Aluminum Oxide as a Partial Replacement for Zinc Oxide in the Vulcanization of Natural Rubber

ABSTRACT This study investigates the feasibility of partially replacing zinc oxide (ZnO) with aluminum oxide (γ‐Al 2 O 3 ) as a coactivator in the vulcanization of natural rubber (NR). Six rubber vulcanizate samples were prepared with varying concentrations (in phr) of ZnO and γ‐Al 2 O 3 : 5/0, 4/1, 3/2, 2/3, 1/4, and 0/5. The vulcanizates were characterized through vulcanization testing, swelling tests, tensile testing, and scanning electron microscopy (SEM). Vulcanization kinetics analysis showed that NR vulcanization using ZnO and Al 2 O 3 combinations follows first‐order kinetics, while vulcanization using only γ‐Al 2 O 3 does not conform to this model. Although γ‐Al 2 O 3 did not accelerate the crosslink formation, it facilitated the vulcanization reaction by reducing scorch time and optimal cure time, while increasing both the cure rate index (CRI) and vulcanization rate ( R v ). Tensile testing demonstrated that the vulcanizate containing 2 phr ZnO and 3 phr γ‐Al 2 O 3 exhibited the highest stress at break (27.1 MPa), suggesting that up to 60% of ZnO can be successfully replaced with γ‐Al 2 O 3 as a coactivator. SEM analysis revealed that the NR vulcanizate with 2 phr ZnO and 3 phr γ‐Al 2 O 3 had a more uniform dispersion of vulcanizing agents compared to the sample containing only ZnO.