A crystalline modified polylactic acid material and a method for preparing the same

Abstract

The application discloses a crystalline modified polylactic acid material and a preparation method thereof. The crystalline modified polylactic acid material is prepared through processes such as melt blending and granulation of polylactic acid and a crystalline modifier, and the prepared material has the advantages of excellent mechanical property and good heat resistance.

Description

Technical Field

[0001] This invention discloses a polylactic acid material and its preparation method, specifically in the field of polylactic acid material crystallization modification technology. Background Technology

[0002] PLA is a high-performance biodegradable polyester with broad future development prospects. However, pure PLA is hard and brittle, requiring toughening modification. Common modification methods mainly involve improving the crystallinity of polylactic acid materials through copolymerization, blending, introducing cross-linking structures, and nanocomposites, thereby improving their toughness and heat resistance. Introducing compatibilizers, such as polypropylene grafted with maleic anhydride (PP-g-MAH) and polyethylene grafted with glycidyl methacrylate (PE-g-GMA), to improve the compatibility between PLA and polymers such as polybutylene adipate / terephthalate (PBAT) and polycaprolactone (PCL), while achieving good results, contradicts the fact that polypropylene (PP) and polyethylene (PE) are not biodegradable, violating the original intention of using PLA materials.

[0003] Improving the crystallinity of polylactic acid (PLA) materials is one of the important routes to improve their hydrolysis resistance, thermal properties, and heat resistance. Accelerating the crystallization rate of PLA can not only reduce production costs but also shorten the production cycle. Correspondingly, methods to improve the crystallization rate of PLA mainly include adding plasticizers to increase the migration rate of PLA molecular chains and adding nucleating agents to provide heterogeneous nucleation nuclei to increase the nucleation rate. Adding highly efficient nucleating agents has advantages such as good nucleation effect and low dosage, and can also improve its mechanical properties.

[0004] Currently, nucleating agents mainly consist of inorganic compounds, small organic molecules, and polymers. Inorganic compounds such as talc, carbon nanotubes, silica, montmorillonite, and graphene exhibit good nucleation properties for polylactic acid (PLA). However, due to the poor compatibility between inorganic nucleating agents and polymeric materials, they cannot meet production requirements. Therefore, improving the interfacial compatibility between nucleating agents and PLA through surface modification methods is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a polylactic acid material and its preparation method to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a crystallization-modified polylactic acid material, comprising, by weight, the following materials: 100 parts polylactic acid and 1-15 parts crystallization modifier;

[0007] Furthermore, the crystallization modifier is polylactic acid-modified graphene oxide.

[0008] Further, the preparation method of the polylactic acid modified graphene oxide is as follows: 10 parts of graphene oxide and 20 parts of lactide are dispersed in CHCl3, a protective gas is introduced, and 0.1 parts of tin 2-ethylhexanoate are added as a polymerization catalyst. The mixture is heated to 115°C and stirred for 12 hours. Then it is washed and dried at 60°C for 12 hours to obtain PLA-GO.

[0009] Furthermore, the polylactic acid-modified graphene oxide is maleic anhydride-grafted polylactic acid-modified graphene oxide.

[0010] Furthermore, the preparation method of the maleic anhydride-grafted polylactic acid-modified graphene oxide is as follows: 10 parts of PLA-GO and 1 part of MAH are mixed at 160℃ and 60 rpm for 1.5 min, then 0.08 parts of DCP are added, and the mixture is mixed for another 8.5 min. After cooling, MAH-PLA-GO is obtained.

[0011] Furthermore, the maleic anhydride-grafted polylactic acid-modified graphene oxide is anamine-modified maleic anhydride-grafted polylactic acid-modified graphene oxide.

[0012] Furthermore, the preparation method of the amino-modified maleic anhydride-grafted polylactic acid-modified graphene oxide is as follows: 10 parts of MAH-PLA-GO are dispersed in CHCl3, 1 part of N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine is added, the temperature is raised to 60℃ and the reaction is stirred for 5h, and the product is washed and dried for 6-36h to obtain the product.

