Film-coated polylactic acid material capable of being composted at home and synthesis process of film-coated polylactic acid material

Abstract

The invention discloses a laminating polylactic acid material capable of being composted at home and a synthesis process of the laminating polylactic acid material. The synthesis process comprises the following steps: (1) taking lactide, and carrying out polymerization reaction under the action of an initiator and a catalyst to obtain polylactic acid; (2) melting and mixing polylactic acid, the activated filler, polyglycolic acid and a chain extender to obtain modified polylactic acid; (3) stirring and mixing the modified polylactic acid and a propenyl elastomer; (4) adding glycerol into the material obtained in the step (3), continuously mixing for 10-15 minutes, and then transferring into an extruder for melt extrusion; and (5) carrying out quenching treatment on the extruded material obtained in the step (4) by using liquid nitrogen to obtain the polylactic acid material. The polylactic acid material disclosed by the invention is good in flexibility and hydrophilicity, high in degradation rate and good in impact strength, the hydrolysis rate during household composting is increased, and recycling of household composting is facilitated.

Description

Technical Field

[0001] The invention relates to the field of polymer materials, in particular to a coated polylactic acid material capable of being home composted, and also to a synthesis process of the material. Background Art

[0002] Polylactic acid (PLA) is a thermoplastic aliphatic polyester that can be extracted from corn, potatoes, or starch. Under certain soil and compost conditions, it completely degrades into carbon dioxide and water, without causing environmental pollution. PLA exhibits excellent biocompatibility, biodegradability, thermal and mechanical properties, and is widely used in disposable tableware, food packaging, and biomedical devices.

[0003] However, traditionally, polylactic acid is synthesized by polymerization reaction of lactide under the action of initiators and catalysts. The aforementioned process has failed to overcome the limitations of polylactic acid itself. The resulting polylactic acid material has poor flexibility, low impact strength and elongation at break, which greatly hinders its application in many fields. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a coated polylactic acid material that can be home-composted and a synthesis process thereof to obtain a polylactic acid material with high degradation efficiency and good flexibility.

[0005] The synthesis process of a home compostable coated polylactic acid material comprises the following steps:

[0006] (1) taking lactide and performing a polymerization reaction under the action of an initiator and a catalyst to obtain polylactic acid;

[0007] (2) melt-mixing the polylactic acid obtained in step (1), an activated filler, polyglycolic acid, and a chain extender to obtain a modified polylactic acid;

[0008] (3) stirring and mixing the modified polylactic acid and propylene elastomer obtained in step (2);

[0009] (4) adding glycerol to the material obtained in step (3), continuing to mix for 10 to 15 minutes, and then transferring the mixture into an extruder for melt extrusion;

[0010] (5) Using liquid nitrogen to rapidly cool the extruded material obtained in step (4) to obtain a polylactic acid material.

[0011] As a further improvement to the above scheme, in step (1), the mass ratio of lactide to initiator is 200 to 500:1, and the amount of the catalyst used is equivalent to 0.1% to 0.5% of the mass of the lactide. In the present invention, lactide undergoes epoxidation in the presence of the catalyst to form epoxypropionate, which then undergoes ring-opening polymerization in the presence of the initiator to form polylactic acid, a long-chain polymer.

[0012] As a further improvement to the above scheme, the initiator includes ethanol, and the concentration of ethanol is 5% to 10%, and the catalyst includes stannous octoate. The present invention uses an ethanol solution in this concentration range to delay chain termination reaction, reduce the probability of chain transfer reaction, and obtain a better degree of polymerization.

[0013] As a further improvement of the above scheme, the polymerization reaction obtains polylactic acid, and its specific operation is as follows: heating the reactor to 200-300°C, and evacuating the reactor, replacing the air therein with argon, cooling to room temperature, adding lactide, initiator and catalyst in sequence, and inflating and degassing the reactor 5 times. Finally, the vacuum degree of the reactor is maintained at 600-800 Pa, the reactor is sealed, stirred and heated to 120-150°C, reacted for 5-8 hours, and then cooled to room temperature to obtain polylactic acid.

[0014] As a further improvement of the above scheme, in step (2), the method for obtaining modified polylactic acid by melt mixing is specifically performed as follows: heating the reactor to 100-200°C, evacuating the reactor, replacing the air therein with argon, cooling the reactor to room temperature, sequentially adding polylactic acid, activated filler, polyglycolic acid and chain extender, maintaining the vacuum degree of the reactor at 600-800 Pa, sealing the reactor, stirring and heating to 120-150°C, reacting for 4-6 hours, and cooling the reactor to room temperature to obtain modified polylactic acid.

