Domestic compost modified polylactic acid suitable for film spraying and preparation method of domestic compost modified polylactic acid

Abstract

The invention discloses household compost modified polylactic acid suitable for film spraying and a preparation method thereof, and relates to the technical field of modified plastics. The key point of the technical scheme is as follows: the material comprises 70-80 wt% of polylactic acid, 15-20 wt% of poly (butylene succinate)-adipate, 3-5 wt% of amorphous polylactic acid, 1-2 wt% of polyphosphate, 0.2-0.5 wt% of a lubricant, 0.1-0.2 wt% of a heat stabilizer and 0.1-0.2 wt% of an anti-hydrolysis agent. The invention aims to provide household compost modified polylactic acid suitable for film spraying and a preparation method of the household compost modified polylactic acid.

Description

Technical Field

[0001] The invention relates to the technical field of modified plastics, and more particularly to a home-compostable modified polylactic acid suitable for laminating and a preparation method thereof. Background Art

[0002] Paper is one of the best raw materials for disposable products because it comes from nature and can be biodegraded after being discarded, or recycled and cleaned before being pulped for the production of recycled paper. However, when used in food contact products, paper does not have waterproof and oil-proof properties because its fibers are exposed, so its surface needs to be treated. The usual practice is to apply a polymer film on one or both sides of the paper to block water and oil. This processing technology is called paper coating technology. The coating process effectively solves the problem of poor barrier properties of paper, so it is widely used in various types of paper tableware.

[0003] The traditional laminating process uses polyethylene as the laminating layer because of its good processing performance and excellent barrier properties. However, in the home composting system, polyethylene cannot be composted with paper, and mixing with the pulp during paper recycling will also affect the quality of recycled paper, so it is gradually being eliminated by the industry.

[0004] Some manufacturers use acrylic resin coating to treat paper. Because the coating thickness is low, the impact on the paper re-slurry system is small. However, acrylic resin coating has poor barrier properties, strong odor, and cannot be home composted. Therefore, its scope of use is limited and it cannot enter the home composting system.

[0005] Polylactic acid is an internationally recognized biodegradable plastic that is derived from organisms, has good barrier properties, does not contain harmful ingredients, and has no odor. It is the latest choice for environmentally friendly paper coating. However, polylactic acid cannot be composted at home, which limits its application in home compostable products.

[0006] Therefore, a new technical solution is urgently needed to solve the above technical problems. Summary of the invention

[0007] In view of the shortcomings of the prior art, the object of the present invention is to provide a home compostable modified polylactic acid suitable for lamination and a method for producing the same.

[0008] The above technical purpose of the present invention is achieved through the following technical scheme: a home compostable modified polylactic acid suitable for coating, comprising 70-80wt% polylactic acid, 15-20wt% polybutylene succinate-adipate, 3-5wt% amorphous polylactic acid, 1-2wt% polyphosphate, 0.2-0.5wt% lubricant, 0.1-0.2wt% heat stabilizer, and 0.1-0.2wt% anti-hydrolysis agent.

[0009] The present invention is further configured as follows: the weight average molecular weight of the polylactic acid is 70,000-100,000; and the melt mass flow rate at 190° C. and 2.16 kg load is 10-25 g / 10 min.

[0010] The present invention is further configured as follows: the weight average molecular weight of the polybutylene succinate-adipate is 30,000-40,000; and the melt mass flow rate at 190° C. and 2.16 kg load is 5-8 g / 10 min.

[0011] The present invention is further configured as follows: the weight average molecular weight of the amorphous polylactic acid is 30,000-50,000; and the melt mass flow rate at 190° C. and 2.16 kg load is 30-40 g / 10 min.

[0012] The present invention is further configured as follows: the weight average molecular weight of the polyphosphate is 6000-11000, and the phosphorus content is 9.5-11%.

[0013] The present invention is further configured as follows: the melt volume flow rate of the polyphosphate ester at 230° C. and 2.16 kg load is 18-20 ml / 10 min.

