Preparation of multi-walled carbon nanotubes@graphene/thermoplastic vulcanizate composites and study on its thermoelectric properties

This work mainly used the synergistic effect of one- and two-dimensional fillers (Multi-walled carbon nanotubes (MWCNTs)@graphene (GE)) to improve the thermoelectric and mechanical properties of thermoplastic vulcanizate (TPV). MWCNTs@GE/polypropylene-maleic anhydride (PP-MA) masterbatch were first prepared by melt-graft blending. The structure, crystallinity and microstructure of MWCNTs@GE/PP-MA masterbatch were characterized. Then MWCNTs@GE/TPV composites with unique network structure were prepared by dynamic vulcanization method. The effects of the amount of MWCNTs@GE on the phase structure, electrical conductivity, thermal conductivity and mechanical properties of MWCNTs@GE/TPV composites were studied. The results show that the combination of MWCNTs and GE has a synergistic effect and can be used as nucleating agent to improve crystallization peak temperature (T_c) and crystallinity of PP (X_c) and reduce crystal size of the PP crystal plane (L_Crystallite) in the crystallization process, compared with the masterbatch prepared with single filler. In the MWCNTs@GE/PP-MA masterbatch, MWCNTs and GE are uniformly dispersed in PP-MA and have strong bonding force with the matrix. The MWCNTs@GE/TPV composites show an obvious "island" structure, and the cross-linked butyl rubber (IIR) rubber is dispersed in the PP-MA phase as micron size particles. MWCNTs and GE are uniformly dispersed in the continuous phase PP-MA, and the distance between MWCNTs and GE is less than 1 µm, forming the MWCNTs@GE network structure. When the content of MWCNTs@GE in MWCNTs@GE/TPV composites reaches 3wt%, the alternating current (AC) electrical conductivity, thermal conductivity, elongation at break and tensile strength reach the best value.