Study on thermal-storage stability of polyurethane dispersions prepared via Prepolymer method

In order to explore the thermal-storage stability of waterborne polyurethane (WPU) fabricated by prepolymer method, a series of WPUs were prepared with polyether polyol (PPG), aliphatic isocyanate (IPDI), dimethylol propionic acid (DMPA), 1, 4-butanediol (BDO), triethyl amine (TEA) and hydrazine hydrate (HyHy). Effects of -NCO content of prepolymer, ratio of [NCO] to [H] after post-extension, HyHy dilution ratio and adding time, and solid content of WPU, were detailedly investigated. The viscosity and appearance of WPUs were used to characterize the stability during the thermal-storage process. Decreasing the -NCO content of prepolymer, ratio of [NCO] to [H] after post-extension and solid content (SC) of WPUs, viscosity rise for WPUs in thermal-storage process decreased significantly; increasing the dilution ratio of H₂O to HyHy and prolonging the addition time of HyHy aqueous solution in the post-extension process, WPUs with stable viscosity under thermal-storage environment could be obtained. The mechanism for thermal-storage stability affected with “cage effect” was proved. The systematic study on the influencing factors and mechanism of thermal-storage stability in this study is of great significance to the understanding of prepolymer method and to promote the industrialization of WPUs via prepolymer method.