Structure-property relationships of poly(tetrafluoroethylene)poly(tetrafluoroethylene-co-vinylidene fluoride-co-hexafluoropropylene) blends

The morphology and mechanical properties of emulsion blended samples of pol y(tetrafluoroethylene) (PTFE) and poly(tetrafluoroethylene-co-vinylidine fl uoride-co- hexafluoropropylene) (FKM) were investigated. Film samples with varying levels of PTFE content and varying degrees of FKM covalent cross-li nking were produced. It was observed at room temperature that below 50 wt% PTFE content, cross-linking the FKM can have a much larger influence on the tensile modulus than changing the PTFE content. Above 50 wt% PTFE, however , the modulus showed a near exponential increase with respect to increasing PTFE content. Without cross-linking, the toughness of the cast blends was shown to systematically decrease as the PTFE content was increased. However , when the FKM was cross-linked in film-form with 20-60 wt% PTFE, more stre ss was apparently transferred to the PTFE particulate leading to a higher e longation-to-break and a higher toughness. DMA analyses revealed a systemat ic increase of the storage moduli with increasing PTFE content. A tan delta peak at ca. -10 degreesC was observed which corresponds to the glass trans ition of the FKM and the magnitude of this peak was observed to decrease sy stematically with decreasing FKM content or with increasing levels of FKM c ross-linking. For the levels of cross-linking tested, however, this peak re duction due to cross-linking was not observed to be as significant as incre asing the PTFE content. For all PTFE content levels studied, the transmissi on electron microscopy (TEM) examination revealed a dispersed morphology fo r the PTFE particulate with the FKM forming a continuous matrix. The PTFE p articulate were observed to be ca. 0.2 mum in size and only slightly aggreg ated. The phase images from the tapping-mode atomic force microscopy showed that this is a useful technique for imaging morphology that lies parallel to the plane of the film surface, and for developing correlations with the TEM results of the bulk structure. (C) 2001 Elsevier Science Ltd. All right s reserved.