Reinforcement of dipped natural rubber film by in situ alkylated silica

Abstract

Tetraethoxysilane (TEOS) and alkyltrialkoxysilane; vinyltriethoxysilane (VTOS), ethyltriethoxysilane (ETOS), and methacryloxypropyltrimethoxysilane (MPS) were used as precursors to generate silica via a sol-gel process in natural rubber latex to prepare silica-reinforced dipped NR films. These silanes were mixed with the latex incorporating 0.7% NH₃ and vulcanizing agents. The silane-latex mixture was maturated for 24 hr before it was used in a glass-former dipping process in order to prepare vulcanized films. The conversion of silanes silica in the latex was initiated by heating the latex-coated former at 80°C for 24 hr. The percentages of conversions of silanes from highest to lowest were TEOS (77.1%), VTOS (65.2%), MPS (18.7%), and ETOS (5.9%), depending on the size and polarity of the alkyl group in the silane. The mixture of TEOS and alkyltrialkoxysilanes was required to generate silica inside the NR latex in order to produce the films with high silica contents. By TEM analysis, the in situ silica particles were observed around rubber particle. The particle size of in situ silica was smaller than 100 nm. The silica particles were well dispersed in the rubber matrix as observed by SEM. Results of mechanical test suggested that the vinyl group on the situ generated silica (from VTOS) probably took part in the sulfur vulcanization process. The inclusion of silica in the dipped films did not enhance the thermal stability of the dipped films as analyzed by TGA.