A novel method for the synthesis of solvent-free and high-solid-content waterborne polyurethanes by introducing a small amount of polyethylene glycol

In the study, the synthesis process involved the reaction of dimethylolbutyric acid and polytetramethylene ether glycol 1000 (PTMG1000) with hexamethylene diisocyanate (H12MDI), taking advantage of their mutual dissolution at high temperatures. The chain-extension reaction with 1,4-butanediol (BDO) was successfully conducted without the use of organic solvents. The emulsification reaction was carried out using the polyurethane prepolymer at 60% solids content, along with aqueous dispersions of polyethylene glycol (PEG) with varying molecular weights and amounts as interfacially active agents. Fourier transform infrared spectroscopy analysis suggested potential hydrogen bonding interactions between the PEG molecular chain and the polyurethane chain. Rheometer analysis demonstrated a significant reduction in viscosity with the addition of 1-5 wt.% PEG, accompanied by an increase in average particle size. This phenomenon was attributed to the formation of a hydrophilic lubrication layer of PEG around the water-based polyurethane (WPU) microcells. Among them, WPU films containing 4 wt.% PEG4000 not only exhibited soft properties with a mechanical elongation rate exceeding 2000% but also showed excellent storage stability. The addition of long-chain PEG facilitated the formation of a lubrication layer between the microcells, contributing to spatial stabilization and reducing particle aggregation at high solids content. It is noteworthy that this solvent-free process, without any organic solvents, together with the adjusted PEG content, successfully synthesized waterborne polyurethanes with low viscosity and high solids content. This provides a new sustainable and environmentally friendly method for the future production of waterborne polyurethanes. The force between a small amount of PEG chains and WPU micelles. image