[0013] A method for preparing a crystallization-modified polylactic acid material involves co-mixing polylactic acid and a crystallization modifier at 160-180℃ for 8-14 minutes, followed by granulation after cooling.

[0014] Specifically: Polylactic acid is vacuum dried at 40-100℃ for 12-26 hours before being mixed with the crystallization modifier.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] 1. In-situ polymerization of PLA-GO on the surface of graphene oxide to generate polylactic acid (PLA) inhibits the aggregation of graphene oxide through the steric hindrance effect of the polymer chains. Compared with traditional macromolecular surface modification, this method can greatly improve the compatibility between PLA-GO and PLA-GO substrate, and avoid the deterioration of the mechanical properties of the material after the addition of graphene oxide. The addition of PLA-GO can play a role in heterogeneous nucleation, inducing epitaxial crystallization of PLA substrate and improving the crystallinity of PLA substrate.

[0017] 2. MAH-PLA-GO was prepared by grafting maleic anhydride onto PLA-GO material, followed by further grafting N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine onto maleic anhydride. Compared with traditional amination-modified graphene oxide (graphene oxide has a limited number of carboxyl groups on its surface, resulting in fewer reaction sites with N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine), the polylactic acid chains polymerized on the graphene oxide surface are longer, and a single polylactic acid chain can be grafted with a large amount of maleic anhydride, providing more active sites for reaction with N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine and promoting the dispersion of N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine.

[0018] 3. During the crystallization process, A-MAH-PLA-GO first forms microcrystals through intermolecular hydrogen bonding. For example, the C=O on the carboxyl / ester group of polylactic acid forms hydrogen bonds with the NH in A-MAH-PLA-GO. The intermolecular C=O and NH in A-MAH-PLA-GO form hydrogen bonds, which act as nucleating agents to induce the epitaxial crystallization of PLA. At the same time, the graphene substrate itself is also a heterogeneous nucleation site, thus endowing PLA with excellent heat resistance and toughness. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the reaction of polylactic acid modifying graphene oxide.

[0020] Figure 2 This is a schematic diagram of the reaction of maleic anhydride grafted with polylactic acid to modify graphene oxide.

[0021] Figure 3 This is a schematic diagram of the reaction of maleic anhydride grafted with polylactic acid to modify graphene oxide. Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Material testing methods: Impact strength is tested according to GB / T 1843, and tensile strength and elongation at break are tested according to GB / T1040.2.

[0024] Crystallization performance test: Weigh 6mg of sample and test its crystallization parameters by DSC under N2 atmosphere. There are two temperature control programs: (1) Non-isothermal crystallization test: First, heat from 25℃ to 200℃ at a heating rate of 5℃ / min, hold at the temperature for 5min to eliminate thermal history, and then cool down to 25℃ at a cooling rate of 5℃ / min. Record the DSC curve of non-isothermal crystallization of the sample. (2) Isothermal crystallization test: First, heat from 25℃ to 200℃ at a heating rate of 10℃ / min, hold at the temperature for 5min to eliminate thermal history, and then quickly cool down from 200℃ to 130℃ and hold at the temperature for 60min.

[0025] Sample preparation: PLA material was vacuum dried at 70℃ to reduce its moisture content to below 0.02%. Cooling was performed according to GB / T 9352, using method A, with an average cooling rate of 10℃ / min ± 5℃ / min and a molding temperature of 190℃.

[0026] Preparation of polylactic acid modified graphene oxide (PLA-GO): 10g of graphene oxide and 20g of lactide were dispersed in 250ml of CHCl3. After purging with a protective gas, 0.1g of tin(II) 2-ethylhexanoate (Sn(Oct)2) was added as a polymerization catalyst. The mixture was heated to 115℃ and stirred for 12h. The mixture was then washed with chloroform, methanol and deionized water and dried at 60℃ for 12h to obtain PLA-GO.

