Abstract
Unbleached lignocellulosic wood fiber materials of low porosity are of great interest as eco-friendly load-bearing materials because their yield is much higher than that for “pure” wood cellulosics. The difference between comparable materials based on lignocellulose fibers or nanocellulose is investigated. The structure, surface area, mechanical properties, moisture sorption, and optical properties of films based on fibers or microfibrillated lignocellulose (MFLC) were characterized as a function of lignin content, and the environmental impact was compared. The modulus and tensile strength of comparable fiber and MFLC films (≈25% porosity) increased up to an optimum lignin content (11–17%) and then decreased at a very high lignin content. Hot-pressed MFLC films with little porosity showed excellent properties, 230–260 MPa strength, 17–20 GPa modulus, and 81 MPa wet strength. The mechanical property values of hot-pressed wood fibers with 25% porosity were also as high as 154 MPa strength and 13.2 GPa modulus, which are higher than those of comparable materials reported in the literature. Because hot-pressed lignocellulose fibers can be readily recycled and show low cumulative energy demand, they are candidates for semistructural engineering materials. MFLC is of great interest for coatings, films, adhesives, and as additives or in high-technology applications.
Highlights
Materials from wood fibers are from renewable resources and are of great interest as eco-friendly materials, with potential to replace fossil-based plastics and composites in some applications
The main objective is to compare films prepared from unbleached kraft fibers or microfibrillated lignocellulose (MFLC) based on the same fibers in which property changes are investigated as a function of lignin content
MFLC are prepared by mechanical fibrillation,[27] oxidation[40] or enzymatic hydrolysis[36] has been used
Summary
Materials from wood fibers are from renewable resources and are of great interest as eco-friendly materials, with potential to replace fossil-based plastics and composites in some applications. The main objective is to compare films prepared from unbleached kraft fibers or MFLC based on the same fibers in which property changes are investigated as a function of lignin content. Such fiber materials are of interest as “green” loadbearing materials, with a higher yield than high-purity cellulosic fibers. Fiber aqueous suspensions (0.3-0.4 wt %) were vacuum-filtrated to wet sheets (∼70% moisture) using a Finnish hand-sheet former (Lorentzen & Wettre, Sweden) They were cold-pressed and hot-pressed (185 °C for 20 min) into dense structures with about.
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