Hardness–Elastic Modulus Relationship for Nitrile Rubber and Nitrile Rubber–Polyvinyl Chloride Blends

Nitrile rubber (NBR) and nitrile rubber–polyvinyl chloride (NBR-PVC50/50) (NVC55) blends are vulcanized by sulphur curing system using high abrasion furnace carbon black (CB-HAF) and graphite (GT) as reinforcements in the present investigation. The mechanical properties of the compositions are evaluated. The relationship of durometer hardness with Young’s modulus (E) is determined and compared with theoretical models of the literature. It is observed that the relationship is not in good agreement with any literature model for full range of hardness from 49 to 88 Shore ‘A’ (SA). While some models are more applicable to low hardness range, some others are better applicable to higher range. However, log (modulus) is found to be varying linearly with Shore ‘A’ hardness. The compressive modulus (EC) of the compositions is calculated using the theoretical relationship with hardness from the literature. The ratio of calculated compressive modulus to measure Young’s modulus for NBR and NVC55 compositions is evaluated as a function of hardness and compared with the available literature data. The ratio for NBR compositions is almost identical for two models, while for NVC55 compositions, one model results in constant ratio irrespective of hardness, and the other predicts a widely varying ratio depending on hardness.