A polylactic acid nucleating agent, a heat-resistant polylactic acid composition and a preparation method thereof

Abstract

The present invention belongs to the field of heat-resistant polylactic acid technology, and specifically relates to a class of heat-resistant polylactic acid compositions and preparation methods thereof. The present invention uses furfural derivative furoyl chloride to prepare a series of furan dihydrazide-containing thermoplastic polyester nucleating agents. On this basis, a heat-resistant polylactic acid composition is prepared by melt blending according to a mass ratio of 100 parts polylactic acid to 0.3-1 parts nucleating agent. The heat-resistant polylactic acid composition can significantly improve the heat resistance and transparency of heat-resistant polylactic acid plastic products. The nucleating agent has a wide range of raw materials and a simple preparation process. It can effectively increase the crystallization rate of the heat-resistant polylactic acid composition and has good industrial prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of biodegradable polyesters, and particularly relates to a polylactic acid nucleating agent, a heat-resistant polylactic acid composition and a preparation method thereof. Background Art

[0002] As human production and daily life continue to increase their demand for polymer materials, primarily plastics, the accumulation of waste plastics in nature and the resulting white pollution are also increasing. Polylactic acid (PLA) is a biodegradable polymer that can be degraded into water and carbon dioxide under conditions such as composting. Its widespread use can effectively address the current severe white pollution problem and aligns with current sustainable development concepts.

[0003] However, polylactic acid is a semi-crystalline polymer material with poor crystallization ability and slow crystallization rate. Under conventional processing conditions, only amorphous products can be obtained. It cannot withstand temperatures above 60°C, which seriously limits the application range of polylactic acid materials. Adding nucleating agents is an effective means to regulate the crystallization behavior of polymers. Nucleating agents can provide heterogeneous nucleation sites in the polymer melt, accelerate the crystallization rate of the polymer and reduce the crystal size of the polymer, thereby improving the crystallinity and heat resistance of the product. Nucleating agents for polylactic acid can be divided into two categories: inorganic nucleating agents and organic nucleating agents. Inorganic nucleating agents usually include talc, montmorillonite, carbon black, apatite, etc., but the nucleating effect of such nucleating agents is poor. When added in small amounts, the nucleating effect is not obvious. When the content is high, the product is prone to become brittle, affecting the use effect.

[0004] Patent CN111333910A discloses a class of rare earth aryl phosphates containing amino groups, which can be used as nucleating agents for polylactic acid to increase its Vicat softening temperature. Patent CN113150381A discloses a 1,4-naphthalene dicarboxylic acid dinicotinamide polylactic acid nucleating agent, which can improve the crystallinity of polylactic acid and enhance its heat resistance. However, these nucleating agents are mostly derived from petrochemical resources and even contain heavy metal ions, which are not in line with the current sustainable development strategy and have potential hidden dangers to the human body or the environment. At the same time, these nucleating agents have poor compatibility with polylactic acid, which will affect the mechanical properties and transparency of the product. Therefore, the development of a green and environmentally friendly polylactic acid nucleating agent with a high crystallization rate, good heat resistance and good compatibility is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] To address the technical issues in existing polylactic acid (PLA) nucleating agents, which are mostly derived from petrochemical resources and have poor compatibility with polymers, the present invention provides a polylactic acid nucleating agent, a heat-resistant polylactic acid composition, and a preparation method thereof. This bio-based nucleating agent exhibits excellent nucleation properties, effectively improving the crystallinity, heat resistance, and compatibility of polylactic acid with polymers.

[0006] In the first aspect, the present invention provides a polylactic acid nucleating agent having the structural formula:

[0007]

[0008] Where n is a natural number ranging from 2 to 6.

[0009] In a second aspect, the present invention provides a method for preparing a polylactic acid nucleating agent, comprising the following steps:

[0010] S1. Add alkyl dicarboxylic acid dimethyl ester, hydrazine hydrate, and alcohol solvent into a reactor and reflux at 70-100° C. to generate the corresponding alkyl dihydrazide;

[0011] S2, adding the alkyl dihydrazide and the acid binding agent prepared in step S1 to a high boiling point solvent, respectively, adding furoyl chloride dropwise thereto at a temperature of -10°C-25°C, then heating to 60-100°C for reaction to obtain alkyl dicarboxylic acid difuryl hydrazide, and separating and purifying to obtain the nucleating agent;

[0012] The number of carbon atoms in the dimethyl alkyl dicarboxylate is 6-12.

[0013] Furthermore, the alkyl dicarboxylic acid dimethyl ester used is at least one selected from the group consisting of dimethyl adipate, dimethyl suberate, and dimethyl sebacate.

