Five synthetic resins
Polyethylene (PE), Polyvinyl Chloride (PVC), Polystyrene (PS), Polypropylene (PP) and ABS resin are five general-purpose resins and are the most widely used synthetic resin materials
English name of polyethylene: polyethylene, abbreviated as PE, is a kind of thermoplastic resin made by polymerization of ethylene. In industry, it also includes copolymers of ethylene and a small amount of α-olefins. Polyethylene is odorless, non-toxic, feels like wax, has excellent low temperature resistance (minimum use temperature can reach -70～-100℃), good chemical stability, can withstand most acids and alkalis (not resistant to oxidation) Acid), insoluble in common solvents at room temperature, low water absorption, excellent electrical insulation
Polyethylene resin is a non-toxic, odorless white powder or granules, milky white appearance, waxy feel, low water absorption rate, less than 0.01%. The polyethylene film is transparent and decreases as the crystallinity increases. Polyethylene film has low water permeability but high air permeability, which is not suitable for fresh-keeping packaging but suitable for moisture-proof packaging. Flammable, with an oxygen index of 17.4, low smoke when burning, a small amount of molten drops, yellow flame on the basket, and paraffin smell. Polyethylene has better water resistance. The surface of the product is non-polar, difficult to bond and print, and the surface treatment has been improved. Many branches have poor resistance to photodegradation and oxidation.
The heat resistance of polyethylene is not high, and it has improved with the increase of relative molecular mass and crystallinity. Good low temperature resistance, brittleness temperature can generally reach below -50℃; and with the increase of relative molecular mass, the lowest can reach -140℃. The linear expansion coefficient of polyethylene is large, up to (20-24)×10-5/K. Higher thermal conductivity.
Polyethylene is an alkane inert polymer with good chemical stability. It is resistant to corrosion by acid, alkali and salt aqueous solutions at room temperature, but not to strong oxidants such as fuming sulfuric acid, concentrated nitric acid and chromic acid. Polyethylene is insoluble in common solvents below 60°C, but it will swell or crack after prolonged contact with aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, etc. After the temperature exceeds 60℃, it can be dissolved in toluene, amyl acetate, trichloroethylene, turpentine, mineral oil and paraffin wax; when the temperature is higher than 100℃, it can be dissolved in tetralin. Because the polyethylene molecule contains a small amount of double bonds and ether bonds, its weather resistance is not good, and sunlight and rain will cause aging. It is necessary to add antioxidants and light stabilizers to improve.
Polypropylene, English name: Polypropylene, Japanese name: ポリプロピレン Molecular formula: C3H6nCAS Registration number: 9003-07-0 Abbreviation: PP is a thermoplastic resin produced by the polymerization of propylene.
Non-toxic, odorless, low density, strength, stiffness, hardness and heat resistance are better than low-pressure polyethylene, can be used at about 100 degrees. Has good electrical properties and high-frequency insulation is not affected by humidity, but becomes brittle at low temperatures, not wear-resistant, easy to age. Suitable for the production of general mechanical parts, corrosion-resistant parts and insulation parts. Common acid and alkali organic solvents have almost no effect on it and can be used in tableware.
PP is a semi-crystalline material, which is harder than PE and has a higher melting point. Since the PP temperature of the homopolymer type is very brittle when it is higher than 0C, many commercial PP materials are random copolymers containing 1 to 4% ethylene or block copolymers with a higher ratio of ethylene content. Copolymer PP materials have lower heat distortion temperature (100℃), low transparency, low gloss, and low rigidity, but have stronger impact strength. The impact strength of PP increases with the increase of ethylene content . The Vicat softening temperature of PP is 150C. Due to the high crystallinity, this material has good surface stiffness and scratch resistance. PP does not have the problem of environmental stress cracking. Generally, PP is modified by adding glass fiber, metal additives or thermoplastic rubber. The flow rate MPP of PP ranges from 1 to 40. PP materials with low MFR have better impact resistance but lower ductility. For the same MFR material, the strength of the copolymer type is higher than that of the homopolymer type. Due to crystallization, the shrinkage of PP is quite high, generally 1.8 to 2.5%. And the direction uniformity of shrinkage is much better than PE-HD and other materials. Adding 30% glass additives can reduce the shrinkage to 0.7%. Both homopolymer and copolymer PP materials have excellent moisture absorption resistance, acid and alkali corrosion resistance, and solubility resistance. However, it is not resistant to aromatic hydrocarbon (such as benzene) solvents, chlorinated hydrocarbon (carbon tetrachloride) solvents, etc. PP, like PE, still has oxidation resistance at high temperatures.
PP pipe is the full name of polypropylene plastic pipe. It is non-toxic, hygienic, high temperature resistant and recyclable. It is mainly used in the indoor cold and hot water supply system of buildings, and also widely used in heating systems. Including the following 3 types:
PP-B (block copolymer polypropylene) tube
PP-C (modified copolymer polypropylene) tube
PP-R (Random Copolymer Polypropylene) pipe, also known as type III polypropylene pipe
The most commonly used is the PP-R tube
Polyvinyl chloride (PVC)
The English name of Polyvinyl Chloride is Polyvinyl chloride polymer, which is slightly yellow, translucent and shiny. Transparency is better than polyethylene and polypropylene, and worse than polystyrene. It is divided into soft and hard polyvinyl chloride according to the amount of additives. Soft products are soft and tough, feel sticky, and the hardness of hard products is higher than low density polyethylene. Below polypropylene, whitening occurs at the bend. Common products: plates, pipes, soles, toys, doors and windows, wire sheaths, stationery, etc. It is a polymer material that uses a chlorine atom to replace a hydrogen atom in polyethylene.
