Thermal Stabilization of Wood/Polypropylene Composites Through Addition of Unmodified, Low-Cost Kraft Lignin

Wood/polymer composites are elegant strategies to produce materials with good performance and reduced cost. However, the addition of a lignocellulosic fiber is often responsible for the decreased thermal stability, decreasing their appeal as building materials. Here, we aimed to improve the thermal stability of wood/polypropylene composites through addition of unmodified, low-cost, abundant, ready-to-use kraft lignin. Besides thermal behavior, the composites were analyzed concerning to water relationships, colorimetric parameters, mechanical properties, and morphological features. The wood/propylene composites with and without lignin showed a very similar morphology with good interaction between matrix and biomasses. Thickness swelling decreased as function of lignin increment. The composites with 4, 12 and 20 wt% of lignin content had temperatures at 10% mass loss shifted toward higher temperatures (332, 350 and 362 °C, respectively) compared to wood/polypropylene (326 °C). Flexural strength of wood/propylene composite was preserved (42 MPa) at 4 wt% of lignin addition and tensile strength was kept unaltered in all ratios of lignin/wood (14–19 MPa).