CN111763304A - A kind of lignin oligomer epoxy resin and preparation method thereof - Google Patents

Abstract

The invention discloses a lignin oligomer epoxy resin and a preparation method thereof. In the method, a lignin oligomer epoxy resin is prepared by performing a ring-opening reaction between lignin reduction degradation oligomer and epichlorohydrin under the action of a phase transfer catalyst, and then performing a ring-closing reaction in the presence of an alkali. The preparation method of the invention is simple and convenient, and the prepared lignin oligomer epoxy resin has the mechanical properties of the cured product equivalent to the bisphenol A epoxy resin, and has excellent thermal stability.

Description

A kind of lignin oligomer epoxy resin and preparation method thereof

technical field

The invention relates to a lignin oligomer epoxy resin and a preparation method thereof, in particular to a method for preparing an epoxy resin by reacting a partially reductive and degraded lignin oligomer with epichlorohydrin, which belongs to bio-based polymer materials field.

technical background

As a natural phenolic polymer compound with abundant reserves in nature, lignin has a wide range of sources and low price, and its molecular structure contains a variety of active groups such as phenolic hydroxyl, alcohol hydroxyl, and carboxyl groups, which can replace traditional fossil resources to synthesize epoxy resins. Especially its macromolecular rigid skeleton can endow the epoxy resin with good mechanical properties and thermal stability. However, lignin has a complex chemical structure and composition, low reactivity, and is insoluble in most organic solvents, which restricts its development and utilization in the field of epoxy resins.

At present, there are three main ways for the application of lignin in epoxy resin: (1) direct blending of lignin with epoxy resin in the form of additives and modifiers (Green Chemistry, 2018, 20(7): 1459– 1466); (2) After the lignin was modified by pretreatment such as demethylation, phenolation, methylolation, and amination, it replaced bisphenol A to synthesize epoxy resin (Progress in Polymer Science, 2014, 39 (7). ): 1266–1290); (3) degrading lignin into oligomers to replace bisphenol A to synthesize epoxy resins (Biomacromolecules, 2017, 18(8): 2640–2648). Compared with the previous two methods, the synthesis of epoxy resins with lignin-degraded oligomers has the outstanding advantages of good compatibility and high lignin replacement rate, which is an effective way for high-value utilization of lignin in the field of epoxy resin materials.

Patent CN 201910934089.1 reports a lignin oligomer and its preparation method. The lignin reduction degradation oligomer obtained by the method not only has high phenolic hydroxyl content (≥362 mg/g), high reactivity and good organic solvent dissolution It is an ideal raw material to effectively replace lignin to synthesize epoxy resin.

In the present invention, a novel bio-based epoxy resin is prepared by using the partially degraded oligomer of lignin obtained by the above method, and the small molecular compounds in the lignin oligomer are removed by solvent separation, so as to effectively improve the mechanical properties of the epoxy resin cured product, and the method is simple and convenient. The obtained epoxy resin has the same mechanical properties of cured products as bisphenol A epoxy resin, and has excellent thermal stability, which can replace bisphenol A epoxy resin in coatings, adhesives, composite materials, roads transportation, etc.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an oligomer epoxy resin based on partial reduction and degradation of lignin and a preparation method thereof.

其中lignin为木质素。The present invention adopts the following technical scheme: a lignin oligomer epoxy resin is prepared by ring-opening reaction of lignin oligomer and epichlorohydrin under the action of a phase transfer catalyst, and then ring-closing reaction in the presence of alkali to prepare lignin Elemental oligomer epoxy resin, the structural formula is:

Wherein lignin is lignin.

The preparation method of the lignin oligomer epoxy resin comprises the following steps: a ring-opening reaction of a lignin oligomer and epichlorohydrin under the action of a phase transfer catalyst, and then a ring-closing reaction in the presence of an alkali to prepare a low-lignin epoxy resin. Polymer epoxy resin, the synthesis reaction formula is:

The described lignin oligomer is a partial reduction and degradation oligomer of lignin and its solvent-separated oligomer prepared according to the method of patent CN 201910934089.1, the molecular weight is 500g/mol～2000g/mol, and the phenolic hydroxyl content is 0.35mol/100g～0.90 mol/100g.

