An aging-resistant polypropylene composite material and its preparation method

Abstract

This invention discloses an aging-resistant polypropylene composite material and its preparation method, comprising, by weight parts: 90 to 100 parts of polypropylene resin; 3 to 7 parts of compatibilizer; 1 to 3 parts of composite aging-resistant agent; and 1 to 3 parts of lubricant. The compatibilizer is polypropylene grafted with maleic anhydride; the lubricant is oxidized polyethylene wax; and the composite aging-resistant agent includes an isocyanate-functionalized antioxidant covalently bonded to silica. This invention utilizes silica as a carrier for covalently linking the isocyanate-functionalized antioxidant, effectively avoiding the problems of easy migration and loss of antioxidants in traditional addition methods, and extending the aging resistance of the polypropylene composite material.

Description

Technical Field

[0001] This invention relates to the field of polypropylene composite materials technology, and in particular to an aging-resistant polypropylene composite material and its preparation method. Background Technology

[0002] Polymer materials are materials composed of polymer compounds as a matrix and other additives. They can be broadly classified into three categories: plastics, rubber, and fibers. Among them, plastics refer to materials that can be molded into a certain shape under certain temperature, pressure, and other conditions and maintain that shape at room temperature. Based on their thermal processing, they can be divided into thermoplastic plastics and thermosetting plastics. Common plastics include polycarbonate (PC), polyethylene (PE), polypropylene (PP), and polymethyl methacrylate (PMMA).

[0003] Polypropylene (PP) is a semi-crystalline thermoplastic polymer made from propylene monomers through an addition polymerization reaction. It is non-toxic, odorless, transparent, and lightweight. Its chemical formula is (C3H6). n Density 0.89-0.92 g / cm³ 3 Polypropylene has a melting point of 164-176 ℃, softens at around 155 ℃, and has an operating temperature range of -30-140 ℃. It is lightweight, wear-resistant, and easy to dye, making it widely used in the textile industry. It also possesses good insulation properties and is used to manufacture the casings of electronic devices. Furthermore, it exhibits good chemical stability and mechanical properties. However, due to the presence of many methylated tertiary carbon atoms in the polypropylene main chain, which are susceptible to oxygen attack, polypropylene has poor weather resistance. Its performance significantly degrades after several months of outdoor use. Therefore, there is a need to find methods for preparing long-lasting, aging-resistant polypropylene.

[0004] In existing technologies, antioxidants are mostly added directly to the polypropylene matrix in small molecule form. These antioxidants are prone to migration and loss during polypropylene processing and use, leading to a significant decrease in their anti-aging effect over long-term service. For example, research on migration-resistant polypropylene antioxidants shows that the traditional antioxidant 1010 has a high migration rate in polypropylene. It requires methods such as layered inorganic carrier intercalation or the construction of interlayer fencing structures to significantly reduce migration and precipitation, thereby improving service life under high-temperature aging conditions. Summary of the Invention

[0005] The purpose of this invention is to provide an aging-resistant polypropylene composite material. This invention utilizes silica as a carrier for covalently linking isocyanate-based functionalized antioxidants, effectively avoiding the problems of easy migration and loss of antioxidants in traditional addition methods, and extending the aging resistance of polypropylene composite materials.

[0006] To solve this technical problem, the technical solution of the present invention is as follows: An aging-resistant polypropylene composite material, comprising, by weight parts:

[0007] The compatibilizer is polypropylene grafted with maleic anhydride, model B1, with a grafting rate ≥0.8% and a melt index of 60-80 g / 10 min, purchased from KOAS Chemical Co., Ltd.; the lubricant is oxidized polyethylene wax with an acid value of 15-25 mgKOH / g.

[0008] The composite anti-aging agent includes an isocyanate-functionalized antioxidant supported by covalent bonds of silica, and the structural formula of the isocyanate-functionalized antioxidant supported by covalent bonds of silica is as follows: .

[0009] The method for preparing the isocyanate-functionalized antioxidant supported by covalent bonds of silica includes the following steps: After drying the nano-silica, it was added to toluene, stirred and dispersed, and then an isocyanate-functionalized antioxidant was added. The mixture was heated under reflux under a nitrogen atmosphere. The hydroxyl groups OH and -NCO on the surface of the silica reacted to form urethane bonds. After completion, the solid was centrifuged, washed with toluene, and vacuum dried to obtain antioxidant-grafted nano-silica. The structural formula of the isocyanate-functionalized antioxidant is as follows: .

[0010] The isocyanate-functionalized antioxidant is prepared as follows: Under a nitrogen atmosphere, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid was added to acetone and stirred. Triethylamine was added first, followed by the dropwise addition of toluene-2,4-diisocyanate. After the addition was complete, the mixture was heated and stirred to induce an amidation reaction. After the reaction was completed, the solvent was removed by rotary evaporation to obtain the isocyanate-functionalized antioxidant.

[0011] The composite anti-aging agent also includes a cashew phenol-piperidine derivative, the structural formula of which is as follows: , where n is 1 to 3.

[0012] The preparation method of the cashew phenol-piperidine derivative includes the following steps: Cashew nut phenol, 4-piperidine carboxamide and formaldehyde were added to methanol and petroleum ether as solvents. The mixture was slowly heated and stirred under nitrogen atmosphere and refluxed. Nitrogen gas was introduced and stirring continued. After the reaction was completed, the solvent was removed by rotary evaporation, and the solid was washed with ethyl acetate and dried under vacuum to obtain the cashew nut phenol-piperidine derivative.

