Preparation And Properties Of Soybean Oil Based UV-curable Waterborne Polyurethane/TiO₂ Organic-Inorganic Hybrid Coating

Resins made by modification of soybean oil are widely used in many fields due to their renewable raw materials, environment friendly and comparable properties to those of petrochemicals. Combining the advantages of soybean oil based resins, UV curing technology and waterborne technology has become one focus of current research in this field. Moreover, many researchers become interested in development of nanocomposite technology in order to overcome the disadvantages of resins made from modified natural polymers, such as low mechanical strengths and susceptibility to mould.In this study, a series of soybean oil based UV curable waterborne polyurethane（SOUCWPU） were synthesized, which dispersabilities in water, UV curing process and physical properties were investigated. Then UV curable SOUCWPU/TiO₂ organic-inorganic hybrid coating was prepared using the sol-gel method. The cyclic photocatalysis of the hybrid coating treated at different temperatures was studied using a contact angle measurement. The detailed process and results of the experiment are as follows:SOUCWPU was synthesized through four steps. Firstly, epoxidized soybean oil was modified by acrylic acid to prepare acrylated epoxidized soybean oil（AESO）. Secondly, the formed hydroxyl was grafted by succinic acid anhydride（SAA） in different ratios to obtain SAA-modified acrylated epoxidized soybean oil（SAESO）. Thirdly, the residual hydroxyl groups were chain extended via isophorone diisocyanate（IPDI） in different ratios to yield soybean oil based UV curable polyurethane（SOUCPU）. Finally, the obtained resins were neutralized by triethyl amine to prepare soyean oil based UV-curable waterborne polyurethane（SOUCWPU）. All intermediate and final products were characterized by Fourier transform infrared spectroscopy（FTIR） and 1H Nuclear Magnetic Resonance（1H NMR）.The dispersability of different systems of SOUCWPU in water were investigated. The results showed that the dispersability was greatly improved from stratified to completely transparent with increasing content of carboxylic acid and degree of neutralization. The resin 0.6SAA-0.6R-80%（the molar ratios of SAA and IPDI were both 0.6, and the degree of neutralization was 80%） exhibited good solubility in water.Photopolymerization processes were investigated by FTIR. The results showed that the final double bond conversion was increased first and then decreased with increasing thickness, radiation height and photoinitiator content. The highest final double bond conversion was 87.6% when the photoinitiator dose was 5 wt%, coating thickness was 50 μm, irradiation distance was 15 cm and curing time was 40 s.The physical properties of all cured samples were measured, which results showed that the physical properties were greatly improved by incorporation of carboxyl acid for cured SOUCPU film. With increasing content of IPDI in SOUCWPU, the pencil hardness increased, but flexibility decreased. On the contrary, the pencil hardness decreased and the flexibility increased with increasing content of carboxyl acid. The resin 0.6SAA-0.8R-80% exhibited the best performance, among all samples with 3H of pencil hardness, 0 level of adhesion and 0.5 mm of flexibility.SOUCWPU/TiO₂ organic-inorganic UV curable hybrid coating was further prepared via sol-gel. The photocatalytic performance of the hybrid coating treated under different temperatures were studied by measuring the contact angles during cyclic of UV light irradiation. The results indicated that contact angle decreased more obviously under 253.7 nm light irradiation with higher TiO₂ sol, which was further enhanced with increasing treatment temperature. Moreover, the contact angle showed recovered tendency after removing the light and decreased again with the secondly irradiation. When the Ti O2 sol content was 10% and heat treatment temperature was 120°C, the contact angle of hybrid coating decreased from 71° to 31° after 4 h of irradiation, which further decreased to 15° after 1 h without light. Then it gradually increased to 22° after 3 h without light, which could decrease to 16° again with further irradiating. Thus, the prepared hybrid coaing exhibited perfect and recycled photocatalytic property, which might be expected to overcome the moldy drawback of natural polymers.