CN115536996A - Preparation method of cellulose nano-fibril reinforced full-biodegradable composite material - Google Patents
Preparation method of cellulose nano-fibril reinforced full-biodegradable composite material Download PDFInfo
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Abstract
The invention discloses a preparation method of a cellulose nano-fibril reinforced fully biodegradable composite material, belonging to the technical field of high polymer materials. The operation steps are as follows: (1) Firstly, preparing cellulose nano-fibrils by taking paper pulp cellulose as a raw material; (2) Secondly, preparing a composite material of thermoplastic starch and cellulose nanofibrils by taking cellulose nanofibrils, starch and a plasticizer as raw materials; (3) And then processing the composite material of the thermoplastic starch and the cellulose nanofibrils, poly (butylene adipate terephthalate) (PBAT) and an auxiliary agent to prepare the full-biodegradable composite material. The technical scheme provided by the invention can solve the technical problems of poor mechanical strength and water resistance of the poly (butylene adipate-terephthalate) and starch composite material when the starch content is higher. The invention has simple production process, wide raw material source, high economic practicability and wide application prospect.
Description
Technical Field
The invention belongs to the technical field of high polymer materials, and particularly relates to a preparation method of a cellulose nanofibril reinforced fully biodegradable composite material.
Background
With the development of times and social progress, sustainable development and environmental protection are more and more emphasized by people, a series of problems such as environmental pollution and energy shortage caused by the characteristics of non-regeneration, non-degradation and the like of petroleum-based plastics are more and more serious, white pollution becomes a focus of attention of all parties, and biodegradable materials are being promoted and used more vigorously. Poly (butylene adipate terephthalate) (PBAT) is petroleum-based degradable copolyester, has good flexibility, film forming property and mechanical property, is widely applied to the fields of packaging materials, hygienic products and the like, but has the problems of low stiffness, poor opening property, high cost and the like. Therefore, modification and cost reduction are important means for improving the application and popularization of the biodegradable material. Starch has attracted extensive attention due to its characteristics of wide raw material source, low price, renewability, little environmental pollution, complete degradability, etc. Thermoplastic starch (TPS) is prepared by adding plasticizer to make starch have plasticity, thus improving the processing property and use property of starch, and thus the plasticized starch can be blended with biodegradable polymer for modification to improve the comprehensive properties of materials and reduce the cost.
At present, starch-based biodegradable plastics are generally prepared by plasticizing starch, modifying the starch to improve the thermoplastic film-forming property of the starch, and then simply blending the starch-based biodegradable plastics and other functional additives for injection molding. The publication No. CN110845830A discloses a starch filled polylactic acid and polybutylene adipate-terephthalate full-biodegradable composite material and a preparation method thereof, and the problems of poor toughness and brittleness and easy breakage of polylactic acid are solved by simply blending and extruding the polylactic acid, the polybutylene adipate-terephthalate, starch, glycerol, a coupling agent and the like; publication No. CN113088044A discloses a starch-filled fully biodegradable plastic and a preparation method thereof, and also a method for blending and extruding polybutylene adipate-terephthalate, starch, a plasticizer, a reinforcing agent, a dispersing agent and the like, thereby solving the defect of difficult film blowing of the polybutylene adipate-terephthalate and reducing the cost. However, such starch filled composites have poor mechanical strength and water resistance compared to pure biodegradable plastics, especially when the starch content is high. The thermoplastic starch material is sensitive to the environmental humidity, and is easy to absorb water during storage and use, so that the mechanical property of the composite material is reduced; in addition, the thermoplastic starch has recrystallization phenomenon, so that the product has poor dimensional stability and becomes brittle, and the use requirement cannot be met.
Therefore, the development of the starch-based biodegradable plastic with high mechanical strength, good water resistance and low cost and the preparation method thereof are the key points for wide application.
Disclosure of Invention
In order to improve the mechanical property of a poly (butylene adipate terephthalate) (PBAT) and starch blending material and keep higher starch addition amount, the invention provides a preparation method of a cellulose nanofibril reinforced fully biodegradable composite material.
