Development of transparent protective self-healing coatings

Student thesis: Doctoral Thesis

Abstract

Functional self-repair systems found in living organisms have inspired scientists to design artificial materials able to recover from wear and damage. One of the current goals in the field of self-healing materials includes creation of such materials for optical purposes.The work presented in this thesis was focused on the development of novel, thermally-triggered, self-healing polyurethane coatings to be used as protective layers. Such materials must fulfil certain requirements: (i) the coating must be clear, transparent and exhibit haze below 2%, (ii) the coating must have a hardness of B or above, determined by the pencil hardness test, (iii) the glass transition temperature of the coating must be above room temperature and below 80 °C in order to enable a convenient, thermally-triggered healing, and (iv) the healing must be rapid, taking less than 10 minutes, and efficient, resulting in damage recovery of above 90%.To achieve the requirements a series of waterborne aliphatic polyurethanes based on polyols of various lengths and structures were synthesised. Followed the choice of the most suitable polyol, different isocyanates were examined, including hexamethylene diisocyanate and isophorone diisocyanate.Subsequently, several chain extenders, including diol, alkoxyamine and diamine of various lengths and structures, were tested. Finally, various crosslinkers and internal emulsifiers were studied. The self-healing process was examined in detail and relationship between the self-healing process and the morphology of the materials was established. Optimally designed coatings obtained up to 100% recovery within 10 minutes at 60 ˚C. The self-healing properties were found to be linked to phase-mixing of polyurethane matrix, creating an amorphous, homogenous and non-ordered polymer matrix with low haze values and high glass transition temperatures. At elevated temperatures a rearrangement of polymer was obtained, leading to the healing of scratches and disappearance of damage.
Date of Award1 Apr 2018
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SupervisorJohn Liggat (Supervisor) & (Supervisor)

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