The solvent separation oligomer is prepared by the following method: dissolving the lignin partial reduction degradation oligomer in a polar organic solvent, adding a non-polar organic solvent, and distilling the insolubles under reduced pressure to obtain a solvent separation low polymer. polymer.

Described polar organic solvent is any one or the mixture of more than two in methylene chloride, ethyl acetate, acetone, chloroform; Described non-polar solvent is petroleum ether, n-hexane, n-pentane. For any one, the dosage is 1 to 10 times the volume of the polar organic solvent.

Described phase transfer catalyst is benzyl triethyl ammonium chloride, benzyl trimethyl ammonium chloride, tetrabutyl ammonium bromide, tetrabutyl ammonium chloride, tetrabutyl ammonium hydrogen sulfate, dodecyl Any one or a mixture of two or more of trimethylammonium chloride or tetradecyltrimethylammonium chloride is used in an amount of 1% to 5% of the mass of the lignin oligomer.

The dosage of the epichlorohydrin is 4 times to 30 times of the quality of the lignin oligomer.

The alkali is any one or a mixture of two or more of sodium hydroxide, potassium hydroxide and calcium hydroxide, and the ratio of the amount of the phenolic hydroxyl group in the alkali to the lignin oligomer is 0.5 to 2.5:1 .

The ring-opening reaction temperature is 70°C～120°C, the ring-opening reaction time is 2h～10h, the ring-closing reaction temperature is 40°C～80°C, and the ring-closing reaction time is 1h～5h.

The optimal preparation reaction conditions are: the amount of phase transfer catalyst is 2.0% of the mass of the lignin oligomer, the ring-opening reaction temperature is 100 °C, the ring-opening reaction time is 8h, and the amount of the phenolic hydroxyl group in the alkali and the lignin oligomer is equal to The ratio is 2:1, the closed-loop reaction temperature is 70°C, and the closed-loop reaction time is 3h; under the reaction conditions, the obtained epoxy resin is liquid or solid according to the molecular weight of the lignin oligomer.

Beneficial effects:

1. The present invention prepares novel bio-based epoxy resins by partially reducing and degrading lignin oligomers, effectively overcoming the key problems affecting its high-value application such as complex chemical structure and composition of lignin, low reactivity, and poor solubility in organic solvents, It is of great significance for realizing the efficient and high-value utilization of lignin resources and expanding its application in epoxy resin and other polymer materials.

2. The method for preparing the lignin oligomer epoxy resin is simple and convenient, and the obtained lignin oligomer epoxy resin has the mechanical properties of the cured product equivalent to bisphenol A epoxy resin, and has excellent thermal stability.

Description of drawings

Fig. 1 Infrared spectrum of lignin oligomer epoxy resin.

Figure 2 ¹ H NMR map of lignin oligomer epoxy resin.

Figure ^313C NMR map of lignin oligomer epoxy resin.

In the infrared spectrum of the lignin oligomer epoxy resin (Fig. 1), the broad peak at 3490cm ^-1 is the characteristic absorption peak of –OH, and at 2928cm ^-1 is –OCH ₃ and –CH ₃ , –CH in the side chain ₂ – C–H stretching vibration absorption peak. 1589cm ^-1 , 1506cm ^-1 , 1454cm ^-1 are the characteristic absorption peaks of lignin phenylpropane skeleton, and 907cm ^-1 is the characteristic absorption peak of epoxy group.

In the ¹ H NMR spectrum of the lignin oligomer epoxy resin (Figure 2), the characteristic peaks of the methine hydrogen of the epoxy group at the chemical shifts of 3.67 ppm to 3.86 ppm, the chemical shifts of 2.61 ppm to 2.83 ppm, and In the ¹³ C NMR spectrum (Fig. 3), the chemical shifts from 44.6 ppm to 56.0 ppm are characteristic peaks of epoxy groups.

