The individual fibers of an elastomeric fabric must be completely covered with a thin film of an elastic material without any fiber-to-fiber bonding .The film causes a high degree of recovery from deformations owing to its particular structure of widely spaced crosslinks.
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 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 Dehnungsprufgerat 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 elastomeric finishes is ASTM D 496496:’Standard Test Method for Tension and Elongation of Elastic Fabrics (Constant-Rate-of-Extension Type Tenting 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 .