PS material basic introduction general purpose polystyrene

Time:2021-06-25 11:58:54 / Popularity: / Source:

PS (polystyrene series plastic) refers to a type of plastic that includes styrene-based in macromolecular chain, including styrene and its copolymers. Specific varieties include ordinary polystyrene (GPPS) and high-impact polystyrene (HIPS), expandable polystyrene (EPS) and metallocene polystyrene (SPS), etc.


General-purpose polystyrene is a kind of thermoplastic resin, which is a shiny, transparent bead or granular solid. Density 1.04~1.09, transparency 88%~92%, refractive index 1.59~1.60. Under action of stress, birefringence occurs, so-called stress-optical effect. Melting temperature of product is 150~180℃, thermal decomposition temperature is 300℃, heat distortion temperature is 70~100℃, and the long-term use temperature is 60~80℃. At 5~6℃ lower than heat distortion temperature, after annealing, stress can be relieved and heat distortion temperature can be increased. If a little α-methylstyrene is added in production process, heat resistance grade of general-purpose polystyrene can be improved.
It is soluble in aromatic hydrocarbons, chlorinated hydrocarbons, aliphatic ketones and esters, but it can only swell in acetone. It can withstand action of certain mineral oils, organic acids, alkalis, salts, lower alcohols and their aqueous solutions. Water absorption rate is low, its mechanical properties and dimensional stability can still be maintained in a humid environment. Optical performance is second only to acrylic resin. Excellent electrical properties, high volume resistivity and surface resistivity, are not affected by temperature and humidity changes, and are not affected by corona discharge. Radiation resistance is also very good. Its main disadvantages are brittleness and easy cracking, low impact strength, poor heat resistance, inability to withstand boiling water, can only be used at lower temperatures and lower loads. It has poor sunlight resistance and is flammable. It emits black smoke when it burns and has a special smell.

Manufacturing method

General-purpose polystyrene is made by radical polymerization or ionic polymerization using styrene as monomer. Production methods include bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization. Nowadays, main methods used in industrial production are suspension polymerization and bulk polymerization.
1. Bulk polymerization method. Put styrene monomer into pre-polymerization kettle, add a small amount of additives and initiators, heats and stirs at 95~115℃ for pre-polymerization. After conversion rate reaches 20%~35%, it is sent to a tower reactor with a stirrer for continuous polymerization. Polymerization temperature was increased to about 170℃ step by step to achieve complete conversion. A small amount of unreacted styrene is released from top of tower, can be recycled and reused. Polymer is continuously discharged from bottom of tower, is extruded and pelletized to obtain finished product, is packaged and then shipped out. Process is as follows.
2. Suspension polymerization method. Using styrene as monomer, water as medium, using gelatin or starch, polyvinyl alcohol, hydroxyethyl cellulose and other protective gums or magnesium carbonate, magnesium silicate, calcium phosphate and other insoluble inorganic salts as dispersants, maleic anhydride-styrene copolymer sodium salt as auxiliary dispersant, and benzoyl peroxide as initiator to initiate polymerization at around 85℃. It is also possible to perform high-temperature polymerization at a high temperature above 100℃ in an autoclave without using an initiator. Polymer is washed, separated, dried to obtain a colorless and transparent fine bead resin.

Forming processing

Polystyrene has good fluidity, good processing properties, easy coloring, and good dimensional stability. It can be processed into various parts by injection molding, extrusion, blow molding, foaming, thermoforming, bonding, coating, welding, machining, printing and other methods, and is especially suitable for injection molding.
During injection molding, materials can generally be used directly without drying. But in order to improve quality of product, it can be pre-dried in a blast oven at 55~70℃ for 1~2h. Specific processing conditions are roughly as follows: barrel temperature is about 200°C, mold temperature is 60~80℃, injection temperature is 170~220℃, 60~150MPa, and compression ratio is 1.6~4.0. In order to eliminate internal stress, molded product can be treated in an infrared lamp or a blast oven at a constant temperature of 70℃ for 2 to 4 hours.
When extruding, L/D ratio of screw generally used is 17~24, cooled by air, and extruding temperature is 150~200℃.
In blow molding, parison made by injection molding and extrusion molding can be used for blow molding to obtain the desired product. Blowing pressure is generally 0.1~0.3MPa.


