Glass Fiber Reinforced PP Flame Retardant

This material is based on copolymer polypropylene (PP, melt flow rate 12g/10min, ethylene content 8%), and is mixed with alkali-free glass fiber (diameter 13μm, length 3mm, treated with silane coupling agent KH550), ammonium polyphosphate (APP, polymerization degree 1000, phosphorus content 31%), melamine urea-formaldehyde resin (curing degree 85%), maleic anhydride grafted PP (grafting rate 1.2%) and antioxidant (1010 and 168 are compounded at 1:2) in a precise ratio of 45:30:20:3:2. Glass fiber accounts for 30%, and this ratio has been determined through hundreds of tests: if it is too high (>35%), it will be difficult for the flame retardant to evenly wrap the glass fiber, forming a local flame retardant blind area, and it is easy to have droplets when burning; if it is too low (<25%), it will not provide sufficient mechanical support, and the product will be easy to deform. APP and melamine urea-formaldehyde resin are compounded in a ratio of 3:2 to form an efficient phosphorus-nitrogen synergistic system - APP begins to decompose at 250°C, releasing phosphoric acid as an acid source, catalyzing the dehydration of PP molecular chains into carbon; melamine urea-formaldehyde resin decomposes at 300°C, releasing ammonia and carbon dioxide as gas sources, causing the carbon layer to foam and expand to 15 times its original volume, and glass fibers are interspersed in it, like a skeleton to enhance the structural stability of the carbon layer and prevent the carbon layer from collapsing at high temperatures. The mixing process needs to be divided into three steps: the first step is to put PP and maleic anhydride grafted PP into a high-speed mixer and premix them at 80℃ for 5 minutes until they are molten; the second step is to add glass fiber, adjust the speed to 800 rpm, and mix for 8 minutes to make the glass fiber initially dispersed; the third step is to add APP, melamine urea-formaldehyde resin and antioxidant, increase the speed to 900 rpm, and continue to mix for 15 minutes until the glass fiber is evenly dispersed and no agglomeration is visible to the naked eye. Granulation is carried out by a twin-screw extruder (length-to-diameter ratio 40:1), and the temperature of each zone is strictly controlled: 170℃ in zone 1, 180℃ in zone 2, 195℃ in zone 3, and 190℃ in zone 4. The screw speed is 350 rpm. Through the specially designed mixing section, it is ensured that the glass fiber is not over-sheared and the retention length is greater than 2mm. The final product has been tested and found to have a tensile strength of 85MPa (GB/T 1040), a flexural strength of 120MPa (GB/T 9341), a simply supported beam impact strength of 6.5kJ/m² (GB/T 1043), an oxygen index of 32% (GB/T 2406), and a flame retardant performance of UL94 V-0 (1.6mm thickness). The vertical combustion self-extinguishing time is less than 3 seconds, and there is no droplet. It truly achieves the dual standards of strength and flame retardancy, and is suitable for various structural load-bearing parts.

The subtlety of this product lies in the synergistic effect of the complementary symbiosis between glass fiber and flame retardant. Glass fiber is evenly dispersed in the PP matrix with a proportion of 30%, forming a three-dimensional network distribution, which not only offsets the weakening of the mechanical properties of the matrix by the flame retardant, but also increases the tensile strength of the product by 60% compared with the pure PP flame retardant system, and the bending modulus reaches 4500MPa (GB/T 9341), far exceeding the unreinforced flame retardant PP (2500MPa). The flame retardant system (APP and MCA are compounded at a ratio of 4:1) is filled in the gaps between the glass fibers in a nano-scale dispersed state. The two do not interfere with each other but help each other - when encountering fire, the phosphoric acid released by APP quickly diffuses to the surface of the glass fiber, reacts with the silicon element in the glass fiber to form silicate, and enhances the bonding force between the carbon layer and the glass fiber; the gas produced by the decomposition of MCA causes the carbon layer to expand, and the presence of glass fiber limits the cracking caused by excessive expansion of the carbon layer, forming a dense and elastic thermal insulation barrier. The combustion test shows that within 30 seconds, the thickness of the carbon layer can reach 20 times that of the original product, the porosity is 80%, and the thermal conductivity is reduced to 0.03W/(m・K), which can effectively block heat transfer. In the -40℃ low-temperature impact test, the impact strength of the product reached 5.2kJ/m², which is 40% higher than the flame-retardant PP without glass fiber, thanks to the impact resistance of glass fiber and the toughening effect of grafted PP. The heat deformation temperature (under a load of 1.82MPa) reaches 160℃ (GB/T 1634), which is 50℃ higher than the pure PP flame retardant system, and can withstand short-term high temperature environment. Taking the injection molded motor housing as an example, after 1000 hot and cold cycles (-40℃ to 120℃) tests, its mechanical property retention rate is 90%, and its flame retardant performance still reaches UL94 V-0 level, without cracks, which fully proves the synergistic effect of flame retardancy and mechanical properties, and can achieve a perfect balance between structural load-bearing and fire safety.

