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3.9 Lignin plasticization via reactive extrusion for sustainable biomaterials

The increasing concerns about the environmental consequences of plastic waste and depletion of fossil fuels highlight the need for novel sustainable materials. Lignin, by-product of the forest industry, is the second most abundant natural polymer, but it is currently exploited for low-value applications. In this work, unrefined industrial lignin was modified by one-step reactive extrusion with a bio-sourced additive. The plasticised lignin was structurally characterised by nuclear magnetic resonance and Fourier-transform infrared spectroscopy, confirming that the reaction had taken place during extrusion. The lowering of the glass transition temperature from thermal analyses indicated the plasticization. In a second step, the plasticised lignin was melt processed with biodegradable poly(butylene adipate-co-terephthalate) for biomaterials up to 80 wt.% lignin content. The deformability and toughness measured by tensile tests were greatly improved compared to a reference biomaterial based on unmodified lignin. The feasibility of film blowing, up to 40 wt.% modified lignin, was demonstrated, indicating the potential use of biomaterials for sustainable packaging films. Successful mechanical recycling of aged blown films showed a possible end-of-life strategy and the biomaterials circularity.