Structural and Mechanical Properties of Hemp Fibers: Effect of Progressive Removal of Hemicellulose and Lignin

Hemicellulose and lignin were progressively removed from hemp fiber by hydrolysis. SEM, FTIR, XRD analysis and tensile properties evaluation on technical fibers were carried out to understand the structural and mechanical properties of hemp fibers. Significant influence of hemicellulose and lignin content on tensile properties was verified by ANOVA. The fiber tensile strength and initial modulus were decreased with the extensive removal of hemicellulose, along with a constant increasing of elongation at rupture. Torsion and expansion were observed in hemp fibers. It was suggested that the internal structure destruction and reorganization in the ultimate fiber cells was the main reason for the variation of mechanical properties when hemicellulose was gradually dissolved. On the other hand, fiber individualization was achieved by lignin removal and contributed to the elevation of fiber tensile properties. The elongation at break of the hemp fibers decreased slightly with the removal of lignin. NaClO2 solution treatment affected the fiber cells slightly, but effectively changed the properties of the middle lamella jointing between the ultimate fiber cells. The mechanical properties of the hemp fiber were mainly decided by the shearing between single fibers caused by the plastic-like deformation of the middle lamella.