[0014] The present invention is further configured as follows: the lubricant is a hydroxycarboxylate oligomer, and its structure is (COHCOOR) n , wherein R is one or more of sulfonic acid, amino, amide or carbonyl structures, and the relative molecular weight of the hydroxycarboxylate oligomer is 1500-3000.

[0015] The present invention is further configured as follows: the heat stabilizer is one or more of tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenyl bisphosphite, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate or tris[2,4-di-tert-butylphenyl]phosphite.

[0016] The present invention is further configured as follows: the anti-hydrolysis agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide.

[0017] A method for producing the modified polylactic acid comprises the following steps: (1) After mixing polylactic acid, polybutylene succinate-adipate, amorphous polylactic acid and polyphosphate, the mixture is dew-point dried. During drying, the dew point of the drying air is lower than -35°C, the drying temperature is 55°C, and the drying time is not less than 2 hours, ensuring that the water content of the mixture is lower than 200 ppm.

[0018] (2) The heat stabilizer is vacuum dried. During drying, the air pressure in the drying tank is not higher than 30Pa, the drying temperature is 50°C, and the drying time is not less than 1 hour to ensure that the water content of the heat stabilizer is less than 200ppm.

[0019] (3) Using nitrogen as the conveying medium, the dried mixture and the heat stabilizer are respectively fed into different weight loss scales 1 and 2 of the weight loss metering system. The above-mentioned weight loss metering system also includes two other weight loss scales, which are used to measure the lubricant and the anti-hydrolysis agent respectively. The materials measured by the weight loss metering system enter the main feeding port of the co-rotating parallel twin-screw extruder.

[0020] (4) During granulation, the processing temperature is 150-170°C, the length-to-diameter ratio of the co-rotating parallel twin-screw extruder is 54:1, it contains 2 independent vacuum devolatilization chambers, and is divided into 9 independent temperature control zones, and the length-to-diameter ratio of each temperature control zone is 6:1.

[0021] (5) The modified polylactic acid after granulation is dew-point dried. During drying, the dew point of the drying air is lower than -35°C, the drying temperature is 55°C, and the drying time is not less than 2 hours, ensuring that the water content of the modified polylactic acid is lower than 200ppm.

[0022] (6) Using nitrogen as the medium, the dried modified polylactic acid is fed into a cast extruder, and is compounded with the corona-treated paper through extrusion casting, i.e., laminating. During the laminating process, the laminating temperature is 140-150°C, the laminating speed is 100-120 m / min, and the laminating layer thickness is 10-15 μm.

[0023] The present invention has the following beneficial effects: 1. It improves the thermal stability of polylactic acid, inhibits the thermal degradation of polylactic acid in the heat process of melt processing, makes the viscosity of polylactic acid melt more consistent, improves the stability in the coating process, and ensures the consistency of the coating layer thickness; 2. Reduced the crystallinity of polylactic acid. Polylactic acid is a crystalline plastic with a certain degree of crystallinity. In the crystal region, the molecular chains of polylactic acid are closely arranged, which improves rigidity and reduces degradation performance. Therefore, reducing the crystallinity of polylactic acid can reduce the compactness of the molecular chains of polylactic acid, improve the flexibility of the coating layer, and reduce the thickness of the coating layer; 3. The degradation performance of polylactic acid has been improved by adding low molecular weight polyphosphate. Under home composting conditions, polyphosphate provides more active free radicals, promotes the breakage of ester bonds, and provides the phosphorus source required for microbial activity, thereby further accelerating the degradation rate of polylactic acid and ultimately meeting the requirements of home composting. DETAILED DESCRIPTION

[0024] The present invention is described in further detail below. Specific embodiment 1:

[0026] A home compostable modified polylactic acid suitable for coating comprises 70-80wt% of polylactic acid, 15-20wt% of polybutylene succinate-adipate, 3-5wt% of amorphous polylactic acid, 1-2wt% of polyphosphate, 0.2-0.5wt% of lubricant, 0.1-0.2wt% of heat stabilizer and 0.1-0.2wt% of anti-hydrolysis agent.

