FOAMING

FOAMING

Process:- 

Expanded or foamed plastics are low density materials made by foaming gas bubbles in the plastics while in liquid or molten state. A variety of processes and type of products are available depending upon the type of polymer and the structure. Foe polyurethane foams, bubbles are produced in the low molecular weight mixture of reactants undergoing polymerization, partly arising from gases produced in the condensation process but usually supplemented by blowing agent like volatile fluorocarbon liquid. Flexible polyurethane foams are open cell type, like sponges. Rigid or flexible thermoplastic materials like PVC, polyurethane, polystyrene etc. may be formed in the following methods.

1)    By dispersing a blowing agent in the material and heating it above its softening temperature. The blowing agent foams a large number of small bubbles in the material, and may be a volatile liquid such as pentane used in expanded polystyrene, or an unstable chemical such as azodicarbonamide, releasing much gas when heated.

2)    By dissolving a gas such as nitrogen or carbon dioxide in the heated plastic at high pressure. When the pressure is released, a large number of small bubbles are formed and grow in the soft plastic. This process may be carried out in autoclaves or continuously in extrusion machine, the plastic expanding as it leaves the extrusion tube.

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