PS plastic (polystyrene)
English name: Polystyrene
Specific gravity: 1.05 g/cm3
Mold shrinkage: 0.6-0.8%
Molding temperature: 170-250℃
Drying conditions: ---picture


Main performance

a. Mechanical properties: high strength, fatigue resistance, dimensional stability, and small creep (very few changes under high temperature conditions);
PS plastic sheet
b. Heat aging resistance: enhanced UL temperature index reaches 120~140℃ (long-term outdoor aging is also very good);
c. Solvent resistance: no stress cracking;
d. Stability to water: easy to decompose in contact with water (use caution in high temperature and high humidity environments);
e. Electrical performance:
1. Insulation performance: excellent (humidity and high temperature can maintain stable electrical performance, it is an ideal material for manufacturing electronic and electrical parts);
2. Dielectric coefficient: 3.0-3.2;
3. Arc resistance: 120s
f. Molding processability: injection molding or extrusion molding by ordinary equipment. Due to fast crystallization speed and good fluidity, mold temperature is also lower than that of other engineering plastics. When processing thin-walled parts, it only takes a few seconds, and it only takes 40-60s for large parts.


a. Electronic appliances: connectors, switch parts, household appliances, accessory parts, small electric covers or (heat resistance, flame resistance, electrical insulation, molding processability);
b. Car:
1. Exterior parts: mainly include corner grids, engine heat vent covers, etc.;
2. Internal parts: mainly include endoscope stays, wiper brackets and control system valves;
3. Automotive electrical parts: automotive ignition coil twisted tubes and various electrical connectors, etc.
c. Mechanical equipment: belt drive shaft of video tape recorder, electronic computer cover, mercury lamp cover, electric iron cover, baking machine parts, and a large number of gears, cams, buttons, electronic watch casings, camera parts (with heat resistance and flame retardant requirements)


According to different needs, following adhesives can be selected:
1. G-955: One-component room temperature curing soft elastic shockproof adhesive, resistant to high and low temperature, but bonding speed is slow, glue usually takes 1 day or several days to cure.
2. KD-833 instant adhesive can quickly bond PS plastic in a few seconds or tens of seconds, but adhesive layer is hard and brittle, it is not resistant to hot water immersion above 60 degrees.
3. QN-505, two-component glue, soft glue layer, suitable for PS large area bonding or compounding. But high temperature resistance is poor.
4. QN-906: Two-component glue, high temperature resistance.
5. G-988: One-component room temperature vulcanizate. After curing, it is an elastomer with excellent waterproof, shockproof adhesive, high and low temperature resistance. If thickness is 1-2mm, it will basically cure in 5-6 hours and have a certain strength. It takes at least 24 hours to fully cure. Single-component, no need to mix, just apply after extruding and let it stand without heating.
6. KD-5600: UV curing adhesive, bonding transparent PS sheets and plates, can achieve no trace effect, need to be cured by ultraviolet light. Effect is beautiful after sticking. But high temperature resistance is poor.

Material performance

Excellent electrical insulation (especially high-frequency insulation), colorless and transparent, light transmittance second only to plexiglass, coloring, water resistance, good chemical stability, general strength, but brittle, easy to produce stress cracking, is not resistant to organic solvents such as benzene and gasoline. It is suitable for making insulating transparent parts, decorative parts, chemical instruments, optical instruments and other parts.
Forming performance
⒈Amorphous material, low moisture absorption, does not need to be fully dried, is not easy to decompose, but coefficient of thermal expansion is large, it is easy to produce internal stress. It has good fluidity and can be molded by screw or plunger injection machine.
⒉It is advisable to use high material temperature, high mold temperature, and low injection pressure. Prolonging injection time is beneficial to reduce internal stress, prevent shrinkage and deformation.
⒊Various forms of gates can be used, gates are connected with plastic parts arc, so as not to damage plastic parts when gate is removed. Demolding angle is large and ejection is uniform. Wall thickness of plastic parts is uniform, preferably without inserts. If there are inserts, they should be preheated.


PS is widely used in optical industry because of its good light transmittance. It can be used to manufacture optical glass and optical instruments, as well as transparent or bright colors, such as lampshades, lighting appliances, etc. PS can also produce many electrical components and instruments that work in a high-frequency environment. Since PS plastic is a difficult-to-inert surface material, it is necessary to use professional PS glue to bond in industry.
Using PS alone as a product has high brittleness. Adding a small amount of other substances to PS, such as butadiene, can significantly reduce brittleness and improve impact toughness. This plastic is called impact-resistant PS, its mechanical properties are greatly improved. Many mechanical parts and components with excellent performance are made from plastics.

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