Defence of doctoral thesis: Erfan Oliaei – Lignocellulose Biocomposites– A Comparison of Wood Fibers and Microfibrillated Lignocellulose

All-lignocellulose composites, meaning densified fiber or fibril materials without added binder, show interesting mechanical properties and can be eco-friendly. Composites based on hot-pressed microfibrillated lignocellulose (MFLC) and lignocellulosic wood fiber (WF) reinforcements are compared with respect to processing, structure, mechanical properties, and eco-indicators. Also, these reinforcements are compared in hot-pressed degradable lignocellulosic crosslinked polycaprolactone (c-PCL) biocomposites based on in-situ polymerization of new caprolactone oligomers.

The intermediate lignin content (≈11%) was favorable for MFLC preparation, although the cumulative energy demand was high for mechanical disintegration from unbleached softwood kraft pulp. The mechanical properties were much better for random-in-plane MFLC compared with WF composites due to lower porosity, better interfiber bonding, and smaller-scale defects. Data for strain-field development during tensile tests was in support of these findings. For c-PCL biocomposites, much higher ultimate strength was obtained for the c-PCL/MFLC composites compared with c-PCL/WF. The most important reason was the strainhardening behavior combined with higher strain to failure, since the scale of developing defects was much smaller with MFLC reinforcement.

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