Somjate Patcharaphun, Veerades Pinsanor, Siripong Junpoonsup, and Narongrit Sombatsompop

pp. 75 - 90

Abstract

The objective of this work was to study the effect of silica (SiO₂) and calcium carbonate (CaCO₃)
on compounding torque, mechanical, physical, morphological properties, and swelling behaviour of cellular
natural rubber, using a compression moulding and conventional vulcanisation (CV) system with
oxybisbenzenesulphonylhydrazine (OBSH) as a blowing agent, the moulding cure temperature and time
being 160^oC and 7 mins respectively. The cellular rubber vulcanisates were characterised with respect
to tensile strength, abrasion resistance, thermal aging, swelling and deswelling behaviours. The results indicated that the addition of 20 phr SiO₂ in the rubber compound was the most preferable for the tensile
strength and abrasion resistance, this being associated with reinforcing effects between the silica and rubber
molecules, which also promoted the swelling resistance in toluene during equilibrium state. In the case of
CaCO₃ filler, added into the rubber compounds having 20 phr SiO2 , the optimum CaCO₃ content to maintain the overall properties was between 20 and 30 phr. The CaCO₃ above 30 phr reduced the tensile and
abrasive properties of the compounds due to the excessive fillers (silica and calcium carbonate) contents
being greater than 50 phr. Addition of CaCO₃ had no effect on the swelling behaviour of the compounds.
Considering the effect of thermal aging in the SiO₂ filled rubber compounds, it was observed that the mechanical properties of non-filler cellular rubber tended to decrease whereas the swelling resistance increased
with aging, this being due to the desulphuration of the surphur crosslinks. However, the properties of the NR
compounds containing 20 phr SiO₂ and various contents of CaCO₃ were unaffected by thermal aging. In
summary, the recommended mixed fillers contents for SiO₂ and CaCO3 in this work were 20 phr and 20 -
30 phr, respectively.