Detailed ways

A lignin oligomer epoxy resin and a preparation method thereof. The synthetic reaction formula of this epoxy resin is as follows:

The method is implemented through the following steps:

In the first step, the lignin oligomer and epichlorohydrin undergo a ring-opening reaction at 70℃～120℃ for 2h～10h under the action of a phase transfer catalyst;

In the second step, the reaction system is cooled to 40°C to 80°C, a certain amount of alkali is added in batches, the ring-closure reaction is performed for 1 h to 5 h, washed with water, and the organic phase is distilled under reduced pressure to obtain a lignin oligomer epoxy resin.

The lignin oligomer described in the first step is a partial reduction and degradation oligomer of lignin prepared according to the method of patent CN 201910934089.1 and its solvent-separated oligomer (molecular weight 500g/mol～2000g/mol, phenolic hydroxyl content 0.35mol) /100g～0.90mol/100g);

The solvent-separated oligomer is prepared by the following method: dissolving the lignin partial reduction and degradation oligomer in any one or two or more of polar organic solvents such as dichloromethane, ethyl acetate, acetone, and chloroform The mixture is added with petroleum ether, n-hexane, n-pentane and other non-polar organic solvents, and the amount is 1 to 10 times the volume of the polar organic solvent, and the insolubles are distilled under reduced pressure to obtain solvent-separated oligomers.

The dosage of the epichlorohydrin is 4 times to 30 times of the quality of the lignin oligomer;

Described phase transfer catalyst is benzyl triethyl ammonium chloride, benzyl trimethyl ammonium chloride, tetrabutyl ammonium bromide, tetrabutyl ammonium chloride, tetrabutyl ammonium hydrogen sulfate, dodecyl Any one or a mixture of two or more in trimethyl ammonium chloride and tetradecyl trimethyl ammonium chloride, the optimum dosage is 2% of the quality of the lignin oligomer;

The optimal temperature of the ring-opening reaction is 100°C, and the optimal time of the ring-opening reaction is 8h.

The alkali described in the second step is any one or a mixture of more than two in sodium hydroxide, potassium hydroxide and calcium hydroxide, and the ratio of the amount of the phenolic hydroxyl group in the alkali and the lignin oligomer is the best is 2:1;

The optimal temperature for the closed-loop reaction is 70°C, and the optimal time for the closed-loop reaction is 3h.

Example 1

In a four-necked round-bottomed flask with a stirrer, a thermometer and a reflux condenser, add 8.0g lignin oligomer (molecular weight 998g/mol, phenolic hydroxyl content 0.65mol/100g), 115g epichlorohydrin, stir to dissolve , 0.16 g of benzyl triethyl ammonium chloride was added, and the temperature was raised to 70 °C for 8 h. The temperature was lowered to 50 °C, 4.11 g of sodium hydroxide was added in batches, the temperature was raised to 70 °C and the reaction was performed for 3 h. After the reaction, wash with water for 3 to 4 times, and distill the organic phase under reduced pressure to obtain a lignin oligomer epoxy resin with an epoxy value of 0.26 mol/100 g.

Example 2

In a four-necked round-bottomed flask with a stirrer, a thermometer and a reflux condenser, add 10.2g lignin oligomer (molecular weight 998g/mol, phenolic hydroxyl content 0.65mol/100g), 145g epichlorohydrin, stir to dissolve , 0.10 g of tetrabutylammonium bromide was added, and the temperature was raised to 100 °C for 4 h. The temperature was lowered to 50 °C, 2.61 g of sodium hydroxide was added in batches, the temperature was raised to 60 °C and the reaction was performed for 3 h. After the reaction was completed, washed with water for 3 to 4 times, and the organic phase was distilled under reduced pressure to obtain a lignin oligomer epoxy resin with an epoxy value of 0.27 mol/100 g.

