In this paper, the behavior of water absorption on PMMA-Hinoki combination(WPC) has been investigated, following the hygroscopicity experiment of the previous report (IV).
The specimens(10(R) ×50(T) ×5(L) mm) of Hinoki(Chamaecyparis Obtusa ENDL.) were impregnated with methy methacrylate(MMA), using various treatment conditions, and cured by the catalyst-heat technique as described in the previous report.
The ASE(anti-swelling efficiency) measurements were made on vacuum-dry and water-soaked specimens. The specimens were allowed to soak until equilibrium swelling was reached. The dimensional change in tagential direction were then measured and the ASE was calculated.
The results obtained are as follows :
The behavior of water absorption on WPC shows a different phenomenon from that of hygroscopicity. Namely, the results concerning the relation between ASE and polymer content(Fig. 3) showed a tendency approximately similar to those of Loos' study. Although an inverse proportional relation between polymer content and water absorption is obtained(Fig. 2), at higher polymer content the ASE values tend to drop off and show values near to zero. As the reason for this, it is assumed that at high polymer content the specimens shrink due to the shrinkage of the monomer during polymerization, and thus during swelling this shrinkage stress is relieved causing greater than normal swelling.