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What is Polypropylene？
Polypropylene (PP for short) is a thermoplastic synthetic resin made from propylene monomers through addition polymerization. It is an important member of the polyolefin family. Due to its low cost, diverse properties, and ease of processing, it has become one of the most widely used plastic varieties and has an irreplaceable position in industries such as industry, daily necessities, medical care, and packaging.
Molecular Structure: The molecular chain of polypropylene is composed of repeating propylene units (-CH₂-CH (CH₃)-). According to the spatial arrangement of methyl groups (-CH₃) in the molecular chain, it can be divided into isotactic polypropylene (methyl groups are regularly arranged on one side of the main chain, with high crystallinity and good strength, accounting for the mainstream of the market), syndiotactic polypropylene (methyl groups are alternately arranged, with good flexibility), and atactic polypropylene (methyl groups are arranged disorderly, with low crystallinity, mostly used as auxiliary materials).
Core Properties:
Physical Properties: It has a low density (0.90-0.91g/cm³, which is one of the lighter common plastics), good impact resistance (slightly poor at low temperatures, which can be improved through modification), moderate surface hardness, and better light transmittance than polyethylene.
Chemical Stability: It is resistant to most acids, alkalis, and organic solvents (such as ethanol and gasoline), but not to strong oxidizing substances (such as concentrated nitric acid), and can withstand hot water below 80°C.
Thermal Properties: The melting point is about 165°C, and it can be used for a long time at around 100°C, making it suitable for making high-temperature resistant tableware (such as microwave oven lunch boxes).
Processability: It is easy to process by injection molding, extrusion, blow molding, etc., with a high yield rate. Moreover, it can be modified by adding fillers (such as glass fiber), tougheners, etc., to expand the performance range.
The industrial production of polypropylene uses propylene monomers as raw materials, mainly adopting coordination polymerization processes (such as Ziegler-Natta catalysts, metallocene catalysts). The core processes include:
Raw Material Refining: Remove impurities in propylene (such as moisture and sulfides) to ensure the stability of the polymerization reaction.
Polymerization Reaction: Under the action of a catalyst, propylene monomers undergo addition polymerization in a reaction kettle to form polypropylene resin (powder or granular). Reaction conditions (temperature, pressure, catalyst type) determine key indicators such as molecular weight and crystallinity of the product.
Pelletizing and Modification: The polymerized resin is melted and pelletized to obtain basic PP pellets; according to requirements, antioxidants, colorants, reinforcing materials, etc., are added to make modified PP (such as impact-resistant PP, flame-retardant PP).
Packaging Industry: Due to its good chemical resistance and sealing performance, it is often used to make food packaging bags (such as snack bags, composite films), beverage bottles (such as mineral water bottle caps), turnover boxes, etc.; in B-end scenarios, it can be used as packaging materials for industrial parts or made into moisture-proof and wear-resistant transportation pallets.
Daily Necessities and Consumer Electronics: Such as plastic tableware (bowls, spoons), toys, washing machine inner tubs, mobile phone shells, etc., utilizing its lightweight and easy-to-process characteristics.
Industry and Engineering: Glass fiber reinforced PP (FRPP) can be used to make pipes, valves, and chemical equipment casings, which can withstand medium-strength acid and alkali corrosion; in the automotive industry, it is used to produce bumpers, instrument panels and other components to reduce the weight of the car body.
Medical Field: PP that meets food-grade and medical standards (such as atactic copolymer PP) can be used to make syringes, infusion bags, medical trays, etc., because it is non-toxic and resistant to sterilization (can be sterilized by high-temperature steam).
Textiles and Non-woven Fabrics: Polypropylene fibers (polypropylene) can be made into polypropylene spunbond non-woven fabrics, used in masks, surgical gowns, geotextiles, （nonwoven or woven）weed control barrier,row cover etc., and are widely used in B-end health protection and infrastructure projects.
Compared with similar materials such as polyethylene (PE) and polyvinyl chloride (PVC), polypropylene is unique in that:
It has higher hardness and better heat resistance than PE (can be used in microwave ovens), but its low-temperature toughness is poor;
It does not contain plasticizers (such as phthalates) in PVC, so it has better safety and is suitable for food contact and medical scenarios;
The cost is lower than that of polycarbonate (PC) and polyamide (PA), and it has higher cost performance in scenarios with medium and low strength requirements.
In short, relying on the combined advantages of "low cost + multiple properties + easy processing", polypropylene has become an indispensable material in modern industry and daily life, and its modified products can better meet the personalized needs of B-end customers for temperature resistance, weather resistance, strength, etc.
