SynopsisThe tensile properties of TiOp6lled poly(viny1 acetate) were studied a t strain rates of 100%/min. to 5,00O%/min. at 25OC. after exposure to relative humidities of 10, 25, 51, 70, and 90% for 160 hr. Filler concentrations studied were 0, 10, 20, 30, and 40 wt.-% TiOz. The change in tensile properties with greater humidity was dependent on filler content. As the filler content increased, strength was lowered, elongation increased, and stiffness decreased with greater humidity. Generally, changes in tensile properties with humidity were less pronounced at higher strain rates. A mechanism is proposed where HzO alters the packing of polymer chains and affects the interaction of filler with polymer.
The diffusion of oxygen and arson through poly(vinyl acetate) filled with 12% by volume of titanium dioxide was studied. It was found that the activation energy of gas diffusion in each case was about 56% of the corresponding value fur diffusion in the unfilled polymer above its glass transition temperature. Furthermore, the activation energies for diffusion in the filled polymer appeared to be the same at temperatures above and below the transition temperature, in contrast with the observation by Meares that the activation energy for diffusion in the unfilled polymer has a higher value above Tg. The decrease in the activation energy of gas diffusion as a result of filler incorporation is discussed in terms of the possible decrease in the internal pressure of the filled system. It is postulated that a decrease in the configurational entropy of the polymer accompanies the incorporation of the filler. The explanation is consistent with the results of organic vapor sorption experiments.
A model is proposed for the solution of gases in polymers. Gas molecules are assumed to reside in the “free” volume without net disruption of polymer–polymer contacts. A number of conclusions result from this model, which are in excellent agreement with experimental results.
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