Rheological characterization on thermal degradation of ethylene-tetrafluoroethylene copolymer

• Degradation of ethylene-tetrafluoroethylene copolymer is revealed.
• Molecular weight distribution was characterized by rheological properties.
• Effect of oxygen on the degradation is clarified.

Oscillatory shear modulus in the molten state is evaluated carefully considering the rheological change during the measurement at high temperature for ethylene-tetrafluoroethylene copolymer (ETFE). The results provide the information on the molecular weight distribution as well as the degradation behaviors, which is affected by the environmental condition, i.e.  , the existence of oxygen. Even under a nitrogen atmosphere, ETFE is thermally unstable in the molten state; ETFE shows random chain scission reaction without crosslinking. The steady-state shear compliance Je0, which depends on the molecular weight distribution greatly, is not changed during the chain scission. It suggests that the chain scission occurs with keeping the molecular weight distribution. Considering the classical theory on the random scission reaction, the experimental result indicates that Mw/Mn of the initial ETFE sample, prior to the exposure to thermal history, is close to 2. In contrast, under air condition, ETFE shows crosslinking reaction even in the cone-and-plate rheometer. The degree of crosslinking is quantitatively estimated by the plateau modulus G′plateauG′plateau in the low frequency region. The result suggests that the crosslinking occurs as a first order reaction.

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