Ozone degradation of vulcanized EPDM (ethylene-propylene-diene rubber) was investigated by changing atmospheric humidity. Ozone exposure test of a carbon black filled EPDM vulcanizate was carried out with 100 pphm ozone at 40 °C, for 168 hours under relative humidity (RH) at 80 and 20%, after a strain of 20% stretching. The degradation of the vulcanizates was assessed by morphology observation with digital microscopy and SEM (scanning electron microscopy). Ozone cracks did not appear on the surface of the vulcanizates exposed with ozone at 80%RH and 20%RH, but white blooms identified as ZDMC (zinc dimethyldithiocarbamate) appeared on the surface of them. The ozone degradation of the EPDM was attributed to a chain scission of the rubber molecules by hydroxyl radical generated due to a reaction of moisture and ozone.

We inspected here whether the gel-network structure model of cross-linked rubber, which consists of three different regions, the gel-balls of very highly cross-linked, the molecular bundles of slightly cross-linked which connect the gel-balls each other and the uncross-linked regions, is valid or not in comparison with AFM observation and fractured surface of the real cross-linked rubber.
(1) AFM image shows that two domains of hard and soft exist in the cross-linked rubber, where the spherical hard domains are surrounded by the soft domains, thus both the domains are alternately arranged. At a large extension mutual movement of both the domains agrees well with the movement expected for both the cross-linked phase (gel-ball) and the uncross-linked phase in the gel-network structure model.
(2) Fracture patterns left on fractured surface for tear fracture, fatigue fracture and wear fracture of the crosslinked rubber indicate the existence of several weak boundaries in the cross-linked rubber. These weak boundaries are consistent with the intrinsic weakness of the gel-network structure, resulting from the weak boundaries between gel-balls.
(3) These results indicate that the gel-network structure model is suitable to express the inside real structure of the cross-linked rubber, qualitatively at least.

The structural formation behaviors during molding processes for practical polymers, such as crosslinking for rubbers and injection molding for thermoplastics, are often not well understood. In this Part Ⅳ , in-situ observation of the crosslinking and crystallization processes using synchrotron X-ray sources was introduced as a useful method to elucidate the temporal changes in structures, by adjusting the time resolution to match the processing times. Crosslinking reaction of sulfur-based rubber compounds was investigated by time-resolved X-ray adsorption fine structure (XAFS) measurements. The Zn K-edge XANES (X-ray absorption near-edge structure) spectra obtained during the crosslinking revealed that the decreasing behavior of the amount of zinc oxide (ZnO) give a good indicator of the crosslinking reaction, involving the transformation of ZnO into zinc sulfide (ZnS). In-situ observation of crystallization processes of isotactic polypropylene (iPP) during the injection molding was investigated by time-resolved wide-angle X-ray scattering (WAXS) measurements. The changes in the WAXS patterns under various molding conditions such as mold temperature and injection speed were directly related to the crystallization behaviors of iPP.