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:
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.)
SCOPE
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 internation...

General Information

• Status: Published
• Publication Date: 14-Jan-2021
• ICS: 17.040.99 - Other standards related to linear and angular measurements
• ICS: 83.140.99 - Other rubber and plastics products
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.20 - Plastic Lumber

Relations

• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM D883-20 - Standard Terminology Relating to Plastics
• Effective Date: 01-Jan-2020
• Refers: ASTM D883-19c - Standard Terminology Relating to Plastics
• Effective Date: 01-Aug-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• Effective Date: 15-Apr-2019
• Refers: ASTM E831-19 - Standard Test Method for Linear Thermal Expansion of Solid Materials by Thermomechanical Analysis
• Effective Date: 01-Apr-2019
• Refers: ASTM D883-19 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2019
• Refers: ASTM D883-18a - Standard Terminology Relating to Plastics
• Effective Date: 01-Dec-2018
• Refers: ASTM D883-18 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2018
• Refers: ASTM E456-13A(2017)e3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E456-13A(2017)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM D883-17 - Standard Terminology Relating to Plastics
• Effective Date: 15-Aug-2017
• Refers: ASTM D6117-16 - Standard Test Methods for Mechanical Fasteners in Plastic Lumber and Shapes
• Effective Date: 01-Jun-2016
• Refers: ASTM E831-14 - Standard Test Method for Linear Thermal Expansion of Solid Materials by Thermomechanical Analysis
• Effective Date: 01-Aug-2014

Overview

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) provides a standardized approach for testing and reporting the linear thermal expansion properties of plastic lumber products. Developed by ASTM International, this test method is essential for understanding and accounting for dimensional changes in plastic lumber due to temperature fluctuations. These products are widely used in the construction industry, often as building materials, and are manufactured predominantly from recycled plastics or plastic composites.

Key Topics

• Thermal Expansion Measurement: The standard outlines a precise method for calculating the coefficient of linear thermal expansion (α) by measuring the lengths of plastic lumber samples at three discrete temperatures within the –30°F to 140°F (–34.4°C to 60°C) range.
• Product-Oriented Testing: The method evaluates the expansion properties of plastic lumber and shapes in their “as manufactured” form, making it a product, not a material property, test.
• Applicability: While primarily created for plastic lumber, the standard is also relevant for similar products made from virgin resin or other plastic composites.
• Precision: Measurements are made with a caliper accurate to 0.001 in. (0.025 mm), ensuring consistent results. However, the method provides values accurate to two significant figures, acknowledging the inherent variability in recycled plastic products.
• Practical Temperature Range: The specified testing range represents typical environmental conditions plastic lumber may experience, making the results highly relevant for real-world applications.
• Factors Affecting Accuracy: The method aims to isolate thermal expansion but notes that humidity, residual stress, voids, inclusions, and material heterogeneity may introduce some variability.

Applications

• Construction and Building Materials: The thermal expansion coefficient is a critical property for engineers, architects, and builders using plastic lumber in outdoor and structural applications. Accurate knowledge of thermal expansion helps accommodate potential dimensional changes in decking, fencing, landscaping, and other installations.
• Product Development and Quality Control: Manufacturers use this standard to benchmark new plastic lumber products, ensure compliance with specifications, and verify quality during production.
• Design Evaluation: Structural designers utilize the tested values to anticipate joint movements, dimensional changes, and potential misalignments caused by daily and seasonal temperature variations.
• Recycled Plastics Industry: Given the prominence of recycled content in plastic lumber, this method offers a consistent approach to account for the variability and performance of non-homogeneous, recycled-based materials.

Related Standards

Users of ASTM D6341-21 may also reference the following ASTM standards for complementary information:

• ASTM D883: Terminology Relating to Plastics
• ASTM D4065: Practice for Plastics - Dynamic Mechanical Properties: Determination and Report of Procedures
• ASTM D6117: Test Methods for Mechanical Fasteners in Plastic Lumber and Shapes
• ASTM E456: Terminology Relating to Quality and Statistics
• ASTM E831: Test Method for Linear Thermal Expansion of Solid Materials by Thermomechanical Analysis

Note: There is currently no known ISO equivalent to ASTM D6341-21. The standard is utilized internationally in accordance with the World Trade Organization’s principles for standardization.

