Polypropylene composite material with antibacterial function and preparation method thereof

Abstract

The invention relates to the technical field of material science, and discloses a polypropylene composite material with an antibacterial function and a preparation method of the polypropylene composite material. 1-2 parts of silver ions; 0.5 to 2 parts of a toughening agent; 0.1 to 0.5 part of a lubricant; 0.5 to 1.5 parts of nano titanium dioxide; the preparation method comprises the following steps: mixing the components according to the mass ratio, and ensuring uniform dispersion through a high-shear mixing technology; then carrying out cooling water bath treatment and granulation; and finally, molding by using an injection molding process. Through an improved mixing process and introduction of silver ions and nano titanium dioxide, the antibacterial property of the material is remarkably improved, meanwhile, the mechanical property and biodegradability of the material are enhanced, and the method solves the problems that in the prior art, polypropylene is insufficient in antibacterial property, an additive is not uniform in dispersion and poor in long-term stability. The defect that the antibacterial efficiency is attenuated along with time is overcome through a double antibacterial mechanism, and a more durable and more efficient antibacterial effect is achieved.

Description

Technical Field

[0001] The present invention relates to the field of material science and technology, and in particular to a polypropylene composite material with antibacterial function and a preparation method thereof. Background Art

[0002] Polypropylene is a high-performance thermoplastic polyolefin material with excellent mechanical properties, chemical stability, biocompatibility, and processability. However, polypropylene itself lacks antimicrobial properties and is susceptible to bacterial growth, limiting its further adoption in applications requiring high hygiene and safety standards.

[0003] To address this issue, antimicrobial composite materials are typically prepared by introducing antimicrobial additives (such as silver ions, nano-zinc oxide, and nano-titanium dioxide) into a polypropylene matrix. However, in existing technologies, these inorganic antimicrobial components have poor dispersion in the non-polar polypropylene matrix and are prone to agglomeration, resulting in unstable antimicrobial effects.

[0004] In addition, commonly used physical blending methods, such as conventional low-shear mixing and single-speed stirring, are difficult to achieve uniform distribution of antibacterial components, especially for nano-scale particles, which are more prone to local enrichment or aggregation, thereby reducing the overall antibacterial efficiency and physical properties of the material.

[0005] Therefore, the present invention proposes a polypropylene composite material with antibacterial function and a preparation method thereof to address the deficiencies of the prior art. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the present invention provides a polypropylene composite material with antibacterial function and a preparation method thereof, which solves the problems of insufficient antibacterial performance of polypropylene, uneven dispersion of additives and poor long-term stability in the existing technology.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: a polypropylene composite material with antibacterial function, comprising the following components in parts by weight: 90-98 parts of polypropylene; 1-2 parts of silver ions; 0.5-2 parts of a toughening agent; 0.1-0.5 parts of a lubricant; and 0.5-1.5 parts of nano-titanium dioxide.

[0008] Polypropylene: Polypropylene (Polypropylene) is a petroleum-based thermoplastic with excellent mechanical properties, chemical resistance, high thermal stability, and good processing properties, making it suitable for a wide range of applications. Polypropylene also has good biocompatibility, low toxicity, and recyclability, making it considered an environmentally friendly material that meets the needs of modern sustainable development.

[0009] In this technology, polypropylene, as the base material, provides excellent mechanical properties and thermal stability, enabling the composite material to maintain strong impact resistance and structural stability in a variety of operating environments. Polypropylene's excellent processability allows it to be combined with other functional additives (such as antimicrobial ingredients and nanomaterials) to enhance the material's additional functions, such as antimicrobial, UV protection, and antistatic properties.

[0010] By optimizing and modifying the polypropylene substrate and adding suitable functional fillers or additives, the overall performance of its composite material can be significantly improved. In particular, in terms of improving the antibacterial function, the effective addition of antibacterial components such as nanosilver and nanozinc oxide can achieve a long-term and stable antibacterial effect.

[0011] Silver ions (Ag + ): Silver ions have a strong antibacterial effect, effectively inhibiting the growth of microorganisms such as bacteria and fungi, especially in aqueous solutions. Silver ions bind to microbial cell walls, inhibiting their metabolic activity and achieving this antibacterial effect. The mechanism of action of silver ions is that they react with sulfur amino acid groups and proteins in cells, disrupting the integrity of cell membranes, inhibiting DNA synthesis, and leading to cell death.

[0012] When silver ions are added to polypropylene-based composites, they are gradually released as the external environment changes, providing a sustained antimicrobial effect. Silver ion release typically occurs through surface diffusion or through degradation of the composite. This process helps provide long-term antimicrobial protection during the composite's use.

[0013] Toughening agent: Tougheners are a class of additives that increase the toughness of polymers. Common examples include rubber and thermoplastic elastomers. Through molecular chain interactions, they can reduce the brittleness of composite materials, making them more impact-resistant, resistant to crack propagation, and exhibiting improved processing properties.

[0014] Tougheners form an elastic phase within the polypropylene matrix, reducing the material's tendency to fracture under stress and improving its impact and fatigue resistance. Tougheners typically have flexible chain segments in their molecular structure, which absorb some of the energy under stress, thereby preventing brittle fracture in polypropylene. The addition of tougheners is key to improving the processability and durability of polypropylene.

[0015] Lubricant: Lubricants reduce the friction coefficient of polypropylene composites, reduce heat generation during processing, and improve processing fluidity. Common lubricants include fatty acids and metal soaps. These lubricants not only improve the material's processability but also enhance the surface smoothness and appearance.

[0016] Lubricants form a thin film between polypropylene molecules, reducing intermolecular friction, thereby reducing shear heat during processing and improving material flow and molding properties. The addition of lubricants can significantly reduce the internal friction of composite materials, helping to improve the precision and surface quality of products during the molding process.

[0017] Nano titanium dioxide: Nano-titanium dioxide, as a functional filler, possesses strong UV absorption, antioxidant, and antibacterial properties. Its surface can adsorb and degrade harmful substances, protecting composite materials from UV radiation damage and extending their service life. Furthermore, the addition of nano-TiO2 can enhance the mechanical properties and thermal stability of composite materials.

