ASTM D2538-18

Standard Practice for Fusion of Poly(Vinyl Chloride) (PVC) Compounds Using a Torque Rheometer

SIGNIFICANCE AND USE
5.1 When PVC compounds are mixed under appropriate conditions of heat and shear, a fused mass is produced. This mass has certain melt characteristics which can be defined with a torque rheometer operated under fixed conditions of shear and temperature. The fusion characteristics of a PVC compound are manifest as fusion time, fusion torque, melt torque, melt viscosity, and heat and color stability.  
5.2 A control lot is to be used as a standard against which other test results are to be compared. Test data are to be evaluated relative to the control lot.
SCOPE
1.1 This practice covers the relative fusion characteristics of poly(vinyl chloride) compounds.  
1.2 The test procedures appear in the following order:    
Section  
Fusion Test  
9    
Thermal Stability Test  
10    
Color-Hold Stability Test  
11    
Shear Stability Test  
12  
1.3 The values stated in SI units are to be regarded as the standard.  
1.4 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. Specific hazards statements are given in Section 8.  
Note 1: There are no ISO standards covering the primary subject matter of this ASTM standard.  
1.5 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.

General Information

• Status: Published
• Publication Date: 31-Oct-2018
• ICS: 83.080.20 - Thermoplastic materials
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.15 - Thermoplastic Materials

Relations

• Replaces: ASTM D2538-02(2010) - Standard Practice for Fusion of Poly(Vinyl Chloride) (PVC) Compounds Using a Torque Rheometer
• Effective Date: 01-Nov-2018
• 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 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 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 D1600-18 - Standard Terminology for Abbreviated Terms Relating to Plastics (Withdrawn 2024)
• Effective Date: 01-Jan-2018
• Refers: ASTM D883-17 - Standard Terminology Relating to Plastics
• Effective Date: 15-Aug-2017
• Refers: ASTM D1600-14 - Standard Terminology for Abbreviated Terms Relating to Plastics
• Effective Date: 01-Feb-2014
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM D1600-13 - Standard Terminology for Abbreviated Terms Relating to Plastics
• Effective Date: 15-Apr-2013
• Refers: ASTM D883-12e1 - Standard Terminology Relating to Plastics
• Effective Date: 15-Nov-2012

Overview

ASTM D2538-18 is the internationally recognized standard practice for analyzing the relative fusion characteristics of poly(vinyl chloride) (PVC) compounds using a torque rheometer. Developed by ASTM International, this standard is essential for the plastics industry, providing a consistent methodology to assess critical processing parameters such as fusion time, fusion torque, melt torque, melt viscosity, heat stability, and color stability of PVC compounds. Utilizing torque rheometers under controlled heat and shear conditions, ASTM D2538-18 enables accurate comparison between PVC compound lots to ensure quality control and manufacturing consistency.

Key Topics

Fusion Characteristics of PVC:

• Evaluates how PVC compounds transition from powder to a fused mass when mixed under heat and shear.
• Key output parameters include fusion time, fusion torque, melt torque, heat stability, color hold, and shear sensitivity.

Test Methods Included:

• Fusion Test: Measures fusion torque and fusion time with the torque rheometer, identifying optimal processing conditions.
• Thermal Stability Test: Determines compound resistance to thermal degradation.
• Color-Hold Stability Test: Assesses the compound’s ability to maintain color during processing.
• Shear Stability Test: Evaluates the material’s sensitivity to shear, essential for determining consistency in processing performance.

Significance and Use:

• Provides a control standard for comparing multiple PVC batches.
• Ensures that the fusion and stability characteristics meet predetermined quality requirements.
• Promotes reproducibility of results between laboratories by specifying apparatus, procedures, and reporting methods.

Safety Considerations:

• Users must observe safety, health, and environmental precautions when conducting tests.
• Details of specific hazards and safe handling are noted within the standard.

Applications

Industrial Quality Control:

• Widely used by PVC compound manufacturers, processors, and quality assurance laboratories to maintain product consistency.
• Ensures that PVC compounds perform reliably during molding, extrusion, and other fabrication processes.

Research and Development:

• Facilitates the development of new PVC formulations by providing quantifiable metrics for comparing processability and stability.
• Supports optimization of lubricant, stabilizer, and pigment content in PVC compounds for enhanced processing efficiency.

