Nanocellulose-modified Waterborne Polyurethane And Its Application In Wood Coating

In recent years,with the increase of environmental pollution and the deterioration of the ecological environment,people have to re-examine the relationship between economic development and environmental protection.Now all countries in the world are practicing the concept of coordinated development of economic development and environmental protection.With the people’s awareness of environmental protection and the introduction of national policies,safe,non-toxic,environmentally friendly water-based paint came into being.Waterborne polyurethane is a kind of advanced product in waterborne coating.It has good chemical resistance,good leveling property and hard film.However,despite its many advantages,its physical and mechanical properties are still inferior to those of traditional solvent-based coatings.Thus,people are looking for a variety of modification methods to improve the comprehensive properties of polyurethane,and to further expand its scope of application.Nanocellulose has the characteristics of light weight,biodegradability,renewability,biocompatibility,and because of its size in the nanosize,the large specific surface area and small scale effect are significant.Nanocellulose also has high aspect ratio,high crystallinity-generated high Young’s modulus,high strength and other characteristics,making it potential utilization in the reinforced composite materials.In this study,nanocellulose was prepared by TEMPO pretreatment combined with mechanical method,and its microstructure and chemical composition were characterize d.Nanocellulose-modified polyurethane emulsion was prepared by physical blending an d chemical grafting method.The nanocellulose-modified polyurethane emulsion was use d to explore the effect of different nanocellulose addition on the physical and mechani cal properties of the film,and the optimum proportion was determined.Under the o-pt imum ratio,the emulsions and coatings prepared by the two methods were characteri-z ed and tested,respectively.The main conclusions are as follows:(1)Under the preparation way of TEMPO preoxidation combined with mechanical method,the diameter of the obtained nanocellulose is mainly distributed between 20~ 40 nm,and the aspect ratio is about 50 ~ 100.(2)The nanocomposite emulsion was prepared by physical mixing method with nanocellulose as filler.The effects of 0.1wt%,0.2wt% and 0.4wt% addition on the properties ofmodified films were investigated.The results showed that the overall performance of the modified film method was the best when the addition of nanocellulose was 0.1wt%.Compared with the unmodified water-based polyurethane film,the hardness can be increased by 6.9%,and the abrasion resistance increased by 10.9% and the tensile strength up to 39.5% impr ovement without affecting the appearance of the film.At the same time,the adhesion will be slightly reduced,and dry time will be extended;the water resistance,chemical resistance,and grinding cannot be significantly affected.The results show that the dis persion of nanocellulose in the modified film is relatively uniform,and it does not ha ve any effect on the crystal form of the modified film.The results show that the disp ersion of nanocellulose in the modified film is relatively uniform,which does not hav e a substantial effect on the crystal form of the modified film,but it reduces the ther mal stability of the modified film to a certain extent.(3)The nanocellulose-modified waterborne polyurethane emulsion was prepared by chemical grafting with nanofibers as filler.The effects of 0.1wt%,0.2wt% and 0.4wt% addition on the properties of modified films were investigated.The results show that when the amount of nanocellulose is 0.1wt%,the hardness can be increased by 13.9%,and the wear resistance can be increased by 1.3% and the tensile strength can be increased by 58.7%;at the same time,the adhesion will be slightly reduced,and dry time will be extended;water resistance,chemical resistance,and grinding have no significant impact.Most of the properties of the nanocellulose-modified film present better results than those of the unmodified coating,except to the thermal stability of the modified film without obvious improvement.Overall,the comprehensive performance of nano-cellulose chemical modified water-based polyurethane is better than the physical properties of water-based polyurethane modified performance.