[0018] Nano-titanium dioxide has a large specific surface area and a highly active surface area, enabling strong interactions with the polypropylene matrix, improving the material's mechanical properties and weather resistance. Nano-TiO2's UV absorption and antibacterial properties enable it to play multiple roles in composite materials, enhancing both UV resistance and antibacterial properties. Its potent photocatalytic activity enables TiO2 to degrade certain harmful substances, further enhancing the material's durability and environmental performance.

[0019] Preferably, the silver ions are stabilized and coated by citric acid or active polyvinyl pyrrolidone ligands, and the particle size of the silver ions is in the range of 5-50 nm.

[0020] Citric acid, as a small molecule organic acid, can form a stable complex structure on the surface of silver ions. Its carboxyl group can bind to silver ions (Ag + ) to coordinate with silver ions, reducing the free energy of silver ions and enhancing their dispersibility in the polymer system. At the same time, the weakly acidic environment of citric acid can moderately control the release rate of silver ions, avoid their rapid migration or agglomeration in the material, and ensure the long-term stability of the antibacterial effect. In addition, polyvinylpyrrolidone (PVP) is a polymer stabilizer that contains pyrrolidone groups (C4H7NO), which can form coordination bonds with silver ions, improve their stability in the polypropylene matrix, and provide good water dispersibility, so that silver ions can be evenly embedded in the polypropylene matrix, avoiding the decline in local antibacterial effect caused by silver ion agglomeration.

[0021] Furthermore, since the particle size range of silver ions is controlled within 5-50nm, its specific surface area is significantly improved, which enhances the probability of contact with the cell wall of microorganisms, thereby effectively destroying the integrity of the bacterial cell membrane, leading to metabolic dysfunction and ultimate death of the bacteria. When silver nanoparticles are small in size, they can penetrate the bacterial cell membrane, interact with the protein and DNA of the bacteria, and interfere with their replication and metabolic processes. At the same time, silver ions can be continuously released on the surface of the material and bind to the sulfhydryl (-SH) groups in the bacterial cells, causing protein denaturation and inactivation, thereby exerting a long-term antibacterial effect. In addition, due to the small particle size, the surface plasmon resonance effect of silver ions is enhanced, which can effectively absorb and reflect ultraviolet light, further enhancing the antibacterial activity under light conditions, while avoiding the problem of traditional antibacterial agents becoming ineffective due to light decomposition.

[0022] Preferably, the toughening agent is polycaprolactone or low molecular weight polyurethane.

[0023] Polycaprolactone (PCL): Polycaprolactone (PCL) is a polymer with excellent flexibility and a low glass transition temperature (Tg), which allows it to maintain a certain degree of flexibility and plasticity even at low temperatures. PCL is a linear polymer with a long molecular chain and a certain degree of flexibility. When added to polypropylene, it can effectively improve the impact toughness and crack resistance of the composite material. The addition of PCL as a toughening agent not only improves the flexibility of polypropylene, but also enhances its processability.

[0024] The flexible molecular chains of polycaprolactone act as stress dispersers within the polypropylene matrix. When the composite is subjected to external forces, the PCL molecular chains effectively absorb and disperse the external stress, thereby slowing the material's fracture and crack propagation. PCL's low glass transition temperature allows it to maintain excellent flexibility at both room and low temperatures, resulting in the composite material exhibiting strong impact resistance in a variety of environments. Furthermore, PCL exhibits good compatibility with polypropylene, effectively enhancing the composite's overall mechanical properties.

[0025] Low molecular weight polyurethane (PU): Low-molecular-weight polyurethane (PU) is a highly flexible and tunable polymer compound commonly used as a toughening agent, adhesive, and sealant in a variety of materials. Low-molecular-weight PU can provide composite materials with improved elasticity and tensile properties, thereby improving the toughness of the material. Through the structural design of its soft and hard segments, PU can create distinct mechanical response regions within the composite material, further enhancing the material's impact toughness and ductility.

[0026] When used as a toughening agent, low-molecular-weight polyurethane (PU) typically enhances the toughness of composite materials through the interaction between its soft and hard segments. The soft segment, typically composed of flexible polyether or polyester components, absorbs and stores strain energy under external forces, while the hard segment provides strength and rigidity. When added to a polypropylene matrix, the soft segment effectively disperses stress, reduces crack propagation, and improves the material's impact resistance. Furthermore, PU exhibits good compatibility within the polypropylene matrix, resulting in a relatively stable toughening effect.

[0027] Combined toughening effect of polycaprolactone and low molecular weight polyurethane: In practical applications, the combined use of PCL and PU can achieve a more outstanding toughening effect. Working synergistically through different mechanisms, the two can significantly improve the material's impact toughness and ductility while maintaining its overall strength. PCL's low glass transition temperature maintains the material's flexibility in low-temperature environments, while PU's soft and hard segment structure provides the material with a wider range of mechanical adjustment. By properly proportioning PCL and PU, the composite material can maintain excellent mechanical properties while meeting the toughness requirements of different application scenarios.

[0028] The combined effect of PCL and PU significantly enhances the toughness of the composite. PCL improves the material's fracture toughness, while the addition of PU further enhances its impact and fatigue resistance. This synergistic effect allows the composite to better disperse and absorb energy when subjected to external impact, reducing the occurrence of brittle fracture and improving its overall crack resistance and ductility.

[0029] Preferably, the nano-titanium dioxide is subjected to surface modification treatment, wherein the treatment includes hydrophilic or lipophilic modification to enhance its dispersibility in the polypropylene matrix and utilize photocatalysis to improve the antibacterial properties of the material.

