Polymer manufacturing, common problems

Extmsion is a common way for soHd products such as plastics to emerge from closed manufacturing systems. Normally a polymer is hot when extmded and may contain additives and oligomers that are volatile at elevated tempera-tures. The result is Aiming at the extmder head. These fumes can result in employee annoyance, housekeeping problems, and, at worst, depending on composition, health ha2ards. 

As important as batteries are to modern civilization, a number of inherent problems are associated with them. For example, the lead-storage battery present in all modern motor vehicles is very heavy (it contains one of the densest of common metals, lead) and it must be continually recharged, eventually wears out, and presents serious environmental problems during its manufacture and disposal. After the discovery of conductive polymers, many scientists hoped and dreamed that these materials could he used to make efficient, lightweight plastic batteries. 

A wide range of plastics with different properties has been used in the construction of laboratory apparatus. In spite of the adsorption ability of the polymers and, therefore, the risk of analyte loss by adsorption on container walls, contamination arising from residual catalysts and additives used in their manufacture is the main problem. Among the most common plastics used in manufacturing laboratory containers are low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP) and polytetrafluoro-ethylene (PTFE). 

Specific methods have been established for quite a large number of compounds or analytic problems. Among these are amino acids, sugars in food, common organic adds in food, vitamins, and additives (e.g., antioxidants) in polymers. Column manufacturers may have an applications database from which they can recommend a column and a method. However, it is recommended to rely on literature methods only, if the methods are well established and have been proved out in many laboratories. EPA methods or pharmacopoeia methods fall into this category, but a single reference on a method for an uncommon analyte should be viewed with caution. It is not unconunon that such a method does not work or does not work well when duplicated. In such a case, we are actually better off to develop a new method ourselves. 

Different processes are nsed in industry for the manufacture of polymers by fi-ee-radical chain polymerization. Among them homogeneous bulk polymerization is economically the most attractive and yields products of higher purity and clarity. But it has problems associated with the heat of polymerization, increases in viscosity, and removal of unreacted monomer. This method is nevertheless used for the manufacture of PVC, polystyrene, and poly(methyl methacrylate). More common processes are homogeneous solution polymerization and heterogeneous suspension polymerization. 

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