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How Plastic is Made

Most people do not realize how plastic is made much less how it behaves in the molten state. To begin lets define Polymerization- The process of combining short molecules to make long molecules. (The word polymer comes from the word “poly” a Greek word meaning many, the last part of the word “mer” means unit derived from the Greek word “moros”.) All polymers have long chains. Each Monomer that becomes part of the polymer molecular chain  is held together with a force called a covalent bond. Covalent bonds are formed when the monomers and a catalyist that promotes bonding are put under high heat and pressure in a huge silo at the plastics processing plant. Once the polymer is formed the residual catalyist must be washed out of the plastic.  At this point the polymers are in the form of  a powder. Once the powder is washed and dried it is re-melted  and extruded in long strands that are choped up into pellets in a process  called pelletizing.

Long and Thin

  • Typical length of a polymer molecule is 0.000001 inch (0.0000254 mm)
  • Typical length to diameter ratio of a polymer is 1000 to 1.
  • Thousands to ten thousands monomers make up a polymer.
  • If they were 100 yards (91.44 M) long, they would only be 1 inch (25.4 millimeter) in diameter. But not all chains are the same length. The melt index is only an average  and is not exact.

Plastic Molecular Structure

Plastic Starts as Monomer

From the Greek words

Mono = One

Meros = Part

Why certain plastic behavior is like it is has a lot to do with how it is made and what kinds of chemicals are used to make the plastic. Each monomer is carefully selected to produce the right engineering properties to do perform in the context it is used in. The two basic types of polymers can be categorized as amorphous or semi-crystalline and then there are engineering grades that mix the two polymers that can really confuse us.