EFFECTS OF MECHANICAL AND CHEMICAL PROPERTIES ON TRANSPORT IN FLUOROPOLYMERS .2. PERMEATION

摘要

This is the second part of a study of chemical structure-physical property-performance relationships among several fluoropolymers and Liquid penetrants, focusing on their permeation behavior. That behavior was consistent with the chemical and physical characteristics of the polymers, in that it depended on thermodynamic properties of the various penetrants (e.g., molecular volume, solubility parameters, and polarity). Relatively inert PFA showed effects only of molecular size. Similarly inert, but structurally modified ETFE showed nearly random dependence on all the properties. In contrast, ECTFE exhibited dipole-dipole bonds and PVDF embodied II-bonds; and both types of bonding affected permeability systematically. For example, ECTFE was most susceptible to polar compounds (dichloromethane and chlorobenzene), and PVDF was most susceptible to H-bonded liquids (phenol and methyl ethyl ketone). The permeation behaviors of several combinations showed unusual dependence on time, thickness, and other factors such as temperature, processing conditions, chemical structure, and swelling due to relaxation. The Cattaneo-Maxwell model was used to fit transient permeation-rate data of relatively well-behaved ETFE. In contrast, a new kinetic model was devised to interpret more complex transient permeation behavior, particularly the observed acceleration in ECTFE. (C) 1997 John Wiley & Sons, Inc. [References: 22]