[0030] Nano-titanium dioxide (TiO2) is prone to agglomeration in a polymer matrix due to its strong surface energy, affecting its uniform dispersion and final performance. Its surface chemical properties can be regulated and controlled by hydrophilic or lipophilic modification, thereby improving its compatibility in a polypropylene matrix. For example, lipophilic modification is performed by a silane coupling agent (such as γ-aminopropyltriethoxysilane, KH550), making it easier for nano-TiO2 to interact with polypropylene molecules, thereby improving its uniform dispersion in the matrix and thus enhancing the mechanical properties and stability of the material. Hydrophilic modification, such as treatment with polyacrylic acid or polyethylene glycol (PEG), can increase the dispersibility of TiO2 in aqueous systems and improve its processing adaptability under specific environments. In addition, the photocatalytic antibacterial effect of nano-TiO2 comes from its electronic transition process under ultraviolet light irradiation, that is, after TiO2 absorbs ultraviolet light (wavelength <385nm), its valence band electrons (e- ) jumps to the conduction band, and a hole (h + These photogenerated carriers can react with water or oxygen to generate hydroxyl radicals (·OH) and superoxide anion radicals (O2 - ), these active substances can destroy bacterial cell membranes, proteins, and nucleic acid structures, thereby achieving a strong antibacterial effect. After appropriate surface modification, the photocatalytic efficiency of TiO2 can be further improved, while reducing the interfacial instability between it and the matrix polymer, ensuring the long-term antibacterial performance.

[0031] Preferably, the purity of the polypropylene is 98%-99.5%.

[0032] The purity of polypropylene directly impacts the integrity of its molecular structure and performance. High-purity polypropylene minimizes impurities during the polymerization process, thereby reducing defects and inhomogeneities within the molecular chain and improving the material's mechanical and processing properties. In composite materials, high-purity polypropylene exhibits improved transparency, reduced brittleness, higher tensile strength, and better ductility, thereby ensuring the mechanical properties of the final composite.

[0033] High-purity polypropylene has more uniform and regular molecular chains, free of impurities, resulting in stronger interactions between polypropylene molecules, thus improving its overall mechanical properties. Polypropylene with lower purity may contain more short chains or impurities, which can affect the interactions between molecular chains, leading to increased brittleness and reduced strength. High-purity polypropylene, on the other hand, has longer and more stable molecular chains, which help improve the tensile strength, impact resistance, and ductility of the composite material, allowing it to withstand greater external forces in actual use without breaking.

[0034] The present invention also provides a method for preparing a polypropylene composite material with antibacterial function, comprising the following steps: S1. Mixing polypropylene, silver ions, toughening agent, lubricant and nano-titanium dioxide according to mass fractions to provide uniform initial raw material distribution for subsequent high shear mixing; During this stage, polypropylene, silver ions, toughening agents, lubricants, and nano-titanium dioxide are preliminarily mixed in the specified mass fractions. This step ensures uniform distribution of each component within the composite, laying the foundation for subsequent high-shear mixing. This preliminary mixing ensures that each additive is uniformly distributed throughout the composite, preventing the aggregation or uneven distribution of certain components, which could affect the overall performance of the material.

[0035] During the initial mixing stage, by mixing the different components in a certain mass ratio, mechanical action allows for initial contact and dispersion of the components. However, this stage of mixing primarily serves to establish the foundation for subsequent high-shear mixing. Because different substances (such as polypropylene, toughening agents, and silver ions) exist in the composite material, each with its own molecular structure and compatibility, initial mixing can effectively reduce the formation of large particles, providing a preliminarily uniform system for high-shear mixing and avoiding uneven particle distribution.

[0036] S2, using high shear mixing technology to evenly disperse the mixture in S1, so that the mixture has good fluidity and uniform antibacterial properties during the injection molding process; At this stage, the mixture in S1 is further processed using high-shear mixing technology. High-shear mixing, through intense shear forces in a relatively short period of time, allows for a more uniform dispersion of the various components. This is particularly crucial for the dispersion of tiny particles such as nano-titanium dioxide and silver ions. High-shear mixing refines each component of the composite material, allowing them to better perform their respective functions within the composite.

[0037] High shear mixing technology breaks the interfacial tension between different substances by applying high-speed rotating mechanical force, so that a small, uniform particle distribution is formed between the components. Especially in the processing of nano-scale materials (such as nano-titanium dioxide), high shear mixing can effectively disperse nanoparticles in the polypropylene matrix, avoiding the agglomeration of particles, thereby enhancing the mechanical properties, UV resistance and antibacterial properties of the material. In addition, high shear mixing can also help silver ions to be evenly dispersed, thereby providing a uniform antibacterial effect during subsequent use. In this process, toughening agents and lubricants are also evenly dispersed, which helps to improve the toughness and processing properties of the composite material.

[0038] S3, controlling the temperature of the mixture obtained in S2 to 25° C.-30° C. by a cooling water bath to form granules, and granulating the mixture obtained in S2 using a pelletizing process to obtain uniform granules; The temperature of the molten composite material obtained by S2 is controlled at 25°C-30°C by a cooling water bath, so that it is gradually solidified and forms particles. At the same time, the cooled material is granulated by a pelletizing process to obtain uniform pellets. In this process, the role of the cooling water bath is to quickly reduce the temperature of the material, prevent excessive oxidative degradation, ensure the stability of polypropylene, and inhibit the decrease in antibacterial ability of silver ions due to high-temperature volatilization. The pelletizing process ensures that the obtained particles have uniform morphology and moderate particle size, so that they have good fluidity and processing performance during subsequent injection molding. At the same time, a reasonable cooling rate (avoiding too fast or too slow) can optimize the crystallinity of the material, thereby improving the mechanical properties and heat resistance of the polypropylene composite material.

[0039] S4. Molding the particles obtained in S3 using an injection molding process.

[0040] The particles obtained from S3 are formed using an injection molding process. During this process, the polypropylene composite material is plasticized and injected into the mold cavity using steps such as heating and plasticization, pressure injection, and mold cooling to form a product of the desired shape. The appropriate injection temperature can ensure that the polypropylene matrix is ​​fully melted, while avoiding thermal degradation caused by excessive temperature, ensuring that the antibacterial properties of silver ions and nano-titanium dioxide are not damaged. Reasonable control of the injection speed can avoid filler segregation and improve the uniformity of the product, while the adjustment of the cooling rate directly affects the crystallization behavior of the product, thereby optimizing the rigidity, toughness and balanced shrinkage rate of the material, and ultimately preparing a high-performance polypropylene composite material with a stable antibacterial effect.