The preparation operation steps of the cellulose nano fibril reinforced full biodegradable composite material are as follows:
(1) Preparation of cellulose nanofibrils
(1.1) dispersing 5-10 g of paper pulp cellulose into 1500mL of 5-8 wt% sodium hydroxide (NaOH) solution, stirring and reacting for 10-12 h at 25-35 ℃, and washing with water to be neutral to obtain pretreated cellulose;
the paper pulp cellulose is flax pulp cellulose, bamboo pulp cellulose or wood pulp cellulose;
(1.2) 7.42g of sodium carbonate (Na) 2 CO 3 ) And 2.52g sodium bicarbonate (NaHCO) 3 ) Dissolving in 500mL of deionized water to form a buffer solution; ultrasonically dissolving 0.1g of 2, 6-tetramethylpiperidine oxynitride (TEMPO) and 1g of sodium bromide (NaBr) in a buffer solution, adding 5-8 g of pretreated cellulose, slowly dropwise adding 10mL of 2-4 mol/L sodium hypochlorite (NaClO) solution under stirring, adjusting the pH value of a reaction system to 10.4-10.8 by using 4mol/L dilute hydrochloric acid solution, stirring and reacting in a 30-DEG C constant-temperature water bath kettle for 2-7 h, adding 10mL of absolute ethyl alcohol to terminate the reaction, washing a reaction product to be neutral by water, and then adding water to the reaction productSex;
(1.3) preparing a reaction product into a mixture with the cellulose content of 1-2 wt% by using water, and homogenizing under high pressure to obtain translucent gelatinous cellulose nanofibrils;
the length of the cellulose nano-fibril is 3-8 mu m, and the diameter is 3-10 nm;
(2) Preparation of a composite of thermoplastic starch and cellulose nanofibrils
Uniformly stirring and mixing 700-750 g of raw starch, 250-300 g of plasticizer and 800-1000 g of gelatinous cellulose nanofibrils to obtain a premix, and mixing and plasticizing the premix in a double-screw extruder at 25 ℃ for 10min, wherein the rotating speed of a screw is 100-150 rpm; raising the temperature of the double-screw extruder, and extruding and granulating to obtain the composite material of the thermoplastic starch and the cellulose nano-fibrils;
the native starch is corn starch, or tapioca starch, or wheat starch;
the plasticizer is glycerol;
(3) Preparation of a composite of polybutylene adipate terephthalate (PBAT), thermoplastic starch and cellulose nanofibrils
Fully mixing 500g of poly (butylene adipate-terephthalate) (PBAT), 500g of thermoplastic starch and cellulose nanofibril composite material, 5-10 g of compatibilizer, 1-5 g of dispersant and 2g of antioxidant in a high-speed mixer at the room temperature of 800-1500 rpm for 5-10 min; extruding and granulating in a double-screw extruder, wherein the rotating speed of the screw of the extruder is 200-300 rpm, and obtaining the granular full-biodegradable composite material;
the melt mass flow rate of the polybutylene adipate terephthalate (PBAT) is 4 g/10min, and the carboxyl content is 30 mol/t;
the compatibilizer is a compound with a molecular structure containing at least 2 isocyanate functional groups, and specifically is one of toluene diisocyanate, diphenylmethane diisocyanate and methylcyclohexane diisocyanate;
the dispersing agent is one of calcium stearate, zinc stearate and sodium stearate;
the antioxidant is 1010, or one half of each of the antioxidant 1010 and the antioxidant 168, or one half of each of the antioxidant 1010 and the antioxidant 1076;
the tensile strength of the fully biodegradable composite material is 14.3-15.2 MPa, the elongation at break is 232-258%, and the water absorption rate is 6.8-9.2%.
The further technical scheme is as follows:
in the step (1.3), high-pressure homogenization conditions are as follows: the pressure is 80-90 MPa, the temperature is 60-70 ℃, and the process is repeated for 6-8 times.
In the step (2), the native starch is dried at a temperature of 80 ℃ for 4 hours in advance.
In the step (2), the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; the temperature of the seven sections of independent temperature control areas is respectively 90 ℃, 100 ℃, 110 ℃ and 100 ℃.
In step (3), polybutylene adipate terephthalate (PBAT) is dried at a temperature of 80 ℃ for 6h in advance.
