充てん剤配合ゴムの繰返し変形による物理結合変化

抄録

In the previous paper¹⁾, it was concluded from the NMR studies by means of X-rays of the crosslink density and the combined type of sulfur, that the rubber molecules of filled vulcanizates formed three different phases, the highly motional and uncrosslinked, the unmotional and collectively crosslinked, and the degenerated phase around the fillers. However, these phases were not apparently separated, but had a continuous distribution from the highly motional to the unmotional.
In this paper, the behaviours under cyclic deformation of these vulcanizates which had wide distribution of molecular mobility have been investigated by NMR method with respect to stresses by energy and entropy, density and crosslink density. Natural rubber vulcanizates loaded with white fillers, CaCo₃ (I), CaCO₃ (II), ZnO, MgCO₃ and clay and carbon blacks, HAF, MPC and FT were adopted as samples. These were cyclically extended to the extension ratio α=5 and the above properties were measured at every cycle.
The results are as follows:
1) From changes in density and crosslink density, it is deduced that the bond of rubber molecules to the white fillers is weak and cavities have appeared on the surface of the fillers in the direction of extension, but in case of carbon black loaded vulcanizates, the bond is strong and the degenerated phase around the fillers has increased by extension.
2) Stresses by entropy and energy of filled vulcanizates, have both increased, and the rubber molecules tend to separate into more motional and more unmotional phases. The greater the amount of the degenerative phase around the fillers, the greater these tendencies are.
3) In case of smaller extension (Strain ±20%) and multicyclic deformations, the case is the same as in larger extensions; the mobility of rubber molecules of filled vulcanizates also proceed to two different states, more ordered and more disordered. Then the phases become separated more apparently after the cyclic deformations.