Evaluation of elastomeric finishes

The simplest, but not necessarily the best, way of evaluating elastomeric finishes is the template method. The fabric is stretched by hand with, it is to be hoped, constant force in both warp and fill or weft and wale directions. The residual elongation is determined by the fabric s dimensional change. This method suffers from difficulties in repeatability owing to the variable stretching forces. 

A more reliable extension tester is produced by Hepatex AG, Wattwil, Switzerland. This machine (the Dehnungspriifgerat DP-5) has hydraulic damping and constant tension controls to provide reproducible stretching forces to the fabric. Fabrics can be tested in the wet or dry states. The degree of elasticity, E, can be calculated by  

Another suitable method for evaluating elastomeric finishes is ASTM D 4964-96 Standard Test Method for Tension and Elongation of Elastic Fabrics (Constant-Rate-of-Extension Type Tensile Testing Machine) . Fabric samples are formed into loops and are placed through several extension-recovery cycles under controlled conditions. Table 12.2 shows an overview of test methods for elastomeric finishes. 

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