Common plastic classification and use

In the examination of public institutions, scientific and technological knowledge is a compulsory subject every year. Judging from the propositional laws, scientific and technological knowledge mainly examines the knowledge of physics, chemistry and biology related to life. Among them, in the chemical knowledge, the classification and use of plastics are often investigated. In order to facilitate everyone to master this part, the author sorts out the knowledge related to plastics to help everyone take the test.

   First, the examination center

  (1) Concept

  Plastic is a synthetic or natural high molecular polymer, which can be arbitrarily kneaded into various shapes and can keep the shape unchanged after the material or plastic material product.

  The main component of plastic is resin. Resin accounts for about 40% to 100% of the total weight of plastics.

  (2) Classification

  1. General purpose plastic

  People will look for some plastic varieties with large output, low price, wide application and wide influence.

  Main varieties: polyethylene, polypropylene, polyvinyl chloride, polystyrene and other varieties.

  2. Engineering plastics

  Engineering plastics refer to plastics that can be used as engineering materials and replace metal to manufacture machine parts.

  Main varieties: polyimide, polyphenylene sulfide, polysulfone, aromatic polyamide, polyarylate, polyphenylester, polyaryletherketone, liquid crystal polymer and fluororesin, etc.

  3. Special plastics

  Special plastics generally refer to plastics with special functions that can be used in special application fields such as aviation and aerospace.

  Main varieties: reinforced plastics, foamed plastics.

   (3) Common plastic products and their characteristics

  1.PS (polystyrene)

  Material features: low cost, transparent and dyeable, dimensional stability, high rigidity. The disadvantages are high fragmentation, poor solvent resistance and temperature difference.

  Common applications: stationery, toys, housings for electrical appliances, and cup boxes or disposable tableware for beverages in fast food restaurants.

  Contraindications: Do not cook instant noodles in a microwave oven.

  2.PET (polyethylene terephthalate).

  Material Features: Heat-resistant to 65°C, cold-resistant to -20°C, only suitable for warm or frozen drinks, easy to deform when loaded with high-temperature liquids or heated, and there are substances that are harmful to the human body melted out.

  Common applications: mineral water bottles, carbonated beverage bottles, etc.

  Contraindications: Do not put it in the car to bask in the sun; do not pack alcohol, oil and other substances.

  3.HDPE (High Density Polyethylene)

  Material features: non-toxic, tasteless, crystallinity of 80% to 90%, softening point of 125 to 135°C, use temperature up to 100°C; good wear resistance, toughness and cold resistance.

  Common applications: white medicine bottles, cleaning supplies, containers for bath products.

  Contraindications: Do not use it as a water cup, or use it as a storage container for other items.

  4.PVC (polyvinyl chloride)

  Material features: It is one of the plastic products with the largest output in the world, it is cheap and widely used. However, the thermal stability is poor. Long-term heating will cause decomposition, release HCL gas, and make PVC discolored. The operating temperature is generally between -15 and 55 degrees.

  Common applications: raincoats, building materials, plastic films, plastic boxes, etc.

  Contraindications: Not for use in food packaging.

  5.PP (polypropylene)

  Material features: The common melting point is as high as 167°C, and the special PP for microwave ovens is resistant to high temperature of 120°C and low temperature of -20°C. It is the only plastic box that can be placed in a microwave oven and can be reused after careful cleaning.

  Common applications: soy milk bottle, yogurt bottle, juice drink bottle, microwave lunch box.

  Contraindications: Remove the lid when placing it in the microwave.