A polylactic acid composite material, its preparation method and application

Abstract

The present invention discloses a polylactic acid composite material, a preparation method thereof and an application. The polylactic acid composite material of the present invention comprises: 60-85 parts of polylactic acid, 15-30 parts of talcum powder, and 0.5-10 parts of a copolymer of butylene adipate and butylene terephthalate; the polylactic acid comprises poly-L-lactic acid and poly-D-lactic acid, and the mass percentage of poly-D-lactic acid relative to polylactic acid is 0.3%-2%; the molar percentage of the units derived from terephthalic acid in the copolymer of butylene adipate and butylene terephthalate in the diacid units ≤ 50%; 5 μm ≤ the particle size D of the talcum powder 95 ≤ 21 μm. By combining polylactic acid with a specific poly-D-lactic acid content, talcum powder with a specific particle size and a copolymer of butylene adipate and butylene terephthalate with a specific T content, the present invention significantly improves the resistance of the polylactic acid composite material to hygrothermal aging.

Description

Technical Field

[0001] The present invention relates to the technical field of compositions of polymer compounds, and more specifically, to a polylactic acid composite material, a preparation method thereof, and an application thereof. Background Art

[0002] Polylactic acid is a biodegradable polymer material prepared by chemical synthesis from renewable plant resources. Its glass transition temperature is 60°C, and it is in a glassy state at room temperature, which results in severe brittleness, low impact strength, and difficulty in being applied alone. Currently, a multi-component blending modification method is generally used to improve the toughness of polylactic acid. Moreover, to maintain the degradation performance of polylactic acid, the blending modification components also need to have good biodegradability. Therefore, poly(butylene adipate-co-terephthalate) (PBAT) with good biodegradability, excellent elongation at break, and low elastic modulus is commonly used to improve the brittleness of polylactic acid. For example, a biodegradable polyester film is disclosed in the prior art. The film includes 20-50 parts of polylactic acid and 50-80 parts of poly(butylene adipate-co-terephthalate). By blending poly(butylene adipate-co-terephthalate) with polylactic acid, the toughness of polylactic acid is significantly improved.

[0003] In addition, the toughness and strength of polylactic acid can also be improved by crosslinking modification. For example, a fully biodegradable toughened and high-strength polylactic acid-based composite material is disclosed in the prior art. The composite material is composed of polylactic acid, epoxidized vegetable oil or its derivatives, and a peroxide initiator. After drying and mixing, it is prepared by an in-situ grafting crosslinking reaction in a mixer. The introduced grafting crosslinking structure toughens the composite material while maintaining high strength, so that polylactic acid is widely used in biodegradable mulch films. However, the above-mentioned melt blending modification or grafting crosslinking modification is difficult to effectively improve the heat resistance or wet heat resistance of polylactic acid, resulting in its limited application in environmentally friendly tableware, especially difficult to be applied to biodegradable products such as biodegradable coated paper cups or biodegradable straws that need to be in contact with high-temperature liquids for a long time. Summary of the Invention

[0004] An object of the present invention is to overcome the defects and deficiencies of the poor wet heat aging resistance of existing polylactic acid composite materials, and to provide a polylactic acid composite material.

[0005] Another object of the present invention is to provide a preparation method of a polylactic acid composite material.

[0006] Another object of the present invention is to provide an application of the above-mentioned polylactic acid composite material in the preparation of environmentally friendly tableware.

[0007] Another object of the present invention is to provide a biodegradable paper cup or straw containing the above-mentioned polylactic acid composite material.

[0008] The above object of the present invention is achieved by the following technical solutions:

[0009] The present invention protects a polylactic acid composite material, which comprises the following components by weight:

[0010] 60-85 parts of polylactic acid, 15-30 parts of talcum powder, and 0.5-10 parts of a copolymer of butylene adipate and butylene terephthalate;

[0011] Among them, the polylactic acid includes poly-L-lactic acid and poly-D-lactic acid, and the mass percentage of poly-D-lactic acid relative to polylactic acid is 0.5% to 2%; in the copolymer of butylene adipate and butylene terephthalate, the molar percentage of the unit derived from terephthalic acid in the diacid unit ≤ 50%; the particle size of the talcum powder satisfies: 5μm ≤ D 95 ≤ 21μm.