[0013] The mass ratio of the cashew phenol-piperidine derivative to the isocyanate-functionalized antioxidant supported by silica covalent bonds in the composite anti-aging agent is 1:(2 to 4).

[0014] In the composite anti-aging agent, the cashew phenol-piperidine derivative and the isocyanate-functionalized antioxidant covalently supported by silica are physically mixed or chemically linked. Further introduction of the synergistic anti-aging cashew phenol-piperidine derivative onto the surface of the prepared antioxidant grafted onto nano-silica enhances the duration and effectiveness of the composite anti-aging agent. This invention utilizes cashew phenol... and 4-piperidinecarboxamide Using cashew nut shells as raw materials, a Mannich reaction was successfully carried out in the presence of formaldehyde HCHO, resulting in the reaction of cashew nut shells + HCHO + piperidine-NH2 → cashew nut shells-CH2-NH-piperidine + H2O, thus successfully preparing cashew nut shells-piperidine derivatives. .

[0015] Subsequently, the silanol hydroxyl groups (Si-OH) formed after the hydrolysis of propyl 3-(trimethoxysilyl)methacrylate (KH-570) on the silica surface undergo a dehydration condensation reaction, such as Si-OH + Si-OH → Si-O-Si + H2O. The double bond structure in KH-570 provides conditions for the subsequent free radical copolymerization of cashew phenol-piperidine derivatives on the NAO@SiO2 surface. Then, under the initiation of azobisisobutyronitrile (AIBN), the carbon-carbon double bonds in the C15 long chain of the cashew phenol-piperidine derivative and the double bonds in KH-570 undergo a free radical copolymerization reaction, linking the cashew phenol-piperidine derivative to the SiO2 surface. This improves the aging resistance while also enhancing the dispersibility of the composite antioxidant. The invention ultimately prepares a composite anti-aging agent Cpd-NAO@SiO2 with a triple anti-aging mechanism, possessing the physical barrier effect of SiO2 and the free radical quenching effects of hindered phenols and hindered amines. In this composite anti-aging agent, SiO2 acts as a physical barrier against ultraviolet radiation, delaying the generation of free radicals and strengthening the resin matrix as a second phase. The hindered amine structure in the cashew phenol-piperidine derivative generates nitric oxide radicals (NO·) under light or oxygen, undergoing reactions such as NO· + R· → NOR. This efficiently captures alkyl free radicals (R·) formed during resin matrix aging, forming esters (NOR) and thus interrupting the free radical chain reaction process of aging. The hindered phenolic structure in the cashew phenol-piperidine derivative and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid can undergo reactions such as Ph-OH + ROO· → Ph-O· + ROOH, rapidly and effectively capturing peroxide radicals (ROO·) formed during PP aging and generating phenoxy radicals and peroxides, thereby blocking the aging chain reaction. Through the combination of chemical and physical methods, the prepared polypropylene composite material exhibits excellent anti-aging properties and long-lasting anti-aging performance.

[0016] Another objective of this invention is to provide a method for preparing the aging-resistant polypropylene composite material proposed in this invention. This invention effectively enhances the uniform dispersion of antioxidants by using silica as a carrier to effectively chemically bond isocyanate-functionalized antioxidants, thereby extending the aging resistance of the obtained polypropylene composite material.

[0017] To solve this technical problem, the technical solution of the present invention is: a method for preparing aging-resistant polypropylene composite materials, comprising the following steps: S1. First, place the polypropylene resin and polypropylene grafted maleic anhydride in a vacuum drying oven to dry them according to the proportion. Then, add oxidized polyethylene wax and composite anti-aging agent to the dried polypropylene resin and polypropylene grafted maleic anhydride according to the proportion, mix them evenly, and the mixed raw materials are obtained. S2. Preheat the twin-screw extruder. After preheating, add the mixture obtained in step one. The material that is evenly mixed by the extruder is fed into the granulator for granulation to obtain a long-lasting aging-resistant polypropylene composite material.

[0018] The preferred extrusion process parameters for step S2 are as follows: the block temperatures are set sequentially to 170–185℃, 180–195℃, 185–205℃, 190–210℃, 195–215℃, 200–220℃, and 200–220℃, and the screw speed is 300 rpm to 400 rpm.

[0019] By adopting the above technical solution, the beneficial effects of the present invention are: This invention first uses 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid and toluene-2,4-diisocyanate (TDI) as raw materials, and the following condensation reaction occurs between the carboxyl group (-COOH) and the isocyanate group (-NCO): -COOH + -NCO → -CO-NH- + CO2; An amide bond -CO-NH- is formed, while the phenolic hydroxyl group Ph-OH in 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid is located between the two tert-butyl-C(CH3)3 groups, exhibiting significant steric hindrance. This severely affects the reactivity of the phenolic hydroxyl group, causing the isocyanate group to preferentially react with the carboxyl group to form an amide bond. The isocyanate-functionalized antioxidant is obtained by chemically linking 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid and toluene-2,4-diisocyanate. Subsequently, the isocyanate-functionalized antioxidant undergoes the following nucleophilic addition reaction between the silanol group -Si-OH on the silica surface and the isocyanate group -NCO of the isocyanate-functionalized antioxidant: -Si-OH + -NCO → -Si-O-CO-NH-; By forming stable urethane bonds -NH-CO-O-, isocyanate-functionalized antioxidants are covalently linked to the silica surface, thus avoiding the problems of easy migration and loss of antioxidants in traditional addition methods, and effectively improving the aging resistance and mechanical properties of the obtained polypropylene composite material. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the chemical reaction process of antioxidant-grafted nano-silica and cashew phenol-piperidine derivatives prepared in Example 1 of the present invention. Figure 2 This is a schematic diagram of the chemical reaction process of the composite anti-aging agent prepared in Example 1 of the present invention; Figure 3 This is a simulation diagram of the reaction mechanism of the composite anti-aging agent prepared in Example 1 of the present invention; Figure 4This is a comparison diagram of the polypropylene composite materials prepared in Comparative Example 1 and Example 1 of the present invention after unaged and aged for 300 h. in, Figure 4 In Figures a and b, the polypropylene material prepared in Comparative Example 1 is compared before and after aging. In Figures c and d, the polypropylene material prepared in Example 1 is compared before and after aging.