[0027] Infrared spectroscopy characterization revealed that at 3441 cm⁻¹ -1 1738cm -1 1651cm -1 1415cm -1 1228cm -1 and 1080cm -1 The peaks at this point exhibit typical GO characteristic peaks, corresponding to hydroxyl (-OH), carbonyl stretching vibration (C=O), and unoxidized carbon-carbon sp. 2 The stretching vibrations (C=C), C–O–H deformation vibrations, C–O stretching vibrations of epoxy groups, and C–O bending vibrations can reach 1187 cm⁻¹. -1 and 1457cm -1 Absorption peaks of the stretching vibration of COC and the asymmetric bending vibration of -CH3 were observed at 1095 cm⁻¹, which are characteristic peaks of PLA. -1 and 1738cm -1 The enhanced C–O and C=O stretching vibration peaks indicate that PLA was successfully decorated on the functional groups of the GO surface.

[0028] Preparation of maleic anhydride-grafted polylactic acid modified graphene oxide MAH-PLA-GO: 10g of PLA-GO and 1g of MAH were added to a torque rheometer and mixed at 160℃ and 60rpm for 1.5min. Then, 0.08g of DCP was added and the mixture was mixed for another 8.5min. After cooling, MAH-PLA-GO was obtained.

[0029] Preparation of A-MAH-PLA-GO modified graphene oxide (A-MAH-PLA-GO) by amino-modified maleic anhydride grafted with polylactic acid: 10g of MAH-PLA-GO was dispersed in CHCl3, and 1g of N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine was slowly added. The mixture was heated to 60℃ and stirred for 5h. Then, it was washed with chloroform, methanol and deionized water and dried at 60℃ for 12h to obtain A-MAH-PLA-GO.

[0030] Preparation of crystallization-modified polylactic acid material: Polylactic acid and crystallization modifier were added to a torque rheometer and mixed together at 160℃ for 11 min at a speed of 60 rpm. After cooling, the mixture was granulated to obtain the final product.

[0031] Comparative Example 1: 100 parts of polylactic acid, granulated and then molded at 190°C.

[0032] Comparative Example 2: 100 parts polylactic acid and 10 parts commercially available talc were mixed, granulated, and then molded at 190°C.

[0033] Comparative Example 3: 100 parts polylactic acid and 10 parts commercially available graphene were mixed, granulated, and then molded at 190°C.

[0034] Comparative Example 4: 100 parts of polylactic acid and 10 parts of commercially available graphene oxide were mixed, granulated, and then molded at 190°C.

[0035] Comparative Example 5: 100 parts of polylactic acid and 10 parts of polyethylene glycol macromolecular-grafted graphene oxide (prepared according to Example 3 of CN114907679A) were mixed, granulated, and then molded at 190°C.

[0036] Example 1: 100 parts of polylactic acid and 1 part of PLA-GO were mixed, granulated, and then molded at 190°C.

[0037] Example 2: 100 parts of polylactic acid and 10 parts of PLA-GO were mixed, granulated, and then molded at 190°C.

[0038] Example 3: 100 parts of polylactic acid and 15 parts of PLA-GO were mixed, granulated, and then molded at 190°C.

[0039] Example 4: 100 parts of polylactic acid and 1 part of MAH-PLA-GO were mixed, granulated, and then molded at 190°C.

[0040] Example 5: 100 parts of polylactic acid and 10 parts of MAH-PLA-GO were mixed, granulated, and then molded at 190°C.

[0041] Example 6: 100 parts polylactic acid, 10 parts PLA-GO, and 1 part MAH were mixed, granulated, and then molded at 190°C.

[0042] Example 7: 100 parts of polylactic acid and 15 parts of MAH-PLA-GO were mixed, granulated, and then molded at 190°C.

[0043] Example 8: 100 parts of polylactic acid and 1 part of A-MAH-PLA-GO were mixed, granulated, and then molded at 190°C.

