Study On The Moisture-proof Mechanism Of Bamboo Coated By Lacquer

Bamboo decorative material with natural environmental protection, special texture, canadjust the temperature and humidity in the indoor environment control. But the bamboomaterial itself easily absorb moisture, mildew and easy to deform.So application space ofbamboo decoration material are limited. Raw lacquer is a natural paint which has a long historyin China.It has the characteristics of environmental protection and proofing humidity. Becausethe raw lacquer, limited by complex painting process and slow drying properties, lacquerpainting technology has not been used in the decoration materials widely. If the bamboo andlacquer combined, can inherit and carry forward the Chinese lacquer painting process, but alsocan give the connotation of bamboo decorative material new, far-reaching significance. Thispaper adopts lacquer to coat bamboo and study on the moisture-proof mechanism of bamboocoated by raw lacquer.The concrete research contents and results are as follows:(1) The hygroscopic variation of lacquer painting bambooThe equilibrium moisture content of lacquer painting bamboo is less than the equilibriummoisture content of bamboo, the lacquer coating treatment makes bamboo have moistureproofability.The moisture absorption rate of bamboo coated by lacquer increases with the changes oftemperature and humidity. In the same temperature, moisture content increases with increasinghumidity; in the same humidity conditions, decreases with the increase of temperature.The hygroscopicity of bamboo treated to brush paint is better than bamboo treated to rubpaint. Along with the increase of rub paint and brush paint coating layer, moisture absorption ofbamboo is small, the moisture-proof ability is more excellent.The proffing-moisture capacity of bamboo coated with raw lacquer is strongest, witchcoated by water-based paint is the second,witch coated by tung oil is the weakest.The impact of painting with raw lacquer on the hygroscopicity of bamboo is the greatest,witch of Oak (Quercus mongolica) is the second,witch of pine (Mongolica litv) is the least. The moisture absorption curve of bamboo and bamboo coated by lacquer has nosimilarities, suggesting that the moisture absorption mechanism of bamboo changes afterpainting lacquer. Lacquer painting can effectively reduce the moisture absorption of bamboo,reducing the moisture rate, the proffing-moisture ability enhancement. The moisture absorptionmechanism of lacquer painting of bamboo changed. Lacquer painting made the surfaceporosity decreases, the surface free energy decrease. At the same time, lacquer immerse inbamboo, bamboo pores were filled, the bamboo inner surface is reduced, thus thehygroscopicity of lacquer painting of bamboo can be reduced.(2) Effects of lacquer painting bamboo’s application performanceThe dimensional stability of lacquer painting bamboo is enhanced, the tate of moistureexpansion increases with increasing humidity, the tangential moisture expansion rate is greaterthan the radial moisture expansion rate. Oak (Quercus mongolica) and pine (Mongolica litv)have similar results. The moisture expansion rate lacquer painting bamboo in the above25℃environment compared with bamboo without painting decreased by23.2%,31.7%,17.5%, theaverage was25%; The moisture expansion rate lacquer painting bamboo in the above35℃environment compared with bamboo without painting decreased by42%,20%,13.7%, theaverage was25%. Lacquer painting bamboo has better dimensional stability.By measuring water contact angle, the water contact angle with bamboo coated by lacquerincreased1.54times than bamboo withount painting, the water contact angle with bamboocoated by tung oil increased1.60times than bamboo withount painting. For bamboo, Oak(Quercus mongolica) and pine (Mongolica litv), the reduction of water contact angle of coatedby lacquer is the biggest, the impact of water-based paint coating is the least.Determination of the surface free energy sugess that, the surface free energy of bamboo’soutside surface can be reduced from50.64mJ/m2to32.71mJ/m2; the surface free energy ofinside surface can be reduced from59.82mJ/m2to27.33mJ/m2.Prevention and treatment of mixed mould and blue stain fungi experimental results showthat the protective effect of bamboo coated by lacquer did not reach the expected result.Lacquer paiting did not completely cover all experimental samples, bamboo did not be isolated from the external environment, and blue mold, the bamboo channel witch can be invaded bymould and blue stain fungi has not been cut off.(3) Physical microstructure changes of lacquer painting bambooThrough the ESEM microscope observation, found that lacquer immersion bamboostructure obviously, catheter and parenchyma cells were observed in the presence of lacquerpolymer. The lacquer can form polymers by pitting, parenchyma cells.Bamboo coated with lacquer was scaned by XCT to observe the existence of lacquer inbamboo. To preserve the3D image of bamboo’s components and catheter,remove the image ofbamboo’s components.The3D image observe that the polymer are existed in the parenchymacell of bamboo coated by lacquer. The image of lacquer bamboo wictch is removed itscomponents suggeste that raw lacquer is axial distribution in bamboo basicly.The study found that lacquer components can be immersed into the bamboo’s parenchymacells and catheter.The amount of immersece is concented with the thickness and the Coatingweight of lacquer.(4)The changes of chemical structure of bamboo coated by raw lacquerThe functional group of methane and biphenyl compounds is increased on the lacquerpaiting bamboo’s surface,and the total amount of benzene ring is increased.The guaiacyl ligninof lacquer painting bamboo and C=O of lignin carbon skeleton is weakened,the acetyl group ofhemicelluloses of bamboo coated by lacquer is weakened, the hydroxyl content of celluloseand hemicelluloses in bamboo coated by lacquer. The moisture absorption of paiting lacquerbamboo reduced.In the presence of oxygen, lacquer laccase can catalyze and oxidize guaiacyl lignin ofbamboo. Laccase catalyze and oxidize guaiacol which is removed hydrogen electronic in thehydroxyl, lead to the bamboo lignin is degraded and form phenoxy quinone, the oxygenmolecular is returned to water. On the hand,the phenolic oxygen free radical is disproportionateto chinone,and on the other hand,rearranged into aryl carbon free radical to become complexcompound with Carbon carbon coupling. Hydrogen electrons are gived birth in the process ofcatalytic oxidation. And the free hydroxyl of cellulose and hemicelluloses which is surrounded by seven electrons have the strong ablity of obtain electrons.The results show that the freehydroxyl is restored to water by hydrogen electrons,the amount of the free hydroxyl ofcellulose and hemicelluloses reduce witch lead to the moisture content of bamboo coated bylacquer.The O/C ratio of bamboo’s outside surface after lacquer paiting decend from0.31to0.18,the O/C ratio of bamboo’s inside surface after lacquer paiting decend from0.28to0.17. Thedecreasing O/C ratio show that the ability of surface wettability of bamboo coated by lacquerreduce, lacquer coating bamboo has good proff-moisture capacity.