Evaluation of Cellulose Esters in Tire Tread Formulations

Cellulose Esters (CE) are high glass transition temperature thermoplastic biopolymers that are made using up to 60% bio-renewable raw materials. Application of CEs as a potential functional filler in tire tread formulations was evaluated by partially replacing silica with CE in a standard silica-filled tire tread formulation. It was found that CEs of suitable molecular weight, glass transition temperature and molecular structure/composition melt disperse as small particles to impart several improvements to the properties of the tread formulation. CEs within a suitable glass transition range that melt and flow at the tire processing temperature act as a processing aid, and thereby reduce the energy required for compounding and dispersing the silica. The same CEs solidify upon cooling and perform as functional fillers at tire operating temperatures. In addition, CEs can also interfere with the silica-silane chemistry; therefore, separating the silica-silane and CE additions was found key to obtain the best impact of the CEs in silica-filled tread formulations. Replacement of 8 phr silica by 8 phr CE resulted in improved strain to failure, stress at break, and low strain modulus, but deteriorated the high strain (300%) modulus. Partial replacement of silica by CE also significantly improved the hot adhesion strength. In addition, CEs increased the tan delta at 0 °C, indicating positive impact on wet traction. However, CEs also increased tan delta at 60 °C indicating negative impact on rolling resistance. The initial evaluation indicates that CEs can act as sustainable functional filler in the tread formulation with potential towards several performance benefits. Further development towards finer size dispersion and formulation optimization is required to attain its full potential.