Improving the swelling, mechanical, and electrical properties in natural rubber latex/carbon nanotubes nanocomposites: Effect of the sonication method

Conductive polymeric composites are exciting for future electronic applications given the possibility to ally electrical conductivity and flexibility. However, the high viscosity of plasticized elastomers difficult the dispersion of conductive fillers in an elastomeric matrix is difficult. This research aimed to compare the use of bath or probe sonication to disperse multi‐walled carbon nanotubes (MWCNT) in the lower‐viscosity natural rubber latex. The MWCNT concentration varied from 0.5 to 2.5 wt%, and the coagulated compounds were vulcanized after compounding in a two‐roll mill. Nanocomposite's swelling behavior was determined by Flory–Rehner crosslink density and Kraus theory, indicating better dispersion in probe sonication, which also was conducted in lesser time and applied lower energy than bath sonication. This result is evidenced through tensile strength and hardness tests, as the better MWCNT dispersion improved the reinforcement due to greater filler–matrix interaction. The electrical response was obtained by impedance spectroscopy, with higher conductivities also found in tip‐sonicated samples. In addition, cyclic strain fatigue test was realized from 20% to 100% strain during 20,000 cycles with simultaneous impedance measurement, reinforcing the better distribution of MWCNT in the probe‐sonicated nanocomposites with higher tensile stress (Payne's effect) and conductivity retention than bath sonicated. The comparison made between bath and probe sonication applied directly in the natural rubber latex to disperse carbon nanotubes proposes significant differences in the nanocomposite's morphological structure. The better efficiency of probe sonication resulted in superior swelling, mechanical and electrical properties, with lower energy and time consumption. In addition, the percolation can be achieved with lower filler concentration by choosing the right sonication procedure.