[0021] Figure 5 The image shows the FT-IR spectrum of the cashew phenol-piperidine derivative prepared in Example 1 of this invention. Figure 6 The FT-IR image is of the antioxidant-grafted nano-silica prepared in Example 1 of this invention. Figure 7 The image shows the FT-IR spectrum of the composite anti-aging agent prepared in Example 1 of this invention. Detailed Implementation

[0022] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0023] Example 1

[0024] This embodiment discloses a long-lasting aging-resistant polypropylene composite material, which, by weight, includes the following components: 100 parts of polypropylene resin, 5 parts of compatibilizer, 2 parts of composite aging-resistant agent, and 2 parts of lubricant.

[0025] The compatibilizer is polypropylene grafted with maleic anhydride, model B1, with a grafting rate ≥0.8% and a melt index of 60-80 g / 10 min, purchased from KOAS Chemical Co., Ltd.; the lubricant is oxidized polyethylene wax with an acid value of 15-25 mgKOH / g.

[0026] The preparation method of the composite anti-aging agent includes the following steps: S1. Under a nitrogen atmosphere, 0.05 mol of 95% pure 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid was added to 100 ml of 99.5% pure acetone. After stirring for 5 min, 0.3 mmol of 99.5% pure triethylamine was added to the mixture, followed by dropwise addition of 0.05 mol of 99.5% pure toluene-2,4-diisocyanate. After the addition was complete, the mixture was stirred at 50 °C for 4 h. After the reaction was complete, the solvent was removed by rotary evaporation at 40 °C to obtain the isocyanate-functionalized antioxidant, denoted as NAO. The main processes involved in the above reaction are as follows: -COOH + -NCO → -CO-NH- + CO2, which is a typical amidation reaction. However, the phenolic hydroxyl group is hindered by the steric hindrance formed by the tert-butyl-C(CH3)3 groups on both sides. In this invention, the steric hindrance group is tert-butyl-C(CH3)3, and the steric hindrance effect is more obvious, which can achieve high selectivity in step S1.

[0027] S2. 3 g of nano-silica with an average particle size of 20 nm, a specific surface area of ​​200 m² / g, and a purity of 99.5% was dried at 120 °C for 6 h. Then, the dried nano-silica was added to 500 ml of toluene with a purity of 99.5%, stirred and dispersed, and then 3 g of the isocyanate-functionalized antioxidant obtained in step S1 was added. The mixture was refluxed at 110 °C for 12 h under a nitrogen atmosphere. After the reaction was completed, the solid was centrifuged and washed three times with toluene. Then, it was vacuum dried at 55 °C for 10 h to obtain antioxidant-grafted nano-silica, denoted as NAO@SiO2. The main processes involved in the above reaction are as follows: Si-OH + -NCO → Si-O-CO-NH-, which is a typical polyurethane reaction that generates urethane bonds.

[0028] S3. Add 10 mmol of 98% pure cashew nut shell powder, 10 mmol of 97% pure 4-piperidine carboxamide, 10.5 mmol of formaldehyde, 15 ml of 99.9% pure methanol, and 5 ml of ACS grade petroleum ether to a three-necked flask. Then, slowly heat to 65 °C at 3 °C / min and stir and reflux for 1 h under nitrogen atmosphere. Then, stop the nitrogen gas and continue stirring for 8 h. After the reaction is complete, remove the solvent by rotary evaporation at 50 °C, take the solid, wash with ethyl acetate, and dry under vacuum at 55 °C for 10 h to obtain the cashew nut shell powder-piperidine derivative, denoted as Cpd. The main process involved in the above reaction is the Mannich reaction. The principle of the Mannich reaction is the condensation of an amine, an aldehyde, and at least one reactive hydrogen atom. According to the Mannich reaction principle, the ortho- and tho-positions of phenol are reactive sites. In cashew phenol, of the two ortho- and tho-positions of the phenolic hydroxyl group, the one closer to the C15 long chain has weaker reactivity / selectivity than the other ortho-active hydrogen atom due to the steric hindrance of the long chain. Therefore, the reaction process is as shown in the attached diagram. Figure 1 As shown.

[0029] S4. Add 3 g of NAO@SiO2 obtained in step S2 and 0.3 g of KH-570 with a purity of 98% to 100 ml of ethanol with a purity of 99.9%. Stir and disperse, and react at 50 °C for 2 h. Then add 1 g of cashew phenol-piperidine derivative obtained in step S3 and 0.1 g of azobisisobutyronitrile with a purity of 98%. Under nitrogen atmosphere protection, stir and polymerize at 70 °C for 8 h. After the reaction is completed, centrifuge to collect the solid, wash with ethanol, and vacuum dry at 55 °C for 10 h to obtain the target composite anti-aging agent, denoted as Cpd-NAO@SiO2.

