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neerajsinghvns : amorphous   3

Crystalline vs. Amorphous PET;;;
All PET materials are hygroscopic, so exposure to a humid environment will cause them to absorb moisture. This moisture causes a cleavage in the polymer chain during melt and results in a degradation of the physical properties of the product produced.

Virgin PET
Virgin PET is usually in a crystalline state (indicated by its white color) when it is purchased from a supplier.
Reground PET
Regrind PET material is usually not crystalline, but amorphous and clear in color.
Agitating the material while heating it to a temperature of about 180˚ F will convert the material from its amorphous state to a crystallized state, ready for drying. We call this process crystallizing but technically, it is a re-crystallization of the material.
states  state  properties  plastics  plastic  crystalline  amorphous  PET 
april 2013 by neerajsinghvns
What's the difference between Crystalline and Amorphous States?;;;;;;

What's the difference between Crystalline and Amorphous States?;;;

The nature of crystalline and amorphous polymer states is often misconstrued and misused. The term amorphous means to have no defined shape, or an easily altered shape, like a liquid or a rubber. Crystalline, on the other hand, insinuates that there is a regular, defined pattern to the molecular aggregates --- crystallized carbon forms a substance we call “diamond”. These terms are used to define two separate “solid” states that exist particularly in polymers. The confusing part is that they coexist in many polymers --- the so-called semi-crystalline polymers.

The amorphous nature of polymers is analogous to a plateful of spaghetti --- loose and randomly coiled. While the crystalline state is more like the uncooked spaghetti in the box --- the chains are all tightly bundled and ordered in the same direction.

In a polymer, these two states coexist,
plastics  difference  between  crystalline  and  amorphous  states  plastic 
april 2013 by neerajsinghvns
Why do plastics get brittle when they get cold?
A key factor in the molecules’ ability to slip and slide is temperature. Specifically, there is something called the “glass transition temperature” (Tg), which is the point below which an amorphous solid (such as glass, polymers, tire rubber, or cotton candy) goes from being ductile to brittle. For most common materials, says Rutledge, this temperature is so high or so low that it is not easily observed - the Tg of window glass is 564 degrees C, and that of tire rubber is -72 degrees C.
solid  amorphous  Tg  glass  transition  temperature  why  do  plastics  brittle  when  they  get  cold 
april 2013 by neerajsinghvns

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