Effect of process variables on molecular weight and mechanical properties of water-based polyurethane dispersion

Water-based polyurethane dispersions (PUD) were prepared by polyaddition reaction using poly (hexamethylene adipate) glycol (polyol 66), isophorone diisocyanate (IPDI), dimethylol propionic acid (DMPA), and 1,6-hexane diamine (HDA) as chain extender. Various formulations were designed to investigate the effects of process variables such as molar ratio of NCO to OH (NCO/OH), DMPA content, and neutralization degree on molecular weight and mechanical properties. Universal testing machine (UTM) was used for the mechanical properties of emulsion cast film of the PUD. The molecular weights were measured by gel permeation chromatography (GPC). Evolution of the weight average molecular weight (M̄w) and mechanical properties were significantly affected by the neutralization degree during the chain extension. It was found that the M̄w increased when the NCO/OH molar ratio increased, subsequently mechanical properties such as tensile strength and 100% modulus improved dramatically. However, the elongation decreased as the NCO/OH increased.