A recycled pp composite material with both flame retardant and antibacterial properties and a preparation method thereof

Abstract

The application discloses a recycled PP composite material with both flame-retardant and antibacterial properties and a preparation method thereof, and relates to the technical field of recycled PP composite materials.The recycled PP composite material with both flame-retardant and antibacterial properties comprises the following raw materials in parts by weight: 60-75 parts of recycled polypropylene, 15-25 parts of modified magnesium hydroxide, 3-8 parts of modified chitosan, 2-5 parts of ethylene-vinyl acetate copolymer, 0.5-1.5 parts of silane coupling agent KH-550, 8-15 parts of ammonium polyphosphate, 0.3-0.8 parts of calcium stearate, 1-3 parts of nano titanium dioxide and 0.2-0.6 parts of tributyl citrate.The recycled PP composite material has the following advantages: the recycled PP is used as a base material, is environment-friendly and low in cost;the modified magnesium hydroxide and modified chitosan are compounded, so that the recycled PP composite material has both excellent flame-retardant and antibacterial properties;the preparation process is clear and controllable, the raw materials are compatible, the product has stable performance, and the recycled PP composite material has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of recycled PP composite material technology, specifically to a recycled PP composite material with both flame retardant and antibacterial properties and its preparation method. Background Technology

[0002] Polypropylene (PP), a general-purpose thermoplastic, boasts numerous advantages such as low density, excellent mechanical properties, ease of processing and molding, and low cost, leading to its widespread application in various fields including automotive manufacturing, electronics, building materials, and daily necessities packaging. However, with the continuous increase in the use of PP products, a large amount of waste PP products is generated. These waste products are difficult to degrade naturally, causing not only serious resource waste but also placing enormous pressure on the ecological environment. Therefore, recycling and reusing waste PP not only aligns with the sustainable development concept of resource recycling but also effectively alleviates the environmental burden, possessing significant economic and social value.

[0003] However, during the recycling process, the molecular chains of recycled PP are prone to breakage, leading to varying degrees of decline in the material's mechanical properties and thermal stability, thus limiting its application in high-end fields. Furthermore, traditional PP materials lack flame-retardant and antibacterial properties, further broadening its application limitations. In fields with high safety and hygiene requirements, such as electronics, building interiors, and medical devices, the material is highly flammable upon contact with an open flame, producing large amounts of toxic and harmful gases during combustion, potentially causing safety accidents. In addition, PP products are prone to the growth of bacteria, mold, and other microorganisms during use, which not only leads to product aging and deterioration but may also spread diseases, endangering human health.

[0004] Currently, while some flame-retardant or antibacterial PP materials exist on the market, most only possess a single flame-retardant or antibacterial function, making it difficult to simultaneously meet the comprehensive performance requirements of multiple scenarios. Furthermore, existing composite materials combining flame-retardant and antibacterial properties mostly use virgin PP as the base material, resulting in higher costs. Additionally, the dispersion of flame retardants and antibacterial agents within the base material is poor, easily leading to agglomeration and unstable overall material performance. Moreover, some flame retardants and antibacterial agents also have environmental issues, contradicting the modern trend of green and environmentally friendly materials development.

[0005] Therefore, developing a composite material with excellent flame retardant properties, antibacterial properties, good mechanical properties and environmental friendliness, based on recycled PP, while optimizing its preparation process and reducing production costs, has become an urgent technical challenge in the field of PP material recycling and reuse. This is of great significance for promoting the high-value utilization of recycled PP. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a recycled PP composite material with both flame-retardant and antibacterial properties and its preparation method, solving the problems of performance degradation, single-function limitations, poor filler dispersibility, insufficient environmental friendliness, and difficulty in high-value utilization of recycled PP.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A recycled PP composite material with both flame retardant and antibacterial properties comprises the following raw materials in parts by weight: 60-75 parts recycled polypropylene, 15-25 parts modified magnesium hydroxide, 3-8 parts modified chitosan, 2-5 parts ethylene-vinyl acetate copolymer, 0.5-1.5 parts silane coupling agent KH-550, 8-15 parts ammonium polyphosphate, 0.3-0.8 parts calcium stearate, 1-3 parts nano titanium dioxide, and 0.2-0.6 parts tributyl citrate.

[0008] Furthermore, the recycled polypropylene has a melt flow rate of 2-5 g / 10 min at 230℃ and 2.16 kg load to ensure processability and moldability. The ash content is ≤0.5 wt%, and impurities are removed by screening to reduce the interference of impurities on performance. The particle size is controlled at 2-5 mm to ensure uniform mixing and sufficient melt blending of raw materials, avoiding dispersion defects caused by uneven particle size, and synergistically improving the mechanical stability and processing consistency of the composite material.

[0009] Furthermore, the nano-titanium dioxide is anatase type, which endows it with highly efficient photocatalytic activity, with a particle size of 10-30 nm and a specific surface area of ​​50-80 m². 2 / g, enhancing the synergistic antibacterial effect with modified chitosan, rapidly generating active oxygen to kill microorganisms, while improving the thermal stability of the material, avoiding the impact of particle agglomeration on antibacterial efficiency and mechanical properties; the VA content of the ethylene-vinyl acetate copolymer is 15%-20%.

