Structure and properties of flax vs. lyocell fiber-reinforced polylactide stereocomplex composites

A commonly used natural cellulose fiber (flax) and a regenerated cellulose fiber (Lyocell) were used at 20 wt% to reinforce polylactide stereocomplex (sc-PLA) composites. Composites were prepared by melt compounding cellulose fibers and an equivalent proportion of PLLA/PDLA, followed by injection molding. The structures and properties of these two kinds of cellulose fiber/sc-PLA composites were compared and evaluated. The results showed that the total crystallinity and stereocomplex crystallite content of composites could be increased by reinforcing with cellulose fibers, and Lyocell fibers were more effective in accelerating crystallinity and the formation of stereocomplex crystallites than flax fibers. Mechanical properties of Lyocell fibers were much poorer than those of flax fibers, and the interfacial adhesion values of Lyocell/sc-PLA composites were inferior to those of flax/sc-PLA composites. Lyocell/sc-PLA composites showed higher impact strength and similar tensile strength vs. flax/sc-PLA composites, but the Young’s modulus values of Lyocell/sc-PLA composites were lower than those of flax/sc-PLA composites. The Vicat softening temperatures of both flax/sc-PLA and Lyocell/sc-PLA composites were increased to nearly 100 °C higher than that of PLLA. Lyocell/sc-PLA composites showed the highest Vicat softening temperature of ~ 170 °C.