Standard Active Last Updated: Jan 28, 2021
ASTM D6341-21

Standard Test Method for Determination of the Linear Coefficient of Thermal Expansion of Plastic Lumber and Plastic Lumber Shapes Between –30 and 140°F (–34.4 and 60°C)

Significance and Use

5.1 The coefficient of linear thermal expansion, α, between temperatures T1 and T2 for a specimen whose length is L0 at the reference temperature, is given by the following equation:

Equation D6341-21_1

Where L1 and L2 are the specimen lengths at temperatures T1 and T2, respectively. α is, therefore, obtained by dividing the linear expansion per unit length by the change in temperature.

5.2 The nature of most plastics and the construction applications for which plastic lumber and plastic lumber shapes are used, make –30 to 140°F (–34.4 to 60°C) a practical temperature range for linear thermal expansion measurements. Where testing outside of this temperature range or when linear thermal expansion characteristics of a particular plastic are not known through this temperature range, particular attention shall be paid to the factors mentioned in 1.2 and it is possible that special preliminary investigations by thermo-mechanical analysis, such as what is prescribed in Practice D4065 for the location of transition temperatures, will be required, in order to avoid excessive error. If such a transition point is located, a separate coefficient of expansion for a temperature range below and above the transition point shall be determined. For specification and comparison purposes (provided it is known that no transition exists in this range), the range from –30 to 140°F (–34.4 to 60°C) shall be used. (For reference, glass transition and melting point temperatures of typical resins used in plastic lumber products are given in Appendix X2 of this test method.)


1.1 This test method covers the determination of the coefficient of linear thermal expansion for plastic lumber and plastic lumber shapes to two significant figures. The determination is made by taking measurements with a caliper at three discrete temperatures. At the test temperatures and under the stresses imposed, the plastic lumber shall have a negligible creep or elastic strain rate, or both, insofar as these properties would significantly affect the accuracy of the measurements.

1.1.1 This test method details the determination of the linear coefficient of thermal expansion of plastic lumber and plastic lumber shapes in their “as manufactured” form. As such, this is a test method for evaluating the properties of plastic lumber or shapes as a product and not a material property test method.

1.2 The thermal expansion of plastic lumber and shapes is composed of a reversible component on which it is possible to superimpose changes in length due to changes in moisture content, curing, loss of plasticizer or solvents, release of stresses, phase changes, voids, inclusions, and other factors. This test method is intended to determine the coefficient of linear thermal expansion under the exclusion of non-linear factors as far as possible. In general, it will not be possible to exclude the effect of these factors completely. For this reason, the test method can be expected to give a reasonable approximation but not necessarily precise determination of the linear coefficient of thermal expansion.

1.3 Plastic lumber and plastic lumber shapes are currently made predominately with recycled plastics where the product is non-homogeneous in the cross-section. However, it is possible that this test method will also be applicable to similar manufactured plastic products made from virgin resins or other plastic composite materials.

1.4 The values stated in inch-pound units are to be regarded as the standard. The SI units given in parentheses are for information only.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

Note 1: There is no known ISO equivalent to this standard.

1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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Book of Standards Volume: 08.03
Developed by Subcommittee: D20.20
Pages: 5
DOI: 10.1520/D6341-21
ICS Code: 17.040.99; 83.140.99