[0012] Optionally, the Z-average molecular weight of the above polylactic acid is 200,000 to 350,000, and it can be derived from self-made or commercially available products; for example, it can be prepared by the following preparation method:

[0013] S1. After mixing L-lactic acid, D-lactic acid and a first catalyst (such as stannous octoate) evenly, carry out a polycondensation reaction at 90-110°C and 3-7 Kpa for 8-10 h to obtain an oligomer; then carry out vacuum distillation on the oligomer at a temperature of 180-200°C and 100-104 Pa to obtain a lactide intermediate product;

[0014] S2. Dissolve the lactide intermediate product obtained in the above step in an initiator (such as hexanediol), add a second catalyst (such as stannous octoate), first carry out a ring-opening polymerization reaction at 130-150°C and a relative pressure of 100,000-110,000 Pa for 3-5 h, then keep the relative pressure unchanged, and continue the reaction at 170-190°C for 2-3 h to obtain a polymer solid; finally, dissolve the obtained polymer solid by refluxing with a chloroform aqueous solution, filter and precipitate to obtain a polylactic acid resin.

[0015] The content of PDLA in the above polylactic acid can be measured by the following method: Test pure PLLA and pure PDLA by gas chromatography to obtain their spectral peaks; under the same test conditions, test the target polylactic acid, and calculate the content of PDLA in the target polylactic acid through the peak areas δ PLLA and δ PDLA of PLLA and PDLA corresponding on the gas chromatogram. The calculation formula is: η = δ PDLA / (δ PLLA +δ PDLA )*100%.

[0016] The particle size of the above talcum powder can be measured by the following method: calcine the polylactic acid composite material at 700°C for 20 min, and then measure it with a laser particle size analyzer. The copolymer of the above butylene adipate and butylene terephthalate is measured according to the standard of GB / T3682.1-2018, and its melt mass flow rate is 3-6 g / 10 min under the conditions of 190°C and 2.16 kg.

[0017] Preferably, the polylactic acid composite material comprises the following components in parts by weight: 74-76.5 parts of polylactic acid, 22-24 parts of talcum powder, and 1.5-2 parts of the copolymer of butylene adipate and butylene terephthalate.

[0018] Preferably, the mass percentage of poly-D-lactic acid relative to polylactic acid is 0.5%-1.2%; specifically, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1% or 1.2%.

[0019] Optionally, the particle size of the talcum powder satisfies: 8 μm ≤ D 95 ≤ 16 μm; preferably 10 μm ≤ D 95 ≤ 15 μm.

[0020] Optionally, the Z-average molecular weight (Mz) of the polylactic acid is 240,000-260,000, specifically it can be 240,000, 245,000, 250,000, 255,000 or 260,000. The Z-average molecular weight of polylactic acid can be determined by gel permeation chromatography, specifically as follows:

[0021] Dissolve the sample in tetrahydrofuran, analyze it with a Waters 2410 gel chromatograph of Waters Company in the United States, the column temperature is 25°C, tetrahydrofuran is used as the solvent and eluent phase, the flow rate is 1.0 mL / min, polystyrene standards with different molecular weights are used as the calibration curve, and the retention time is 50 min.

[0022] Optionally, the molar percentage of aromatic carboxylic acid units in the copolymer of butylene adipate and butylene terephthalate is 45%-50% or 47%-50%.

[0023] The mass percentage of polylactic acid in the polylactic acid composite material of the present invention is ≥ 60%. Without compromising the effects of the present invention, it may also contain common additives such as pigments, antioxidants, antistatic agents, lubricants, and opening agents.

[0024] The present invention also protects a preparation method of the above polylactic acid composite material, which comprises the following steps:

[0025] Mix polylactic acid, talcum powder, and a copolymer of butylene adipate and butylene terephthalate, and then melt and extrude them to obtain the polylactic acid composite material. Specifically, the temperature of the above-mentioned melt extrusion is 140-240 °C.

