Research On The Synergistic Mechanism Of Cooked Tung Oil And Brick Powder In The Production Process Of Ancient Building Painted Ground Poles

The color painting drawn on Chinese ancient wooden architectures has survived several centuries,which mainly benefits from the superior coating material-Dizhang.Therefore,discovering the interaction among various materials involved in Dizhang making craft.On the basis of the previous studies in our group,this paper mainly focuses on the interaction between refined tung oil and brick powder,aiming at revealing the role of brick powder played in improving the performance of Dizhang.There are three parts of the research contents included in this paper.(1)The roles of Zhangdan and Tuzi played in the curing process of refined tung oil were investigated.(2)The effect of brick powder on the curing of refined tung oil and the mechanical properties and the corresponding mechanism was explored.(3)The effect of brick powder on the binding of pigment with the surface of the film formed by refined tung oil was studied and its mechanism was proposed.Based on the above research,the following results could be obtained:Firstly,the effect of Zhangdan and Tuzi on the solidification of refined tung oil in the traditional craft of making Dizhang was studied,and the following results were obtained:(1)The microscopic morphology of films formed by refined tung oil in which Zhangdan and Tuzi exist alone or together were observed by ultra-depth three-dimensional microscope and scanning electron microscope(SEM).The results show that the curing of refined tung oil actually is an aerobic polymerization.Zhangdan can obviously promote the curing of tung oil to form a film.Zhangdan induces fast curing and formation of a film on the surface of the oil,keeping the air from the inner of refined tung oil beneath the film and thus inhibiting the curing of the oil beneath the film.The curing of the oil at the surface inducing shrinkage of the formed film,generating sparse but deep wrinkles.In contrast,Tuzi has a negative effect on the curing of the tung oil,slowing down the polymerization of tung oil.As a result,there is a relatively small shrinkage of the formed film,presenting sparse and shallow wrinkles.The cross section of the film formed by tung oil in which either Zhangdan or Tuzi existing alone is smooth.When Zhangdan and Tuzi coexist,the formed film presents dense shallow wrinkles,and an obvious pore structure appears in the cross section of the film.Above different morphologies of the formed films are related to the difference in the effects of Zhangdan and Tuzi on the tung oil curing.For the situation where Zhangdan and Tuzi present alone,the curing rate is different,but the difference is only reflected in the overall shrinkage of the film on the surface of the oil.While the refined tung oil in presence of Zhangdan and Tuzi contains two components having opposite effects,one promoting curing and another slowing curing.The shrinkage induced by fast curing has a stress effect on the phase of slow curing to deform,forming the pore structure throughout from the surface to the interior.(2)The results of rheometer,IR,UV-vis and 1HNMR spectroscopy show that the conjugated diene of tung oil decreases significantly when Zhangdan and Tuzi coexist,which indicates that the coexistence of Zhangdan and Tuziis conducive to the polymerization of tung oil.Compared with Tuzi,Zhangdan has a more obvious catalytic action on the polymerization of tung oil.These different catalytic effects account for the above-mentioned various morphologies of films formed by tung oil containing different components.In particular,the formation of the internal pore structure when Zhangdan and Tuzicoexist is an inevitable result of their different effects on the polymerization of tung oil.To some extent,the microscopic mechanism of the combined effect of Zhangdan and Tuzi onthe dryness of inner and outer tung oil film involved in the traditional craft was revealed.(3)The viscosity,the generation of hydroperoxides and free radicals duringthe tung oil curing were determined by chemiluminescence and ESR.The results show that Zhangdan can promote the formation of hydroperoxides,and the Tuzi can promote the decomposition of hydroperoxides.This difference is consistent with the different catalytic effect of them on thepolymerization of tung oil.The second part of the work studied the effect of brick powder on the curing of tung oil in the traditional craft of Dizhang.The following results were obtained.(1)The results show that brick powder as a filling material could significantly enhance the mechanical properties including compressive,tensile and bendingof refined tung oil.Within a certain limit,the more brick powder is used,the more obvious this enhancement is.As a filler,dispersive distribution of brick powderin the tung oil matrix makes the stress distribution uniform,increasing resistanceto the shrinkage of cured tung oil.Therefore,it shows strong anti-compressibility and anti-bending.Besides,the addition of brick powder alsoincreases the homogeneity of the microstructure of the internal cured oil and reduces the weak binding site caused by the internal heterogeneity of cured oil in absence of brick powder.Thus,the tensile properties of the film are enhanced.(2)The results of UV-vis spectra,IR spectra,NMR spectra,ESR spectra and chemiluminescence spectra show that the amount of oxygenadsorbed on brick powderhas obvious effects on the amount of peroxides,free radicals and alkene bonds,and the viscosity during refining tung oil.Brick powder completely adsorbing oxygen is beneficial to increase the content of peroxides and free radicals,accompanying decreased content of alkene bonds and increased viscosity.Based on the above results,the mechanism of the synergistic effect of brick powder with tung oil on the tung oil polymerizationwas proposed.That is brick powder with a porous structure that can adsorb oxygen,promotingthe polymerizationof internal tung oil beneath the formed oil film.Thirdly,brick powderas an important part of Dizhangnot onlycan strengthen the mechanical properties of Dizhangbut also may enhance the adhesion between the paint layer and the surface of Dizhang.Therefore,the influence of the composite coating consisting of brick powder and tung oil on the adhesion properties of pigmentlayer was studied.The following results were obtained.(1)The results of contact angle measurementshow that the film formed by a composite of brick powder and tung oil has a stronger hydrophobicitycompared with that formed by tung oil.It relates to the increased surface roughness of the film formed by refined tung oil due to the addition of brick powder.(2)It was found that polishing the composite coating of brick powder and tung oil before painting is beneficial to enhance the adhesion of the pigmentlayer on the surface of Dizhang.The gelatin used in traditional painting has a remarkable property of wet swelling and drying shrinkage.Hydrophilic porous brick powderexposed after the above-mentioned polishing has the adsorption and binding effect on the pigmentlayer containing gelatin,thus enhancing the binding strength between the paint layer and the surface of the Dizhang.It not only inhibits the warping and peeling of the paint layercaused by drying but also strengthens adhesion of pigment on the surfaceof Dizhang preventing fading.This thesis focuses on the role of brick powder played in the traditional craft of Dizhang.It reveals the synergistic effect of Zhangdan and Tuzi on the internal and external polymerizationof tung oil,accounting forthe scientific essence contained in the prior experience of balancing surface drying and internal drying in the traditional craft.Moreover,it was found that brick powder can enhance not only the mechanical properties of the composite coating of tung oil but also the adhesion of the pigmentlayer on the Dizhangsubstrate.In particular,it was found that the brick powder could promote the polymerization of the internal tung oil beneath the already formed film.These findings are of positive significance for deepening the scientific connotation behind the traditional craft of painting on Chinese ancient wooden architectures and valuable for composite materials today.