A modified talc powder for polylactic acid nucleating agent, a preparation method and application thereof

Abstract

This invention relates to a modified talc powder for polylactic acid (PLA) nucleating agents, its preparation method, and its application. Belonging to the field of nucleating agent technology, it is prepared through the following three-step reaction: phthalic anhydride and talc powder are dissolved in an organic solvent, heated and stirred to obtain a homogeneous mixture. After cooling, the precipitate is collected and vacuum-dried to obtain a powder. The obtained powder is dissolved in an aqueous solution of tetraalkylammonium hydroxide, heated under reflux, cooled, and the solid is collected and vacuum-dried to obtain a catalyst. The obtained catalyst is mixed with lactide and an initiator, heated and stirred to react, thoroughly washed, and the solid is collected and vacuum-dried to obtain the modified talc powder for PLA nucleating agents. The preparation method of the nucleating agent of this invention is simple, with mild reaction conditions, convenient operation, and easy industrialization. After melt blending with PLA, it improves the crystallinity of PLA and enhances its thermal properties.

Description

Technical Field

[0001] This invention relates to the field of nucleating agent technology, and more specifically, to a modified talc powder for polylactic acid nucleating agents, its preparation method, and its application. Background Technology

[0002] Polylactic acid (PLA), also known as polylactide, is mainly synthesized from lactic acid and its cyclic dimer lactide via direct polycondensation and ring-opening polymerization, respectively. PLA is a polymer made from renewable resources, possessing biodegradability and biocompatibility. Under composting conditions, it can be completely decomposed into carbon dioxide and water within 3-6 months. Therefore, promoting the use of PLA can reduce petroleum resource consumption, playing a role in energy conservation and emission reduction, and is of great significance to environmental protection. PLA materials have excellent degradation performance and biocompatibility, and can be used to prepare various plastic products, packaged foods, fast food containers, non-woven fabrics, etc. Its strength, degradation time, and processability basically meet the requirements of tissue engineering scaffold materials, drug controlled release carriers, and various biomedical functional materials. However, its slow crystallization rate during processing leads to prolonged processing cycles, and its poor heat resistance greatly limits the application areas of PLA products.

[0003] Currently, the most common method to improve the properties of polylactic acid (PLA) is to add nucleating agents. The addition of nucleating agents can increase the crystallization temperature and crystallization rate of PLA, thereby improving its thermal properties.

[0004] Talc powder's main component is natural hydrated magnesium silicate, a colorless, transparent, or white powder at room temperature. It is insoluble in water and is a chemically inert inorganic salt with good lubricity, fire resistance, and stability. Adding talc powder under various plastic processing conditions can not only improve material properties, such as tensile strength, tensile strain at break, flexural strength, and flexural modulus, but also effectively reduce material costs. In practical processing applications, talc powder is a commonly used inorganic nucleating agent for polylactic acid (PLA).

[0005] Due to the high amount of inorganic fillers added, their compatibility with the polymer matrix is ​​poor, and voids and defects are easily formed at the interface during composite formation, resulting in low interfacial strength. Coupling agents can be used to modify the surface of the fillers. The most common method is to use silane coupling agents, such as 3-aminopropyltriethoxysilane (APTES) and vinyltriethoxysilane (VTES), to modify the surface of talc powder and use them as fillers to improve the performance of polylactic acid. (Journal of Applied Polymer Science, 2013, 129(3): 1019-25; Materials Chemistry and Physics, 2017, 196, 62-74). Summary of the Invention

[0006] In view of the fact that existing biodegradable plastics, represented by polylactic acid (PLA), typically use talc as an inorganic nucleating agent in industrial applications, the present invention aims to: 1) provide a method for preparing modified talc for PLA nucleating agents; 2) provide modified talc prepared using the above method; and 3) provide applications of the modified talc as a PLA nucleating agent. The modified talc for PLA nucleating agents prepared by this invention can improve the compatibility between inorganic fillers and polymer matrices.

