Segregated MWCNT Structure Formation in Conductive Rubber Nanocomposites by Circular Recycling of Rubber Waste

The reclamation and devulcanization processes of rubber waste change its cross-link density and sol-gel proportions, which are essential in the reprocessing of reclaimed rubber (RR), especially in the dispersion of nanofillers throughout the RR matrix. In this work, conductive elastomers based on RR/carbon nanotubes (CNTs) were prepared. Proper control of the quality of RR is needed to ensure the effective formation of conductive pathways within the matrix. Therefore, this work aimed to control a segregated CNT network by manipulating how the RR is prepared. Three alternative devulcanization conditions were tested: (a) physical reclaiming, (b) thermomechanical reclaiming, and (c) thermochemical reclaiming. These techniques resulted in three types of RRs. Nanocomposite based on the physically RR presented the highest tensile strength, reaching approximately 15 MPa with addition of 2 phr of CNT. This was due to a comparatively lesser destruction of the rubber network and the formation of a segregated structure of CNT filler in the nanocomposite. Therefore, the conductive performance was significantly enhanced from 4.5 x 10-10 S/cm for unfilled to 1.25 x 10-6 S/cm with CNT dose as low as 1 vol %. The segregated CNT network, whose formation was assisted by gel fraction and excluded volume in RR, also resulted in a very low electrical percolation threshold phi c, which was significantly reduced from 0.78 vol % for low cross-linked RR to 0.14 vol % for high cross-linked RR. This could reduce CNT filler use by 80% whereas 100% of pristine rubber would be replaced, and mechanical and electrical properties would improve. The approach described in this work will be helpful in manufacturing conductive rubber products efficiently yet sustainably with recycling of rubber waste.