Kraft lignin as filler in PLA to improve ductility and thermal properties

• Kraft lignin (KL) was acetylated (AKL) and both were mixed with PLA by extrusion.
• PLA-lignin blends presented high hydrophobicity, especially in blends with AKL.
• Addition of lignins improves thermal stability of PLA.
• High content of lignin decreases maximum strength, especially with Kraft lignin.
• Elongation at break increased with the addition of low contents of AKL.

Kraft lignin (KL) and acetylated Kraft lignin (AKL) were used as filler for the elaboration of composites with poly(lactic acid) (PLA) in different concentrations (0.5, 1, 5, 10 and 20%) by extrusion method at 200 °C. Characterization of both lignins has been performed using HPLC, FT-IR, GPC, DSC and TGA. KL presented only 0.3% of ash content and molecular weight around 2000 g/mol. The esterification increased the molecular weight and decreases the polydispersity of the lignin (AKL). Also, AKL had lower Tg and higher thermal stability than unmodified Kraft lignin. Lignin content increased the thermal stability of PLA, with the addition of both types of lignins. Contact angle was measured to assess the change in the hydrophobicity of PLA with the addition of lignins. Mechanical properties of different materials were also investigated in order to know the effect of lignin addition in PLA. Maximum strength was not severely affected at low concentrations of both lignins, but it decreased dramatically, especially in composites with 10 and 20% of KL. Elongation at break increased with the addition of low contents of AKL, at high content of both lignins the material becomes quite brittle.