[0026] The application of the above-mentioned polylactic acid composite material in the preparation of environmentally friendly tableware is also within the protection scope of the present invention.

[0027] A degradable paper cup or straw containing the above-mentioned polylactic acid composite material is also within the protection scope of the present invention.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] By combining polylactic acid with a specific content of poly-D-lactic acid, talcum powder with a specific particle size, and a copolymer of butylene adipate and butylene terephthalate with a specific T (aromatic carboxylic acid unit) content, the present invention significantly improves the moisture and heat aging resistance of the polylactic acid composite material. Specific Embodiments

[0030] The present invention will be further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventionally purchased raw material reagents.

[0031] 1. Raw Material Reagents

[0032] (1) Polylactic acid, self-made, for example, can be prepared by the following preparation method:

[0033] S1. Add L-lactic acid, D-lactic acid, and a first catalyst (stannous octoate) to a reaction vessel, stir evenly, and carry out a polycondensation reaction at a temperature of 100 °C and a pressure of 5 KPa. After 9 hours, water is distilled off to obtain an oligomer. The obtained oligomer is subjected to vacuum distillation at a temperature of 190 °C and a pressure of 102 Pa until no product distills out, and the time is 11 hours to obtain an intermediate lactide product.

[0034] S2. Dissolve the lactide intermediate obtained in the above steps in an initiator (hexanediol), add a second catalyst (stannous octoate), and carry out ring-opening polymerization. Specifically: first react at a temperature of 150 °C and a relative pressure of 110,000 Pa for 4 h, then react at a temperature of 180 °C and a relative pressure of 110,000 Pa for 2.5 h to obtain a polymer. Dissolve the obtained polymer solid by refluxing with a 5% (W / W) chloroform aqueous solution. After filtering the solution, precipitate with ethanol five times the volume of chloroform to obtain a white flocculent precipitate, and obtain polylactic acid resin. The mass percentage of PDLA in polylactic acid is regulated by controlling the ratio of L-lactic acid monomer and D-lactic acid monomer. The Z-average molecular weight of polylactic acid is mainly affected by the reaction temperature, the type and dosage of the catalyst, that is, the Z-average molecular weights of polylactic acids 1-6 are basically the same, as shown in Table 1 specifically.

[0035] Table 1 Z-average molecular weights of different polylactic acids and mass percentages of PDLA therein

[0036]

[0037] The content of PDLA in the above polylactic acid can be determined by the following method: Test pure PLLA and pure PDLA by gas chromatography to obtain the spectral peaks of the two; under the same test conditions, test the target polylactic acid, and through the peak areas δ PLLA and δ PDLA of the corresponding PLLA and PDLA spectral peaks on the gas chromatogram, calculate the content of PDLA in the target polylactic acid, and the calculation formula is: η = δ PDLA / (δ PLLA +δ PDLA ) * 100%.

[0038] (2) Filler

[0039] Talc powder is purchased from Haicheng Tianyuan Chemical Industry Company, with the model TY90-13-A. Before being used to prepare the polylactic acid composite material, it is first ground and sieved, and talc powders 1-6 with different particle size distributions are obtained by the mesh number of the sieve; the D 95 of talc powder-1 is measured by a laser particle size analyzer to be 5 μm, the D 95 of talc powder-2 is 10 μm, the D 95 of talc powder-3 is 15 μm, the D 95 of talc powder-4 is 20 μm, the D 95 of talc powder-5 is 3 μm, and the D 95 of talc powder-6 is 25 μm.

[0040] Calcium carbonate is purchased from Omya Company, with the model OMYACARB 1T-CU. Before being used to prepare the polylactic acid composite material, it is first ground and sieved, and D 95Calcium carbonate with a size of 5 μm.