Regulatory and Compliance Standards:

• Assists companies in meeting industry and market requirements by providing documented test results.
• Serves as a reference standard for interlaboratory studies and method validation.

End-Product Performance:

• Important for manufacturers of profiles, films, pipes, and cables where precise control of material properties translates into better product performance.

Related Standards

ASTM D883 - Terminology Relating to Plastics
ASTM D1600 - Terminology for Abbreviated Terms Relating to Plastics
ASTM E691 - Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

Note: There are currently no ISO standards covering the principal subject matter of ASTM D2538-18.

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Keywords: ASTM D2538-18, PVC fusion, torque rheometer, poly(vinyl chloride) testing, fusion torque, melt stability, color-hold stability, shear sensitivity, PVC quality control, plastics testing standards.

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: D2538 − 18
Standard Practice for
Fusion of Poly(Vinyl Chloride) (PVC) Compounds Using a
Torque Rheometer
This standard is issued under the fixed designation D2538; 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 Determine the Precision of a Test Method
1.1 This practice covers the relative fusion characteristics of
3. Terminology
poly(vinyl chloride) compounds.
3.1 Definitions—Definitions are in accordance with Termi-
1.2 The test procedures appear in the following order:
nologies D883 and D1600 unless otherwise indicated.
Section
4. Summary of Practice
Fusion Test 9
Thermal Stability Test 10
4.1 A sample of powder-mix compound is added to the
Color-Hold Stability Test 11
heated roller mixer chamber and is transformed into a fused
Shear Stability Test 12
mass.
1.3 The values stated in SI units are to be regarded as the
4.2 The resulting torque curve can be used to determine the
standard.
relative fusion time and fusion characteristics.
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
5. Significance and Use
responsibility of the user of this standard to establish appro-
5.1 When PVC compounds are mixed under appropriate
priate safety, health, and environmental practices and deter-
conditions of heat and shear, a fused mass is produced. This
mine the applicability of regulatory limitations prior to use.
mass has certain melt characteristics which can be defined with
Specific hazards statements are given in Section 8.
a torque rheometer operated under fixed conditions of shear
NOTE 1—There are no ISO standards covering the primary subject
and temperature. The fusion characteristics of a PVC com-
matter of this ASTM standard.
pound are manifest as fusion time, fusion torque, melt torque,
1.5 This international standard was developed in accor-
melt viscosity, and heat and color stability.
dance with internationally recognized principles on standard-
5.2 A control lot is to be used as a standard against which
ization established in the Decision on Principles for the
other test results are to be compared. Test data are to be
Development of International Standards, Guides and Recom-
evaluated relative to the control lot.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
6. Apparatus
2. Referenced Documents
6.1 Microprocessor Torque Rheometer, equipped with a
high-shear mixer with roller-style blades, bowl-jacket
2.1 ASTM Standards:
thermocouple, stock thermocouple, and temperature recorder.
D883 Terminology Relating to Plastics
D1600 Terminology forAbbreviatedTerms Relating to Plas-
NOTE 2—Atorque rheometer without microprocessor capability can be
tics used to perform the fusion, thermal stability, and color hold tests.
E691 Practice for Conducting an Interlaboratory Study to
6.1.1 For flexible and rigid compounds, use a Type 6 roller
