Research On In-situ Electrochemical Cleaning And Parallel Deacidification And Reinforcement Of Paper Cultural Relics

Cleaning is an important subject of the restoration of paper cultural relic.Traditionally,water or other functional lotions have been applied to remove the contaminations or discolorations from paper by dissolution or chemical reaction.However,these methods generate some drawbacks including the diffusion of contaminants and the deterioration of paper property.For a good control of zone and a minor influence of solution on the treated paper,the hydrogel loading functional detergents,as a newly emerging cleaning method,removes stains from the paper surface via dissolution and adsorption layer by layer.Nonetheless,due to the poor capacity of mass transfer of hydrogel,there are some limitations such as low efficiency,depressed applicability and difficulty to reuse in the hydrogel-based cleaning process.It is of great significance to explore a high efficiency cleaning method with good controllability for cleaning area and degree,favourable applicability and reusability.To this end,the electrochemistry was innovatively incorporated into the hydrogel cleaning process to construct an electrochemical cleaning system,which comprised ?-PbO2 as the anode and conductive hydrogel electrode pen as the anode.In this thesis,several typical types of conductive hydrogel electrode pens were synthesized and,a systematic study was performed on the relevant issues that affected the cleaning performance and the paper property.This is hopeful to provide theoretical and technical support for the application of electrochemical cleaning.Deacidification and strengthening are another important subjects of the restoration of paper cultural relic.In order to solve the issues of conventional process,such as aggregation of deacidification agent,uneven deacidification,color change of the treated paper and complex operation,a deacidification method based on the application of nanoparticles of alkaline earth metal hydroxide dispersing in short-chain alcohol was developed in recent years.Generally,the mechanical strength of the acidized paper is weak,and it is very important to strengthen the paper when it is deacidified.The integration of deacidification and strengthening in one operation is the direction of the restoration of paper cultural relic.The cellulose derivative,with a similar structure to cellulose,strengthens the paper via filling the gaps and forming "bridges" between paper fibers by hydrogen bonding.Based on this,a method was proposed and carried out to simultaneously deacidify and strengthen the acidized paper by the Mg(OH)2 nanosheet(Mg(OH)2 NS)ethanol dispersion that was stabilized by ethyl cellulose(EC).The effect of the EC/Mg(OH)2 NS ethanol dispersion on the properties of paper and the mechanism of deacidification and strengthening were investigated to develop a simple and highly effective way for restoring the acidized paper.Based on the research purpose mentioned above,the main contents of this thesis and the obtained conclusions are as follows.(1)A plate electrode with the ?-PbO2 as interconnecting layer and the ?-PbO2 as active outer layer was prepared by a continuous two-steps electrodeposition on the surface of the stainless steel plate.Initiation by ammonium persulfate,the aniline was in situ polymerized in the polyacrylamide hydrogel(PAM)to obtain a conductive polyacrylamide/polyaniline composite hydrogel electrode(PAM/PANI),in which the polyaniline was doped by hydrochloric acid.The composition,structure,and performance of the plate electrode and PAM/PANI were characterized by XRD,SEM,FT-IR,universal testing machine(UTM)and dynamic rheometer(DRM).The results showed that the service life of the ?-PbO2 based electrode was very long and,to some extent,the mechanical performance and conductivity of the synthesized hydrogel were improved by PANI.The electrochemical cleaning system based on electrodes of ?-PbO2 and PANI/PAM could fully clean the organic contamination(safranine T)on the paper under 4 mA/cm2 within 5 min,which indicated the feasibility of the in situ electrochemical cleaning for removing the paper stains.Nonetheless,the leakage of doped acid and the weak strength of the hydrogel electrode resulted in the acidification of the treated paper and an insufficient control of the cleaning region.