[0030] The main processes involved in the above reaction are as follows: ①: The silanol groups formed by the hydrolysis of KH-570 and the silanol groups on the surface of silica undergo the following reaction: -Si-OH + -Si-OH → -Si-O-Si- + H2O, covalently linking KH-570 and modified silica through a dehydration condensation reaction between hydroxyl groups. ②: As shown in the attached figure. Figure 2 The azobisisobutyronitrile (AIBN) shown forms free radicals upon heating: -CN=NC- → 2*-C-· + N2, which activates the polymerization process. In addition, AIBN is used to activate free radical copolymerization between different C=C monomers to form Cpd-NAO@SiO2, further enhancing the synergistic performance of the resulting composite anti-aging agent.

[0031] The method for preparing the above-mentioned long-lasting aging-resistant polypropylene composite material includes the following steps: Step 1: First, place the polypropylene resin and polypropylene-grafted maleic anhydride in a vacuum drying oven at 70 ℃ and dry for 10 h. Then, add oxidized polyethylene wax and composite anti-aging agent to the dried polypropylene resin and polypropylene-grafted maleic anhydride in proportion and mix evenly to obtain the mixed raw material. Step 2: Preheat the twin-screw extruder, setting the block temperatures in sequence to 175℃, 185℃, 195℃, 200℃, 205℃, 210℃, and 215℃, with a screw speed of 300 rpm. After preheating, add the mixture obtained in Step 1. The material, which is uniformly mixed through the extruder, is then fed into a granulator for granulation to obtain a long-lasting, aging-resistant polypropylene composite material.

[0032] Example 2

[0033] This embodiment discloses a long-lasting aging-resistant polypropylene composite material, which, by weight, includes the following components: 100 parts of polypropylene resin, 3 parts of compatibilizer, 1 part of composite aging-resistant agent, and 2 parts of lubricant.

[0034] The preparation method of the composite anti-aging agent and the method of the long-lasting anti-aging polypropylene composite material are the same as those in Example 1.

[0035] Example 3

[0036] This embodiment discloses a long-lasting aging-resistant polypropylene composite material, which, by weight, includes the following components: 100 parts of polypropylene resin, 7 parts of compatibilizer, 3 parts of composite aging-resistant agent, and 2 parts of lubricant.

[0037] The preparation method of the composite anti-aging agent and the method of the long-lasting anti-aging polypropylene composite material are the same as those in Example 1.

[0038] Example 4

[0039] This embodiment discloses a long-lasting aging-resistant polypropylene composite material, which, by weight, includes the following components: 100 parts of polypropylene resin, 5 parts of compatibilizer, 2 parts of composite aging-resistant agent, and 2 parts of lubricant.

[0040] The preparation method of the composite anti-aging agent includes the following steps: S1. Under a nitrogen atmosphere, 0.05 mol of 95% pure 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid was added to 100 ml of 99.5% pure acetone. After stirring for 5 min, 0.3 mmol of 99.5% pure triethylamine was added to the mixture, followed by dropwise addition of 0.05 mol of 99.5% pure toluene-2,4-diisocyanate. After the addition was complete, the mixture was stirred at 50 °C for 4 h. After the reaction was complete, the solvent was removed by rotary evaporation at 40 °C to obtain the isocyanate-functionalized antioxidant, denoted as NAO. S2. 3 g of nano-silica with an average particle size of 20 nm, a specific surface area of ​​200 m² / g, and a purity of 99.5% was dried at 120 °C for 6 h. Then, the dried nano-silica was added to 500 ml of toluene with a purity of 99.5%, stirred and dispersed, and then 3 g of the isocyanate-functionalized antioxidant obtained in step S1 was added. The mixture was refluxed at 110 °C for 12 h under a nitrogen atmosphere. After the reaction was completed, the solid was centrifuged and washed three times with toluene. Then, it was vacuum dried at 55 °C for 10 h to obtain antioxidant-grafted nano-silica, denoted as NAO@SiO2. The method for preparing the above-mentioned long-lasting aging-resistant polypropylene composite material includes the following steps: Step 1: Place polypropylene resin and polypropylene grafted maleic anhydride in a vacuum drying oven at 70 ℃ and dry for 10 h. Then, add oxidized polyethylene wax and antioxidant grafted nano silica to the dried polypropylene resin and polypropylene grafted maleic anhydride in proportion and mix evenly to obtain the mixed raw material. Step 2: Preheat the twin-screw extruder, setting the block temperatures in sequence to 175℃, 185℃, 195℃, 200℃, 205℃, 210℃, and 215℃, with a screw speed of 300 rpm. After preheating, add the mixture obtained in Step 1. The material, which is uniformly mixed through the extruder, is then fed into a granulator for granulation to obtain a long-lasting, aging-resistant polypropylene composite material.

[0041] Example 5

[0042] This embodiment discloses an aging-resistant polypropylene composite material, which, by weight, includes the following components: 100 parts of polypropylene resin, 5 parts of compatibilizer, 2 parts of compounded aging-resistant agent, and 2 parts of lubricant.

[0043] The compound anti-aging agent is obtained by physically mixing the antioxidant-grafted nano-silica NAO@SiO2 prepared according to steps S1 and S2 in Example 1 and the cashew phenol-piperidine derivative Cpd prepared in step S3 at a mass ratio of 3:1.