[0010] Furthermore, the modified magnesium hydroxide is prepared using the following specific steps: A1. Add magnesium hydroxide to a mixture of anhydrous ethanol and deionized water, and ultrasonically disperse for 30-40 min to obtain a suspension; add citric acid to the suspension, heat to 60-65℃, stir for 1.5-2 h, and adjust the pH of the system to 5.5-6.0 with 25% ammonia water; add silane coupling agent KH-570 dropwise, heat to 75-80℃, and maintain the temperature for 3-4 h with continuous stirring; after the reaction is completed, centrifuge, wash 3-4 times with anhydrous ethanol, and vacuum dry at 80-90℃ for 12 h to obtain the first modified magnesium hydroxide; The first modification involves esterification of citric acid with the hydroxyl groups on the surface of magnesium hydroxide to introduce carboxyl active groups. At the same time, the pH value is adjusted to create a suitable environment for the grafting of silane coupling agent KH-570. After the alkoxy groups of the silane coupling agent are hydrolyzed, they undergo condensation reactions with carboxyl and hydroxyl groups, grafting organic groups onto the surface of magnesium hydroxide, reducing surface polarity, improving compatibility with organic substrates, and breaking the tendency of agglomeration.

[0011] A2. Disperse the first-modified magnesium hydroxide in acetone and sonicate for 20 min to obtain a suspension. Add p-toluenesulfonic acid and heat to 55-60℃. Add the total amount of ammonium polyphosphate and pentaerythritol to the system in 3 batches and stir continuously for 4-5 h. After the reaction is completed, centrifuge and wash with acetone 2-3 times to remove unreacted monomers. Dry under vacuum at 100-110℃ for 10 h to obtain the second-modified magnesium hydroxide. The second modification uses p-toluenesulfonic acid as a catalyst to promote the esterification reaction of ammonium polyphosphate with pentaerythritol to form polyphosphate ester compounds. These compounds are attached to the surface of magnesium hydroxide after the first modification through chemical bonding or physical coating, forming a flame-retardant and synergistic layer. This enhances the synergistic effect with ammonium polyphosphate in the subsequent system and lays the foundation for improving the overall flame-retardant performance.

[0012] A3. Disperse the second modified magnesium hydroxide in anhydrous ethanol, heat to 70-75℃, purge with nitrogen for protection, add 10% sodium hydroxide solution to adjust the pH to 8.0-8.5 to activate the surface hydroxyl groups; then add 2,3-epoxypropyltrimethylammonium chloride dropwise, keep the reaction at this temperature for 3-3.5h, and continuously purge with nitrogen during the reaction; after the reaction is complete, centrifuge, wash with deionized water until neutral, and vacuum dry at 90-100℃ for 12h to obtain modified magnesium hydroxide.

[0013] The third modification involves activating the hydroxyl groups on the surface of magnesium hydroxide under alkaline conditions. The introduced 2,3-epoxypropyltrimethylammonium chloride undergoes a ring-opening reaction with the hydroxyl groups through epoxy groups, achieving the grafting of cationic groups. At the same time, it imparts a permanent positive charge to the surface of magnesium hydroxide, which helps to electrostatically adsorb with the phospholipid bilayer of bacterial membranes, synergistically improving antibacterial efficiency. This further optimizes the interfacial bonding force between magnesium hydroxide and non-polar PP substrate, while enhancing its dispersion stability in the system, ensuring the efficient performance of flame retardant function.

[0014] Furthermore, the ratio of magnesium hydroxide, anhydrous ethanol, deionized water, citric acid, and silane coupling agent KH-570 in A1 is 500g: 400-500ml: 5-6ml: 40-50g: 20-30ml.

[0015] Furthermore, the ratio of the first modified magnesium hydroxide, acetone, p-toluenesulfonic acid, ammonium polyphosphate, and pentaerythritol in A2 is 500g: 300-400ml: 2-4g: 75-100g: 25-35g.

[0016] Furthermore, the ratio of the second modified magnesium hydroxide, anhydrous ethanol, and 2,3-epoxypropyltrimethylammonium chloride in A3 is 500g: 250-300ml: 15-25g.

[0017] Furthermore, the modified chitosan is prepared using the following specific steps: B1. Add chitosan to isopropanol, sonicate for 15 min, add oxalic acid, heat to 50-55℃, and stir for 2 h; adjust the pH of the system to 10-11 with 30% sodium hydroxide solution, add 3-chloro-2-hydroxypropyltrimethylammonium chloride dropwise, heat to 65-70℃, and keep the temperature for 5-6 h; after the reaction is complete, adjust the pH to neutral with 2% dilute hydrochloric acid, centrifuge, wash 3 times with isopropanol, and vacuum dry at 60-70℃ for 15 h to obtain the first modified chitosan. In the first modification, oxalic acid first activates the chitosan molecular chain and breaks some hydrogen bonds. Under alkaline conditions, the epoxy group of 3-chloro-2-hydroxypropyltrimethylammonium chloride undergoes a ring-opening reaction with the hydroxyl and amino groups of chitosan to achieve quaternization modification, introduce cationic active groups, significantly improve the antibacterial activity of chitosan, and enhance its ability to destroy bacterial cell membranes.

