A strengthened nano-carbon network endowing the uniaxially oriented polyamide composite with super-high strength

The double-doped polyamide 12 (PA) composites (PACs) with modified multi-walled carbon tubes (m-MWCNTs) and functionalized graphene (FGr) and the corresponding uniaxially oriented PACs (O-PACs) were prepared. It shows that there are some interactions between the uniformly dispersed nano-fillers and polymer matrices such as hydrogen bond, acid-base ion pair, chemical bond formed by an amide-amide exchange reaction, and induced crystallization, which help the performance improvements of these composites. An incompact nano-carbon network formed by the cross-distribution of m-MWCNTs and FGr in the PACs has been transferred into a strengthened one via intertwining the contact sites of m-MWCNTs with FGr in O-PACs. After orientation, the original PA crystals are further oriented and some new oriented PA crystals are formed. Compared with the PACs, the crystallinities and crystal orientation degrees of O-PACs are enhanced, while the grain sizes are refined. The mechanical strengths and conductivities of O-PACs are improved significantly due to the strengthened nano-carbon network, the interactions between this network and PA matrices, and the oriented crystal structure. When the contents of FGr and m-MWCNTs are both 0.3 wt%, a perfect and strengthened nano-carbon network has been formed in O-PAC4, whose tensile strength reaches 509.21 MPa. • A kind of O-PACs with super-high strength have been prepared by double-doping approach and orientation technology. • A strengthened nano-carbon network is formed, leading to the significant enhancement of O-PAC's strength. • A “fishing net” structure from the strengthened nano-carbon network can prevent crazes or cracks growth in damage process.