[0044] The method for preparing the above-mentioned polypropylene composite material includes the following steps: Step 1: Place polypropylene resin and polypropylene grafted maleic anhydride in a vacuum drying oven at 70 ℃ and dry for 10 h. Then, add oxidized polyethylene wax and compound anti-aging agent to the dried polypropylene resin and polypropylene grafted maleic anhydride in proportion and mix evenly to obtain the mixed raw material. Step 2: Preheat the twin-screw extruder. Set the block temperatures in sequence to 175 ℃, 185 ℃, 195 ℃, 200 ℃, 205 ℃, 210 ℃, and 215 ℃, and the screw speed to 300 rpm. After preheating, add the mixture obtained in Step 1. The material that is evenly mixed by the extruder is then fed into the granulator for granulation to obtain the aging-resistant polypropylene composite material.

[0045] Comparative Example 1 This comparative example discloses a polypropylene composite material, which, by weight, comprises the following components: 100 parts of polypropylene resin and 2 parts of lubricant.

[0046] The method for preparing the above-mentioned polypropylene composite material includes the following steps: Step 1: Place the polypropylene resin in a vacuum drying oven at 70 ℃ and dry it for 10 h. Then, add oxidized polyethylene wax to the dried polypropylene resin and the polypropylene grafted maleic anhydride in proportion and mix evenly to obtain the mixed raw material. Step 2: Preheat the twin-screw extruder. Set the block temperatures in sequence to 175 ℃, 185 ℃, 195 ℃, 200 ℃, 205 ℃, 210 ℃, and 215 ℃, and the screw speed to 300 rpm. After preheating, add the mixture obtained in Step 1. The material that is uniformly mixed by the extruder is then fed into the granulator for granulation to obtain the polypropylene composite material.

[0047] Comparative Example 2 This comparative example discloses an aging-resistant polypropylene composite material, which, by weight, comprises the following components: 100 parts of polypropylene resin, 5 parts of compatibilizer, 2 parts of compounded aging-resistant agent, and 2 parts of lubricant.

[0048] The compound anti-aging agent is obtained by mixing antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0049] The method for preparing the above-mentioned polypropylene composite material includes the following steps: Step 1: Place polypropylene resin and polypropylene grafted maleic anhydride in a vacuum drying oven at 70 ℃ and dry for 10 h. Then, add oxidized polyethylene wax and compound anti-aging agent to the dried polypropylene resin and polypropylene grafted maleic anhydride in proportion and mix evenly to obtain the mixed raw material. Step 2: Preheat the twin-screw extruder. Set the block temperatures in sequence to 175 ℃, 185 ℃, 195 ℃, 200 ℃, 205 ℃, 210 ℃, and 215 ℃, and the screw speed to 300 rpm. After preheating, add the mixture obtained in Step 1. The material that is evenly mixed by the extruder is then fed into the granulator for granulation to obtain the aging-resistant polypropylene composite material.

[0050] Comparative Example 3 This comparative example discloses an aging-resistant polypropylene composite material, which, by weight, comprises the following components: 100 parts of polypropylene resin, 5 parts of compatibilizer, 2 parts of aging resistant agent, and 2 parts of lubricant.

[0051] The anti-aging agent is nano-silica with an average particle size of 20 nm, a specific surface area of ​​200 m² / g, and a purity of 99.5%.

[0052] The method for preparing the above-mentioned polypropylene composite material includes the following steps: Step 1: Place polypropylene resin and polypropylene grafted maleic anhydride in a vacuum drying oven at 70 ℃ and dry for 10 h. Then, add oxidized polyethylene wax and compound anti-aging agent to the dried polypropylene resin and polypropylene grafted maleic anhydride in proportion and mix evenly to obtain the mixed raw material. Step 2: Preheat the twin-screw extruder. Set the block temperatures in sequence to 175 ℃, 185 ℃, 195 ℃, 200 ℃, 205 ℃, 210 ℃, and 215 ℃, and the screw speed to 300 rpm. After preheating, add the mixture obtained in Step 1. The material that is evenly mixed by the extruder is then fed into the granulator for granulation to obtain the aging-resistant polypropylene composite material.

[0053] Comparative Example 4 This comparative example discloses an aging-resistant polypropylene composite material, which, by weight, comprises the following components: 100 parts of polypropylene resin, 5 parts of compatibilizer, 2 parts of compounded aging-resistant agent, and 2 parts of lubricant.

[0054] The compound anti-aging agent is obtained by mixing the same nano-silica as in Comparative Example 3 and the NAO prepared in step S1 in Example 1 at a mass ratio of 1:1.

[0055] The method for preparing the above-mentioned polypropylene composite material includes the following steps: Step 1: Place polypropylene resin and polypropylene grafted maleic anhydride in a vacuum drying oven at 70 ℃ and dry for 10 h. Then, add oxidized polyethylene wax and compound anti-aging agent to the dried polypropylene resin and polypropylene grafted maleic anhydride in proportion and mix evenly to obtain the mixed raw material. Step 2: Preheat the twin-screw extruder. Set the block temperatures sequentially to 175℃, 185℃, 195℃, 200℃, 205℃, 210℃, and 215℃, with a screw speed of 300 rpm. After preheating, add the mixture obtained in Step 1. The uniformly mixed material from the extruder is then fed into a granulator for granulation to obtain the aging-resistant polypropylene composite material. Performance Testing Impact and tensile specimens were obtained by injection molding using standard mechanical specimen injection molds for all embodiments and comparative examples, and performance tests were conducted. The test results are shown in Table 1, which shows the performance test results of polypropylene composite materials.

