous solution, the mixture was further mixed with stirring, and the reaction was carried out for 5 minutes. After the reaction was completed, deionized water was used to wash the powder according to the above washing step, and then the powder was placed in a jet drying oven at 80°C for drying. Finally, the powder and 0.1 mass part (based on 100 mass parts of homopolymerized polypropylene powder) of antioxidant 1010, 0.1 mass part of antioxidant 168, and 0.1 mass part of calcium stearate were melt extruded and pelletized in a twin-screw extruder. The temperature of the extruder feeding section was 190-200°C, the temperature of the mixing section was 200-210°C, and the head temperature was 190-200°C. After extrusion and pelletizing, the melt index, contact angle, and grafting ratio were tested, and the test results are shown in Table 2.

Comparative Example S1

[0141] Based on 100 parts by mass of a homopolymerized polypropylene powder (the same as that of Example S1), maleic anhydride (5 parts by mass) and dicumyl peroxide (0.005 part by mass) were dissolved in acetone (50 parts by mass) to obtain a maleic anhydride acetone solution; sodium hydroxide (5 parts by mass) was dissolved in deionized water (50 parts by mass) to obtain a sodium hydroxide aqueous solution; the maleic anhydride acetone solution was added to the polypropylene powder with mechanical stirring under vacuum and sufficiently mixed, then the mixture was dried (dried in a jet drying oven at 80°C). The dried polypropylene/maleic anhydride blend powder after drying was irradiated with a microwave (power 700W) for 3 minutes under a nitrogen atmosphere. After the microwave irradiation was completed, the powder was immersed in deionized water for 10 minutes, and the deionized water was replaced. This was repeated 3 times to ensure the removal of maleic anhydride monomers that were not involved in the grafting reaction. Then the powder was placed in a jet drying oven at 80°C for drying. The sodium hydroxide aqueous solution was added to the dried maleic anhydride-grafted polypropylene powder with stirring under vacuum, and mixed sufficiently. After adding the sodium hydroxide aqueous solution, the mixture was further mixed with stirring, and the reaction was carried out for 5 minutes. After the reaction was completed, deionized water was used to wash the powder according to the above washing step, then the powder was placed in a jet drying oven at 80°C for drying. Finally, the powder and 0.1 mass part of antioxidant 1010, 0.1 mass part of antioxidant 168, and 0.1 mass part of calcium stearate were melt extruded and pelletized in a twin-screw extruder. The temperature of the extruder feeding section was 190-200°C, the temperature of the mixing section was 200-210°C, and the head temperature was 190-200°C. After extrusion and pelletizing, the melt index, contact angle, and grafting ratio were tested, and the test results are shown in Table 2.

Example S2

[0142] Except that the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Comparative Example S2

[0143] Except that the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Comparative Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S3

[0144] Except that the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Comparative Example S3

[0145] Except that the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Comparative Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S4

[0146] Except that the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 10 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Comparative Example S4

[0147] Except that the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 10 minutes under a nitrogen atmosphere, the rest were the same as those of Comparative Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S5

[0148] Except that sodium hydroxide (1 part by mass) was dissolved in deionized water (50 parts by mass) to obtain an aqueous solution of sodium hydroxide, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Comparative Example S5

[0149] Except that sodium hydroxide (1 part by mass) was dissolved in deionized water (50 parts by mass) to obtain an aqueous solution of sodium hydroxide, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Comparative Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S6

[0150] Except that sodium hydroxide (8 parts by mass) was dissolved in deionized water (50 parts by mass) to obtain an aqueous solution of sodium hydroxide, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Comparative example S6

[0151] Except that sodium hydroxide (8 parts by mass) was dissolved in deionized water (50 parts by mass) to obtain an aqueous solution of sodium hydroxide, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Comparative Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S7

[0152] Except that sodium hydroxide (10 parts by mass) was dissolved in deionized water (50 parts by mass) to obtain a sodium hydroxide aqueous solution, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Comparative Example S7

