ASTM D3591: Inherent Viscosity (Logarithmic Viscosity Number) of PVC

ASTM D3591 test method determines the logarithmic viscosity number of compounded or processed poly vinyl chloride (PVC) homo-polymers. The formulation of the resins is kept in mind, and the extraction with diethyl ether helps get rid of additives from the resins. The test method results are displayed in SI units, and the necessary precautionary measures are observed.

Talk to an Expert

ASTM D3591: Inherent Viscosity (Logarithmic Viscosity Number) of PVC

TRUSTED BY

Precision-driven testing for dimensional accuracy and compliance

Overview
Scope, Applications, and Benefits
Test Process
Specifications
Instrumentation
Results and Deliverables

Overview

ASTM D3591 is the standard method of testing the logarithmic viscosity number (intrinsic viscosity) of a solution of polyvinyl chloride (PVC) resins. Intrinsic viscosity is a measure of the polymer’s average molecular weight and is directly related to its mechanical properties, processing behavior, and consistency.

This method applies to all types of PVC resins, including suspension, emulsion, and bulk-polymerized grades, whether plasticized or unplasticized. Generally speaking, higher viscosity values indicate higher molecular weight, which provides improved strength and impact resistance; lower viscosity values indicate easier processability.

Scope, Applications, and Benefits

Scope

ASTM D3591 evaluates the molecular characteristics of PVC by measuring the flow behavior of dilute polymer solutions through a capillary viscometer.

It evaluates:

Logarithmic viscosity number (intrinsic viscosity)
Relative molecular weight trends
Polymer chain length characteristics
Resin uniformity and consistency
Processability indicators

The method applies to suspension, emulsion, and bulk-polymerized PVC grades.

Applications

PVC pipe and profile manufacturing
Flexible flooring and coatings
Synthetic leather production
Film and sheet extrusion
Cable insulation materials
Quality control laboratories
PVC resin research and development

Benefits

Provides standardized molecular weight indicators
Supports resin grade selection
Improves processing control
Assists in product development
Ensures batch-to-batch consistency
Enhances quality assurance programs

Test Process

Sample Preparation

PVC resin is dried, dissolved in cyclohexanone or THF, and conditioned at 30°C to ensure uniformity and remove air bubbles.

Flow Measurement

Flow times of the pure solvent and the prepared solution are measured using a capillary viscometer.

Data Calculation

Intrinsic viscosity is calculated from the flow-time ratios using standard equations.

Result Reporting

The logarithmic viscosity number is reported in mL/g.

Technical Specifications

Parameter	Details
Applicable Materials	PVC resins
Resin Forms	Powder or granules
Solvent	Cyclohexanone or THF
Typical Concentration	0.4 g PVC / 100 mL solvent
Test Temperature	30°C ± 0.1°C
Viscometer Type	Ubbelohde or Ostwald