Internal friction studies of halogenated hydrocarbon polymers
Roberts, John M.
Master of Science
The effect of thermal history and mechanical deformation on the internal friction and dynamic shear modulus of polychlorotrifluoroethylene (PCTFE) and polytetrafluoroethylene (PTFE) was studied using a free oscillating torsional pendulum (1 Hz.) operating between 4.2° K and 3°K. Scanning electron micrographs of specimen fracture surfaces were made to correlate the mechanical properties with the observed morphology. In PCTFE, a new low temperature & relaxation was found which Increased in intensity with increasing crystallinity. This relaxation is similar to those found in several other polymers and attributed to motion of crystalline defects. The relaxation occurs around 48 K and has an activation energy of roughly 3 kcal/mole. The crystallinity of PTFE was not changed, and evidenoe supporting a relaxation in this polymer is not conclusive. Large uniaxial deformation resulted in the reduction of the low temperature internal friction in both polymers (disappearance of the S relaxation in PCTFE), and the enhancement of the higher temperature if relaxations in both polymers. This made the speotra appear to be those of very low crystallinity specimens. This fact combined with the morphology seen in the micrographs suggests that the deforming stress acts through the lnterorystalllne links to destroy the order in the crystallites.