[0027] In this embodiment, poly-L-lactic acid with an optical purity of 96% and a weight average molecular weight of 100,000 is used; the melt mass flow rate at 190° C. and a load of 2.16 kg is 20 g / 10 min.

[0028] In this embodiment, polybutylene succinate-adipate with a biomass content higher than 60% is used, and the weight average molecular weight of polybutylene succinate-adipate is 40,000; the melt mass flow rate at 190° C. and a load of 2.16 kg is 8 g / 10 min.

[0029] In this embodiment, amorphous polylactic acid with an optical purity of 70% of lactic acid monomer and a weight average molecular weight of 50,000 is used; the melt mass flow rate at 190° C. and a load of 2.16 kg is 30 g / 10 min.

[0030] In this embodiment, polyphosphate with a phosphorus content of 10.9% is used, with a weight average molecular weight of 11,000 and a melt volume flow rate of 18 ml / 10 min at 230° C. and a load of 2.16 kg.

[0031] In this embodiment, the lubricant selected R is an amidohydroxycarboxylate oligomer, and its structure is (COHCOOR) n , wherein the relative molecular weight of the hydroxycarboxylate oligomer is 2600.

[0032] In this embodiment, the heat stabilizer is tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenyl bisphosphite and tris[2,4-di-tert-butylphenyl]phosphite in a weight ratio of 1:1.

[0033] In this embodiment, the anti-hydrolysis agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide. Specific embodiment 2:

[0035] A method for producing modified polylactic acid comprises the following steps: (1) Mix polylactic acid, polybutylene succinate-adipate, amorphous polylactic acid and polyphosphate and then perform dew point drying. During drying, the dew point of the drying air is lower than -35°C, the drying temperature is 55°C, and the drying time is not less than 2 hours, ensuring that the water content of the mixture is less than 200 ppm.

[0036] (2) The heat stabilizer is vacuum dried. During drying, the air pressure in the drying tank is not higher than 30Pa, the drying temperature is 50°C, and the drying time is not less than 1 hour to ensure that the water content of the heat stabilizer is less than 200ppm.

[0037] (3) Using nitrogen as the conveying medium, the dried mixture and the heat stabilizer are respectively fed into different weight loss scales 1 and 2 of the weight loss metering system. The above-mentioned weight loss metering system also includes two other weight loss scales, which are used to measure the lubricant and the anti-hydrolysis agent respectively. The materials measured by the weight loss metering system enter the main feed port of the co-rotating parallel twin-screw extruder.

[0038] (4) During granulation, the processing temperature is 150-170°C, the length-to-diameter ratio of the co-rotating parallel twin-screw extruder is 54:1, it contains 2 independent vacuum devolatilization chambers, and is divided into 9 independent temperature control zones, and the length-to-diameter ratio of each temperature control zone is 6:1.

[0039] (5) The modified polylactic acid after granulation is subjected to dew point drying. During drying, the dew point of the drying air is lower than -35°C, the drying temperature is 55°C, and the drying time is not less than 2 hours, ensuring that the water content of the modified polylactic acid is lower than 200ppm.

[0040] (6) Using nitrogen as the medium, the dried modified polylactic acid is fed into a cast extruder, and is compounded with the corona-treated paper through extrusion casting, i.e., laminating. During laminating, the laminating temperature is 140-150°C, the laminating speed is 100-120 m / min, and the laminating layer thickness is 10-15 μm. Specific embodiment 3:

[0042] A home compostable modified polylactic acid suitable for laminating, the modified polylactic acid comprising the following components in percentage by weight: Table 1

[0043] The polylactic acid, polybutylene succinate-adipate, amorphous polylactic acid, polyphosphate and thermal stabilizer are dried according to the drying method of the present invention, and the water content of each component to be dried is ensured to be less than 200 ppm.