[0041] Preferably, the equipment used for mixing in step S1 is a high-speed mixer, and a multi-stage variable speed stirring mode is adopted during the mixing process of the high-speed mixer, the speed range of which is set to 500-1500 rpm, and the stirring time is controlled to be 3-10 minutes.

[0042] In step S1, a high-speed mixer is used for mixing, and a multi-stage variable speed stirring mode is adopted during the mixing process. The speed range is set to 500-1500 rpm, and the stirring time is controlled to be 3-10 minutes. The purpose of this step is to ensure that the polypropylene, silver ions, toughening agent, lubricant, and nano-titanium dioxide are evenly distributed before entering the high-shear mixing, avoid filler agglomeration or delamination, and improve the stability of subsequent processing.

[0043] High-speed mixers use multi-stage variable-speed mixing to apply varying shear forces at different stages, achieving high uniformity of powdered or granular components in a short period of time. At low speeds of 500-800 rpm, the mixer provides relatively gentle stirring, allowing lighter fillers (such as silver ions and nano-titanium dioxide) to gradually come into contact with the polypropylene, reducing the possibility of filler agglomeration. When the speed is increased to 1000-1500 rpm, the high-speed rotating blades or paddles exert stronger shear and centrifugal forces on the material, ensuring uniform dispersion of the filler in the matrix and preventing stratification due to particle size differences.

[0044] Furthermore, controlling the mixing time (3-10 minutes) is crucial for ensuring uniformity. Too short a mixing time can lead to uneven filler distribution, impacting the material's subsequent fluidity and antimicrobial properties. Too long a mixing time can cause localized temperature rise, leading to surface adhesion of the material particles and compromising the processing properties of the final product. Properly controlling the mixing time ensures that the material achieves the desired dispersion within an appropriate timeframe while preventing material degradation or filler agglomeration.

[0045] Preferably, the equipment used in the high shear mixing technology is a twin-screw extruder, the screw speed of which is controlled at 50-120 rpm, the shear pressure is controlled at 15-30 MPa, and the temperature gradient is controlled at 170-210°C.

[0046] In high-shear mixing technology, a twin-screw extruder is used as the core equipment, with screw speed controlled at 50-120 rpm, shear pressure at 15-30 MPa, and a temperature gradient set at 170-210°C. The purpose of this step is to further evenly disperse the materials initially mixed in the S1 stage through high-temperature melting and high shear forces, ensuring that functional fillers such as silver ions and nano-titanium dioxide are evenly and stably distributed in the polypropylene matrix, thereby improving the material's fluidity and antibacterial properties.

[0047] The twin-screw extruder can break the agglomeration of fillers while melting polypropylene, promoting the uniform dispersion of fillers such as silver ions and nano-titanium dioxide in the matrix. When the screw speed is set at 50-120rpm, the low-speed zone (50-80rpm) is mainly used for the initial plasticization of the material, ensuring that the material can melt and flow before entering the high-shear zone, while in the medium-high speed zone (80-120rpm), the filler is further dispersed through high shear action, so that the overall uniformity of the material is improved. If the screw speed is too low, the filler will not be fully dispersed, affecting the antibacterial effect; if the speed is too high, it may cause excessive shearing of the molten material, causing the molecular chain to degrade, affecting the mechanical properties of the final product.

[0048] The setting of shear pressure (15-30MPa) is crucial in this process. When the shear pressure is 15-20MPa, the material is mainly conveyed by the screw, forming a molten fluid inside the extruder, but the filler may still have slight agglomeration. When the shear pressure is increased to 20-30MPa, the high pressure can promote a more stable and uniform dispersion of the filler in the matrix while avoiding the generation of microscopic defects. If the pressure is lower than 15MPa, the filler cannot be fully dispersed. Excessive pressure (over 30MPa) may lead to reduced material fluidity and even performance degradation due to excessive shear.

[0049] The temperature gradient (170-210°C) is set to optimize the melting and mixing state of the materials in different processing areas. In the front section (170-180°C), the temperature is relatively low, which is mainly used for the initial plasticization of polypropylene to prevent silver ions or nano-titanium dioxide from being prematurely exposed to high temperatures and agglomerating. In the middle section (180-195°C), the temperature is increased, which is mainly used for high-shear mixing to ensure that the filler is fully dispersed, the material flows evenly, and the processing stability is improved. In the back section (195-210°C), the temperature is appropriately increased to reduce the viscosity of the material, improve the fluidity, and facilitate extrusion and granulation. If the temperature is lower than 170°C, polypropylene may not be fully melted, affecting the uniformity of the material; and if it exceeds 210°C, it may cause material degradation and affect the finality of the product.

[0050] Preferably, the equipment used in the pelletizing process is a pelletizer, the cutter speed of which is set at 500-3000 rpm, the feed speed is controlled at 2-10 m / min, and the pelletizing length ranges from 0.5 to 5 mm.

[0051] During this process, the pelletizer's cutter speed (500-3000 rpm) directly affects the morphology and uniformity of the pellets. A higher cutter speed (approximately 3000 rpm) improves cutting efficiency and is suitable for high-speed production of high-viscosity materials while ensuring uniform pellet size. A lower speed (around 500 rpm) is suitable for low-speed extrusion to prevent degradation of heat-sensitive materials such as polypropylene due to excessive frictional heat. Therefore, the cutter speed setting needs to be adjusted according to specific production needs to ensure pelletizing efficiency while preventing thermal degradation of the material, which could lead to a decrease in antibacterial properties.

[0052] Controlling the feed rate (2-10m / min) is closely related to the extrusion speed. Feeding too fast may lead to uneven pelletizing or blockage, while feeding too slowly may cause material accumulation or irregular pellet shapes. A reasonable feed rate not only ensures the continuous stability of the pelletizing process, but also matches the discharge rate of the extrusion section, maintaining appropriate tension during cutting, reducing the generation of irregular pellets, and improving the fluidity of the pellets, making them more suitable for subsequent injection molding.

[0053] The pellet length range (0.5-5mm) determines the final pellet specifications. Generally, shorter pellets (0.5-2mm) have better flowability and are suitable for high-precision injection molding, while longer pellets (3-5mm) are suitable for general plastic molding processes such as extrusion or blow molding. In this solution, by properly controlling the pellet length, the pellets can ensure stable melting behavior and rheological properties during the subsequent injection molding process, reducing problems such as filler sedimentation or uneven flow, thereby optimizing the quality of the molded product.

