Effect of self-assembly of nucleator adsorbed at the interface by H-bonding on the crystallization and mechanical behaviors of iPP hybrids

Abstract

DCHT (N, N-dicyclohexylterephthalamide) as a common type of β-nucleator could self-assemble into various morphologies in iPP (isotactic polypropylene) matrix and further affect its crystallization behaviors. In this study, a third component of PA11 (polyamide 11) was intentionally introduced into iPP hybrids to tune the adsorption and assembly of DCHT by forming hydrogen bonds, whose effects on the crystallization and mechanical properties of iPP hybrids at different processing temperature (T_f) were investigated in detail. It is observed that DCHT could form flower-like crystals at higher T_f, while it tends to aggregate and form rod-like crystal with high concentration in the hybrids. DSC results show that DCHT could lost its nucleation ability at low concentration. With the increase of DCHT concentration, the residual DCHT in the matrix could induce the crystallization of iPP as β-nucleation site. A core-shell structure was observed for the first time in which the shell as the interface layer is formed by DCHT assembly and iPP crystal. It is a key to greatly improve the toughness of the hybrids and the strength of the interface layer between PA11 and iPP by self-assembling and crystallizing at the interface. By changing the PA11 hard core to the TPU (Thermoplastic polyurethanes) soft core at a higher T_f of 280 °C, the impact strength of iPP/20TPU/0.5DCHT hybrid reaches 13 kJ/m², which is 4 times of pure iPP, while the tensile strength only slightly decreases. This study provided a new strategy to optimize the mechanical properties of iPP by forming the core-shell structure and meanwhile tunning the assembly of nucleator at the interface.