PS – Polystyrene
PS is one of the oldest known vinyl compounds. Amorphous polymer made from addition polymerization of styrene. Homopolymer (crystal):- Clear and colorless with excellent optical properties and high stiffness. It is brittle until biaxially oriented when it becomes flexible and durable. Graft copolymer or blend with elastomers- Impact polystyrene (IPS): Tough, white or clear in color, and easily extruded or molded. Properties are dependent upon the elastomer %, but are grouped into medium impact (Izod<1.5 ft-lb), high impact (Izod between 1.5 to 2.4 ft-lb) and super-high impact (Izod between 2.6 and 5 ft-lb).
Polystyrene was discovered in 1839 by Eduard Simon, an apothecary in Berlin. From storax, the resin of the Turkish sweetgum tree Liquidambar orientalis, he distilled an oily substance, a monomer that he named styrol. Several days later, Simon found that the styrol had thickened, presumably from oxidation; into a jelly he dubbed styrol oxide ("Styroloxyd"). The company I. G. Farben began manufacturing polystyrene in Ludwigshafen, Germany, about 1931, hoping it would be a suitable replacement for die-cast zinc in many applications. Success was achieved when they developed a reactor vessel that extruded polystyrene through a heated tube and cutter, producing polystyrene in pellet form. In 1959, the Koppers Company in Pittsburgh, Pennsylvania, developed expanded polystyrene (EPS) foam. In 1937, the Dow Chemical company introduced polystyrene products to the U.S. market.
Polystyrene is generally classified as 1) Crystal polystyrene (general purpose) 2) Impact polystyrene (HIPS). Polystyrene is produced by suspension, bulk/mass, or solution polymerization.
LG Chem, Polimeri Europa, The Dow Chemical, Styron, Dow, SABIC, Nova chemicals and Supreme Petrochem Ltd, are some of the leading producers of polystyrene in the world.
The global capacity of LLDPE is 28 (‘000 MT) and the demand is 22 (‘000 MT). The capacity is expected to increase to 35 (‘000) MT in 2016 with demand reaching 30 (‘000 MT). In India total PS capacity is expected to reach 472 KTA by 2016-17.
Applications of PS include
Injection Moulding- Packaging- Cosmetic containers- Toys and novelties- Imitation jewellary- Louvres/Lampshades- Crystalwares- Stationery items- Audio Cassettes- Office fixtures- Computer disk reels- Medical applications- Petri disnes- Pill bottles- Pipettes- Ball Pens- Beads. Extrusion- Packaging- Egg cartons- Meat & poultrytrays- Packages for fast-food takeouts- Oriented PS- Blister packs- Food packaging
Industrial applications- Liners for refrigerators- Air conditioner components- Transistor/TV/Tape recorder cabinets- Wall clocks- Electrical Fittings- Video and Audio cassettes- Consumer electronics products- Automobile tail lightings and reflectors- Novelties, toys, shoe heels, furniture
Solution (bulk) polymerization is commonly referred to as mass polymerization in the industry. The vast majority of all polystyrene produced today is produced via this technology. The common solvents used in this process are the styrene monomer itself and ethyl benzene. The two types of mass polymerization are batch and continuous, of which continuous mass is by far the most popular.
Batch mass polymerization consists of a polymerization section containing agitated vessels polymerizing up to 80% conversion in a batch method. The polymerized solution is then pumped to a batch finishing section for either devolatisation or plate and frame final polymerization and grinding. The most widely used process for polymerization of polystyrene today is the continuous mass process. This solution is continuously prepared in a holding vessel and will then be injected into the reactor system.