Creep deformation cracking of polyethylene in methanol

Compression-moulded high-density polyethylene with a large spherulite size was deformed in methanol, an environment cracking agent. The mechanical test involved constant load creep in tension. At smaller loads corresponding to longer lifetimes, the final failure consisted of a macroscopic crack oriented perpendicular to the tensile axis. Deformed specimens were etched in permanganic acid and the spherulitic and lamellar structures near the macroscopic crack were examined using optical, scanning electron and transmission electron microscopy. The large-scale fracture was the result of crack nucleation in the interlamellar regions and subsequent sub-critical crack growth with micro-cracks joining up to form larger cracks.