Practical Value

Adopting ASTM D6341-21 enables the consistent and reliable determination of the linear coefficient of thermal expansion for plastic lumber products. This, in turn, supports safe, durable, and high-performance construction applications, especially as the use of sustainable, recycled materials in building grows. By understanding and mitigating the effects of thermal expansion, stakeholders ensure the long-term integrity and functionality of plastic lumber installations.

Keywords: ASTM D6341, thermal expansion, plastic lumber, recycled plastics, construction materials, linear coefficient of expansion, standard test method, building materials, plastic composites

Standards Content (Sample)

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.
Designation: 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)
This standard is issued under the fixed designation D6341; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* 1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This test method covers the determination of the coef-
responsibility of the user of this standard to establish appro-
ficient of linear thermal expansion for plastic lumber and
priate safety, health, and environmental practices and deter-
plastic lumber shapes to two significant figures. The determi-
mine the applicability of regulatory limitations prior to use.
nation is made by taking measurements with a caliper at three
discrete temperatures. At the test temperatures and under the
NOTE 1—There is no known ISO equivalent to this standard.
stresses imposed, the plastic lumber shall have a negligible
1.6 This international standard was developed in accor-
creep or elastic strain rate, or both, insofar as these properties
dance with internationally recognized principles on standard-
would significantly affect the accuracy of the measurements.
ization established in the Decision on Principles for the
1.1.1 Thistestmethoddetailsthedeterminationofthelinear
Development of International Standards, Guides and Recom-
coefficient of thermal expansion of plastic lumber and plastic
mendations issued by the World Trade Organization Technical
lumber shapes in their “as manufactured” form.As such, this is
Barriers to Trade (TBT) Committee.
a test method for evaluating the properties of plastic lumber or
shapes as a product and not a material property test method. 2. Referenced Documents
2.1 ASTM Standards:
1.2 The thermal expansion of plastic lumber and shapes is
composed of a reversible component on which it is possible to D883 Terminology Relating to Plastics
D4065 Practice for Plastics: Dynamic Mechanical Proper-
superimpose changes in length due to changes in moisture
content, curing, loss of plasticizer or solvents, release of ties: Determination and Report of Procedures
D6117 Test Methods for Mechanical Fasteners in Plastic
stresses, phase changes, voids, inclusions, and other factors.
This test method is intended to determine the coefficient of Lumber and Shapes
linear thermal expansion under the exclusion of non-linear E456 Terminology Relating to Quality and Statistics
factors as far as possible. In general, it will not be possible to E831 Test Method for Linear Thermal Expansion of Solid
exclude the effect of these factors completely. For this reason, Materials by Thermomechanical Analysis
the test method can be expected to give a reasonable approxi-
3. Terminology
mation but not necessarily precise determination of the linear
coefficient of thermal expansion. 3.1 Definitions:
3.1.1 Definitions of terms applying to these test methods
1.3 Plastic lumber and plastic lumber shapes are currently
appear in Terminology D883. For terms relating to precision
made predominately with recycled plastics where the product
and bias and associated issues, the terms used in this test
is non-homogeneous in the cross-section. However, it is
method are in accordance with the definitions in Terminology
possible that this test method will also be applicable to similar
E456.
manufactured plastic products made from virgin resins or other
3.1.2 plastic lumber, n—a manufactured product made pri-
plastic composite materials.
marily from plastic materials (filled or unfilled), typically used
1.4 The values stated in inch-pound units are to be regarded
as a building material for purposes similar to those of tradi-
as the standard. The SI units given in parentheses are for
tional lumber, which is usually rectangular in cross-section.
information only.
(Terminology D883)
This test method is under the jurisdiction ofASTM Committee D20 on Plastics
and is the direct responsibility of Subcommittee D20.20 on Plastic Lumber. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Jan. 15, 2021. Published January 2021. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1998. Last previous edition approved in 2016 as D6341 - 16. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D6341-21. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6341 − 21
