The deformation behaviour of multilayered tapes based on polystyrene-poly(2,6-dimethyl-l,4-phenylene ether) (PS-PPE) and polyethylene (PE) layers is investigated for PS-PPE layer thicknesses varying from 50 down to 0.05/~m. Two (rather than one) transitions can be observed in decreasing the PS-PPE layer thickness (d). The first transition at d~ 1/~m is enabled by a stress transfer mechanism that is similar to the mechanism operating in fragmentation tests in fibre reinforced composites and is operative through the non-zero but still low level of interlayer adhesion (Gic~5Jm -2) between PS-PPE and PE. This can be exploited practically by the introduction of a significant level of interlayer adhesion via the incorporation of a diblock copolymer between the PS-PPE and PE layers which, finally, results in a multilayered system with a strain-to-break of pure PE. The second transition at 0.5/~m > d > 0.05/~m (dependent on the network density) is associated with a change in deformation mechanism from crazing to shear deformation as revealed by optical light microscopy during tensile testing. The strain-to-break below the second transition corresponds to a value comparable with the stretching of the entanglement network to its full extension (2max). The critical layer thickness found coincides with the experimentally determined critical thickness as already reported for the non-adhering core-shell rubber-modified PS-PPE systems in part 2 of this series. The absolute value of the critical layer/ligament thickness and its dependence on the network density can be explained by the previously introduced energy-based model or, alternatively, by the detailed micromechanical analysis of the craze growth mechanism as proposed by Kramer.
Посилання на статтю:
Deformation and toughness of polymeric systems: 5. A critical examination of multilayered structures / M. C. M.vanderSanden*, L.G.C. Buijs, F.O. de Bieand H. E. H. Meijer // Polymer. – 1994. – Vol 35. – P. 2783-2792.