head with a rotor ratio of 3 Drive: 2 Driven.
1 NOTE 3—AType 5 roller head can also be used, but the data generated
This practice is under the jurisdiction ofASTM Committee D20 on Plastics and
cannot be compared with the Type 6 data.
is the direct responsibility of Subcommittee D20.15 on Thermoplastic Materials.
Current edition approved Nov. 1, 2018. Published December 2018. Originally
6.2 Quick-Loading Powder Chute or equivalent.
approved in 1969. Last previous edition approved in 2010 as D2538 – 02(2010).
DOI:10.1520/D2538-18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Suitable equipment may be obtained from C. W. Brabender, 50 E. Wesley St.,
Standards volume information, refer to the standard’s Document Summary page on South Hackensack, NJ 07606, and Haake Buchler Instruments, 244 Saddle River
the ASTM website. Rd., Saddle Brook, NJ 07662.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2538 − 18
6.3 Brass Knife. where:
V = volume of mixer bowl without rotors, and
6.4 Brass Wool or Brush.
D = volume displacement or rotors.
6.5 Insulated Gloves.
NOTE4—Thecorrectsamplesizeforthemixeriswhenthefusioncurve
will duplicate itself. As the mixer wears, it will be necessary to increase
6.6 Balance, 500-g minimum capacity, with a 0.1-g sensi-
the sample size to reproduce a fusion curve equivalent to previous curves.
tivity.
9.3.2 Weigh a sample of the test compound in accordance
6.7 Beaker, stainless steel, 400 mL.
with 9.3.1. With the mixer running, position the quick-loading
6.8 Oven.
chute on the roller-head mixer and pour in the sample com-
6.9 Aluminum Foil. pound. Place the ram into the chute and add the weight. When
the torque curve indicates maximum torque has been reached,
6.10 Timer.
remove the loading chute and weight.
6.11 Long-Nose Pliers.
9.3.3 Continue mixing until the melt torque achieves a
6.12 Hand-Press Mold.
steady state.
9.3.4 Stop the mixer and open the bowl. Clean the com-
7. Materials
pound from the bowl and blades using the brass knife or wool,
or both.
7.1 Poly(Vinyl Chloride) Resin.
9.3.5 Reassemble the mixing bowl and repeat 9.3.2 – 9.3.4
7.2 Filter.
for additional tests. Since some cooling takes place when
7.3 Lubricants.
cleaning the bowl, allow sufficient time to confirm that the
mixing bowl has reached equilibrium at the test temperature
7.4 Plasticizer.
before using again.
7.5 Process-Aid.
NOTE 5—The quick-loading chute should be at the same temperature at
7.6 Impact Modifier.
the start of each test. Heat or cool as required.
7.7 Stabilizer.
9.4 Interpretation of Torque Rheometer Fusion Test Curve
7.8 Pigments. (Fig. 1):
9.4.1 A—Loading Peak—The point of maximum torque of
8. Hazards
the unfused, cold raw material.
9.4.2 B—Minimum—The time from the point of loading to
8.1 Do not exceed the power capacity of the instrument, as
the point of minimum torque.
damage to the mixer or to the torque rheometer may result.
9.4.3 FS—Inflection Point—The change in the slope of the
8.2 Do not attempt to clean or poke objects into the mixer
curve after the minimum. It will help to characterize the speed
while it is running.
of the particle rearrangement (see fusion speed).
8.3 Gloves with sufficient insulation to enable the operator
9.4.4 X—Maximum—Fusion Torque—The point where the
to handle the hot equipment should be worn when conducting
fused material has its maximum torque.
these tests.
9.4.5 E—End Point—User-defined endpoint where the
torque curve is stable and steady.
9. Fusion Test Method
9.4.6 Melt Torque—The fusion where the torque curve is
9.1 Compound Preparation:
relatively flat (not displayed in the graph).
9.1.1 The compound may be beaker-mixed, blended in an
9.4.7 A.X—Fusion Time—Time between the loading peak
intensive mixer or a ribbon blender, or blended and pelletized.
A and the Maximum (fusion Torque) X.
If the compound is beaker-mixed, the total weight of the
