Study On Waterborne Polyurethane Modified By Two Nanomaterials For Wood Coatings

The release of VOCs from organic coatings for furniture is one of the main sources of environmental pollution in the wood industry today.Under the background that the current ecological environment management has risen to the national strategy,the development and utilization of green non-polluting waterborne coatings have been widely recognized by practitioners.Among many waterborne coatings,waterborne polyurethane coatings have become one of the most promising waterborne coatings in the household industry because of its advantages of environmental protection,good leveling and good toughness,and are favored by the industry.However,after waterborne polyurethane film forming,the physical and mechanical properties such as hardness,wear resistance and tensile strength still lower than those of the traditional solvent-based coatings,which limit the further application of waterborne polyurethane coatings.Therefore,waterborne polyurethane needs to be modified to further improve its performance.Nanocellulose with hemicellulose is an one-dimensional natural renewable nanomaterial,which has the advantages of high aspect ratio,abundant hydroxyl groups and easy modification and bonding of dendritic structure.In addition,graphene oxide is a two-dimensional nano-material,which has the advantages of high mechanical strength,large specific surface area,more active groups and good hydrophilicity.Therefore,exploring the modification of waterborne polyurethane coating by these two nano-materials has research significance and application value.In this study,nanocellulose containing hemicellulose was prepared by TEMPO treatment and graphene oxide was derived by HUMMER method.On this basis,the two kinds of nanomaterials are used as reinforcements to modify the waterborne polyurethane.The effects of physical and chemical modification of these two materials and their different dosages on the physical and mechanical properties of coating film were studied.At the same time,compared with the commercially available waterborne polyurethane paint,which in combination with structural characterization,the better modification method was determined.The final conclusions are as follows:(1)The nanocellulose prepared by the TEMPO treatment was added to waterborne polyurethane by physical blending and chemical grafting to modify waterborne polyurethane.The effects of the addition amount of nanocellulose at 0.1 wt%,0.2 wt%,0.3 wt% and 0.4wt% on the properties of waterborne polyurethane were studied under two modification methods.The experimental results show that the aspect ratio of nanocellulose prepared by TEMPO method is higher than 1000.When polyurethane was modified by physical blending,0.1 wt% of nanocellulose is uniformly dispersed in the paint film,and the comprehensive performance of the modified waterborne polyurethane were more better: Compared with unmodified waterborne polyurethane(the control group in this study),the tensile strength,wear resistance and pendulum hardness of the paint film increased by 39.1%,17.40% and8.73%,respectively.The glossiness,adhesion,water/alkali/alcohol resistance,surface dry time and other properties were not significantly affected.The aggregation form and thermal stability of the modified paint had no substantial change.Compared with the commercial paint,the glossiness,wear resistance,pendulum hardness and tensile strength of the modified paint were better;When polyurethane was modified by chemical grafting,0.1 wt% of nanocellulose is uniformly dispersed in polyurethane and chemically bonded with polyurethane.The modification effect of paint film was the better: Compared with the control group,the tensile strength,wear resistance and pendulum hardness of the modified paint film increased by 43.62%,19.16% and 9% respectively.The glossiness,adhesion,water/alkali/alcohol resistance and surface dry time of the modified paint were not significantly affected.Compared with the commercial paint,the glossiness,wear resistance,pendulum hardness and tensile strength of the modified paint were better.Overall,chemical grafting modified waterborne polyurethane has better properties than physical blending modified waterborne polyurethane,which is mainly due to the chemical bonding between nanocellulose and waterborne polyurethane.(2)Graphene oxide prepared by HUMMER was added to waterborne polyurethane by physical blending and chemical grafting to modify waterborne polyurethane.The effects of0.1 wt%,0.4 wt%,0.7 wt%,and 1 wt% of graphene oxide on the properties of waterborne polyurethane were studied under two modification methods.The experimental results show that when 0.1wt% of graphene oxide is added,the graphene is dispersed uniformly in thepaint film,and the physical and chemical modified paint film has better performance;Under the condition of physical blending modification,compared with the control group,the tensile strength,wear resistance and pendulum hardness of the modified paint film increased by62.23%,14.76% and 12.7% respectively;Under the chemical modification conditions,compared with the control group,the tensile strength,wear resistance and pendulum hardness of the modified paint film increased by 66.22%,16.96% and 14.29% respectively.The glossiness,adhesion,water/alkali/alcohol resistance and surface dry time were not significantly affected;and the glossiness,wear resistance,pendulum hardness and tensile strength of synthetic paint were better than those of commercial paint.Overall,chemical grafting modified waterborne polyurethane has better properties than physical blending modified waterborne polyurethane,which is mainly due to the chemical bonding between graphene oxide and waterborne polyurethane.