[0014] Furthermore, in step S1, the molar ratio of dimethyl alkyl dicarboxylate to hydrazine hydrate is 1:8-12.

[0015] Furthermore, the molar ratio of the alkyl dihydrazide to furoyl chloride in step S2 is 1:2-2.5.

[0016] Furthermore, the molar ratio of the acid binding agent to furoyl chloride in step S2 is 1-1.5:1.

[0017] Furthermore, the alcohol solvent is at least one of methanol, ethanol, isopropanol, and n-butanol.

[0018] Furthermore, the high boiling point solvent is at least one of toluene, xylene, acetonitrile, dimethyl sulfoxide, N,N'-dimethylformamide, and N,N'-dimethylacetamide.

[0019] Furthermore, the acid binding agent is triethylamine or pyridine.

[0020] In a third aspect, the present invention provides a method for preparing another type of polylactic acid nucleating agent, comprising the following steps:

[0021] R1, reflux methyl furoate in an alcohol solvent and react with hydrazine hydrate to generate furohydrazide;

[0022] R2, adding furohydrazide and an acid-binding agent to a high-boiling-point solvent, adding alkyl dicarboxylic acid chloride dropwise at -10°C to room temperature, then reacting at 60-100°C to obtain alkyl dicarboxylic acid difuryl hydrazide, and obtaining the nucleating agent after separation and purification;

[0023] The molar ratio of the alkyl dicarboxylic acid chloride to furohydrazide is 1:2-2.5;

[0024] The number of carbon atoms in the alkyl dicarboxylic acid chloride is 6-12.

[0025] Furthermore, the molar ratio of methyl furoate to hydrazine hydrate is 1:4-6.

[0026] Furthermore, the molar ratio of the acid binding agent to the alkyl dicarboxylic acid chloride is 2-3:1.

[0027] Furthermore, the alkyl dicarboxylic acid chloride used is 1,6-adipoyl chloride, 1,8-suberyl chloride or 1,10-decanedioyl chloride.

[0028] Furthermore, the alcohol solvent used is at least one of methanol, ethanol, isopropanol, and n-butanol.

[0029] Furthermore, the high boiling point solvent used is at least one of toluene, xylene, acetonitrile, dimethyl sulfoxide, N,N'-dimethylformamide, and N,N'-dimethylacetamide.

[0030] Furthermore, the acid binding agent used is triethylamine or pyridine.

[0031] In a fourth aspect, the present invention provides a heat-resistant polylactic acid composition, which comprises, by weight, 100 parts of polylactic acid and 0.1-3 parts of a nucleating agent, alkyl dicarboxylic acid difuryl hydrazide;

[0032] The structural formula of the nucleating agent alkyl dicarboxylic acid difuryl hydrazide is:

[0033]

[0034] Where n is a natural number ranging from 2 to 6.

[0035] Furthermore, in the heat-resistant polylactic acid composition, the mass ratio of the nucleating agent to polylactic acid is preferably 0.3-1:100.

[0036] In a fifth aspect, the present invention provides a method for preparing a heat-resistant polylactic acid composition, comprising the following steps:

[0037] T1. Dry the polylactic acid and nucleating agent in a vacuum oven at 50-80°C for 12-24 hours and pre-mix them after drying;

[0038] T2. Place the mixed materials in an internal mixer at a mixing temperature of 175-200° C. for not less than 10 minutes and a rotor speed of 15-30 rpm to obtain the heat-resistant polylactic acid composition.

[0039] Beneficial effects:

[0040] The novel nucleating agent provided by the present invention belongs to the hydrazide class of compounds and can be dissolved in a polylactic acid matrix. It promotes polymer crystallization through unique self-assembly behavior, resulting in a significant nucleating effect and greatly increasing the crystallization rate of polylactic acid. It has good compatibility with polylactic acid and is evenly dispersed in the matrix. Even a small amount of addition can promote polymer crystallization. Compared with inorganic minerals, it can better avoid the degradation of the mechanical properties of polymer products. The heat-resistant polylactic acid composition products of the present invention have good transparency, are simple to prepare, and are easy to implement for large-scale industrial production, showing good implementation value and market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is the synthetic route of sebacic acid hydrazide in Example 1;

[0042] Figure 2 The synthetic route of sebacoyl difurylcarboxylic acid hydrazide in Example 1 is as follows;

[0043] Figure 3 1H-NMR diagram of sebacoyl difurylcarboxylic acid hydrazide in Example 1;

[0044] Figure 4 The DSC curves of the samples in Examples 3, 4 and 5 were obtained by cooling at 10°C / min.

