Cooling Dimensional stability

A related class of polymers is the crystalline, thermoplastic materials. These also are fabricated by heating to a high temperature so diat they flow but when they are cooled ordered regions develop within them, which makes them translucent. They have much tendency to flow because of these mechanical crosslinks" and have good dimensional stability. Polyediylene and polypropylene belong to this class. Here the chain is simple and regular so that different polymer molecules, or different parts of the same molecule, can pack next to each other. The same situation exists with Teflon" (polytetrafl uoroethylene). 

Extrusion temperature of the PVDF/PMMA was in the range of 220°C-240°C. The preferred drawdown ratio of the first bubble was in the range of 10 1 to 15 1, and 2 1 to 3.75 1 forthe second bubble. The desirable blowup ratio ranged from 1.5 1 to 1.75 1. A cooling air temperature of 10°C-20°C was required while the hot air temperature, before the second bubble, varied from 120°C-140°C. The film can be dimensionally stabilized by an annealing process at 120°C for 5 minutes. 

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