Property investigation of ready-to-use silica-filled rubber composites containing a curing agent prepared by a simple latex compounding method

Abstract

A ready-to-use silica-filled rubber compound containing a curing agent was successfully prepared by a latex compounding method, followed by coagulation using a calcium chloride solution. This preparation technique provided a silica-filled compound with a small silica loss (ca. 1–5 % wt.). The rubber compounds were then subjected to various milling levels, ranging from 10 to 40 passes, prior to being tested for rheological and mechanical properties. The results reveal a reduction in compound viscosity with increasing milling levels. This may be attributed to the mastication effect (mostly dominant in the unfilled compounds) and the improved filler dispersion (particularly in the filled compounds). The magnitude of the Payne effect, an indicator of filler-filler interaction, of the heavily filled compounds (30–50 phr) was reduced by almost 50 % when the number of milling passes increased from 10 to 40 passes. The results suggest the improvement of silica dispersion with increasing the number of milling passes. Unfortunately, without a surface treatment of silica, the silica network was reformed when the rubber was subjected to high temperatures. This phenomenon was particularly obvious in the heavily filled compounds. Due to the improved silica dispersion in the highly filled compounds, increasing the milling pass from 10 to 40 passes resulted in noticeable increases in tensile strength (> 30 %) and elongation at break (> 30 %). Hardness, on the other hand, slightly decreased (10–15 %) with the increasing milling level. Overall, the silica-filled rubber compounds prepared by this technique had relatively high mechanical properties despite the absence of silane coupling agents. This technique can, therefore, be applied to prepare highly loaded silica-filled compounds without the need for expensive high-shear mixers.