Example 3

In a four-necked round-bottomed flask with a stirrer, a thermometer and a reflux condenser, add 10.3g of lignin oligomers (molecular weight 998g/mol, phenolic hydroxyl content 0.65mol/100g), 147g epichlorohydrin, stir and dissolve , 0.20 g of benzyl trimethyl ammonium chloride was added, and the temperature was raised to 110 °C for 2 h. The temperature was lowered to 50 °C, 2.64 g of sodium hydroxide was added in batches, the temperature was raised to 80 °C and the reaction was performed for 2 h. After the completion of the reaction, washing with water 3 to 4 times, the organic phase is distilled under reduced pressure to obtain a lignin oligomer epoxy resin with an epoxy value of 0.33 mol/100 g.

Example 4

In a four-necked round-bottomed flask with a stirrer, a thermometer and a reflux condenser, add 40g lignin oligomer (molecular weight 998g/mol, phenolic hydroxyl content 0.65mol/100g), 560g epichlorohydrin, stir to dissolve, 0.80 g of benzyltriethylammonium chloride was added, and the temperature was raised to 100 °C for 8 h. The temperature was lowered to 50 °C, 20.6 g of sodium hydroxide was added in batches, the temperature was raised to 70 °C and the reaction was performed for 3 h. After the reaction, wash with water 3 to 4 times, and distill the organic phase under reduced pressure to obtain a lignin oligomer epoxy resin with an epoxy value of 0.40 mol/100 g.

Example 5

In a four-necked round-bottomed flask with a stirrer, a thermometer and a reflux condenser, add 75g of lignin oligomers (molecular weight 1489g/mol, phenolic hydroxyl content 0.56mol/100g), 900g epichlorohydrin, stir to dissolve, 1.50 g of tetrabutylammonium chloride was added, and the temperature was raised to 90 °C for 8 h. The temperature was lowered to 50 °C, 33.8 g of sodium hydroxide was added in batches, the temperature was raised to 70 °C and the reaction was performed for 3 h. After the completion of the reaction, washing with water 3 to 4 times, the organic phase was distilled under reduced pressure to obtain a lignin oligomer epoxy resin with an epoxy value of 0.39 mol/100 g.

Example 6

In a four-necked round-bottomed flask with a stirrer, a thermometer and a reflux condenser, add 93g of lignin oligomers (molecular weight 2056g/mol, phenolic hydroxyl content 0.46mol/100g), 825g epichlorohydrin, stir and dissolve, 2.79g of benzyltriethylammonium chloride was added, and the temperature was raised to 110°C for 8h. The temperature was lowered to 50°C, 34.4 g of sodium hydroxide was added in batches, the temperature was raised to 70°C and the reaction was performed for 3h. After the reaction was completed, washed with water for 3 to 4 times, and the organic phase was distilled under reduced pressure to obtain a lignin oligomer epoxy resin with an epoxy value of 0.37 mol/100 g.

Example 7

In a four-necked round-bottomed flask with a stirrer, a thermometer and a reflux condenser, add 152g of lignin oligomers (molecular weight 1451g/mol, phenolic hydroxyl content 0.43mol/100g), 800g epichlorohydrin, stir and dissolve, 6.10 g of benzyl triethyl ammonium chloride was added, and the temperature was raised to 110 °C for 5 h. The temperature was lowered to 50 °C, 32.3 g of sodium hydroxide was added in batches, the temperature was raised to 60 °C and the reaction was performed for 2 h. After the reaction, wash with water for 3 to 4 times, and distill the organic phase under reduced pressure to obtain a lignin oligomer epoxy resin with an epoxy value of 0.32 mol/100 g.

The cured product of the epoxy resin and methyltetrahydrophthalic anhydride had a flexural strength of 54.5 MPa, a tensile strength of 40.5 MPa, an impact strength of 8.70 kJ/m ² , and a T _d (5%) of 324.0°C.

