Upgrading lignin side-streams from forest biomass pretreatment : biocomposites development and characterization

Lignin is a polymeric constituent of vascular plants’ pectocellulosic walls. It is a by-product, poorly upgraded from pulp and paper, and biorefinery industries. To evaluate their potential in agrocomposites field, commercial lignins (sodium lignosulfonates and Kraft lignin) were processed along with corn cob, an agro-industrial residue used hereby as a natural fibre. Firstly, a compression-moulding process allowed the combination of hydrated sodium lignosulfonates and corn cob particles. The impact of three factors (particle size, fibre content, and compacting pressure) on compressive mechanical properties was measured. Although sodium lignosulfonates cross-linking by commercial laccases was highlighted in solution, addition of such enzymes to agrocomposites formulations did not improve their flexural strength (maximum value of 5.3 MPa). The acoustic insulation properties of agrocomposites (sound transmission loss of 60 dB) and their thermal conductivity of 0.143 W.m - 1.K -1 may suggest applications in the building sector. Secondly, nine formulations of bio-based materials were developed by twin-screw extrusion, and then injection moulding, combining a bio-based thermoplastic polymer matrix (polylactic acid and/or poly(butylene succinate)) with technical lignins (2.5 to 20% (m/m) Kraft lignin or sodium lignosulfonates), and corn cob particles (5 to 19% (m/m)). The addition of Kraft lignin led to increased hardness of the materials up to 50%, and more hydrophobicity compared to polylactic acid. Nevertheless, their mechanical strengths decreased (by a maximum of 40%), and materials exhibited a more brittle fracture profile. In the presence of corn cob, transfer of forces from matrix to fibres was not ideal since de-bonding was detected at the interfaces under irreversible flexural stress. However, these bio-based materials exhibited mechanical, and thermal properties that made them suitable for synthetic plastics substitution while adding value to by-products of agricultural, and forest industries