Modification Of Waterborne Nitrocellulose Emulsion And Its Application In Coating

Solvent nitrocellulose lacquer has a long history and is one of the most common used paint for woodenware and other decorations. However, it faces the drawbacks of excessive content of volatile organic compounds(VOC), which is not conducive to environmental protection and harmful to human health, due to the usage of organic solvent as the dispersion medium. Owing to the advantages of high hardness, low VOC, environmental and less harmful to human body, water-based nitrocellulose lacquer has attracted the growing concern of the community. Meanwhile, the film of conventional waterborne nitrocellulose(WNC) emulsion is often brittle and has low performance in flexibility, water resistance, thermal stability, etc., limiting its development to industrial application. Therefore, it has great economic value and application prospects to explore the preparation of WNC emulsion with good performance in the emulsion and its filming.Referring a large number relevant literature, a cross-linked waterborne nitrocellulose emulsion(GWNC) with core-shell structure and excellent properties was prepared through the orthogonal experiment to optimize the process recipe and conditions to improve the overall performance, where glycerol was added as crosslink agent. A silicone-modified waterborne nitrocellulose emulsion(SWNC) was prepared through the modification by methyl silicone oil. And a polyvinyl alcohol / waterborne nitrocellulose emulsion(PVA/WNC) was prepared via the blends modification by PVA. Specific work is divided into three parts as follows.(1) Waterborne nitrocellulose(WNC) emulsion was synthesized by modification of WNC with methyl silicone oil. Effects of the molar ratio of isophorone diisocyanate(Tri-IPDI) and nitrocellulose(NC) and the content of the methyl silicone oil on the properties of the emulsion and coating were defined by Fourier transform infrared spectroscopy(FT-IR), particle size analysis, thermal gravimetric analysis(TGA), etc. The results showed that the stability of the obtained emulsion was good and the water resistance, surface hydrophobicity, and thermal properties of the coating were significantly improved when the addition of n(IPDI)/n(NC) and methyl silicone oil content were 0.50 and 7%(ω/ω) respectively.(2) Crosslinked waterborne nitrocellulose emulsion was prepared utilizing glycerol as the cross-linking agent. Effects of the content of IPDI trimer and glycerol on the properties of the emulsion and the water resistance of the film were studied via the particle size analysis and water absorption testing. Simultaneously, effects of the amount of glycerol and plasticizer on the properties of the film were defined through the thermal gravimetric analysis(TGA) and mechanical testing. The results showed that, compared to the samples without cross-linking agent, not only the stability of the obtained emulsion, but also the water resistance and mechanical properties of the coating had been improved when the addition of cross-linking agent and plasticizer were 5.0% and 1.5% respectively.(3) Waterborne nitrocellulose and polyvinyl alcohol(WNC/PVA) hybrid emulsion was prepared by blending WNC emulsion with PVA. Characterization methods such as Fourier transform infrared spectroscopy(FT-IR), transmission electron microscopy(TEM), mechanical testing and water absorption test were carried out to define the material compatibility and the effect of PVA content on the mechanical properties, water resistance and thermal properties of the composites. The results showed that there existed good compatibility between PVA and WNC due to the intermolecular hydrogen bonds. When the content of PVA was 15%, the hybrid emulsion had excellent stability with the tensile strength, fracture elongation and water absorption of the film to be 4.0MPa, 299.0% and 18.4% respectively.