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Introduction to some kinds of plastics

Today we will introduce some kinds of plastic material. 

1. Polyvinyl chloride(PVC)

Actually the PVC is polyvinyl chloride, which is a polymer formed by the polymerization of vinyl chloride monomer in initiators such as peroxides and azo compounds, or under the action of light and heat, according to the mechanism of free radical polymerization.

PVC is a white powder with an amorphous structure with a small degree of branching. The glass transition temperature is 77~90℃, and it begins to decompose at about 170℃[1]. It has poor stability to light and heat. , it will decompose to produce hydrogen chloride, and further autocatalytic decomposition, causing discoloration, and the physical and mechanical properties also drop rapidly. In practical applications, stabilizers must be added to improve the stability to heat and light.

PVC is widely used in building materials, industrial products, daily necessities, floor leather, floor tiles, artificial leather, pipes, wires and cables, packaging films, bottles, foam materials, sealing materials, fibers, etc.


2. Polyethylene(PE)

PVC is a thermoplastic resin obtained by polymerizing ethylene. In industry, copolymers of ethylene with small amounts of alpha-olefins are also included. Polyethylene is odorless, non-toxic, feels like wax, has excellent low temperature resistance (minimum operating temperature can reach -100~-70°C), good chemical stability, and can resist most acid and alkali erosion (not resistant to oxidation nature acid). Insoluble in common solvents at room temperature, low water absorption, excellent electrical insulation.

PE can be divided into high-density PE, low-density PE and linear low-density PE according to the polymerization method, molecular weight and chain structure.

I: High density PE (HDPE): produced by gas phase method and slurry method. Its natural color cylindrical or oblate particles, smooth surface, no mechanical impurities, thermoplastic. If it is powder, the color is white. HDPE will oxidize when heated in the air or exposed to sunlight. It is resistant to most acid and alkali corrosion, has low water absorption, can remain soft at low temperature, and has high electrical insulation. Mainly used in the production of film products, daily necessities and industrial containers, pipes, fishing nets, wires and cables, etc.

II: Low density PE (LDPE): mainly produced by high pressure tubular method and kettle method. Its surface is dull, milky white waxy particles, odorless, non-toxic, tasteless, melting point is 130~145℃. Insoluble in water, corrosion resistance, low water absorption, good low temperature flexibility, high electrical insulation. Mainly used in agricultural film, industrial packaging film, daily necessities, wires, coatings, mechanical parts, etc.

III: Linear low density PE (LLDPE): It is mainly produced by full density polyethylene equipment. The typical production process is Innovene process and UCC's Unipol process. LLDPE and LDPE have better environmental stress crack resistance and electrical insulation, higher heat resistance, and higher impact and puncture resistance. Mainly used for daily necessities, pipes, cables, etc. by injection molding, extrusion, blow molding and other molding methods.


3. Polypropylene(PP)

Polypropylene is PP, a high-density, side-chain-free, high-crystallinity linear polymer with excellent comprehensive properties. Common products: basins, barrels, furniture, films, woven bags, bottle caps, car bumpers, etc.

polypropylene is a non-toxic, odorless, tasteless milky white high crystalline polymer with a density of only 0. 90--"0. 91g/cm3, which is one of the lightest varieties of all plastics. It is particularly stable to water, the water absorption rate in water is only 0.01%, and the molecular weight is about 80,000 to 150,000. The formability is good, but the shrinkage rate is large (1% to 2.5%). Some parts with high dimensional accuracy are difficult to meet the requirements, and the surface gloss of the product is good.

pp material has excellent chemical resistance, heat resistance, electrical insulation, high-strength mechanical properties and good high wear-resistant processing properties, etc., and is widely used in various industries, such as machinery, automobiles, electronic appliances, construction , textiles, food, etc.

Disadvantages of PP: low dimensional accuracy, insufficient rigidity, poor weather resistance, it has the phenomenon of post-shrinkage, and after demolding, it is easy to age, become brittle, and easy to deform. In daily life, the commonly used fresh-keeping boxes are made of PP materials.


4. Polycarbonate(PC)

Polycarbonate, also known as PC plastic; is a high molecular polymer containing carbonate groups in the molecular chain. According to the structure of ester groups, it can be divided into aliphatic, aromatic, aliphatic-aromatic and other types. Among them, the low mechanical properties of aliphatic and aliphatic-aromatic polycarbonates limit their application in engineering plastics.