[0056] Impact strength was tested according to GB / T 1043.2-2018 "Determination of Impact Strength of Plastic Cantilever Beams", using notched impact specimens.

[0057] Tensile strength tests were conducted in accordance with GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics".

[0058] Aging tests were conducted according to GB / T 16422.2-2022 "Laboratory Light Source Exposure Test Methods for Plastics - Part 2: Xenon Arc Lamp", with the following parameters: irradiance of 0.5 W / (m²) at 340 nm. 2At a relative humidity of 65% and a blackboard temperature of 65℃, the tensile strength measured after the same aging time was used as the aging resistance evaluation data.

[0059] Table 1 Tensile strength test results of polypropylene composites

[0060] Table 2 Impact strength test results of polypropylene composites

[0061] From Table 1 (tensile strength test results) and Table 2 (impact strength test results) of the polypropylene composite material, it can be seen that the tensile strength and impact strength of the polypropylene composite material without the addition of composite anti-aging agent in Comparative Example 1 are 22.65 MPa and 7.55 kJ / m, respectively. 2 After 300 hours of aging, the retention rates of tensile strength and impact strength were 49.71% and 40.26%, respectively.

[0062] As the amount of composite anti-aging agent increased from 1 part in Example 2 to 2 parts in Example 1 and 3 parts in Example 3, the tensile strength and impact strength of the resulting PP composite material were 23.42 MPa, 24.62 MPa, 24.85 MPa and 7.85 kJ / m, respectively. 2 8.13 kJ / m 2 7.98 kJ / m 2 The trends in tensile strength and impact strength indicate that adding a SiO2-based composite anti-aging agent to the polypropylene resin matrix can effectively improve the mechanical properties of polypropylene composites. However, a larger addition amount leads to a decrease in the impact strength of the polypropylene composites. With the increase in the amount of composite anti-aging agent, the retention rates of tensile strength and impact strength of the obtained polypropylene composites after 300 h of aging are 80.40%, 87.16%, and 88.79%, and 76.43%, 84.62%, and 88.35%, respectively. The upward trend in the retention rates of tensile strength and impact strength indicates that, within a reasonable range, a larger addition amount of anti-aging agent effectively improves the aging resistance of polypropylene composites.

[0063] Comparing Examples 1, 4, and 5, it was found that the improved bonding stability and variety of aging resistance mechanisms among the components of the composite aging resistant agent led to an increase in the aging resistance of the PP composite material.

[0064] In Example 5, NAO@SiO2 and Cpd are not chemically bonded, and their tensile strength and impact strength retention rates after 300 h of aging are 81.85% and 78.86%, respectively. In Example 1, NAO@SiO2 and Cpd are stably bonded through free radical copolymerization, and their tensile strength and impact strength retention rates are 87.16% and 84.62%, respectively. This indicates that the stable bonding between the components in the composite anti-aging agent can effectively improve the anti-aging properties. At the same time, in Example 5, there is no chemical bond between NAO@SiO2 and Cpd. After the addition of polypropylene resin, the polypropylene resin matrix enters between NAO@SiO2 and Cpd, forming a gap, which prevents the anti-aging mechanisms of the two from working well together and fails to capture free radicals effectively, thereby interrupting the aging chain reaction.

[0065] Example 4 uses NAO@SiO2 as the composite anti-aging agent, with tensile strength and impact strength retention rates of 81.42% and 77.79%, respectively. Example 1 uses Cpd-NAO@SiO2 as the composite anti-aging agent, with tensile strength and impact strength retention rates of 87.16% and 84.62%, respectively. In addition to the mechanism of SiO2 blocking ultraviolet rays and delaying the generation of free radicals, and the mechanism of NAO's hindered phenol capturing the peroxide free radicals ROO· formed during PP aging through Ph-OH + ROO· → Ph-O· + ROOH to block the chain reaction of aging, Example 1 also has the mechanism of Cpd's hindered amine capturing the alkyl free radicals R· formed during PP aging through NO· + R· → NOR to interrupt the free radical chain reaction of aging. This shows that the multi-mechanism composite anti-aging agent can effectively improve the anti-aging properties.

[0066] Comparative Examples 4, 2, 3 and 4 show that the formation of urethane bonds (-NH-CO-O-) between NAO and SiO2 to form stable chemical bonds can effectively improve the dispersibility and aging resistance of the anti-aging agent in the resin matrix.

[0067] Example 4 uses NAO@SiO2 as the composite anti-aging agent, and its tensile strength and impact strength retention rates after 300 h of aging are 81.42% and 77.79%, respectively. Comparative Example 3 uses SiO2 as the anti-aging agent, and its tensile strength and impact strength retention rates are 70.65% and 64.37%, respectively. Comparative Example 2 uses a conventional antioxidant 1010 + antioxidant 168 compound scheme, and its tensile strength and impact strength retention rates are 72.35% and 65.23%, respectively. Comparative Example 4 uses a SiO2 and NAO compound scheme as the anti-aging agent, and its tensile strength and impact strength retention rates are 75.55% and 70.64%, respectively. The data show that as the anti-aging agent changes from SiO2 in Comparative Example 3 to the NAO+SiO2 compound scheme in Comparative Example 4 and the NAO@SiO2 composite scheme in Example 4, the anti-aging effect of the anti-aging agent gradually increases as the chemical connection between NAO and SiO2 is established.

