Tough and strong polyamide 6,6 with oriented morphologies via pressure induced flow processing

Abstract

Polyamide 6,6 (PA 6,6) is widely used as a key synthetic material. However, its applications are constrained by rather low toughness. The existing methods of toughening show limited improvements and sometimes may take the sacrifice of tensile strength. In this study, we proposed a novel way, named pressure induced flow (PIF) processing, to simultaneously boost the toughness and strength of PA 6,6. The toughness measured as impact strength increased by ∼340%, while the tensile strength increased by 164% at the same time. Scanning electron microscope observations revealed stratified morphologies in the PIF processed PA 6,6 with abundant oriented crazes and cavities, which are believed to be dominantly responsible for toughening and enhancement. Results in wide angle X-ray diffraction patterns suggested that Brill transition took place in PIF processing at a temperature higher than 160°C or under a pressure above 600 MPa. This led to an increase in resistance and reduction of ductility for the materials, resulting in a minor decline of toughness when processing temperature or pressure reached somewhat higher values (such as 160°C and 600 MPa). The PIF processing brought an orientation of (100) plane along flow direction, which might account for increase and orientation of crazes and cavities in the fractured surface of materials. In parallel to its advantages of energy saving, easy handling and easy controlling, PIF processing is expected to find broad industrial applications due to its unique effect on toughening and strengthening of semicrystalline polymer materials such as PA 6,6.