A high-strength antibacterial polypropylene composite material and its preparation method

Abstract

This application discloses a high-strength antibacterial polypropylene composite material and its preparation method. The composite material comprises: 100 parts polypropylene, 15-25 parts glass fiber, 1-8 parts compatibilizer, 3-6 parts unsaturated polyester, 1-5 parts stabilizer, 0.1-0.5 parts initiator, 0.1-0.3 parts metal ion antibacterial agent, and 0.2-1.5 parts antioxidant; the stabilizer is selected from at least one of methyl methacrylate, acrylonitrile, and divinylbenzene; the melt processing temperature of the polypropylene material is 160-175℃. This application effectively reduces the anisotropic shrinkage rate difference in glass fiber reinforced polypropylene by forming a micro-crosslinked structure, thereby reducing appearance quality defects caused by the anisotropic shrinkage characteristics of current glass fiber reinforced polypropylene materials.

Description

Technical Field

[0001] This application relates to the field of polypropylene materials, and in particular to a high-strength antibacterial polypropylene composite material and its preparation method. Background Technology

[0002] Polypropylene, a general-purpose thermoplastic, is widely used in automotive parts, appliance housings, and packaging materials due to its advantages such as light weight, chemical resistance, ease of processing and molding, and low cost. However, ordinary polypropylene has relatively limited mechanical strength, dimensional stability, and creep resistance, making it difficult to meet the stringent performance requirements of high-end structural components. Therefore, glass fiber reinforcement technology is widely used in polypropylene modification, significantly improving the material's rigidity, tensile strength, and heat resistance by adding glass fibers to the matrix. For example, patent application CN113388189A discloses a glass fiber-containing polypropylene composition that effectively improves the material's creep resistance and mechanical properties by optimizing fiber dispersion and interfacial bonding.

[0003] However, as applications expand towards thinner walls and lighter weights, the limitations of glass fiber reinforced polypropylene (GFRP) materials are becoming increasingly apparent. Specifically, due to its high aspect ratio, glass fiber tends to be highly oriented along the flow direction during injection molding or extrusion, resulting in a significant difference in thermal shrinkage rates parallel and perpendicular to the flow direction. This anisotropic shrinkage is particularly pronounced in thin-walled planar structures (such as electronic device housings and thin-walled containers), causing problems like edge warping, surface wrinkles, and even localized cracking, severely restricting the dimensional accuracy and appearance quality of the products. Furthermore, traditional GFRP lacks antibacterial properties, limiting its application in fields with high hygiene requirements, such as medical devices (e.g., housings) and food packaging (e.g., containers). Therefore, developing a GFRP composite material that combines high mechanical strength, low shrinkage anisotropy, and long-lasting antibacterial properties has become a key direction for overcoming existing technological bottlenecks and expanding the material's application scenarios. Summary of the Invention

[0004] This application provides a high-strength antibacterial polypropylene composite material and its preparation method. By forming a micro-crosslinked structure in glass fiber reinforced polypropylene, the difference in its anisotropic shrinkage rate is effectively reduced, thereby reducing the appearance quality defects caused by the anisotropic shrinkage characteristics of current glass fiber reinforced polypropylene materials.

[0005] In a first aspect, this application provides a high-strength antibacterial polypropylene composite material, which comprises the following components in parts by weight:

[0006] The composition comprises 100 parts polypropylene, 15-25 parts glass fiber, 1-8 parts compatibilizer, 5-10 parts unsaturated polyester, 1-5 parts stabilizer, 0.1-0.5 parts initiator, 0.1-0.3 parts metal ion antibacterial agent, and 0.2-1.5 parts antioxidant; wherein the stabilizer is selected from at least one of methyl methacrylate, acrylonitrile, and divinylbenzene; and the melt processing temperature of the polypropylene material is 160-175℃.

[0007] In any of the above technical solutions, the stabilizer contains 30-50 wt% divinylbenzene.

[0008] In any of the above technical solutions, the initiator is dicumyl peroxide.

[0009] In any of the above technical solutions, the polypropylene is linear isotactic polypropylene with a melt index of 20-30 g / 10 min at 230℃ / 2.16 kg.

