Anti-aging modified polylactic acid composite material and preparation method thereof

Abstract

This invention relates to the field of polymer materials technology, and discloses an anti-aging modified polylactic acid composite material and its preparation method. The material uses 100 parts by weight of polylactic acid resin as a base, and includes 0.5–3.0 parts by weight of a composite anti-aging additive and 0.2–0.8 parts by weight of a lubricant. The composite anti-aging additive is composed of an antioxidant, a hydrolytic stabilizer, and a light stabilizer in a mass ratio of 1:1:1. Preparation involves vacuum drying, high-speed mixing, and melt extrusion granulation. This invention utilizes the hydrolytic stabilizer to preferentially cap the carboxyl groups of polylactic acid, eliminating its consumption of hindered phenolic antioxidants and hindered amine light stabilizers. This achieves synergistic protection against heat-oxidation, damp heat, and ultraviolet aging, resulting in a mechanical retention rate of over 85% after aging, a yellowing index below 0.5, and good processing fluidity. It is suitable for biodegradable products with high weather resistance requirements.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to an anti-aging modified polylactic acid composite material and its preparation method. Background Technology

[0002] Polylactic acid (PLA) is a fully biodegradable polymer material made from renewable agricultural and forestry biomass resources such as corn, cassava, and straw through fermentation and polymerization. It features high mechanical strength, excellent rigidity, good transparency, and versatility in molding and processing, and can be manufactured using conventional plastic processing techniques such as extrusion, injection molding, blow molding, and hot pressing. With increasing environmental awareness and the expanding application areas of bio-based materials, PLA's market demand continues to grow due to its environmental advantages, including compostability and biodegradability, and renewable raw materials. Its applications have expanded from packaging materials and disposable tableware to fields requiring high long-term material stability, such as electronic appliance casings, automotive interior parts, outdoor equipment, and agricultural mulch films.

[0003] However, the main chain of polylactic acid (PLA) molecules contains a large number of polar ester bonds, making it highly sensitive to heat, oxygen, moisture, and ultraviolet radiation. It is prone to varying degrees of aging and degradation during high-temperature melting, storage, transportation, and long-term outdoor service. Specifically, during high-temperature processing, thermo-oxidative degradation mainly occurs, with molecular chain breakage leading to decreased melt strength and significantly reduced mechanical properties of the finished product. In humid and hot environments, ester bonds hydrolyze to generate terminal carboxyl and hydroxyl groups. These terminal carboxyl groups further catalyze hydrolysis, forming an autocatalytic cycle that causes rapid embrittlement and a sharp decrease in strength. Under ultraviolet irradiation, free radical chain oxidation reactions are easily triggered, leading to surface powdering, yellowing, and discoloration of the product, along with simultaneous deterioration of its physicochemical properties. These multiple aging pathways overlap, severely restricting the widespread application of PLA in harsh environments such as high temperature and humidity, and strong sunlight.

[0004] To address the aging problem of polylactic acid (PLA), existing technologies include modifications by adding single antioxidants, hydrolysis stabilizers, or light stabilizers. However, single additives can only protect against specific types of aging and are insufficient to cope with the aging conditions caused by the coupling of multiple environmental factors. Current research has attempted to use a combination of multiple additives, but these methods generally suffer from the following shortcomings: (1) Poor compatibility between additives and the PLA matrix, uneven dispersion, and easy migration and precipitation during high-temperature processing, affecting the appearance and long-term stability of the product; (2) High additive dosage, which not only increases costs but also degrades the mechanical properties and processing fluidity of the substrate; (3) More importantly, the terminal carboxyl groups generated by PLA hydrolysis consume hindered phenolic antioxidants and hindered amine light stabilizers, leading to antagonistic effects between the compounded additives, weakening their individual protective effects, and making it difficult to meet the requirements of high-end products in terms of long-term weather resistance. Therefore, it is urgent to develop a modified PLA composite material that can simultaneously resist three aging modes: thermo-oxidative, hydrolytic, and ultraviolet, and where each additive has a synergistic effect. Summary of the Invention

[0005] The purpose of this invention is to provide an anti-aging modified polylactic acid composite material and its preparation method, which solves the problems in the prior art that polylactic acid materials are difficult to resist multiple aging processes such as heat and oxygen, damp heat and ultraviolet radiation at the same time, and that compounded additives have antagonistic effects and insufficient long-term stability.

[0006] To achieve the above objectives, the present invention provides an anti-aging modified polylactic acid composite material, the composite material being made of components comprising the following parts by weight: 100 parts of polylactic acid resin; 0.5–3.0 parts of compound anti-aging additives; Lubricant 0.2–0.8 parts; The composite anti-aging additive is composed of antioxidants, hydrolytic stabilizers and light stabilizers in a mass ratio of 1:1:1.

[0007] The antioxidant is a compound system composed of hindered phenolic antioxidants and phosphite antioxidants, wherein the mass ratio of the hindered phenolic antioxidants to the phosphite antioxidants is 1:0.5 to 2.