[0045] Figure 5 1 is a heat flow curve diagram of isothermal crystallization of samples in Example 3, Example 4 and Example 5 at 120°C;

[0046] Figure 6 Graph showing relative crystallinity versus crystallization time for isothermal crystallization of the samples in Examples 3, 4, and 5 at 120°C. DETAILED DESCRIPTION

[0047] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[0048] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all the embodiments.

[0049] The preferred embodiments of the present invention will be described in detail below with reference to the examples. It should be understood that the following examples are provided for illustrative purposes only and are not intended to limit the scope of the present invention. Those skilled in the art may make various modifications and substitutions to the present invention without departing from the purpose and spirit of the present invention.

[0050] Test instrument model: The nuclear magnetic resonance spectrometer used was Vaian DLG400 (Varian, USA), and the differential scanning calorimeter used was DSC25 (TA, USA).

[0051] Example 1 (Preparation of nucleating agent, sebacoyl difurylcarboxylic acid hydrazide, n=6)

[0052] (1) Preparation of Sebacic Acid Hydrazide: 11.52 g of dimethyl sebacate, 12.52 g of hydrazine hydrate (80%) and 30 mL of anhydrous ethanol were added to a reaction flask and refluxed at 80°C for 8 h. During this period, a large amount of white solid precipitated. After the reaction was completed, the mixture was cooled to room temperature, filtered and washed with anhydrous ethanol. After drying, 10.48 g of a white solid with a metallic luster was obtained. The yield was 91%. The synthetic route is shown in FIG. Figure 1 .

[0053] (2) Preparation of Sebacyldifuroylhydrazide: 4.61 g of sebacylhydrazide, 4.45 g of triethylamine and 50 mL of anhydrous acetonitrile were placed in a reaction flask. 5.74 g of furoyl chloride was added dropwise to the reaction system at 0°C. After the addition was completed, the temperature was raised to 80°C for reaction for 8 h. After the reaction was completed, the reaction was cooled to room temperature. The filter cake was washed once with water and once with anhydrous ethanol by suction filtration. After drying, 5.44 g of white powder was obtained, i.e., the polylactic acid nucleating agent, with a yield of 65%. The synthetic route is shown in FIG. Figure 2 .

[0054] The product was characterized by H NMR spectroscopy. Figure 3 .

[0055] Example 2 (Preparation of nucleating agent: adipoyldifurylcarboxylic acid hydrazide, n=2)

[0056] (1) Preparation of adipic acid hydrazide: 17.42 g of dimethyl adipate, 31.29 g of hydrazine hydrate (80%) and 50 mL of anhydrous ethanol were added to a reaction flask and refluxed at 90°C for 8 h. During this period, a large amount of white solid precipitated. After the reaction was completed, the mixture was cooled to room temperature, filtered and washed with anhydrous ethanol. After drying, 15.68 g of a white solid with a metallic luster was obtained. The yield was 95%. The synthetic route is shown in FIG. Figure 1 .

[0057] (2) Preparation of adipic acid difuroyl hydrazide: 17.42 g of adipic acid dihydrazide, 20.24 g of triethylamine and 100 mL of anhydrous acetonitrile were placed in a reaction flask, and 26.11 g of furoyl chloride was added dropwise to the reaction system at 0°C. After the addition was completed, the temperature was raised to 80°C and the reaction was continued for 10 h. After the reaction was completed, the mixture was cooled to room temperature, the filter cake was washed once with water and once with anhydrous ethanol, and dried to obtain 21.38 g of white powder, i.e., polylactic acid nucleating agent, with a yield of 59%.

[0058] Example 3 (Blending)

[0059] The nucleating agent prepared in Example 1 and polylactic acid (number average molecular weight of 103,000) were dried in a vacuum oven at 60°C for 12 hours. 60g of polylactic acid and 0.18g of nucleating agent were mixed in a ziplock bag and then melt-mixed in a SU-70B micro-internal mixer. The mixer melt temperature and the three temperature control zone temperatures were set to 180°C, 179°C, 178°C, and 175°C, respectively, and the rotor speed was set to 15 rpm. Non-isothermal crystallization by DSC revealed a crystallization temperature of 124°C.

[0060] Example 4 (Comparative Example)

[0061] The commercial nucleating agent sebacyl dibenzoyl hydrazide (trade name TMC300) and polylactic acid (number average molecular weight of 103,000) were dried in a vacuum oven at 60°C for 12 hours. 60g of polylactic acid and 0.18g of the nucleating agent were premixed in a ziplock bag and then melt-mixed in a SU-70B micro-internal mixer. The mixer's melt temperature and the three controlled temperature zones were set at 180°C, 179°C, 178°C, and 175°C, respectively, and the rotor speed was set at 15 rpm. Non-isothermal DSC crystallization testing revealed a crystallization temperature of 96°C.

