Deterioration of Contemporary Kaihua Handmade Paper: Evolution of Molecular, Supermolecular and Macroscopic Structures

Valued for its toughness and durability, Kaihua paper has been famous in China since the Qing Dynasty and is in the focus of the study on paper life extension. Understanding of the complex degradation behavior of handmade paper under various aging conditions is an essential precondition for preparing contemporary long-life handmade paper. However, reactions sequence and quantitative analysis of microstructure of cellulose and its relation to macroscopic deterioration of handmade paper still are difficult to interpret. Herein, different types of Kaihua handmade papers, produced by various raw materials and crafts, were artificially aged to study the different evolution of their multi-scale structures in dry-heat (DH) and wet-heat (WH) conditions systematically. Two-dimensional correlation spectroscopy (2D-COS) distinguished possible carbonyl vibrations involving hydrolysis and oxidation of cellulose and gave sequential changes of various carbonyl groups, illustrating different evolution behaviors of molecular structure of papers in DH and WH aging process. The energy and distance of hydrogen bond, crystal size and microfiber accessibility were quantitatively calculated during the degradation of cellulose. The dual roles of water molecules, as plasticizers for fibers and as carriers of protons, continuously promoting the hydrolysis of cellulose at molecular and supramolecular scales were elucidated further. In addition, correlations between microstructural evolution and macroscopic deterioration of handmade papers involving reduced mechanical properties and yellowing were revealed.