Basic knowledge of plastics
DATE：2022/12/8 9:01:54 / READ： / SOURCE：This station
Basic knowledge of plastics
1.1 Characteristics of plasticsPlastics refer to materials that can be plasticized under certain temperature and pressure with synthetic or natural polymers as the basic components and plasticizers, fillers and other auxiliary components. The characteristics of plastics are as follows.
(1) Plastic products are relatively light, the density is about 0.83~2.3g/cm3, and the weight is only 1/2 of aluminum. It is of great significance to apply them to mechanical equipment that requires reducing their own weight.
(2) The chemical corrosion resistance is superior to that of metal materials. It has strong corrosion resistance to acids, alkalis and chemicals. It is a material widely used in chemical equipment.
(3) Plastic products have good electrical insulation performance and low dielectric loss, and can be used as materials in the electrical industry.
(4) It has good wear resistance and can be used as antifriction and wear-resistant materials in light load equipment.
(5) Sound elimination and heat insulation performance are excellent. The transmission gear made of plastic has low transmission noise and vibration; Foam plastic is a good heat insulation material.
(6) The modified reinforced plastic has good mechanical properties. It can replace metal materials in some aspects and has outstanding advantages in reducing the weight of equipment.
(7) Disadvantages: the heat resistance of products is poor, and most products cannot be used in the environment above 100 ℃; Very poor thermal conductivity, high coefficient of thermal expansion, flammable and easy to age; The strength and rigidity of products cannot be compared with that of metal materials.
For the identification of raw materials used for plastic product molding, under the condition that the manufacturer does not have complex analytical instruments, simple methods such as density detection, combustion and solubility detection are generally used to determine the plastic variety. The density value shall be tested according to GB 1033 standard.
See Table 1-1 for comparison of characteristics and performance of several common plastic products.
1.2.1 Combustion characteristics of plastic products
By observing the phenomenon caused by the burning of plastic products, the varieties of plastics can be identified, and the method is relatively simple. However, pay attention to safety. The specific test method requirements are as follows.
① Take about 0.1g of sample and place it on clean glass or stainless steel plate; Heat it with a small fire on the gas lamp until it emits smoke. Observe the color and smell of the smoke and whether the burning speed is fast or slow. Test the acid-base property of the decomposed gas with test paper (wet).
② Move the sample to the high temperature area of the flame, observe the flammability of the sample, the fast or slow burning speed, and the color of the flame.
③ Move the sample away from the flame zone to see whether the sample continues to burn or self extinguishes; Observe the shape of the residue.
The combustion characteristics of different plastics are shown in Table 1-2.
Flame retardant plastics include: polytetrafluoroethylene, polytrifluorochloroethylene, perfluoro (ethylene propylene copolymer), perfluoroalkoxy polymer, polytrifluorochloroethylene ethylene copolymer, polyvinylidene fluoride, vinylidene fluoride hexafluoropropylene copolymer, tetrafluoroethylene hexafluoropropylene copolymer, polysulfone, polyethersulfone, aromatic polyamide, polyvinyl chloride, polyvinylidene chloride, chlorinated polyvinyl chloride, polyphenylene sulfide, melamine formaldehyde plastics.
Plastics with poor flame retardancy include silicone plastics, polysulfone, polyphenylene ether, polycarbonate, epoxy plastics, phenolic plastics, aliphatic polyamide, diallyl phthalate, urea formaldehyde plastics, chlorinated polyethylene, and chlorosulfonated polyethylene.
Flammable plastics include polyethylene, polypropylene, polystyrene, polyoxymethylene, polyethylene terephthalate, polybutylene terephthalate, acrylic plastic, cellulose plastic, polyurethane and unsaturated polyester.
1.2.2 Solubility of plastic products
The dissolution of plastic products can be understood as the increase in the distance between molecular chains due to the interaction between solute molecules and solvent molecules. In addition to some linear polymers such as polytetrafluoroethylene, general plastics can be dissolved in some solvents. In the work, it is possible to identify plastic varieties by means of different plastic melting behaviors. See Table 1-3 for the solubility of common plastics.
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