Piezoresistive Natural Rubber Composites: A Comparison Between Low-­ Temperature Glutaraldehyde Curing Agents and Conventional Sulfur Curing Systems

This study examines the piezoresistive behavior of natural rubber (NR) composites cured with sulfur (S) and glutaraldehyde (GA) and reinforced with a hybrid conductive system of conductive carbon black (CCB) and carbon nanotubes (CNT). GA-cured NR composites demonstrated superior mechano-­ electrical performance, achieving a tensile modulus of 2.05 MPa at 100% strain, tensile strength of 9.6 MPa, electrical conductivity of 10.2 μS/cm, and a gauge factor of 226 at 300%–500% strain. The improvement in modulus and piezoresistive response is attributed to the homogeneous distribution of crosslink points in the GA-­ cured NR network. Notably, the secondary electrical signal peak observed in S-­ cured NR sensors was eliminated with GA curing. Furthermore, GA-­ cured composites exhibited reduced signal drift (dynamic cycling) and relaxation (quasi-­ static cycling) compared to S-­ cured composites. Long-­ term soft tendon actuator tests confirmed the enhanced stability of GA-­ cured systems. These findings indicate that GA-­ cured NR composites with hybrid CCB/CNT fillers combine high stretchability, stability, and sensitivity, making them promising candidates for high-­ performance piezoresistive sensors. Leveraging renewable NR, this approach supports sustainable development while enabling applications in wearable electronics, soft robotics, and health monitoring systems.