(2)Alginate sodium alginate/polyacrylamide hydrogel electrode(CSPH)crosslinked by Ca2+ was prepared by a two-steps method.Several technologies including FT-IR,SEM,TG,DSC,UTM and DRM were applied to characterize the composition,structure and mechanical properties of the hydrogel.The results indicated that Ca2+ not only promoted the conductivity of the hydrogel but also boosted its mechanical strength,resulting in a maximum compressive stress of 4.8 MPa for the CSPH.The cleaning efficiency of the electrochemical system composed by ?-PbO2 and CSPH was systematically studied.The results showed that this system could thoroughly remove the stains such as the organic dyestuff,commercial drinks,tideline and mildew at a few mA/cm2 within several minutes.Without any affect on the inorganic pigments and mimeograph handwriting on the paper,the electrochemical cleaning system worked only on the strictly controlled area.In addition,the electrochemical cleaning did not significantly influence the microstructure,molecular structure,crystallization structure and mechanical properties of the paper.This study further proved the feasibility of the in situ electrochemical cleaning for the remove of paper stains.Unfortunately,the migration of ions in the hydrogel electrode caused a significant decline of the hydrogel strength in a continuous utilization.(3)The reduced graphene oxide(rGO)/polyacrylamide(PAM)/montmorillonite nanoplates(MMT)composite conductive hydrogel electrode(rGPM)was fabricated by an in situ polymerization-reduction method.The structure and performance of the rGPM were characterized by technologies of SEM,XRD,FT-IR,UTM,DRM,and so on.The results showed that the MMT acting as a reversible multiple crosslinker significantly increased the mechanical properties of the hydrogel electrode,making a maximum compressive stress of 7.6 MPa for the rGPM.The electrochemical cleaning system based on rGPM and ?-PbO2 could completely remove various stains on the paper under several mA/cm2 within a few minutes.The hydrogel electrode could be readily peeled off from the surface of the treated paper without leaving any extra component after cleaning.This cleaning system did not generate an obvious adverse effect on the structure and property of paper fibers.The strength of rGPM electrode only exhibited a small loss after a long duration of electrochemical treatment.Compared with electrode pens of PAM/PANI and CSPH,rGPM is the more suitable one for the electrochemical cleaning system.Based on the results of various experiments,a stain-removing mechanism for the electrochemical cleaning was proposed as follows.When the external power is switched on,the water slow releasing from the hydrogel electrode pass through the treated paper and generate hydroxyl radicals on the surface of PbO2 electrode;the hydroxyl radicals in situ break or decompose the contaminant to form a colorless product only in the attached area.The cleaning extent and the cleaning region could be easily controlled by the regulation of voltage and contacting area.(4)The Mg(OH)2 NS with the diameter less than 100 nm was prepared by the sol-gel method using gelatin as a surface stabilizer.The Mg(OH)2 NS was steadily dispersed in the EC ethanol solution.This dispersion could synchronously de-acidify and strengthen the paper by a simple process of coating or spraying.In this process,the EC ethanol solution carrying Mg(OH)2 NS filled the gaps of paper fibers and formed a protective film on the fibers surface.On the one hand,EC wrapping Mg(OH)2 NS could not only avoid the direct damage of paper fibers by the alkali,but also slowly release the alkali for deacidification.On the other hand,EC could improve the mechanical strength of paper by means of filling and bridging the fibers.On the basis of the above functions,the suspension based on Mg(OH)2 NS in the EC ethanol solution simultaneously de-acidified and strengthened the treated paper and,promoted its durability.The results showed that the pH and mechanical strength of the treated paper could be effectively improved when the concentrations of Mg(OH)2 NS and EC were 5.0 and 16.0 g/L,respectively.In this thesis,the electrochemistry is incorporated into hydrogel cleaning to innovatively construct a conductive hydrogel based electrochemical cleaning system for paper cleaning.This system is highly efficient,well controllable,widely applicable,reusable and very small impact on the paper.Moreover,a simple and efficient method based on a stable EC/Mg(OH)2 NS ethanol suspension is developed for the simultaneous deacidification and strengthening of paper.These studies reveal academic significance and application prospect in the restoration field of paper cultural relics.