Comprehensive Insight into Foams Made of Thermomechanical Pulp Fibers and Cellulose Nanofibrils via Microwave Radiation

Abstract

The lack of sustainable and scalable processes to produce lowdensity foams made solely of renewable materials has long been a challenge. This study investigates a novel approach to produce all-renewable foams from thermomechanical pulp fibers (TMP) and cellulose nanofibrils (CNF) using microwave radiation. The foams were produced without foaming agents or chemical reinforcing agents, and CNF was the only binder in the foam network. The foams were produced in two orientation modes simply by controlling the design of the mold in which the desired shape was formed prior to drying. This resulted in foam samples with fibers aligned horizontally (XY-foam) and vertically (Z-foam) due to the natural tendency of elongated fibers to lay horizontally in the plane upon loading the sample. The compressive moduli of the foams were strongly dependent on the orientation of the fibers (0.85 MPa versus 3.72 MPa at 0.10 g/cm 3 ). XYfoams exhibited a thickness recovery of up to 85% within 1 min after compression and almost full recovery after soaking in water and redrying. The thermal conductivity was as low as 0.046 W/m.K. The foams also had the potential to be used in sound absorption applications. The new chemical-free process to form all-renewable fiber-based foams can be scaled up much easier than other foaming technologies.

Modeling Microwave Heating and Drying of Lignocellulosic Foams through Coupled Electromagnetic and Heat Transfer Analysis

“…TMP and CNF were mixed at a composition of 95 wt.% and 5 wt.%, respectively, based on their dry masses. This 5 wt.% CNF was adequate to ensure structural integrity of the foams [36]. The initial solid content of CNF was 3 wt.% and additional water was added at a ratio of 17 g for each gram of dry TMP fibers.…”

Fundamentals of Hybrid Cellulose Nanofibril Foam Production by Microwave-Assisted Thawing/Drying Mechanism

“…A non-conventional technique to produce foams from lignocellulosic materials using microwave (MW) drying has been recently reported. , In these studies, low-density foams from thermomechanical pulp fibers and wood sawdust were prepared using microwave drying, and CNFs were added as a binder. Compared to convection/oven drying, this method is considerably faster and more energy-efficient. , During microwaving, heat is generated when a dielectric material with induced or permanent dipoles is subjected to microwave radiation.…”

Chemical Binder-Free and Oven-Dried Lignocellulose/Clay Composite Foams: Flame Resistance, Thermal Insulation, and Recyclability

“…By contrast, the lack of a solid-to-liquid transition in the case of cellulose and lignocellulose demands other routes to produce foam materials. For instance, porous structures can be developed from cellulose and lignocellulose by ice-templating (via freeze-drying), − solvent exchange (via supercritical drying), solution casting, additive manufacturing, , or air/oven drying . The former two approaches are relatively expensive and complicated (need for lyophilization or high-pressure operations) and/or involve organic solvents, discouraging the scalable production of bulky building thermal insulation materials.…”

“…porous structures can be developed from cellulose and lignocellulose by ice-templating (via freeze-drying), 17−19 solvent exchange (via supercritical drying), 20 solution casting, 21 additive manufacturing, 22,23 or air/oven drying. 24 The former two approaches are relatively expensive and complicated (need for lyophilization or high-pressure operations) and/or involve organic solvents, discouraging the scalable production of bulky building thermal insulation materials. Solution casting is generally used to prepare porous film and is not suitable for bulky foams.…”