High-Density Molded Cellulose Fibers and Transparent Biocomposites Based on Oriented Holocellulose.

Eco-friendly materials based on well-preserved and nanostructured wood cellulose fibers are investigated for the purpose of load-bearing applications, where optical transmittance may be advantageous. Wood fibers are subjected to mild delignification, flow orientation, and hot-pressing to form an oriented material of low porosity. Biopolymer composition of the fibers is determined. Morphology is studied by SEM, cellulose orientation is quantified by x-ray diffraction, and effect of beating is investigated. Hot-pressed networks are impregnated by MMA monomer and polymerized to form thermoplastic wood fiber/PMMA biocomposites. Tensile tests are performed, as well as optical transmittance measurements. Structure-property relationships are discussed. High-density molded fibers from holocellulose have mechanical properties comparable with nanocellulose materials, and are recyclable. The thermoplastic matrix biocomposites showed superior mechanical properties (Young's modulus of 20 GPa and ultimate strength of 310 MPa) at a fiber volume fraction of 52%, with high optical transmittance of 90%. The study presents a scalable approach for strong, stiff and transparent molded fibers/biocomposites.