Influence of initiators on the sintering discolouration of PTFE

Abstract

PTFE homopolymer synthesised using ammonium persulfate initiator discolours at sintering temperatures of approximately 380 °C. No report on this phenomenon is available in the open literature. To shed light on the problem, PTFE samples were synthesised using various initiators and different pH buffers. The initiators used included ammonium persulfate, sodium persulfate, potassium permanganate, di-tertiary butyl peroxide and hydrogen peroxide. Borax and potassium carbonate were used as the buffering agents. The samples were pressed into discs and sintered at 380 °C. The samples were analysed using FTIR and Raman spectroscopy to determine the influence of decomposition of the end-groups during sintering. Each initiator resulted in unique end-groups, with a suggestion of multiple termination reactions in several of the samples. The discolouration of the samples occurs because of amorphous carbon deposition into the polymer matrix after elimination from the end-groups during sintering. The level of discolouration is dependent on the type and concentration of initiator used.