[0018] B2. Dissolve the first-modified chitosan in deionized water and heat to 70-75℃; slowly add 85% phosphoric acid by mass, stir for 1 hour, then add urea, heat to 90-95℃, and keep warm for 3-4 hours; after the reaction is complete, cool to room temperature, adjust the pH to 7.0 with 25% ammonia water by mass, concentrate under reduced pressure until obvious stringing occurs when the system is stirred, and the reaction ends when there is no flow after stirring is stopped. Dry the product under vacuum at 80-90℃ to constant weight, pulverize and pass through an 80-mesh sieve to obtain the second-modified chitosan. The second modification involves phosphorylating chitosan with phosphoric acid to introduce phosphate groups. Then, with the help of the cross-linking effect of urea, the chitosan molecular chains are promoted to form a more stable three-dimensional network structure, which improves its thermal stability and antibacterial durability and avoids the decline of antibacterial performance due to structural damage during subsequent processing and use.

[0019] B3. Disperse the second modified chitosan in anhydrous ethanol and sonicate for 20 min. Add 1% hydrochloric acid solution to adjust the pH of the solution to 3.0-3.5 and stir for 10 min to activate the system. While stirring, slowly add methyltrimethoxysilane dropwise at a rate of 1-2 ml / min. Heat to 60-65℃ and stir for 4-5 h. After the reaction is complete, centrifuge and wash twice with anhydrous ethanol. Dry under vacuum at 70-80℃ for 12 h to obtain modified chitosan.

[0020] The third modification involves hydrolyzing methyltrimethoxysilane under acidic conditions to generate silanol groups. These silanol groups then undergo a condensation reaction with the hydroxyl groups on the surface of chitosan, achieving silanization modification. This forms an organosilicon layer on the chitosan surface, reducing surface polarity and improving compatibility and dispersion uniformity with the PP substrate. Simultaneously, it works synergistically with nano-titanium dioxide to further enhance the durability of the antibacterial effect.

[0021] Furthermore, the ratio of chitosan, isopropanol, oxalic acid, and 3-chloro-2-hydroxypropyltrimethylammonium chloride in B1 is 500g: 1500-1800ml: 30-40g: 100-120g.

[0022] Furthermore, the ratio of the first modified chitosan, deionized water, phosphoric acid, and urea in B2 is 500g: 800-1000ml: 80-100ml: 60-80g.

[0023] Furthermore, the ratio of the second modified chitosan, anhydrous ethanol, and methyltrimethoxysilane in B3 is 500g: 600-700ml: 40-60ml.

[0024] A method for preparing a recycled PP composite material with both flame-retardant and antibacterial properties includes the following steps: S1. Place the recycled polypropylene in a forced-air drying oven and dry it at 80-90℃ for 4-5 hours to remove surface oil and moisture; dry the modified magnesium hydroxide, modified chitosan, and nano titanium dioxide at 100℃ for 2 hours respectively, and set them aside for later use. S2. Take 60-75 parts of dried recycled polypropylene, 15-25 parts of modified magnesium hydroxide, 3-8 parts of modified chitosan, 2-5 parts of ethylene-vinyl acetate copolymer, 0.5-1.5 parts of silane coupling agent KH-550, 8-15 parts of ammonium polyphosphate, 0.3-0.8 parts of calcium stearate, 1-3 parts of nano titanium dioxide, and 0.2-0.6 parts of tributyl citrate and add them to a high-speed mixer. Set the speed to 800-1000 r / min, the mixing temperature to 60-70℃, and the mixing time to 15-20 min to obtain a uniform premix. S3. Add the premixed material to the twin-screw extruder and set the temperatures of each section of the extruder as follows: Zone 1 160-170℃, Zone 2 175-185℃, Zone 3 185-195℃, Zone 4 190-200℃, Die head temperature 180-190℃, screw speed 200-250 r / min, and vacuum degree -0.08MPa. After melt blending and extrusion, the material is processed into composite material particles by a water-cooled pelletizer. S4. Dry the composite material particles at 80℃ for 3 hours to remove moisture; use an injection molding machine for injection molding, with an injection temperature of 180-200℃, a mold temperature of 40-50℃, an injection pressure of 80-100MPa, a holding pressure of 50-60MPa, and a holding time of 10-15s, to obtain recycled PP composite material products with both flame retardant and antibacterial properties.

