Free shrinkage tests are used to evaluate the unrestrained linear heat shrinkage of thin plastic films for packaging applications e.g. shrink wrap and shrink sleeve materials.
Heat shrinkage is determined by comparing the dimensions of pre cut samples before and after heating in an oil bath, typically set at 90°C for polyvinyl chloride (PVC) or 115°C for low density polyethylene (LDPE).
Standards and Accreditation
Smithers Pira testing is performed to British standard BS 2782 method 643A or ASTM 2732. The methods differ primarily in the dimensions of the test pieces used.