Vulcanized rubber consists of a network structure with defects, where the network structure comprises an inhomogeneous cross-linking structure. These structures become more complex through thermal oxidation. In this study, we used multiple-quantum (MQ) NMR to investigate crosslink inhomogeneity of network structure in thermal-oxidized isoprene rubber (IR). We measured reference decay I_REF and double-quantum build-up decay I_DQ to obtain the fraction of network component (FA) and distribution of residual dipolar coupling constant (D_res). Among analytical methods, setting D_res to a logarithmic axis without fixing the distribution shape proved most appropriate. We observed that increased thermal-oxidation time led to decreased F_A and expanded D_res distribution. The 100% modulus S100 showed a positive linear correlation with the median value of D_res distribution (D_m), with correlation improving when using F_A×D_m instead of D_m alone. For dry specimens, elongation at break (λ_B) decreased as the quartile deviation of D_res distribution (QD) increased. These results indicate that thermal oxidation increases crosslink inhomogeneity of network structure, suggesting that mechanical properties affected by thermal oxidation can be characterized using D_res distribution parameters.

Liquid 1,2-polybutadiene (1,2-PB) contributes to improve rubber hardness, elasticity, and oil resistance as its 1,2-vinyl groups undergo crosslinking reactions to form network structures. Therefore, it has been used as an additive in various rubber products such as EPDM, SBS, and HNBR. Recently, it was reported that 1,2-epoxidized liquid PB can react with halogen compounds such as chlorine and fluorine. In chlorinated rubber formulations, lead compounds (PbO) have traditionally been used as acid acceptor. However, with the increasing global emphasis on the Sustainable Development Goals (SDGs), there is increasing demand for safer and more environment friendly materials.

In this study, 1,2-epoxidized PB was evaluated as an additive for epichlorohydrin rubber (GECO) formulations. The results show that 1,2-epoxidized PB can be used not only as a mechanical property modifier but also as an effective acid acceptor for GECO formulations. The replacement of lead monoxide (PbO) is required due to increasingly restricted REACH and RoHS regulations.

Ozone cracking, which significantly affects the durability of rubber products, is typically evaluated based on surface observations in accordance with Japanese Industrial Standards (JIS).

In practical applications, however, evaluating crack depth is critically important, as it directly relates to product integrity and human safety.

By employing X-ray computed tomography (CT), we have established a method for quantitatively evaluating both crack depth and crack length.

This article explores the phenomenological aspects of the mechanical behavior of polymer solids, particularly focusing on their linear viscoelastic responses in the initial stages of deformation. The standard linear solid model is employed as the primary framework, with serving as a foundational tool to understand rheological responses. The characteristic times, such as relaxation and retardation times, are derived from static and dynamic tests, and their temperature dependence is discussed based on the time-temperature superposition principle. In addition, this article deals with a discussion on dissipation process based on the Eyring theory of thermally activated flow.