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CHAPTER 3: THERMAL AND CHEMICAL PROPERTIES FOR
PLASTIC MATERIALS
3.1 Thermal Properties for Plastics
The thermal properties of polymer materials are important because polymer material
is not resistant high temperature change. High temperature change will cause polymer
to loss their properties.
a. Thermal stress
Thermal stress can be defined as internal stress caused by the change in
temperature. The Stress resulting from restrained thermal expansion and
contraction.
Figure 3.1: Thermal stress equation.
Heated or cooled uniformly (no temperature changes), therefore there is no
expansion or contraction, the specimen will be stress free.
b. Thermal expansion
Thermal expansion is the tendency of polymeric material to change in shape,
volume, and area in response to a change in temperature. Under the effects of
increasing temperature material will expand. This can lead to significant changes
in dimensions.
The Coefficient of Thermal Expansion (α), is a material property which
characterizes the ability of a plastic to expand under the effect of temperature
change.
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