[0041] (3) Copolymer of butylene adipate and butylene terephthalate (PBAT)

[0042] PBAT-1, the molar ratio of aromatic carboxylic acid units to diacid units is 47%, the melt mass flow rate is 4 g / 10 min, the grade is A400 NC801, and the manufacturer is Zhuhai Jinfa Biology;

[0043] PBAT-2, the molar ratio of aromatic carboxylic acid units to diacid units is 50%, the melt mass flow rate is 4 g / 10 min, the grade is KB700 NC801, and the manufacturer is Zhuhai Jinfa Biology;

[0044] PBAT-3, the molar ratio of aromatic carboxylic acid units to diacid units is 55%, the melt mass flow rate is 4 g / 10 min, the grade is KB700 NC802, and the manufacturer is Zhuhai Jinfa Biology.

[0045] The melt mass flow rate of the above PBAT was tested under the conditions of 190 °C and 2.16 kg according to the GB / T3682.1-2018 standard; the T content can be determined by the following method: the T content is the molar ratio of aromatic carboxylic acid units to diacid units in the copolymer of butylene adipate and butylene terephthalate, where the content of butylene terephthalate units is tested by 1HNMR, using deuterated chloroform as the solvent and TMS as the internal standard, and the result is calculated according to the following formula:

[0046]

[0047] Among them, T% is the content of butylene terephthalate units, S 8.1 is the absorption peak area at 8.1 ppm in the 1H NMR spectrum, S 2.3 is the absorption peak area at 2.3 ppm in the 1H NMR spectrum.

[0048] 2. The polylactic acid composite materials of the examples and comparative examples of the present invention were prepared by the following preparation method:

[0049] Mix polylactic acid, talcum powder and the copolymer of butylene adipate and butylene terephthalate, and then add them to a twin-screw extruder and melt-extrude at 140-240 °C to obtain the polylactic acid composite material.

[0050] 3. Performance testing

[0051] The polylactic acid composite materials of each example and comparative example were randomly divided into Group A and Group B. Among them, in Group A, the test was directly carried out according to the method specified in GB / T 1040.2-2022 "Plastics - Determination of tensile properties - Part 2: Test conditions for moulding and extrusion plastics" at a tensile rate of 50 mm / min, and the tensile strength I was measured; in Group B, after being placed at a temperature of 60 °C and a humidity of 60% for 9 days, the tensile strength was then tested according to the above method, and the tensile strength II was measured; the tensile strength retention rate (%) = tensile strength II / tensile strength I * 100%.

[0052] Examples 1 to 12 and Comparative Examples 1 to 10

[0053] The weight parts of each component in the polylactic acid composite materials of Examples 1 to 12 and Comparative Examples 1 to 10 are shown in Tables 2 and 3.

[0054] Table 2 Weight parts of each component in the polylactic acid composite materials of Examples 1 to 12

[0055]

[0056] Table 3 Weight parts of each component in the polylactic acid composite materials of Comparative Examples 1 to 10

[0057]

[0058] The performance test results of the polylactic acid composite materials in each example and comparative example according to the above-mentioned method are shown in Table 4.

[0059] Table 4 Test results of each example and comparative example

[0060] Number Tensile strength retention rate / % Example 1 61 Example 2 63 Example 3 64 Example 4 61 Example 5 62 Example 6 62 Example 7 61 Example 8 62 Example 9 61 Example 10 62 Example 11 63 Example 12 64 Comparative Example 1 56 Comparative Example 2 58 Comparative Example 3 57 Comparative Example 4 55 Comparative Example 5 45 Comparative Example 6 55 Comparative Example 7 47 Comparative Example 8 52 Comparative Example 9 53 Comparative Example 10 50

[0061] According to the data in Table 4, the tensile strength retention rate of the polylactic acid composite materials in Examples 1 to 12 reached more than 60%, indicating that the polylactic acid composite materials of the present invention have excellent resistance to wet and heat aging performance. At the same time, it can be seen from Examples 1 to 4 and Comparative Examples 1 to 2 that the content of poly-D-lactic acid in polylactic acid has an important influence on the tensile strength retention rate of the polylactic acid composite material, showing a trend of first increasing and then decreasing with the increase of the content of poly-D-lactic acid. Specifically, when the mass percentage of poly-D-lactic acid relative to polylactic acid < 0.3% or > 2%, it is difficult to effectively improve the resistance to wet and heat aging performance of the polylactic acid composite material; when the mass percentage of poly-D-lactic acid relative to polylactic acid is in the range of 0.3% to 2%, the polylactic acid composite materials all have good resistance to wet and heat aging performance, and have more excellent performance when the mass percentage is 0.5% to 1.2%.