In the step (3), the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; the temperature of the seven sections of independent temperature control areas is 130 ℃, 140 ℃, 145 ℃, 150 ℃ and 145 ℃.
Compared with the prior art, the beneficial technical effects of the invention are embodied in the following aspects:
(1) The method takes pulp cellulose as a raw material, adopts a method of combining sodium hydroxide pretreatment with 2, 6-tetramethylpiperidine oxynitride (TEMPO) catalytic oxidation with high-pressure mechanical treatment to prepare the cellulose nanofibrils, effectively improves the oxidation degree and the reaction efficiency of the cellulose, and the prepared cellulose nanofibrils have larger length-diameter ratio and better dispersity, the length is 3-8 mu m, and the diameter is 3-10 nm.
(2) The cellulose nano-fibrils are used as the reinforcing filler, and can form a hydrogen bond network with the starch base at the interface when the starch base material is reinforced, so that the starch base and the cellulose have good interface compatibility, in addition, the cellulose nano-fibrils have high strength and large rigidity, and the rigid nano-fibrils can form a rigid nano-fiber network due to the hydrogen bond action between the adjacent nano-fibers, so that the mechanical property of the composite material can be enhanced, and the moisture sensitivity of the material can be improved, so that the composite material has good mechanical strength, water resistance and thermal stability.
(3) The starch and the cellulose have the characteristics of wide raw material sources, low price, reproducibility, small environmental pollution, complete degradation and the like, and the composite material prepared by utilizing the starch and the cellulose can effectively relieve the white pollution and relieve the crisis of biochemical energy shortage. The fully biodegradable composite material prepared from the poly (butylene adipate-terephthalate) solves the problem of difficult application of the downstream poly (butylene adipate-terephthalate) material, reduces the production cost, can meet the performance requirements of the degradable film bag industry, is non-toxic and harmless, and ensures the use safety. When the addition amount of the thermoplastic starch and cellulose nanofibril composite material is 50wt%, the tensile strength of the polybutylene adipate-terephthalate and starch composite material reaches 15.2MPa, and the water absorption rate is only 6.8%.
(4) The preparation method disclosed by the invention is simple in production process, wide in raw material source, high in economic practicability and capable of solving the technical problems of poor mechanical strength and water resistance of the poly (butylene adipate-terephthalate) and starch composite material when the starch content is high.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments.
Example 1
The preparation operation steps of the cellulose nano fibril reinforced full biodegradable composite material are as follows:
(1) Preparation of cellulose nanofibrils
(1.1) dispersing 5g of flax pulp cellulose into 1500mL of 7wt% sodium hydroxide (NaOH) solution, stirring and reacting at 25 ℃ for 12h, and washing with water to be neutral after the reaction is finished to obtain the pretreated cellulose.
(1.2) 7.42g of sodium carbonate (Na) 2 CO 3 ) And 2.52g sodium bicarbonate (NaHCO) 3 ) Dissolving in 500mL of deionized water to form a buffer solution; 0.1g of 2, 6-tetramethylpiperidine nitroxide (TEMPO) and 1g of sodium bromide (NaBr) are ultrasonically dissolved in a buffer solution, 5g of pretreated cellulose is added, then 10mL of sodium hypochlorite (NaClO) solution with the concentration of 2mol/L is measured, the sodium hypochlorite solution (NaClO) solution is slowly dripped into the suspension under stirring, 4mol/L of dilute hydrochloric acid solution is used for adjusting the pH value of a reaction system to 10.4, the reaction system is stirred in a constant-temperature water bath at 30 ℃ for 6 hours and is added with 10mL of absolute ethyl alcohol for stopping the reaction, and a reaction product is washed to be neutral by water.
(1.3) preparing a mixture with the cellulose content of 1-2wt% by using water for reaction products, and carrying out high-pressure homogenization under the following conditions: repeating the steps for 8 times under the pressure of 80MPa and the temperature of 70 ℃ to obtain the translucent gelatinous cellulose nanofibrils.
The cellulose nanofibrils have a length of 3 to 8 μm and a diameter of 3 to 10nm.
(2) Preparation of a composite of thermoplastic starch and cellulose nanofibrils
The corn starch is dried at 80 deg.C for 4 hr.
