Plasma modification of man-made cellulose fibers (Lyocell) for improved fiber/matrix adhesion in poly(lactic acid) composites

The present study investigates the influence of different plasma treatments on the tensile characteristics of lyocell fibers and the interfacial interactions of lyocell fibers in a poly(lactic acid) matrix. For the investigations, the fibers were coated by an amine-functional, nanoporous layer (a-C:H:N) using a gaseous mixture of NH3:C2H4 of 1:1 and 5:3, respectively, an oxygen-functional layer (a-C:H:O) with CO2:C2H4 and CO2 posttreatment, or an oxygen-functional layer (a-C:H:O) comprising hydroxyl groups with H2O:C2H4 and H2O posttreatment. As reference, uncoated fibers and fibers coated with a crosslinked, amorphous hydrocarbon layer (a-C:H) without functional group incorporation were investigated. While the different treatments maintained the tensile strength of the lyocell fibers, which were all in the range between 295 and 338 N/mm2, the interfacial shear strength, measured by the pull-out test, was clearly influenced. The best improvement of the fiber/matrix adhesion was obtained by a plasma treatment with a mixture of water vapor and ethylene resulting in an interfacial shear strength of 17.8 N/mm2 in comparison to the untreated lyocell fiber with 10.3 N/mm2. Amine-functional plasma polymers (a-C:H:N) were also found to be suitable for adhesion-promoting interlayers on lyocell fibers in poly(lactic acid). (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013