Effect of hydroxyl value of acrylic polyol and type of crosslinkers on the properties of Polyurethane coetings

Acrylic polyol base polyurethane coatings were prepared by reacting polyol with hexamethylene diisocyanate (HDI) base prepolymer. Five different types of acrylic polyol based on their hydroxyl value and two type of HDI prepolymer i.e. HDI biuret and HDI trimer were used as a hardners, for preparation of Polyurethane coating. The effect of hydroxyl value of acrylic polyol on PU coating properties like physical, mechanical and chemical properties were studied. The base and hardners were mixed prior to application of coating in a NCO: OH ratio of 1:1. It was found that the as hydroxyl value of polyol increases, it forms a hard film due to high cross-linked structure than low hydroxyl value polyol. Also HDI prepolymer with higher functionality gives better coating properties.