9.4.8 FS 620 %—Fusion Speed—The speed of the pro-
compound should equal the amount charged to the roller-head
gressing fusion of the particles.
bowl.
9.5 Report—Report the following information:
9.2 Equipment Preparation:
9.5.1 The fusion torque to the nearest 100 m·g.
9.2.1 Mount the roller head on the torque rheometer.
9.5.1.1 Report to the nearest 25 m·g when usinga0to 1000
9.2.2 Select a temperature/rotor speed combination that will
scale.
permit the test to be completed within a reasonable time
9.5.2 The fusion time to the nearest ⁄2 min.
constraint. Suggested combinations for several types of PVC
9.5.3 The melt torque to the nearest 100 m·g.
compound are found in Appendix X2.
9.5.3.1 Report to the nearest 25 m·g when usinga0to 1000
9.2.3 With the mixer empty and running, zero the recording
pen on the chart. scale.
9.3 Procedure:
NOTE 6—If the melt torque is not steady, approximate the value and
9.3.1 Determine the sample size to be added to the mixer, note whether the torque is increasing or decreasing.
using the following formula:
9.5.4 Temperature of test, rotor revolutions per minute, and
sample size 5 V 2 D 365% 3specific gravity (1) sample size used.
@~ ! #
D2538 − 18
A: Loading Peak t: A.X = Fusion Time
B: Minimum v: FS ± 20 % = Fusion Speed
FS: Inflection Point
X: Maximum
E: End
FIG. 1 Torque Rheometer Fusion Test Curve
10. Thermal Stability Test Method 10.5.1 The compound heat stability to the nearest ⁄2 min,
and
10.1 Prepare the test compound in accordance with 9.1.
10.5.2 The temperature of test, rotor revolutions per minute,
10.2 Prepare the test equipment in accordance with 9.2.
and the sample size used.
10.3 Procedure:
10.3.1 Weigh a sample of the test compound in accordance
11. Color-Hold Stability Test Method
with 9.3.1. With the mixer running, position the quick-loading
11.1 Prepare the test compound in accordance with 9.1.
chute on the roller-head mixer and pour in the sample com-
pound. Place the ram into the chute and add the weight. When 11.2 Prepare the test equipment in accordance with 9.2.
thetorquecurveindicatesfusion,removetheloadingchuteand
11.3 Procedure:
weight.
11.3.1 Weigh a sample of the test compound in accordance
10.3.2 Continue running until there is a sudden rise in the
with 9.3.1. With the mixer running, position the quick-loading
torque curve, indicating decomposition of the PVC compound.
chute on the roller-head mixer and pour in the sample com-
10.3.3 Stop the mixer and open the bowl. Clean the com-
pound. Place the ram into the chute and add the weight. When
pound from the bowl and blades using the brass knife or wool,
thetorquecurveindicatesfusion,removetheloadingchuteand
or both.
the weight.
10.3.4 Reassemble the mixing bowl and repeat 10.3.1 –
11.3.2 Using the point of maximum torque (fusion torque)
10.3.3 for additional tests. Confirm that the bowl has reached
as zero time, remove a sample of the compound at regular time
the test temperature before starting.
intervals of 2, 3, or 5 min. Stop the rotors and use a pair of
10.4 Interpretation of Torque Rheometer Curve (Fig. 1):
long-nose pliers to remove a sample from the bowl. Restart the
10.4.1 Compound Heat Stability—The time from the point
rotors. Place the compound into a hand press to shape the
of maximum torque (fusion torque) to the point of sudden
sample. Trim the sample and return the excess to the mixing
torque increase.
bowl.
10.5 Report—Report the following information: 11.3.3 Mount the samples in a sequential time order.
D2538 − 18
11.3.4 Continue sampling until the desired color change has 12.3.3 When the sample run is finished, use the micropro-
been observed. cessor to plot the torque versus revolutions per minute. Use the
plotted curve for analysis.
NOTE 7—Depleting the sample from the bowl can affect the amoun
...

