Structure–Property Study of Waterborne Polyurethane Coatings with Different Hydrophilic Contents and Polyols

Abstract

In this study, water dispersed paints were produced using polyester polyol, isophorone diisocyanate (IPDI) and hydrophilic monomers. Two sets of experiments were performed. In the first group, the effects of various proportions of the hydrophilic monomers dimethylol propionic acid (DMPA) and tartaric acid (TA) on the state of dispersion, physical, mechanical, and surface properties were investigated. The total hydrophilic content was fixed at 3.5 wt% of solids. In the second group, waterborne polyurethanes were prepared by using mixed polyols as the physical properties of waterborne polyurethanes were highly affected by the composition and the molecular chain length of the soft segment. Hence, in the second group, up to 20 wt% of polyester polyol (diol) was replaced by poly(propylene‐ethylene) copolymer polyol (triol) leading to branched polyurethanes. Only DMPA was used in this case as the ionic building block. The effects of polyester/polyether ratio on the state of dispersion, physical, mechanical, and surface properties were examined. For the first group of experiments, the increase in the amount of TA in the polymer yields coarser particle sizes and broadened particle size distributions. The increase of TA content yielded an increase in the hardness and in the contact angles with water. Upon replacing part of polyester polyol with polyether triol, higher values for average particle sizes and broadened particle size distributions were obtained. It also yielded an increase in hardness values and an increase in contact angles with water. It was found that replacing more than 15 wt% of polyester in the total polyol with polyether caused drastic changes in the state of dispersion and other properties due to a change in the internal structure. All samples showed superior impact resistance and flexibility.

Keywords:

• Paint
• Water dispersed
• Polyurethane
• Dimethylol propionic acid
• Tartaric acid
• Particle size
• Branching