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978-3-8439-1144-3, Reihe Ingenieurwissenschaften
Physical properties of melt processable polytetrafluoroethylene and its blends
133 Seiten, Dissertation Technische Universität Dresden (2013), Softcover, A5
This work is concerned with study of novel melt processable polytetrafluoroethylene (MP PTFE) materials as well as development and study of MP PTFE blends with polyetheretherketone (PEEK). MP PTFE is a newly developed copolymer of tetrafluoroethylene (TFE) and perfluoropropyl vinyl ether (PPVE) comprising a small amount of comonomer although sufficient to obtain tough material with molecular weight allowing its processing by conventional processing method used for thermoplastic materials e.g. injection moulding, extrusion etc.
MP PTFE has been investigated with respect to its molecular structure, microstructure and their influence on the end-use properties. The molecular structure has been characterised in terms of molecular weight, molecular weight distribution and comonomer content. Considering materials with comparable molecular weight, increasing comonomer content leads to increasing number of intercrystalline connections namely tie molecules and entanglements, and these are of great importance for the end-use properties of semicrystalline polymers. The end-use properties of MP PTFE including tensile properties, fatigue life, viscoelastic behaviour as well as environmental stress cracking resistance (ESCR) have been studied and compared with those of polytetrafluoroethylene (PTFE), modified PTFE and perfluoroalkoxy copolymer (PFA). Within the group of examined fluoropolymers, MP PTFEs exhibit improved stiffness at elevated temperature and stress relaxation resistance. However, the ultimate tensile properties, ESCR and fatigue life of MP PTFE materials are less favoured and this fact is attributed to the lower number of the intercrystalline connections.
Melt-processability of MP PTFE allows its melt blending with a second polymeric component in order to achieve blend with improved specific properties. MP PTFE/PEEK blends studied in this work are attractive materials due to the combination of low coefficient of friction and universal chemical resistance of MP PTFE with good wear resistance and mechanical strength of PEEK while maintaining high thermal stability of both. MP PTFE/PEEK blends have been investigated with regard to their processing, miscibility, phase morphology and tensile properties. In order to improve their end-use properties an attempt of reactive compounding with the electron beam irradiated MP PTFE has been made. For the reactive compatibilized blends an improvement in the phase morphology and mechanical properties was found.