Extruded polypropylene foams with radially gradient porous structures and selective filtration property via supercritical CO2 foaming

Abstract

Original polypropylene (PP) foams with radially gradient porous structures and selective filtration were developed through the supercritical CO2 assisted extrusion foaming couple with the stretching auxiliary. Firstly, the relationship among the physical characteristics, processing technology and microstructure of the polymer foams were studied. Specially, the effect of the tensile strain hardening and its spatial confinement of the high melt strength PP (HMSPP) in the extensional flow field on the condensed matter physics and foaming behavior of the polymer foams were revealed. Remarkably, the orientation degree of the modified PP foams could be ~47.2 higher than the traditional ones in different zones. Secondly, the compression experiments and theoretical calculated analysis showed the mechanical properties of the as-prepared PP foams exhibited obvious directionality, which is beneficial to recycle and squeeze wastewater. Besides, the corresponding characterization methods and self-made filter device were used to demonstrate the selective filtration performance of the as-prepared PP foams. Interestingly, the water droplet could pass the 3D lengthy PP foam strips, while the ultrafine wasted materials were blocked due to the unique micro-structures. Gradient porous polymer foams without any modification are firstly demonstrated to be interesting materials with the potential applications in the selective filtration properties.