A heat-resistant polylactic acid composition, its preparation method and application

Abstract

The present invention discloses a heat-resistant polylactic acid composition, a preparation method thereof, and an application thereof. The heat-resistant polylactic acid composition of the present invention comprises the following components in parts by weight: 15-85 parts of polylactic acid, 10-30 parts of talc powder, and 25-55 parts of polybutylene succinate with a melting point of 110-115 °C. The heat-resistant polylactic acid composition of the present invention uses polybutylene succinate with a relatively high degree of crystallinity and heat resistance to enhance the heat resistance of polylactic acid, and combines the promoting effect of talc powder on the crystallization performance of polylactic acid to further improve its heat resistance; there is a mutually promoting dispersion effect between polybutylene succinate with a specific melting point and talc powder, which can not only increase the entanglement degree of molecular chains between polybutylene succinate and polylactic acid, but also be beneficial to enhancing the dispersion uniformity of talc powder and its compatibility with polylactic acid, thereby effectively improving the mechanical properties of the polylactic acid composition.

Description

Technical Field

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

[0002] Polylactic acid (PLA) is a biodegradable polyester material. It not only has good processing properties and can be processed by various techniques such as extrusion molding, injection molding, or blown film; but also the waste PLA products can be naturally degraded into water and carbon dioxide, which is environmentally friendly and widely used in disposable lunch boxes or food packaging containers; however, at present, the heat resistance of polylactic acid products is poor and it is difficult to be applicable to application scenarios at higher temperatures.

[0003] To improve the heat resistance of polylactic acid, in the prior art, it is generally solved by adding a biodegradable and rigid structure material or a heat-resistant material with high crystallinity for blending, or by changing the molecular chain structure and orientation structure of polylactic acid. For example, adding an aliphatic biodegradable polyester PBS with higher crystallinity and heat resistance to polylactic acid to enhance the heat resistance of polylactic acid; however, the interfacial bonding between PBS and polylactic acid is weak, resulting in limited improvement in the heat resistance of the blend of the two, and PBS itself has a high crystallinity, which will also lead to low strength and poor toughness of the composite material. Summary of the Invention

[0004] The object of the present invention is to overcome the defects and deficiencies that the existing PLA / PBS composite materials are difficult to simultaneously have high heat resistance, high strength, and high toughness, and to provide a heat-resistant polylactic acid composition.

[0005] Another object of the present invention is to provide a heat-resistant polylactic acid composition.

[0006] Another object of the present invention is to provide an application of the above heat-resistant polylactic acid composition in the preparation of heat-resistant disposable articles.

[0007] Another object of the present invention is to provide a disposable tableware or food packaging bag material containing the above heat-resistant polylactic acid composition.

[0008] The above objects of the present invention are achieved by the following technical solutions:

[0009] The present invention protects a heat-resistant polylactic acid composition, which includes the following components by weight parts:

[0010] 15 - 85 parts of polylactic acid, 10 - 30 parts of talcum powder, 25 - 55 parts of polybutylene succinate;

[0011] Among them, the melting point of the polybutylene succinate is 110°C - 115°C.

[0012] The heat-resistant polylactic acid composition of the present invention forms a composite system with polybutylene succinate (PBS) having a specific melting point, talcum powder and polylactic acid (PLA). The polybutylene succinate with higher crystallinity and heat resistance is used to enhance the heat resistance of polylactic acid, and talcum powder is combined to improve the crystallization performance of polylactic acid and further enhance its heat resistance. Moreover, the inventors found through research that there is a mutual promotion and dispersion effect between the polybutylene succinate with a specific melting point and talcum powder, which can not only increase the entanglement degree of molecular chains between polybutylene succinate and polylactic acid, but also facilitate the enhancement of the dispersion uniformity of talcum powder and its compatibility with polylactic acid, thereby effectively improving the mechanical properties of the polylactic acid composition.

[0013] The melting point of the above polybutylene succinate can be obtained by DSC test. Specifically, NETZSCH DSC-214 can be used for the test, and the test method is as follows: First, the sample to be tested is heated from 30°C to 220°C at a heating rate of 10°C / min and held at 220°C for 3 min to eliminate the thermal history, then cooled to 30°C at a rate of 10°C / min, and then heated to 220°C at a rate of 10°C / min; among them, the melting point is taken from the second heating curve.

[0014] In addition, the melt mass flow rate of the above polybutylene succinate is 15-30 g / 10 min (test standard: ISO 1133, test conditions: 2.16 kg, 190°C).

[0015] Preferably, the heat-resistant polylactic acid composition, by weight, comprises the following components: 30-50 parts of polylactic acid, 15-25 parts of talcum powder, and 35-45 parts of polybutylene succinate.

