The Synthesis Of Two-component Waterborne Polyurethane And The Study Of Film Formation Machanism

Combining the good film properties of solvent-borne polyurethane with low VOC values of waterborne technology, two-component waterborne polyurethane systems have become the focus in the field of waterborne coatings in the past decades. The intentions of this issue are to prepare an ideal hydroxyl component, hydroxy terminated polyurethane dispersion, and discuss the influences of various factors to its performance, then mixed hydroxyl component with isocyanate to prepare film, looking for appropriate curing technic conditions, and discuss details of the film formation mechanism.Great impacts on the performance of hydroxy terminated polyurethane dispersion prepared by acetone method have been found exerted by factors during synthesis progress including the dosage of dimethylolpropionic acid (DMPA), the mol ratio of NCO to OH in pre-ploymer progress R_预, the mol ratio of NCO to OH in the whole dosage R_总, the trimethylolpropane(TMP) dosage and the degree of neutralization. The proper ratio of these factors is determined according to the film performance: 4.0%～5.0% of DMPA, 1.7～1.8 of R_预, 0.7～0.8 of R_总, 3.37%～5.07% for the dose of TMP and 100% of degree of neutralization.Full and homogeneous mixation and dispersal between the two components of waterborne polyurethane is the basic guarantee of best performance, which is mainly determined by the chosen polyol and isocyanate and the mixing approach. Appropriate conditions of curing progress have been decided according to final film performance: 30℃-50℃of temperature, 1.2-1.5 of molar proportion of the two components NCO and OH, 0.05%-0.1% of catalyst dose, and the category of catalyst is chosen according to practical need.It's discovered that the temperature and catalyst has great effect on the film formation progress. The increasing of curing temperature and the use of catalyst both have great influence on the progress of film formation. Higher curing temperature is favored by both physical film formation and chemical film formation progress, but also comes the negative effect of fast volatilization of water; while the use of catalyst hinders physical film formation,but do good to the progress of chemical film formation.The reaction speeds using three different curing agent respectively are found different after detailed anlysis of the chemical reaction progress with the combination of methods of ATR-FTIR and isothermal calorimeter. The data from isothermal calorimeter indicates that the reaction heat of isocyanate and polyol in the dispersion systhem is obvious lower than that in bulk system.The water resisting property of waterborne polyurethane film could be improved by increasing the degree of film crosslinking. Analysis of the film structure by IR indicates obvious existence of hydrogen bonding in the system. Proton provider N-H forms hydrogen bonding with -C=O of most urethano (with a consistence of 83.2% of the whole urethano) and part of uramido (with a consistence of 32.6% of the whole uramido), while all the ester from polyester diol are in free.