Development of discrete nanopores I: Tension of polypropylene/polyethylene copolymer blends

Porous polymeric materials can be prepared by using micromechanical deformations. The development of porous structures in the tension of polyolefin blends are studied with the goal of developing a novel technique to make porous films. It is found in polypropylene/polyethylene copolymer blends of near 50/50 weight ratio that a metallocene polymer pair can produce stable nanopores throughout a wide range of strain, ∼50-700%. Its strain-to-break was relatively high, although its continuous phase is a brittle polypropylene. The typical size of nanopores is 10-300 nm; they start to develop at approximately 50% strain. The disruption of craze-like structures into discrete nanopores seems to be the key mechanism in stabilizing pore development. Varying stretching direction and speed controls the pore morphology.