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: D2538 − 02 (Reapproved 2010) D2538 − 18
Standard Practice for
Fusion of Poly(Vinyl Chloride) (PVC) Compounds Using a
Torque Rheometer
This standard is issued under the fixed designation D2538; 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 practice covers the relative fusion characteristics of poly(vinyl chloride) compounds.
1.2 The test procedures appear in the following order:
Section
Fusion Test 9
Thermal Stability Test 10
Color-Hold Stability Test 11
Shear Stability Test 12
1.3 The values stated in SI units are to be regarded as the standard.
1.4 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. Specific hazards statements are given in Section 8.
NOTE 1—There are no ISO standards covering the primary subject matter of this ASTM standard.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
D883 Terminology Relating to Plastics
D1600 Terminology for Abbreviated Terms Relating to Plastics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions—Definitions are in accordance with Terminologies D883 and D1600 unless otherwise indicated.
4. Summary of Practice
4.1 A sample of powder-mix compound is added to the heated roller mixer chamber and is transformed into a fused mass.
4.2 The resulting torque curve can be used to determine the relative fusion time and fusion characteristics.
5. Significance and Use
5.1 When PVC compounds are mixed under appropriate conditions of heat and shear, a fused mass is produced. This mass has
certain melt characteristics which can be defined with a torque rheometer operated under fixed conditions of shear and temperature.
The fusion characteristics of a PVC compound are manifest as fusion time, fusion torque, melt torque, melt viscosity, and heat and
color stability.
This practice is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.15 on Thermoplastic Materials.
Current edition approved Nov. 1, 2010Nov. 1, 2018. Published March 2011December 2018. Originally approved in 1969. Last previous edition approved in 20022010 as
D2538 – 02.D2538 – 02 DOI:10.1520/D2538-02R10.(2010). DOI:10.1520/D2538-18.
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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2538 − 18
5.2 A control lot is to be used as a standard against which other test results are to be compared. Test data are to be evaluated
relative to the control lot.
6. Apparatus
6.1 Microprocessor Torque Rheometer, equipped with a high-shear mixer with roller-style blades, bowl-jacket thermocouple,
stock thermocouple, and temperature recorder.
NOTE 2—A torque rheometer without microprocessor capability can be used to perform the fusion, thermal stability, and color hold tests.
6.1.1 For flexible and rigid compounds, use a Type 6 roller head with a rotor ratio of 3 Drive: 2 Driven.
NOTE 3—A Type 5 roller head can also be used, but the data generated cannot be compared with the Type 6 data.
6.2 Quick-Loading Powder Chute or equivalent.
6.3 Brass Knife.
6.4 Brass Wool or Brush.
6.5 Insulated Gloves.
6.6 Balance, 500-g minimum capacity, with a 0.1-g sensitivity.
6.7 Beaker, stainless steel, 400 mL.
6.8 Oven.
6.9 Aluminum Foil.
6.10 Timer.
6.11 Long-Nose Pliers.
6.12 Hand-Press Mold.
7. Materials
7.1 Poly(Vinyl Chloride) Resin.
7.2 Filter.
7.3 Lubricants.
7.4 Plasticizer.
7.5 Process-Aid.
7.6 Impact Modifier.
7.7 Stabilizer.
7.8 Pigments.
8. Hazards
8.1 Do not exceed the power capacity of the instrument, as damage to the mixer or to the torque rheometer may result.
8.2 Do not attempt to clean or poke objects into the mixer while it is running.
8.3 Gloves with sufficient insulation to enable the operator to handle the hot equipment should be worn when conducting these
tests.
9. Fusion Test Method
9.1 Compound Preparation:
9.1.1 The compound may be beaker-mixed, blended in an intensive mixer or a ribbon blender, or blended and pelletized. If the
compound is beaker-mixed, the total weight of the compound should equal the amount charged to the roller-head bowl.
9.2 Equipment Preparation:
9.2.1 Mount the roller head on the torque rheometer.
9.2.2 Select a temperature/rotor speed combination that will permit the test to be completed within a reasonable time constraint.
Suggested combinations for several types of PVC compound are found in Appendix X2.
9.2.3 With the mixer empty and running, zero the recording pen on the chart.
Suitable equipment may be obtained from C. W. Brabender, 50 E. Wesley St., South Hackensack, NJ 07606, and Haake Buchler Instruments, 244 Saddle River Rd.,
Saddle Brook, NJ 07662.
D2538 − 18
A: Loading Peak t: A.X = Fusion Time
B: Minimum v: FS ± 20 % = Fusion Speed
FS: Inflection Point
X: Maximum
E: End
FIG. 1 Torque Rheometer Fusion Test Curve
9.3 Procedure:
9.3.1 Determine the sample size to be added to the mixer, using the following formula:
sample size 5 V 2 D 365 % 3specific gravity (1)
@~ ! #
where:
V = volume of mixer bowl without rotors, and
D = volume displacement or rotors.