[0062] In addition, it can be found from Example 1, Examples 5 to 7 and Comparative Examples 3 to 5 that the type and particle size of the polylactic acid composite material also have an important impact on the heat and humidity aging resistance performance. Not any filler can effectively improve the heat and humidity aging resistance performance of the polylactic acid composite material. Comparative Example 5 also proves that when the filler is calcium carbonate, the improvement effect on the heat and humidity aging resistance performance of the polylactic acid composite material is extremely limited, while talc powder has a significant improvement effect compared with calcium carbonate. Moreover, it can also be found that the particle size of talc powder will also affect the heat and humidity aging resistance performance of the polylactic acid composite material. When its particle size D 95 is 3 μm or 25 μm, although there is still a certain improvement effect compared with calcium carbonate, the improvement amplitude is small and cannot meet the application requirements; while when its particle size D 95 is 5 to 20 μm, the tensile strength retention rate of the polylactic acid composite material reaches more than 60%. When the particle size D 95 is 10 to 15 μm, the polylactic acid composite material has better heat and humidity aging resistance performance, and the tensile strength retention rate reaches 62%.

[0063] It can be seen from Example 1, Example 8 and Comparative Example 6 that the T content in PBAT will also affect the heat and humidity aging resistance performance of the polylactic acid composite material. When the T content is too high, it is not conducive to the improvement of the heat and humidity aging resistance performance of the polylactic acid composite material. It can be seen that the content of poly-D-lactic acid in polylactic acid, the type and particle size of the filler, and the T content in PBAT jointly determine the heat and humidity aging resistance performance of the polylactic acid composite material.

[0064] The above embodiments of the present invention are merely examples for clearly explaining the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A polylactic acid composite material, characterized in that, Comprising the following components by weight parts: 60 - 85 parts of polylactic acid, 15 - 30 parts of talcum powder, 0.5 - 10 parts of copolymer of butylene adipate and butylene terephthalate; Among them, the polylactic acid includes poly-L-lactic acid and poly-D-lactic acid, and the mass percentage of poly-D-lactic acid relative to polylactic acid is 0.5% - 1.2%; In the copolymer of butylene adipate and butylene terephthalate, the molar percentage of the unit derived from terephthalic acid in the diacid units is 45% to 50%; the particle size of the talc powder satisfies: 5 μm ≤ D 95 ≤ 21 μm.

2. The polylactic acid composite material according to claim 1, wherein Comprising the following components by weight parts: 74 - 76.5 parts of polylactic acid, 22 - 24 parts of talcum powder, 1.5 - 2 parts of copolymer of butylene adipate and butylene terephthalate.

3. The polylactic acid composite material according to claim 1, wherein The particle size of the talcum powder satisfies: 8μm ≤ D 95 ≤ 16μm.

4. The polylactic acid composite material according to claim 1, wherein, The Z-average molecular weight of the polylactic acid is 240,000 - 260,000.

5. A method for preparing the polylactic acid composite material according to any one of claims 1 to 4, characterized in that, Comprising the following steps: Mixing the polylactic acid, talcum powder and copolymer of butylene adipate and butylene terephthalate, and melt-extruding to obtain the polylactic acid composite material.

6. The preparation method according to claim 5, characterized in that, The temperature of the melt-extrusion is 140 - 240 °C.

7. Use of the polylactic acid composite material according to any one of claims 1 - 4 in the preparation of environmentally friendly tableware.

8. A degradable paper cup or straw, characterized in that, Comprising the polylactic acid composite material according to any one of claims 1 - 4.

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