[0054] Preferably, the equipment used in the injection molding process is an injection molding machine, the injection temperature of the injection molding machine is 185°C-200°C, the injection speed is 30mm / s-50mm / s, and the cooling rate is 0.5°C / s-1.0°C / s.

[0055] Injection molding is an efficient and precise molding method suitable for the large-scale production of thermoplastic composite products. In this technical solution, the composite material, after undergoing a twin-screw extruder and high-shear mixing process, is heated to an appropriate temperature within the injection molding machine. It is then injected into the mold under high pressure and solidified under certain cooling conditions. Properly setting injection molding process parameters can effectively ensure the dimensional accuracy, surface quality, and mechanical properties of the product.

[0056] The core principle of injection molding is to utilize the meltability of thermoplastic materials. Through heating, pressurizing, and cooling, the material solidifies in the mold and forms the desired shape. During this process, controlling temperature, injection speed, and cooling rate are critical factors in ensuring product quality. Appropriate process parameters ensure uniform material flow in the mold, avoiding defects such as shrinkage cavities, deformation, and bubbles, while maximizing the material's physical and functional properties.

[0057] Control of injection temperature (185℃-200℃): In this solution, the injection molding machine's injection temperature is set between 185°C and 200°C. This temperature range is optimized based on the melting characteristics of polypropylene and the processing requirements of the composite material. Temperatures that are too low may result in insufficient material fluidity, incomplete filling, and the formation of cold spots or weld marks. Temperatures that are too high may cause material degradation or decomposition, affecting the quality of the final product.

[0058] Within the 185°C-200°C temperature range, the polypropylene matrix fully melts and maintains good fluidity, ensuring the material can smoothly fill the mold. This temperature range also effectively prevents material degradation, ensuring that antimicrobial components (such as silver ions) and functional fillers (such as nano-titanium dioxide) do not thermally degrade, thereby maintaining the material's antimicrobial properties and mechanical stability. Proper temperature control ensures uniform flow of the composite material in the molten state and maintains excellent overall performance after molding.

[0059] Influence of injection speed (30mm / s-50mm / s): The injection speed is set between 30mm / s and 50mm / s to ensure that the material fills the mold quickly during the injection process and to avoid defects caused by excessively high or low speeds. Too low an injection speed may result in incomplete material filling, forming weld lines or surface defects; while too high a speed may cause excessive shear heat, increasing the risk of material degradation and easily causing defects such as flash or bubbles.

[0060] Proper injection speed control optimizes material fluidity, ensuring uniform filling of the mold cavity and minimizing weld mark formation. Within the 30mm / s-50mm / s range, the material rapidly fills the mold while avoiding thermal degradation and uneven flow caused by excessive shear forces. Furthermore, this speed range effectively minimizes the agglomeration of silver ions and nano-titanium dioxide, ensuring uniform distribution of the antimicrobial agent throughout the material and enhancing the antimicrobial efficacy and mechanical properties of the final product.

[0061] Optimization of cooling rate (0.5℃ / s-1.0℃ / s): The cooling rate is set between 0.5°C / s and 1.0°C / s to ensure rapid solidification while reducing internal stress and shrinkage. A cooling rate that is too fast may result in significant residual stress within the material, affecting the dimensional stability and mechanical properties of the product. A cooling rate that is too slow may lead to uneven cooling, resulting in warping or deformation.

[0062] The cooling rate directly affects the crystallization behavior and internal stress release of the material. For the polypropylene matrix, an appropriate cooling rate can avoid its low crystallinity and ensure that the material has good mechanical strength and heat resistance. Within the cooling range of 0.5℃ / s-1.0℃ / s, the material can gradually solidify and effectively reduce warping deformation and internal defects after molding. In addition, a reasonable cooling rate helps to maintain the uniform distribution of silver ions and nano-titanium dioxide, preventing them from migrating or aggregating during the cooling process, thereby maintaining the antibacterial and optical properties of the material.

[0063] The present invention provides a polypropylene composite material with antibacterial function and a preparation method thereof. It has the following beneficial effects: 1. The present invention adopts a technical solution of synergistic modification of silver ions and nano-titanium dioxide. Through the stabilization and coating of silver ions and the photocatalytic effect of nano-titanium dioxide, the antibacterial properties of the composite material are effectively improved. Compared with the existing solutions of using only metal ions or nanofillers, which easily lead to the problem of short-lasting antibacterial effect or poor dispersibility, the dual antibacterial mechanism of the present invention solves the problem of antibacterial efficacy decaying over time, and achieves a more lasting and efficient antibacterial effect.

[0064] 2. This invention ensures the long-term stability of the composite material's mechanical properties and antimicrobial efficacy by optimizing the use of high-purity polypropylene. High-purity polypropylene reduces the interference of impurities on silver ion release, improving the composite material's durability and sustained antimicrobial efficacy. Compared to existing solutions using low-purity polypropylene, which can lead to unstable mechanical properties and weakened antimicrobial efficacy, this invention effectively addresses these issues, significantly enhancing the composite material's practicality and reliability.

[0065] 3. This invention utilizes multi-stage variable-speed stirring technology to evenly disperse all components at varying speeds, resulting in a more stable material mixing effect. Compared to existing single-speed stirring solutions, this technology significantly improves the dispersion of the antimicrobial material, ensuring the uniformity of each molecular component, and significantly enhancing the antimicrobial performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 It is a flow chart of the preparation method of the present invention. DETAILED DESCRIPTION

[0067] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the present specification. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0068] See also Figure 1 , Example 1: Component ratio (parts by mass): 90 parts of polypropylene, with a purity of 98%; 1 part of silver ion; 0.5 part of toughening agent; 0.1 part of lubricant; and 0.5 part of nano titanium dioxide.

[0069] Specific preparation steps: Weighing of raw materials: Take each component according to the above ratio to ensure the ratio is accurate.

