Polylactic acid composite material as well as preparation method and application thereof

Abstract

The polylactic acid composite material comprises the following components in parts by weight: 40-85 parts of polylactic acid; 5 to 30 parts of degradable polyester; 10 to 30 parts of talcum powder; the maximum weight loss rate temperature Tx of the polylactic acid ranges from 320 DEG C to 375 DEG C; the end carboxyl group content of the degradable polyester is less than or equal to 50mol KOH / t; according to the total weight of the polylactic acid composite material, the content of fluorine in the composite material is less than 100 ppm. According to the invention, polylactic acid with a proper Tx range and polyester with low terminal carboxyl group content are selected, and the fluorine content in the composite material is controlled, so that the defect of material accumulation at a die orifice in the melt extrusion process of the biodegradable polylactic acid composition can be effectively improved.

Description

Technical Field

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

[0002] During the extrusion production process of biodegradable polylactic acid composite materials, the die orifice is prone to material accumulation. If the material accumulation is severe, it will affect the extrusion stability. In the prior art, the die orifice can only be cleaned by stopping the machine and then restarting production. However, stopping the machine for cleaning will affect the production continuity and cause waste of materials.

[0003] Currently, to solve the problem of material accumulation at the die orifice, fluorine-containing processing aids are usually added. On the one hand, this causes great pollution to the environment and is carcinogenic; on the other hand, a certain amount of fluorine element is contained in the commonly used talcum powder in this field. When the fluorine element content in the polylactic acid composite material is too high, it will also lead to an increase in material accumulation at the die orifice. For example, in patent CN 114044962 A. There are also patented technologies that solve the problem of material accumulation at the die orifice through the combination of various lubricants. For example, patent CN115716958 A expounds that through the synergistic effect of the internal lubricant polyethylene wax, zinc stearate, and PPA, the die orifice cleaning cycle can be greatly improved. However, improving the material accumulation at the die orifice by adding processing aids will, on the one hand, increase the cost, and on the other hand, it is also easy to cause a decrease in mechanical properties. Summary of the Invention

[0004] The purpose of the present invention is to provide a polylactic acid composite material that can improve the material accumulation at the die orifice.

[0005] The present invention is achieved through the following technical solutions: A polylactic acid composite material, by weight, comprises the following components: 40 - 85 parts of polylactic acid; 5 - 30 parts of biodegradable polyester; 10 - 30 parts of talcum powder; The range of the maximum weight loss rate temperature Tx of the polylactic acid is 320 - 375 °C; The carboxyl end group content of the biodegradable polyester ≤ 50 mol KOH / t; Based on the total weight of the polylactic acid composite material, the fluorine element content in the composite material is less than 100 ppm.

[0006] Preferably, the range of the maximum weight loss rate temperature Tx of the polylactic acid is 340 °C - 370 °C.

[0007] There is a close relationship between the maximum weight loss rate of polylactic acid and the thermal degradation degree of PLA. After PLA undergoes thermal degradation, it will cause changes in the tensile shear at the die orifice during the melt extrusion process of the material, thereby affecting the material accumulation at the die orifice.

[0008] Preferably, the carboxyl end group content of the biodegradable polyester is ≤ 40 mol KOH / t.

[0009] The D50 average particle size range of the talcum powder is 3 - 10 microns.

[0010] The method for determining the carboxyl end group of the polyester is as follows: using a mixed solution of o-cresol and chloroform as the solvent, the mass ratio of o-cresol to chloroform is 7:3, and an automatic potentiometric titrator is used to test the carboxyl end group value. The test method is FZ / T 50012-2006 "Determination of Carboxyl End Group Content in Polyester - Titrimetric Analysis Method"; The method for determining the fluorine element in the polyester composition is as follows: Weigh the polyester composition and place it in the crucible of an oxygen bomb calorimeter. Put 20 mL of absorbent solution at the bottom of the oxygen bomb calorimeter, fill it with oxygen, ignite it, and after fully absorbing for 45 min - 60 min, dilute the solution to 50 mL. After filtration, use an ion chromatograph to determine the concentration of the fluorine element, and then the content of the fluorine element in the composition can be calculated based on the concentration of the fluorine element in the prepared solution and the fluorine element concentration standard curve; among them, the standard curve is calibrated by a fluoride ion solution.

