Study On The Synthesis And Properties Of Waterborne Polyurethane Coating Agent

Waterborne polyurethane is dispersible in water medium, which has hydrophilic groups in the molecular chain, with strong affinity for water. Not only it has the excellent properties of solvent-borne polyurethane with good low temperature resistance, great adhesion, as well as outstanding toughness combined with good flexibility, but also advantages of innocuity, incombustibility, low odor, energy conservation, security, convenient operation processing, and good film-forming breathability. Recently, the rising price of organic solvent and the strict limitation of using organic solvent and discharging waste from environmental protection department are leading to the replacement of solvent-borne polyurethane.At present, most materials used in local research of waterborne polyurethane are in the type of toluene diisocyanate, which has bad weather ability, easy yellowing, and can't meet special requests of market. With the development of the living standard of people and the increasingly urgent demand for environmental protection, health and high performance products, the green chemicals gradually become the future development's main current. Therefore, aliphatic waterborne polyurethane will become the main direction.A series of aliphatic waterborne polyurethane emulsions were prepared from hexamethylene diisocyanate (HDI), polybutylene glycol adipate (PBA), dimethylolpropionic acid (DMPA) and small molecular dihydric alcohol. And then cross linked with cross-linking agent, coating on cotton fabrics.The property of the WPU emulsion, the mechanical property of the WPU film, the thermodynamic analysis of the WPU film and the whiteness, the water pressure resistance and the moisture-penetrability of coating fabrics were investigated from different factors such as -COOH content, molar ratio of NCO/ON, soft segment and china extender. The experimental data showed that: As the content of -COOH increased, the particle size decreased, the viscosity increased and the stability of the emulsion got improved but water-resistance of the film weakened. The tensile strength of the film had the trend of increasing and the glass transition temperature shifted to low and the melt point shifted to high so the microphase separation degree increased and the heat stability have no significant change. With the increase of NCO/OH molar ratio, the particle size increased, the viscosity decreased and the stability of the emulsion got worse, water-resistance of the film got improved. The tensile strength of the film first increased and then decreased and the glass transition temperature shifted to high, the microphase separation degree decreased, and the heat stability decreased significantly.As the molecular weight of PBA increased, the WPU emulsion changed from translucent to milk-white, the viscosity first decreased gradually and then increased, and the stability of the WPU emulsion decreased; water-resistance of the film gets improved. The glass transition temperature shifted to low and the melt point shifted to high so the microphase separation degree increased, and the heat stability increased. Different chain-extender had different affects on the properties of WPU but the most significant one was on the mechanical property, WPU with EDA had a good rebound resilience, with BRA had a strong intension and the one with BDO fallen in between.WPU were applied on cotton coating, whiteness and moisture permeability of the cotton decreased while water pressure resistance of the cotton increased after coating. The effects of the technological factors on coating application were studied such as temperature, time and coating amounts, and so on. With the molecular weight of PBA increased, the water pressure resistance of the cotton increased and the moisture permeability of the cotton decreased.