Deteriorated Paper Conservation With Cellulose Solution Based On NaOH/urea Solvent

Natural cellulose can be dissolved directly in NaOH/urea aqueous solution,and the obtained cellulose solution remains the original molecule structure of cellulose.When using this cellulose solution as paper strengthening solution,the fibers deposited on the paper are similar to those in paper.Meanwhile,the cellulose solution can also neutralize the acid in paper and extend the life of paper.But the very strong alkalinity of the cellulose solution will quickly corrode paper,this is the primary obstacle that must be overcame in the application of paper strengthening.In this study,we used suitable solvents such as ethanol and ethyl acetate to impregnate paper,and then sprayed the cellulose solution on it to overcome the strong alkalinity of the cellulose solution.Four kinds of paper with different aging degrees were chosen as model paper?Xuan paper,Book 1,Book 2 and Printing paper?.In order to evaluate the properties of the cellulose solution as paper strengthening solution,the tensile strength,number of double folds,tearing strength,brightness and glossiness,anti-aging properties,structure of fiber,pH,thickness,and basic weight of the model paper before and after treatment were tested.Based on the characteristic of selectively dissolving fibers in NaOH/urea system,the model paper was treated in situ with low concentration NaOH/urea solution.The mechanical properties,apparent properties and structure of fiber of the treated papers were tested.The shortcoming of the strong alkalinity of the cellulose solution can be overcame by pretreating the papers with ethanol before spraying the cellulose solution on them,which makes it possible for the cellulose solution based on NaOH/urea solvent to strengthen deteriorated paper.After treatment,the tensile strength,number of double folds and anti-aging properties of Xuan paper and Book 1were improved.The appearance,thickness,basic weight and structure of fiber,cellulose crystallinity of the papers changed slightly.In addition,the cellulose solution not only neutralized the acid in the papers,but deposited alkaline substance on the papers.However,the contact time between the cellulose solution and the papers should be controlled within a matter of seconds,otherwise the mechanical properties of the papers would decrease rapidly,and this is not conducive to strengthening operation.Mixing a certain amount of ethyl acetate in ethanol can greatly extend the time that the papers contacted with the cellulose solution.Within 8 min,the mechanical properties of the papers remained at a high level.Compared with ethanol as the pretreatment solution,the mechanical properties of the papers improved remarkably after the pretreatment of ethyl acetate,especially for their number of double folds.The number of double folds of Xuan Paper,Book 1 and Book 2 significantly increased from 1,4 and 9 times to 62,35 and 111 times,respectively.The treatment substantially improved the anti-aging properties of the papers.After heat aging of 3days,the tensile strength,number of double folds and tearing strength of the untreated samples reduced remarkably,while the tensile strength and tearing strength of treated samples remained basically unchanged,the number of double folds decreased after the heating age,but still much higher than those of the original untreated samples.The appearance,thickness,structure of fiber and cellulose crystallinity of the papers remained unchanged after treatment.Meanwhile,the acid in the papers was also neutralized.Using the low concentration NaOH/urea system to treat the papers in situ can effectively improve the mechanical properties of the papers.After treatment,the tensile strength of Book 2 and Printing paper increased from 2.56 kN·m^-1 and 2.14kN·m^-1 to 3.41 kN·m^-1 and 3.98 kN·m^-1,respectively.The number of double folds significantly enhanced from 9 and 183 times to 40 and 1890 times.The tearing strength increased from 134.3 mN and 206.6 mN to 202.6 mN and 300.3 mN.In addition,the brightness,glossiness and cellulose crystallinity of the treated papers changed slightly.However,the surface of the papers after treatment is not flat,it may be due to the NaOH/urea system selectively dissolve the paper fibers,and the swelling and shrinkage of fibers during the treatment.Spraying cellulose solution and controlling the dissolved fiber in situ can significantly improve the mechanical properties of paper,this provides a new idea for paper conservation and the strengthening of other fiber materials.