[0068] The tensile and impact strengths of the SiO2 scheme in Comparative Example 3, the NAO+SiO2 composite scheme in Comparative Example 4, and the antioxidant 1010+antioxidant 168 composite scheme in Comparative Example 2 were 23.54 MPa, 23.93 MPa, 23.76 MPa, and 7.83 kJ / m, respectively. 2 7.97 kJ / m 2 7.91 kJ / m 2 The tensile strength and impact strength of Example 4 were 24.38 MPa and 8.06 kJ / m, respectively. 2 There are significant differences. This is because there are no chemical bonds between the anti-aging agent components in Comparative Examples 3, 4, and 2. Due to the presence of hydroxyl and methyl groups in the resin matrix, the anti-aging agent undergoes hydrogen bonding, leading to agglomeration and weakening of the mechanical properties of the PP composite material. In contrast, in Example 4, the hydroxyl groups on the surfaces of NAO and SiO2 are consumed by the urethane bond -NH-CO-O-, which weakens the hydrogen bonding of NAO@SiO2. At the same time, the NAO molecular chains on the surface of SiO2 extend into the polypropylene resin, allowing the polypropylene resin to fully combine with NAO@SiO2, improving the agglomeration of SiO2 and enhancing its dispersibility, while also increasing the mechanical properties of the polypropylene composite material.

[0069] The anti-migration ability of the aging-resistant polypropylene composite materials prepared in Examples 1, 4, 2, and 4 was tested using the following methods: 10 g of the aging-resistant polypropylene composite material was extracted with anhydrous ethanol at 60 °C for 48 h. The migration amount of the antioxidant containing 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid was determined by HPLC-UV method. A C18 reversed-phase column was used, with methanol as the mobile phase for gradient elution, and the detection wavelength was 280 nm. The antioxidant migration amount was quantitatively calculated based on the peak area and corresponding standard curve in the test results and expressed as migration rate.

[0070] Table 3. Test results of the anti-migration ability of polypropylene composite materials

[0071] Table 3 shows the results of the anti-migration ability test of polypropylene composite materials. Comparative Example 2, using a combination of antioxidants 1010 and 168, had an antioxidant content of 18.08 mg of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid in the ethanol solution after immersion extraction, with a migration rate of 19.72%. Comparative Example 4, using a NAO+SiO2 combination, had an antioxidant content of 13.09 mg of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid in the ethanol solution after immersion extraction, with a migration rate of 14.27%. Example 4, using the NAO@SiO2 scheme, had an antioxidant content of 8.68 mg of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid in the ethanol solution after immersion extraction, with a migration rate of 9.47%. The composite anti-aging agent Cpd-NAO@SiO2 prepared in Example 1, after being made into a polypropylene composite material, contained 4.91 mg of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid in the ethanol solution after soaking and extraction, with a migration rate of 7.67%. The migration rate of Example 1 was reduced by 1.8%, 12.05%, and 6.6% compared to Example 4, Comparative Example 2, and Comparative Example 4, respectively. The percentage indicates that the Cpd-NAO@SiO2 composite anti-aging agent prepared by chemical bonding in Example 1 has a better anti-migration effect compared with the compound schemes in Comparative Examples 2 and 4. Furthermore, it was found from Comparative Examples 2, 4, 4, and 1 that as the anti-aging agent was adjusted from the antioxidant 1010 + antioxidant 168 compound scheme in Comparative Example 2 and the NAO + SiO2 compound scheme in Comparative Example 4 to the NAO@SiO2 and Cpd-NAO@SiO2 composite scheme in Example 4 and Example 1, the hindered phenolic component NAO in the anti-aging agent changed from being free to being linked with SiO2 through urethane bonds -NH-CO-O-. The migration rate of the anti-aging agent in the corresponding polypropylene composite material decreased accordingly, indicating that stable chemical bonding can effectively improve the anti-migration ability of the anti-aging agent in the polypropylene composite material.

[0072] like Figure 4 The figures shown are comparative images of the polypropylene composite materials prepared in Comparative Example 1 and Example 1 before and after aging. In Comparative Example 1, the sample without the anti-aging agent showed obvious yellowing before aging (a) and after aging for 200 h (b). In contrast, the sample in Example 1 with the composite anti-aging agent prepared in this invention did not show obvious yellowing before aging (a) and after aging for 200 h (b). This indicates that the composite anti-aging agent prepared in this invention has good anti-aging effect and effectively inhibits yellowing.

[0073] like Figure 5 The image shown is the FT-IR spectrum of the cashew phenol-piperidine derivative prepared in Example 1 of this invention, at 3405 cm⁻¹. -1 and 1356 cm -1 These peaks correspond to the characteristic peaks of the -OH group in phenolic hydroxyl groups. 2889 cm⁻¹ -1 and 2816 cm -1 The peaks at 1582 cm⁻¹ are characteristic of cashew phenol, consisting of methyl-CH₃ and methylene-CH₂- groups. -1 1512 cm -1 and 1561 cm -1 Characteristic peaks of the benzene ring skeleton appeared at 1260 cm⁻¹. Additionally, at 1260 cm⁻¹... -1 and 1283 cm -1 The CN characteristic peak at the point is related to the Mannich reaction in the reaction process, confirming the successful synthesis of the target product, cashew phenol-piperidine derivative.

