Polypropylene materials are commonly modified through various methods, including mineral reinforcement and toughening, weather resistance treatment, glass fiber reinforcement, and flame retardant modification. These modifications allow the material to be used in a wide range of applications within the home appliance industry.
Mineral reinforcement is one of the most widely used modification techniques. Common minerals added to polypropylene include calcium carbonate, talc, wollastonite, glass microbeads, and mica powder. These additives not only enhance the mechanical properties and impact resistance of the material, but also reduce molding shrinkage, improving dimensional stability. Additionally, since minerals are significantly cheaper than polypropylene, this method helps lower overall production costs. Today, many washing machines use mineral-reinforced polypropylene for their inner drums, replacing older stainless steel models. This material is also used for components like pulsators and laundry outlets. For example, Haier alone uses approximately 1,700 tons annually, with each drum weighing around 2 kg. In addition, microwave ovens often use mineral-reinforced polypropylene for parts such as door seals, speaker flares, and horn brackets. The addition of minerals improves heat resistance, making it suitable for high-temperature environments inside microwaves. Moreover, refrigerator shelves are now mostly made from this type of modified polypropylene, which solves issues like panel warping that were common with traditional ABS materials.
Weather-resistant polypropylene is designed to address the issue of degradation caused by exposure to light, heat, and oxygen. Polypropylene contains unstable tertiary carbon groups, which can lead to discoloration and loss of strength over time, limiting its use in outdoor applications. By modifying the material, its durability under harsh weather conditions is significantly improved. This type of polypropylene is mainly used for outdoor parts of household appliances, such as air conditioner casings. Compared to traditional metal-coated plastics, it offers advantages such as reduced weight, lower cost, and better corrosion resistance. This technology was first developed in the early 1990s by Japanese companies like Sumitomo and Mitsubishi Chemical.
Glass fiber-reinforced polypropylene is used when higher mechanical performance is required for engineering components. While standard polypropylene has tensile strength between 20–30 MPa and flexural modulus between 800–1,500 MPa, glass fiber reinforcement can significantly improve these properties. Reinforced versions typically have tensile strength of 65–85 MPa, bending strength of 70–95 MPa, and flexural modulus of 3,000–4,500 MPa—comparable to reinforced ABS but with better heat resistance. Glass fiber-reinforced polypropylene can withstand temperatures up to 135–145°C, making it ideal for components like fan blades in refrigerators and air conditioners. It is also used for high-speed washing machine drums due to its superior mechanical performance and lower cost compared to other reinforced materials.
Flame-retardant modified polypropylene is essential for safety in electrical and electronic components of household appliances. Many countries require materials to meet UL94 V0 flame resistance standards. Since polypropylene is inherently flammable, it is usually treated with bromine-based or antimony composite flame retardants. This modification ensures that the material will self-extinguish in case of fire and can withstand high temperatures, such as 650°C or even 750°C on a glow wire. Flame-retardant polypropylene is commonly used for parts like washing machine control panels, wire housing, refrigerator evaporator trays, and air ducts, where fire safety is critical.
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