Researchers from UK investigated self-healing efficiency of coatings, synthesized from polycarbonate polyol with molecular mass of 500 Da and hexamethylene diisocyanate or isophorone diisocyanate, without a chain extender, with aliphatic diol with two to five carbon atoms or with diethylene glycol. Self-healing efficiency of coatings were examined by comparison of haze before damage and at intervals after damage which was made by a steel-wool scratch instrument and then coatings were left to heal at room temperature and at 60 °C. The tests were repeated after 12 weeks in order to investigate ageing of the polymers. UV weathering test was also performed.
It was revealed that up to 100% recovery within 10 min at 60 °C and partial recovery at room temperature were found for optimally designed coatings. The self-healing property was found to be linked to macro-organisation of polymer chains caused by interactions between hard segments and soft segments of the polyurethane moiety, leading to phase-mixing, promoted by bulky, non-symmetrical isophorone diisocyanate, or phase-separation, promoted by linear, symmetrical hexamethylene diisocyanate. Moreover, it was also found that coatings are resistant to UV weathering.
This article is published in Progress in Organic Coatings, Volume 122, September 2018, Pages 1-9.