Cellulose Fiber Reinforced Poly(lactic acid) (PLA) Composites - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 176

(Bal-Tec sputter coater SCD 005, Bal-Tec, Liechtenstein) and mounted on aluminium
holders using double-sided electrically conducting carbon adhesive tabs. A high volt-
age of 10 kV was used for making the photographs. The SEM investigation was used
to study the fracture surface of the tensile specimens.
disCussioN aNd results
Fiber Characteristics
The characteristics of lyocell and kenaf were investigated by determining fineness and
tensile properties. The results show clear differences. Figure 1 gives an overview of
the tensile characteristics and the width.
Figure 2. Tensile strength (left) and fineness measured as fiber and fiber bundle width (right) of lyocell
and kenaf (mean values, standard deviations are shown as error bars; dots show the dimension of
the fiber diameter).
The best tensile characteristics were achieved by lyocell fibers with 0.33 tex with
a tensile strength of 555 N/mm², followed by lyocell 0.13 tex with 519 N/mm², lyocell
0.67 tex with 442 N/mm² and lyocell 1.5 tex with 332 N/mm². The highest tensile
strength was measured for the kenaf fiber bundles with a tensile strength of 653 N/
mm². Due to the bigger fiber diameter and the probability of more defects in the cross-
section the tensile strength decreases in trend with an increasing fiber diameter for the
lyocell fibers (Vetrotex, 1995).
Composite Characteristics
Influence of the Semi-finished Product
Composites reinforced with multilayer webs and needle felts were produced by the
compression molding technique CP-1 with fiber reinforcements of 20 and 40 mass%.
The tensile characteristics have shown clear influences of the composites whether
multilayer webs or needle felts were used for the composite production, while the
Charpy impact strength has shown lower differences. Considering the tensile strength
a better reinforcement effect to the pure PLA sample was achieved by using the needle
felts as reinforcements in comparison to multilayer web reinforced composites (Figure
3). As shown in Figure 3 a higher tensile strength was proved with increasing fiber
fineness for a fiber reinforcement of 40 mass%. For the multilayer webs a reinforce-
ment effect could only be measured for the webs produced from the lyocell 1.3 fibers
with 42 N/mm². The tensile strength of the pure PLA matrix was determined to be