[0010] This application utilizes dynamic crosslinking technology to construct a mildly micro-crosslinked network by introducing unsaturated polyester, initiator, and stabilizer into polypropylene resin, thereby suppressing the shrinkage anisotropy of glass fiber reinforced polypropylene. During melt processing, the initiator (such as dicumyl peroxide) decomposes upon heating to generate free radicals, which attack the tertiary carbon atoms of the polypropylene molecular chain to form macromolecular free radicals (PP·). At this time, the double bonds of the stabilizer (such as methyl methacrylate / MMA) capture the free radicals through chain transfer, generating a more stable intermediate (such as PP-MMA·), improving crosslinking activity and reducing β-fracture of the polypropylene main chain caused by free radicals, thus avoiding excessive molecular weight reduction that would affect its mechanical properties. The stable intermediate further undergoes a grafting reaction with the double bonds of the unsaturated polyester (at which time, monoolefin stabilizers such as methyl methacrylate and acrylonitrile participate in the grafting reaction as comonomers), forming crosslinking points and producing localized micro-crosslinked gels.

[0011] The aforementioned moderate crosslinking reaction is beneficial for balancing the anisotropy of material shrinkage and improving strength properties. Divinylbenzene's bifunctional nature allows it to simultaneously link two polypropylene chains or polypropylene and unsaturated polyester chains, significantly increasing crosslinking density. However, excessive use (greater than 50 wt%) will degrade material flexibility and notched impact strength. Furthermore, using divinylbenzene alone as a stabilizer can easily cause material hardening and embrittlement, leading to a decrease in notched impact strength and tensile strength. Mono-alkenyl stabilizers such as methyl methacrylate have weaker crosslinking effects; when combined with divinylbenzene, they can form a sufficient crosslinking network to balance shrinkage stress while avoiding excessive crosslinking that could lead to decreased flexibility or even embrittlement. Ultimately, this reduces the difference in shrinkage between the parallel and perpendicular directions to below 0.3%, effectively alleviating warping and cracking problems in thin-walled products while maintaining good mechanical properties.

[0012] It is worth noting that the stabilizer used in this application should not be a polar monomer such as maleic anhydride, as its chain transfer properties are poor, making it difficult to effectively capture free radicals and form stable intermediates. This may lead to accelerated β-splitting of the polypropylene backbone, a decrease in molecular weight, and negatively impact mechanical properties. Furthermore, it may trigger side reactions and interfere with the formation of the crosslinked network.

[0013] In any of the above technical solutions, the unsaturated polyester is prepared by polycondensation of an unsaturated diacid or anhydride, a saturated diacid, pyridine-containing terephthalic acid, and a diol in a molar ratio of 0.4-0.5:0.4-0.5:0.1-0.2:1.

[0014] In any of the above technical solutions, the pyridine-containing terephthalic acid is selected from 2-(4-pyridyl)terephthalic acid and / or 2,5-bis(pyridin-4-yl)terephthalic acid.

[0015] In any of the above technical solutions, the metal ion antibacterial agent is selected from zinc ion antibacterial agents and / or silver ion antibacterial agents.

[0016] In the synthesis of unsaturated polyesters, pyridine-containing terephthalic acids (such as 2,5-bis(pyridin-4-yl)terephthalic acid) are introduced to endow the polyester chains with nitrogen-containing coordinating groups. These pyridine groups can form coordination networks with metal ions, reducing anisotropy without degrading the material's notched impact strength, thus achieving a synergistic improvement in antibacterial function and appearance. On the other hand, they can coordinate with metal ion antibacterial agents (such as silver or zinc ions) to form stable metal-organic complexes, firmly anchoring the antibacterial agent within the polypropylene matrix and preventing migration loss during processing or use. Furthermore, the electron-donating properties of the pyridine groups enhance the redox activity of metal ions, further improving the efficiency of the antibacterial agent in disrupting bacterial cell membranes. Experiments show that the composite material containing pyridine polyester achieves an inhibition rate of over 99% against *Escherichia coli* and *Staphylococcus aureus*, and retains over 90% of its antibacterial activity after 50 washes.

[0017] In any of the above technical solutions, the raw materials of the compatibilizer include the following components in parts by weight: 100 parts of maleic anhydride modified liquid polybutadiene, 10-30 parts of hydroxy acrylate, and 0.5-2 parts of catalyst. The maleic anhydride modified liquid polybutadiene and hydroxy acrylate are subjected to an esterification reaction under a catalyst to obtain the compatibilizer.

