Plastic Structures and Morphology

This behavior of morphology basically occurs with TP, not TS, plastics. When TSs are processed, their individual chain segments are strongly bonded together during a chemical reaction that is irreversible. 

Plastic molecules that can be packed closer together can more easily form crystalline structures in which the molecules align themselves in some orderly pattern. During 

The amorphous TPs, which have their molecules going in all different directions, are normally transparent. Compared to crystalline types, they undergo only small volumetric changes when melting or solidifying during processing. Tables 2-4 to 2-8 compare the basic performance of crystalline and amorphous plastics. Exceptions exist, particularly with respect to the plastic compounds that include additives and reinforcements. 

As symmetrical molecules approach within a critical distance, crystals begin to form in the areas where they are the most densely packed. A crystallized area is stiffer and stronger, a noncrystallized (amorphous) area tougher and more flexible. With increased crystallinity, other effects occur. As an example, with polyethylene there is increased resistance to creep, heat, and stress cracking as well as increased mold shrinkage. 

In general, crystalline types of plastics are more difficult to process, requiring more-precise control during fabrication, have higher melting temperatures and melt viscosities. 

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