[0044] Example 9: 100 parts of polylactic acid and 10 parts of A-MAH-PLA-GO were mixed, granulated, and then molded at 190°C.

[0045] Example 10: 100 parts of polylactic acid and 15 parts of A-MAH-PLA-GO were mixed, granulated, and then molded at 190°C.

[0046] Example 11: 100 parts of polylactic acid, 10 parts of MAH-PLA-GO, and 1 part of N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine were mixed, granulated, and then molded at 190°C.

[0047] Example 12: 100 parts of polylactic acid, 10 parts of PLA-GO, 1 part of MAH, and 1 part of N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine were mixed, granulated, and then molded at 190°C.

[0048] Example 13: 100 parts of polylactic acid and 5 parts of N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine were mixed, granulated, and then molded at 190°C.

[0049] Example 14: 100 parts of polylactic acid, 5 parts of MAH, and 5 parts of N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine were mixed, granulated, and then molded at 190°C.

[0050] Example 15: 100 parts polylactic acid, 5 parts GO, 5 parts MAH, and 5 parts N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine were mixed, granulated, and then molded at 190°C.

[0051] The experimental results are as follows:

[0052] Where: tensile strength is in MPa, elongation at break is in %, and impact strength is in kJ / m. 2Thermal decomposition temperature, initial crystallization temperature, and crystallization temperature are in °C; semi-crystallization time at 130 °C is in min; and crystallinity is in °C.

[0053] Serial Number Tensile strength Elongation at break Impact strength Thermal decomposition temperature Initial crystallization temperature Crystallization temperature 130℃ semi-crystallization time Crystallinity Comparative Example 1 35.5 3.2 6.10 251 107.3 93.2 25.0 8.64 Comparative Example 2 38.2 1.7 11.09 258 108.1 97.0 17.9 27.1 Comparative Example 3 26.4 1.8 3.71 256 107..9 96.9 17.4 26.4 Comparative Example 4 40.1 1.9 10.17 256 108.2 97.2 17.5 27.8 Comparative Example 5 48.7 17.2 3.05 261 109.9 98.3 17.5 36.4 Example 1 37.9 5.5 8.75 253 109.7 98.5 17.5 29.9 Example 2 50.5 18.2 12.07 258 110.4 99.7 17.1 30.6 Example 3 56.4 24.9 20.24 261 113.8 102.5 16.2 38.2 Example 4 38.2 10.5 10.21 260 111.5 100.4 13.3 37.7 Example 5 50.7 21.0 16.97 263 112.1 101.5 12.9 32.5 Example 6 50.6 17.7 12.20 258 110.4 100.7 15.6 40.5 Example 7 56.9 26.2 24.57 264 114.2 103.9 10.4 46.2 Example 8 43.1 18.5 12.60 268 121.5 110.6 6.1 58.2 Example 9 60.4 32.1 30.1 273 127.9 115.2 3.4 60.8 Example 10 63.5 35.5 32.2 274 128.2 119.4 2.1 63.2 Example 11 51.0 23.1 19.20 264 113.4 102.1 12.1 35.5 Example 12 50.4 21.5 14.25 260 110.8 99.7 16.8 33.4 Example 13 36.2 5.5 8.21 257 115.4 103.9 11.3 23.1 Example 14 36.2 10.4 9.52 259 115.5 104.1 11.3 24.9 Example 15 39.5 11.4 10.19 259 116.3 104.6 10.9 30.5

[0054] Analysis of the table above shows that PLA-GO, MAH-PLA-GO, and A-MAH-PLA-GO all significantly improve the mechanical and impact properties of polylactic acid (PLA) materials. They also generally increase the crystallinity of PLA and shorten the crystallization time. Comparing Example 2 and Comparative Example 5, the mechanical properties of Example 2 are slightly improved compared to Comparative Example 5, while the crystallinity is similar. However, the impact strength of Example 2 is significantly better than that of Comparative Example 5. Further comparison of Examples 5 and 9 reveals even greater performance improvements.