[0153] Except that sodium hydroxide (10 parts by mass) was dissolved in deionized water (50 parts by mass) to obtain an aqueous solution of sodium hydroxide, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Comparative Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S8

[0154] Except that potassium hydroxide (5 parts by mass) was dissolved in deionized water (50 parts by mass) to obtain an aqueous solution of potassium hydroxide, and the dry powder of polypropylene/maleic anhydride mixture after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Comparative Example S8

[0155] Except that potassium hydroxide (5 parts by mass) was dissolved in deionized water (50 parts by mass) to obtain an aqueous solution of potassium hydroxide, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those in Comparative Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2. Example S9

[0156] Except that calcium hydroxide (5 parts by mass) was dissolved in deionized water (50 parts by mass) to obtain an aqueous solution of calcium hydroxide, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Comparative Example S9

[0157] Except that calcium hydroxide (5 parts by mass) was dissolved in deionized water (50 parts by mass) to obtain an aqueous solution of calcium hydroxide, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Comparative Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S10

[0158] Except that maleic anhydride (1 part by mass) was dissolved in acetone (50 parts by mass) to obtain a maleic anhydride acetone solution, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S11

[0159] Except that maleic anhydride (8 parts by mass) was dissolved in acetone (50 parts by mass) to obtain a maleic anhydride acetone solution, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S12

[0160] Except that maleic anhydride (10 parts by mass) was dissolved in acetone (50 parts by mass) to obtain a maleic anhydride acetone solution, and the dry powder of polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 7 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S13

[0161] Except that based on 100 parts by mass of an impact copolymerized polypropylene powder, the dry powder of the polypropylene/maleic anhydride blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S14

[0162] Except that based on 100 parts by mass of an impact copolymerized polypropylene powder, acrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain an acrylic acid acetone solution, and the dried polypropylene/acrylic acid mixture powder after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melt index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S15

[0163] Except that based on 100 parts by mass of a random copolymerized polypropylene powder, the dry powder of the polypropylene/maleic acid blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S16

[0164] Except that based on 100 parts by mass of a random copolymerized polypropylene powder, acrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain an acrylic acid acetone solution, and the dried polypropylene/acrylic acid powder after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S17

[0165] Except that acrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain an acrylic acid acetone solution, and the dry powder of polypropylene/acrylic acid blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melt index, contact angle and grafting ratio, and the results thereof were shown in Table 2.

Example S18

[0166] Except that methacrylic acid (5 parts by mass) was dissolved in acetone (50 parts by mass) to obtain an acetone solution of methacrylic acid, and the dry powder of the polypropylene/methacrylic acid blend after drying was irradiated with a microwave (power 700W) for 5 minutes under a nitrogen atmosphere, the rest were the same as those of Example S1. The sample was tested by melting index, contact angle and grafting ratio, and the results thereof were shown in Table 2. Table 2

[0167] It can be seen from Table 2 that the examples of the present invention involving polypropylene grafted with an organic acid salt under microwave irradiation without the addition of an initiator have a higher grafting ratio than the comparative examples of polypropylene grafted by melt mixing with the addition of an initiator, and the melt index of the polypropylene after grafting does not increase, that is, the molecular weight does not decrease. Clearly, the chain scission phenomenon of the main chain of the polypropylene resins grafted with an organic acid salt obtained in the examples of the present invention was controlled, thereby ensuring that the mechanical properties of the resins were not damaged. In addition, it can be seen that in the comparative examples involving grafting by microwave irradiation with the addition of a peroxide, even under the condition of microwave grafting irradiation, the melt index of the polypropylene increased sharply due to the addition of the peroxide; and due to the completion between the grafting reaction and the self-polymerization reaction, with the same microwave irradiation time, the grafting ratio of the samples obtained without the addition of a peroxide was always greater than that of the samples obtained with the addition of a peroxide.