[0015] As a further improvement to the above scheme, the mass ratio of the polylactic acid, activated filler, and polyglycolic acid is 1:0.1-0.3:0.05-0.15, and the amount of the chain extender used is equivalent to 10% to 15% of the mass of the polylactic acid. In the present invention, the chain extender and polyglycolic acid are used to modify the polylactic acid by introducing hydroxyl groups, so that the resulting copolymer molecular chain contains both lipophilic lactic acid hard segments and hydrophilic polyhydroxyl soft segments, giving the material a certain degree of flexibility and good hydrophilicity, increasing the hydrolysis rate of the polylactic acid during home composting, and thus accelerating its degradation rate.

[0016] As a further improvement to the above scheme, a silane coupling agent and bamboo fiber are blended in water under ultrasonic conditions to obtain the activated filler. The mass ratio of the silane coupling agent to the bamboo fiber is 0.15 to 0.25:1, and the amount of water added is equivalent to 1 to 1.5 times the total amount of the silane coupling agent and the bamboo fiber. The purpose of adding bamboo fiber in the present invention is to introduce amorphous fillers into the material, reduce the mobility of the molecular chain to inhibit crystallization, reduce the crystallinity to facilitate the penetration of water molecules, thereby improving the degradation efficiency and facilitating the use of the material in home composting. In addition, considering that bamboo fiber is extremely hydrophilic and can absorb water to the interface, resulting in a weakened bonding force between the bamboo fiber and the polylactic acid and easy breakage, the present invention further introduces a silane coupling agent to modify the surface of the bamboo fiber, and couples with an organic functional alkoxysilane at the bamboo fiber-polylactic acid interface to improve the bonding force between the bamboo fiber and the polylactic acid, thereby improving the strength of the material.

[0017] As a further improvement of the above solution, the ultrasonic conditions are: ultrasonic power 200-400 W, ultrasonic time 35-55 min. In the present invention, the above ultrasonic conditions can achieve a better dispersion effect and facilitate the surface modification of bamboo fiber by silane.

[0018] As a further improvement to the above solution, the chain extender is at least one of polytrimethylene carbonate, a polyurethane vulcanizer, hydroquinone dihydroxyethyl ether, diethylene glycol, and toluenediamine. In the present invention, the chain extender is added to extend the molecular chain and increase the molecular weight, thereby reducing the molecular chain mobility, slowing the crystallization rate, and thereby reducing the material's crystallinity. Reduced material crystallinity means looser molecular arrangement, making it more susceptible to moisture and other degradation factors, thereby increasing the degradation rate.

[0019] As a further improvement to the above scheme, in step (3), the amount of the propylene-based elastomer added is equivalent to 2% to 6% of the mass of the modified polylactic acid, and the stirring and mixing are carried out in a high-speed stirring mixer at a stirring speed of 1400 to 1600 r / min and a stirring time of 20 to 30 minutes. The purpose of introducing the degradable propylene-based elastomer in the present invention is to absorb impact energy, reduce material strength, and thereby improve the impact strength of the lactic acid material.

[0020] As a further improvement to the above scheme, in step (4), the amount of glycerol added is equivalent to 1% to 4% of the mass of the modified polylactic acid, and the melt extrusion temperature is 160 to 200°C. In the present invention, the purpose of introducing glycerol is to lower the glass transition temperature of the material. In combination with the rapid cooling treatment, the melt is quickly supercooled to below the glass transition temperature, forming an amorphous structure, reducing the opportunity for molecular chain relaxation and inhibiting crystal growth, thereby obtaining a polylactic acid material with good degradability and fast degradation rate.

[0021] As a further improvement of the above solution, the polylactic acid material obtained in step (5) is coated on household paper cups through a casting machine.

[0022] As a further improvement to the above solution, and / or, the polylactic acid material obtained in step (5) is coated on household paper tableware by a casting machine. The polylactic acid material of the present invention is coated on household items such as paper cups or paper tableware to impart better oil and water resistance to the aforementioned items.

