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.

Copyright William Andrew, Inc. 2008 under license agreement with Books24x7

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