Slurry-pad interactions

FIGURE 2.13 Weight gain of the pad specimens exposed to slurry, deionized water, pH 4 and pH 11 buffer solutions. 

DMA tests were eondueted with the specimens soaked in various environments for 0, 24, 72, 168, and 320 h. Pads exposed to slurry showed the lowest storage modulus G (especially at the temperatures below 0 °C) and the highest chain mobility reflected by the highest peak of the damping curve. The effect of time for which pads were soaked in pH 4 buffer solution on the reduction of the pad s dynamic storage modulus (i.e., pad softening) is shown in Fig. 2.14. The pad softening due to the increase in the chain mobility can be 

FIGURE 2.14 Effect of soaking time in pH 4 buffer solution on the reduction of the pad dynamic storage modulus (pad softening). DMA tests are conducted at 1, 10, and 100 Hz. 

The heat peaks of the nonreversing and reversing MDSC traces can be associated with nonreversible reactions such as a chemical reaction or cure and reversible reactions such as plasticizing processes in PU resin. Pad samples exposed to all tested media showed nonreversing heat peaks between 70 and 100 °C. Therefore, nonreversible chemical reactions are responsible for the pad softening. Endothermic irreversible heats reached their maximum value after approximately 180 h of exposure, as shown in Fig. 2.15. This suggests that chemical reactions that lead to pad softening are complete after approximately 180 h of exposure. 

FIGURE 2.15 Time dependence of endothermic heat related to an irreversible chemical reaction. Endothermic heat of pads soaked in pH 4, pH 11 buffer solutions, slurries, and DIW was measured using MDSC. 

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