[0018] In any of the above technical solutions, the temperature of the esterification reaction is 90–120°C.

[0019] In any of the above technical solutions, the hydroxyacrylate is selected from at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, and hydroxybutyl methacrylate.

[0020] In any of the above technical solutions, the catalyst is p-toluenesulfonic acid.

[0021] This application uses a relatively high amount of unsaturated polyester. To ensure the compatibility and dispersibility of the two phases, a specific compatibilizer is used. This compatibilizer combines the nonpolar backbone of polybutadiene with the polar side groups (ester groups or unreacted hydroxyl groups) of acrylate. The nonpolarity of its polybutadiene backbone is similar to that of PP, and the interfacial bonding can be enhanced through chain segment entanglement or van der Waals forces. The acrylate segments form hydrogen bonds or dipole interactions with the ester groups in the unsaturated polyester, improving the compatibility of the two phases and ensuring the crosslinking effect. In addition, the polybutadiene backbone in this compatibilizer has a certain toughening effect, which helps to improve the loss of flexibility caused by crosslinking and improve its impact strength.

[0022] In any of the above technical solutions, the glass fiber has a length of 1 to 5 mm, an aspect ratio of ≥20, and its surface is treated with a silane coupling agent.

[0023] In any of the above technical solutions, the silane coupling agent is selected from at least one of vinyl silane coupling agents, amino silane coupling agents, and epoxy silane coupling agents.

[0024] In any of the above technical solutions, the amount of silane coupling agent used is 2-4% of the glass fiber mass.

[0025] The surface treatment with silane coupling agent described in this application refers to the process of uniformly spraying a silane coupling agent solution, such as an ethanol solution, onto the glass fiber surface using a spray method, and then curing it at 110–120°C for 20–30 minutes.

[0026] Secondly, this application provides a method for preparing a high-strength antibacterial polypropylene composite material, comprising:

[0027] Polypropylene, compatibilizer, unsaturated polyester, stabilizer, and initiator are mixed evenly and fed into a screw extruder. The mixture is melt-blended at 160–175°C for 5–10 minutes. Then, glass fiber, antioxidant, and metal ion antibacterial agent are added from the side feed port. The mixture is further blended at 190–220°C for 3–6 minutes and then extruded and granulated to obtain the final product.

[0028] In summary, this application has the following beneficial effects:

[0029] The high-strength antibacterial polypropylene composite material provided in this application significantly reduces the anisotropy of glass fiber reinforced polypropylene through dynamic micro-crosslinking technology, controlling the difference in shrinkage rate between the parallel and perpendicular directions to within 0.3%, effectively solving the warping and cracking problems of thin-walled products. Simultaneously, the coordination effect of pyridine-containing polyester and metal ion antibacterial agents endows the material with long-lasting antibacterial properties and the ability to further inhibit anisotropy, achieving an antibacterial rate exceeding 99% and excellent wash resistance. The material combines high mechanical strength with good processing flowability (melt index 20–30 g / 10 min), making it suitable for automotive interiors, electronic housings, and medical devices. The preparation process achieves synergistic optimization of dynamic crosslinking and fiber dispersion through segmented temperature control (premixing modification at 160–175℃ and final mixing at 190–220℃), providing a wide process window suitable for industrial production. Detailed Implementation

[0030] Preparation Example

[0031] Preparation Example 1: An unsaturated polyester with the following raw material formulation:

[0032] Maleic anhydride 220.6g (2.25mol), phthalic anhydride 333.3g (2.25mol), 2,5-bis(pyridin-4-yl)terephthalic acid 125g (0.5mol), propylene glycol 380.5g (5.0mol), p-toluenesulfonic acid (catalyst) 50g.

[0033] The preparation process is as follows:

[0034] Maleic anhydride, phthalic anhydride, 2,5-bis(pyridin-4-yl)terephthalic acid, and propylene glycol were added to a reactor, and the mixture was heated to 160°C under ammonia protection. A catalyst was added, and the temperature was gradually increased to 190°C. The mixture was stirred for 4 hours. A vacuum was then applied to -0.095 MPa, and the reaction continued for 2 hours to remove byproduct water. The mixture was cooled to 80°C, and the product was discharged as a pale yellow viscous polyester with an acid value ≤15 mg KOH / g.

