Synthesis of Isostearic Acid/Dimer Fatty Acid-Based Polyesteramide Polyol for the Development of Green Polyurethane Coatings

Abstract

Bio-based polyurethane (PU) coatings were prepared from novel branched isostearic acid (ISA) and long chains dimer fatty acid. Fatty amide was synthesized by the amidation of ISA with diethanolamine and the required hydroxyl functionality was developed via condensation polymerization with dimer fatty acid to produce polyesteramide polyol. The structure of the synthesized ISA based fatty amide (ISAFA) and polyesteramide polyol (ISAPEP) were identified using Fourier-transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1HNMR). The number average molecular weight of prepared polyesteramide polyol was assessed by gel permeation chromatography (GPC), while the rheological behavior was examined by the rheometer. Polyurethane metal coatings were developed from polyesteramide polyol, which crosslinks with hexamethylene diisocyanate (PU-H) and toluene diisocyanate (PU-T) and studied the influence of isocyanate structure on final PU coatings. A comparison in the crosslinks density of PU films was investigated by the gel content method. Differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA) were performed to evaluate the glass transition temperature (Tg) and thermal stability of the PU coatings. The surface roughness of prepared PU coatings was examined by Atomic force microscopy (AFM). The PU coated metal panels and films were examined for swelling resistance, hydrophobicity, mechanical, and coating properties. Results confirmed that bio-based long chain fatty acids provided hydrophobicity, flexibility and impact resistance to final PU coatings. It also noted that PU-T coating resulted in increasing thermal, mechanical, and coating properties compared to PU-H coating and this resulted from the structure of TDI, which contribute to higher crosslink density (i.e. presence of aromatic ring).