Enhancement of resistance of polyethylene to seawater-promoted degradation by surface modification
- Polyethylene, when repeatedly stressed and exposed to seawater (e.g. ships' ropes), undergoes mechanical and chemical degradation.
- Surface treatments of the polyethlyene can improve resistance to this degradation.
- The author studied two methods of surface treatment:
- Plasma (glow discharge, air) followed by diacid (adipic acid) or triisocyanate (DM100, = ?) co-polymerization
- Electron irradiation with 500 kEV electrons.
- Also mention CASING (crosslinking by activated species of inert gasses) as a popular method of surface treatment.
- Diffuse-in crosslinkers is a third, popular these days ...
- Others diffuse in at temperature e.g. a fatty acid - derived molecule, which is then bonded to e.g. heparin to reduce the thrombogenicity of a plastic.
- Measured surface modifications via ATR IR (attenuated total reflectance, IR) and ESCA (aka XPS)
- Expected results, carbonyl following the air glow discharge ...
- Results:
- Triisocyanate, ~ 6x improvement
- diacid, ~ 50 x improvement.
- electron irradiation, no apparent degradation!
- Author's opinion that this is due to carbon-carbon crosslink leading to mechanical toughening (hmm, evidence?)
- Quote: since the PE formulation studied here was low-weight, it was expected to lose crystallinity upon cyclic flexing; high density PE's have in fact been observed to become more crystalline with working.
- Very interesting, kinda like copper. This could definitely be put to good use.
- Low density polyethylene has greater chain branching and entanglement than high-density resins; when stressed the crystallites are diminished in total bulk, degrading tensile properties ... for high-density resins, mechanical working loosens up the structure enough to allow new crystallization to exceed stress-induced shrinkage of crystallites; hence, the crystallinity increases.
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