[0044] The feed ratio of the weight-loss metering system was set according to the ratio described in Table 1, and the above raw materials were added in proportion and granulated. During granulation, the processing temperature was 155°C.

[0045] The modified polylactic acid after granulation is dew-point dried. When the water content of the modified polylactic acid is less than 200ppm, the dried modified polylactic acid is sent to a casting extruder with nitrogen as the medium, and is compounded with the corona-treated paper through extrusion casting, i.e., laminating. During laminating, the laminating temperature is 140°C and the laminating layer thickness is 10μm.

[0046] During the above-mentioned modified polylactic acid coating process, the coating line speed can reach 100 m / min, and the peel strength can reach 0.45 N / 25 mm. The coated paper products have been tested and meet the degradation requirements of EN-13432 for household composting. Specific embodiment 4:

[0048] A home compostable modified polylactic acid suitable for laminating, the modified polylactic acid comprising the following components in percentage by weight: Table 2

[0049] The polylactic acid, polybutylene succinate-adipate, amorphous polylactic acid, polyphosphate and thermal stabilizer are dried according to the drying method of the present invention, and the water content of each component to be dried is ensured to be less than 200 ppm.

[0050] The feed ratio of the weight-loss metering system was set according to the ratio described in Table 2, and the above raw materials were added in proportion and granulated. During granulation, the processing temperature was 155°C.

[0051] The modified polylactic acid after granulation is dew-point dried. When the water content of the modified polylactic acid is less than 200ppm, the dried modified polylactic acid is sent to a casting extruder with nitrogen as the medium, and is compounded with the corona-treated paper through extrusion casting, i.e., laminating. During laminating, the laminating temperature is 140°C and the laminating layer thickness is 10μm.

[0052] During the above-mentioned modified polylactic acid coating process, the coating line speed can reach 110 m / min, and the peel strength can reach 0.65 N / 25 mm. The coated paper products have been tested and meet the degradation requirements of EN-13432 for household composting. Specific embodiment 5:

[0054] A home compostable modified polylactic acid suitable for laminating, the modified polylactic acid comprising the following components in percentage by weight: Table 3

[0055] The polylactic acid, polybutylene succinate-adipate, amorphous polylactic acid, polyphosphate and thermal stabilizer are dried according to the drying method of the present invention, and the water content of each component to be dried is ensured to be less than 200 ppm.

[0056] The feeding ratio of the loss-in-weight metering system was set according to the ratio described in Table 3, and the above raw materials were added in proportion and granulated. During granulation, the processing temperature was 155°C.

[0057] The modified polylactic acid after granulation is dew-point dried. When the water content of the modified polylactic acid is less than 200ppm, the dried modified polylactic acid is sent to a casting extruder with nitrogen as the medium, and is compounded with the corona-treated paper through extrusion casting, i.e., laminating. During laminating, the laminating temperature is 140°C and the laminating layer thickness is 10μm.

[0058] During the above-mentioned modified polylactic acid coating process, the coating line speed can reach 140 m / min, and the peel strength can reach 0.42 N / 25 mm. The coated paper products have been tested and found to meet the degradation requirements for household composting in EN-13432.

[0059] Comparative Example: The commercially available polylactic acid is produced by TotalEnergies Corbion and is model Lx175.

[0060] When the above-mentioned commercially available polylactic acid coating is processed, the coating line speed can reach 60 m / min and the peel strength can reach 0.22 N / 25 mm. After testing, the coated paper products do not meet the degradation requirements for home composting in EN-13432.

[0061] Table 4

[0062] The specific embodiments are merely explanations of the present invention and are not limitations of the present invention. After reading this specification, those skilled in the art may make modifications to the embodiments without any creative contribution as needed. However, such modifications are protected by the patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A home compostable modified polylactic acid suitable for coating, characterized in that: The invention comprises 70-80wt% of polylactic acid, 15-20wt% of polybutylene succinate-adipate, 3-5wt% of amorphous polylactic acid, 1-2wt% of polyphosphate, 0.2-0.5wt% of lubricant, 0.1-0.2wt% of heat stabilizer and 0.1-0.2wt% of anti-hydrolysis agent.