3.1.2.1 Discussion—Plastic lumber is typically supplied in analysis, such as what is prescribed in Practice D4065 for the
sizes similar to those of traditional lumber board, timber and location of transition temperatures, will be required, in order to
dimension lumber; however the tolerances for plastic lumber avoid excessive error. If such a transition point is located, a
and for traditional lumber are not necessarily the same. separatecoefficientofexpansionforatemperaturerangebelow
(Terminology D883) and above the transition point shall be determined. For speci-
fication and comparison purposes (provided it is known that no
3.1.3 resin, n—a solid or pseudosolid organic material often
transition exists in this range), the range from –30 to 140°F
of high molecular weight, which exhibits a tendency to flow
(–34.4 to 60°C) shall be used. (For reference, glass transition
when subjected to stress, usually has a softening or melting
and melting point temperatures of typical resins used in plastic
range, and usually fractures conchoidally. (Terminology D883)
lumberproductsaregiveninAppendixX2ofthistestmethod.)
3.1.3.1 Discussion—In a broad sense, the term is used to
designate any polymer that is a basic material for plastics.
6. Apparatus
(1982)
6.1 Conditioning Chamber, capable of conditioning test
3.2 Definitions of Terms Specific to This Standard:
specimens at temperatures in the range of –30 to 140°F, 6
3.2.1 plastic lumber shape, n—a plastic lumber product
1.8°F (–34.4 to 60°C, 6 1°C).
which is generally not rectangular in cross-section.
6.2 Caliper, capable of measuring the length of the speci-
4. Summary of Test Method
men with an accuracy of 0.001 in. (0.025 mm). For a given test
4.1 This test method is intended to provide a means of
or test series, the same caliper shall be used for all measure-
determining the coefficient of linear thermal expansion of
ments.The calipers shall be kept and used at room temperature
plastic lumber and plastic lumber shapes, which have the
(73.4°F (23°C)).
potential to contain inclusions and voids. This test method is a
6.3 Thermometer or Thermocouple, capable of an accuracy
product test method, and not a materials test method.
of 60.5°F (60.3°C) when measuring the temperature of the
Furthermore, this test method is not designed to provide more
conditioning chamber.
than two significant figures of accuracy in the result. The test
methodinvolvesusingsolid,fullcross-sectionedmembers(see
7. Test Specimen
Note 2), as manufactured, of approximately 12 in. (300 mm) in
length. In view of the low thermal conductivity of these
7.1 Test specimens for determining thermal expansion of
materials it is impractical to make dynamic temperature plastic lumber and plastic lumber shapes shall be cut from the
variations in a reasonable length of time. Therefore, measure-
“as manufactured” profile. Great care shall be taken in cutting
mentsaretakenoneachsampleafterconditioning48hormore and machining the ends so that smooth, flat, parallel surfaces
at three discrete temperatures, –30, 73.4, and 140°F, 6 3.6°F
and sharp, clean edges result and are parallel to within ⁄300 of
(–34.4, 23, and 60°C, 6 2°C), no more than 1 min after the specimen length perpendicular to the long axis of the
removal from the temperature chamber. The measuring device specimen. Plastic lumber is generally non-uniform through the
used is a caliper capable of measuring to the nearest 0.001 in.
cross-section; machining operations other than those required
(0.025 mm), and is utilized at ambient temperature. to provide flat, parallel ends shall not be carried out. A line
parallel to the length shall be marked with an indelible ink
NOTE 2—It is acceptable to evaluate hollow cross-section products with
marker on an uncut surface along the full length of the
this test method provided it can be shown that negligible dimensional
changes occur in the prescribed measurement time interval. specimen.Lengthmeasurementsofthesamplearetobecarried
out on the surfaces adjacent to the drawn lines (on the cut
5. Significance and Use
faces) at each end of the specimen, at a location very near the
5.1 The coefficient of linear thermal expansion, α, between ends of the line.
temperatures T and T foraspecimenwhoselengthis L atthe
1 2 0
7.2 Thestandardtestspecimenshallbeintheformofaright
reference temperature, is given by the following equation:
cylinder or prism whose length is a minimum of 12 6 0.25 in.
1 L 2 L 1 ∆L
(300 6 6.4 mm) (see Note 3).
2 1
α 5 · 5 · (1)
L T 2 T L ∆T
0 2 1 0
NOTE 3—It is acceptable to utilize this test method to determine the
linear coefficient of thermal expansion for other sample directions (that is,
Where L and L are the specimen lengths at temperatures T
1 2 1
