Mechanical properties of wetlaid lyocell and hybrid fiber-reinforced composites with polypropylene

The random wetlay process was used to fabricate thermoplastic composite sheets reinforced with chopped lyocell (regenerated cellulose from the N-methylmorpholine-N-oxide process) fibers, and with blends of lyocell and steam-exploded hardwood (SEW) fibers. Polypropylene (PP) served as matrix material in compression-molded composites reinforced with 25–65 wt.% fiber. Tensile and flexural properties of the resulting composites were compared with those reported for melt-processed (injection-molded) rayon fiber-reinforced PP composites. Association between fiber and matrix was also observed using scanning electron microscopy (SEM). Mechanical properties of wetlaid composites were found to be generally comparable with those of melt-processed composites over similar ranges of fiber loading. The fiber length-preserving advantage of the wetlay process was found to produce superior composite flexural properties. Tensile properties on the other hand, were found to require the presence of an interfacial binding agent. Results of hybrid composite studies revealed surprisingly high strength and modulus retention when as much as 60% of lyocell fibers were replaced with SEW fibers. The addition of wood fibers may potentially result in substantial savings in fiber cost.