[0016] Optionally, the polylactic acid includes poly-L-lactic acid and poly-D-lactic acid, and the mass percentage of the poly-D-lactic acid relative to the polylactic acid is 0.5%-2%, specifically it can be 0.5%, 0.8%, 1.2%, 1.5% or 2.0%. It has been found through research that when the polylactic acid includes poly-D-lactic acid and its mass fraction is 0.5%-2%, it is more conducive to the crystallization of polylactic acid and the improvement of its heat resistance.

[0017] Among them, the content of PDLA in polylactic acid can be determined by the following method: Pure PLLA and pure PDLA are tested by gas chromatography to obtain their spectral peaks; under the same test conditions, the target polylactic acid is tested, and through the peak areas δ PLLA and δ PDLA of the corresponding PLLA and PDLA spectral peaks on the gas chromatogram, the content of PDLA in the target polylactic acid is calculated, and the calculation formula is: η = δ PDLA / (δ PLLA +δ PDLA) *100%.

[0018] Optionally, the crystallization temperature of the heat-resistant polylactic acid composition is 110°C to 115°C; the Z-average molecular weight of the polylactic acid is 200,000 to 350,000; the particle size D 95 of the talc powder is 3 to 30 μm.

[0019] The crystallization temperature of the above heat-resistant polylactic acid composition can be obtained by DSC testing. First, the sample to be tested is heated from 30°C to 220°C at a heating rate of 10°C / min and held at 220°C for 3 min to eliminate the thermal history, then cooled to 30°C at a rate of 10°C / min, and then heated to 220°C at a rate of 10°C / min; the crystallization temperature is taken from the cooling curve.

[0020] The Z-average molecular weight of the polylactic acid can be determined by gel permeation chromatography as follows: The sample is dissolved in tetrahydrofuran and analyzed using a Waters 2410 gel chromatograph from Waters Corporation of 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 of different molecular weights are used as the calibration curve, and the retention time is 50 min.

[0021] Specifically, the mass ratio of silicon dioxide in the above talc powder is 50% to 65%, and can specifically be 51%, 53%, 55%, 57%, 59%, 60%, 61% or 62%; the Z-average molecular weight of the polylactic acid can be 200,000, 250,000, 300,000 or 350,000, and the particle size D 95 of the talc powder is 3 μm, 10 μm, 18 μm, 25 μm or 30 μm. Among them, the mass fraction of silicon dioxide in the above talc powder can be measured according to the SNT 2949-2011 standard, and the particle size D 95 of the talc powder is measured by a laser particle size analyzer.

[0022] It should also be noted that the total mass ratio of polylactic acid and polybutylene succinate in the above heat-resistant polylactic acid composition is greater than or equal to 50%. Without affecting its effects, other additives such as opening agents, lubricants, antioxidants, etc. can also be added to the composition of the present invention.

[0023] The present invention also protects a preparation method of the above heat-resistant polylactic acid composition, which includes the following steps: mixing polylactic acid, talc powder and polybutylene succinate, and melt-extruding to obtain the heat-resistant polylactic acid composition.

[0024] Among them, a twin-screw extruder can be used for melt-extrusion in the above preparation method, and the temperature of melt-extrusion is 140°C to 240°C.

[0025] The application of the above-mentioned heat-resistant polylactic acid composition in degradable disposable products is also within the protection scope of the present invention.

[0026] A disposable tableware or food packaging bag material containing the above-mentioned heat-resistant polylactic acid composition is also within the protection scope of the present invention.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The heat-resistant polylactic acid composition of the present invention forms a composite system with polybutylene succinate with a specific melting point, talcum powder and polylactic acid. The polybutylene succinate with a higher crystallinity and heat resistance is used to enhance the heat resistance of polylactic acid, and talcum powder is combined to increase the crystallinity of polylactic acid and further improve its heat resistance. Moreover, the inventor found through research that there is a mutual promotion and dispersion effect between polybutylene succinate with a specific melting point and talcum powder, which can not only improve the entanglement degree of molecular chains between polybutylene succinate and polylactic acid, but also be beneficial to enhancing the dispersion uniformity of talcum powder and its compatibility with polylactic acid, thereby effectively improving the mechanical properties of the polylactic acid composition. Specific Embodiments

[0029] 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.

[0030] 1. Raw Material Reagents

[0031] (1) Polylactic acid (PLA), self-made, for example, can be obtained through the following preparation method:

[0032] S1. Add L-lactic acid, D-lactic acid and the first catalyst (stannous octoate) into 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 h, water is distilled out 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 h to obtain a lactide intermediate product.

