Recycling by product massive number of types of plastic, they each carry a resin identification code, and must be sorted before they can be recycled. This can be costly; while metals can be sorted using electromagnets, no such 'easy sorting' capability exists for plastics. In addition to this, while labels do not need to be removed from bottles for recycling, lids are often made from a different kind of non-recyclable plastic. To help in identifying the materials in various plastic items, resin identification code numbers 1-6 have been assigned to six common kinds of recyclable plastic resins, with the number 7 indicating any
Polystyrene the chains from aligning with sufficient regularity to achieve any crystallinity. The plastic has a glass transition temperature "T" of ~90 °C. Polymerisation is initiated with free radicals. Ziegler–Natta polymerization can produce an ordered "syndiotactic" polystyrene with the phenyl groups positioned on alternating sides of the hydrocarbon backbone. This form is highly crystalline with a "T" of . Syndiotactic polystyrene resin is currently produced under the trade name XAREC by Idemitsu corporation, who use a metallocene catalyst for the polymerisation reaction. Polystyrene is chemically very inert, being resistant to acids and bases but is easily dissolved by many chlorinated solvents,