Mechanism of degradation induced embrittlement in polyethylene

Abstract The thermal oxidation of polyethylene films in air at 80 °C and 90 °C has been studied by tensile testing, IR spectrophotometry and molar mass determination from rheometric measurements. In the conditions under study, the polymer predominantly undergoes chain scission and embrittles suddenly when the weight average molar mass reaches a critical value (90 kg mol −1 ), far before significant damage of the entanglement network ( M e  = 1.9 kg mol −1 ) in the amorphous phase. The following embrittlement mechanism is proposed: chain scission in the amorphous phase induces chemicrystallization. The thickness of the interlamellar amorphous layer ( l a ) decreases until a critical value of the order of 6–7 nm, below which plasticity cannot be activated and the polymer behaves in a brittle manner, as previously shown for virgin polyethylene. Using ( l a , M W ) maps, it is possible to explain the differences observed in the embrittlement behaviour of semi-crystalline polymers predominantly undergoing chain scission.

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