Weighing 750g of corn starch, 250g of plasticizer glycerol and 800g of gelatinous cellulose nanofibrils; stirring to fully mix, and mixing and plasticizing the premix in a double-screw extruder at 25 ℃ for 10min, wherein the screw rotating speed is 120rpm; the double-screw extruder is a co-rotating double-screw extruder, and the length-diameter ratio is 48:1, the diameter of the screw is 22mm; dividing the composite material into seven sections of independent temperature control areas from a feed inlet to a die head, setting the temperatures of the seven sections of independent temperature control areas to be 90 ℃, 100 ℃, 110 ℃ and 100 ℃ respectively for extrusion, and carrying out air cooling, drawing strips, granulating and drying on the extruded composite material of the thermoplastic starch and the cellulose nanofibrils for later use.
(3) Preparation of a composite of polybutylene adipate terephthalate (PBAT), thermoplastic starch and cellulose nanofibrils
The poly (butylene adipate terephthalate) (PBAT) was dried beforehand at 80 ℃ for 6h.
Weighing 500g of polybutylene adipate terephthalate (PBAT), 500g of a thermoplastic starch and cellulose nanofibril composite material, 5g of toluene diisocyanate serving as a compatibilizer, 5g of calcium stearate serving as a dispersing agent and 2g of an antioxidant 1010; fully mixing for 10min in a high-speed mixer at the rotating speed of 800rpm at room temperature; putting the mixture into a double-screw extruder to extrude and granulate, wherein the rotating speed of the screws is 300rpm; the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; the temperature of the seven sections of independent temperature control areas are respectively set to be 130 ℃, 140 ℃, 145 ℃, 150 ℃ and 145 ℃; obtaining the granular full-biodegradable composite material. The fully biodegradable composite material of example 1 had a tensile strength of 14.3MPa, an elongation at break of 258% and a water absorption of 9.2%.
The melt mass flow rate of the polybutylene adipate-terephthalate is 4 g/10min, and the carboxyl content is 30 mol/t.
Example 2
The preparation operation steps of the cellulose nano fibril reinforced full biodegradable composite material are as follows:
(1) Preparation of cellulose nanofibrils
(1.1) dispersing 8g of bamboo pulp cellulose into 1500mL of 5wt% sodium hydroxide solution, stirring and reacting for 10h at 30 ℃, and washing with water to be neutral after the reaction is finished to obtain the pretreated cellulose.
(1.2) dissolving 7.42g of sodium carbonate and 2.52g of sodium bicarbonate in 500mL of deionized water to form a buffer; ultrasonically dissolving 0.1g of 2, 6-tetramethylpiperidine oxynitride and 1g of sodium bromide in a buffer solution, adding 7g of pretreated cellulose, measuring 10mL of sodium hypochlorite solution with the concentration of 3mol/L, slowly and dropwise adding the sodium hypochlorite solution into the suspension under stirring, adjusting the pH value of a reaction system to 10.6 by using 4mol/L of dilute hydrochloric acid solution, stirring the mixture in a constant-temperature water bath at 30 ℃ for reaction for 5 hours, adding 10mL of absolute ethyl alcohol to stop the reaction, and washing a reaction product to be neutral by using water.
(1.3) preparing a mixture with the cellulose content of 1-2wt% by using water for reaction products, and carrying out high-pressure homogenization under the following conditions: repeating the steps for 6 times under the pressure of 85MPa and the temperature of 60 ℃ to obtain the translucent gelatinous cellulose nanofibrils.
The cellulose nanofibrils have a length of 3 to 8 μm and a diameter of 3 to 10nm.
(2) Preparation of a composite of thermoplastic starch and cellulose nanofibrils
Drying the cassava starch at 80 ℃ for 4h in advance.