[0007] To achieve the above objectives, the specific solution adopted by the present invention is as follows:

[0008] In a first aspect, a method for preparing modified talc powder for polylactic acid nucleating agents includes the following steps:

[0009] Step 1: Dissolve phthalic anhydride and talc in an organic solvent, heat and stir to obtain a homogeneous mixture, collect the precipitate after cooling, and vacuum dry to obtain a powdery substance;

[0010] Step 2: Dissolve the powdered substance obtained in Step 1 in an aqueous solution of tetraalkylammonium hydroxide, heat under reflux, cool and collect the solid, and dry it under vacuum to obtain the catalyst;

[0011] Step 3: Mix the catalyst obtained in Step 2 with lactide and initiator, heat and stir to react, wash thoroughly and collect the solid, and dry under vacuum to obtain modified talc powder for polylactic acid nucleating agent.

[0012] Preferably, the mass ratio of phthalic anhydride to talc in step one is 0.5 to 4:1.

[0013] Preferably, the organic solvent mentioned in step one is selected from N,N-dimethylacetamide, N-methylpyrrolidone, and N,N-dimethylformamide.

[0014] Preferably, the heating and stirring in step one involves a reaction temperature of 100–150°C and a reaction time of 4–15 hours.

[0015] Preferably, the tetraalkylammonium hydroxide mentioned in step two is selected from tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0016] Preferably, the mass ratio of the powdered substance to tetraalkylammonium hydroxide in step two is 1 to 5:1.

[0017] Preferably, the heating reflux temperature in step two is 100–150°C, and the time is 4–10 hours.

[0018] Preferably, the heating and stirring temperature in step three is 105–180°C, and the time is 2–12 hours.

[0019] Preferably, the initiator mentioned in step three is selected from sodium tert-butoxide, potassium tert-butoxide, and polyethylene glycol monomethyl ether.

[0020] Preferably, the mass ratio of the catalyst to lactide in step three is 0.01 to 0.2.

[0021] Secondly, the modified talc powder for polylactic acid nucleating agents prepared by the above preparation method.

[0022] Thirdly, the above-mentioned modified talc is used as a nucleating agent for polylactic acid. Preferably, the application involves blending the modified talc with polylactic acid, wherein the amount of modified talc added during blending is 0.5–8.0 wt%.

[0023] Compared with the prior art, the talc powder for polylactic acid nucleating agents of the present invention has the following advantages and beneficial effects:

[0024] 1. The catalyst of the present invention utilizes the hydroxyl groups on the surface of talc powder to phthalate talc powder and react it with quaternary ammonium salt, and then uses it for the ring-opening polymerization of lactide to synthesize a modified talc nucleating agent.

[0025] 2. The preparation method of the nucleating agent of the present invention is simple, the reaction conditions are mild, the operation is convenient, and it is easy to industrialize.

[0026] 3. The nucleating agent for polylactic acid (PLA) is talc powder, which is melt-blended with PLA. This improves the crystallization ability of PLA and enhances its thermal properties. Attached Figure Description

[0027] Figure 1 The images show a comparison of the crystal morphology of (a) PLA, (b) Talc (Example 7-2), and (c) Talc-g-pla (Example 7-5) blends with polylactic acid at 3, 5, and 10 min. Detailed Implementation

[0028] The present invention will be further described in detail below through specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0029] Unless otherwise specified, the raw materials used in the following examples can be obtained through conventional commercial channels.

[0030] Example 1

[0031] Step 1: Add 3g of talc to 20mL of N,N-dimethylacetamide solution containing 2.34g of phthalic anhydride. Heat and stir at 150℃ for 15 hours under nitrogen protection. Cool the resulting solid-liquid mixture to room temperature and pour in deionized water. Filter to obtain the precipitate, wash with 250mL of ethanol solution for 4 hours, and dry to obtain a white solid.

[0032] Step 2: Add 2.62 g of the white solid prepared in Step 1 and 2.94 g of tetraethylammonium hydroxide (25%) aqueous solution to a 25 mL round-bottom flask, and stir until homogeneous at room temperature. Reflux the mixture at 150 °C for 10 hours, cool, and filter. Collect the solid and dry it under reduced pressure in a vacuum drying oven for 12 hours to obtain the catalyst Talc-cat-A.

