Preparation method and application of high-amylose starch / polylactic acid graft copolymer

Abstract

The present invention belongs to the field of polymer materials and particularly relates to a method for preparing a high-amylose starch / polylactic acid graft copolymer and its application. The method comprises the following steps: dissolving high-amylose starch in an organic solvent, adding lactide and a catalyst, and reacting at 60-110°C for 5-11 hours under an inert atmosphere to obtain the high-amylose starch / polylactic acid graft copolymer. The preparation method is simple and the resulting high-amylose starch / polylactic acid graft copolymer exhibits excellent mechanical properties, including an elongation at break of 10-330%, an elastic modulus of 20-270 MPa, and a Shore hardness of 4.5-67 HD.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and in particular relates to a preparation method and application of a high-amylose starch / polylactic acid graft copolymer. Background Art

[0002] With the rapid development of the world economy, polymer materials have brought convenience to our lives and improved the quality of life. At the same time, the damage caused to the ecological environment by "white pollution" cannot be ignored. People have also realized the harm caused to the environment by discarded non-degradable polymer materials. Biodegradable plastics have attracted much attention as a substitute for traditional non-degradable plastics. Among them, bio-based materials represented by polylactic acid are of great help in increasing the supply of green products and reducing dependence on petrochemical resources.

[0003] However, the development of polylactic acid is restricted by the problems of difficult preparation technology and high production cost of lactide, the raw material of polylactic acid. At present, the development of starch-polylactic acid (PLA) based biodegradable materials has become a focus. However, starch / PLA based biodegradable materials have problems such as difficulty in starch plastic processing, poor compatibility, and poor water resistance, which seriously restrict the application of starch / PLA based biodegradable materials.

[0004] In-situ melt grafting polymerization is currently used to graft polylactic acid segments onto high-amylose starch macromolecules to achieve the purpose of improving the starch-polylactic acid interface adhesion, increasing compatibility, and reducing the production cost of polylactic acid materials. Ultimately, high-amylose starch-polylactic acid-based biodegradable composite materials with excellent performance are prepared, and the chemical composition and molecular properties of polylactic acid are changed to balance the performance of polylactic acid and expand its application market. However, the preparation cost of the above method is relatively high, and a certain amount of waste liquid is generated during the preparation process, which requires solvent recovery.

[0005] Therefore, based on the above problems, the project adopted a chemical modification method to successfully graft copolymerize high-amylose starch with lactide to obtain a graft copolymer of high-amylose starch / polylactic acid. Summary of the Invention

[0006] In order to improve the deficiencies of the existing technology, the purpose of the present invention is to provide a method for preparing a high-amylose starch / polylactic acid graft copolymer and its application. By using lactide and high-amylose starch with superior performance compared to ordinary starch as raw materials, a high-amylose starch / polylactic acid material with excellent performance and complete biodegradability is prepared.

[0007] In a first aspect, the present invention provides a method for preparing a high-amylose starch / polylactic acid graft copolymer, comprising the following steps:

[0008] Dissolving high-amylose starch in an organic solvent, adding lactide and a catalyst, and reacting at 60-110° C. for 5-11 hours under an inert atmosphere to obtain a high-amylose starch / polylactic acid graft copolymer;

[0009] According to an embodiment of the present invention, the high-amylose starch is selected from at least one of corn starch, sweet potato starch, pea starch, and wheat starch, for example, high-amylose corn starch.

[0010] According to an embodiment of the present invention, the amylose content in the high-amylose starch is greater than or equal to 70%, and preferably the amylose content in the high-amylose starch is greater than or equal to 80%.

[0011] According to an embodiment of the present invention, the water content of the high-amylose starch is lower than 0.02%, preferably the water content of the high-amylose starch is lower than 0.015%.

[0012] According to an embodiment of the present invention, the organic solvent is DMSO or DMF, preferably DMSO.

[0013] According to an embodiment of the present invention, the molar volume ratio of the high-amylose starch to the organic solvent is 1:1 to 1:10, for example, 1:3, 1:4, 1:5, 1:6, or 1:7.