Weighing 700g of tapioca starch, 300g of plasticizer glycerol and 900g of gelatinous cellulose nanofibrils; stirring to fully mix, and mixing and plasticizing the premix in a double-screw extruder at 25 ℃ for 10min, wherein the screw rotating speed is 100rpm; the double-screw extruder is a co-rotating double-screw extruder, and the length-diameter ratio is 48:1, the diameter of the screw is 22mm; dividing the composite material into seven sections of independent temperature control areas from a feed inlet to a die head, setting the temperatures of the seven sections of independent temperature control areas to be 90 ℃, 100 ℃, 110 ℃ and 100 ℃ respectively for extrusion, and carrying out air cooling, drawing strips, granulating and drying on the extruded composite material of the thermoplastic starch and the cellulose nanofibrils for later use.
(3) Preparation of composite materials of polybutylene adipate-terephthalate, thermoplastic starch and cellulose nanofibrils
The poly (butylene adipate-terephthalate) is dried for 6h at 80 ℃ in advance.
Weighing 500g of polybutylene adipate-terephthalate, 500g of thermoplastic starch and cellulose nanofibril composite material, 8g of compatibilizer diphenylmethane diisocyanate, 3g of dispersant zinc stearate, 1g of antioxidant 1010 and 1g of antioxidant 168; fully mixing for 8min in a high-speed mixer at the rotating speed of 1000rpm at room temperature; putting the mixture into a double-screw extruder to extrude and granulate, wherein the rotating speed of the screws is 250rpm; the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; the temperature of the seven sections of independent temperature control areas are respectively set to be 130 ℃, 140 ℃, 145 ℃, 150 ℃ and 145 ℃; obtaining the granular poly-full biodegradable composite material. The fully biodegradable composite material of example 2 had a tensile strength of 14.8MPa, an elongation at break of 232% and a water absorption of 8.5%.
The melt mass flow rate of the polybutylene adipate-terephthalate is 4 g/10min, and the carboxyl content is 30 mol/t.
Example 3
The preparation operation steps of the cellulose nano fibril reinforced full-biodegradable composite material are as follows:
(1) Preparation of cellulose nanofibrils
(1.1) dispersing 10g of softwood pulp cellulose into 1500mL of 8wt% sodium hydroxide solution, stirring at 35 ℃ for reaction for 11h, and washing with water to be neutral after the reaction is finished to obtain the pretreated cellulose.
(1.2) dissolving 7.42g of sodium carbonate and 2.52g of sodium bicarbonate in 500mL of deionized water to form a buffer; ultrasonically dissolving 0.1g of 2, 6-tetramethylpiperidine oxynitride and 1g of sodium bromide in a buffer solution, adding 8g of pretreated cellulose, measuring 10mL of a 4mol/L sodium hypochlorite solution, slowly and dropwise adding the sodium hypochlorite solution into the suspension under stirring, adjusting the pH value of a reaction system to 10.8 by using a 4mol/L dilute hydrochloric acid solution, stirring the reaction system in a constant-temperature water bath at 30 ℃ for reaction for 4 hours, adding 10mL of absolute ethyl alcohol to stop the reaction, and washing a reaction product to be neutral by water.
(1.3) preparing the reaction product into a mixture with the cellulose content of 1-2wt% by using water, and carrying out high-pressure homogenization under the following conditions: the pressure is 90MPa, the temperature is 70 ℃, and the process is repeated for 7 times to obtain the translucent gelatinous cellulose nanofibrils.
The cellulose nanofibrils have a length of 3 to 8 μm and a diameter of 3 to 10nm.
(2) Preparation of a composite of thermoplastic starch and cellulose nanofibrils
The wheat starch is dried for 4h at 80 ℃.
Weighing 720g of wheat starch, 280g of plasticizer glycerol and 1000g of gelatinous cellulose nanofibrils; stirring to fully mix, and mixing and plasticizing the premix in a double-screw extruder at 25 ℃ for 10min, wherein the screw rotating speed is 150rpm; the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; dividing the composite material into seven sections of independent temperature control areas from a feed inlet to a die head, setting the temperatures of the seven sections of independent temperature control areas to be 90 ℃, 100 ℃, 110 ℃ and 100 ℃ respectively for extrusion, and carrying out air cooling, drawing strips, granulating and drying on the extruded composite material of the thermoplastic starch and the cellulose nanofibrils for later use.
(3) Preparation of composite of polybutylene adipate-terephthalate, thermoplastic starch and cellulose nanofibrils
The poly (butylene adipate-terephthalate) is dried for 6h at 80 ℃ in advance.