[0055] Based on comparative examples 2, 3, and 4, and Example 2, we can see that the polylactic acid (PLA) grafted graphene oxide (PMO) material exhibits significant improvements in various properties. This indicates that the steric hindrance effect of the polymer chains on the PMO surface inhibits PMO aggregation, greatly enhancing the compatibility between PLA-GO and the PMO substrate. This avoids the deterioration of material mechanical properties caused by aggregation after adding traditional inorganic fillers to PLA. Simultaneously, the addition of PLA-GO can act as a heterogeneous nucleation agent, inducing epitaxial crystallization of the PLA substrate and increasing its crystallinity.

[0056] Comparing Examples 5, 9, and 11, the direct addition of N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine has almost no effect on the mechanical properties of the material, a slight increase in impact strength, and a limited increase in crystallinity, indicating that the grafting method may be more conducive to improving the various properties of PLA. Further comparison of Examples 10 and 15 shows that the performance parameters of Example 10 are significantly better than those of Example 15. This indicates that compared with traditional amino-modified graphene oxide (graphene oxide has a limited number of carboxyl groups on its surface, resulting in fewer reaction sites with N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine), the polylactic acid chains polymerized on the surface of graphene oxide are longer. A single polylactic acid chain can graft a large amount of maleic anhydride, providing more active sites for reaction with N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine, promoting the dispersion of N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine, improving the grafting degree of N'-acetyl-5-(aminomethyl)furan-2-carboxylhydrazine, and enhancing the crystallinity and mechanical properties of the crystallized polylactic acid material.

[0057] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0058] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0059] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A crystalline modified polylactic acid material comprising, in parts by mass: polylactic acid 100 parts, crystalline modifier 1 to 15 parts; characterized in that: The crystallization modifier is polylactic acid modified graphene oxide; The polylactic acid modified graphene oxide is prepared by dispersing 10 parts of graphene oxide in 20 parts of propiolactone in CHCl3, introducing a protective gas, adding 0.1 part of 2-ethylhexanoic acid tin as a polymerization catalyst, heating to 115°C, and stirring for 12 hours, followed by washing and drying at 60°C for 12 hours.

2. The crystalline modified polylactic acid material of claim 1, wherein: The polylactic acid modified graphene oxide is maleic anhydride grafted polylactic acid modified graphene oxide.

3. The crystalline modified polylactic acid material of claim 2, wherein: The maleic anhydride grafted polylactic acid modified graphene oxide is prepared by mixing 10 parts of PLA-GO with 1 part of MAH at 160°C and a rotation speed of 60 rpm for 1.5 minutes, then adding 0.08 parts of DCP and continuing to mix for 8.5 minutes, and then cooling to obtain MAH-PLA-GO.

4. The crystalline modified polylactic acid material of claim 2, wherein: The maleic anhydride grafted polylactic acid modified graphene oxide is amine-modified maleic anhydride grafted polylactic acid modified graphene oxide.

5. The crystalline modified polylactic acid material of claim 4, wherein: The amine-modified maleic anhydride grafted polylactic acid modified graphene oxide is prepared by dispersing 10 parts of MAH-PLA-GO in CHCl3, adding 1 part of N'-acetyl-5- (aminomethyl) furan-2-formyl hydrazine, heating to 60°C, and stirring for 5 hours, and then washing and drying the product for 6-36 hours.

6. The method of claim 1-5, wherein the crystalline modified polylactic acid material is prepared by: The polylactic acid and the crystallization modifier are mixed together at 160-180°C for 8-14 minutes, cooled, and then granulated to obtain the product.

7. The method for preparing the crystallized modified polylactic acid material according to claim 6, characterized in that: The polylactic acid and the crystallization modifier are vacuum dried at 40-100°C for 12-26 hours before mixing.

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