Preparation and characterisation of polyurethane coatings based on polyester polyol
Purpose ‐ The purpose of this paper is to describe how to synthesise polyurethane resins by using different polyester polyols and HDI isocyanurate. The polyester polyols were prepared by reacting single diol with different diacids. The effects of these polyester polyols on the performance properties of the coating films are studied. Design/methodology/approach ‐ A series of hydroxyl-terminated polyester polyols were synthesised by using 1,4-cyclohexanedimethanol (1,4-CHDM) with different diacids such as 1,3-cyclohexanedicarboxylic acid (1,3-CHDA), 1,4-CHDA, adipic acid (AA), azelaic acid (AZA), and isophthalic acid (IPA). The general properties including acid number, hydroxyl number average molecular weight, polydispersity index, and viscosity of these polyester polyols were evaluated. Different coating formulations were developed by using polyester polyols and HDI isocyanurate. These coatings were applied on sand blasted mild steel panels and glass panels and were cured in hot air oven. Various mechanical, thermal and chemical resistance properties of the coating films were evaluated. Findings ‐ The paper shows that, the polyurethane coatings have good resistance to water and other chemicals and can be used safely in exterior applications. In polyester polyols for polyurethane coating, CHDA showed a good balance in mechanical properties, which may be attributed to its unique cycloaliphatic structure and 1,4-substitution. The polyester polyol based on aromatic diacids provided polyurethane coatings with maximum hardness and high T g. Research limitations/implications ‐ The polyurethane resins were prepared from polyester polyol (made up of cyclohexanedimethanol (CHDM) and CHDA, IPA, AA, and AZA). Besides, this, it can be synthesised from some other polyester polyols (having different acids and alcohols) or polyether polyols. In addition to this, some other isocyanates such as TDI, MDI, HMDI, etc. can also be used. Practical implications ‐ The paper has provided a better solution for developing high solid polyurethane coatings for exterior applications due to presence of cycloaliphatic compounds. Originality/value ‐ In this paper, cyclohexyl dibasic acids have been used as the replacement for the aromatic dibasic acids. In aromatic dibasic acids, the phenyl ring readily absorbs UV-light limiting the photo-oxidative stability of the polyesters. So, these studies will help to develop high-solid polyurethane coatings which could find numerous industrial applications in surface coatings.
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