PC is a linear carbonated polyester in which the carbonic acid groups are alternately arranged with other groups, and these groups can be aromatic, aliphatic, or both. Bisphenol A PC is the most important industrial product.PC is an almost colorless glassy amorphous polymer with good optical properties. PC high molecular weight resin has high toughness, Izod notched impact strength is 600~900J/m, and the heat distortion temperature of unfilled grades is about 130°C, which can be increased by 10°C after glass fiber reinforcement. The flexural modulus of PC can reach more than 2400MPa, and the resin can be processed into large rigid products. Below 100°C, the creep rate under load is very low. PC has poor hydrolysis resistance and cannot be used for products that are repeatedly subjected to high pressure steam. And PC material is flame retardant. Antioxidant.

The main performance defects of PC are that the hydrolysis resistance is not high enough, it is sensitive to notch, organic chemical resistance, scratch resistance is poor, and it will turn yellow when exposed to ultraviolet light for a long time. Like other resins, PC is susceptible to attack by certain organic solvents.


5. Polystyrene (PS)

PS (polystyrene plastics) It refers to a polymer synthesized by free radical addition polymerization of styrene monomer, and its chemical formula is (C8H8)n. It is a colorless and transparent thermoplastic with a glass transition temperature higher than 100°C, 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.

Usually polystyrene is an amorphous random polymer, which has excellent heat insulation, insulation and transparency. The long-term use temperature is 0-70 ° C, but it is brittle and easy to crack at low temperature.

Polystyrene is easy to process and form, and has the advantages of transparency, cheapness, rigidity, insulation, and good printability. It can be widely used in light industry market, daily decoration, lighting instructions and packaging. In the electrical aspect, it is a good insulating material and thermal insulation material, which can be used to make various instrument shells, lampshades, optical and chemical instrument parts, transparent films, capacitor dielectric layers, etc.


6. polyethylene terephthalate(PET)

Polyethylene terephthalate is synthesized from dimethyl terephthalate and ethylene glycol by transesterification or esterification with terephthalic acid and ethylene glycol, and then bishydroxyethyl terephthalate is synthesized. obtained by polycondensation. It is a crystalline saturated polyester, which is a milky white or light yellow, highly crystalline polymer with a smooth and shiny surface. It is a common resin in life and can be divided into APET, RPET and PETG

PET is a milky white or light yellow highly crystalline polymer with a smooth and shiny surface. It has good creep resistance, fatigue resistance, abrasion resistance and dimensional stability, low wear and high hardness, and has the greatest toughness among thermoplastics: good electrical insulation performance, small temperature influence, but poor corona resistance. Non-toxic, weather resistant, chemical resistant, low water absorption, resistant to weak acids and organic solvents, but not resistant to hot water immersion and alkali.

The glass transition temperature of PET resin is high, the crystallization speed is slow, the molding cycle is long, the molding cycle is long, the molding shrinkage rate is large, the dimensional stability is poor, the crystallization molding is brittle, and the heat resistance is low.


7. Acrylonitrile Butadiene Styrene plastic (ABS)

ABS plastic is a terpolymer of three monomers, acrylonitrile (A), butadiene (B) and styrene (S). The relative content of the three monomers can be changed arbitrarily to make various resins.

ABS plastic has the common properties of three components, acrylonitrile (A) makes it resistant to chemical corrosion, heat resistance, and has a certain surface hardness, butadiene (B) makes it have high elasticity and toughness, and styrene (S) makes it have the processing and molding characteristics of thermoplastics and improve electrical properties. performance. Therefore, ABS plastic is a kind of "tough, hard and rigid" material with easily available raw materials, good comprehensive performance, low price and wide application. ABS plastic has been widely used in machinery, electrical, textile, automobile, aircraft, ship and other manufacturing industries and chemicals.

The appearance of ABS is opaque and ivory-colored granules, which are non-toxic, odorless, and low in water absorption. Its products can be colored in various colors and have a high gloss of 90%. ABS has good bonding with other materials, and is easy to surface printing, coating and plating. The oxygen index of ABS is 18.2, it is a flammable polymer, the flame is yellow, there is black smoke, it is burnt but not dripping, and it emits a special cinnamon smell



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