Hybrids from HNBR and in situ polymerizable cyclic butylene terephthalate (CBT): Structure and rolling wear properties

Hybrids composed of peroxide-curable hydrogenated acrylonitrile-butadiene rubber (HNBR) and cyclic butylene terephthalate oligomers (CBT) were produced. CBT was expected to polymerize in situ when curing the HNBR. Extraction, differential scanning calorimetry (DSC), dynamic-mechanical thermal analysis (DMTA), wide-angle X-ray scattering (WAXS) and atomic force microscopy (AFM) were adopted to investigate the CBT conversion and the phase structure of the hybrids before (T = 190 °C; HNBR-(p)CBT) and after annealing (T = 250 °C; HNBR-pCBT). Unlubricated rolling wear properties of the related compounds with different CBT contents were assessed in orbital rolling ball (steel)-on-plate (rubber) test rig (Orbital-RBOP). The dynamic coefficient of friction and the specific wear rate were determined. Both (p)CBT and pCBT improved the rolling wear resistance of the hybrids compared to plain HNBR. However, the polymerized CBT (pCBT) improved the wear properties more than the unpolymerized CBT ((p)CBT). The wear mechanisms were identified by inspecting the worn surfaces in scanning electron microscope (SEM) and are discussed as a function of (p)CBT/pCBT modification. Changes in the structure and properties of the hybrids caused by the annealing-induced polymerization of CBT were analyzed.