[0070] Mixing: Add all ingredients to a high-speed mixer, initially at 550 rpm, and continue stirring for 4 minutes. Then increase the speed to 1450 rpm and continue stirring for 9 minutes to ensure uniform dispersion.

[0071] High-shear melt blending: The uniformly mixed materials are fed into a twin-screw extruder with a screw speed of 55 rpm, a shear pressure of 17 MPa, and a processing temperature of 170°C (feeding zone) → 185°C (melting zone) → 200°C (homogenization zone) → 195°C (extrusion zone). This process ensures uniform dispersion of the filler while preventing degradation of the polypropylene.

[0072] Cooling and Granulation: The extruded melt is cooled in a 25°C water bath, rapidly solidifying before entering a pelletizer. The cutter speed is set at 1200 rpm, the feed rate is 6 m / min, and the pellet size is approximately 1.8 mm, ensuring uniform pellet morphology for subsequent processing.

[0073] Injection Molding: The pellets are fed into an injection molding machine for molding. The injection temperature is set at 190°C, the injection speed is 35 mm / s, and the cooling rate is 0.5°C / s. The final product has a smooth surface, stable dimensions, and no traces of silver ion precipitation.

[0074] Example 2: Component ratio (parts by mass): 98 parts of polypropylene, with a purity of 99.5%; 2 parts of silver ions; 2 parts of toughening agent; 0.5 parts of lubricant; and 1.5 parts of nano titanium dioxide.

[0075] Specific preparation steps: Weighing of raw materials: Take each component according to the above ratio to ensure the ratio is accurate.

[0076] Mixing: Add all ingredients to a high-speed mixer and mix at 800 rpm for 6 minutes, then at 1500 rpm for 2 minutes to ensure uniform dispersion.

[0077] High-shear melt blending: The uniformly mixed materials are fed into a twin-screw extruder with a screw speed of 55 rpm, a shear pressure of 17 MPa, and a processing temperature of 170°C (feeding zone) → 185°C (melting zone) → 200°C (homogenization zone) → 195°C (extrusion zone). This process ensures uniform dispersion of the filler while preventing degradation of the polypropylene.

[0078] Cooling and Granulation: The extruded melt is cooled in a 25°C water bath, rapidly solidifying before entering a pelletizer. The cutter speed is set at 1200 rpm, the feed rate is 6 m / min, and the pellet size is approximately 1.8 mm, ensuring uniform pellet morphology for subsequent processing.

[0079] Injection Molding: The pellets are fed into an injection molding machine for molding. The injection temperature is set at 190°C, the injection speed is 35 mm / s, and the cooling rate is 0.5°C / s. The final product has a smooth surface, stable dimensions, and no traces of silver ion precipitation.

[0080] Example 3: Component ratio (mass parts): polypropylene: 94 parts, purity 99%; silver ion: 1.5 parts Toughener (polycaprolactone): 2 parts; Lubricant (polyethylene wax): 0.3 parts; Nano titanium dioxide: 2 parts.

[0081] Specific preparation steps: Raw material weighing: Weigh each component strictly according to the ratio to ensure that the proportion of each component is accurate and correct to avoid affecting the material performance in subsequent steps.

[0082] Mixing: Add all ingredients to a high-speed mixer and initially set the speed to 600 rpm. Mix for 5 minutes to ensure a roughly even distribution of all ingredients. Then increase the speed to 1450 rpm and continue mixing for 4 minutes to enhance homogeneity.

[0083] High-shear melt blending: The uniformly mixed materials are fed into a twin-screw extruder with a screw speed of 60 rpm, a shear pressure of 20 MPa, and processing temperatures ranging from 175°C (feed zone) to 200°C (extrusion zone). This step ensures uniform dispersion of all fillers in the polypropylene matrix while preventing polypropylene degradation.

[0084] Cooling and Granulation: The extruded melt is cooled in a 28°C water bath to rapidly solidify. The solidified material is then fed into a pelletizer with a blade speed set at 1300 rpm and a feed rate of 6 m / min. The pellets are cut to a size of approximately 2 mm, ensuring uniform pellets suitable for subsequent processing.

[0085] Injection molding: After drying, the pellets are fed into the injection molding machine for molding. The injection temperature is set at 200°C, the injection speed is 40mm / s, and the cooling rate is set at 0.7°C / s to ensure that the final product has good dimensional stability and a smooth surface.

[0086] Example 4: Component ratio (parts by mass): polypropylene: 92 parts, purity 99%; silver ion: 1 part; toughening agent (polyurethane): 3 parts; lubricant (polyethylene wax): 0.5 parts; nano titanium dioxide: 3.5 parts.

[0087] Specific preparation steps: Raw material weighing: Accurately weigh each component according to the ratio to ensure the accuracy of the ratio and avoid affecting the performance of the product due to inappropriate ratio.

[0088] Mixing: Place all components in a mixer, set the initial speed to 500 rpm, and stir for 6 minutes to ensure basic uniformity of the material. Then increase the speed to 1400 rpm and stir for 4 minutes to ensure that the toughening agent and antimicrobial ingredients are completely dispersed.

[0089] High shear melt blending: The mixed materials enter the twin-screw extruder, the screw speed is set to 65 rpm, the shear pressure is 22 MPa, and the temperature gradient is set from 170 ° C (feeding zone) to 200 ° C (extrusion zone) to ensure the uniformity of the material and avoid polypropylene degradation.

[0090] Cooling and Granulation: The extruded melt is cooled in a 27°C water bath to rapidly solidify. The solidified material is then fed into a pelletizer with a blade speed of 1300 rpm and a feed rate of 6 m / min. The pellet size is approximately 2.2 mm.

[0091] Injection molding: After the pellets are dried, they are fed into the injection molding machine for molding. The injection temperature is set at 195°C, the injection speed is 38mm / s, and the cooling rate is controlled at 0.6°C / s to ensure that the final product has a smooth surface, stable dimensions, and no silver ion precipitation.

[0092] Example 5: Component ratio (parts by mass): polypropylene: 95 parts, purity 98%; silver ion: 1 part; toughening agent (low molecular weight polyurethane): 2.5 parts; lubricant (polyethylene wax): 0.3 parts; nano titanium dioxide: 1.2 parts.

