Effects of the NCO/OH molar ratio and the silica contained on the properties of waterborne polyurethane resins

Abstract

Waterborne polyurethane resins (WPUs) were synthesized with polytetramethylene ether glycol (PTMG), dimethylolpropionic acid (DMPA), isophorone diisocyanate (IPDI), triethylamine (TEA) and ethylenediamine (EDA) as the raw materials of polyol, internal emulsifier, isocyanate, neutralizer and chain extender, respectively. The NCO/OH molar ratios used for the pre-polymerization were set as 1.6/1, 1.8/1 and 2.0/1. Furthermore, tetraethoxysilane (TEOS) was added to the WPUs to prepare the WPU/silica organic-inorganic hybrids by the sol-gel process. The characteristics of WPUs prepared with different NCO/OH molar ratios, and the properties of WPU and WPU/silica films were investigated. The results show that WPUs prepared with higher NCO/OH molar ratios have suspensions with lower viscosity, smaller average particle size and smaller average molecular weight, and lead the films to have more urea and amide structure, better solvent resistance, higher tensile strength, modulus and break energy, lower molecular chain activity, and smaller damping peak height, but weaker thermal resistance. The network structure of silica can limit the activity of the soft-segment, increase the stiffness of the hard-segment and enhance the thermal resistance of WPUs films.