[0035] Preparation Example 2: An unsaturated polyester with the following raw material formulation:

[0036] Maleic anhydride 245.2g (2.5mol), phthalic anhydride 296.2g (2.0mol), 2-(4-pyridyl)terephthalic acid 125g (0.5mol), ethylene glycol 310.4g (5.0mol), p-toluenesulfonic acid (catalyst) 50g.

[0037] The preparation process is as follows:

[0038] Maleic anhydride, phthalic anhydride, 2-(4-pyridyl)terephthalic acid, and propylene glycol were added to a reactor, and the mixture was heated to 160°C under ammonia protection. A catalyst was added, and the temperature was gradually increased to 185°C. The mixture was stirred for 3 hours. A vacuum was then applied to -0.095 MPa, and the reaction continued for 2 hours to remove byproduct water. The mixture was cooled to 80°C, and the resulting product was a pale yellow viscous polyester with an acid value ≤12 mg KOH / g.

[0039] Preparation Example 3: An unsaturated polyester with the following raw material formulation:

[0040] Maleic anhydride 232.1g (2.0mol), phthalic anhydride 292.3g (2.0mol), 2,5-bis(pyridin-4-yl)terephthalic acid 250g (1mol), butanediol 450.6g (5.0mol), p-toluenesulfonic acid (catalyst) 60g.

[0041] The preparation process is as follows:

[0042] Maleic anhydride, phthalic anhydride, 2,5-bis(pyridin-4-yl)terephthalic acid, and propylene glycol were added to a reactor, and the mixture was heated to 160°C under ammonia protection. A catalyst was added, and the temperature was gradually increased to 5°C. The mixture was stirred for 4 hours. A vacuum was then applied to -0.095 MPa, and the reaction continued for 3 hours to remove byproduct water. The mixture was cooled to 80°C, and the product was discharged as a pale yellow viscous polyester with an acid value ≤10 mg KOH / g.

[0043] Preparation Example 4, an unsaturated polyester, differs from Preparation Example 1 in that 2,5-bis(pyridin-4-yl)terephthalic acid is replaced with an equimolar amount of terephthalic acid. The raw material formulation is as follows:

[0044] Maleic anhydride 220.6g (2.25mol), phthalic anhydride 333.3g (2.25mol), terephthalic acid 83.1g (0.5mol), propylene glycol 380.5g (5.0mol), p-toluenesulfonic acid (catalyst) 50g.

[0045] The preparation process is the same as in Preparation Example 1.

[0046] Preparation Example a: A compatibilizer was prepared by the following operation:

[0047] 1 kg of maleic anhydride-modified liquid polybutadiene (Evonik POLYVEST® MA-75) was mixed thoroughly with 0.2 kg of hydroxyethyl acrylate and 0.01 kg of p-toluenesulfonic acid. Under nitrogen protection, the mixture was heated to 110 °C and stirred for 3 h. The reaction solution was cooled to below 60 °C, and an appropriate amount of acetone was added to precipitate the product. After filtration, the product was vacuum dried for 24 h to obtain the compatibilizer.

[0048] Preparation Example b: A compatibilizer was prepared by the following operation:

[0049] 1 kg of maleic anhydride-modified liquid polybutadiene (Ricon 131MA17) was mixed with 0.1 kg of hydroxyethyl methacrylate and 0.01 kg of p-toluenesulfonic acid until homogeneous. Under nitrogen protection, the mixture was heated to 100 °C and stirred for 4 h. The reaction solution was cooled to below 60 °C, and an appropriate amount of acetone was added to precipitate the product. After filtration, the product was vacuum dried for 24 h to obtain the compatibilizer.

