Dimensionally Stable Cellulose Aerogel Strengthened by Polyurethane Synthesized In Situ

Abstract

Fibrillary cellulose and nanocellulose are widely applied as fillers for the improvement of the mechanical properties, thermostability, and biodegradability of polymers. Here, an opposite concept is suggested which is to use cellulose for structure‐forming and directing the scaffold, whereas polymers serve for its modification. Cellulose possesses excellent properties, but they are badly affected by water; its mechanical strength drops sharply, cellulosic materials swell, become dimensionally unstable, and susceptible to fungal degradation. The deterioration of properties gives no way of using methods of wet chemistry for cellulose treatment. To obviate this problem, dimensionally stable aerogels are prepared from microfibrillated cellulose. Their stability allows them to be treated in solutions of isocyanate. Polyurethane synthesized in situ is attached covalently to cellulose through hydroxyl groups. Polymer coating further stabilizes the 3D microfibrillar network, Young's modulus increases by more than two orders of magnitude and differences in the properties of aerogels in the dried and wetted states are minimized. Improvement of the mechanical strength makes cellulose aerogels better suitable for various applications than present cellulosic materials.

Structure of oleogels from κ-carrageenan templates as affected by supercritical-CO2-drying, freeze-drying and lettuce-filler addition

“…Nevertheless, ice crystals could crack the polymeric network, which would easily release the absorbed oil (Betz, García-González, Subrahmanyam, Smirnova, & Kulozik, 2012;Scherer, 1993). A second possibility to steer aerogel physical properties could be the modification of the hydrogel composition by the addition of filling components able to prevent the structural collapse by physically separating polymeric chains (Verdolotti, Stanzione, Khlebnikov, & Silant, 2019). In this regard, supercritical drying of lettuce has been demonstrated to lead to soft aerated materials, able to absorb huge oil amounts into a porous structure stabilised by the three-dimensional organisation of cellular tissue (Plazzotta, Calligaris, & Manzocco, 2018a;2018b).…”

Vat Photopolymerization of Nanocellulose-Reinforced Vegetable Oil-Based Resins: Synergy in Morphology and Functionalization

“…As a result, absorbance peaks appear, assigned to coupled NH and CN bending vibrations at 1157 cm −1 , NH stretching and CN bending vibrations at 1530 cm −1 , and hydrogen-bonded CO groups in the urethane at 1694 cm −1 . 32 When an excess HMDI is added, the urethane groups react with free isocyanate groups. This reaction forms a crosslinked polymer layer on the NCC surface, as evidenced by the intense absorption maximum at 1651 cm −1 assigned to the carbonyl on the urea group.…”

A Review of the Surface Modification of Cellulose and Nanocellulose Using Aliphatic and Aromatic Mono- and Di-Isocyanates

“…CNFs with amine groups on the surface were prepared by reacting the CNFs with HMDI and certain alkyl diamines (Scenario 2) [112]. To improve its mechanical properties, a CNF aerogel was cross-linked with HMDI by immersing it in a solution of HMDI in acetone [113].…”