[0168] It can further be seen from Table 2 that for the organic acid salt grafted polypropylenes according to the present invention, they were carried from the non-hydrophilicity (contact angle greater than 90°C) of the polypropylene raw material to hydrophilicity, or even the contact angle can reach 0°. Additionally, as can be seen from the comparison between Table 1 and Table 2, after the hydroxide was added, the water contact angle of the organic acid grafted polypropylene having the same grafting ratio was evidently smaller than the water contact angle of the organic acid grafted polypropylene. Thus, the addition of the hydroxide could further increase the polarity of the grafted polypropylene.

Claims (49)

1. Polypropylene resin grafted with polar monomer, characterized in that the grafted polypropylene resin does not contain initiator residues, and the polar monomer is capable of absorbing microwaves so as to increase its temperature in the microwave field to above 200°C and selected from the group consisting of organic acids as well as anhydrides, esters and salts of organic acids; wherein the side groups of the polar monomer on the main chain of polypropylene molecules, and the grafting ratio of the polar monomer is 0.01%-8%; and wherein the melt index of the grafted polypropylene resin is less than or equal to the melt index of the polypropylene resin as the graft base. 2. Polypropylene resin according to claim 1, characterized in that the polar monomer is selected from the group consisting of maleic anhydrides, maleic anhydride acids and esters, (meth)acrylic acids, (meth)acrylic acid anhydride and esters, vinyl acetates, alkenyl sulfonic acids and anhydrides and esters thereof, p-styryl formic acid, p-styryl acetic acid, itaconic acid, oleic acid, arachidonic acid and combinations thereof and salt forms thereof. 3. Polypropylene resin according to claim 2, characterized in that the (meth)acrylic acid ester is glycidyl methacrylate. 4. Polypropylene resin according to any one of claims 1 to 3, characterized in that the grafting ratio is from 0.01% to 6%. 5. Polypropylene resin according to any one of claims 1 to 4, characterized in that the value of the water contact angle of the grafted polypropylene resin is less than 90° or less than 65°, or 50°-0°, as measured on a film prepared from the grafted polypropylene resin by a solution method. 6. Polypropylene resin according to any one of claims 1 to 5, characterized in that the polypropylene resin as the graft base is selected from the group consisting of propylene homopolymers and propylene copolymers and mixtures thereof. 7. Polypropylene resin according to claim 6, characterized in that the polypropylene resin as the grafted base is selected from the group consisting of random propylene copolymers. 8. Polypropylene resin according to claim 7, characterized in that the comonomer in the propylene random copolymer is selected from the group consisting of ethylene, α-olefins, in addition to propylene, and combinations thereof. 9. The polypropylene resin of claim 7, wherein the comonomer in the propylene random copolymer is selected from the group consisting of ethylene, C4, C5, C6 to C8-α-olefins, and combinations thereof. 10. Polypropylene resin according to claim 6, characterized in that the polypropylene resin as the graft base is an impact polypropylene resin, which comprises a rubber phase in addition to a propylene homopolymer, the rubber phase being a copolymer formed by propylene and the comonomer of at least one selected from the group consisting of ethylene and α-olefins in addition to propylene. 11. Polypropylene resin according to claim 10, characterized in that the rubber phase is a copolymer formed by propylene and the comonomer of at least one selected from the group consisting of ethylene, C4, C5, C6 to C8 α-olefins. 12. Polypropylene resin according to any one of claims 1 to 11, characterized in that the polypropylene resin used as the graft base is in a solid form including powder, pellets or articles. 13. Polypropylene resin according to claim 12, characterized in that the polypropylene resin used as the graft base is polypropylene powder obtained by polymerization using a spherical catalyst. 