Plasma Modification of Man-made Cellulose Fibers (Lyocell) for Improved Fiber/Matrix Adhesion in Poly(lactic acid) Composites

摘要

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 NH_3:C_2H_4 of 1:1 and 5:3, respectively, an oxygen-functional layer (a-C:H:O) with CO_2:C_2H_4 and CO_2 posttreatment, or an oxygen-functional layer (a-C:H:O) comprising hydroxyl groups with H_2O:C_2H_4 and H_2O 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/mm~2, 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/mm~2 in comparison to the untreated lyocell fiber with 10.3 N/mm~2. 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).