[0093] Specific preparation steps: Raw material weighing: Weigh each component according to the ratio to ensure accuracy to avoid unstable performance of the finished product.

[0094] Mixing: Add all ingredients to a high-speed mixer, set the initial speed to 600 rpm, mix for 5 minutes, increase to 1500 rpm and continue mixing for 4 minutes to ensure uniform dispersion.

[0095] High shear melt blending: The mixed materials are fed into a twin-screw extruder with the screw speed set to 60 rpm, the shear pressure to 20 MPa, and the temperature controlled to 175°C (feeding zone) to 195°C (extrusion zone) to ensure good fusion of polypropylene and various fillers.

[0096] Cooling and granulation: The extrudate was cooled in a 30°C water bath and then fed into a pelletizer. The cutter speed was set at 1300 rpm, the feed rate was 6 m / min, and the pellet size was approximately 1.7 mm.

[0097] Injection molding: After drying, the pellets are fed into the injection molding machine for molding. The injection temperature is set at 185°C, the injection speed is set at 35mm / s, and the cooling rate is set at 0.5°C / s to ensure that the final product is stable and has no obvious defects.

[0098] Comparative Example 1: Compared with Example 1, no silver ions and nano titanium dioxide are used. The preparation process is the same as that of Example 1.

[0099] Comparative Example 2: Compared with Example 2, the purity of the polypropylene is 90%, and no nano titanium dioxide is used. The preparation process is the same as that of Example 2.

[0100] Comparative Example 3: Compared with Example 3, the component ratio is the same. In the mixing step, all components are added to the high-speed mixer. The multi-stage variable speed stirring mode is not adopted. The speed is set to 600 rpm and stirring is carried out for 5 minutes. The other preparation processes are the same as those in Example 3.

[0101] Experiment 1: Experimental steps: Sample preparation: The materials of Example 1 and Comparative Example 1 were selected and processed into 0.5 mm thick films with a size of 10 cm×10 cm.

[0102] The samples were sterilized by ultraviolet light (UV irradiation for 30 min) to ensure sterility.

[0103] Prepare LB agar medium, sterilize it by high pressure (121°C, 15 min), pour it into a culture dish and cool it to solidify.

[0104] test: Staphylococcus aureus and Escherichia coli were selected and cultured in LB medium until the logarithmic growth phase (OD600=0.5).

[0105] Use a sterile cotton swab to evenly spread the bacterial solution on the surface of the agar medium to ensure a uniform bacterial layer.

[0106] Place the experimental sample in the center of the culture medium after applying the bacterial solution, and press it gently to make it fully contact with the agar surface.

[0107] The cells were cultured in a 37°C constant temperature incubator for 24 hours.

[0108] examine: After 24 hours, the diameter of the inhibition zone was measured using an electronic vernier caliper (unit: mm). The same sample was measured three times (in different directions) and the average value was taken.

[0109] Data Records: The diameters of the inhibition zones of different samples were recorded, and each sample was measured three times to calculate the average value.

[0110] The antibacterial effects of Example 1 and Comparative Example 1 were statistically analyzed.

[0111] Experimental data: Table 1: Antibacterial performance test results The antibacterial results showed significant differences, with the inhibition zone of Example 1 significantly larger than that of Comparative Example 1, indicating stronger antibacterial performance. Silver ions can bind to bacterial membrane proteins, disrupting their function and ultimately leading to cell death. Nano-titanium dioxide, on the other hand, produces hydroxyl radicals through photocatalytic reactions. These free radicals further oxidize the bacterial cell wall, enhancing the antibacterial effect. The synergistic effect of these two makes Example 1 far more effective than Comparative Example 1 in antibacterial performance.

[0112] On the other hand, the antibacterial effect of Comparative Example 1 was significantly reduced due to the lack of silver ions and nano-titanium dioxide. The diameter of the inhibition zone was small, and some samples even showed bacterial penetration. This shows that reducing the silver ion content alone is not conducive to maintaining high antibacterial efficacy.

[0113] Experimental data show that the diameter of the inhibition zone in Example 1 is approximately 30%-50% higher than that in Comparative Example 1, indicating that the addition of nano-titanium dioxide not only enhances antibacterial activity but also potentially increases the sustained release of silver ions, prolonging the antibacterial effect. This result has important practical implications for applications in medical protection, food packaging, and other fields.

[0114] Experiment 2: Experimental steps: Sample preparation: The materials of Example 1 and Comparative Example 1 were selected and the preparation process was the same, and they were processed into 0.5 mm thick films with a size of 10 cm×10 cm.

[0115] All samples were sterilized by ultraviolet light (UV irradiation for 30 min) to ensure sterility.

[0116] Prepare LB agar medium, sterilize it by high pressure (121°C, 15 min), pour it into a culture dish and cool it to solidify.

[0117] test: Staphylococcus aureus and Escherichia coli were selected and cultured in LB medium until the logarithmic growth phase (OD600=0.5).

[0118] Use a sterile cotton swab to evenly spread the bacterial solution on the surface of the agar medium to ensure a uniform bacterial layer.

[0119] Place the experimental sample in the center of the culture medium after applying the bacterial solution, and press it gently to make it fully contact with the agar surface.

[0120] The cells were cultured in a 37°C constant temperature incubator for 24 hours.

[0121] Inspection: After 24 hours, use an electronic vernier caliper to measure the diameter of the inhibition zone (unit: mm).

[0122] The same sample was measured three times (in different directions) and the average value was taken to reduce the measurement error.

[0123] Experimental data: Table 2: Antibacterial performance test results The antibacterial results show that the inhibition zone of Example 2 is significantly larger than that of Comparative Example 2, indicating that Example 2 has stronger antibacterial properties. Example 2 uses polypropylene with a purity of 99.5% and contains nano-titanium dioxide to enhance the antibacterial effect. These ingredients significantly improve the antibacterial performance through synergistic effects, especially in the inhibition of Staphylococcus aureus. Nano-titanium dioxide generates hydroxyl radicals through photocatalytic reactions. These free radicals further oxidize the bacterial cell wall, enhancing the antibacterial effect, thereby significantly improving the antibacterial properties of the material.