[0033] S2. Dissolve the lactide intermediate product obtained in the above step in an initiator (hexanediol), add the second catalyst (stannous octoate), and carry out a ring-opening polymerization reaction. Specifically: first react at a temperature of 150 °C and a relative pressure of 110000 Pa for 4 h, and then react at a temperature of 180 °C and a relative pressure of 110000 Pa for 2.5 h to obtain a polymer. The obtained polymer solid is refluxed and dissolved in a 5% (W / W) chloroform aqueous solution. After the solution is filtered, it is precipitated with ethanol 5 times the volume of chloroform to obtain a white flocculent precipitate, which is different polylactic acid resins.

[0034] By controlling the ratio of L-lactic acid monomer and D-lactic acid monomer, the mass percentage of PDLA in polylactic acid is regulated. 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 to 3 are basically the same, as shown below:

[0035] Polylactic acid-1, the mass fraction of poly-D-lactic acid in polylactic acid is 0.5%, and Mz is 240,000;

[0036] Polylactic acid-2, the mass fraction of poly-D-lactic acid in polylactic acid is 1.2%, and Mz is 250,000;

[0037] Polylactic acid-3, the mass fraction of poly-D-lactic acid in polylactic acid is 2%, and Mz is 260,000.

[0038] The content of PDLA in the above-mentioned polylactic acid can be measured by the following method: Pure PLLA and pure PDLA are tested by gas chromatography to obtain their spectral peaks; under the same test conditions, the target polylactic acid is tested, and through the peak areas δ PLLA and δ PDLA of the corresponding PLLA and PDLA spectral peaks on the gas chromatogram, the content of PDLA in the target polylactic acid is calculated. The calculation formula is: η = δ PDLA / (δ PLLA +δ PDLA )*100%.

[0039] (2) Filler

[0040] Talc powder is purchased from Heshan Chemical Industry (Liaoning) Co., Ltd., with the model of A-50. Before being used to prepare polylactic acid composites, it is first ground and screened, and talc powders 1 to 4 with different particle size distributions are obtained by the mesh number of the sieve.

[0041] The D 95 of talc powder is measured by a laser particle size analyzer, and the mass fraction of silicon dioxide in talc powder is measured according to the standard of SNT 2949-2011, as shown below:

[0042] Talc powder-1, D 95 = 10 μm;

[0043] Talc powder-2, D 95 = 18 μm;

[0044] Talc powder-3, D 95 = 30 μm;

[0045] Talc powder-4, D 95 = 3 μm.

[0046] Silica was purchased from Hubei Huifu Nanomaterials Co., Ltd., with the model HB-612. Before being used to prepare the polylactic acid composite material, it was first ground and screened, and silica with D 95 = 5 μm was obtained through the mesh number of the sieve.

[0047] (3) Poly(butylene succinate) (PBS)

[0048] PBS-1, with a melting point of 112.5 °C, grade A200 NC801, manufacturer Jinfa Biology, Zhuhai, China;

[0049] PBS-2, with a melting point of 115 °C, grade PBS FZ91PM, manufacturer Mitsubishi, Japan;

[0050] PBS-3 (melting point 106 °C) and PBS-4 (melting point 118 °C) were prepared by the following preparation method:

[0051] S1. Mix 1,4-butanedioic acid, 1,4-butanediol and a catalyst, and keep it for 1 - 5 hours under the conditions of a pressure of 50 - 100 kPa and a temperature of 180 - 250 °C; after introducing CO2, keep it for 10 - 30 min;

[0052] S2. Reduce the pressure of the reaction system to less than 100 Pa, keep the temperature at 230 - 250 °C, continue the reaction for 3 - 6 hours, fill with nitrogen, and pelletize to obtain PBS-3 or PBS-4.

[0053] Among them, PBS-3 and PBS-4 with different melting points can be obtained by changing the amounts of 1,4-butanedioic acid, 1,4-butanediol and the catalyst. The melting point of PBS can be obtained by DSC testing. The specific testing method is as follows: First, heat the sample to be tested from 30 °C to 220 °C at a heating rate of 10 °C / min, and keep it at 220 °C for 3 min to eliminate the thermal history, then cool it to 30 °C at a rate of 10 °C / min, and then heat it to 220 °C at a rate of 10 °C / min; the melting point is taken from the second heating curve.

[0054] 2. The heat-resistant polylactic acid compositions of each example and comparative example of the present invention were prepared by the following preparation method:

[0055] Weigh each component according to the formula, mix them evenly, and then add them to a twin-screw extruder for melt blending and extrusion pelletization to obtain the heat-resistant polylactic acid composition; among them, the length-diameter ratio of the screw of the twin-screw extruder is 40:1, the barrel temperature is 140 - 240 °C, and the screw speed is 250 - 500 rpm.