[0050] Preparation example c, a compatibilizer, is prepared according to the following operation:

[0051] 1 kg of maleic anhydride-modified liquid polybutadiene (Ricon 131MA20) was mixed thoroughly with 0.3 kg of hydroxypropyl acrylate and 0.02 kg of p-toluenesulfonic acid. Under nitrogen protection, the mixture was heated to 120 °C and stirred for 3 h. The reaction solution was cooled to below 60 °C, and an appropriate amount of acetone was added to precipitate the product. After filtration, the product was vacuum dried for 24 h to obtain the compatibilizer. Example

[0052] Example 1: A high-strength antibacterial polypropylene composite material was prepared according to the following steps:

[0053] Raw material preparation: Linear isotactic polypropylene (230℃ / 2.16kg, melt index 30g / 10min): 1.0kg; Glass fiber (length 3mm, aspect ratio 25, surface treated with vinyl silane coupling agent, dosage 3wt%) 0.2kg; Compatibilizer (Preparation Example a) 0.05kg; Unsaturated polyester (Preparation Example 1) 0.08kg; Stabilizer (methyl methacrylate and divinylbenzene in a mass ratio of 6:4) 0.04kg; Dicumyl peroxide 0.003kg; Silver ion antibacterial agent (ADM-Ag08) 0.002kg; Antioxidant (antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1) 0.01kg.

[0054] The preparation steps are as follows:

[0055] Polypropylene, compatibilizer, unsaturated polyester, stabilizer, and initiator are premixed and added to the main feed port of a twin-screw extruder. The extruder temperatures are set as follows: 160℃ (feeding zone), 170℃ (melting zone), and 175℃ (mixing zone). The speed is 200 rpm, and the extruder is melt-blended for 8 minutes.

[0056] Glass fiber, antioxidant, and antibacterial agent are added from the side feed port. The temperature is raised to 190°C (melting zone) and 210°C (mixing zone), and the mixture is kneaded for 5 minutes. The mixture is then extruded and granulated, and finally cut into composite material particles by water cooling.

[0057] Example 2: A high-strength antibacterial polypropylene composite material was prepared according to the following steps:

[0058] Raw material preparation: Linear isotactic polypropylene (230℃ / 2.16kg, melt index 20g / 10min): 1.0kg; Glass fiber (length 1mm, aspect ratio 20, surface treated with vinyl silane coupling agent, dosage 2wt%) 0.15kg; Compatibilizer (Preparation Example b) 0.08kg; Unsaturated polyester (Preparation Example 2) 0.05kg; Stabilizer (acrylonitrile and divinylbenzene in a mass ratio of 5:5) 0.05kg; Dicumyl peroxide 0.001kg; Zinc ion antibacterial agent (iHeir-907) 0.001kg; Antioxidant (antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1) 0.02kg.

[0059] The preparation steps are as follows:

[0060] Polypropylene, compatibilizer, unsaturated polyester, stabilizer, and initiator are premixed and added to the main feed port of a twin-screw extruder. The extruder temperatures are set as follows: 160℃ (feeding zone), 165℃ (melting zone), and 170℃ (mixing zone). The speed is 200 rpm, and the mixture is melt-blended for 10 minutes.

[0061] Glass fiber, antioxidant, and antibacterial agent are added from the side feed port. The temperature is raised to 195°C (melting zone) and 210°C (mixing zone), and the mixture is kneaded for 5 minutes. The mixture is then extruded and granulated, and finally cut into composite material particles by water cooling.

[0062] Example 3: A high-strength antibacterial polypropylene composite material was prepared according to the following steps:

[0063] Raw material preparation: Linear isotactic polypropylene (230℃ / 2.16kg, melt index 30g / 10min): 1.0kg; Glass fiber (length 5mm, aspect ratio 30, surface treated with vinyl silane coupling agent, dosage 4wt%) 0.25kg; Compatibilizer (Preparation Example c) 0.03kg; Unsaturated polyester (Preparation Example 3) 0.1kg; Stabilizer (methyl methacrylate and divinylbenzene in a mass ratio of 7:3) 0.04kg; Dicumyl peroxide 0.005kg; Silver ion antibacterial agent (ADM-Ag08) 0.003kg; Antioxidant (antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1) 0.02kg.

[0064] The preparation steps are as follows:

[0065] Polypropylene, compatibilizer, unsaturated polyester, stabilizer, and initiator are premixed and added to the main feed port of a twin-screw extruder. The extruder temperatures are set as follows: 160℃ (feeding zone), 175℃ (melting zone), and 175℃ (mixing zone). The speed is 300 rpm, and the mixture is melt-blended for 5 minutes.

