| UV curable waterborne coatings combine the advantages of UV curing technology and waterborne coatings. It is not only safety, pollution-free and high-efficiency, but also with excellent performance. So, it has become the dominant direction of coating filed. However, compared with solvent based coatings, their water resistance were poorer. Based on this, we prepared a kind of UV-curable waterborne polyurethane coating whose water resistance is better with isophorone diisocyanate(IPDI), renewable castor oil(CO, containing hydroxyl and double bond), 1, 4-butanediol(BDO) and hydroxy ethyl acrylate(HEA) through the design of molecular structure. The backbone and end groups of the polyurethane were both provided with unsaturated double bonds. The influence of castor oil on the preparation of the emulsions and the properties of the films were studied. In order to further improve the properties of castor oil based UVWPU coating, organic- inorganic nanocomposite material were prepared by adding organic montmorillonite. The effect of organic montmorillonite on the properties of the coating films were researched. The main contents are as fllows:1. Based on the molecular structure of the raw materials and the target polymer molecular design, some UV curable waterborne polyurethane emulsions were prepared using castor oil-a natural product. The emulsions and the cured films were respectively marked as D-32, D-34, D-36, D-38 and C-32, C-34, C-36, C-38 when n(OH(CO)) / n(NCO) were 0.32, 0.34, 0.36 and 0.38. The results showed that the n(OH(CO)) / n(NCO) must be less than or equal to 0.38, otherwise it would be easy to fail under the same reaction condition. The dilution stability and centrifugal stability of the emulsions were good, and its average particle size were all in nanometer grade, among which D-32, D-34, D-36 were less than 100 nm. The cured films had good water resistance, the water swell of C-32, C-34, C-36, and C-38 were 18%, 14%, 11%, and 8% after immersing in water for 72 h. Although slight discoloration appeared, they kept completeness. The films turned back to transparent after adsorbent water was evaporated. The thermal stability, tensile strength and gel were gradually increased with the increase dosage of castor oil, but the elongation at break increased first and then decreased. Peculiarly, T5% and T10% of C-38 could respectively reach 280 oC and 299 o C. Compared with polyether based UVWPU, the gel of these films were lower.2. KH570-MMT were obtained using γ-methacryloxypropyltrimethoxysilane(KH570) to modify Na+-montmorillonite(Na+-MMT). Infrared spectroscopy, XRD, thermogravimetric analysis et al modern analytical methods were used to characterize its structure. To prepare KH570-MMT / UVWPU nanocomposite coating, UVWPU emulsion was mixed with KH570-MMT. The experimental results showed that silane coupling agent(KH570) were successfully grafted onto the surface of montmorillonite, and the organic rate was about 4.87%. The dispersity of organic montmorillonite in coating is good. The thermal stability, water resistance, Young modulus and gel of the composite films were increased compared with pure UVWPU. However, the elongation at break increased first and then decreased.3. O-MMT were prepared through sol-gel method and cation exchange. First, KH570 grafted onto the surface of Na+-MMT. Then, protonated KH550 intercalated the MMT by cation exchange. In order to analyze the structure of O-MMT, the O-MMT need to be washed and dried, and some modern analytical methods such as infrared spectroscopy, XRD, thermogravimetric analysis, were used to characterize its structure. Mixing O-MMT and UVWPU emulsion together to prepare organic-inorganic nanocomposite material. The experimental results showed that the O-MMT were obtained successfully, its organic rate was about 11.58%. The dispersity of the organic montmorillonite in the composite film was better than Na+-MMT. Compared to pure UVWPU, the thermal stability, modulus and gel of the composite films increased, elongation at break increased first and then decreased. Water swell decreased with the loading increase, however, it raised slightly when the addition reached 5%. |
