In situ fibrillation of CO2-philic polymers: Sustainable route to polymer foams in a continuous process

In this study, in situ polymer–fibrillar blends of polypropylene (PP)/polytetrafluoroethylene (PTFE) are prepared. Dynamic oscillatory shear experiments confirm that the PTFE elongates into fibrils during blending and forms a physical network of entanglements in the melt which results in gel-like properties. Uniaxial extensional flow experiments show strain-induced hardening behaviour. CO2 solvency in the PP/PTFE fibrillar blend is enhanced due to the CO2-philic character of PTFE. Remarkably, adding only 0.3 wt% of PTFE is sufficient to markedly enhance the CO2 sorption capacity of the matrix. Continuous foam extrusion of the in situ fibrillar blend reveals a three orders of magnitude increase in bubble density, a ten-fold increase in volume expansion ratio, and a marked broadening of the foaming window with respect to neat PP. These improvements are attributed to the simultaneous enhancement in CO2 solvency and strain-hardening behaviour of the melt in the in situ fibrillar blend.