widthorthickness)ifdesired.However,theaccuracyofthemeasurements
and T , respectively. α is, therefore, obtained by dividing the
willbesignificantlyreducedduetothegenerallysmallerlineardimension.
linear expansion per unit length by the change in temperature.
5.2 The nature of most plastics and the construction appli-
8. Conditioning
cations for which plastic lumber and plastic lumber shapes are
8.1 Conditioning—Condition the test specimens at –30,
used, make –30 to 140°F (–34.4 to 60°C) a practical tempera-
73.4, and 140°F 6 3.6°F (–34.4, 23, and 60°C 6 2°C) for not
ture range for linear thermal expansion measurements. Where
less than 48 h at each temperature prior to testing, unless
testingoutsideofthistemperaturerangeorwhenlinearthermal
otherwisespecifiedbythecustomerorproductspecification.In
expansion characteristics of a particular plastic are not known
cases of disagreement, the tolerance shall be 61.8°F (61°C).
through this temperature range, particular attention shall be
paid to the factors mentioned in 1.2 and it is possible that 8.2 Test Conditions—Conduct measurements in a laboratory
special preliminary investigations by thermo-mechanical atmosphere of 73.4 6 3.6°F (23 6 2°C), within 1 min or less
D6341 − 21
after removal from the conditioning environment unless oth- ∆L 5 L α∆T (4)
~ !
erwise specified by the customer or product specification. In
where:
cases of disagreement, the tolerance shall be 61.8°F (61°C).
α = Coefficient of linear thermal expansion in (in./in.)/°F ((cm/cm)/
°C)),
NOTE 4—Experience indicates that the linear coefficient of thermal
∆L = change in length of test specimen, in in. (cm) due to heating or
expansion of plastic lumber products is not affected by humidity.
to cooling,
8.3 If products are tested for which the linear coefficient of
L = length of test specimen in in. (cm) at a reference temperature, T
thermal expansion is known or believed to be potentially (usually ambient temperature), and
∆T = temperature difference, in °F (°C), over which the change in the
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D6341 − 16 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)
This standard is issued under the fixed designation D6341; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
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 safety, health, and healthenvironmental 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.
This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.20 on Plastic Lumber.
Current edition approved April 1, 2016Jan. 15, 2021. Published April 2016January 2021. Originally approved in 1998. Last previous edition approved in 20142016 as
D6341 - 14a.D6341 - 16. DOI: 10.1520/D6341-16.10.1520/D6341-21.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6341 − 21
2. Referenced Documents
2.1 ASTM Standards:
D883 Terminology Relating to Plastics
D4065 Practice for Plastics: Dynamic Mechanical Properties: Determination and Report of Procedures
D5033 Guide for Development of ASTM Standards Relating to Recycling and Use of Recycled Plastics (Withdrawn 2007)
D6117 Test Methods for Mechanical Fasteners in Plastic Lumber and Shapes
E456 Terminology Relating to Quality and Statistics
E831 Test Method for Linear Thermal Expansion of Solid Materials by Thermomechanical Analysis
3. Terminology
3.1 Definitions:
3.1.1 Definitions of terms applying to these test methods appear in Terminology D883. For terms relating to precision and bias
and associated issues, the terms used in this test method are in accordance with the definitions in Terminology E456.
3.1.2 plastic lumber, n—a manufactured product made primarily from plastic materials (filled or unfilled), typically used as a
building material for purposes similar to those of traditional lumber, which is usually rectangular in cross-section. (Terminology
D883)
3.1.2.1 Discussion—
Plastic lumber is typically supplied in sizes similar to those of traditional lumber board, timber and dimension lumber; however
the tolerances for plastic lumber and for traditional lumber are not necessarily the same. (Terminology D883)
3.1.2 plastic lumber shape, n—a plastic lumber product which is generally not rectangular in cross-section.
3.1.3 resin, n—a solid or pseudosolid organic material often of high molecular weight, which exhibits a tendency to flow when
subjected to stress, usually has a softening or melting range, and usually fractures conchoidally. (Terminology D883)
3.1.3.1 Discussion—
In a broad sense, the term is used to designate any polymer that is a basic material for plastics. (1982)
3.2 Additional definitions of terms applying to this test method appear in Terminology D883 and Practice D5033.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 plastic lumber shape, n—a plastic lumber product which is generally not rectangular in cross-section.
4. Summary of Test Method