[0008] The hindered phenolic antioxidant is selected from at least one of antioxidant 1010 and antioxidant 1076, and the phosphite antioxidant is antioxidant 168.

[0009] The hydrolysis stabilizer is bis(2,6-diisopropylphenyl)carbodiimide.

[0010] The light stabilizer is a UV absorber or a hindered amine light stabilizer. The UV absorber is selected from at least one of UV-531 and UV-P, and the hindered amine light stabilizer is selected from at least one of UV-770 and UV-944.

[0011] The lubricant is selected from at least one of pentaerythritol stearate and ethylene bis-stearamide.

[0012] A method for preparing an anti-aging modified polylactic acid composite material includes the following steps: The polylactic acid resin was vacuum dried at 70–90°C for 4–8 hours. The dried polylactic acid resin is mixed at high speed with composite anti-aging additives and lubricants to obtain a premix. The premixed material is melt-extruded, cooled, and pelletized to obtain an anti-aging modified polylactic acid composite material.

[0013] The premixed material obtained by high-speed mixing of the dried polylactic acid resin with composite anti-aging additives and lubricants specifically includes: The high-speed mixing speed is 800-1200 r / min, and the mixing time is 3-10 minutes.

[0014] Specifically, the premixed material is melt-extruded, cooled, and pelletized to obtain an anti-aging modified polylactic acid composite material, which includes: The melt extrusion is performed using a twin-screw extruder with a processing temperature of 170–210°C and a screw speed of 250–450 r / min.

[0015] Specifically, the premixed material is melt-extruded, cooled, and pelletized to obtain an anti-aging modified polylactic acid composite material, which includes: The vacuum degree of the twin-screw extruder during the extrusion process is -0.05 to -0.09 MPa.

[0016] This invention discloses an anti-aging modified polylactic acid composite material and its preparation method. Using polylactic acid resin as a matrix, a composite anti-aging additive and lubricant, composed of an antioxidant, a hydrolysis stabilizer, and a light stabilizer in a 1:1:1 ratio, are added. The material is prepared using a process route of vacuum drying, high-speed mixing, and melt blending extrusion. The hydrolysis stabilizer preferentially caps the terminal carboxyl groups generated by the hydrolysis of polylactic acid, eliminating the consumption of hindered phenolic antioxidants and hindered amine light stabilizers by the terminal carboxyl groups. This allows the three additives to each play their respective roles in capturing free radicals and inhibiting ester bond hydrolysis within the same system. The synergistic effect of absorbing ultraviolet energy enables the composite material to resist thermo-oxidative aging, humid heat aging, and ultraviolet aging simultaneously, without compromising the mechanical properties and processing fluidity of the substrate, by adding only 0.5 to 3.0 parts of additives. This effectively solves the problems of polylactic acid being unable to cope with multiple coupled aging conditions and the antagonistic effect of compounded additives in the existing technology. The mechanical property retention rate of the material after thermo-oxidative, humid heat, and hot water aging all reach more than 85%, and the yellowing index after ultraviolet aging is less than 0.5, which significantly extends the service life of the material in harsh environments. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0018] Figure 1 This is a flowchart of the preparation method of the anti-aging modified polylactic acid composite material of the present invention. Detailed Implementation

[0019] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0020] Example 1

[0021] Weigh out the following by weight: 100 parts polylactic acid resin, 2.0 parts composite anti-aging additive (antioxidant is antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1; hydrolytic stabilizer is bis(2,6-diisopropylphenyl)carbodiimide; light stabilizer is UV-531 in a mass ratio of 1:1:1), and 0.5 parts lubricant (PETS-4).

[0022] Polylactic acid resin was dried in a vacuum drying oven at 80°C for 6 hours; each component was added to a high-speed mixer according to the formula and mixed at 1000 r / min for 5 minutes until uniform to obtain a premix; the premix was added to a twin-screw extruder and melt-blended, extruded, water-cooled, air-dried and pelletized to obtain an anti-aging modified polylactic acid composite material.

[0023] Extrusion process parameters: temperature range 175~205℃, screw speed 350r / min, vacuum degree -0.07MPa.

[0024] Example 2

[0025] Weigh out the following components by weight: 100 parts polylactic acid resin, 2.5 parts composite anti-aging additive (antioxidant is antioxidant 1076 and antioxidant 168, mass ratio 1:1.5; hydrolytic stabilizer is bis(2,6-diisopropylphenyl)carbodiimide; light stabilizer is UV-770, mass ratio 1:1:1), and 0.5 parts lubricant (EBS). The preparation process is the same as in Example 1.

[0026] Example 3

[0027] Weigh out the following components by weight: 100 parts polylactic acid resin, 1.5 parts composite anti-aging additive (antioxidant is antioxidant 1010 and antioxidant 168, mass ratio 1:2; hydrolytic stabilizer is bis(2,6-diisopropylphenyl)carbodiimide; light stabilizer is UV-P, mass ratio of the three is 1:1:1), and 0.5 parts lubricant (PETS-4). The preparation process is the same as in Example 1.

[0028] Comparative Example 1 It is made of pure polylactic acid resin and processed using the same drying and extrusion process, without adding any anti-aging additives or lubricants.

