Study on the effect of ball milling time towards the stability of carbon black dispersion and carbon black masterbatch properties

Abstract

Carbon black (CB) is a reinforcing filler. The CB primary challenge is its tendency to form aggregates and agglomerates during the typical rubber compounding. This subsequently decreased the reinforcing efficiency. The aim of this study is to investigate an alternative method to prepare CB filled compound via CB masterbatch. In the CB masterbatch preparation, CB is dispersed in an alkaline medium; i.e. butylamine; via ball milling. Then, the stable colloid obtained was mixed with high ammonia natural rubber (HANR) latex. The coagulated colloid mixture is known as CB masterbatch. The CB masterbatch will then undergo typical rubber compounding. The filled compound cure characteristics and filled vulcanizate properties were investigated. Ball milling time is crucial in obtaining a stable CB colloid as a long ball milling time is hypothesized to result in a lower CB structure. During ball milling, butylamine will change the surface chemistry of CB and if there are sufficient charges at the CB surface, repulsive forces among the CB particles is created. The repulsive forces can prevent coalescence among the particles and resulted in a lower CB structure. In this study ball milling times studied were 15 minutes, 1 hour, 2 hours and 24 hours. The results show that CB particle size reduce with the ball milling time and zeta potential showed that the colloid stability improved with longer ball milling time. The mechanical properties results are in agreement with the particle size and zeta potential of the CB dispersion. When comparing the CB filled vulcanizate prepared from CB masterbatch with the CB filled vulcanizate prepared via a typical compounding method, the former showed better properties. Vulcanizate from masterbatch has tensile strength at 23.76 MPa while typical compounding has 16.77 MPa. As conclusion, higher ball milling time results in lower CB structure and subsequently improve the reinforcing efficiency of the filled vulcanizate.