[0025] This invention provides a recycled PP composite material with both flame-retardant and antibacterial properties, and its preparation method, which has the following beneficial effects: 1. This invention uses recycled polypropylene as the base material, realizing the high-value reuse of waste PP resources. This alleviates the environmental pressure caused by waste plastics and reduces material production costs, aligning with the concept of green and sustainable development. Through rigorous screening and pretreatment of recycled PP, combined with reasonable raw material compatibility and optimized preparation processes, the invention effectively compensates for the mechanical property degradation caused by molecular chain breakage in recycled PP. This results in a composite material with excellent tensile strength, impact toughness, and processing fluidity, solving the problems of poor performance and limited applications of traditional recycled PP products. It broadens the application scenarios of recycled PP materials and can meet the basic performance requirements of various fields.

[0026] 2. The product utilizes the synergistic flame-retardant effect of modified magnesium hydroxide and ammonium polyphosphate to construct a highly efficient flame-retardant system, significantly improving the flame-retardant performance of the material. After multiple modification processes, the compatibility of the modified magnesium hydroxide with the substrate is greatly improved. During combustion, it rapidly decomposes, absorbs heat, and releases inert gases, inhibiting flame spread and blocking oxygen. Ammonium polyphosphate promotes char layer formation, further enhancing the flame-retardant effect, enabling the composite material to achieve an ideal flame-retardant rating. Furthermore, no toxic or harmful gases are released during combustion, overcoming the shortcomings of traditional flame-retardant materials such as poor environmental performance and low flame-retardant efficiency. This meets the application needs of fields with high requirements for flame-retardant safety, such as electronics, electrical appliances, and building interiors.

[0027] 3. This composite material possesses long-lasting and stable antibacterial properties through the synergistic antibacterial effects of modified chitosan and nano-titanium dioxide. Modified chitosan, through chemical modification, introduces active groups, significantly enhancing its antibacterial activity. It can disrupt bacterial cell membrane structures and inhibit microbial reproduction. Anatase nano-titanium dioxide generates reactive oxygen species under light, effectively killing various bacteria and molds. The synergistic effect of these two materials effectively inhibits microbial growth on the material surface, preventing product aging and deterioration due to bacterial contamination, while reducing the risk of disease transmission. This addresses the pain point of traditional PP materials being prone to bacterial growth, making it suitable for applications with strict hygiene requirements, such as medical devices and daily necessities packaging.

[0028] 4. This invention, through targeted modification of key functional components and the combination of auxiliary components such as silane coupling agent KH-550 and ethylene-vinyl acetate copolymer, significantly improves the dispersion uniformity and interfacial bonding of each component in the substrate, avoiding performance fluctuations caused by functional filler agglomeration. Simultaneously, the optimized preparation process is simple and parameters are controllable. From raw material drying, mixing, melt blending to injection molding, each step is carried out under mild conditions and is easily industrialized, ensuring the stability and consistency of product performance. Furthermore, all raw materials used in the product are environmentally friendly components, free of harmful additives, and the production process has low energy consumption, balancing performance, environmental protection, and industrial production requirements, thus possessing significant economic value and market competitiveness. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: Preparation of recycled PP composite material with both flame retardant and antibacterial properties. The specific preparation steps are as follows: S1. Place the recycled polypropylene in a forced-air drying oven and dry it at 80℃ for 4 hours to remove surface oil and moisture; dry the modified magnesium hydroxide, modified chitosan, and nano titanium dioxide at 100℃ for 2 hours respectively, and set aside for later use. S2. Take 60 parts of dried recycled polypropylene, 15 parts of modified magnesium hydroxide, 3 parts of modified chitosan, 2 parts of ethylene-vinyl acetate copolymer, 0.5 parts of silane coupling agent KH-550, 8 parts of ammonium polyphosphate, 0.3 parts of calcium stearate, 1 part of nano titanium dioxide, and 0.2 parts of tributyl citrate and add them to a high-speed mixer. Set the speed to 800 r / min, the mixing temperature to 60℃, and the mixing time to 15 min to obtain a uniform premix. S3. Add the premixed material to the twin-screw extruder and set the temperatures of each section of the extruder as follows: Zone 1 160℃, Zone 2 175℃, Zone 3 185℃, Zone 4 190℃, and the die head temperature 180℃. The screw speed is 200 r / min, and the vacuum degree is -0.08 MPa. After melt blending and extrusion, the material is processed into composite material particles by a water-cooled pelletizer. S4. Dry the composite material particles at 80℃ for 3 hours to remove moisture; use an injection molding machine to injection mold at an injection temperature of 180℃, a mold temperature of 40℃, an injection pressure of 80MPa, a holding pressure of 50MPa, and a holding time of 10s to obtain a recycled PP composite material product with both flame retardant and antibacterial properties.