[0029] Performance test results Test conditions: 1. Thermo-oxidative aging: 150℃, aging for 500 hours; 2. Damp heat aging: 85℃ / 85% relative humidity (RH), aging for 500 hours; 3. Ultraviolet aging: Using a UVB 340nm light source, irradiated for 300 hours; 4. Hydrolysis treatment: Soak in 70℃ hot water for 168 hours.

[0030] Testing standards: Tensile strength test according to GB / T1040.1-2006, impact strength test according to GB / T1043.1-2008, yellowing index test according to GB / T2409-2013.

[0031]

[0032] Results Analysis As can be seen from the data in the table above, compared with unmodified pure polylactic acid (Comparative Example 1), the modified composite materials obtained in Examples 1-3 of this invention show a significant improvement in anti-aging properties: Significantly improved anti-aging performance: After heat-oxidation, damp heat, ultraviolet aging and hydrolysis treatment, the mechanical property retention rate is much higher than that of pure PLA, proving that the triple synergistic system of the present invention can effectively resist degradation caused by multi-factor coupling. Excellent appearance stability: The yellowing index after ultraviolet aging is extremely low, indicating that the material is not easy to discolor or turn powdery after long-term use, and its appearance quality is stable. Balanced overall performance: While achieving excellent anti-aging effects, the material maintains good mechanical properties and processing fluidity, and the amount of additives is low, which has significant industrial application value and market prospects.

[0033] In summary, this invention, through a reasonable component ratio and synergistic anti-aging system design, significantly improves the resistance to multiple aging processes of polylactic acid while retaining its biodegradability, mechanical properties, and processability. It can be widely used in the field of biodegradable products with high requirements for long-term stability and weather resistance.

[0034] The above-disclosed embodiments are merely one or more preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art can understand that all or part of the processes for implementing the above embodiments and equivalent changes made in accordance with the claims of this application still fall within the scope of this application.

Claims

1. An anti-aging modified polylactic acid composite material, characterized in that, The composite material is made of components comprising the following parts by weight: 100 parts of polylactic acid resin; 0.5–3.0 parts of compound anti-aging additives; Lubricant 0.2–0.8 parts; The composite anti-aging additive is composed of antioxidants, hydrolytic stabilizers and light stabilizers in a mass ratio of 1:1:

1.

2. The anti-aging modified polylactic acid composite material as described in claim 1, characterized in that, The antioxidant is a compound system composed of hindered phenolic antioxidants and phosphite antioxidants, wherein the mass ratio of the hindered phenolic antioxidants to the phosphite antioxidants is 1:0.5 to 2.

3. The anti-aging modified polylactic acid composite material as described in claim 2, characterized in that, The hindered phenolic antioxidant is selected from at least one of antioxidant 1010 and antioxidant 1076, and the phosphite antioxidant is antioxidant 168.

4. The anti-aging modified polylactic acid composite material as described in claim 1, characterized in that, The hydrolysis stabilizer is bis(2,6-diisopropylphenyl)carbodiimide.

5. The anti-aging modified polylactic acid composite material as described in claim 1, characterized in that, The light stabilizer is an ultraviolet absorber or a hindered amine light stabilizer. The ultraviolet absorber is selected from at least one of UV-531 and UV-P, and the hindered amine light stabilizer is selected from at least one of UV-770 and UV-944.

6. The anti-aging modified polylactic acid composite material as described in claim 1, characterized in that, The lubricant is selected from at least one of pentaerythritol stearate and ethylene bis-stearamide.

7. A method for preparing an anti-aging modified polylactic acid composite material, used to prepare the anti-aging modified polylactic acid composite material according to any one of claims 1 to 6, characterized in that, Includes the following steps: The polylactic acid resin was vacuum dried at 70–90°C for 4–8 hours. The dried polylactic acid resin is mixed at high speed with composite anti-aging additives and lubricants to obtain a premix. The premixed material is melt-extruded, cooled, and pelletized to obtain an anti-aging modified polylactic acid composite material.

8. The method for preparing the anti-aging modified polylactic acid composite material as described in claim 7, characterized in that, The dried polylactic acid resin is mixed at high speed with a composite anti-aging additive and a lubricant to obtain a premix, which specifically includes: The high-speed mixing speed is 800-1200 r / min, and the mixing time is 3-10 minutes.

9. The method for preparing the anti-aging modified polylactic acid composite material as described in claim 7, characterized in that, The premixed material is melt-extruded, cooled, and pelletized to obtain an anti-aging modified polylactic acid composite material, specifically comprising: The melt extrusion is performed using a twin-screw extruder with a processing temperature of 170–210°C and a screw speed of 250–450 r / min.

10. The method for preparing the anti-aging modified polylactic acid composite material as described in claim 9, characterized in that, The premixed material is melt-extruded, cooled, and pelletized to obtain an anti-aging modified polylactic acid composite material, specifically comprising: The vacuum degree of the twin-screw extruder during the extrusion process is -0.05 to -0.09 MPa.

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