2. The home compostable modified polylactic acid suitable for coating according to claim 1, characterized in that: The weight average molecular weight of the polylactic acid is 70,000-100,000; and the melt mass flow rate at 190° C. and a load of 2.16 kg is 10-25 g / 10 min.

3. The home compostable modified polylactic acid suitable for coating according to claim 1, characterized in that: The weight average molecular weight of the polybutylene succinate-adipate is 30,000-40,000; and the melt mass flow rate at 190° C. and a load of 2.16 kg is 5-8 g / 10 min.

4. The home compostable modified polylactic acid suitable for coating according to claim 1, characterized in that: The weight average molecular weight of the amorphous polylactic acid is 30,000-50,000; and the melt mass flow rate at 190° C. and a load of 2.16 kg is 30-40 g / 10 min.

5. The home compostable modified polylactic acid suitable for coating according to claim 1, characterized in that: The weight average molecular weight of the polyphosphate is 6000-11000, and the phosphorus content is 9.5-11%.

6. The home compostable modified polylactic acid suitable for coating according to claim 1, characterized in that: The polyphosphate has a melt volume flow rate of 18-20 ml / 10 min at 230° C. and a load of 2.16 kg.

7. The home compostable modified polylactic acid suitable for coating according to claim 1, characterized in that: The lubricant is a hydroxycarboxylate oligomer, and its structure is (COHCOOR) n , wherein R is one or more of sulfonic acid, amino, amide or carbonyl structures, and the relative molecular weight of the hydroxycarboxylate oligomer is 1500-3000.

8. The home compostable modified polylactic acid suitable for coating according to claim 1, characterized in that: The heat stabilizer is one or more of tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenyl diphosphite, tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] pentaerythritol ester or tris[2,4-di-tert-butylphenyl]phosphite.

9. The home compostable modified polylactic acid suitable for coating according to claim 1, characterized in that: The anti-hydrolysis agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide.

10. A method for producing the modified polylactic acid according to claims 1 to 9, characterized in that: The steps include: (1) After mixing polylactic acid, polybutylene succinate-adipate, amorphous polylactic acid and polyphosphate, dew point drying is performed. During drying, the dew point of the drying air is lower than -35°C, the drying temperature is 55°C, and the drying time is not less than 2 hours, ensuring that the water content of the mixture is less than 200 ppm; (2) The heat stabilizer is vacuum dried. During drying, the air pressure in the drying tank is not higher than 30Pa, the drying temperature is 50°C, and the drying time is not less than 1 hour to ensure that the water content of the heat stabilizer is less than 200ppm; (3) Using nitrogen as the conveying medium, the dried mixture and the heat stabilizer are respectively fed into different weight loss scales 1 and 2 of the weight loss metering system. The weight loss metering system also includes two other weight loss scales, which are used to measure the lubricant and the anti-hydrolysis agent, respectively. The materials measured by the weight loss metering system enter the main feeding port of the co-rotating parallel twin-screw extruder; (4) During granulation, the processing temperature is 150-170°C, the length-to-diameter ratio of the co-rotating parallel twin-screw extruder is 54:1, it contains 2 independent vacuum devolatilization chambers, and is divided into 9 independent temperature control zones, and the length-to-diameter ratio of each temperature control zone is 6:1; (5) The modified polylactic acid after granulation is subjected to dew point drying. During drying, the dew point of the drying air is lower than -35°C, the drying temperature is 55°C, and the drying time is not less than 2 hours, ensuring that the water content of the modified polylactic acid is lower than 200ppm; (6) Using nitrogen as the medium, the dried modified polylactic acid is fed into a cast extruder, and is compounded with the corona-treated paper through extrusion casting, i.e., laminating. During the laminating process, the laminating temperature is 140-150°C, the laminating speed is 100-120 m / min, and the laminating layer thickness is 10-15 μm.

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