[0031] Example 2: Preparation of recycled PP composite material with both flame retardant and antibacterial properties. The specific preparation steps are as follows: S1. Place the recycled polypropylene in a forced-air drying oven and dry it at 90℃ for 5 hours to remove surface oil and moisture; dry the modified magnesium hydroxide, modified chitosan, and nano titanium dioxide at 100℃ for 2 hours respectively, and set aside for later use. S2. Take 75 parts of dried recycled polypropylene, 25 parts of modified magnesium hydroxide, 8 parts of modified chitosan, 5 parts of ethylene-vinyl acetate copolymer, 1.5 parts of silane coupling agent KH-550, 15 parts of ammonium polyphosphate, 0.8 parts of calcium stearate, 3 parts of nano titanium dioxide, and 0.6 parts of tributyl citrate and add them to a high-speed mixer. Set the speed to 1000 r / min, the mixing temperature to 70℃, and the mixing time to 20 min to obtain a uniform premix. S3. Add the premixed material to the twin-screw extruder and set the temperatures of each section of the extruder as follows: Zone 1 170℃, Zone 2 185℃, Zone 3 195℃, Zone 4 200℃, and Die head temperature 190℃. The screw speed is 250 r / min, and the vacuum degree is -0.08 MPa. After melt blending and extrusion, the material is processed into composite material particles by a water-cooled pelletizer. S4. Dry the composite material particles at 80℃ for 3 hours to remove moisture; use an injection molding machine for injection molding at an injection temperature of 200℃, a mold temperature of 50℃, an injection pressure of 100MPa, a holding pressure of 60MPa, and a holding time of 15s to obtain a recycled PP composite material product with both flame retardant and antibacterial properties.

[0032] Example 3: Preparation of recycled PP composite material with both flame retardant and antibacterial properties. The specific preparation steps are as follows: S1. Place the recycled polypropylene in a forced-air drying oven and dry it at 85℃ for 4.5h to remove surface oil and moisture; dry the modified magnesium hydroxide, modified chitosan, and nano titanium dioxide at 100℃ for 2h respectively, and set aside for later use. S2. Take 67 parts of dried recycled polypropylene, 20 parts of modified magnesium hydroxide, 5 parts of modified chitosan, 3 parts of ethylene-vinyl acetate copolymer, 1 part of silane coupling agent KH-550, 11 parts of ammonium polyphosphate, 0.5 parts of calcium stearate, 2 parts of nano titanium dioxide, and 0.4 parts of tributyl citrate and add them to a high-speed mixer. Set the speed to 900 r / min, the mixing temperature to 65℃, and the mixing time to 17 min to obtain a uniform premix. S3. Add the premixed material to the twin-screw extruder and set the temperatures of each section of the extruder as follows: Zone 1 165℃, Zone 2 180℃, Zone 3 190℃, Zone 4 195℃, and the die head temperature 185℃. The screw speed is 225 r / min, and the vacuum degree is -0.08 MPa. After melt blending and extrusion, the material is processed into composite material particles by a water-cooled pelletizer. S4. Dry the composite material particles at 80℃ for 3 hours to remove moisture; use an injection molding machine for injection molding at an injection temperature of 190℃, a mold temperature of 45℃, an injection pressure of 90MPa, a holding pressure of 55MPa, and a holding time of 12s to obtain a recycled PP composite material product with both flame retardant and antibacterial properties.

[0033] Example 4: Preparation of modified magnesium hydroxide. The specific preparation steps are as follows: A1. Add 500g of magnesium hydroxide to a mixture of 400ml of anhydrous ethanol and 5ml of deionized water, and sonicate for 30min to obtain a suspension. Add 40g of citric acid to the suspension, heat to 60℃, stir for 1.5h, and adjust the pH of the system to 5.5 with 25% ammonia. Add 20ml of silane coupling agent KH-570, heat to 75℃, and keep the temperature for 3h while stirring continuously. After the reaction is complete, centrifuge, wash three times with anhydrous ethanol, and vacuum dry at 80℃ for 12h to obtain the first modified magnesium hydroxide. A2. Disperse 500g of first-modified magnesium hydroxide in 300ml of acetone, sonicate for 20min to obtain a suspension, add 2g of p-toluenesulfonic acid, and heat to 55℃; add a total of 75g of ammonium polyphosphate and 25g of pentaerythritol to the system in 3 batches, and stir continuously for 4h; after the reaction is completed, centrifuge, wash twice with acetone to remove unreacted monomers, and dry under vacuum at 100℃ for 10h to obtain second-modified magnesium hydroxide; A3. Disperse 500g of the second-modified magnesium hydroxide in 250ml of anhydrous ethanol, heat to 70℃, purge with nitrogen for protection, add 10% sodium hydroxide solution to adjust the pH to 8.0 to activate the surface hydroxyl groups; then add 15g of 2,3-epoxypropyltrimethylammonium chloride, keep the reaction at the temperature for 3h, and continuously purge with nitrogen during the reaction; after the reaction is completed, centrifuge, wash with deionized water until neutral, and vacuum dry at 90℃ for 12h to obtain modified magnesium hydroxide.