[0074] like Figure 6 The image shown is the FT-IR spectrum of the antioxidant-grafted nano-silica prepared in Example 1 of this invention, at 3436 cm⁻¹. -1 The intensity of the hydroxyl peak decreased significantly at 2967 cm⁻¹; -1 and 2872 cm -1 The characteristic CH peak appears at 3352 cm⁻¹. -1 The acromion of NH appeared at 2263 cm; in addition, at 2263 cm -1 The isocyanate group -NCO characteristic peak at 1702 cm⁻¹ has largely disappeared, indicating that the antioxidant is fully bonded to the surface of the nano-silica. Furthermore, at 1702 cm⁻¹... -1 The presence of a distinct C=O characteristic peak indicates that antioxidant-grafted silica was successfully prepared using nano-silica, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, and toluene-2,4-diisocyanate.

[0075] like Figure 7The image shown is the FT-IR spectrum of the composite anti-aging agent prepared in Example 1 of this invention, at 3405 cm⁻¹. -1 The characteristic peak of the hydroxyl group (-OH) is still present. 2882 cm⁻¹ -1 and 2803 cm -1 The peak at 1728 cm⁻¹ is characteristic of methyl-CH₃ and methylene-CH₂-, and the introduction of KH-570 causes changes in both peak shape and intensity; -1 The presence of the characteristic peak at 1618 cm⁻¹ indicates that the C=O formed in the preceding steps is stable and reliable; -1 The peak at 1582 cm⁻¹ is a C=C unsaturated peak, and its intensity is significantly lower than that of the cashew phenol-piperidine derivative, indicating the occurrence of free radical copolymerization, thus proving that the method of this invention has successfully prepared the composite anti-aging agent. Furthermore, at 1582 cm⁻¹... -1 1512 cm -1 and 1561 cm -1 The characteristic peaks of the benzene ring skeleton at 1085 cm⁻¹ and at 1085 cm⁻¹ -1 The presence of the Si-O-Si characteristic peaks further confirms the successful synthesis of the target product, the waist-shaped composite anti-aging agent.

Claims

1. An aging-resistant polypropylene composite material, characterized in that: According to the number of parts by weight: ； The compatibilizer is polypropylene grafted with maleic anhydride; the lubricant is oxidized polyethylene wax. The composite anti-aging agent includes an isocyanate-functionalized antioxidant supported by covalent bonds of silica, and the structural formula of the isocyanate-functionalized antioxidant supported by covalent bonds of silica is as follows: 。 2. The aging-resistant polypropylene composite material according to claim 1, characterized in that: The method for preparing the isocyanate-functionalized antioxidant supported by covalent bonds of silica includes the following steps: After drying the nano-silica, it was added to toluene, stirred and dispersed, and then an isocyanate-functionalized antioxidant was added. The mixture was heated under reflux under a nitrogen atmosphere. The hydroxyl groups OH and -NCO on the surface of the silica reacted to form urethane bonds. After completion, the solid was centrifuged, washed with toluene, and vacuum dried to obtain antioxidant-grafted nano-silica. The structural formula of the isocyanate-functionalized antioxidant is as follows: 。 3. The aging-resistant polypropylene composite material according to claim 2, characterized in that: The isocyanate-functionalized antioxidant is prepared as follows: Under a nitrogen atmosphere, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid was added to acetone and stirred. Triethylamine was added first, followed by the dropwise addition of toluene-2,4-diisocyanate. After the addition was complete, the mixture was heated and stirred to induce an amidation reaction. After the reaction was completed, the solvent was removed by rotary evaporation to obtain the isocyanate-functionalized antioxidant.

4. The aging-resistant polypropylene composite material according to claim 1, characterized in that: The composite anti-aging agent also includes a cashew phenol-piperidine derivative, the structural formula of which is as follows: , where n is 1 to 3.

5. The aging-resistant polypropylene composite material according to claim 4, characterized in that: The preparation method of the cashew phenol-piperidine derivative includes the following steps: Cashew nut phenol, 4-piperidine carboxamide and formaldehyde were added to methanol and petroleum ether as solvents. The mixture was slowly heated and stirred under nitrogen atmosphere and refluxed. Nitrogen gas was introduced and stirring continued. After the reaction was completed, the solvent was removed by rotary evaporation, and the solid was washed with ethyl acetate and dried under vacuum to obtain the cashew nut phenol-piperidine derivative.

6. The aging-resistant polypropylene composite material according to claim 4, characterized in that: The mass ratio of the cashew phenol-piperidine derivative to the isocyanate-functionalized antioxidant supported by silica covalent bonds in the composite anti-aging agent is 1:(2 to 4).

7. The aging-resistant polypropylene composite material according to claim 4, characterized in that: In the composite anti-aging agent, the cashew phenol-piperidine derivative and the isocyanate-functionalized antioxidant supported by silica covalent bonds are physically mixed or chemically linked.

8. A method for preparing the aging-resistant polypropylene composite material according to any one of claims 1 to 6, characterized in that: Includes the following steps: S1. First, place the polypropylene resin and polypropylene grafted maleic anhydride in a vacuum drying oven to dry them according to the proportion. Then, add oxidized polyethylene wax and composite anti-aging agent to the dried polypropylene resin and polypropylene grafted maleic anhydride according to the proportion, mix them evenly, and the mixed raw materials are obtained. S2. Preheat the twin-screw extruder. After preheating, add the mixture obtained in step one. The material that is evenly mixed by the extruder is fed into the granulator for granulation to obtain a long-lasting aging-resistant polypropylene composite material.

9. The method according to claim 8, characterized in that: The extrusion process parameters for step S2 are as follows: the block temperatures are set sequentially to 170–185℃, 180–195℃, 185–205℃, 190–210℃, 195–215℃, 200–220℃, and 200–220℃, and the screw speed is 300 rpm to 400 rpm.

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