Research on mechanical properties of Phyllostachys edulis heat treatment materials based on cellulose skeleton

  Objective  This paper aims to analyze the changes of microstructure and micromechanical properties of fiber cell, the main carrier cell of moso bamboo in the process of heat treatment, in order to explain the changes of macromechanical properties of moso bamboo from the perspective of structural-activity relationship among fiber cells.

  Method  The cell wall matrix of four-year-old moso bamboo was removed with acid sodium chlorite solution and sodium hydroxide solution to obtain fiber cells with only cellulose. The untreated bamboo and bamboo fiber cells were subjected to saturated steam heat treatment at 140 and 200 ℃ for 8 h. Then, the physical and mechanical properties (density, flexural and tensile properties) and the micromechanical properties of fiber cells, such as single fiber tensile properties, cell wall hardness and elastic modulus, were measured. Scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and polymerization degree were used to characterize the changes in morphology and microstructure of cellulose before and after heat treatment.

  Result  The density, bending and tensile properties of moso bamboo decreased with the increase of heat treatment temperature. The tensile strength and elastic modulus of fiber cells were not significantly affected by heat treatment at 140 ℃, but the tensile strength of fiber cells decreased sharply when the heat treatment temperature was increased to 200 ℃, from 808.30 MPa without heat treatment to 479.23 MPa. In addition, with the increase of heat treatment temperature, the hardness of fiber cell wall increased. After heat treatment, the micromorphology of fiber cells with only cellulose remained basically unchanged, and the crystallinity of cellulose increased, intermolecular hydrogen bond increased, and polymerization degree decreased.

  Conclusion  Heat treatment can reduce the density, bending and tensile properties of moso bamboo, and reduce the tensile strength of moso bamboo fiber cells with only cellulose, but can change the micromechanical properties of fiber cell wall to a certain extent. This is closely related to the change of crystallinity, hydrogen bond system and polymerization degree of cellulose after heat treatment.