Recent advancements in rubber nanocomposites

This paper discusses rubber nanocomposites prepared via melt blending and based on the following nanofillers: organically modified clays (OC), carbon nanotubes (CNT) and graphitic nanofillers made by few layers of graphene (nanoG). Attention is focussed on structure of nanofillers and nanocomposites, filler networking, dynamic and quasi-static mechanical behavior of nanocomposites at medium and large strain. As rubber nanocomposites find their large scale application in tyre compounds, nanocomposites based on hybrid filler system, with a nanostructured filler such as carbon black (CB), are in particular examined. It is shown that ultimate dispersion of individual layers of nanofillers in the polymer matrix is achieved through the chemical modification of nanofillers. Low crystalline order in the interlayer space of a layered nanofiller (such as OC and nanoG) leads to easier delamination that can be as well achieved through the use of mechanical energy. Individual nanofiller layers and tubes give rise to filler networking at low nanofiller concentration, particularly in the presence of CB. Hybrid filler systems lead to nanocomposites initial moduli much higher than those calculated through the sum of initial modulus of composites containing either only CB or only the nanofiller. Interestingly, nanofillers enhance the matrix modulus by a multiplication factor that depends only on the nanofiller type and content, no matter if the matrix is a neat or a CB filled polymer. Furthermore, the filler-polymer interfacial area was found to be a parameter able to correlate the mechanical behavior of both a nano- (CNT) and a nanostructured (CB) fillers. By plotting values of the composite initial modulus vs the filler-polymer interfacial area, points due to CB, CNT and to the hybrid CB-CNT system lie on the same curve. CNT are able to promote the mechanical reinforcement of rubber matrices, in the absence and in the presence of a nanostructured filler such as CB, at low and high deformations, independently of the crosslinking system.