[0033] Example 2

[0034] Step 1: Add 3g of talc to 20mL of N-methylpyrrolidone solution containing 4.44g of phthalic anhydride. Heat and stir at 100°C for 14 hours in atmospheric pressure. Cool the resulting solid-liquid mixture to room temperature and add deionized water. Filter to obtain the precipitate, wash with 500mL of ethanol solution for 5 hours, and dry to obtain a white solid.

[0035] Step 2: Add 2.62 g of the white solid prepared in Step 1 and 2.12 g of tetrapropylammonium hydroxide (25%) aqueous solution to a 25 mL round-bottom flask, and stir until homogeneous at room temperature. Reflux the mixture at 150 °C for 4 hours, cool, and filter. Collect the solid and dry it under reduced pressure in a vacuum drying oven for 12 hours to obtain the catalyst Talc-cat-B.

[0036] Example 3

[0037] Step 1: Add 3g of talc to 20mL of N,N-dimethylformamide solution containing 11.7g of phthalic anhydride. Heat and stir at 120℃ for 9 hours under nitrogen protection. Cool the resulting solid-liquid mixture to room temperature and add deionized water. Filter to obtain the precipitate, wash with 350mL of ethanol solution for 1 hour at room temperature, and dry to obtain a white solid.

[0038] Step 2: Add 2.62 g of the white solid prepared in Step 1 and 7.7 g of tetrabutylammonium hydroxide (25%) aqueous solution to a 25 mL round-bottom flask, and stir until homogeneous at room temperature. Reflux the mixture at 100 °C for 7 hours, then cool and filter. Collect the solid and dry it under reduced pressure in a vacuum drying oven for 12 hours to obtain the catalyst Talc-cat-C.

[0039] Example 4: Modified talc nucleating agent Talc-pla-A

[0040] Weigh 200 mg of lactide monomer into a Schlenk tube and add a stir bar. Heat at 110 °C and stir until the lactide is completely melted. Then add 1 mg of polyethylene glycol monomethyl ether initiator and 20 mg of catalyst Talc-cat-A. After reacting for 10 hours, stop stirring and quench the reaction in an ice-water bath to obtain the crude product.

[0041] The crude product was dissolved in dichloromethane, centrifuged, and the supernatant was collected. Excess anhydrous ethanol was added to precipitate the solid. The solid product was dried overnight in a vacuum drying oven at 40°C to obtain talc powder Talc-pla-A for polylactic acid nucleating agents.

[0042] Example 5: Modified talc nucleating agent Talc-pla-B

[0043] Weigh 200 mg of lactide monomer into a Schlenk tube and add a stir bar. Heat at 120 °C and stir until the lactide is completely melted. Then add 1.5 mg of sodium tert-butoxide initiator and 10 mg of Talc-cat-B catalyst. After reacting for 6 hours, stop stirring and quench the reaction in an ice-water bath to obtain the crude product.

[0044] The crude product was dissolved in dichloromethane, centrifuged, and the supernatant was collected. Excess anhydrous ethanol was added to precipitate the solid. The solid product was dried overnight in a vacuum drying oven at 40°C to obtain talc powder Talc-pla-B for polylactic acid nucleating agents.

[0045] Example 6: Modified talc nucleating agent Talc-pla-C

[0046] Preheat the magnetic stirrer to the reaction temperature of 180°C. Weigh 200 mg of lactide monomer into a Schlenk tube and add a stir bar. Heat and stir until the lactide is completely melted, then add 40 mg of catalyst Talc-cat-C and 1 mg of initiator potassium tert-butoxide. After reacting for 2.5 hours, stop stirring and quench the reaction in an ice-water bath to obtain the crude product.

[0047] The crude product was dissolved in dichloromethane, centrifuged, and the supernatant was collected. Excess anhydrous ethanol was added to precipitate the solid. The solid product was dried overnight in a vacuum drying oven at 40°C to obtain talc powder Talc-pla-C for polylactic acid nucleating agents.