[0023] A coated polylactic acid material is produced using the aforementioned synthesis process for a home-compostable coated polylactic acid material. The polylactic acid material of the present invention has good biodegradability and can be completely degraded by natural microorganisms after use, ultimately producing carbon dioxide and water. This material is environmentally friendly and suitable for home composting. Specifically, it can be decomposed in home composting to convert it into humus and mineral nutrients, thereby enabling the ecological recycling of waste into organic fertilizer.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention introduces amorphous fillers into the material, reduces the activity of molecular chains to inhibit crystal formation, reduces crystallinity to facilitate the penetration of water molecules, thereby improving degradation efficiency and facilitating the use of the material in household composting.

[0026] The present invention uses polytrimethylene carbonate + polyglycolic acid to introduce hydroxyl groups to modify polylactic acid, so that the obtained copolymer molecular chain contains both lipophilic lactic acid hard segments and hydrophilic polyhydroxyl soft segments, making the material have certain flexibility and good hydrophilicity, thereby increasing the hydrolysis rate of polylactic acid during home composting, thereby accelerating its degradation rate.

[0027] The present invention introduces a degradable propylene-based elastomer to absorb impact energy, reduce material strength, and thus improve the impact resistance of the lactic acid material. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the embodiments. Additional aspects and advantages of the present invention will be partially given in the following description, partially become apparent from the following description, or be understood through practice of the present invention. It should be understood that the following description is only intended to explain the present invention and is not intended to limit the present invention.

[0029] As used herein, the terms "comprises," "includes," "contains," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0030] When amount, concentration or other value or parameter is expressed as range, preferred range, or a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when disclosing a range of "1 to 5", the described range should be interpreted as including ranges of "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When a numerical range is described in this article, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0031] The specific embodiments of the present invention are described in detail below.

[0032] Example 1

[0033] This embodiment provides a synthesis process for a home-compostable coated polylactic acid material, which comprises the following steps:

[0034] (1) Lactide is polymerized in the presence of stannous octoate and a 5% ethanol solution to obtain polylactic acid, wherein the mass ratio of the lactide to the ethanol solution is 200:1; the amount of stannous octoate used is equivalent to 0.1% of the mass of the lactide. The specific operation of the polymerization reaction to obtain polylactic acid is as follows: heating the reactor to 200°C, evacuating the reactor, replacing the air therein with argon, cooling the reactor to room temperature, sequentially adding lactide, ethanol solution and stannous octoate, and then inflating and deflating the reactor 5 times, and finally maintaining the vacuum degree of the reactor at 600 Pa. The reactor is sealed, stirred and heated to 120°C, reacted for 5 hours, and then cooled to room temperature to obtain polylactic acid.

[0035] In this embodiment, lactide undergoes epoxidation reaction under the action of stannous octoate to form epoxy propionate, and epoxy propionate undergoes ring-opening polymerization reaction under the action of ethanol to form polylactic acid, a long-chain polymer.

[0036] (2) The polylactic acid obtained in step (1) is melt-mixed with an activated filler, polyglycolic acid and polytrimethylene carbonate, wherein the mass ratio of polylactic acid, activated filler and polyglycolic acid is 1:0.1:0.05; the amount of polytrimethylene carbonate used is equivalent to 10% of the mass of the polylactic acid, to obtain modified polylactic acid. The method for obtaining the modified polylactic acid by melt-mixing comprises the following steps: heating a reactor to 100° C., evacuating the reactor, replacing the air therein with argon, cooling the reactor to room temperature, sequentially adding polylactic acid, activated filler, polyglycolic acid and polytrimethylene carbonate, maintaining the vacuum degree of the reactor at 600 Pa, sealing the reactor, stirring and heating to 120° C., reacting for 4 hours, and cooling the reactor to room temperature to obtain the modified polylactic acid.

[0037] In this embodiment, the purpose of adding polytrimethylene carbonate is to extend the molecular chain and increase the molecular weight, thereby reducing the activity of the molecular chain, slowing down the crystallization rate, and thus reducing the crystallinity of the material. The reduction in the crystallinity of the material means that the molecular arrangement is looser, and thus it is more susceptible to the influence of moisture and other degradation factors, thereby increasing the degradation rate.

[0038] The activated filler was obtained by blending a silane coupling agent and bamboo fiber in water for 35 minutes under an ultrasonic power of 200 W. The mass ratio of the silane coupling agent to the bamboo fiber was 0.15:1, and the amount of water added was equivalent to 1 times the total amount of the silane coupling agent and bamboo fiber. In this embodiment, the aforementioned ultrasonic conditions achieved a good dispersion effect and facilitated the surface modification of the bamboo fiber by the silane.