[0124] On the other hand, Comparative Example 2 used 90% pure polypropylene and lacked effective antimicrobial ingredients like nano-titanium dioxide, resulting in a significant reduction in its antimicrobial effectiveness. The inhibition zone diameters in Comparative Example 2 were smaller, and some samples showed bacterial penetration, indicating that lower purity and the lack of effective antimicrobial ingredients significantly reduced antimicrobial performance.

[0125] Experimental data shows that the diameter of the inhibition zone in Example 2 is approximately 30%-40% higher than that in Comparative Example 2. This indicates that the high purity of polypropylene and the addition of nano-titanium dioxide not only significantly enhance antimicrobial activity but also potentially increase the sustained release of other antimicrobial components, extending the duration of antimicrobial activity. This result has important practical implications for applications in medical protection, food packaging, and other fields.

[0126] Experiment 3: Experimental steps: Sample preparation: The materials of Example 3 and Comparative Example 3 were selected. Comparative Example 3 did not adopt the multi-stage variable speed stirring mode. The speed was set to 600 rpm and stirred for 5 minutes. The other preparation processes were the same as those of Example 3. They were processed into 0.5 mm thick films with a size of 10 cm×10 cm.

[0127] The samples were sterilized by ultraviolet light (UV irradiation for 30 min) to ensure sterility.

[0128] Prepare LB agar medium, sterilize it by autoclaving (121°C, 15 minutes), and pour it into a Petri dish to cool and solidify.

[0129] test: Staphylococcus aureus and Escherichia coli were selected and cultured in LB medium until the logarithmic growth phase (OD600=0.5).

[0130] Use a sterile cotton swab to evenly spread the bacterial solution on the surface of the agar medium to ensure a uniform bacterial layer.

[0131] Place the experimental sample in the center of the culture medium after applying the bacterial solution, and press it gently to make it fully contact with the agar surface.

[0132] The cells were cultured in a 37°C constant temperature incubator for 24 hours.

[0133] examine: After 24 hours, the diameter of the inhibition zone was measured using an electronic vernier caliper (unit: mm).

[0134] The same sample was measured three times (in different directions) and the average value was taken to reduce the measurement error.

[0135] Data Records: The diameters of the inhibition zones of different samples were recorded, and each sample was measured three times to calculate the average value.

[0136] The antibacterial effects of Example 3 and Comparative Example 3 were statistically analyzed to compare the effects of the mixing method on the antibacterial performance.

[0137] Experimental data: Table 3: Antibacterial performance test results The antibacterial performance of Example 3 is significantly better than that of Comparative Example 3, especially in the diameter of the inhibition zone of Staphylococcus aureus.

[0138] The diameters of the inhibition zones of Comparative Example 3 on Staphylococcus aureus and Escherichia coli were smaller than those of Example 3, indicating that the single-speed stirring method has poor dispersibility, resulting in a weakened antibacterial effect.

[0139] The experimental results show that the use of multi-stage variable speed stirring mode can disperse the material more evenly, thereby improving the antibacterial effect.

[0140] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A polypropylene composite material with antibacterial function, characterized in that: The composition includes the following parts by weight: Polypropylene 90-98 parts; 1-2 parts of silver ions; 0.5-2 parts of toughening agent; 0.1-0.5 parts of lubricant; 0.5-1.5 parts of nano titanium dioxide.

2. The polypropylene composite material with antibacterial function according to claim 1, characterized in that: The silver ions are stabilized and coated by citric acid or active polyvinyl pyrrolidone ligands, and the particle size of the silver ions is in the range of 5-50 nm.

3. The polypropylene composite material with antibacterial function according to claim 1, characterized in that: The toughening agent is polycaprolactone or low molecular weight polyurethane.

4. The polypropylene composite material with antibacterial function according to claim 1, characterized in that: The nano titanium dioxide is subjected to surface modification treatment, wherein the treatment includes hydrophilic or lipophilic modification to enhance its dispersibility in a polypropylene matrix and utilize photocatalysis to improve the antibacterial performance of the material.

5. The polypropylene composite material with antibacterial function according to claim 1, characterized in that: The purity of the polypropylene is 98%-99.5%.

6. A method for preparing a polypropylene composite material with antibacterial function, for preparing a polypropylene composite material with antibacterial function as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Mixing polypropylene, silver ions, toughening agent, lubricant and nano-titanium dioxide according to mass fractions to provide uniform initial raw material distribution for subsequent high shear mixing; S2, using high shear mixing technology to evenly disperse the mixture in S1, so that the mixture has good fluidity and uniform antibacterial properties during the injection molding process; S3, controlling the temperature of the mixture obtained in S2 to 25° C.-30° C. by a cooling water bath to form granules, and granulating the mixture obtained in S2 using a pelletizing process to obtain uniform granules; S4. Molding the particles obtained in S3 using an injection molding process.

7. The method for preparing a polypropylene composite material with antibacterial function according to claim 6, characterized in that: The equipment used for mixing in S1 is a high-speed mixer. During the mixing process of the high-speed mixer, a multi-stage variable speed stirring mode is adopted, the speed range of which is set to 500-1500 rpm, and the stirring time is controlled to be 3-10 minutes.

8. The method for preparing a polypropylene composite material with antibacterial function according to claim 6, characterized in that: The equipment used in the high shear mixing technology is a twin-screw extruder, the screw speed of which is controlled at 50-120 rpm, the shear pressure is controlled at 15-30 MPa, and the temperature gradient is controlled at 170-210°C.

9. The method for preparing a polypropylene composite material with antibacterial function according to claim 6, characterized in that: The equipment used in the pelletizing process is a pelletizer, the cutter speed of which is set at 500-3000 rpm, the feed speed is controlled at 2-10 m / min, and the pelletizing length range is 0.5-5 mm.

10. The method for preparing a polypropylene composite material with antibacterial function according to claim 6, characterized in that: The equipment used in the injection molding process is an injection molding machine, the injection temperature of the injection molding machine is 185°C-200°C, the injection speed is 30mm / s-50mm / s, and the cooling rate is 0.5°C / s-1.0°C / s.

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