NOTE 4—The correct sample size for the mixer is when the fusion curve will duplicate itself. As the mixer wears, it will be necessary to increase the
sample size to reproduce a fusion curve equivalent to previous curves.
9.3.2 Weigh a sample of the test compound in accordance with 9.3.1. With the mixer running, position the quick-loading chute
on the roller-head mixer and pour in the sample compound. Place the ram into the chute and add the weight. When the torque curve
indicates maximum torque has been reached, remove the loading chute and weight.
9.3.3 Continue mixing until the melt torque achieves a steady state.
9.3.4 Stop the mixer and open the bowl. Clean the compound from the bowl and blades using the brass knife or wool, or both.
9.3.5 Reassemble the mixing bowl and repeat 9.3.2 – 9.3.4 for additional tests. Since some cooling takes place when cleaning
the bowl, allow sufficient time to confirm that the mixing bowl has reached equilibrium at the test temperature before using again.
NOTE 5—The quick-loading chute should be at the same temperature at the start of each test. Heat or cool as required.
9.4 Interpretation of Torque Rheometer Fusion Test Curve (Fig. 1):
9.4.1 Fusion Torque—A—Loading Peak—The point of maximum torque.torque of the unfused, cold raw material.
9.4.2 Fusion Time—B—Minimum—The time from the point of loading to the point of maximumminimum torque.
9.4.3 FS—Inflection Point—The change in the slope of the curve after the minimum. It will help to characterize the speed of
the particle rearrangement (see fusion speed).
9.4.4 X—Maximum—Fusion Torque—The point where the fused material has its maximum torque.
9.4.5 E—End Point—User-defined endpoint where the torque curve is stable and steady.
9.4.6 Melt Torque—The fusion where the torque curve is relatively flat.flat (not displayed in the graph).
D2538 − 18
9.4.7 A.X—Fusion Time—Time between the loading peak A and the Maximum (fusion Torque) X.
9.4.8 FS 620 %—Fusion Speed—The speed of the progressing fusion of the particles.
9.5 Report—Report the following information:
9.5.1 The fusion torque to the nearest 100 m·g.
9.5.1.1 Report to the nearest 25 m·g when using a 0 to 1000 scale.
9.5.2 The fusion time to the nearest ⁄2 min.
9.5.3 The melt torque to the nearest 100 m·g.
9.5.3.1 Report to the nearest 25 m·g when using a 0 to 1000 scale.
NOTE 6—If the melt torque is not steady, approximate the value and note whether the torque is increasing or decreasing.
9.5.4 Temperature of test, rotor revolutions per minute, and sample size used.
10. Thermal Stability Test Method
10.1 Prepare the test compound in accordance with 9.1.
10.2 Prepare the test equipment in accordance with 9.2.
10.3 Procedure:
10.3.1 Weigh a sample of the test compound in accordance with 9.3.1. With the mixer running, position the quick-loading chute
on the roller-head mixer and pour in the sample compound. Place the ram into the chute and add the weight. When the torque curve
indicates fusion, remove the loading chute and weight.
10.3.2 Continue running until there is a sudden rise in the torque curve, indicating decomposition of the PVC compound.
10.3.3 Stop the mixer and open the bowl. Clean the compound from the bowl and blades using the brass knife or wool, or both.
10.3.4 Reassemble the mixing bowl and repeat 10.3.1 – 10.3.3 for additional tests. Confirm that the bowl has reached the test
temperature before starting.
10.4 Interpretation of Torque Rheometer Curve (Fig. 1):
10.4.1 Compound Heat Stability—The time from the point of maximum torque (fusion torque) to the point of sudden torque
increase.
10.5 Report—Report the following information:
10.5.1 The compound heat stability to the nearest ⁄2 min, and
10.5.2 The temperature of test, rotor revolutions per minute, and the sample size used.
11. Color-Hold Stability Test Method
11.1 Prepare the test compound in accordance with 9.1.
11.2 Prepare the test equipment in accordance with 9.2.
11.3 Procedure:
11.3.1 Weigh a sample of the test compound in accordance with 9.3.1. With the mixer running, position the quick-loading chute
on the roller-head mixer and pour in the sample compound. Place the ram into the chute and add the weight. When the torque curve
indicates fusion, remove the loading chute and the weight.
11.3.2 Using the point of maximum torque (fusion torque) as zero time, remove a sample of the compound at regular time
intervals of 2, 3, or 5 min. Stop the rotors and use a pair of long-nose pliers to remove a sample from the bowl. Restart the rotors.
Place the compound into a hand press to shape the sample. Trim the sample and return the excess to the mixing bowl.
11.3.3 Mount the samples in a sequential time order.
11.3.4 Continue sampling until the desired color change has been observed.
NOTE 7—Depleting the sample from the bowl can affect the amount of working the compound receives. Select a time sequence that does not remove
more than half the sample.
11.3.5 Stop the mixer and open the bowl. Clea
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