Molding 101
Polymers
Polymer Viscosity
Properties of Plastics
Injection Molding
Screw and Check Ring
Commonly Used Calculations
Polymers

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 called polymerization. 

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 materials (Nylons).

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