[0014] According to an embodiment of the present invention, the molar ratio of the high-amylose starch to lactide is 1:2 to 1:8, for example, 1:3, 1:4, 1:5, or 1:6.

[0015] According to an embodiment of the present invention, the grafting reaction temperature is 60-110°C, preferably 80°C.

[0016] According to an embodiment of the present invention, the grafting reaction time is 5-11 hours, preferably 8 hours.

[0017] According to an embodiment of the present invention, the catalyst is selected from triethylamine, hydrochloric acid, sulfuric acid, sodium hydroxide or ionic liquid, preferably triethylamine.

[0018] According to an embodiment of the present invention, the amount of the catalyst used is 0.5-1.0% of the amount of lactide used, preferably 0.6-0.8% of the amount of lactide used.

[0019] According to an embodiment of the present invention, the average molecular weight of the high-amylose starch / polylactic acid graft copolymer is 80,000-135,000.

[0020] In a second aspect, the present invention further provides an application of the high-amylose starch / polylactic acid graft copolymer prepared by the above method in a degradable material.

[0021] In a third aspect, the present invention further provides a method for preparing a degradable material, comprising the following steps: mixing the high-amylose starch / polylactic acid graft copolymer with polylactic acid and a plasticizer to obtain a degradable material.

[0022] According to an embodiment of the present invention, the mass ratio of the high-amylose starch / polylactic acid graft copolymer to polylactic acid and plasticizer is (5-30): (50-80): (10-20).

[0023] According to an embodiment of the present invention, the plasticizer is selected from at least one of citric acid esters, epoxy soybean oil, and polyols, such as glycerol.

[0024] In a fourth aspect, the present invention also provides a degradable material prepared by the above method.

[0025] In a fifth aspect, the present invention also provides a use of the above-mentioned degradable material in food packaging and disposable products.

[0026] According to an embodiment of the present invention, the degradable material is used in food packaging boxes, fresh-keeping boxes, ground films, and lunch boxes.

[0027] Beneficial effects

[0028] The present invention first reacts high-amylose starch with lactide to obtain a high-amylose starch / polylactic acid graft copolymer having excellent mechanical properties. After being blended with polylactic acid and a plasticizer in a specific ratio, the compatibility of the components is improved. The mixture obtained by adding the high-amylose starch / polylactic acid graft copolymer has excellent mechanical properties. In addition, the addition of low-cost high-amylose starch reduces the cost of polylactic acid materials. At the same time, the preparation method of the present invention is simple, the conditions are relatively mild, the cost is low, and it can be used for industrial mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the NMR spectrum of the starch / polylactic acid graft copolymer synthesized in Example 10 of the present invention.

[0030] Figure 2 This is the infrared spectrum of the starch / polylactic acid graft copolymer synthesized in Example 10 of the present invention. DETAILED DESCRIPTION

[0031] The following will further describe the biodegradable material of the present invention, its preparation method, and its application in detail with reference to specific examples. It should be understood that the following examples are merely illustrative and illustrative of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above-mentioned content of the present invention are encompassed within the scope of protection intended by the present invention.

[0032] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0033] In the following Examples 1-12 and Comparative Examples 1-2, the amylose content in the high-amylose corn starch is 71-73%.

[0034] Example 1

[0035] A method for preparing a high-amylose starch / polylactic acid degradable material comprises the following steps:

[0036] S101: Dry the high-amylose corn starch (molar molecular weight less than 0.02%), add 1 mol of high-amylose corn starch (based on a molar molecular weight of 162) and DMSO (solvent) in a molar volume ratio of 1:3 into a reaction flask, and stir at 60°C until the high-amylose corn starch is completely dissolved; add 3 mol of lactide (to starch feed ratio of 3:1) and 0.5% triethylamine to a reactor, and react at 60°C under nitrogen protection for 5 hours to obtain a high-amylose corn starch / polylactic acid graft copolymer; the grafting rate is 90-95%, and the average molecular weight of the obtained polymer is 90,000;

[0037] S102: 10 parts of the prepared high-amylose corn starch / polylactic acid graft copolymer, 80 parts of polylactic acid, and 10 parts (by mass) of plasticizer glycerol are added to a stirring device and stirred to obtain a mixture.