[0034] Example 5: Preparation of modified magnesium hydroxide. The specific preparation steps are as follows: A1. Add 500g of magnesium hydroxide to a mixture of 500ml of anhydrous ethanol and 6ml of deionized water, and sonicate for 40min to obtain a suspension. Add 50g of citric acid to the suspension, heat to 65℃, stir for 2h, and adjust the pH of the system to 6.0 with 25% ammonia. Add 30ml of silane coupling agent KH-570, heat to 80℃, and keep the temperature for 4h while stirring continuously. After the reaction is complete, centrifuge, wash 4 times with anhydrous ethanol, and vacuum dry at 90℃ for 12h to obtain the first modified magnesium hydroxide. A2. Disperse 500g of first-modified magnesium hydroxide in 400ml of acetone and sonicate for 20min to obtain a suspension. Add 4g of p-toluenesulfonic acid and heat to 60℃. Add 100g of ammonium polyphosphate and 35g of pentaerythritol to the system in three batches and stir continuously for 5h. After the reaction is completed, centrifuge and wash three times with acetone to remove unreacted monomers. Dry under vacuum at 110℃ for 10h to obtain second-modified magnesium hydroxide. A3. Disperse 500g of the second-modified magnesium hydroxide in 300ml of anhydrous ethanol, heat to 75℃, purge with nitrogen for protection, add 10% sodium hydroxide solution to adjust the pH to 8.5 to activate the surface hydroxyl groups; then add 25g of 2,3-epoxypropyltrimethylammonium chloride, keep the reaction at this temperature for 3.5h, and continuously purge with nitrogen during the reaction; after the reaction is completed, centrifuge, wash with deionized water until neutral, and dry under vacuum at 100℃ for 12h to obtain modified magnesium hydroxide.

[0035] Example 6: Preparation of modified chitosan. The specific preparation steps are as follows: B1. Add 500g of chitosan to 1500ml of isopropanol, sonicate for 15min, add 30g of oxalic acid, heat to 50℃, and stir for 2h. Adjust the pH of the system to 10 with 30% sodium hydroxide solution, add 100g of 3-chloro-2-hydroxypropyltrimethylammonium chloride, heat to 65℃, and keep the temperature for 5h. After the reaction, adjust the pH to neutral with 2% dilute hydrochloric acid, centrifuge, wash 3 times with isopropanol, and vacuum dry at 60℃ for 15h to obtain the first modified chitosan. B2. Dissolve 500g of the first-modified chitosan in 800ml of deionized water and heat to 70℃; slowly add 80ml of 85% phosphoric acid and stir for 1h; then add 60g of urea and heat to 90℃ for 3h; after the reaction is complete, cool to room temperature and adjust the pH to 7.0 with 25% ammonia; concentrate under reduced pressure until the system shows obvious stringing when stirred and no flowability after stirring is stopped; dry the product under vacuum at 80℃ to constant weight, pulverize and pass through an 80-mesh sieve to obtain the second-modified chitosan. B3. Disperse 500g of the second-modified chitosan in 600ml of anhydrous ethanol and sonicate for 20min. Add 1% hydrochloric acid solution to adjust the pH of the solution to 3.0 and stir for 10min to activate the system. While stirring, slowly add 40ml of methyltrimethoxysilane dropwise at a rate of 1ml / min. Heat to 60℃ and stir for 4h. After the reaction is complete, centrifuge, wash twice with anhydrous ethanol, and vacuum dry at 70℃ for 12h to obtain the modified chitosan.

[0036] Example 7: Preparation of modified chitosan. The specific preparation steps are as follows: B1. Add 500g of chitosan to 1800ml of isopropanol, sonicate for 15min, add 40g of oxalic acid, heat to 55℃, and stir for 2h. Adjust the pH of the system to 11 with 30% sodium hydroxide solution, add 120g of 3-chloro-2-hydroxypropyltrimethylammonium chloride, heat to 70℃, and keep the temperature for 6h. After the reaction is complete, adjust the pH to neutral with 2% dilute hydrochloric acid, centrifuge, wash 3 times with isopropanol, and vacuum dry at 70℃ for 15h to obtain the first modified chitosan. B2. Dissolve 500g of the first-modified chitosan in 1000ml of deionized water and heat to 75℃; slowly add 100ml of 85% phosphoric acid and stir for 1h; then add 80g of urea and heat to 95℃ for 4h; after the reaction is complete, cool to room temperature and adjust the pH to 7.0 with 25% ammonia; concentrate under reduced pressure until the system shows obvious stringing when stirred and no flowability after stirring is stopped; dry the product under vacuum at 90℃ to constant weight, pulverize and pass through an 80-mesh sieve to obtain the second-modified chitosan. B3. Disperse 500g of the second-modified chitosan in 700ml of anhydrous ethanol and sonicate for 20min. Add 1% hydrochloric acid solution to adjust the pH of the solution to 3.5 and stir for 10min to activate the system. While stirring, slowly add 60ml of methyltrimethoxysilane dropwise at a rate of 2ml / min. Heat to 65℃ and stir for 5h. After the reaction is complete, centrifuge, wash twice with anhydrous ethanol, and vacuum dry at 80℃ for 12h to obtain the modified chitosan.