[0066] Glass fiber, antioxidant, and antibacterial agent are added from the side feed port. The temperature is raised to 195°C (melting zone) and 220°C (mixing zone), and the mixture is kneaded for 4 minutes. The mixture is then extruded and granulated, and finally cut into composite material particles by water cooling.

[0067] Example 4, a high-strength antibacterial polypropylene composite material, differs from Example 1 in that the stabilizer uses a combination of methyl methacrylate and divinylbenzene, wherein the amount of divinylbenzene is 60 wt%.

[0068] Example 5, a high-strength antibacterial polypropylene composite material, differs from Example 1 in that the stabilizer uses a combination of methyl methacrylate and divinylbenzene, wherein the amount of divinylbenzene is 20wt%.

[0069] Example 6, a high-strength antibacterial polypropylene composite material, differs from Example 1 in that divinylbenzene is replaced with an equal mass of methyl methacrylate in the stabilizer.

[0070] Example 7, a high-strength antibacterial polypropylene composite material, differs from Example 1 in that divinylbenzene is replaced with methyl methacrylate in the stabilizer at an equal mass.

[0071] Example 8, a high-strength antibacterial polypropylene composite material, differs from Example 1 in that the unsaturated polyester of Preparation Example 4 is replaced with the unsaturated polyester of Preparation Example 1 in equal mass.

[0072] Example 9, a high-strength antibacterial polypropylene composite material, differs from Example 1 in that the compatibilizer prepared in Preparation Example a is replaced with an equal mass of maleic anhydride-grafted polypropylene (grafting rate 1.2%).

[0073] Example 10, a high-strength antibacterial polypropylene composite material, differs from Example 1 in that an equal mass of maleic anhydride-modified liquid polybutadiene (Evonik POLYVEST® MA-75) replaces the compatibilizer prepared in Preparation Example a. Comparative Example

[0074] Comparative Example 1 is a high-strength antibacterial polypropylene composite material, which differs from Example 1 in that the stabilizer is replaced with an equal mass of polypropylene in the raw materials of the composite material.

[0075] Comparative Example 2 is a high-strength antibacterial polypropylene composite material, which differs from Example 1 in that unsaturated polyester is replaced with an equal mass of polypropylene in the raw materials of the composite material.

[0076] Comparative Example 3, a high-strength antibacterial polypropylene composite material, was prepared according to the following steps:

[0077] Raw material preparation: Linear isotactic polypropylene (230℃ / 2.16kg, melt index 30g / 10min): 1.0kg; Glass fiber (length 3mm, aspect ratio 25, surface treated with vinyl silane coupling agent, dosage 3wt%) 0.2kg; Maleic anhydride grafted polypropylene (grafting rate 1.2%) 0.05kg; Silver ion antibacterial agent (ADM-Ag08) 0.002kg; Antioxidant (antioxidant 1010 and antioxidant 168 in a 1:1 mass ratio) 0.01kg.

[0078] The preparation steps are as follows:

[0079] Polypropylene, antioxidant and antibacterial agent are premixed and added to the main feed port of the twin-screw extruder; the temperature of each zone of the extruder is set as follows: 160℃ (feeding zone), 170℃ (melting zone), 175℃ (mixing zone), speed is 200 rpm, and melt blending is carried out for 8 minutes.

[0080] Glass fiber is added from the side feed port, and the temperature is raised to 190°C (melting zone) and 210°C (mixing zone). The mixture is kneaded for 5 minutes, extruded and granulated, and then water-cooled and pelletized to obtain composite material particles.

[0081] Performance testing

[0082] 1. Shrinkage difference test

[0083] Sample preparation: The composite material particles of the examples and comparative examples were molded into flat samples with dimensions of 150mm × 150mm × 2mm using an injection molding machine at an injection temperature of 200–220℃. Five samples were prepared for each set of examples and comparative examples and placed at room temperature for 24 hours to eliminate internal stress.

[0084] Test method: The test was conducted in accordance with ASTM D955-08 (2014). After the sample was cooled for 24 hours, the dimensional changes in the flow direction (L) and vertical direction (T) were measured. The shrinkage difference was calculated as follows: Shrinkage difference = Shrinkage L - Shrinkage T. The average value of 5 samples was taken.