Example 8

In a four-necked round-bottomed flask with a stirrer, a thermometer and a reflux condenser, add 161g of lignin partial reduction and degradation oligomer (molecular weight 1137g/mol, phenolic hydroxyl content 0.53mol/100g), 800g epichlorohydrin, Stir to dissolve, add 8.10 g of benzyl triethyl ammonium chloride, heat up to 110 ° C and react for 3 h. The temperature was lowered to 50 °C, 20.8 g of sodium hydroxide was added in batches, the temperature was raised to 60 °C and the reaction was performed for 3 h. After the completion of the reaction, washing with water 3 to 4 times, the organic phase was distilled under reduced pressure to obtain a lignin oligomer epoxy resin with an epoxy value of 0.34 mol/100 g.

The epoxy resin and methyltetrahydrophthalic anhydride cured product had a flexural strength of 55.1 MPa, a tensile strength of 42.0 MPa, an impact strength of 9.30 kJ/m ² , and a T _d (5%) of 322.9°C.

Example 9

In a four-necked round-bottomed flask with a stirrer, a thermometer and a reflux condenser, add 172g of lignin partial reduction and degradation oligomer (molecular weight 915g/mol, phenolic hydroxyl content 0.61mol/100g), 1000g epichlorohydrin, Stir to dissolve, add 3.50 g of dodecyl trimethyl ammonium chloride, heat up to 110 ° C and react for 8 h. The temperature was lowered to 50 °C, 52.4 g of sodium hydroxide was added in batches, the temperature was raised to 60 °C and the reaction was performed for 5 h. After the reaction, washing with water 3 to 4 times, the organic phase is distilled under reduced pressure to obtain a lignin oligomer epoxy resin with an epoxy value of 0.32 mol/100 g.

The flexural strength of the cured product of the epoxy resin and methyltetrahydrophthalic anhydride was 18.4 MPa, the impact strength was 4.10 kJ/m ² , and the T _d (5%) was 287.5°C.

Example 10

Dissolve 345g of lignin partial reduction degradation oligomers (molecular weight 1451g/mol, phenolic hydroxyl content 0.43mol/100g) in 500mL of dichloromethane, add 700mL of petroleum ether, and insolubles are distilled under reduced pressure to obtain solvent-separated lignin oligomers 301g (molecular weight 1718g/mol, phenolic hydroxyl content 0.50mol/100g).

In a four-necked round-bottomed flask with a stirrer, a thermometer and a reflux condenser, add 290g of lignin solvent to separate oligomers, 1200g of epichlorohydrin, stir and dissolve, add 5.80g of tetrabutylammonium chloride, and heat up to 100 ℃ reaction 3h. The temperature was lowered to 50°C, 97.2 g of potassium hydroxide was added in batches, the temperature was raised to 60°C and the reaction was performed for 3h. After the reaction, washed with water for 3 to 4 times, and the organic phase was distilled under reduced pressure to obtain a lignin oligomer epoxy resin with an epoxy value of 0.32 mol/100 g.

The cured product of the epoxy resin and methyltetrahydrophthalic anhydride had a bending strength of 74.3 MPa, a tensile strength of 46.8 MPa, an impact strength of 11.1 kJ/m ² , and a T _d (5%) of 327.4°C.

Example 11

Dissolve 238g of lignin partial reduction and degradation oligomers (molecular weight 631g/mol, phenolic hydroxyl content 0.63mol/100g) in 300mL of ethyl acetate, add 600mL of petroleum ether, insolubles are distilled under reduced pressure to obtain a solvent to separate lignin oligomers 197g (molecular weight 836g/mol, phenolic hydroxyl content 0.58mol/100g).

In a four-necked round-bottomed flask with a stirrer, a thermometer and a reflux condenser, add 197g of lignin solvent to separate oligomers, 600g of epichlorohydrin, stir and dissolve, add 3.90g of tetrabutylammonium chloride, and heat up to 100 ℃ reaction 3h. The temperature was lowered to 50 °C, 45.7 g of sodium hydroxide was added in batches, the temperature was raised to 60 °C and the reaction was performed for 3 h. After the reaction, washed with water for 3 to 4 times, and the organic phase was distilled under reduced pressure to obtain a lignin oligomer epoxy resin with an epoxy value of 0.32 mol/100 g.

