The role of reduced graphene oxide on chemical, mechanical and barrier properties of natural rubber composites

Natural rubber (NR)-reduced graphene oxide (rGO) composites were produced via latex mixing and cocoagulation approach followed by static hot-press and twin roll mixing process. Due to the process, a fine control of filler dispersion was obtained and the composites exhibited a three-dimensional rGO network or alternatively a homogeneous dispersion of single rGO platelets. The effect of rGO dispersion on chemical crosslink structure, and their influence on mechanical and barrier properties was thoroughly investigated. Small angle X-ray scattering (SAXS) and solid-state 13C NMR analysis showed that rGO platelets affect the vulcanization process of natural rubber and that the crosslinking sulphur polysulphidic species present in pristine natural rubber decrease with the rGO content. In fact, at rGO content higher than 6 phr, the crosslinking species consist mainly of monosulphidic species which attain a consequent increment of intrinsic crosslinking density. However, the composites with rGO segregated network exhibit both barrier to oxygen and water vapour permeation and mechanical properties improved with respect to pristine rubber and composites with the homogeneous dispersion of single rGO platelets. The results confirm that the morphology of filler has a prominent key role in determining the natural rubber composites properties.