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Abstract
An investigation is reported in which anomalous negative recovery, or ‘overtwist’, occurred when drawn fibres of poly(ethylene terephthalate) (PET) and nylon 6.6 were heat-set in torsion above a certain temperature T s*. For the samples of PET and nylon 6.6 studied, and the chosen setting conditions. T s* was found to be 151 ± 2°C and 133 ± 2°C, respectively. Overtwist was found to decrease with increasing axial tension or after a prior heat-setting treatment without twist. The existence of overtwist and its dependence on twist level and axial tension are explained in terms of the theory of thermoelasticity of a twisted filament. Theory predicts that overtwist will always occur when drawn polymeric filaments are heat-set in torsion at a sufficiently high temperature and setting time.