Weighing 500g of polybutylene adipate-terephthalate, 500g of thermoplastic starch and cellulose nanofibril composite, 10g of compatibilizer methylcyclohexane diisocyanate, 1g of dispersant sodium stearate, 1g of antioxidant 1010 and 1g of antioxidant 1076; fully mixing for 5min in a high-speed mixer at the rotating speed of 1500rpm at room temperature; putting the mixture into a double-screw extruder to extrude and granulate, wherein the rotating speed of the screws is 200rpm; the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; the temperature of the seven independent temperature control areas is 130 ℃, 140 ℃, 145 ℃, 150 ℃ and 145 ℃; obtaining the granular full-biodegradable composite material. The fully biodegradable composite of example 3 had a tensile strength of 15.2MPa, an elongation at break of 245%, and a water absorption of 6.8%.
The melt mass flow rate of the polybutylene adipate-terephthalate is 4 g/10min, and the carboxyl content is 30 mol/t.
Comparative example 1
(1) Preparation of thermoplastic starch
The corn starch is dried at 80 deg.C for 4 hr.
Stirring 750g of corn starch, 250g of plasticizer glycerol and 150mL of deionized water until the components are fully mixed, and mixing and plasticizing for 10min at 25 ℃ in a double-screw extruder, wherein the rotating speed of a screw is 120rpm; the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; dividing the temperature control area into seven sections from a feed inlet to a die head, setting the temperature of the seven sections of independent temperature control areas to be 90 ℃, 100 ℃, 110 ℃ and 100 ℃ respectively for extrusion, air-cooling, stretching, granulating and drying the extruded thermoplastic starch, and storing for later use.
(2) Preparation of composite material of polybutylene adipate-terephthalate and thermoplastic starch
The polybutylene adipate-terephthalate is dried for 6h at 80 ℃ in advance.
Weighing 500g of polybutylene adipate-terephthalate, 500g of thermoplastic starch, 5g of compatibilizer toluene diisocyanate, 5g of dispersant calcium stearate and 2g of antioxidant 1010; fully mixing for 10min in a high-speed mixer at the rotating speed of 800rpm at room temperature; putting the mixture into a double-screw extruder to extrude and granulate, wherein the rotating speed of the screws is 300rpm; the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; the temperature of the seven sections of independent temperature control areas are respectively set to be 130 ℃, 140 ℃, 145 ℃, 150 ℃ and 145 ℃; the granular polybutylene adipate-terephthalate and thermoplastic starch composite material is obtained. The composite material of comparative example 1 had a tensile strength of 10.9MPa, an elongation at break of 278%, and a water absorption of 16.0%.
The melt mass flow rate of the polybutylene adipate-terephthalate is 4 g/10min, and the carboxyl content is 30 mol/t.
Comparative example 2
(1) Preparation of thermoplastic starch
Drying the cassava starch at 80 ℃ for 4h in advance.
700g of cassava starch, 300g of plasticizer glycerol and 150mL of deionized water are stirred to be fully mixed, and are mixed and plasticized for 10min in a double-screw extruder at the temperature of 25 ℃, wherein the rotating speed of a screw is 100rpm; the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; dividing the temperature control area into seven sections from a feed inlet to a die head, setting the temperature of the seven sections of independent temperature control areas to be 90 ℃, 100 ℃, 110 ℃ and 100 ℃ respectively for extrusion, air-cooling, stretching, granulating and drying the extruded thermoplastic starch, and storing for later use.
(2) Preparation of composite material of polybutylene adipate-terephthalate and thermoplastic starch
The polybutylene adipate-terephthalate is dried for 6h at 80 ℃ in advance.
Weighing 500g of polybutylene adipate-terephthalate, 500g of thermoplastic starch, 8g of compatibilizer diphenylmethane diisocyanate, 3g of dispersant zinc stearate, 1g of antioxidant 1010 and 1g of antioxidant 168; fully mixing for 8min in a high-speed mixer at the rotating speed of 1000rpm at room temperature; putting the mixture into a double-screw extruder to extrude and granulate, wherein the rotating speed of the screws is 250rpm; the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; the temperature of the seven sections of independent temperature control areas are respectively set to be 130 ℃, 140 ℃, 145 ℃, 150 ℃ and 145 ℃; the granular polybutylene adipate-terephthalate and thermoplastic starch composite material is obtained. The composite material of comparative example 2 had a tensile strength of 11.5MPa, an elongation at break of 293% and a water absorption of 14.5%.