4.1 This test method is intended to provide a means of determining the coefficient of linear thermal expansion of plastic lumber
and plastic lumber shapes, which have the potential to contain inclusions and voids. This test method is a product test method, and
not a materials test method. Furthermore, this test method is not designed to provide more than two significant figures of accuracy
in the result. The test method involves using solid, full cross-sectioned members (see Note 2), as manufactured, of approximately
12 in. (300 mm) in length. In view of the low thermal conductivity of these materials it is impractical to make dynamic temperature
variations in a reasonable length of time. Therefore, measurements are taken on each sample after conditioning 48 h or more at
three discrete temperatures, –30, 73.4, and 140°F, 6 3.6°F (–34.4, 23, and 60°C, 6 2°C), no more than 1 min after removal from
the temperature chamber. The measuring device used is a caliper capable of measuring to the nearest 0.001 in. (0.025 mm), and
is utilized at ambient temperature.
NOTE 2—It is acceptable to evaluate hollow cross-section products with this test method provided it can be shown that negligible dimensional changes
occur in the prescribed measurement time interval.
5. Significance and Use
5.1 The coefficient of linear thermal expansion, α, between temperatures T and T for a specimen whose length is L at the
1 2 0
reference temperature, is given by the following equation:
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
D6341 − 21
1 L 2 L 1 ΔL
2 1
α5 · 5 · (1)
L T 2 T L ΔT
0 2 1 0
Where L and L are the specimen lengths at temperatures T and T , respectively. α is, therefore, obtained by dividing the linear
1 2 1 2
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.)
6. Apparatus
6.1 Conditioning Chamber, capable of conditioning test specimens at temperatures in the range of –30 to 140°F, 6 1.8°F (–34.4
to 60°C, 6 1°C).
6.2 Caliper, capable of measuring the length of the specimen with an accuracy of 0.001 in. (0.025 mm). For a given test or test
series, the same caliper shall be used for all measurements. The calipers shall be kept and used at room temperature (73.4°F
(23°C)).
6.3 Thermometer or Thermocouple, capable of an accuracy of 60.5°F (60.3°C) when measuring the temperature of the
conditioning chamber.
7. Test Specimen
7.1 Test specimens for determining thermal expansion of plastic lumber and plastic lumber shapes shall be cut from the “as
manufactured” profile. Great care shall be taken in cutting and machining the ends so that smooth, flat, parallel surfaces and sharp,
clean edges result and are parallel to within ⁄300 of the specimen length perpendicular to the long axis of the specimen. Plastic
lumber is generally non-uniform through the cross-section; machining operations other than those required to provide flat, parallel
ends shall not be carried out. A line parallel to the length shall be marked with an indelible ink marker on an uncut surface along
the full length of the specimen. Length measurements of the sample are to be carried out on the surfaces adjacent to the drawn
lines (on the cut faces) at each end of the specimen, at a location very near the ends of the line.
7.2 The standard test specimen shall be in the form of a right cylinder or prism whose length is a minimum of 12 6 0.25 in. (300
6 6.4 mm) (see Note 3).
NOTE 3—It is acceptable to utilize this test method to determine the linear coefficient of thermal expansion for other sample directions (that is, width or
thickness) if desired. However, the accuracy of the measurements will be significantly reduced due to the generally smaller linear dimension.
8. Conditioning
8.1 Conditioning—Condition the test specimens at –30, 73.4, and 140°F 6 3.6°F (–34.4, 23, and 60°C 6 2°C) for not less than
48 h at each temperature prior to testing, unless otherwise specified by the customer or product specification. In cases of
disagreement, the tolerance shall be 61.8°F (61°C).
8.2 Test Conditions—Conduct measurements in a laboratory atmosphere of 73.4 6 3.6°F (23 6 2°C), within 1 min or less after
removal from the conditioning environment unless otherwise specified by the customer or product specification. In cases of
disagreement, the tolerance shall be 61.8°F (61°C).
NOTE 4—Experience indicates that the linear coefficient of thermal expansion of plastic lumber products is not affected by humidity.
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8.3 If products are tested for which the linear coefficient of thermal expansion is known or believed to be potentially affected by
humidity then humidity control settings shall be as agreed upon by the contractual parties.
9. Number of Test Specimens
9.1 A sample size of five shall be used. Each specimen shall be tested at each of the t
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