Abstract
Abstract This work is an investigation on causes of extrusion problem of a high silica- and all silica-filled natural rubber compounds containing a coupling agent. The 67% silica and 33% carbon black, N110 compound (Compound 3) gave a wavy surface of extrudate from a profile die. The 100% silica-filled compound (Compound 4) was too stiff to be extruded. Reference compounds, 100% carbon black (Compound 1) and 33% silica with 67% carbon black (Compound 2), gave smooth extrudates. The amplitude dependence of storage modulus measurements indicated Compound 4 had a poorer dispersion of the filler. Scanning electron microscopy also showed a poorer dispersion for this compound. However, Compound 3 could not be distinguished from Compounds 1 and 2 in the above investigation. Transient shear measurements at very low deformation rate indicated a reaction between natural rubber and the coupling agent, resulting in gel and long-branch formation. Differential scanning calorimetry indicated the coupling reaction was completed at 140°C within the mixing time. By holding the maximum temperature of mixing as low as possible, the extrudate of Compound 3 became smooth, but Compound 4 still did not perform well. Improvement of dispersion is necessary to make Compound 4 extrudable.
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