MOISTURE EFFECTS ON ISOBUTYLENE-ISOPRENE COPOLYMER-BASED COMPOSITE BARRIER .1. MOISTURE DIFFUSION AND DETECTION

Experiments have assessed how moisture and heat influence the function al and structural integrity of butyl rubber matrix composites used as protective barriers. This paper, which is first of a series, reports t he findings on the subjects of moisture diffusion and its effect on ul trasonic wave propagation of composite barriers. On exposure to high h umidity at elevated temperatures, carbon black-reinforced butyl rubber composite barriers were found to absorb substantial moisture, with th e hygroscopic reinforcement phase making a more significant contributi on than the matrix. The moisture diffusion coefficients for both compo site and unreinforced vulcanizate were close to each other at each exp osure temperature, and had the same temperature dependence. The calcul ated activation energies of moisture diffusion indicate that the moist ure absorption rate of the carbon black phase is governed by the moist ure diffusion rate of the matrix. Ultrasonic wave speed appeared to be a viable means of monitoring the moisture absorption of composite bar riers. On exposure to moist heat, relative ultrasonic wave speeds for both composite and unreinforced vulcanizate decreased continuously.