Physical and chemical properties
Stable; not easy to be corroded by acid and alkali; relatively resistant to heat
Polyvinyl chloride has flame retardant (flame retardant value of 40 or more), high chemical resistance (concentration of concentrated hydrochloric acid, sulfuric acid with a concentration of 90%, nitric acid with a concentration of 60% and sodium hydroxide with a concentration of 20%), and mechanical strength And the advantages of good electrical insulation. But its heat resistance is poor, its softening point is 80℃, it begins to decompose and change color at 130℃, and HCI precipitates. It has stable physicochemical properties, insoluble in water, alcohol, gasoline, low leakage of gas and water vapor; it can withstand any concentration of hydrochloric acid, sulfuric acid below 90%, nitric acid 50-60% and below 20% at room temperature Caustic soda solution has certain chemical resistance; it is quite stable to salts, but can be dissolved in organic solvents such as ethers, ketones, chlorinated aliphatic hydrocarbons and aromatic hydrocarbons. In addition, POVC has poor light and thermal stability. It will decompose to produce hydrogen chloride at temperatures above 100°C or prolonged sunlight exposure, and will further automatically catalyze decomposition and discoloration. The physical and mechanical properties will rapidly decline, so it must be added in practical applications. Stabilizer to improve the stability to heat and light.
Industrial PVC resin is mainly amorphous structure, but also contains some crystalline regions (about 5%), so PVC has no obvious melting point, it begins to soften at about 80℃, and the heat distortion temperature (under 1.82MPa load) ) Is 70-71℃, it starts to flow at 150℃ under pressure, and it begins to slowly release hydrogen chloride, causing the PVC to change color (from yellow to red, brown, or even black). The weight average molecular weight of industrial PVC is in the range of 48,000 to 48,000, and the corresponding number average molecular weight is 2 to 195, 000. Most industrial resins have a weight-average relative molecular weight of 100,000-200,000 and a number-average relative molecular weight of 45-64 thousand. Rigid polyvinyl chloride (without plasticizer added) has good mechanical strength, weather resistance and Flame resistance, can be used alone as a structural material, used in the manufacture of pipes, plates and injection products in the chemical industry. Rigid PVC can be used as reinforcement
Polystyrene refers to a polymer synthesized from free radical polycondensation of styrene monomer. The English name is Polystyrene, and the Japanese name is ポリスチロール, abbreviated as PS. It is a colorless transparent thermoplastic with a glass transition temperature higher than 100 degrees Celsius, so it is often used to make various disposable containers that need to withstand the temperature of boiling water, as well as disposable foam lunch boxes
PS is generally a head-tail structure, the main chain is a saturated carbon chain, and the side group is a conjugated benzene ring, which makes the molecular structure irregular and increases
The rigidity of the molecule is increased, making PS a non-crystalline linear polymer. Because of the presence of benzene ring, PS has a high Tg (80 ~ 82 ℃), so it is transparent and hard at room temperature, due to the rigidity of the molecular chain, it is easy to cause stress cracking.
Polystyrene is colorless and transparent, can be colored freely, and its relative density is second only to PP and PE. It has excellent electrical properties, especially good high-frequency characteristics, second to F-4 and PPO. In addition, it is second only to methacrylic resin in light stability, but its radiation resistance is the strongest among all plastics. The most important feature of polystyrene is that it has very good thermal stability and fluidity during melting, so it is easy to form and process, especially injection molding, which is suitable for mass production. The molding shrinkage rate is small, and the dimensional stability of the molded product is also good.
Thermal performance: The maximum working temperature is 60～80℃. When heated above Tg, PS changes to a high-elastic state and maintains this state in a wide range, which makes it convenient for thermoforming. The heat distortion temperature of PS is 70～80℃, and the embrittlement temperature is -30℃. PS degrades violently under high vacuum and 330～380℃.
ABS resin is one of the five major synthetic resins. The chemical name is Acrylonitrile-Butadiene-Styrene Plastic. The English name is Acrylonitrile Butadiene Styrene plastic. Its impact resistance, heat resistance, low temperature resistance, chemical resistance and electrical properties are excellent. It also has the characteristics of easy processing, stable product size, and good surface gloss. It is easy to paint and color. It can also be used for secondary processing such as metal spraying, electroplating, welding, hot pressing and bonding on the surface. It is widely used in machinery and automobiles , Electronic appliances, instrumentation, textile and construction and other industrial fields, it is a thermoplastic engineering plastic with extremely wide application.
ABS resin is currently the polymer with the largest output and the most extensive application. It organically unifies the various properties of PS, SAN, and BS, and has excellent mechanical properties of toughness, rigidity, and rigid phase balance. ABS is a terpolymer of acrylonitrile, butadiene and styrene, A represents acrylonitrile, B represents butadiene, and S represents styrene.
The appearance of ABS is opaque and ivory-colored pellets, and its products can be colored colorfully and have high gloss. The relative density of ABS is about 1.05, and the water absorption rate is low. ABS has good combination with other materials and is easy to surface print, coat and plate. ABS has an oxygen index of 18 to 20. It is a flammable polymer. The flame is yellow with black smoke and emits a special odor.
The heat distortion temperature of ABS is 93~118℃, and the product can be increased by about 10℃ after annealing treatment. ABS can still show a certain toughness at -40 ℃, can be used in the temperature range of -40 ~ 100 ℃.