Research On The Removal And Transformation Of Paper Surface Stains Based On Electrochemical Methods

The removal of stains on the surface of cultural relics is an important direction of cultural relics' protection.Conventional wet cleaning processes use aqueous solutions or other flowing media to dissolve or chemically react with the stain.In particular,for the removal of colored stains,oxidizing solutions are often used to achieve the purpose of decolorization.However,the oxidizing solution cleaning process requires external reagents.The degree of reaction is difficult to control,and there is a risk of residue;The solution diffusion flow may also cause secondary pollution.These factors pose potential risks to the artifacts.In this paper,electrochemical oxidation decolorization is introduced into the field of cultural relic protection.It has several characteristics:active oxidant is generated in situ;the decolorization efficiency is high;the reaction extent is controlled by current,potential and electrolysis time;and there is no risk of residue.With the high liquid retention of the gel,the cleaning area can be controlled at the specified region.It is expected to achieve the purpose of in-situ,high-efficiency,fixed-spot,and controllable removal of stains on the surface of cultural relics.Focusing on the above objectives,the content and achievements of this thesis are as follows:1.Feasibility test for electrochemically removing stains on the surface of cultural relics:A stainless steel-PbO2 electrode was prepared;the electrochemical activity of the electrode was examined by electrolyzing safranin T dye in an aqueous solution.The electrode was characterized to confirm the structure is stainless steel,?-PbO2 or ?-PbO2 by design.The accelerated life test showed that the prepared electrode had a long service life.The feasibility of electrochemical removal of stains on the surface of cultural relics was verified by electrolytic decolorization of dyes and mold spots loaded on paper,using the prepared electrode.2.Gel-assisted electrochemical cleaning:The gel was used as the cathode of the electrochemical system to construct a gel-assisted electrochemical cleaning system.The PVA-PAA-GA hydrogel was synthesized,and the structure and properties of the gel were characterized by SEM,FT-IR,and universal material testing machine(UTM).The high liquid retention of the gel ensures that the cleaning is fixed and controllable.The concern of secondary pollution caused by diffusion is alleviated and efficient decolorization by electrolysis is promoted.By studying the changes of paper structure and properties before and after electrolysis,it is found that the method has little influence on the structure and performance of paper,confirming its in situ,high efficiency and controllability.3.Preparation of pen-shaped composite electrode:In order to expand the application range of electrochemically removing stains on the surface of cultural relics,a pen-shaped composite electrode was prepared.First,micron-sized lead oxide powder was prepared as a host material,and few layer graphene was used as a conductive material.The morphology,composition,conductivity and yield were characterized by SEM,four-probe tester,TEM and TG.The lead oxide powder,PTFE,and graphene-like materials were made into a porous anode film;the morphology of the porous anode film was observed by SEM;and the conductivity was measured by a four-probe tester.The porous anode film,the separator and the cathode gel were encapsulated in the top section of the pen electrode.The electrolysis micro-domain is formed,and the active oxygen generated by the electrolysis diffuses to the outside of the electrolysis micro-domain and acts on the stain.This electrode extends the range of applications for electrochemical stain removal from paper-based thin-layer artifacts to bulk and complex surfaces.4.Application of pen-shaped composite electrode:Pen based composite electrodes were used for electrochemical restoration of paper,wood and ceramic-lead darkened samples.The effect of restoration was evaluated by color difference and pH.The darkened lead samples-were successfully restored to white with a slight increase in pH.By testing the tensile index and the folding resistance of the lead-darkened simulated paper,it was found that the physical properties did not change substantially.Gel-assisted electrochemical technology has been successfully extended to the field of inorganic materials,and lead-darkened cultural relics can be considered for it's controlled,fixed-point and in-situ restoration.This thesis introduces electrochemical oxidation technology into the removal of stains on the surface of artifacts and the restoration of darkened lead white,and with the special properties of gels,a gel-assisted electrochemical cleaning system is constructed.A composite electrode of a porous lead dioxide anode and a gel cathode was prepared,and the application range of the gel-assisted electrochemical cleaning method was extended to the complex surface of the thick relics.At the same time,it is also found that the method and the composite electrode have a better repair effect on the darkened lead-white of the cultural relics.The method has the characteristics of high efficiency,in situ,controllability,wide application range and less influence on the cultural relics.These research results have important significance and high application value in the field of cultural relics restoration.