[0085] 2. Appearance quality assessment

[0086] Sample preparation:

[0087] Injection-molded thin-walled container simulation parts (wall thickness 1mm, dimensions 100mm×50mm×50mm) were prepared at an injection temperature of 200~220℃, with 3 samples prepared for each group.

[0088] Test method: Visually inspect the sample edges for warping, and check for surface ripples or cracks. Defect levels are classified according to the following standards:

[0089] Level 0: No visible defects;

[0090] Grade 1: Slight warping and / or slight wavy wrinkles;

[0091] Level 2: Obvious ripples or cracks;

[0092] Grade 3: Severe warping or cracking;

[0093] Level 4: Product damage.

[0094] 3. Tensile strength test

[0095] Sample preparation: The mixed PVC composition was molded into dumbbell specimens conforming to standard 1A in ISO 527-2-2012 by an injection molding machine (injection temperature 180±5℃, mold temperature 40℃). Five specimens were prepared for each group.

[0096] Test procedures and conditions: The test was conducted according to ISO 527-2-2012 "Plastics — Determination of tensile properties". A universal testing machine (Instron 5567) was used, with a tensile speed of 50 mm / min, an ambient temperature of 23 ± 2℃, and a humidity of 50 ± 5%. The breaking strength (MPa) was recorded.

[0097] 4. Notched impact strength test

[0098] Sample preparation: The composite material particles of the examples and comparative examples were injection molded into 80×10×4mm³ strip samples using an injection molding machine (injection temperature 200~220℃). A V-shaped notch (notch depth 2mm, angle 45°) was cut in the middle of the sample.

[0099] Test method: Following ISO 179-1:2010 "Plastics—Determination of impact strength of simply supported beams", a pendulum impact testing machine was used with an impact energy of 5.5 J, a span of 62 mm, and an ambient temperature of 23±2℃. The notched impact strength (kJ / m²) was calculated. 2 ).

[0100] 5. Antibacterial performance test

[0101] Sample preparation: In accordance with the provisions of ISO 22196-2011, the material was cut into 50mm×50mm×2mm sheet samples and the surface was sterilized with ethanol.

[0102] Antibacterial rate test: Following ISO 22196-2011, *Escherichia coli* (ATCC 8739) and *Staphylococcus aureus* (ATCC 6538) were inoculated at a bacterial concentration of 1×10⁻⁶. 5 CFU / mL. After the sample has been in contact with the bacterial solution for 24 hours, it is eluted and cultured for counting. The inhibition rate is calculated as follows: Inhibition rate = (Number of colonies in the blank group − Number of colonies in the sample group) / Number of colonies in the blank group × 100%.

[0103] Long-lasting antibacterial performance test: Immerse the sample in a solution containing 1% detergent for 50 cycles (5 minutes each time) to repeat the antibacterial rate test.

[0104] Table 1. Performance Test Results

[0105]

[0106] Analysis of experimental results:

[0107] Example 4 (high divinylbenzene content) showed a slight improvement in tensile strength, but a significant decrease in notched impact strength. This indicates that excessive divinylbenzene in the stabilizer will cause a deterioration in its notched impact strength.

[0108] Example 5 (low divinylbenzene content) showed a certain decrease in performance in terms of shrinkage difference, tensile strength, and notched impact strength, indicating that the crosslinking effect of divinylbenzene has a promoting effect on suppressing shrinkage difference and improving strength.

[0109] Example 6 (using methyl methacrylate instead of divinylbenzene) showed increased shrinkage, decreased apparent quality (slight surface ripples and wrinkles, slight edge warping), and decreased tensile strength and notched impact strength. This may be because methyl methacrylate has a weaker reactivity with free radicalized polypropylene, which is detrimental to maintaining its molecular weight stability; and its low crosslinking density as a comonomer is also detrimental to suppressing anisotropic shrinkage.

[0110] Example 7 (using methyl methacrylate instead of divinylbenzene) showed good performance in shrinkage and apparent quality, but its tensile strength and notched impact strength decreased significantly. This may be because the dual active sites of divinylbenzene result in strong crosslinking reactivity; excessive amounts will lead to over-crosslinking between the polypropylene matrix and the unsaturated polyester, causing a sharp deterioration in the material's flexibility and making it brittle, thus reducing tensile strength and notched impact strength.

