New insights into Chinese traditional handmade paper: influence of growth age on morphology and cellulose structure of phloem fibers from Pteroceltis tatarinowii

Phloem fibers from the bark of Pteroceltis tatarinowii are the main raw material for Chinese traditional handmade paper, Xuan zhi. Research on this fiber will contribute to unveil the scientific connotation contained in empirical records, and promote the inheritance of Chinese culture. In this study, the influence of age (5-, 12-, 29- year-old) on the anatomical, morphological, cellulose, and mechanical characteristics of phloem fibers were investigated. The microscopy showed that phloem fibers of P. tatarinowii contained the gelatinous layer. The phloem fibers were thin and long, and microfibril angles were small (4.2° ~ 6.9°). The highest total carbohydrate content of 38.0% was found in the 5-year-old bark, of which glucose accounted for 73.3%. The crystallinity of phloem fiber was decreased from 70.7 to 57.5 with the growing age. Due to a tighter cellulose structure, the 5-year-old phloem fibers exhibited a higher indentation modulus (10.8 ~20.5 GPa) than the others (6.1~15.0 GPa).