A study on some physical properties of conductive Pb/NR composites

Natural rubber (NR)-loaded with the critical concentration (30phr) of N220 black and different concentrations of Lead (Pb) powder were prepared according to the standard method (ASTMD 3185 – (99)). All samples are subjected to the rheometric, mechanical, electrical, and physico-chemical measurements. It is noticed that upon increasing Pb content, minimum torque (ML) and maximum torque (MH) increase, while scorch time (Tsc) and cure time (T90) decrease. The mechanical parameters such as tensile strength (TS) and elongation at break (Eb) decrease, modulus at 300% (M 300 ) increases at 20 phr then decreases, whereas hardness markedly increases upon increasing Pb content. The morphology of Pb-loaded NR composites (Pb/NR) was examined to correlate with observations on mechanical properties by scanning electron microscopy (SEM). A relatively co-continuous morphology was observed for Pb/NR composites. The SEM analysis indicates that there has been a good compatibility within the rubber matrix. The maximum degree of swelling in benzene ( Q m (%))exhibits marked decrease while the crosslink density increases by increasing Pb content. Kinetic parameters such as elastic Gibbs free energy and conformational entropy were determined from Flory–Huggins kinetic model. Furthermore, the marked increase of dc conductivity ( σ dc ) is due to the increase of Pb content which is micro metallic and as a result of that, it is responsible for increasing the conductivity values. Finally, the measurements of σ ac as a function of frequency confirm the hopping conduction mechanism.