A CP/MAS C-13 NMR investigation of cellulose ultrastructure in traditional Chinese handmade papers

Cellulose-based handmade paper records a substantial amount of historical data and promotes human civilization. Due to the complexity of its structure and external factors, the deterioration of paper in the restoration of ancient books cannot be completely stopped. Nonetheless, the lack of microstructure analysis of handmade paper limits the understanding of its aging mechanism and storage life-span. Herein, CP/MAS C-13 NMR method was used to estimate the cellulose types, crystallinity, average lateral fibril dimension (LFD), and the average lateral fibril aggregate dimension (LFAD), relying on integrated spectral fitting from C1, C4, and C6 regions, respectively. Consequently, cellulose I- beta crystals were predominant in all handmade paper samples. Based on the results of C4 and C6 regions by peak separation method, bast paper (Kaihua paper and Yingchun paper) demonstrated a higher crystallinity than bamboo paper (Yuanshu paper). Additional analysis of the C4 data revealed that bast papers exhibit larger cellulose microfibrils, and their LFDs and LFADs were greater than bamboo papers. Moreover, external stress of Wiley milling reduced the LFAD from the original 9 elementary fibrils to 4 elementary fibrils with unchanged LFDs.

Automated summary

Cellulose-based handmade paper plays a significant role in recording historical data and promoting human civilization, but its deterioration remains a challenge. Microstructure analysis of handmade paper is essential for understanding its aging mechanism and storage life-span.