[0011] The test method for the maximum weight loss rate temperature Tx of polylactic acid is as follows: Using a TG209 thermogravimetric analyzer from NETZCH company, measure the thermogravimetric DTG curve and TG curve of the polylactic acid material under a nitrogen atmosphere. The peak temperature of the DTG curve is the maximum weight loss rate temperature Tx, and the heating rate is selected as 10 °C / min.

[0012] The biodegradable polyester described above is selected from at least one of polybutylene succinate (PBS), poly(butylene succinate-co-adipate) (PBSA), polyhydroxyalkanoates (PHA), polycaprolactone (PCL), poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene sebacate-co-terephthalate) (PBSeT), poly(nonanedioate-co-terephthalate-co-butylene glycol), and poly(succinate-co-terephthalate-co-butylene glycol) (PBST).

[0013] The present invention does not limit the viscosity of polylactic acid and the biodegradable polyester. When the viscosity range of polylactic acid is 0.9 dL / g - 2.0 dL / g and the viscosity range of the biodegradable polyester is 1.2 dL / g - 1.9 dL / g, they are all within the common ranges in the field of plastic modification and can achieve the purpose of the present invention.

[0014] The polylactic acid of the present invention can be a commercially available product or obtained by self-preparation. The method is as follows: Add the catalyst, initiator, and lactide into a reaction kettle (the addition amount of the catalyst does not exceed 1.5% and the addition amount of the initiator does not exceed 2% based on the total weight of the catalyst, initiator, and lactide). The temperature for the first-step polymerization reaction is 130 - 180 °C to conduct the initiation reaction. After the reaction is initiated and the viscosity increases, when the monomer conversion rate reaches 20 - 80%, enter the second-step polymerization stage. In the second-step polymerization stage, a static mixer is used, the reaction temperature is 180 - 200 °C, the reaction time is 3 - 8 hours, and a catalyst deactivator (phosphorous acid solution) is added at the end of the reaction. Volatile components are removed by static mixing, and the volatile removal temperature is 200 - 260 °C. Granulation under water, crystallization, and drying are carried out to obtain polylactic acid. By controlling the monomer conversion rate in the first-step polymerization reaction stage and the reaction time in the second-step stage to control the reaction degree, products with different Tx temperatures can be obtained.

[0015] Whether to add 0 - 2 parts of additives can be selected according to actual needs. The additives can be that the organic nucleating agent is a hydrazide-based substance and / or a phenyl phosphate-based substance, and the lubricant is at least one of stearamide, oleic acid amide, erucic acid amide, zinc stearate, a high molecular composite ester of metal soap, ethylene bisstearamide, polyethylene wax, and silicone-based lubricants.

[0016] Generally speaking, the weight percentage content of polylactic acid in the polylactic acid composite material of the present invention is ≥ 35 wt%.

[0017] The preparation method of the polylactic acid composite material of the present invention includes the following steps: Mix each component evenly according to the ratio, and extrude and pelletize through a twin-screw extruder to obtain the polylactic acid composite material.

[0018] The application of the polylactic acid composite material of the present invention is used to prepare biodegradable materials.

[0019] The present invention has the following beneficial effects: By selecting polylactic acid with a high Tx and a degradable polyester with a low terminal carboxyl content, and at the same time controlling the fluorine element content in the composite material, the present invention can effectively improve the defect of die build-up during the melt extrusion process of the biodegradable polylactic acid composition. Embodiment

[0020] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made. These all belong to the protection scope of the present invention.