[0062] Example 5 (Comparative Example)

[0063] Pure polylactic acid (number-average molecular weight of 103,000) was dried in a vacuum oven at 60°C for 12 hours. 60g of the polylactic acid was melt-mixed in a SU-70B micro-internal mixer. The melt temperature and the three control zone temperatures of the mixer were set at 180°C, 179°C, 178°C, and 175°C, respectively, and the rotor speed was set at 15 rpm. Non-isothermal DSC crystallization testing revealed no crystallization peaks on the cooling curve.

[0064] Example 6 (Blending)

[0065] The nucleating agent prepared in Example 2 and the polylactic acid were dried in a vacuum oven at 60°C for 12 hours. 60g of polylactic acid and 0.18g of the nucleating agent were premixed in a ziplock bag and then melt-mixed in a SU-70B micro-internal mixer. The melt temperature and the three temperature control zones of the internal mixer were set to 180°C, 179°C, 178°C, and 175°C, respectively, and the rotor speed was set to 15 rpm. Non-isothermal DSC crystallization testing revealed a crystallization temperature of 118°C.

[0066] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A heat-resistant polylactic acid composition, characterized in that Based on mass components, 100 parts of polylactic acid and 0.1-3 parts of nucleating agent; The structural formula of the nucleating agent is: Where n is a natural number ranging from 2 to 6.

2. The heat-resistant polylactic acid composition according to claim 1, characterized in that Calculated by mass, polylactic acid 100 parts, nucleating agent 0.3-1 part.

3. A method for preparing a heat-resistant polylactic acid composition according to any one of claims 1 to 2, characterized in that: The specific steps are: T1. Dry the polylactic acid and nucleating agent in a vacuum oven at 50-80°C for 12-24 hours and pre-mix them after drying; T2. Place the mixed materials in an internal mixer at a mixing temperature of 175-200° C. for not less than 10 minutes and a rotor speed of 15-30 rpm to obtain the heat-resistant polylactic acid composition.

4. A heat-resistant polylactic acid composition according to claim 1, characterized in that: The nucleating agent is prepared by the following method: S1. Add alkyl dicarboxylic acid dimethyl ester, hydrazine hydrate, and alcohol solvent into a reactor and reflux at 70-100° C. to generate the corresponding alkyl dihydrazide; S2, add the alkyl dihydrazide and acid binding agent to the solvent respectively, and add furoyl chloride dropwise thereto at a temperature of -10°C to 25°C, Then, the temperature is raised to 60-100° C. for reaction to obtain alkyl dicarboxylic acid difuryl hydrazide, which is then separated and purified to obtain the nucleating agent; The molar ratio of the alkyl dihydrazide to furoyl chloride is 1:2-2.5; The number of carbon atoms in the dimethyl alkyl dicarboxylate is 6-12; The solvent is at least one of toluene, xylene, acetonitrile, dimethyl sulfoxide, N,N'-dimethylformamide, and N,N'-dimethylacetamide.

5. The heat-resistant polylactic acid composition according to claim 4, characterized in that The alkyl dicarboxylic acid dimethyl ester is selected from: dimethyl adipate, dimethyl suberate, and dimethyl sebacate.

6. A heat-resistant polylactic acid composition according to claim 1, characterized in that: The nucleating agent is prepared by the following method: R1, reflux methyl furoate in an alcohol solvent and react with hydrazine hydrate to generate furohydrazide; R2, adding furohydrazide and an acid-binding agent to a solvent, adding alkyl dicarboxylic acid chloride dropwise at -10°C to room temperature, then reacting at 60-100°C to obtain alkyl dicarboxylic acid difuryl hydrazide, and obtaining the nucleating agent after separation and purification; The molar ratio of the alkyl dicarboxylic acid chloride to furohydrazide is 1:2-2.5; The number of carbon atoms in the alkyl dicarboxylic acid chloride is 6-12; The solvent is at least one of toluene, xylene, acetonitrile, dimethyl sulfoxide, N,N'-dimethylformamide, and N,N'-dimethylacetamide.

7. The heat-resistant polylactic acid composition according to claim 6, characterized in that The molar ratio of methyl furoate to hydrazine hydrate in step R1 is 1:4-6.

8. The heat-resistant polylactic acid composition according to claim 6, characterized in that The molar ratio of the acid binding agent to the alkyl dicarboxylic acid chloride in step R2 is 2-3:

1.

9. The heat-resistant polylactic acid composition according to claim 6, characterized in that The alkyl dicarboxylic acid chloride used is 1,6-adipoyl chloride, 1,8-suberyl chloride or 1,10-decanedioyl chloride.

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