Eco-Friendly High-Strength Composites Based on Hot-Pressed Lignocellulose Microfibrils or Fibers

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.

Sustainable Wood Nanotechnologies for Wood Composites Processed by In-Situ Polymerization

“…The high energy demand, however, for extracting nanocellulose from the wood pulp fiber cell wall, combined with numerous composite preparation steps (CNF filtering, controlled drying, thermoset precursor impregnation, prepreg stacking and elevated temperature molding), and lack of recycling methods constitute major obstacles to the sustainability of CNF biocomposites. Cumulative energy demand, green-house gas emissions and water depletion indicators are unfavorable for CNF as compared with wood or wood fibers ( Oliaei et al, 2021 ). From a sustainability and processability perspectives, CNF fibrils are problematic for large-scale building materials, but are better suited for films, coatings, aerogels, hydrogels, high-technology devices, or as minor additives in packaging materials.…”

Sustainable Development of Hot-Pressed All-Lignocellulose Composites—Comparing Wood Fibers and Nanofibers

“…This results in higher residual lignin concentration on the outer part of kraft pulp fibers [ 12 ]. Unbleached kraft pulps are less deformed than bleached pulps [ 13 ] and show comparatively fewer fiber twists, curls, and kinks [ 13 , 14 , 15 ]. In addition, unbleached kraft fibers show more limited chemical degradation compared to bleached fibers [ 15 , 16 ].…”

“…Literature data shows 6–17% residual lignin in the fibers may distinctly contribute to the strength, stiffness, and water resistance of molded pulp products [ 14 , 32 , 37 ]. Mild delignification of very high lignin content wood fibers (from 25% to 11%) may increase fiber diameter and reduce cell wall thickness, which facilitates densification of fibers during hot-pressing [ 32 , 38 ].…”

“…In the 1930s, studies of Mason showed that lignin-rich fibers subjected to heat, moisture, and pressure can fuse and create a densified hard-surface fiberboard [ 40 ]. Recent research of Joelsson et al [ 26 ] and Oliaei et al [ 14 ] investigated how moisturized, lignin-rich fibers can bond to form densified fiber structures. Lignin may bind fibers strongly, as Mason described, and tensile strength as a function of density can be significantly higher for hot-pressed lignin-rich fibers, particularly unbleached high-lignin kraft (as will be discussed for Figure 6b), NSSC, or CTMP pulps [ 14 , 26 ].…”

From unavoidable food waste to advanced biomaterials: microfibrilated lignocellulose production by microwave-assisted hydrothermal treatment of cassava peel and almond hull

“…Unlike traditional production of nanofibers, which typically requires use of harsh chemicals, the valorization of a feedstock via acid-free MHT (water alone) is a state-of-the-art concept for defibrillated lignocellulose production akin to microfibrils, nanofibrils, and nanocrystals. The production of microfibrillated lignocellulose materials can lead to a variety of applications, such as, chemical adsorption, manufacturing of cardboard packaging and composites, films and adhesives (Ewulonu et al 2019;Oliaei et al 2021). Although these nanofibers can still contain lignin and/or hemicellulose depending on hydrolysis temperature applied, they show outstanding features, such as low viscosity, good dispersability and excellent polymer matrix affinity (Jang et al 2020;Oliaei et al 2020).…”