Vulcanization: New Focus on a Traditional Technology by Small-Angle Neutron Scattering

Abstract

Vulcanization is the most important and conventional process in preparing rubber products. Network structure in the vulcanizates has been assumed to dominantly determine their physical properties together with network-chain density. Therefore, control of network structure in the vulcanizates is of at most importance for a fundamental design of rubber products. However, inhomogeneity of the network structure has not been much elucidated in spite of the long history of vulcanization since 1839, due to the complicated reactions among rubber and cross-linking reagents. Here, we look more closely at vulcanization and show its new role to control the network inhomogeneity on the basis of small-angle neutron scattering analysis of vulcanized rubbers. Combination and composition of the cross-linking reagents, especially those of zinc oxide with the other reagents, were found to be crucial for the control. A characteristic feature of strain-induced crystallization of the vulcanizates is also accounted for by the notion of network inhomogeneity. These results will be useful for further enhancing the technological potential of the traditional yet indispensable vulcanization.

Nonuniformity in Cross-Linked Natural Rubber as Revealed by Contrast-Variation Small-Angle Neutron Scattering

“…16,20,43 In this case, the squared-Lorentz function may include the intensities from several different structural origins. For instance, the contribution of the polyisoprene chains attaching to the protein aggregates is obvious, as the cross term S PI (q) is positive and significantly large as discussed above.…”

Two‐Phase Network Formation in Sulfur Crosslinking Reaction of Isoprene Rubber

“…Our group has reported the effect of the combination and composition of the sulfur crosslinking reagents on the rubber network formations. Especially, those of zinc oxide (ZnO) with the other reagents were found to be crucial to control the structural network inhomogeneity in the vulcanization of isoprene rubber (IR) by small‐angle neutron scattering (SANS) techniques . The speculated two‐phase inhomogeneous structure of the sulfur crosslinked IR is illustrated in Figure , where the domains of high network‐chain density are embedded in the rubber network matrix.…”

“…Especially, those of zinc oxide (ZnO) with the other reagents were found to be crucial to control the structural network inhomogeneity in the vulcanization of isoprene rubber (IR) by small‐angle neutron scattering (SANS) techniques . The speculated two‐phase inhomogeneous structure of the sulfur crosslinked IR is illustrated in Figure , where the domains of high network‐chain density are embedded in the rubber network matrix. From the results of the SANS measurements, the following mechanism on a benzothiazolesulfenamide‐accelerated curing system with ZnO and stearic acid was proposed: Upon milling and heat‐pressing the rubber compounds, stearic acid is reacted with ZnO to form solubilized zinc stearate in the rubber matrix.…”

Inhomogeneities and Chain Dynamics in Diene Rubbers Vulcanized with Different Cure Systems

“…42,43 Often, however, such approaches are indirect. For instance, in recent work, 44 two different phase components with different cross-link density in sulfur cross-linked natural rubber (NR) samples were deduced from strain-induced crystallization studies.…”