[0021] The sources of the raw materials used in the present invention are as follows: The synthesis method of polylactic acid used in the specific implementation manner of the present invention is as follows: Add a catalyst, an initiator, and lactide into a reaction kettle (based on the total weight of the catalyst, initiator, and lactide, the addition amount of the catalyst is 0.5% and the addition amount of the initiator is 1.2%). The temperature of the first-step polymerization reaction is 140 - 150 °C for an initiation reaction. After the reaction is initiated and the viscosity increases, when the monomer conversion rate reaches 20 - 80% (the specific conversion rate can be seen in the parameters of polylactic acid), enter the second-step polymerization stage. In the second-step polymerization stage, a static mixer is used, the reaction temperature is 180 - 200 °C, and the reaction time is 3 - 8 hours (the specific reaction time can be seen in the parameters of polylactic acid). At the end of the reaction, add a catalyst passivator, phosphorous acid solution, and remove volatiles by static mixing. The volatilization temperature is 200 - 260 °C. Granulate underwater, crystallize, and dry to obtain polylactic acid.

[0022] By controlling the monomer conversion rate in the first step and the reaction time in the second step, polylactic acids with different Tx values can be obtained as follows; Polylactic acid - A: Tx = 370 °C, self - made. The conversion rate in the process is 83%, the reaction duration in the second step is 3.5 h, and the viscosity is 1.539 dL / g; Polylactic acid - B: Tx = 360 °C, self - made. The conversion rate in the process is 68%, the reaction duration in the second step is 5 h, and the viscosity is 1.591 dL / g; Polylactic acid - C: Tx = 340 °C, self - made. The conversion rate in the process is 54%, the reaction duration in the second step is 6 h, and the viscosity is 1.498 dL / g; Polylactic acid - D: Tx = 320 °C, self - made. The conversion rate in the process is 42%, the reaction duration in the second step is 7 h, and the viscosity is 1.620 dL / g; Polylactic acid - E: Tx = 300 °C, self - made. The conversion rate in the process is 30%, the reaction duration in the second step is 8 h, and the viscosity is 1.568 dL / g; Talc powder A: The fluorine element content is 1250 ppm. The D50 particle size of AH - 1250N6 obtained by screening is 6.23 microns, and the manufacturer is Zhuhai Kingfa Supply Chain Management Co., Ltd.; Talc powder B: The fluorine element content is 698 ppm. The D50 particle size of TYT - 777A obtained by screening is 5.82 microns, and the manufacturer is Zhuhai Kingfa Supply Chain Management Co., Ltd.; Talc powder C: The fluorine element content is 324 ppm. The D50 particle size of SK - 6500P obtained by screening is 6.09 microns, and the manufacturer is Zhuhai Kingfa Supply Chain Management Co., Ltd.; Although the following PBS - A to C are of the same brand, due to slight differences in production parameters, the acid value will change. The following PBS acid values are all obtained through actual measurement.

[0023] PBS-A: The carboxyl end group content is 48.7 mol KOH / t, grade A200 NC801, viscosity is 1.632 dL / g, manufacturer: Zhuhai Jinfa Biomaterials Co., Ltd.; PBS-B: The carboxyl end group content is 29.1 mol KOH / t, grade A200 NC801, viscosity is 1.593 dL / g, manufacturer: Zhuhai Jinfa Biomaterials Co., Ltd.; PBS-C: The carboxyl end group content is 64.4 mol KOH / t, grade A200NC801, viscosity is 1.231 dL / g, manufacturer: Zhuhai Jinfa Biomaterials Co., Ltd.; PBAT-A: The carboxyl end group content is 36.3 mol KOH / t, grade A400, manufacturer: Zhuhai Jinfa Biomaterials Co., Ltd.; PBAT-B: The carboxyl end group content is 58.2 mol KOH / t, grade KB700, manufacturer: Zhuhai Jinfa Biomaterials Co., Ltd.

[0024] Each test method: (1) Die lip build-up: Use a single-screw extruder with a diameter of 55, a die hole with a diameter of 4 mm, set the temperature at 185 °C, the extrusion frequency of the extruder at 20 Hz, the traction at 25 Hz, continuously extrude for 1 h, and scrape off all the build-up and weigh it.