14. Polypropylene resin according to any one of claims 1 to 13, characterized in that the grafted polypropylene resin is obtained by subjecting the polar monomer and the solid polypropylene resin to a grafting reaction using microwave irradiation without the addition of an initiator. 15. Polypropylene resin according to claim 14, characterized in that the product obtained after the grafting reaction is still subjected to salt formation. 16. A method for preparing a grafted polypropylene resin as defined in any one of claims 1 to 15, comprising the step of subjecting the polar monomer and the solid polypropylene resin to a grafting reaction using microwave irradiation without the addition of an initiator; wherein the polar monomer is in liquid form; the irradiation powder of the microwave irradiation is 100w-200w; the irradiation time is 1s-120 minutes; the solid polypropylene resin used is free of an antioxidant; and during the grafting reaction, auxiliary grafting monomers are not used. 17. The method of claim 16, wherein the amount of the polar monomer is 0.1 to 10 wt.%, or 1 to 8 wt.% based on the weight of the solid polypropylene resin. 18. Method according to either of claims 16 or 17, characterized in that the polar monomer is in solution form. 19. The method of any one of claims 16 to 18, wherein the irradiation powder of the microwave irradiation is 500-100W; the irradiation time is 1 minute to 30 minutes. 20. Method according to any one of claims 16 to 19, characterized in that it comprises the following steps: 1. mixing the polar monomer with the solid polypropylene resin; and 2. subjecting the mixture obtained in step (1) to microwave irradiation. 21. Method according to claim 20, characterized in that step (2) is carried out under an inert gas atmosphere. 22. Method according to either of claims 20 or 21, characterized in that in step (1), the polar monomer and the solid polypropylene resin are mixed under vacuum conditions. 23. Method according to claim 21, characterized in that in step (2), the inert gas is one or more selected from the group consisting of nitrogen, helium, and argon. 24. Method according to any one of claims 20 to 23, characterized in that the polar monomer is in the form of a solution dissolved in a solvent, and the mixture obtained in step (1) is dried to remove the solvent before step (2). 25. Method according to claim 24, characterized in that the solvent is selected from at least one group of alcohols, ketones, esters and water. 26. Method according to claim 25, characterized in that the solvent is acetone or ethanol. 27. Method according to any one of claims 20 to 26, characterized in that the irradiated mixture obtained in step (2) is washed to remove unreacted polar monomers, and is dried, the solvent used for washing being at least one selected from the group of alcohols, ketones, esters and water. 28. Method according to any one of claims 16 to 27, characterized in that the polar monomer is an organic acid or its anhydride or ester, the product obtained after the grafting reaction under microwave irradiation is further reacted with a base. 29. The method of claim 28, wherein the organic acid-grafted polypropylene powder is mixed and reacted with an aqueous solution of the base under vacuum. 30. The method of claim 29, wherein the method further comprises using a washing solvent to remove unreacted base and drying treatment to obtain an organic acid salt-grafted polypropylene resin. 31. The method of claim 28, wherein the base is selected from the group consisting of ammonia and metal hydroxides. 32. The method of claim 31, wherein the base is selected from the group consisting of sodium hydroxide, potassium hydroxide, barium hydroxide, lithium hydroxide, strontium hydroxide, calcium hydroxide, iron hydroxide, ferrous hydroxide, zinc hydroxide, magnesium hydroxide, cobalt hydroxide, gold hydroxide, aluminum hydroxide, copper hydroxide, beryllium hydroxide, and rare earth hydroxide, and combinations thereof. 33. The method of any one of claims 28 to 32, wherein the amount of the base is 0.1-10% by weight, or 1-8% by weight, based on the weight of the polypropylene resin used. 34. The method of any one of claims 16 to 33, wherein an inorganic microwave absorbing medium is added. 35. The method of claim 34, wherein the amount of the inorganic microwave-absorbing medium is 0.1-10 wt.%, or 1-8 wt.