From Selection of Polymeric Materials: How to Select Design Properties from Different Standards

3.1 Introduction

The thermal properties of thermoplastic materials are equally as important as the electrical and mechanical properties. Unlike metals, thermoplastics are extremely sensitive to changes in temperature. The mechanical, electrical, and chemical properties of thermoplastics are dependent on the thermal properties at which the values were derived. The molecular chain crystallinity has a number of important effects upon the thermal properties of a polymer. Semi-crystalline thermoplastics have a well-defined sharp melting point with thermomechanical rigidity properties. Amorphous thermoplastics, in contrast, have a gradual softening range of the polymer melt.

The thermal behavior of polymeric materials affected by wide differential temperature ranges is a rather complex technical subject. Molecular orientation also has a significant effect on the thermal properties of thermoplastics. The melt flow orientation tends to decrease dimensional stability at higher temperatures. The molecular weight of the polymers also affects the low-temperature flexibility and the impact strength or brittleness. The intermolecular bonding cross-linking and the copolymerization chemical reaction also have a considerable effect on the thermal properties of thermoplastic materials.

Polymers are used over a wide range of temperatures and the effects of temperature and impact of types of loads over a long service time on the physical, electrical, and thermal expansion properties must be established before a thermoplastic material can be used for a particular product application.

The nature of the viscoelasticity characteristics of thermoplastic material is such that temperature is of fundamental importance. In thermoplastic materials, the primary bonds are strong covalent bonds along the molecular chains.

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Polymers and Plastic Resins
Polymers and plastic materials are organic, synthetic or processed polymers that are supplied as raw materials. They typically consist of thermoplastic or thermosetting resins in the form of pellets, powders or liquid resins. These materials can then be molded into a variety of shapes for a wide range of uses.
Thermoplastics and Thermoplastic Resins
Thermoplastics and thermoplastic materials soften when heated and harden when cooled. They can withstand many heating and cooling cycles and are often suitable for recycling.
Polymer and Plastic Composites
Polymer and plastic composites are strengthened with fibers, fillers, particulates, powders and other matrix reinforcements to provide improved strength and/or stiffness. Examples include fiber reinforced plastics (FRPs), sheet molding compounds (SMCs), bulk molding compounds (BMCs), pre-preg materials, and fabricated composite parts.
Adhesive Tapes
Adhesive tapes are used to assemble materials or parts together using a sticky chemical bond.
Elastomer and Rubber Shapes
Elastomers and rubber shapes are natural or synthetic  polymers that exhibit elastic properties and can be formed into finished or semi-finished stock.  These amorphous polymers are usually thermosets, but are also available as thermoplastics. Elastic polymer (elastomer) and  rubber shapes are available in different forms and sizes, and often use filler materials.

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