Cellulose Fiber Reinforced Poly(lactic acid) (PLA) Composites - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 179

Figure 5. Multilayer web reinforced PLA composites (40 mass%) reinforced with untreated (left) and
lignin treated fibers (right) (mean values, standard deviations are shown as error bars; dots show the
dimension of the fiber diameter).
In contrast to the untreated composites the tensile strength decreased with reduced
fiber diameters. It is assumed that this phenomenon is based on the low lignin con-
centration. The concentration (0.01 g lignin/ml ethanol) used could be too low to coat
the big specific surface of the finer fibers while a better and more homogenous coating
took place on the smaller specific surfaces of the coarser fibers. It is supposed that a
raising lignin concentration could lead to a better coating of the finer fibers and thus a
similar trend as described for the untreated fibers should be determined. The fractured
surfaces of lignin treated composites show less and shorter fiber pull-outs. This effect
is demonstrated in Figure 6. Which shows the fractured surface of a 40% Lyocell 6.7-
PLA composite next to a fractured surface of a lignin treated 40% Lyocell 6.7-PLA
composite.
Figure 6. Tensile fractured surface of lyocell 6.7-PLA composites (40 mass%). Left: untreated, right:
lignin treated.