%, based on the weight of the solid polypropylene resin. 36. The method of either claim 34 or 35, wherein the inorganic microwave absorbing medium is selected from the group consisting of metal hydroxides, metal output; metal oxides, graphite materials, ferroelectric materials, electrolysis stone, chalcopyrite, and combinations thereof. 37. The method of claim 36, wherein the inorganic microwave-absorbing medium is selected from the group consisting of potassium hydroxide, barium hydroxide, sodium hydroxide, lithium hydroxide, strontium hydroxide, calcium hydroxide, iron hydroxide, ferrous hydroxide, zinc hydroxide, magnesium hydroxide, cobalt hydroxide, gold hydroxide, aluminum hydroxide, copper hydroxide, beryllium hydroxide, and rare earth hydroxide, ammonium nitrate, potassium nitrate, sodium nitrate, barium nitrate, calcium nitrate, magnesium nitrate, aluminum nitrate, manganese nitrate, zinc nitrate, iron nitrate, ferrous nitrate, copper nitrate, silver nitrate, ammonium chloride, potassium chloride, sodium chloride, barium chloride, calcium chloride, magnesium chloride, aluminum chloride, manganese chloride, zinc chloride, iron chloride, ferrous, copper chloride, ammonium sulfate, potassium sulfate, sodium sulfate, calcium sulfate, magnesium sulfate, aluminum sulfate, manganese sulfate, zinc sulfate, iron sulfate, ferrous sulfate, copper sulfate, silver sulfate, ammonium carbonate, potassium carbonate, sodium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, potassium dihydrogen phosphate, barium titanates, strontium titanates, and copper-calcium titanates, ferric oxide, and iron-ferric oxide, carbon black, graphite powder, graphene oxide and its reduction products, graphene, carbon nanotubes, and activated carbon, ferroelectric materials, electrolysis stones, chalcopyrite, and combinations thereof. 38. Method according to any one of claims 34 to 37, characterized in that prior to microwave radiation, a polar monomer, an inorganic microwave-absorbing medium and a solid polypropylene resin are mixed. 39. Method according to claim 38, characterized in that the mixing is carried out under vacuum conditions. 40. The method of claim 38, wherein the polar monomer is dissolved in a solvent; and/or the inorganic microwave absorbing medium is dissolved or dispersed in a solvent, wherein the solvent used to dissolve the polar monomer and the solvent used to dissolve or disperse the inorganic microwave absorbing medium are the same or different, and are selected from the group consisting of water, alcohols, ketones, and esters. 41. The method of claim 40, wherein after mixing, drying treatment is performed to remove the solvent. 42. Method according to claim 40, characterized in that the inorganic microwave absorbing medium is dissolved or dispersed in a solvent with the addition of a surfactant. 43. The method of any one of claims 38 to 42, wherein the polypropylene resin is first mixed with a polar monomer, and then the resulting mixture is mixed with an inorganic microwave absorbing organic medium. 44. Method according to any one of claims 34 to 43, characterized in that the mixture after irradiation is washed to remove unreacted polar monomers. 45. The method of claim 44, wherein the mixture after irradiation is washed to remove unreacted polar monomers and remove the microwave-absorbing organic medium, and dried. 46. Pellets or articles, characterized in that they are obtained from the graft polypropylene resin, as defined in any one of claims 1 to 15, or the grafted polypropylene resin prepared by the method as defined in any one of claims 16 to 45, through pelletization by melt extrusion or an additional molding process. 47. Pellets or articles according to claim 46, characterized in that the grafted polypropylene resin is added with an additive. 48. Composite materials, coatable film materials or bonding materials, characterized in that they are prepared by bonding the grafted polypropylene resin as defined in any one of claims 1 to 15, or the grafted polypropylene resin prepared by the method as defined in any one of claims 16 to 45 with other polymers. 49. Use of the grafted polypropylene resin as defined in any one of claims 1 to 15, or the grafted polypropylene resin prepared by the method as defined in any one of claims 16 to 45, characterized in that it is for modifying plastics.