Dual-Templating Approach for Engineering Strong, Biodegradable Lignin-Based Foams

Abstract

Technical lignins are generated as byproducts from the wood pulping industry. Although their estimated annual production amounts to approximately 70 million tons, their exploitation as valueadded products remains insignificant. Yet, the diversity in the molecular structure and surface chemistry of technical lignins and their intrinsic role as mechanical support of plants may be an asset to consider in the engineering of plant-inspired materials such as biofoams. Valorization of lignins into solid foams, however, rarely accounts for more than 45−50 wt % of lignins because of their brittle nature. Herein, we report a strategy to develop fully biodegradable lignin-based foams of high stiffness, strength, and toughness that are comparable to, or in some cases exceed, the performance of petroleum-derived foams. A dual-templating approach using ice and cellulose nanofibrils (CNFs) as templates was selected to control the porous architecture of the foams made by the assembly of lignin and cellulose in the cell walls. Foams with varying lignin-to-CNF weight ratios showed enhanced structural and mechanical integrity compared with neat lignin and CNF foams. For 80−90 wt % of lignin, a significant increase (+50%) in the foams' compressive performance was observed. Varying the degree of sulfonation of lignin and in turn its chemical interaction with cellulose enabled the generation of biodegradable composite foams with tunable compressive strength. The greater the colloidal stability of the lignin-CNF suspension, the higher the foams' compressive performance. This study thus discusses an engineering approach for the valorization of technical lignins into sustainable foams that have potential as packaging materials and sandwich panels, in which high stiffness, strength, and toughness per unit weight are required.

Self-assembly fundamentals in the reconstruction of lignocellulosic materials: A review

“…to organize the self-assembly of biological tissue. Another example is provided in a report by Trovagunta et al (2022), wherein the cellulose nanofibrils (CNFs) were used as a template to align lignin particles using an oriented freezing front method. Fig.…”

“…to prepare scaffold structures from different forms of cellulosic nanomaterials, together with chitosan. Trovagunta et al (2022) reported the formation of lignin-based foams, having a high degree of directionality, by use of an oriented freezing front method.…”

“…Terms such as "bio-inspired" are often associated with self-assembly strategies carried out in laboratories (Bond et al 1995;Sanchez et al 2005;Stone and Korley 2010;Wang et al 2013;Cheng et al 2017;Rajasekharan 2017;Parker et al 2018;Yu et al 2018;Enesco et al 2019;Li et al 2019;Chen et al 2020;Trovagunta et al 2022). While marveling at the structures that can be achieved in living organisms, the modern technologist may be prompted to dream up strategies to achieve such patterns without relying so much on nature, even when the intended materials of construction come from plant materials.…”

“…Recent publications dealing with lignin moieties have revealed that the manipulation of solubility has been the most important tool being used to bring about selfassociation (Qian et al 2014;Ratnaweera et al 2015;Li et al 2016;Salentinig and Schubert 2017;Xiong et al 2017a,b;Ashok et al 2018;Mattinen et al 2018;Hubbe et al 2019;Mishra and Ekielski 2019a;Trovagunta et al 2022). The formation of small lignin particles has been a primary focus of such work.…”

Self‐foaming polyurea foams reinforced by nano SiO2 via a non‐isocyanate route

“…PUrFs show typical three-stage compression profiles for cellular solids. 39 A first linear elastic region can be defined at low strain (up to 10%), in which deformation primarily occurs due to the elastic bending of cell walls. The second phase corresponding to a plateau region (from 10% to 50% strain) attributes to the collapse of cell walls.…”