Nanocellulose Removes the Need for Chemical Crosslinking in Tannin-Based Rigid Foams and Enhances Their Strength and Fire Retardancy

Abstract

Thermal insulation and fire protection are two of the most critical features affecting energy efficiency and safety in built environments. Together with the associated environmental footprint, there is a strong need to consider new insulation materials. Tannin rigid foams have been proposed as viable and sustainable alternatives to expanded polyurethanes, traditionally used in building enveloping. Tannin foams structure result from polymerization with furfuryl alcohol via self-expanding. We further introduce cellulose nanofibrils (CNFs) as a reinforcing agent that eliminates the need for chemical crosslinking during foam formation. CNF forms highly entangled and interconnected nanonetworks, at solid fractions as low as 0.1 wt %, enabling the formation of foams that are ca . 30% stronger and ca . 25% lighter compared to those produced with formaldehyde, currently known as one of the best performers in chemically coupling tannin and furfuryl alcohol. Compared to the those chemically crosslinked, our CNF-reinforced tannin foams display higher thermal degradation temperature (peak shifted upward, by 30–50 °C) and fire resistance (40% decrease in mass loss). Furthermore, we demonstrate partially hydrophobized CNF to tailor the foam microstructure and derived physical–mechanical properties. In sum, green and sustainable foams, stronger, lighter, and more resistant to fire are demonstrated compared to those produced by formaldehyde crosslinking.

Versatile Assembly of Metal–Phenolic Network Foams Enabled by Tannin–Cellulose Nanofibers

“…Thawing the frozen tannin-CNF precursors in pure ethanol sets a tannin limit of 10%, after which the local density of the foam cell walls increases sharply and overcomes the cross-linking capacity of tannins observed at lower mass fractions (Figure 3a), thus leading to 40-60% shrinkage and foam collapse (Figure 3f). Tannins are bio-macromolecules that do not form a continuous matrix and are often copolymerized with furfuryl alcohol for material development, [45,46] therefore tannins at a high content (25-50%) within the nanofiber network only act as binders by formation of MPN in the presence of Fe (III) . By thawing the tannin-CNF suspensions in Fe (III) -rich ethanol, the MPN is formed in situ, and leads to strong cell walls that sustain drying stresses even at tannin contents as high as 50% for the CNF/TA and 25% for CNF/CT systems (Figure 3g).…”

Flowthrough Capture of Microplastics through Polyphenol‐Mediated Interfacial Interactions on Wood Sawdust

“…[30][31][32][33][34] For example, the catechol and galloyl moieties of phenolic groups can chelate metal ions and form hydrogen bonds through their hydroxyl groups. [35][36][37][38] They also form 𝜋-𝜋 stackings and undergo hydrophobic interactions with their aromatic groups. Therefore, the phenolic groups offer a means to generate strong interfacial forces to drive the adsorption and capturing processes of (bio)polymer particles, inclusive of NMPs.…”

Green Synthesis of Size-Controllable Polyfurfuryl Alcohol Nanospheres as Novel Bio-adsorbents

“…The dehydration of xylose from lignocellulose produces furfural (FUR), which is then converted to FA by hydrogenation reactions, and 65% of FUR is used to produce FA as a bio-based platform molecule. , FA monomers to polyfurfuryl ethanol (PFA) can be achieved via acid-catalyzed polycondensation . It is important to mention that PFA is used mainly as flame retardants and carbon precursors − and has not been expanded for the sustainable preparation of nanomaterials and high value-added applications.…”

“…5,6 FA monomers to polyfurfuryl ethanol (PFA) can be achieved via acid-catalyzed polycondensation. 7 It is important to mention that PFA is used mainly as flame retardants 8 and carbon precursors 9−12 and has not been expanded for the sustainable preparation of nanomaterials and high value-added applications.…”