Study on Powder Utilization of Waste Tires as a Filler in Rubber Compounding

Abstract

Abstract The recycling of rubber from waste tires and other products has been of commercial and environmental interest for several decades. For recycling, bulk properties are most relevant; whereas, for crumb incorporation both bulk and matrix-crumb interface phenomena are important, which are dealt with in this study. We have taken a crumb rubber of high surface area and a diameter between 100 and 200 µm and incorporated it into uncured natural rubber (NR) or acrylonitrile—butadiene (NBR) containing silica. This non-black reinforcing filler was used to allow a better modulus match between crumb and matrix than would exist for a non-filled system, while allowing visual contrast between the two phases for microscopic examination. The micromechanics of deformation can be investigated using scanning electron microscopy. The crumb rubber was either added as received or used after a surface chlorination step. The matrix was also used unmodified or with a compatibilizer used to facilitate homogenization of polar and nonpolar elastomers. Differences in matrix/crumb polarity and interfaces were therefore able to be investigated. Chlorination of crumb has a beneficial effect in NBR matrix compounds, but causes embrittlement in NR-based compounds. In the former case, some enhanced compatibility is expected, as analogous poly(vinyl chloride) (PVC)/NBR blends are already used. The compatibilizer also imparts improved performance to the NBR/crumb compound, overcoming differences in polarity between the matrix and the nonpolar crumb. However for the NR matrix compound, similar chemical compositions already exist and so the aliphatic-hydrocarbon resin compatibilizer (STRUKTOL) provides no benefit.