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Crystalline polymers are usually opaque because of light scattering on the numerous boundaries between the crystalline and amorphous regions. The density of such boundaries is lower in polymers with very low crystallinity (amorphous polymer) or very high degree of crystalline polymers, consequentially, the transparency is higher. [ 5 ]
In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid) is a solid that lacks the long-range order that is characteristic of a crystal. The terms " glass " and "glassy solid" are sometimes used synonymously with amorphous solid; however, these terms refer specifically to amorphous materials that undergo ...
All polymers (amorphous or semi-crystalline) go through glass transitions. The glass-transition temperature ( T g ) is a crucial physical parameter for polymer manufacturing, processing, and use. Below T g , molecular motions are frozen and polymers are brittle and glassy.
The mesomorphic modification, however, occurs often in industrial processing, since the plastic is usually cooled quickly. The degree of order of the mesomorphic phase ranges between the crystalline and the amorphous phase, its density is with 0.916 g·cm −3 comparatively. The mesomorphic phase is considered as cause for the transparency in ...
Light tends to scatter as it crosses the boundaries between crystallites and the amorphous regions between them, causing the resulting solid to be translucent. [citation needed] Orientation also renders polymers more transparent. [clarification needed] This is why BOPET film and bottles are both crystalline, to a degree, and transparent.
Many plastics are completely amorphous (without a highly ordered molecular structure), [23] including thermosets, polystyrene, and methyl methacrylate (PMMA). Crystalline plastics exhibit a pattern of more regularly spaced atoms, such as high-density polyethylene (HDPE), polybutylene terephthalate (PBT), and polyether ether ketone (PEEK ...
Amorphous and semi-amorphous plastics are less resistant to chemical attack and environmental stress cracking because they lack a crystalline structure. Brittleness can be decreased with the addition of plasticizers , which increases the mobility of amorphous chain segments to effectively lower the glass transition temperature.
Amorphous solids are the opposite of crystalline. The atoms or molecules in amorphous substances are arranged randomly without any long-range order. As a result, they do not have a sharp melting point. The phase transition from solid to liquid occurs over a range of temperatures. [citation needed] Some examples include glass, rubber and some ...