Tensile tests have been performed to study the effect of both
lignins on mechanical properties of PLA. The Young’s modulus,
elongation at break and tensile strength at break of the different
materials are shown in Fig. 8. The strength at break was not severely
affected with low concentrations (0.5–5%) of both types of lignin (KL
and AKL). However, at concentrations greater than 5%, the maximum
strength decreased with increasing lignin content, especially
in materials formed by PLA and unmodified Kraft lignin. There was
a big difference between composites elaborated with PLA and KL
and composites with AKL addition. Other study in which was elaborated
a PLA/unmodified commercial lignin composite by similar
methods were also observed a decrease in the stress at concentrations
of 5% and 10%