[0037] Comparative Example 1: A recycled PP composite material with both flame-retardant and antibacterial properties was prepared. The specific preparation steps are as follows: The remaining steps remain unchanged, except that the modified magnesium hydroxide prepared in Example 4 used in Example 3 is replaced with unmodified magnesium hydroxide to prepare a recycled PP composite material with both flame retardant and antibacterial properties.

[0038] Comparative Example 2: A recycled PP composite material with both flame-retardant and antibacterial properties was prepared. The specific preparation steps are as follows: The remaining steps remain the same, except that the modified chitosan prepared in Example 7 and used in Example 3 is replaced with unmodified chitosan to prepare a recycled PP composite material with both flame retardant and antibacterial properties.

[0039] Comparative Example 3: A recycled PP composite material with both flame-retardant and antibacterial properties was prepared. The specific preparation steps are as follows: The remaining steps remain unchanged, except that the modified magnesium hydroxide prepared in Example 4 used in Example 3 is replaced with unmodified magnesium hydroxide, and the modified chitosan prepared in Example 7 is replaced with unmodified chitosan, so as to prepare a recycled PP composite material with both flame retardant and antibacterial properties.

[0040] Performance testing

[0041]

[0042] Performance test results showed that the recycled PP composite materials prepared in Examples 1-3 exhibited excellent comprehensive performance, with Example 3 showing the best performance. Its tensile strength reached 32.8 MPa, heat distortion temperature was 132℃, flame retardancy rating reached V-0, and antibacterial rates against Escherichia coli and Staphylococcus aureus reached 99.1% and 98.8% respectively after 24 hours. Examples 1 and 2 also possessed good tensile strength (28.5-30.2 MPa), flame retardancy (V-1 to V-0 rating), and antibacterial properties. The yield rate was 92.8%-96.2%; while Comparative Examples 1-3, which used unmodified magnesium hydroxide, unmodified chitosan, or neither, had significantly lower tensile strength (21.1-25.7 MPa), flame retardancy rating (below V-2 to V-1), antibacterial rate (82.9%-92.8%), and heat distortion temperature (112-120℃) than the examples, fully demonstrating that modified magnesium hydroxide and modified chitosan play a key role in improving the flame retardancy, antibacterial properties, and mechanical properties of the composite material.

[0043] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A recycled PP composite material with both flame-retardant and antibacterial properties, characterized in that: It contains the following raw materials in parts by weight: 60-75 parts recycled polypropylene, 15-25 parts modified magnesium hydroxide, 3-8 parts modified chitosan, 2-5 parts ethylene-vinyl acetate copolymer, 0.5-1.5 parts silane coupling agent KH-550, 8-15 parts ammonium polyphosphate, 0.3-0.8 parts calcium stearate, 1-3 parts nano titanium dioxide, and 0.2-0.6 parts tributyl citrate; The modified magnesium hydroxide is prepared using the following specific steps: A1. Add magnesium hydroxide to a mixture of anhydrous ethanol and deionized water, and ultrasonically disperse for 30-40 min to obtain a suspension; add citric acid to the suspension, heat to 60-65℃, stir for 1.5-2 h, and adjust the pH of the system to 5.5-6.0 with 25% ammonia water; add silane coupling agent KH-570 dropwise, heat to 75-80℃, and maintain the temperature for 3-4 h with continuous stirring; after the reaction is completed, centrifuge, wash 3-4 times with anhydrous ethanol, and vacuum dry at 80-90℃ for 12 h to obtain the first modified magnesium hydroxide; A2. Disperse the first-modified magnesium hydroxide in acetone and sonicate for 20 min to obtain a suspension. Add p-toluenesulfonic acid and heat to 55-60℃. Add the total amount of ammonium polyphosphate and pentaerythritol to the system in 3 batches and stir continuously for 4-5 h. After the reaction is completed, centrifuge and wash with acetone 2-3 times to remove unreacted monomers. Dry under vacuum at 100-110℃ for 10 h to obtain the second-modified magnesium hydroxide. A3. Disperse the second modified magnesium hydroxide in anhydrous ethanol, heat to 70-75℃, purge with nitrogen for protection, add 10% sodium hydroxide solution to adjust the pH to 8.0-8.5 to activate the surface hydroxyl groups; then add 2,3-epoxypropyltrimethylammonium chloride dropwise, keep the reaction at this temperature for 3-3.5 hours, and continuously purge with nitrogen during the reaction; after the reaction is complete, centrifuge, wash with deionized water until neutral, and vacuum dry at 90-100℃ for 12 hours to obtain modified magnesium hydroxide; The modified chitosan is prepared using the following specific steps: B1. Add chitosan to isopropanol, sonicate for 15 min, add oxalic acid, heat to 50-55℃, and stir for 2 h; adjust the pH of the system to 10-11 with 30% sodium hydroxide solution, add 3-chloro-2-hydroxypropyltrimethylammonium chloride dropwise, heat to 65-70℃, and keep the temperature for 5-6 h; after the reaction is complete, adjust the pH to neutral with 2% dilute hydrochloric acid, centrifuge, wash 3 times with isopropanol, and vacuum dry at 60-70℃ for 15 h to obtain the first modified chitosan. B2. Dissolve the first-modified chitosan in deionized water and heat to 70-75℃; slowly add 85% phosphoric acid by mass, stir for 1 hour, then add urea, heat to 90-95℃, and keep warm for 3-4 hours; after the reaction is complete, cool to room temperature, adjust the pH to 7.0 with 25% ammonia water by mass, concentrate under reduced pressure until obvious stringing occurs when the system is stirred, and the reaction ends when there is no flow after stirring is stopped. Dry the product under vacuum at 80-90℃ to constant weight, pulverize and pass through an 80-mesh sieve to obtain the second-modified chitosan. B3. Disperse the second modified chitosan in anhydrous ethanol and sonicate for 20 min. Add 1% hydrochloric acid solution to adjust the pH of the solution to 3.0-3.5 and stir for 10 min to activate the system. While stirring, slowly add methyltrimethoxysilane dropwise at a rate of 1-2 ml / min. Heat to 60-65℃ and stir for 4-5 h. After the reaction is complete, centrifuge and wash twice with anhydrous ethanol. Dry under vacuum at 70-80℃ for 12 h to obtain modified chitosan.