The melt mass flow rate of the polybutylene adipate-terephthalate is 4 g/10min, and the carboxyl content is 30 mol/t.
Comparative example 3
(1) Preparation of thermoplastic starch
The wheat starch is dried for 4h at 80 ℃.
Stirring 720g of wheat starch, 280g of plasticizer glycerol and 150mL of deionized water until the mixture is fully mixed, and mixing and plasticizing for 10min in a double-screw extruder at 25 ℃, wherein the rotating speed of a screw is 150rpm; the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; dividing the temperature of the seven independent temperature control areas into seven independent temperature control areas from a feed inlet to a die head, respectively setting the temperatures of the seven independent temperature control areas to 90 ℃, 100 ℃, 110 ℃ and 100 ℃ for extrusion, air-cooling, drawing strips and cutting granules of the extruded thermoplastic starch, and storing the granules for later use after drying.
(2) Preparation of composite material of polybutylene adipate-terephthalate and thermoplastic starch
The polybutylene adipate-terephthalate is dried for 6h at 80 ℃ in advance.
Weighing 500g of polybutylene adipate-terephthalate, 500g of thermoplastic starch, 10g of compatibilizer methylcyclohexane diisocyanate, 1g of dispersant sodium stearate, 1g of antioxidant 1010 and 1g of antioxidant 1076; fully mixing for 5min in a high-speed mixer at the rotating speed of 1500rpm at room temperature; putting the mixture into a double-screw extruder to extrude and granulate, wherein the rotating speed of the screws is 200rpm; the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; the temperature of the seven sections of independent temperature control areas are respectively set to be 130 ℃, 140 ℃, 145 ℃, 150 ℃ and 145 ℃; the granular polybutylene adipate-terephthalate and thermoplastic starch composite material is obtained. The composite of comparative example 3 had a tensile strength of 9.7MPa, an elongation at break of 267% and a water absorption of 15.3%.
The melt mass flow rate of the polybutylene adipate-terephthalate is 4 g/10min, and the carboxyl content is 30 mol/t.
The materials obtained in the above examples and comparative examples were fed into an injection molding machine and injection-molded into standard sample bars by means of a mold. The test method is carried out according to the specification of GB/T17037.1, and a model A die is used for preparing a model 1A sample conforming to GB/T1040.2. Water absorption test: according to the provisions of GB/T1034-2008, the samples are numbered and then are sequentially weighed, then the samples are placed into a water tank to be soaked for 2 days, the samples are taken out and then the mass is wiped dry, and the water absorption rate is calculated. The test results of examples and comparative examples are shown in table 1.
From the test data, compared with the comparative example of the poly (butylene adipate-terephthalate), the starch and the auxiliary agent with the same proportion, the fully biodegradable composite material reinforced by the cellulose nano fibrils basically has the same elongation at break, but the tensile strength and the water resistance are obviously improved, and the data index of the example group is obviously superior to that of the comparative example group. Therefore, according to the specific embodiment of the method, the technical problem that the mechanical strength and the water resistance of the composite material of the polybutylene adipate-terephthalate and the starch are poor when the starch content is high can be solved.
