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 sulfonate salt to prevent hypokalaemia, which is often associated with diarrhea. Polystyrene sulfonic acid, the acid whose salts are the polystyrene sulfonates, has the idealized formula (CHCHCHSOH). The material is prepared by sulfonation of polystyrene: Several methods exist for this conversion, which can lead to varying degree of sulfonation. Usually the polystyrene is crosslinked, which keeps the polymer from dissolving. Since the sulfonic acid group (SOH) is strongly acidic, this polymer neutralizes bases. In this way, various salts of the polymer can be prepared, leading to sodium, calcium, and other salts: These ion-containing polymers are called ionomers. Double substitutions of the