AN INVESTIGATION OF PERMANGANIC ETCHING OF LINEAR LOW-DENSITY POLYETHYLENE

Permanganic etching is a technique of removing material selectively to reveal lamellae in crystalline polymers. It is generally found that populations of lamellae with different thicknesses are removed to different depths. In linear polyethylene we have previously shown that this discrimination is not an inherent property but a consequence of differential deformation during cutting to expose the surface prior to etching. The work is now extended to linear low-density polyethylene to test whether the changed basis of molecular segregation (with more branched molecules crystallizing later) alters the etching behavior. It is shown that thinner lamellae are etched at a faster rate which is only slightly reduced after removing damage due to cutting. This intrinsic differentiation between crystal thicknesses accompanies faster etching rates than for the linear material. It is inferred that this is due to faster chain scission at fold surfaces which are more penetrable for the linear low-density than for the linear polymer; however, chain scission remains slow compared to stem removal. Fold stems are probably removed as entities rather than incrementally, but it is evident that a fold surface region needs to be etched away before a stem can be removed.