[0039] In this embodiment, polytrimethylene carbonate + polyglycolic acid are used to modify polylactic acid by introducing hydroxyl groups, so that the obtained copolymer molecular chain contains both lipophilic lactic acid hard segments and hydrophilic polyhydroxyl soft segments, which makes the material have certain flexibility and good hydrophilicity, increases the hydrolysis rate of polylactic acid during home composting, and thus accelerates its degradation rate.

[0040] In this embodiment, the purpose of adding bamboo fiber is to introduce amorphous fillers into the material, reduce the activity of the molecular chain to inhibit crystallization, reduce the crystallinity to facilitate the penetration of water molecules, thereby improving the degradation efficiency and facilitating the use of the material in home composting. In addition, considering that bamboo fiber is extremely hydrophilic and can absorb water to the interface, resulting in a weakened bonding force between the bamboo fiber and the polylactic acid and easy breakage, the present invention further introduces a silane coupling agent to modify the surface of the bamboo fiber, and couples with an organic functional alkoxysilane at the bamboo fiber-polylactic acid interface to improve the bonding force between the bamboo fiber and the polylactic acid, thereby improving the strength of the material.

[0041] (3) The modified polylactic acid obtained in step (2) and the propylene-based elastomer are stirred and mixed, wherein the amount of the propylene-based elastomer added is equivalent to 2% of the mass of the modified polylactic acid. The stirring and mixing are carried out in a high-speed stirring mixer at a stirring speed of 1400 r / min and a stirring time of 20 min. In this embodiment, the purpose of introducing the degradable propylene-based elastomer is to absorb impact energy, reduce material strength, and thereby improve the impact strength of the lactic acid material.

[0042] (4) Glycerol was added to the material obtained in step (3) in an amount equivalent to 1% of the mass of the modified polylactic acid. The mixture was mixed for 10 minutes and then transferred to an extruder for melt extrusion at a temperature of 160° C. In this embodiment, the purpose of introducing glycerol was to lower the glass transition temperature of the material. The melt was rapidly supercooled to below the glass transition temperature by the rapid cooling treatment to form an amorphous structure, reduce the chance of molecular chain relaxation, and inhibit crystal growth, thereby obtaining a polylactic acid material with good degradability and a fast degradation rate.

[0043] (5) Liquid nitrogen is used to rapidly cool the extruded material obtained in step (4) to obtain a polylactic acid material #1, and the obtained polylactic acid material is coated on a household paper cup by a casting machine. In this embodiment, the polylactic acid material is processed by coating on household items such as paper cups or paper tableware to give the aforementioned items better oil and water resistance. In addition, the degradable properties of the polylactic acid material enable the aforementioned items to be completely degraded by microorganisms in nature after use, ultimately generating carbon dioxide and water, without polluting the environment, and suitable for use in household composting. That is, it can be decomposed by household composting to be converted into humus and mineral nutrients, thereby realizing the ecological reuse of garbage into organic fertilizer.

[0044] Example 2

[0045] This embodiment provides a synthesis process for a home-compostable coated polylactic acid material, which comprises the following steps:

[0046] (1) Lactide is polymerized in the presence of stannous octoate and an 8% ethanol solution to obtain polylactic acid, wherein the mass ratio of the lactide to the ethanol solution is 400:1; the amount of stannous octoate used is equivalent to 0.3% of the mass of the lactide. The specific operation of the polymerization reaction to obtain polylactic acid is as follows: heating the reactor to 260°C, evacuating the reactor, replacing the air therein with argon, cooling the reactor to room temperature, sequentially adding lactide, ethanol solution and stannous octoate, and then inflating and deflating the reactor 5 times, and finally maintaining the vacuum degree of the reactor at 700 Pa, sealing the reactor, stirring and heating the reactor to 130°C, reacting for 7 hours, and cooling the reactor to room temperature to obtain polylactic acid.