[0038] Example 2

[0039] This example is basically the same as Example 1, except that the feed ratio in the copolymer reaction is 4:1, the reaction temperature is 80°C, the grafting rate of the obtained starch / polylactic acid copolymer is 120-135%, and the average molecular weight of the obtained polymer is about 100,000.

[0040] Example 3

[0041] This example is basically the same as Example 1, except that the feed ratio in the copolymer reaction is 5:1, the reaction temperature is 80°C, the grafting rate of the obtained starch / polylactic acid copolymer is 160-175%, and the average molecular weight of the obtained polymer is about 120,000.

[0042] Example 4

[0043] This example is basically the same as Example 1, except that the molar volume in the copolymer reaction is 6:1, the reaction temperature is 80°C, the grafting rate of the obtained starch / polylactic acid copolymer is 165-175%, and the average molecular weight of the obtained polymer is about 125,000.

[0044] Example 5

[0045] This example is basically the same as Example 1, except that the reaction temperature in the copolymer reaction is 80°C, the reaction time is 8 hours, the grafting rate of the obtained starch / polylactic acid copolymer is 115-125%, and the average molecular weight of the obtained polymer is about 95,000.

[0046] Example 6

[0047] This example is basically the same as Example 1, except that the reaction temperature in the copolymer reaction is 80°C, the reaction time is 10 hours, the grafting rate of the obtained starch / polylactic acid copolymer is 125-135%, and the average molecular weight of the obtained polymer is about 105,000.

[0048] Example 7

[0049] This example is basically the same as Example 1, except that the molar volume in the copolymer reaction is 1:4, the reaction temperature is 80°C, the grafting rate of the obtained starch / polylactic acid copolymer is 110-125%, and the average molecular weight of the obtained polymer is about 100,000.

[0050] Example 8

[0051] This example is basically the same as Example 1, except that the molar volume in the copolymer reaction is 1:5, the reaction temperature is 80°C, the grafting rate of the obtained starch / polylactic acid copolymer is 120-135%, and the average molecular weight of the obtained polymer is about 110,000.

[0052] Example 9

[0053] This example is basically the same as Example 1, except that the molar volume in the copolymer reaction is 1:4, the reaction temperature is 90°C, the grafting rate of the obtained starch / polylactic acid copolymer is 130-145%, and the average molecular weight of the obtained polymer is about 115,000.

[0054] Example 10

[0055] This example is basically the same as Example 1, except that in the copolymer reaction, the reaction temperature is 80°C, the reaction time is 8h, the molar volume is 1:4, the reaction temperature is 80°C, the grafting rate of the obtained starch / polylactic acid copolymer is 170-185%, and the average molecular weight of the obtained polymer is about 135,000.

[0056] See also Figure 1 As shown, the starch / polylactic acid copolymer prepared in this embodiment has a -1 In addition to the characteristic absorption peaks of starch at 1747 cm -1 There is an obvious ester carbonyl (C=O) characteristic absorption peak at 1764 cm -1 The position of starch is 1747cm -1There is no characteristic absorption peak at 2941 cm. In addition, the PLA side chain hinders the association between hydroxyl groups. -1 The stretching vibration absorption peak of CH is enhanced. The above results show that after ring opening, lactide is effectively grafted onto the starch skeleton to obtain (high amylose) starch-polylactic acid graft copolymer.

[0057] See also Figure 2 As shown in FIG. 1 , the H NMR spectrum of the starch / polylactic acid polymer prepared in this example is shown, wherein the peaks at chemical shifts δ of 1.28 and 1.45 are H a CH3 and H b The resonance peak of CH3 proton at δ 3.99~3.33 is the absorption peak of hydrogen on starch skeleton and CH in polylactic acid chain (H c ); δ = 4.21 is the proton peak on the C connected to the hydroxyl group at the end of the PLA chain (H d ), δ = 5.19 is the proton peak on the hydroxyl group of the polylactic acid chain (H e ) and the superposition of the proton peaks on the high-amylose starch backbone C-1.

