Advances in instrumentation and technique of torsional pendulum and torsional braid analyses

Abstract

A torsional pendulum which operates throughout the temperature range — 180° ⇄ +650°C, and permits the examination of specimens which conform to ASTM standard D2236 is reported. The same apparatus is used for torsional braid analyses for which a composite specimen is prepared by impregnating a multifilament glass braid with a solution of polymer and thermally removing the solvent. A linear‐with‐angle no‐drag optical transducer which employs the linear transmission region of a pair of polarizers is described. The apparatus has been used for examining thermo‐hysteresis effects in polymers. Hysteresis can arise in polymers from physical time‐dependent phenomena such as crystallization ⇄ fusion, dry atmosphere ⇄ water vapor, annealing ⇄ cracking, and from chemical reactions. Thermally‐induced chemical reactions can be regulated so as to freeze out preferentially longer range relaxations, thereby extending the glassy state behavior to higher temperatures. A comparison of the thermomechanical behavior of a commercially available polyimide film and of a polyimideforming varnish is reported using torsional pendulum and torsional braid analyses.