Effect of lyocell fiber cross-sectional shape on structure and properties of lyocell/PLA composites

Three kinds of lyocell fibers with different cross-sectional profiles including circular, Y-shape, and H-shape (abbreviated as O-, Y-, and H-lyocell) and similar mechanical properties were used to reinforce polylactic acid (PLA) by melt compounding and injection molding. The influence of lyocell cross-section shape on the interfacial shearing force, interface morphology, and mechanical properties of lyocell/PLA composites was investigated. Single fiber pull-out tests showed that the interfacial shearing force between lyocell fibers and PLA matrix was in the order of H-lyocell > Y-lyocell > O-lyocell, which was correlated with the fiber non-roundness factor. The higher the non-roundness factor of lyocell fibers, the better were the mechanical properties of lyocell/PLA composites. The tensile strength, impact strength, and initial dynamic storage modulus of different lyocell/PLA composites were in the order of H-lyocell/PLA > Y-lyocell/PLA > O-lyocell/PLA, which was attributed to higher interfacial contact area and stronger interfacial adhesion of profiled lyocell/PLA composites. Therefore, profiled lyocell fibers may be more promising for use in bio-composite reinforcement than conventional circular lyocell fibers.