Vacuum Paper-freezing Combined Drying Technology After Deacidification Of Paper Aqueous Solution

In China, there is a large number of paper literature of the Republican period. A wide variety of paper literature is an important part of collection in all levels of libraries and archives. But as time goes by, books of Republican period are facing the protection crisis of acidification and embrittlement. It was extremely urgent to rescue the books of the Republican period. As the situation of paper literature acidification became more and more severe,a large number of deacidification technology had been applied to the protection of paper documents. At present, the major method experts in China is aqueous solution deacidification. Drying books quickly and safely after aqueous solution deacidification is the key point in the process of literature protection. In this paper, books after aquatic deacidification was selected as the research object. The whole books after deacidification was treated by vacuum microwave-freeze combined drying.It was practicable to dry the whole book after aqueous solution deacidification by vacuum microwave drying or vacuum freezing drying. However, the two methods both had defects to a certain extent. In this paper, two kinds of drying methods were combined to dry books after deacidification. Through the experiment of eutectic point measurement, combined with the acidification characteristics of deacidification solution, the appropriate deacidification solution was selected, and the experimental process and experimental operating parameters determined.In this paper, Fluent was used to simulate the vacuum freeze-drying process of books, the temperature field distribution was analyzed around the cold trap during pre-freezing and the freeze-drying chamber during freezing-during. At the same time, the temperature field distribution of book and the temperature change of the book center were simulated during the process of pre-freezing and freeze-drying, then the experimental parameters of vacuum freeze-drying were determined.Three kinds of water conversion rate of vacuum microwave-freezing combined drying were used to dry two different thickness paper literature. By combining the performance and appearance of the paper before and after the experiment, the optimum drying process of water conversion rate was determined. The result showed that after drying by three kinds of water conversion rate combined drying process, the whiteness of the paper was significantly improved, the pH of the paper is above 7.5, and the mechanical properties the paper had different degrees of improvement. Among the three kinds of water conversion rate, the paper drying by 30% water conversion rate combined drying was better than others in tensile strength, tearing strength and folding strength. Meanwhile, the vacuum microwave- freezing drying had a significant effect in stable books shape, 30% water conversion rate combined drying was better than the other two in maintaining the steady shape. Taking all factors, the 30% water conversion rate combined drying was determined as the drying method.The results showed that vacuum microwave-freezing combined drying was a practical method to dry books after deacidification. Through a series of comparative experiment of the books of different thickness and different periods,this paper analyzed the indicators of the books. Within the experimental range, the best combined drying process was determined,which not only provides a highly efficient and safe drying method for further large-scale deacidification of paper documents, but also laying a certain theoretical basis and optimization methods for its further application.