[0048] Example 7: Crystallization Performance Test

[0049] Talc powder used as a nucleating agent for polylactic acid (PLA) obtained in Examples 4-6, and unmodified raw talc powder were melt-blended with PLA in a certain proportion (0.5–8.0 wt%) at 180 °C in a torque rheometer. PLA was described using Nature Works 4032D to illustrate the experimental results, but PLA is not limited to 4032D. 5–8 mg of sample was taken and crystallized under a nitrogen atmosphere using a DSC non-isothermal crystallization program: heating to 200 °C at 10 °C / min and holding for 3 min to eliminate thermal history. Then, the temperature was lowered to 0 °C at 50 °C / min, followed by a heating rate of 10 °C / min to 200 °C. The second DSC heating curve was obtained, and the crystallization temperature information is shown in Table 1 below.

[0050] Table 1. Crystallization temperature of polylactic acid after the action of talc and polylactic acid modified with different contents of talc.

[0051] serial number Add nucleating agent Amount added / wt% Crystallization temperature / ℃ Example 7-1 Pure PLA - 110.9 Example 7-2 talcum powder 0.5 104.8 Example 7-3 talcum powder 8.0 96.2 Example 7-4 Talc-pla-A 3.0 99.3 Example 7-5 Talc-pla-B 0.5 101.5 Examples 7-6 Talc-pla-C 8.0 95.0

[0052] Example 8: Crystallization performance tested by polarized light microscopy

[0053] Polylactic acid, along with samples obtained in Examples 7-2 and 7-5, was placed between two glass slides on a hot stage and heated to melt. The samples were then gently pressed to complete sample preparation. The samples were then placed under a microscope (Leica DM4+P, Germany), and the program was set to heat to 200°C, followed by isothermal treatment for 3 minutes to eliminate thermal history. Subsequently, the temperature was lowered to 130°C at a rate of 100°C / min. The isothermal crystallization behavior at 3, 5, and 10 minutes was as follows: Figure 1 As shown.

[0054] It should be noted that the above-described embodiments should be understood as illustrative, not as limiting the scope of protection of this invention. The scope of protection of this invention is defined by the claims. For those skilled in the art, some non-essential improvements and adjustments made to this invention without departing from the essence and scope of this invention still fall within the scope of protection of this invention.

Claims

1. A method for producing a modified talc powder for polylactic acid nucleating agent, characterized by: The method comprises the following steps: Step 1: Dissolve phthalic anhydride and talc in an organic solvent and heat and stir to obtain a uniform mixture, collect the precipitate after cooling, and vacuum dry to obtain a powder; Step 2: Dissolve the powder obtained in step 1 in a tetraalkylammonium hydroxide aqueous solution, heat and reflux, collect the solid after cooling, and vacuum dry to obtain a catalyst; Step 3: Mix the catalyst obtained in step 2 with lactide and an initiator, heat and stir to react, thoroughly wash and collect the solid, and vacuum dry to obtain a modified talc powder for polylactic acid nucleating agent.

2. The method of claim 1, wherein: In step 1, the mass ratio of phthalic anhydride to talc is 0.5-4:1; The organic solvent is selected from N,N-dimethylacetamide, N-methylpyrrolidone, and N,N-dimethylformamide.

3. The method of claim 1, wherein: In step 1, the heating and stirring temperature is 100-150°C, and the reaction time is 4-15 hours.

4. The method of claim 1, wherein: In step 2, the tetraalkylammonium hydroxide is selected from tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide; The mass ratio of the powder to tetraalkylammonium hydroxide is 1-5:

1.

5. The method of claim 1, wherein: In step 2, the heating and reflux temperature is 100-150°C, and the time is 4-10 hours.

6. The method of claim 1, wherein: In step 3, the heating and stirring temperature is 105-180°C, and the time is 2-12 hours.

7. The method of claim 1, wherein: In step 3, the initiator is selected from sodium tert-butoxide, potassium tert-butoxide, and polyethylene glycol monomethyl ether; The mass ratio of the catalyst to lactide is 0.01-0.

2.

8. The modified talc powder for polylactic acid nucleating agent prepared by the method of any one of claims 1-7.

9. The use of the modified talc powder of claim 8 as a polylactic acid nucleating agent.

10. Use according to claim 9, characterized in that: The use is to blend the modified talc powder with polylactic acid, and the addition amount of the modified talc powder during blending is 0.5-8.0 wt%.

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