Comparison study: effect of un-vulcanized and vulcanized NR content on the properties of two-matrix filled epoxy/natural rubber/graphene nano-platelets system

This paper focus in comparing un-vulcanized and vulcanized NR as toughening agent in epoxy resin. The incorporation of graphene nano-platelets (GNP) into two-matrix system has yield conductive materials whilst maintained their polymeric characteristics. Filled systems were prepared via magnetic stirring method and dispersion of GNP in the filled systems using ultrasonic water bath. The aim of this study is to investigate the effect of NR content on physical, mechanical, thermal and electrical performances of un-vulcanized and vulcanized filled systems. There is a great improvement in mechanical properties of vulcanized filled systems as compared to un-vulcanized filled systems. The results showed that the addition of vulcanized NR content at 5 vol% has improved flexural strength, modulus and toughness by 41.28%, 11.9% and 36.26% as compared to un-vulcanized filled system, when comparing at the same NR content. This improvement is attributed to the semi-efficient vulcanization (semi-EV) has transformed soft-like NR phases into high elastic NR phases, at which small vulcanized NR phases acted as energy dissipating center that can bear higher applied load without chain slippage. The flexured and fractured surfaces of filled systems were investigated using scanning electron microscope (SEM) technique to determine particle sizes of NR phases and its toughening mechanism. The formation of more conductive pathways in the vulcanized filled systems was agreed by the XRD analysis. Vulcanized filled systems have higher cross-link density in which implied that vulcanized NR phases are resistant to chemical penetration and cannot be easily removed.