Uniaxial Elongational Viscosity of FEP/ a Small Amount of PTFE Blends

Abstract

Melt rheology of blends consisting of tetrafluoroethylene/hexafluoropropylene (Teflon® FEP) copolymer and a small amount of polytetrafluoroethylene (Teflon® PTFE) has been studied under shear and uniaxial elongational deformations. The blends were prepared in a twin-screw kneader at 320°C. Compatibility of the components was investigated by DSC measurements, resulting in two separated peaks for the blends, which suggested FEP and PTFE were mixed in immiscible state. Structural observations were performed with optical microscope and SEM. It was clearly observed that PTFE uniaxialy elongated like fibril by kneading with FEP, and dispersed relatively uniformly in FEP. Storage modulus G' and complex viscosity η* toward lower frequency region became larger by increasing a loading of PTFE in dynamic shear measurements. The blends showed the strain-hardening property in uniaxial elongational measurements, whose tendency became stronger by increasing a loading of PTFE, though FEP hardly showed strain-hardening property. The results would be explained by the idea that dispersed PTFE fibril deformed during an elongational deformation and then generated a contractile stress, which would be resulted from that long length of dispersed PTFE and a strong adhesive interaction of interfaces between PTFE and FEP.