Polystyrene (PS) is a polymer synthesized from styrene monomers through free radical addition polymerization, with a chemical formula of (C8H8)n. It is a colorless, transparent thermoplastic with a glass transition temperature above 100℃, often used to make disposable containers and foam food boxes that need to withstand boiling water temperatures.

　　Uses

　　Polystyrene is easy to process and mold, and has advantages such as transparency, low cost, rigidity, insulation, and good printability. It can be widely used in light industry, daily decoration, lighting indication, and packaging. In the electrical field, it is an excellent insulating and heat-insulating material, and can be used to make various instrument housings, lampshades, optical and chemical instrument parts, transparent films, capacitor dielectric layers, etc.

　　It can be used in powder and emulsion cosmetics. Used in powder compacts, it has good compressibility and can improve the adhesion of powder. It imparts luster and smoothness to the skin and is a high-grade filler to replace talc and silica.

　　Environmental Issues

　　Due to its low weight (especially foamed types) and low residual value, polystyrene is not easily recycled. Polystyrene is usually not recyclable via kerbside collection. However, industrial reuse of expanded polystyrene has been greatly improved, with many new methods for densification. These methods typically increase density by 15 slugs/ft3 (translator's note: 1 slugs/ft3=1.94055g/cm3) and create a suitable center for recycling operations on clean polystyrene.

　　Material Type

　　Synthetic Material

　　Plastics:

　　Polyethylene; Polyvinyl chloride; Polystyrene; Polyvinyl alcohol; Polypropylene; Polyacrylic acid; Polybutylene; Polyisobutylene; Polysulfone; Polyformaldehyde; Polyamide; Polycarbonate; Polylactic acid; Polytetrafluoroethylene; Polyethylene terephthalate; Epoxy resin; Phenolic resin; Polyurethane

　　Synthetic Rubber:

　　Polybutadiene rubber; Styrene-butadiene rubber; Nitrile rubber; Chloroprene rubber

　　Synthetic Fiber:

　　Polypropylene fiber; Polyester fiber; Polyamide fiber; Acrylic fiber; Spandex; Vinylon; Nylon; Dacron; Kevlar

　　High Impact Type

　　High impact polystyrene is an amorphous polymer produced by graft polymerization of styrene monomers with rubber, or a physical blend of polystyrene and rubber (usually polybutadiene rubber). The resulting polymer is tough, usually white (also available in transparent grades), and very easy to extrude and mold. Its toughness is mainly determined by the ratio and amount of the rubber component. Typical properties of high impact PS are: flexural strength and tensile strength of 13.8～48.3MPa (varies with rubber and additive content); elongation 10～60%; gloss 5～100%. Visual transparency ranges from excellent to poor, shrinkage is about 0.006, and the coefficient of thermal expansion is the same as transparent PS. The properties of high impact PS remain unchanged after γ-ray sterilization, and it has the same solvent resistance as transparent PS. The melt index of high impact PS is 1～10g/min, and the Vicat softening point is 215°F. The commercial production of high impact polystyrene with enhanced properties has broad market prospects. Some special grades include: ultra-high gloss grade, high transparency grade, wear-resistant grade, environmental stress-cracking resistance grade (ESCR), high modulus grade, low gloss grade, and grades with low residual styrene monomer content.

　　The outstanding characteristics of high impact polystyrene are its ease of processing, excellent dimensional stability, high impact strength, and high rigidity. For HIPS, there are limitations in heat resistance, oxygen permeability, UV stability, and oil resistance. Chemically and in terms of properties, high impact polystyrene is produced by dissolving polydiene rubber in styrene monomer before polymerization. Although HIPS can be produced by suspension polymerization, the bulk polymerization method is currently mainly used in industrial production of HIPS. In the bulk polymerization process, the styrene monomer/rubber/additive mixture is passed through a series of reactors with a conversion rate of 70～90%. The polymerization reaction requires heating or the addition of initiators to complete the reaction, then volatile residual monomers are removed from the resin under vacuum, and then granulated and sold.

　　The continuous development of polystyrene technology enables manufacturers to produce grades with more outstanding properties compared to standard PS. Many properties of polystyrene cannot be obtained simultaneously. For example, if impact strength is to be improved, gloss must be sacrificed. Some new resins have appeared, which have the gloss of ABS and high toughness at the same time. Some grades have also been developed that are resistant to various oils when packaging food and resistant to chlorofluorocarbon (CFC) blowing agents when used in refrigerators. Flame-retardant grades (UL V-0 and UL 5-V), high impact polystyrene are already in production and widely used in television housings, commercial machines, and electrical appliances. These resins are easier to process and cheaper than many flame-retardant engineering resins.

　　Expandable Type

　　Used to manufacture products ranging from teacups to household insulation materials. The properties of foam plastics (such as density and impact strength) depend on the size and distribution of the pores, which are controlled by the dispersion rate, percentage content, and volatility of the blowing agent added. Typical blowing agents are pentane and isopentane. Flame-retardant expanded polystyrene, using halogenated hydrocarbons as flame retardants, is widely used as sound insulation and heat insulation layers in buildings and engineering applications. Expandable SAN has been used to manufacture floating products and other gasoline-resistant products.

　　Copolymers

　　They have very good toughness. The main varieties are: styrene-acrylonitrile copolymer (SAN), styrene-maleic anhydride copolymer (SMA), styrene-butadiene-styrene copolymer (SBS), styrene-acrylate copolymer, and their modified forms. SAN has a higher heat distortion temperature than transparent PS, and its solvent resistance is also improved, with excellent permeability resistance. Rubber-modified SAN includes resins such as acrylonitrile-butadiene-styrene copolymer (ABS) and acrylonitrile-styrene-acrylate copolymer (ASA). The heat distortion temperature of S-MA is higher than that of transparent PS, reaching 40°F, and it has excellent transparency and gloss. SMA can be rubber-modified or reinforced with glass fiber. Various modifications of SBS and SBS can be used as components to improve impact resistance, flexibility, and flowability in the production of viscous and bend-resistant products such as mortar, shoe soles, and asphalt felt. SBS is also used in the production of transparent impact-resistant PS. Styrene can copolymerize with acrylate elastomers to produce transparent impact-resistant PS with excellent physical properties.