[0025] Table 1: Component contents (parts by weight) and test results of polylactic acid composites in Examples 1-8 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Polylactic acid - A 60 Polylactic acid - B 60 60 60 40 85 Polylactic acid - C 60 Polylactic acid - D 60 PBS - A 15 15 15 15 5 30 PBS - B 15 PBAT - A 15 Talcum powder B 15 15 15 15 15 15 10 30 Fluoride ion content, ppm 68 72 78 80 76 82 70 89 Die lip buildup weight, g 0.26 0.23 0.24 0.27 0.21 0.22 0.20 0.28 As can be seen from Examples 1-4, when the Tx of polylactic acid is preferably 340 - 370 °C, the build-up is the least.

[0026] As can be seen from Examples 2 / 5 / 6, it is preferred that the carboxyl end group content of the polyester ≤ 40 mol KOH / t.

[0027] Table 2: Component contents (parts by weight) and test results of polylactic acid composites in Examples 9-16 Example 9 Example 10 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Polylactic acid - B 60 60 60 60 60 40 60 Polylactic acid - E 60 PBS - A 15 15 15 15 5 35 PBS - C 15 PBAT - B 15 Talcum powder A 10 15 Talcum powder B 15 15 15 Talcum powder C 15 35 5 Fluoride ion content, ppm 38 86 134 83 79 81 86 25 Die lip buildup, g 0.23 0.25 0.34 0.33 0.35 0.37 0.34 0.32 As can be seen from Example 2 / Example 9 / Comparative Example 1, it is necessary to control the fluorine element content in the polylactic acid composite to be lower than 100 ppm.

[0028] As can be seen from Comparative Examples 2 / 3, the carboxyl end group content of the polyester needs to be ≤ 50 mol KOH / t.

[0029] As can be seen from Comparative Example 4, if the Tx temperature of PLA is lower than 320 °C, die lip build-up is likely to occur.

[0030] As can be seen from Comparative Examples 5 / 6, the content of talcum powder cannot be too high or too low.

Claims

1. A polylactic acid composite material, characterized in that by weight, it comprises the following components: 40 - 85 parts of polylactic acid; 5 - 30 parts of biodegradable polyester; 10 - 30 parts of talcum powder; the temperature range of the maximum weight loss rate temperature Tx of the polylactic acid is 320 - 375 °C; the terminal carboxyl group content of the biodegradable polyester ≤ 50 mol KOH / t; based on the total weight of the polylactic acid composite material, the fluorine element content in the composite material is less than 100 ppm, and the fluorine element is derived from talcum powder.

2. The polylactic acid composite material according to claim 1, characterized in that the temperature range of the maximum weight loss rate temperature Tx of the polylactic acid is 340 °C - 370 °C.

3. The polylactic acid composite material according to claim 1, characterized in that the terminal carboxyl group content of the biodegradable polyester ≤ 40 mol KOH / t.

4. The polylactic acid composite material according to claim 1, characterized in that the biodegradable polyester is selected from at least one of polybutylene succinate / butanediol ester, polybutylene succinate - adipate butanediol ester, polyhydroxy fatty acid ester, polycaprolactone, polyadipic acid / terephthalic acid / butanediol ester, polysebacic acid / terephthalic acid / butanediol ester, polynonanoic acid / terephthalic acid / butanediol ester, polysuccinic acid / terephthalic acid / butanediol ester.

5. The polylactic acid composite material according to claim 1, characterized in that by weight, it further comprises 0 - 2 parts of an auxiliary agent.

6. The polylactic acid composite material as claimed in claim 5, characterized in that the auxiliary agent is selected from hydrazide substances and / or phenyl phosphate substances, and the lubricant is at least one of stearamide, oleic acid amide, erucic acid amide, zinc stearate, high molecular composite ester of metal soap, ethylene bisstearamide, polyethylene wax, silicone lubricant.

7. The preparation method of the polylactic acid composite material according to any one of claims 1 - 6, characterized in that it comprises the following steps: according to the ratio, mix each component evenly, and extrude and pelletize through a twin - screw extruder to obtain the polylactic acid composite material.

8. The application of the polylactic acid composite material according to any one of claims 1 - 6, characterized in that it is used for preparing straws, wires, and film bags.