Cellulose Fiber Reinforced Poly(lactic acid) (PLA) Composites - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 185

Lyocell as an Admixture for Kenaf Fiber Reinforced PLA Composites
Due to the brittle character of the most bast fibers and the PLA matrix the resulting
impact strength of bast fiber reinforced PLA composites is mostly worse than that of
the pure PLA matrix (Bax and Müssig, 2008). Based on the lower price and the wish
to produce stiff components of bast fibers like hemp, flax or kenaf they are used for
many applications in the automobile industry like indoor panels (Anonymous, 2007;
Karus et al., 2006). A limiting factor for some applications is the bad impact behavior
of composites produced from bast fibers and a polymer matrix. Hence, an admixture
of lyocell fibers to bast fibers in a PLA matrix with regard to the impact characteristics
was investigated. The composites were produced by the carding technique with fiber
loads of 40 mass% with a following compression molding step (compression mould-
ing technique CP-2). Different fiber mixtures in a PLA matrix were investigated: 36%
kenaf + 4% lyocell 3.3, 30% kenaf + 10% lyocell 3.3, 20% kenaf + 20% lyocell 3.3,
40% kenaf, and 40% lyocell 3.3.
The results of the impact characteristics are shown in Figure 12. Composites pro-
duced from 40 mass% kenaf fibers show impact strength values of 14 kJ/m² which
are significant (Welch test, α = 0.05) lower than that of the pure PLA matrix (16 kJ/
m²) while composites produced from 40 mass% lyocell 3.3 fibers show significantly
(Welch test, α = 0.05) the highest Charpy impact strength with a value of 85 kJ/m².
Mixing 36% kenaf with 4% lyocell 3.3 lead to values on the level of the pure PLA
matrix (Welch test, α = 0.05). A mixture of 30 mass% kenaf and 10 mass% lyocell
3.3 lead to a significant (U-test, α = 0.05) increase up to a value of 25 kJ/m². The 20
mass% kenaf mixed with 20 mass% lyocell 3.3 resulted in an impact strength more
than 2.5 times higher (37 kJ/m²) than the values measured for 40 mass% kenaf-PLA.
Figure 12. Unnotched Charpy impact strength of kenaf, lyocell and mixed kenaf/lyocell reinforced
PLA composites (mean value as column, standard deviation as error bars).