[0047] (2) melt-mixing the polylactic acid obtained in step (1) with an activated filler, polyglycolic acid and a polyurethane vulcanizer, wherein the mass ratio of the polylactic acid, the activated filler and the polyglycolic acid is 1:0.2:0.1; the amount of the polyurethane vulcanizer is equivalent to 13% of the mass of the polylactic acid, to obtain modified polylactic acid. The method for obtaining the modified polylactic acid by melt-mixing comprises the following specific operations: heating a reactor to 150° C., evacuating the reactor, replacing the air therein with argon, cooling the reactor to room temperature, sequentially adding polylactic acid, activated filler, polyglycolic acid and polyurethane vulcanizer, maintaining the vacuum degree of the reactor at 700 Pa, sealing the reactor, stirring and heating to 140° C., reacting for 5 hours, and cooling the reactor to room temperature to obtain the modified polylactic acid.

[0048] The activated filler is obtained by blending a silane coupling agent and bamboo fiber in water for 45 minutes under an ultrasonic power of 300 W. The mass ratio of the silane coupling agent to the bamboo fiber is 0.2:1, and the amount of water added is equivalent to 1.2 times the total amount of the silane coupling agent and the bamboo fiber.

[0049] (3) The modified polylactic acid obtained in step (2) and the propylene-based elastomer are stirred and mixed, wherein the amount of the propylene-based elastomer added is equivalent to 4% of the mass of the modified polylactic acid. The stirring and mixing are carried out in a high-speed stirring mixer at a stirring speed of 1500 r / min and a stirring time of 25 min.

[0050] (4) Glycerol was added to the material obtained in step (3), with the amount of glycerol added being equivalent to 3% of the mass of the modified polylactic acid. The mixture was mixed for 14 minutes and then transferred to an extruder for melt extrusion at a temperature of 180°C.

[0051] (5) Using liquid nitrogen to rapidly cool the extruded material obtained in step (4) to obtain 2# polylactic acid material, and the obtained polylactic acid material is coated on household paper tableware through a casting machine.

[0052] Example 3

[0053] This embodiment provides a synthesis process for a home-compostable coated polylactic acid material, which comprises the following steps:

[0054] (1) Lactide is polymerized in the presence of stannous octoate and a 10% ethanol solution to obtain polylactic acid, wherein the mass ratio of the lactide to the ethanol solution is 500:1; the amount of stannous octoate used is equivalent to 0.5% of the mass of the lactide. The specific operation of the polymerization reaction to obtain polylactic acid is the same as that in Example 1.

[0055] (2) The polylactic acid obtained in step (1) is melt-mixed with an activated filler, polyglycolic acid, and diethylene glycol, wherein the mass ratio of the polylactic acid, the activated filler, and the polyglycolic acid is 1:0.3:0.15; the amount of the diethylene glycol is equivalent to 15% of the mass of the polylactic acid to obtain modified polylactic acid. The method for melt-mixing to obtain the modified polylactic acid is the same as that in Example 2.

[0056] The activated filler is obtained by blending a silane coupling agent and bamboo fiber in water for 55 minutes under an ultrasonic power of 400 W. The mass ratio of the silane coupling agent to the bamboo fiber is 0.25:1, and the amount of water added is equivalent to 1.5 times the total amount of the silane coupling agent and the bamboo fiber.

[0057] (3) The modified polylactic acid obtained in step (2) and the propylene-based elastomer are stirred and mixed, wherein the amount of the propylene-based elastomer added is equivalent to 6% of the mass of the modified polylactic acid. The stirring and mixing are carried out in a high-speed stirring mixer at a stirring speed of 1600 r / min and a stirring time of 30 min.

[0058] (4) Glycerol was added to the material obtained in step (3), and the amount of glycerol added was equivalent to 4% of the mass of the modified polylactic acid. After continuing to mix for 15 minutes, the mixture was transferred to an extruder for melt extrusion at a temperature of 200°C.

[0059] (5) The same method as in Example 1 was used to obtain polylactic acid material #3.

[0060] Example 4

[0061] This embodiment provides a synthesis process for a home-compostable coated polylactic acid material, which comprises the following steps:

[0062] (1) Lactide is polymerized in the presence of stannous octoate and a 9% ethanol solution to obtain polylactic acid, wherein the mass ratio of the lactide to the ethanol solution is 300:1; the amount of stannous octoate used is equivalent to 0.45% of the mass of the lactide. The specific operation of the polymerization reaction to obtain polylactic acid is as follows: heating the reactor to 240°C, evacuating the reactor, replacing the air therein with argon, cooling the reactor to room temperature, sequentially adding lactide, ethanol solution and stannous octoate, and then inflating and deflating the reactor 5 times, and finally maintaining the vacuum degree of the reactor at 800 Pa. The reactor is sealed, stirred and heated to 120°C, reacted for 6 hours, and then cooled to room temperature to obtain polylactic acid.

