Colloquia

Summary

In the wake of the Paris Agreement and the global push for sustainability, there has been an increase in focus on developing sustainable materials and decreasing carbon emissions worldwide. The rubber industry is one of the sectors with a major impact in reducing greenhouse gas emissions. Enhancing the efficiency of tires and using novel, sustainable materials are key factors in achieving this goal.

One of the main constituents of a rubber compound is the filler, which improves compound properties such as tensile strength, abrasion resistance, tear resistance and modulus. Carbon black is a widely used filler due to its superior in-rubber performance. However, it is derived from non-renewable sources and its production is associated with substantial environmental impacts, including greenhouse gas emissions and resource depletion. Thus, interest has grown in deriving particulate fillers from alternative resources.

In this research, multiple sustainable fillers, including calcium carbonate and lignin materials, have been selected and tested as a (partial) replacement for carbon black in a natural rubber compound. Various aspects of the rubber compounds were characterized, such as their processability, curing behavior, and mechanical properties. The high-potential fillers were then selected to be chemically modified by in-situ coupling agents in order to increase their reinforcing behavior in the rubber compounds.

Based on the results, the partial replacement of up to 33 wt.% of carbon black by two calcium carbonate fillers initially led to inferior in-rubber properties due to the fillers’ lower surface area and lower interaction with the polymer matrix. Upon the chemical modification of these fillers, the filler-filler and polymer-filler interaction of the compounds increased significantly, leading to enhanced processability and mechanical properties, comparable to that of the carbon black-filled reference compound. The complete replacement of carbon black with a lignin filler has also been explored, presenting interesting results. While the full substitution initially showed inferior processing behavior and mechanical properties due to agglomeration and interference with the curing system, the incorporation of various coupling agents has yielded improvements in curing behavior, hardness, and rebound resilience. Despite the observed reduction in elongation at break and tensile strength, suggesting challenges in macro-dispersion, the potential of this filler as a sustainable alternative to carbon black has been demonstrated.