Microcellular and solid polylactide-flax fiber composites

Polylactide-flax fiber composites with 1, 10 and 20 wt% fiber were melt-compounded and subsequently molded via the conventional and microcellular injection-molding processes. Silane was used as a coupling agent. The effects of fiber and silane content on cell morphology, static and dynamic mechanical properties, and crystallization properties have been studied. The average cell size decreased while the cell density increased with the fiber content. The degree of crystallinity increased with the fiber content. Silane treatment of fibers affected neither the cell morphology nor the degree of crystallinity. The toughness and strain-at-break of solid samples decreased with the fiber content while silane treatment increased both properties; however, neither fiber content nor silane treatment had much influence on the toughness and strain-at-break of microcellular samples. The specific modulus of both solid and microcellular samples increased with the fiber content. The specific strength of the solid and microcellular PLA-flax composites were only slightly lower than that of their solid and microcellular pure PLA counterparts. Overall, the toughness, strain-at-break, and specific strength of microcellular samples were found to be lower than that of their solid counterparts. The storage modulus of the PLA-flax composites with 10 and 20% fiber contents was higher than that of pure PLA.