The evolution of morphology during the mechanical ‘plasticisation’ of unfilled vulcanisates of nitrile rubbers*

Optical microscopy was used to investigate features of morphological transformation during the mechanical degradation of unfilled vulcanisates of nitrile butadiene rubbers in a thin mill roll gap and subsequent thermal treatment – revulcanisation without the addition of any components into the degradate. An analytical complex based on a Leica DM-2500 optical microscope, a Leica DFC-420C high-resolution digital colour camera, and a specialised computer desk was used. The influence of the milling time in the 0–40 min range on the morphological parameters and the nature of the fine structure of plasticised specimens was studied. The mechanisms of degradation and structure formation during the plasticisation of vulcanisates were analysed. The formation of an additional three-dimensional skeleton in ‘secondary’ vulcanisates and the build-up of this process with increase in the treatment time of the degradate were found, which may lead to an increase in the mechanical properties to a level exceeding that of the initial vulcanisate. However, increase in compositional inhomogeneity may have an adverse effect on oil resistance.