The hygroscopicity of moso bamboo (Phyllostachys edulis) with a gradient fiber structure

Abstract

Bamboo is a functionally graded material with natural hygroscopicity, and the study of the response of its cell structure to humidity will help expand its use in textiles and engineering structures. For this purpose, in this study, the hygroscopicity of moso bamboo (Phyllostachys edulis) with a gradient fiber structure was assessed by a dynamic vapor sorption (DVS) apparatus and fitted with a Haillwood–Horrobin (H–H) model. The effects of the chemical composition, gradient fiber structure, and mesopore structure of the bamboo were also investigated. The results demonstrate that the hygroscopicity of bamboo gradually increases from the outer to the inner layer along the thickness of the culm wall, which is related to the gradient distribution of the fibers. Based on the H–H model, the hygroscopic mechanism of bamboo was determined as follows. The primary sites derived from amorphous cellulose and hemicellulose act in the low-humidity stage, while the mesopores provide a huge specific surface area (153–132 m2/g), which helps condense water vapor in high-humidity environments. Based on numerical modeling, the hygroscopic ratio of parenchyma cells and fibers was found to be 13:5, indicating that parenchyma cells contribute more to the overall hygroscopicity of moso bamboo. Moreover, the contribution of cellulose to hygroscopicity was found to become gradually higher than that of hemicellulose from the inner to the outer layer due to the increase of the amorphous area (–OH groups). The structure–function relationships between the chemical composition, multi-scale structure, and hygroscopicity identified in this study provide a theoretical basis for bamboo drying and storage technology, as well as the processing and application of bamboo fiber-based composites.