Dispersion and crystallization studies of hyper-branched poly(urea-urethane)s-grafted carbon nanotubes filled polyamide-6 nanocomposites

Multiwalled carbon nanotubes (MWNTs) are functionalized by hyper-branched poly(urea-urethane)s (HPUs) through a polycondensation technique (MWNTs-HPUs). MWNTs-HPUs filled polyamide-6 (PA6) nanocomposites are prepared by melt compounding. MWNTs-HPUs is observed to disperse uniformly in the PA6 matrix, because the grafting of HPUs improves the compatibility between MWNTs-HPUs and PA6. Dynamic mechanical properties of PA6 are effectively modified after the addition of MWNTs-HPUs. The improved dispersion of MWNT-HPUs in PA6 results in the more efficient load-transfer from polymer to MWNTs. In addition, because of the hydrogen-bond between hydroxyl groups on the surface of MWNTs-HPUs and carbonyl groups on the PA6 chains, the interfacial adhesion of PA6 and MWNT is further improved. Compared with PA6/MWNTs nanocomposite, PA6/MWNTs-HPUs nanocomposite has lower crystallization temperature, faster crystallization rate and higher crystalline degree. This is because the grafted HPUs change the surface of MWNTs, which weakens the effect of MWNTs on the crystallization of PA6.