Claims (6)
1. A preparation method of a cellulose nanofibril reinforced full-biodegradable composite material is characterized by comprising the following operation steps:
(1) Preparation of cellulose nanofibrils
(1.1) dispersing 5-10 g of paper pulp cellulose into 1500mL of sodium hydroxide solution with the concentration of 5-8 wt%, stirring and reacting for 10-12 h at the temperature of 25-35 ℃, and washing with water to be neutral to obtain pretreated cellulose;
the paper pulp cellulose is flax pulp cellulose, bamboo pulp cellulose or wood pulp cellulose;
(1.2) dissolving 7.42g of sodium carbonate and 2.52g of sodium bicarbonate in 500mL of deionized water to form a buffer; ultrasonically dissolving 0.1g of 2, 6-tetramethylpiperidine oxynitride and 1g of sodium bromide in a buffer solution, adding 5-8 g of pretreated cellulose, slowly dropwise adding 10mL of sodium hypochlorite solution with the concentration of 2-4 mol/L under stirring, adjusting the pH value of a reaction system to 10.4-10.8 by using dilute hydrochloric acid solution with the concentration of 4mol/L, stirring and reacting in a constant-temperature water bath kettle at 30 ℃ for 2-7 hours, adding 10mL of absolute ethyl alcohol to stop the reaction, and washing the reaction product to be neutral by water;
(1.3) preparing a reaction product into a mixture with the cellulose content of 1-2 wt% by using water, and homogenizing under high pressure to obtain translucent gelatinous cellulose nanofibrils;
the length of the cellulose nano-fibril is 3-8 mu m, and the diameter is 3-10 nm;
(2) Preparation of a composite of thermoplastic starch and cellulose nanofibrils
Uniformly stirring and mixing 700-750 g of raw starch, 250-300 g of plasticizer and 800-1000 g of gelatinous cellulose nanofibril to obtain a premix, and mixing and plasticizing the premix in a double-screw extruder at 25 ℃ for 10min, wherein the rotating speed of a screw is 100-150 rpm; raising the temperature of the double-screw extruder, and extruding and granulating to obtain the composite material of the thermoplastic starch and the cellulose nano-fibrils;
the native starch is corn starch, or tapioca starch, or wheat starch;
the plasticizer is glycerol;
(3) Preparation of composite materials of polybutylene adipate-terephthalate, thermoplastic starch and cellulose nanofibrils
Fully mixing 500g of polybutylene adipate-terephthalate, 500g of a composite material of thermoplastic starch and cellulose nanofibrils, 5-10 g of a compatibilizer, 1-5 g of a dispersant and 2g of an antioxidant in a high-speed mixer at the room temperature of 800-1500 rpm for 5-10 min; extruding and granulating in a double-screw extruder at the screw rotating speed of 200-300 rpm to obtain a granular fully biodegradable composite material;
the melt mass flow rate of the poly (butylene adipate-terephthalate) is 4 g/10min, and the carboxyl content is 30 mol/t;
the compatibilizer is a compound with a molecular structure containing at least 2 isocyanate functional groups, and specifically is one of toluene diisocyanate, diphenylmethane diisocyanate and methylcyclohexane diisocyanate;
the dispersing agent is one of calcium stearate, zinc stearate and sodium stearate;
the antioxidant is 1010, or one half of each of the antioxidant 1010 and the antioxidant 168, or one half of each of the antioxidant 1010 and the antioxidant 1076;
the tensile strength of the fully biodegradable composite material is 14.3-15.2 MPa, the elongation at break is 232-258%, and the water absorption is 6.8-9.2%.
2. The method of claim 1, wherein the cellulose nanofibril-reinforced fully biodegradable composite is prepared by: in the step (1.3), high-pressure homogenization conditions are as follows: the pressure is 80-90 MPa, the temperature is 60-70 ℃, and the process is repeated for 6-8 times.
3. The method of claim 1, wherein the cellulose nanofibril-reinforced fully biodegradable composite is prepared by: in the step (2), the native starch is dried at a temperature of 80 ℃ for 4 hours in advance.
4. The method of claim 1, wherein the cellulose nanofibril-reinforced fully biodegradable composite is prepared by: in the step (2), the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; the temperature of the seven sections of independent temperature control areas is respectively 90 ℃, 100 ℃, 110 ℃ and 100 ℃.
5. The method of claim 1, wherein the cellulose nanofibril-reinforced fully biodegradable composite is prepared by: in step (3), the polybutylene adipate-terephthalate is dried at a temperature of 80 ℃ for 6 hours in advance.
6. The method of claim 1, wherein the cellulose nanofibril-reinforced fully biodegradable composite is prepared by: in the step (3), the double-screw extruder is a co-rotating double-screw extruder, the length-diameter ratio is 48; the temperature of the seven sections of independent temperature control areas is 130 ℃, 140 ℃, 145 ℃, 150 ℃ and 145 ℃.
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