a. What are Polymers?
Polymers are large molecules whose molecular weight can range from the
thousands to millions. Polymers are built up by the repetition of low molecular
weight units. ‘poly’ means many and ‘mer’ = parts. For example: Polyethylene is
made by ‘joining’ many ethylene molecules together. The process of ‘joining’ is
b. What is Polymer Morphology?
Polymer morphology is the arrangement of the polymer molecules. There are two
type of possible arrangements: Amorphous and Crystalline.
c. What are the typical thermal transitions in polymers?
There are three main states in which a polymer can exist and therefore there are
two types of typical transitions the polymer can go through. In the Glassy
state, the plastic is brittle; in the Rubbery or Viscoelastic state, the
plastic is soft and/or tough and in the Melt state the plastic is molten. The
transition temperature at which the polymer changes from brittle to soft/tough
is called the Glass Transition Temperature (Tg). The transition temperature at
which the polymer changes from soft/tough to a melt is called the Melt
Temperature or Tm. Amorphous polymers do not show a clear transition into the
melt and therefore do not exhibit a Tm. The change is gradual and the polymer
softens with increasing temperature. Therefore, in injection molding, amorphous
materials (ABS) have a wide melt processing window compared to crystalline