The cured product of the epoxy resin and methyltetrahydrophthalic anhydride had a bending strength of 112.0 MPa, a tensile strength of 59.8 MPa, an impact strength of 11.1 kJ/m ² , and a T _d (5%) of 325.1°C.

Claims (10)

1. A lignin oligomer epoxy resin characterized by: the lignin oligomer and epoxy chloropropane are subjected to open-loop reaction under the action of a phase transfer catalyst, and then subjected to close-loop reaction in the presence of alkali to prepare the lignin oligomer epoxy resin, wherein the structural formula is as follows:

wherein lignin is lignin.

2. The preparation method of lignin oligomer epoxy resin as claimed in claim 1, characterized in that, the lignin oligomer and epichlorohydrin are subjected to ring opening reaction under the action of phase transfer catalyst, and then subjected to ring closing reaction in the presence of alkali to prepare lignin oligomer epoxy resin, wherein the synthetic reaction formula is as follows:

3. the method of producing a lignin oligomer epoxy resin according to claim 2, wherein: the lignin oligomer is a lignin partial reduction degradation oligomer prepared according to a patent CN 201910934089.1 method and a solvent separation oligomer thereof, and has a molecular weight of 500 g/mol-2000 g/mol and a phenolic hydroxyl group content of 0.35mol/100 g-0.90 mol/100 g.

4. The method of preparing a lignin oligomer epoxy resin according to claim 3, wherein: the solvent separation oligomer is prepared by the following method: and dissolving the lignin partial reductive degradation oligomer in a polar organic solvent, adding a non-polar organic solvent, and distilling insoluble substances under reduced pressure to obtain a solvent separation oligomer.

5. The method of producing a lignin oligomer epoxy resin according to claim 4, wherein: the polar organic solvent is any one or a mixture of more than two of dichloromethane, ethyl acetate, acetone and chloroform; the non-polar solvent is any one of petroleum ether, normal hexane and n-pentane, and the dosage of the non-polar solvent is 1-10 times of the volume of the polar organic solvent.

6. The method of producing a lignin oligomer epoxy resin according to claim 2, wherein: the phase transfer catalyst is any one or a mixture of more than two of benzyltriethylammonium chloride, benzyltrimethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate, dodecyltrimethylammonium chloride or tetradecyltrimethylammonium chloride, and the dosage of the phase transfer catalyst is 1-5% of the mass of the lignin oligomer.

7. The method of producing a lignin oligomer epoxy resin according to claim 2, wherein: the dosage of the epichlorohydrin is 4 to 30 times of the quality of the lignin oligomer.

8. The method of producing a lignin oligomer epoxy resin according to claim 2, wherein: the alkali is any one or a mixture of more than two of sodium hydroxide, potassium hydroxide and calcium hydroxide, and the ratio of the alkali to the amount of phenolic hydroxyl substances in the lignin oligomer is 0.5-2.5: 1.

9. The method of producing a lignin oligomer epoxy resin according to claim 2, wherein: the ring-opening reaction temperature is 70-120 ℃, the ring-opening reaction time is 2-10 h, the ring-closing reaction temperature is 40-80 ℃, and the ring-closing reaction time is 1-5 h.

10. The method for preparing lignin oligomer epoxy resin according to claim 2, wherein the optimal preparation reaction conditions are: the dosage of the phase transfer catalyst is 2.0 percent of the mass of the lignin oligomer, the ring-opening reaction temperature is 100 ℃, the ring-opening reaction time is 8 hours, the mass ratio of alkali to phenolic hydroxyl substances in the lignin oligomer is 2:1, the ring-closing reaction temperature is 70 ℃, and the ring-closing reaction time is 3 hours; under the reaction condition, the obtained epoxy resin is in a liquid state or a solid state according to the molecular weight of the lignin oligomer.

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