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Name: Brisham
Status: student
Grade: other
Country: Mauritius
Date: Summer 2009


Question:
How do the properties of polymers, amorphous substances and crystalline materials relate to their structure?


Replies:
Brisham,

Generally speaking, "crystalline" refers to materials with regular, repeating structures, while "amorphous" refers to materials that are not crystalline. Technically speaking, crystallinity is better defined by its (x-ray) diffraction pattern rather than purely by arrangement of atoms. I am unsure of your grade level, so let me know if you need a little more explanation or if you want more detail on this. In any case, a polymer could be crystalline, or it could be amorphous (and in fact many polymers are both) -- and is the case with many other materials.

Hope this helps,
Burr Zimmerman


Hi Brisham,

I am not sure I understand your question. The naming of a substance as either amorphous or crystalline, is based only on its molecular structure. So in stating a material is either crystalline, or amorphous, you have already classified its molecular structure to a large degree.

Plastics are all either amorphous, or at best, exhibit a very limited amount of crystalline structure. Those plastics that exhibit a limited amount of crystalline structure, such as the polyacetal family (commonly referred to as Delrin), have a tendency to be somewhat more rigid than many amorphous plastics. Semicrystalline plastics also present greater difficulties in molding, because shrinkage upon cooling, tends to be different in different directions of the plastic part, depending on the orientation of the crystals formed when cooling. Amorphous plastics tend to shrink equally in all directions when cooling.

Regards,
Bob Wilson



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