Preparation And Coating Performance Research Of Aloe-Emodin Microcapsules Coated With Urea Formaldehyde Resin

Wood is one of the most common natural materials in furniture manufacturing.As a kind of artificial board,density fiberboard can save resources,so it is widely used in furniture manufacturing.But density fiberboard is prone to moisture absorption,causing mold and bacterial growth.Wood products are often coated with coatings to protect the substrate.The commonly used water-based coatings have the advantages of green and environmental protection,but their antibacterial properties still need to be improved.With the advancement of technology,people have set higher standards for the functionality of water-based coatings,which requires us to conduct pioneering research on water-based coatings.Aloe-emodin is a kind of natural material with antibacterial properties.The microcapsule technology and the natural antibacterial property of aloe-emodin were combined in this study.The antibacterial microcapsules were prepared and added to the water-based coating to prepare paint films,which were coated on the surface of the medium density fiberboard(MDF)to improve the antibacterial property of the coating,so as to better protect the coating and the MDF substrate.In this paper,the preparation process of aloe-emodin microcapsules was optimized,three different emulsifiers were selected,and the effects of emulsifier types and the content of microcapsules added on the physicochemical and antibacterial properties of paint film and MDF surface coating were investigated.The antibacterial microcapsules,photochromism microcapsules and self-repairing microcapsules were combined to study the effect of multiple functional microcapsules on the surface performance of MDF,and enrich the function of waterbased paint on wood surface.The main research findings are as follows:(1)Using urea formaldehyde resin as wall material and aloe-emodin as core material,antibacterial microcapsules were prepared by in-situ polymerization.Orthogonal test and single factor test showed that the optimal preparation process of aloe-emodin microcapsule was as follows: the molar ratio of formaldehyde to urea was 1.2:1,the mass ratio of core material to wall material was 1:15,the reaction temperature of microencapsulation was 50 °C,and the stirring speed of microencapsulation was 600 rpm.The performance of the paint film with microcapsules added is better than that of the films with cores added directly.With the increase of the content of microcapsules,the antibacterial rate of the paint films against Escherichia coli and Staphylococcus aureus gradually increases,reaching 83.6% and 81.6% respectively.The color difference of the paint films increases,the gloss decreases,the transmittance decreases,the tensile property decreases,the breaking elongation decreases,and the roughness increases.When the microcapsule content is 6.0%,the comprehensive performance of the paint film is better.(2)To investigate the effect of emulsifiers on the preparation of microcapsules,SDBS,OP-10,and TWEEEN-80 were selected to explore the optimal type and concentration of emulsifiers.The result is that the concentration of 3.0% is better than 1.0%.The film properties of microcapsules prepared with these three emulsifiers have their own advantages and disadvantages.The highest antibacterial rates against Escherichia coli can reach 77.1%,55.4%and 65.9% respectively,and the highest antibacterial rates against Staphylococcus aureus can reach 72.1%,63.9% and 60.7% respectively.The antibacterial properties of the microcapsules prepared with SDBS as emulsifier were slightly higher than those of the other two groups.With the addition of microcapsule content,the color difference of the three groups of paint films increases,the glossiness decreases,the transmittance decreases,and the roughness increases.(3)To investigate the effect of microcapsules on water-based coatings on wood surfaces,three types of microcapsules prepared with 3.0% concentration of SDBS,OP-10,and TWEEN-80 emulsifiers were added to the water-based coatings and coated on medium density fiberboard.The three sets of coatings were tested and analyzed.The antibacterial properties of the three groups of coatings increased with the increase of the addition content.The antibacterial rate of the MDF surface coating added with SDBS as the emulsifier to Escherichia coli and Staphylococcus aureus was the highest among the three groups,reaching 74.1% and66.0% respectively.The coating of this group had high hardness,low roughness,and optimal overall performance.The antibacterial rates of the coating with OP-10 as the emulsifier can reach 70.0% and 62.8% respectively,while the antibacterial rates of the coating with TWEEN-80 as the emulsifier can reach 67.0% and 61.9% respectively.(4)In order to expand the research on the combination of functional microcapsules and water-based coatings,antibacterial microcapsules using 3.0% SDBS as emulsifier,selfrepairing microcapsules,and photochromic microcapsules were added to water-based coatings separately or in combination,and coated on MDF to analyze the various properties of the coating.From the perspective of antibacterial effect,the photochromic microcapsules have little effect on the antibacterial property,and can be used together with the antibacterial microcapsules.The antibacterial rate against Escherichia coli and Staphylococcus aureus is55.6% and 51.9%,respectively.Self-repairing microcapsules have a significant negative impact on antibacterial activity,with antibacterial rates of 35.7% and 15.4%,respectively,making them unsuitable for combined use with antibacterial microcapsules.From the perspective of color changing effect,the addition of self-repairing microcapsules can accelerate the color changing speed of the coating,making the color changing effect more excellent.The addition of antibacterial microcapsules slightly slows down the color changing speed,and the color changing effect is slightly weakened.From the perspective of self-repairing effect,both antibacterial microcapsules and photochromic microcapsules have weakened the self-repairing ability of self-repairing microcapsules.The width change rate of coating scratches has decreased from 21.88% to 14.76% and 17.56%,respectively.However,compared with the coating without microcapsules,the self-repairing ability still improved.