[0058] Comparative Example 1

[0059] This comparative example is basically the same as Example 1, except that during the blending process, high-amylose starch, polylactic acid, and plasticizer are added to a stirring device in a weight ratio of 10:80:10, and stirred to obtain a mixture.

[0060] Comparative Example 2

[0061] This comparative example is basically the same as Example 1, except that high-amylose starch / polylactic acid graft copolymer, polylactic acid, and plasticizer are added to a stirring device in the weight ratio of 5:85:10, and stirred to obtain a mixture.

[0062] Comparative Example 3

[0063] This comparative example is basically the same as Example 1, except that corn starch (amylose content less than 50%) is used as raw material in the copolymer reaction, the grafting rate of the obtained starch / polylactic acid copolymer is 90%, and the average molecular weight of the obtained polymer is about 60,000.

[0064] Mechanical properties test: According to GB13022-91 film and sheet mechanical properties test method, the tensile strength, elongation at break and elastic modulus of the composite film samples were measured using a CMT 4304 microcomputer-controlled electronic universal testing machine.

[0065] Shore hardness test: The Shore hardness of the sample was determined using the test method in national standard GB 2411-80.

[0066] The mechanical properties of the prepared starch / polylactic acid material were measured, and the results are shown in Table 1:

[0067] Table 1 Properties of the materials prepared in Examples 1-3 and Comparative Examples 1-3

[0068]

[0069] The above examples illustrate the specific embodiments of the present invention. However, the scope of protection of the present invention is not limited to the above-mentioned exemplary embodiments. Any modifications, equivalent substitutions, improvements, etc. made by those skilled in the art within the spirit and principles of the present invention shall be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a high-amylose starch / polylactic acid graft copolymer, characterized in that: The steps include: Dissolving high-amylose starch in an organic solvent, adding lactide and a catalyst, and reacting at 60-110° C. for 5-11 hours under an inert atmosphere to obtain a high-amylose starch / polylactic acid graft copolymer; The amylose content of the high-amylose starch is greater than 70%; the water content of the high-amylose starch is less than 0.02%; The catalyst is triethylamine; The organic solvent is DMSO; The molar ratio of the high-amylose starch to lactide is 1:2 to 1:8, and the amount of the catalyst used is 0.6-0.8% of the amount of lactide used; The average molecular weight of the high-amylose starch / polylactic acid graft copolymer is 80,000-135,000.

2. The method for preparing a high-amylose starch / polylactic acid graft copolymer according to claim 1, wherein: The high-amylose starch is selected from at least one of corn starch, sweet potato starch, pea starch and wheat starch.

3. The method for preparing a high-amylose starch / polylactic acid graft copolymer according to claim 1, wherein: The amylose content in the high-amylose starch is greater than or equal to 80%.

4. The method for preparing a high-amylose starch / polylactic acid graft copolymer according to claim 1, wherein: The high-amylose starch is high-amylose corn starch.

5. The method for preparing a high-amylose starch / polylactic acid graft copolymer according to any one of claims 1 to 4, characterized in that: The water content of the high-amylose starch is less than 0.015%.

6. A method for preparing a degradable material, characterized in that: The method comprises the following steps: mixing the high-amylose starch / polylactic acid graft copolymer prepared by the method according to any one of claims 1 to 5 with polylactic acid and a plasticizer to obtain a degradable material.

7. The method for preparing a degradable material according to claim 6, characterized in that: The mass ratio of the high-amylose starch / polylactic acid graft copolymer to polylactic acid and plasticizer is (5-30):(50-80):(10-20).

8. The method for preparing a degradable material according to claim 6, characterized in that: The plasticizer is selected from at least one of citric acid esters, epoxy soybean oil, and polyols.

9. A degradable material prepared by the method according to any one of claims 6 to 8.

10. Use of the degradable material according to claim 9 in food packaging and disposable products.

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