Material propertiesMechanical properties, gas permeability and cut growth behaviour of natural rubber vulcanizates: Influence of clay types and clay/carbon black ratios

The properties as well as cut growth behaviour of natural rubber (NR) vulcanizates filled with different mineral clay types, namely devolite and calcined, were studied. The effect of partial replacement of clays with carbon black on the properties was also elucidated while the hardness level of the vulcanizates was kept constant. It is found that 2 phr of devolite clay or calcined clay can be replaced by 1 phr of carbon black (N330) to maintain the hardness value. At similar hardness, the cure retardation and resilience of the samples tend to reduce when decreasing the clay/carbon black ratio while torque difference, strength and thermal ageing resistance show the opposite trend. Compared to devolite clay, calcined clay gives NR vulcanizates with lower gas barrier property as well as scorch and cure time, but higher crosslink density, modulus, tear strength and cut tensile strength. The results also reveal that the cut growth behaviour of the vulcanizate changes from a simple lateral growth to oblique crack with partial replacement of the clay with carbon black, corresponding to its higher cut tensile strength.