FORMATION OF SURFACE-STRUCTURE IN VULCANIZATES AND SURFACE-STRUCTURE CHANGES IN AIR

The formation theory of surface structure during vulcanization was dev eloped on the basis of an interfacial concept. The theory showed the c hemical compositions of polar and nonpolar components on the vulcaniza te surface to be determined as an excess interfacial free energy betwe en rubber compounds and molds decreases. The surface free energies of molds reflected clearly the corresponding surface free energy of vulca nizates prepared from copolymers and polar polymers. Nonpolar polymers were not influenced by the surface free energies of molds. The surfac e free energies of vulcanizates decreased slightly with tile concentra tion of network chains owing to the entropy of rubber segments. The su rface free energies of molds affected the chemical compositions at the topmost surface region to the upper surface region on vulcanizates. N DR Vulcanizates with high surface free energy increased tile contact a ngle of water after standing in dry air. In tile dry air environment, topmost surface layer nitrile groups were buried in the bulk of NBR vu lcanizates and butadiene units subsequently overturn to the topmost la yer. In this case, the vulcanizate surface chemical composition was in fluenced only at tile topmost surface region. ESCA spectra N-1s peak i ntensities on NBR vulcanlzates was consistent with these observation.