The basics'

Materials……part 1.

Given that we in the industry process Plastics are we aware of the basics' of what the materials, are? By this, the question is can you state the difference between thermosets and thermoplastics. Are people in the plant educated as to the difference in materials, or simply stated, educated as to the materials they process? In the industry, we tend to forget the longer we are around, some of the basic things. Maybe it doesn't matter, maybe it is assumed, or possibly, no one ever knew.   So many times we learned by following someone around and being shown, but than no one ever really explained the differences or the why.

Thermosets:
These materials crosslink when cured, meaning that they are set for life in the shape they have. If we were to add heat to these materials they do not melt or soften. Examples of these are epoxy, polyester resin, phenolic, and melamine, to name a few. The comparison used is that of an egg, stated once we cracked the egg open to cook it we can not put it back to the original shape.  These materials are cast, injection molded, and compression molded to name some of the processing methods. They cure by the addition of heat to them, or by chemical reaction created by a catalyst (which can generate heat).

Thermoplastics:
These materials as there name implies are effected by heat, should the shape not be to our liking we may apply heat and reshape and or reform. If we add heat to these materials they will melt or soften. Examples of these are ABS, Styrene, Polyethylene, Nylon and Acetal to name a few. The comparison usually used is that of wax, since if we do not like the product in wax we can remelt and reshape it by applying heat. These materials are injection molded, extruded, and compression molded to name a few processing methods.  They are though of two main family types, amorphous and semi crystalline. Though a third family may be polyurethane, this may be classified as its own due to it special characteristics.

Amorphous materials:
These materials have the following basic characteristics:
1- soften upon heating
2- low shrinkage
3- attacked by solvents
4- fair chemical resistance
5- may be transparent, (type dependent)

Examples: ABS, polystyrene, acrylic, and polycarbonate.

Semi-Crystalline materials:
These materials have the following basic characteristics:
1- melt upon heating
2- high shrinkage
3- good solvent resistance
4- good chemical resistance

Examples:  Nylon, polyethylene, polyester, acetal, polypropylene.

Thanks for the time, to be continued.

Steven L Silvey
Sr. Technical Service
General Polymers Division
Ashland Distribution Services

A request,
Over the years (yes too many) I have written and commented on various aspects of the industry and have heard at times that people enjoy the column. My request is to know what further topics would be of interest to you, the readers and or if you have questions what those would be. Please E-mail them to SLSILVEY@Ashland.com.

Thanks,
Steven