[0111] Example 8 (unsaturated polyester without pyridine groups) showed poor performance in terms of anisotropic shrinkage (apparent quality) and long-lasting antibacterial properties. This indicates that the coordination network between pyridine groups and metal ions is beneficial for balancing the differences in anisotropic shrinkage and delaying the migration and precipitation rate of metal ion antibacterial agents.

[0112] Since no specific compatibilizer was used in Examples 9 and 10, their performance in anisotropic shrinkage (apparent quality) and impact strength decreased. This indicates that the compatibilizer obtained by reacting maleic anhydride-modified liquid polybutadiene with hydroxy acrylate has a higher interfacial reinforcement effect in the polypropylene / unsaturated polyester composite system of this application, which is beneficial to the uniform dispersion of the two phases and the formation of a micro-crosslinked network.

[0113] Comparative Example 1 (without stabilizer) performed poorly in terms of shrinkage, appearance quality, and tensile strength. This may be because the absence of stabilizer significantly reduced the crosslinking activity between polypropylene and unsaturated polyester, preventing effective crosslinking. Simultaneously, it caused β-fracture of the polypropylene main chain, resulting in an excessive decrease in molecular weight and a significant loss of strength properties.

[0114] In Comparative Example 2 (without added unsaturated polyester), the performance of anisotropy and strength properties decreased significantly. This is because the polypropylene was only grafted with the stabilizer monomer without forming a cross-linked structure.

[0115] Comparative Example 3 is a conventional glass fiber reinforced polypropylene material, which performs worse than the polypropylene material modified by pyridine grafted unsaturated polyester in this application in terms of anisotropic shrinkage and long-lasting antibacterial properties.

[0116] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-strength antibacterial polypropylene composite material, characterized in that, It includes the following components in parts by weight: The composition comprises 100 parts polypropylene, 15-25 parts glass fiber, 1-8 parts compatibilizer, 5-10 parts unsaturated polyester, 1-5 parts stabilizer, 0.1-0.5 parts initiator, 0.1-0.3 parts metal ion antibacterial agent, and 0.2-1.5 parts antioxidant; wherein the stabilizer is a composition of methyl methacrylate and divinylbenzene or a composition of acrylonitrile and divinylbenzene, and the stabilizer contains 30-50 wt% divinylbenzene; the melt processing temperature of the polypropylene material is 160-175℃. The unsaturated polyester is prepared by polycondensation of unsaturated diacids or anhydrides, saturated diacids, pyridine-containing terephthalic acid, and diols in a molar ratio of 0.4-0.5:0.4-0.5:0.1-0.2:1; the compatibilizer comprises the following components in parts by mass: 100 parts of maleic anhydride-modified liquid polybutadiene, 10-30 parts of hydroxyacrylate, and 0.5-2 parts of catalyst, wherein the maleic anhydride-modified liquid polybutadiene and hydroxyacrylate are subjected to an esterification reaction under a catalyst to obtain the compatibilizer.

2. The composite material according to claim 1, characterized in that, The initiator is dicumyl peroxide.

3. The composite material according to claim 1, characterized in that, The polypropylene is linear isotactic polypropylene, with a melt index of 20-30 g / 10 min at 230℃ / 2.16 kg.

4. The composite material according to claim 1, characterized in that, The pyridine-containing terephthalic acid is selected from 2-(4-pyridyl)terephthalic acid and / or 2,5-bis(pyridin-4-yl)terephthalic acid.

5. The composite material according to claim 1, characterized in that, The hydroxyacrylate is selected from at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, and hydroxybutyl methacrylate.

6. The composite material according to claim 1, characterized in that, The glass fiber has a length of 1-5 mm, an aspect ratio of ≥20, and its surface is treated with a silane coupling agent.

7. A method for preparing a high-strength antibacterial polypropylene composite material, characterized in that, include: According to the raw material ratio of the composite material according to any one of claims 1 to 6, polypropylene, compatibilizer, unsaturated polyester, stabilizer, initiator are mixed evenly and fed into a screw extruder, and melt-blended at 160 to 175°C for 5 to 10 minutes; then glass fiber, antioxidant and metal ion antibacterial agent are added from the side feed port, and the mixture is further kneaded at 190 to 220°C for 3 to 6 minutes, and then extruded and granulated to obtain the final product.

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