Effect of covalent functionalization of multi-walled carbon nanotubes with HDI trimer on mechanical properties of polyaspartate polyurea

Abstract

To improve the mechanical properties of polyaspartate polyurea (PAEP), functionalized multi-walled carbon nanotubes reinforced polyurea composites (HDIT-MWCNTs/PAEP) were prepared by covalently functionalizing multi-walled carbon nanotubes (MWCNTs) with hexamethylene diisocyanate (HDI) trimer. The dispersibility, wettability and interfacial properties of HDI trimer functionalized MWCNTs (HDIT-MWCNTs) in PAEP were analyzed. The tensile properties of HDIT-MWCNTs/PAEP composites were tested and the reinforcement mechanism revealed. The results showed that compared with the pure multi-walled carbon nanotubes (P-MWCNTs), HDIT-MWCNTs were uniformly dispersed in the matrix and the wettability and interfacial properties were greatly improved. The contact angle of PAEP with HDIT-MWCNTs was 32.92°, a reduction of 46.3% compared with the P-MWCNTs. The interfacial energy and adhesion work between PAEP and HDIT-MWCNTs (25.14 mJ m−2, 95.47 mJ m−2) were 46.7% and 24.2% higher than those of P-MWCNTs. When the content of HDIT-MWCNTs was 0.5 phr, the tensile strength and Young’s modulus of the composites reached a maximum of 17.78 MPa and 170.31 MPa; an increase of 28.4% and 90.8% respectively, compared with pure PAEP. According to the cross-section of HDIT-MWCNTs/PAEP, its strengthening mechanism was mainly manifested by the deflection and bifurcation of cracks and the plastic deformation of PAEP matrix due to HDIT-MWCNTs pulling out from the matrix.