[0056] 3. Performance testing

[0057] (1) Heat resistance test: The Vicat softening temperature of the polylactic acid compositions of each example and comparative example was measured according to GB / T 1633 - "Determination of Vicat softening temperature of thermoplastics" to evaluate their heat resistance. The higher the Vicat softening temperature, the better the heat resistance.

[0058] (2) Mechanical property test: The tensile strength was tested according to the standard of GB / T 1040 - 2006, and the tensile rate was 50 mm / min; the notched impact strength was tested according to the standard of GB / T 1843 - 2008, and the notch type was type A notch.

[0059] (3) Crystallization temperature: Obtained by DSC test. First, the sample to be tested was heated from 30 °C to 220 °C at a heating rate of 10 °C / min and held at 220 °C for 3 min to eliminate the thermal history, then cooled to 30 °C at a rate of 10 °C / min, and then heated to 220 °C at a rate of 10 °C / min; the crystallization temperature was taken from the cooling curve.

[0060] Examples 1 - 11 and Comparative Examples 1 - 3

[0061] The weight parts of each component in the heat-resistant polylactic acid compositions in Examples 1 - 11 and Comparative Examples 1 - 3 are shown in Table 1.

[0062] Table 1 Weight parts of each component in the heat-resistant polylactic acid compositions in Examples 1 - 11 and Comparative Examples 1 - 3

[0063]

[0064] The performance test results of the heat-resistant polylactic acid compositions in each example and comparative example according to the above-mentioned method are shown in Table 2.

[0065] Table 2 Test results of each example and comparative example

[0066]

[0067]

[0068] According to the data in Table 2, the Vicat softening temperature of the heat-resistant polylactic acid compositions in Examples 1 - 10 reaches above 75 °C, and the tensile strength ≥ 40 MPa, the notched impact strength ≥ 5.7 KJ / m 2 , indicating that the heat-resistant polylactic acid composition of the present invention not only has excellent heat resistance, but also has good mechanical properties.

[0069] Meanwhile, it can be found from Examples 1 to 3 that the Vicat softening temperature and notched impact strength of the heat-resistant polylactic acid composition increase with the increase in the mass fraction of poly-D-lactic acid in polylactic acid. However, when the content of poly-D-lactic acid is relatively high, the tensile strength will decrease slightly. According to Example 1 and Comparative Example 3, it can be found that when silica is used to replace talcum powder, the heat resistance and mechanical properties of the heat-resistant polylactic acid composition cannot be effectively improved. From the data of Example 1, Example 7 and Comparative Examples 1 to 2, it can be seen that the melting point of PBS plays a key role in the heat resistance and mechanical properties of the heat-resistant polylactic acid composition. When the melting point is too high or too low, the heat-resistant polylactic acid composition cannot have high heat resistance, high tensile strength and high toughness at the same time.

[0070] The above examples of the present invention are merely examples for clearly illustrating 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 variations can be made on the basis of the above description. It is not necessary and impossible to list all implementation manners here. Any modifications, equivalent replacements, improvements, etc. 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 heat-resistant polylactic acid composition, characterized in that, By weight parts, it comprises the following components: 30 to 50 parts of polylactic acid, 15 to 25 parts of talcum powder, 35 to 45 parts of polybutylene succinate; wherein, the melting point of the polybutylene succinate is 110°C to 115°C.

2. The heat-resistant polylactic acid composition according to claim 1, wherein The polylactic acid comprises poly-L-lactic acid and poly-D-lactic acid, and the mass percentage of the poly-D-lactic acid relative to the polylactic acid is 0.5% to 2%.

3. The heat-resistant polylactic acid composition according to claim 1, wherein The crystallization temperature of the heat-resistant polylactic acid composition is 110°C to 115°C.

4. The heat-resistant polylactic acid composition according to claim 1, wherein The Z-average molecular weight of the polylactic acid is 200,000 to 350,000.

5. The heat-resistant polylactic acid composition according to claim 1, wherein The particle size D of the talcum powder 95 is 3 to 30 μm.

6. A method for preparing the heat-resistant polylactic acid composition according to any one of claims 1 to 5, characterized in that, It comprises the following steps: mixing polylactic acid, talcum powder and polybutylene succinate, and melt-extruding to obtain the heat-resistant polylactic acid composition.

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

8. Use of the heat-resistant polylactic acid composition according to any one of claims 1 to 5 in the preparation of degradable disposable articles.

9. A disposable tableware or food packaging bag material, characterized in that, It comprises the heat-resistant polylactic acid composition according to any one of claims 1 to 5.

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