[0063] (2) The polylactic acid obtained in step (1) is melt-mixed with an activated filler, polyglycolic acid, and toluenediamine, wherein the mass ratio of polylactic acid, activated filler, and polyglycolic acid is 1:0.25:0.15; the amount of toluenediamine used is equivalent to 11% of the mass of the polylactic acid, to obtain modified polylactic acid. The specific operation of melt-mixing to obtain the modified polylactic acid is the same as that of Example 1. The method for obtaining the activated filler is the same as that of Example 2.

[0064] (3) The modified polylactic acid obtained in step (2) and the propylene-based elastomer are stirred and mixed, wherein the amount of the propylene-based elastomer added is equivalent to 5% of the mass of the modified polylactic acid. The stirring and mixing are carried out in a high-speed stirring mixer at a stirring speed of 1450 r / min and a stirring time of 27 min.

[0065] (4) Glycerol was added to the material obtained in step (3), with the amount of glycerol added being equivalent to 3.5% of the mass of the modified polylactic acid. The mixture was mixed for 14 minutes and then transferred to an extruder for melt extrusion at a temperature of 170°C.

[0066] (5) The same method as in Example 2 was used to obtain 4# polylactic acid material.

[0067] Comparative Example 1

[0068] The only difference between this comparative example and Example 2 is that no activated filler is introduced in step (2), and 5# polylactic acid material is obtained. The rest is the same as Example 2.

[0069] Comparative Example 2

[0070] The only difference between this comparative example and Example 2 is that polyglycolic acid is not introduced in step (2), and 6# polylactic acid material is obtained. The rest is the same as Example 2.

[0071] Comparative Example 3

[0072] The only difference between this comparative example and Example 2 is that no propylene elastomer is introduced in step (3), and 7# polylactic acid material is obtained. The rest is the same as Example 2.

[0073] Next, we conducted flexibility testing and home composting tests on polylactic acid materials #1 to #7. The flexibility testing included impact resistance and elongation at break. The impact strength of the materials was tested based on the relevant standards of GB / T 1043.1-2008, while the elongation at break was tested based on the relevant standards of GB / T 1040.1, "Tests for Tensile Properties of Plastics." The specific testing process is not detailed here.

[0074] The home composting test was conducted as follows: 7 containers were filled with 100g of vegetable leaves and 100g of dry leaves, respectively, for pulverization. A layer of sand was then added to a 500ml compost container. The pulverized vegetable leaves and dry leaves were then evenly added to the container. 50g of polylactic acid materials #1 to #7 were placed into each of the seven containers, buried within the compost. Finally, a 2-3cm layer of soil was added to introduce microorganisms. Water was added at a level of 10% of the container volume. The compost was stirred every 24 hours. After 7 days of composting, the polylactic acid materials were weighed and the degradation rate was calculated. The test results are shown in Table 1.

[0075] The test results are as follows: the degradation rate of Example 1 is 66.3%, the degradation rate of Example 2 is 65.6%, the degradation rate of Example 3 is 67.1%, the degradation rate of Example 4 is 66.4%, the degradation rate of Comparative Example 1 is 30%, the degradation rate of Comparative Example 2 is 35%, and the degradation rate of Comparative Example 3 is 47%.

[0076] Table 11~7# Polylactic acid material performance comparison

[0077] Impact strength (KJ / m) Elongation at break (%) Degradation rate (%) 1# 116.7 175 75.4 2# 120.1 180 77.2 3# 119.2 178 76.6 4# 118.4 177 77 5# 89.5 56 47.2 6# 78 38 53 7# 68.9 167 70.7

[0078] Analysis of the above results shows that the introduction of activated fillers and the introduction of hydroxyl modification of polyglycolic acid have a positive synergistic effect, which is manifested in the improvement of flexibility, specifically the improvement of impact strength and elongation at break, and the material is easier to degrade, and the degradation rate is significantly improved. The introduction of propylene-based elastomer plays a positive role in improving the impact strength of lactic acid materials.

[0079] The above embodiments are merely preferred implementations of the present invention. Any simple modifications, amendments, and substitutions made to the above embodiments based on the technical essence of the present invention fall within the scope of the technical solution of the present invention.