2. The recycled PP composite material with both flame-retardant and antibacterial properties according to claim 1, characterized in that: The recycled polypropylene was heated to 230°C, with a melt flow rate of 2-5 g / 10 min for 2.16 kg, an ash content of ≤0.5 wt%, and impurities were removed by screening, with a particle size controlled at 2-5 mm.

3. The recycled PP composite material with both flame-retardant and antibacterial properties according to claim 1, characterized in that: The nano-titanium dioxide is anatase type, with a particle size of 10-30 nm and a specific surface area of ​​50-80 m². 2 / g; the VA content of the ethylene-vinyl acetate copolymer is 15%-20%.

4. The recycled PP composite material with both flame-retardant and antibacterial properties according to claim 1, characterized in that: The ratio of magnesium hydroxide, anhydrous ethanol, deionized water, citric acid, and silane coupling agent KH-570 in A1 is 500g: 400-500ml: 5-6ml: 40-50g: 20-30ml; The ratio of the first modified magnesium hydroxide, acetone, p-toluenesulfonic acid, ammonium polyphosphate, and pentaerythritol in A2 is 500g: 300-400ml: 2-4g: 75-100g: 25-35g; The ratio of the second modified magnesium hydroxide, anhydrous ethanol, and 2,3-epoxypropyltrimethylammonium chloride in A3 is 500g: 250-300ml: 15-25g.

5. A recycled PP composite material with both flame-retardant and antibacterial properties according to claim 1, characterized in that: The ratio of chitosan, isopropanol, oxalic acid, and 3-chloro-2-hydroxypropyltrimethylammonium chloride in B1 is 500g: 1500-1800ml: 30-40g: 100-120g; The ratio of the first modified chitosan, deionized water, phosphoric acid, and urea in B2 is 500g: 800-1000ml: 80-100ml: 60-80g; The ratio of the second modified chitosan, anhydrous ethanol, and methyltrimethoxysilane in B3 is 500g: 600-700ml: 40-60ml.

6. A recycled PP composite material with both flame-retardant and antibacterial properties according to claim 1, characterized in that: The preparation method of this recycled PP composite material with both flame retardant and antibacterial properties specifically includes the following steps: S1. Place the recycled polypropylene in a forced-air drying oven and dry it at 80-90℃ for 4-5 hours to remove surface oil and moisture; dry the modified magnesium hydroxide, modified chitosan, and nano titanium dioxide at 100℃ for 2 hours respectively, and set them aside for later use. S2. Take 60-75 parts of dried recycled polypropylene, 15-25 parts of modified magnesium hydroxide, 3-8 parts of modified chitosan, 2-5 parts of ethylene-vinyl acetate copolymer, 0.5-1.5 parts of silane coupling agent KH-550, 8-15 parts of ammonium polyphosphate, 0.3-0.8 parts of calcium stearate, 1-3 parts of nano titanium dioxide, and 0.2-0.6 parts of tributyl citrate and add them to a high-speed mixer. Set the speed to 800-1000 r / min, the mixing temperature to 60-70℃, and the mixing time to 15-20 min to obtain a uniform premix. S3. Add the premixed material to the twin-screw extruder and set the temperatures of each section of the extruder as follows: Zone 1 160-170℃, Zone 2 175-185℃, Zone 3 185-195℃, Zone 4 190-200℃, Die head temperature 180-190℃, screw speed 200-250 r / min, and vacuum degree -0.08MPa. After melt blending and extrusion, the material is processed into composite material particles by a water-cooled pelletizer. S4. Dry the composite material particles at 80℃ for 3 hours to remove moisture; use an injection molding machine for injection molding, with an injection temperature of 180-200℃, a mold temperature of 40-50℃, an injection pressure of 80-100MPa, a holding pressure of 50-60MPa, and a holding time of 10-15s, to obtain recycled PP composite material products with both flame retardant and antibacterial properties.

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