The processing of this product needs to take into account the dispersion of glass fiber and the stability of flame retardant, and the process parameters are finely adjusted. During injection molding, the barrel temperature is set in a gradient: 175℃ in zone 1, 190℃ in zone 2, 200℃ in zone 3, and 195℃ in nozzle, which is 5-10℃ higher than ordinary PP flame retardant. Because glass fiber reinforcement leads to increased melt viscosity, higher temperature is required to reduce viscosity to ensure smooth filling. The screw speed is controlled at 250-300 rpm. Too high speed (>350 rpm) will cause excessive shearing of glass fiber, shortening the length to less than 1.5mm, and reducing mechanical properties by 15%. Too low speed (<200 rpm) will cause uneven mixing and easy delamination of products. The mold temperature is maintained at 60℃, which is higher than the 40℃ of ordinary PP, which can reduce the internal stress caused by the difference in melt cooling rate and reduce the risk of warping. The injection pressure is 120MPa, the holding pressure is 80MPa, and the holding time is 20 seconds to ensure that the melt fully fills the mold cavity, especially the small parts of complex structural parts. When producing extruded sheets, the pulling speed and extrusion volume must be accurately matched (for example, when producing 3mm thick sheets, the pulling speed of 1.2m/min corresponds to an extrusion volume of 25kg/h), and the die temperature is 190℃, so that the glass fiber is oriented along the extrusion direction, the longitudinal tensile strength is increased to 90MPa, the transverse strength is 75MPa, and the longitudinal and transverse strength ratio is controlled within 1.2. Before processing, the material needs to be dried in an 80℃ oven for 4 hours, and the moisture content is strictly controlled below 0.05% to prevent bubbles from being generated during high-temperature processing. The mold needs to be chrome-plated (chromium layer thickness 50μm) to reduce the wear of the glass fiber on the cavity surface and extend the mold life from 50,000 molds of ordinary materials to more than 100,000 molds. Through these fine process controls, the product qualification rate can reach 99%, and the surface finish can reach 50GU, meeting the appearance requirements of high-end products.

This product has been verified by multiple tests and has excellent weather resistance and chemical resistance. In terms of weather resistance, after 1500 hours of QUV aging test (using 340nm lamp, irradiance 0.71W/m², 8 hours of illumination at 60℃/4 hours of condensation at 50℃ cycle), the tensile strength retention rate is 82%, the bending strength retention rate is 80%, and the color difference ΔE=3.0 (GB/T 11186), which is much better than the 70% retention rate and ΔE=5.5 of unreinforced flame retardant PP. The outdoor exposure test was conducted in Sanya, Hainan (high temperature and high humidity environment). The 100×100×3mm test piece was fixed on an exposure rack at a 45° angle facing south. After 12 months of wind, sun and rain, it was observed that there was no powdering on the surface, the gloss retention rate was 75%, the impact strength retention was 75%, and the flame retardant performance still reached UL94 V-0 level. Because 2% carbon black (particle size 20nm) was added to the formula, it can absorb ultraviolet rays and slow down the aging of PP molecular chains. In the chemical resistance test, the test pieces were immersed in 30% sulfuric acid solution, 10% sodium hydroxide solution, 92# gasoline and engine oil respectively. After standing for 24 hours at 25℃, they were taken out, rinsed with deionized water and wiped dry. The test results showed that the weight loss rate in sulfuric acid was 0.3%, in sodium hydroxide was 0.4%, in gasoline was 0.2%, and in engine oil was 0.15%, and there was no cracking, swelling or discoloration. In the simulated automobile engine compartment environment test, the test piece was placed in a 120℃ oven, and the oil vapor was introduced. After 300 hours, the tensile strength decreased by 8%, the bending strength decreased by 7%, and the flame retardant level was still V-0, with no obvious degradation. According to Fourier infrared spectroscopy analysis, the molecular chain of the material was slightly broken after long-term exposure, and the carbonyl index increased slowly, indicating that its anti-aging ability was significantly better than that of ordinary flame-retardant PP. These properties make it not only suitable for indoor structural parts, but also capable of outdoor photovoltaic brackets, automobile engine peripheral parts, chemical equipment shells and other harsh environments, with long-lasting and stable performance.

This product has a wide range of applications due to its high strength and high flame retardancy. In the automotive industry, it is suitable for engine brackets, chassis suspension components, gearbox housings, etc. It has a tensile strength of 85MPa and a flexural modulus of 4500MPa, meeting the mechanical requirements of ISO 1043-1 for automotive structural parts, and its flame retardant performance reaches UL94 V-0 level. It has passed the FMVSS 302 automotive interior combustion test, which can reduce the risk of vehicle fire. In the electronics field, it is used for charging pile housings, circuit breaker housings, motor end covers, etc. It has passed the UL 94 V-0 certification at a thickness of 1.6mm, and the glow wire test at 750℃ does not ignite, meeting the IEC 60695-2-11 standard, ensuring the safety of electrical equipment. In the field of mechanical manufacturing, it can replace some steel for gears, bearing seats, conveyor belt rollers, etc. Its wear resistance coefficient is 0.35 (ASTM D3702), which is equivalent to cast iron, and its weight is only 1/4 of that of steel, reducing the energy consumption of equipment operation. In the construction field, it is used for outdoor structural parts such as photovoltaic brackets and cable trays. Its weather resistance meets the 10-year service life requirement and does not require regular maintenance. When it is connected to metal, the injection molding insert process can be directly used. The bonding strength between metal and plastic reaches 8MPa (GB/T 14486), and no additional welding or bolting is required, simplifying the assembly process. Compared with traditional steel parts, the weight of parts using this product is reduced by 40%, the processing cycle is shortened from 7 days to 30 seconds (injection molding), and the production cost is reduced by 25%. It shows significant advantages in the fields of lightweight, high strength, and flame retardant requirements, and has broad application prospects.