Claims

1. A process for synthesizing a home compostable coated polylactic acid material, characterized in that: The following steps are involved: (1) taking lactide and performing a polymerization reaction under the action of an initiator and a catalyst to obtain polylactic acid; (2) melt-mixing the polylactic acid obtained in step (1), an activated filler, polyglycolic acid, and a chain extender to obtain a modified polylactic acid; (3) stirring and mixing the modified polylactic acid and propylene elastomer obtained in step (2); (4) adding glycerol to the material obtained in step (3), continuing to mix for 10 to 15 minutes, and then transferring the mixture into an extruder for melt extrusion; (5) Using liquid nitrogen to rapidly cool the extruded material obtained in step (4) to obtain a polylactic acid material.

2. The synthesis process of the home compostable coated polylactic acid material according to claim 1, characterized in that: In step (1), the mass ratio of the lactide to the initiator is 200 to 500:1; the amount of the catalyst used is equivalent to 0.1% to 0.5% of the mass of the lactide; The initiator includes ethanol, and the concentration of ethanol is 5% to 10%; the catalyst includes stannous octoate.

3. The synthesis process of the home compostable coated polylactic acid material according to claim 2, characterized in that: The polymerization reaction obtains polylactic acid, and its specific operation is as follows: heating the reactor to 200-300°C, and evacuating the reactor, replacing the air therein with argon, cooling to room temperature, adding lactide, an initiator and a catalyst in sequence, and inflating and evacuating the reactor 5 times, and finally maintaining the vacuum degree of the reactor at 600-800 Pa, sealing the reactor, stirring and heating to 120-150°C, reacting for 5-8 hours, and cooling to room temperature to obtain polylactic acid.

4. The synthesis process of the home compostable coated polylactic acid material according to claim 1, characterized in that: In step (2), the method for obtaining modified polylactic acid by melt mixing is specifically performed as follows: heating the reactor to 100-200°C, evacuating the reactor, replacing the air therein with argon, cooling the reactor to room temperature, sequentially adding polylactic acid, activated filler, polyglycolic acid and chain extender, maintaining the vacuum degree of the reactor at 600-800 Pa, sealing the reactor, stirring and heating to 120-150°C, reacting for 4-6 hours, and cooling the reactor to room temperature to obtain modified polylactic acid.

5. The synthesis process of the home compostable coated polylactic acid material according to claim 4, characterized in that: The mass ratio of the polylactic acid, activated filler and polyglycolic acid is 1:0.1-0.3:0.05-0.15; the amount of the chain extender is equivalent to 10%-15% of the mass of the polylactic acid; The activated filler is obtained by blending a silane coupling agent and bamboo fiber in water under ultrasonic conditions.

6. The synthesis process of the home compostable coated polylactic acid material according to claim 5, characterized in that: The mass ratio of the silane coupling agent to the bamboo fiber is 0.15 to 0.25:1, and the amount of water added is equivalent to 1 to 1.5 times the total amount of the silane coupling agent and the bamboo fiber; the ultrasonic conditions are: ultrasonic power 200 to 400 W, ultrasonic time 35 to 55 minutes; The chain extender is at least one of polytrimethylene carbonate, polyurethane vulcanizer, hydroquinone dihydroxyethyl ether, diethylene glycol and toluene diamine.

7. The synthesis process of the home compostable coated polylactic acid material according to claim 1, characterized in that: In step (3), the amount of the propylene-based elastomer added is equivalent to 2% to 6% of the mass of the modified polylactic acid, and the stirring and mixing are carried out in a high-speed stirring mixer with a stirring speed of 1400 to 1600 r / min and a stirring time of 20 to 30 min.

8. The synthesis process of the home compostable coated polylactic acid material according to claim 1, characterized in that: In step (4), the amount of glycerol added is equivalent to 1% to 4% of the mass of the modified polylactic acid, and the temperature of melt extrusion is 160 to 200°C.

9. The synthesis process of the home compostable coated polylactic acid material according to claim 1, characterized in that: The polylactic acid material obtained in step (5) is coated on household paper cups by a casting machine; And / or, the polylactic acid material obtained in step (5) is coated on household paper tableware through a casting machine.

10. A coated polylactic acid material, characterized in that: The coated polylactic acid material is produced by the synthesis process of the home-compostable coated polylactic acid material according to any one of claims 1 to 9.