ASTM D5225-22

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Designation: D5225 − 17 D5225 − 22
Standard Test Method for
Measuring Solution Viscosity of Polymers with a Differential
Viscometer
This standard is issued under the fixed designation D5225; 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 solution viscosity of polymers using a differential or the modified differential
viscometer. It is applicable to all polymers that dissolve completely without chemical reaction or degradation to form solutions that
are stable with time and temperature. Results of the test are usually expressed as specific viscosity, intrinsic viscosity (limiting
viscosity number), inherent viscosity (logarithmic viscosity number), or relative viscosity (viscosity ratio).
1.2 Since there is more than one type of viscometer available to measure a differential pressure, follow the manufacturer’s
directions applicable to the equipment being used.
1.3 The solution viscosity values are comparable with those obtained using a glass capillary of Test Method D2857. This test
method differs from the glass capillary in that the solvent and the solution are compared at the same time that a test is run. With
a glass capillary, each solution must be referenced back to the solvent run in the same capillary at the same temperature.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
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. For specific hazard statements, see Section 8.
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.
2. Referenced Documents
2.1 ASTM Standards:
D883 Terminology Relating to Plastics
D1243 Test Method for Dilute Solution Viscosity of Vinyl Chloride Polymers
D1600 Terminology for Abbreviated Terms Relating to Plastics
D2857 Practice for Dilute Solution Viscosity of Polymers
This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.70 on Analytical Methods.
Current edition approved Dec. 1, 2017Sept. 1, 2022. Published January 2018September 2022. Originally approved in 1992. Last previous edition approved in 20142017
as D5225 - 14.D5225 - 17. DOI: 10.1520/D5225-17.10.1520/D5225-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on 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
D5225 − 22
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E2935 Practice for Evaluating Equivalence of Two Testing Processes
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms pertaining to plastics used in this test method, refer to Terminology D883. For abbreviations used
in this test method, refer to terminology D1600, unless otherwise indicated. For definitions of terms that appear in this test method
relating to quality and statistics, refer to Terminology E456.
3.1.2 inherent viscosity—viscosity, n—the ratio of the natural logarithm of the relative viscosity to the concentration. The IUPAC
term for inherent viscosity is logarithmic viscosity number.
3.1.3 intrinsic viscosity—viscosity, n—limit of the reduced and inherent viscosities as the concentration of the polymeric solute
approaches zero and represents the capacity of the polymer to increase viscosity. The IUPAC term for intrinsic viscosity is limiting
viscosity number.
3.1.4 reduced viscosity—viscosity, n—the ratio of the specific viscosity to the concentration. Reduced viscosity is a measure of the
specific capacity of the polymer to increase the relative viscosity. The IUPAC term for reduced viscosity is viscosity number.
3.1.5 relative viscosity—viscosity, n—the ratio of the polymer solution pressure to the pressure of the solvent.
3.1.6 specific viscosity—viscosity, n—the relative viscosity minus one.
3.1.7 viscosity constant, K—K, n—baseline reading when solvent is present in both capillaries.
4. Summary of Test Method
4.1 Differential Viscometer (Fig. 1):
4.1.1 The viscosity measurement with the differential viscometer is based on a fluid analog of the Wheatstone Bridge. Pure solvent
NOTE 1—
R , R , R , R = Matched SS Capillary Tubing
1 2 3 4
A, B = Solution Holdup Reservoirs
S , S = Switching Valve
A B
P = Solvent Inlet Pressure Transducer
i
ΔP = Differential Pressure Transducer
FIG. 1 Differential Viscometer
D5225 − 22
at constant inlet pressure P enters a balanced capillary network and flows through, producing a zero or baseline pressure on the
i
differential pressure transducer. Solution is loaded into the sample reservoir A and then injected onstream by means of the
switching valve S . The differential pressure begins to rise until it reaches a steady state value of ΔP proportional to the specific
A
viscosity of the solution. The differential pressure is monitored continuously on a strip chart recorder or computer, providing a
baseline where ΔP is measured. The equation relating ΔP to specific viscosity is:
4ΔP
η 5 (1)
sp
P 2 2ΔP
i
4.1.2 Derivation of the equation is in Annex A1.
4.2 Modified Differential Viscometer (Fig. 2):
4.2.1 The modified differential viscometer has two stainless steel capillaries connected in series with a sample loading/injection
valve before the second capillary. Two differential pressure transducers, P and P , are connected in parallel across the capillaries.
1 2
A pump continuously supplies solvent flow. The ratio of the pressures P and P is proportional to the ratio of the viscosities of
2 1
the fluid in capillary 2 to that in capillary 1.
P η
2 2
5 K 5 K·Relative Viscosity (2)
P η
1 1
4.2.1.1 K, the viscosity constant, is obtained from the baseline reading when solvent is present in both capillaries, so η /η is unity.
2 1
4.2.1.2 With the valve in LOAD position, the sample is flushed through the sample loop by the syringe pump. A baseline reading
is established and recorded by the computer data acquisition system. When the valve is switched to the INJECT position, solvent
flowing from capillary 1 pushes the sample into capillary 2. The differential pressure P will increase due to the higher viscosity
of the sample solution. The steady state value of P /P then yields the value of relative viscosity of the sample.
2 1
P
Relative Viscosity 5 (3)
KP
4.2.1.3 Absolute viscosity of the sample may be calculated from relative viscosity, RV, assuming the viscosity of the solvent is
known.
η~sample!5 RV·η~solvent! (4)
5. Significance and Use
5.1 Solution viscosity values for polymers are related to the average molecular size of that portion of the polymer which dissolves
in the solvent.
6. Apparatus
6.1 Differential Viscometer, or Relative Viscometer, Dilute Solution Viscosity (DSV) System,
6.2 Glass Vial, 25 mL,
FIG. 2 Relative Viscometer
...