Simple Preparation of Cellulosic Lightweight Materials from Eucalyptus Pulp

Abstract

Cellulosic foams and aerogels are tridimensional materials prepared from cellulose fibers and nanostructures that display interesting properties, such as extremely low density, high fluid permeability, sound and heat insulation. Currently, the most common techniques to obtain such porous matrices are gel or foam forming, followed by freeze-drying or critical point drying, which are energy and time-consuming processes for solvent removal. In this work, we present a new methodology to produce cellulosic lightweight materials from eucalyptus pulp, using cellulose fibers partially hydrolyzed with sulfuric acid. This method is based on a drying step easily performed at mild temperatures around 60°C in a convection oven and eliminates the need of more sophisticated drying techniques. In addition, the procedure does not require the use of surfactants or special foam forming equipment. Micro-CT and FESEM analysis showed the formation of a porous and lightweight material (density as low as 0.15 g/cm³), where the fibers are randomly assembled in a 3D-network with a few contact points. Mechanical testing reveled that foams of hydrolyzed fibers have great performance under compressive strain, with high mechanical energy absorption (ca. 360 kJ/m³). This purely cellulosic material is suitable for the incorporation of particles or functional groups aiming a wide range of final applications.

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

“…Relationship between compressive modulus and relative density (a) and comparisons of compressive moduli of different foams at various densities (references in the legend from top to bottom grouped by color , , , , − :) (b).…”

“…A few recent studies have adopted simpler techniques that relied on pretreatment steps and/or the addition of bio-based crosslinkers. Foams were prepared by partially hydrolyzing lignocellulosic fibers using sulfuric acid followed by drying in a convection oven. , Another study highlighted a successful attempt to produce foams by crosslinking sugarcane bagasse fibers with citric acid followed by oven-drying …”

Naturally Hydrophobic Foams from Lignocellulosic Fibers Prepared by Oven-Drying

“…These values are close to the densities of lightweight packaging materials (e.g., corrugated paperboard, 0.03 g/cm 3 ) and lower than those of efficient absorbent materials (e.g., blotting paper, 0.4 g/cm 3 ) . Our previously reported foams prepared from eucalyptus pulp, also made by oven-drying but with a different pretreatment (i.e., H 2 SO 4 ), are denser (0.15 g/cm 3 ) . However, when cellulose fibers are mixed with surfactants and air is incorporated, density values as low as 0.005 g/cm 3 can be achieved (for basis weight comparison and calculations, see Supporting Information, Table S2).…”

“…Cellulose foams are porous lightweight materials that can be obtained by drying liquid foams containing cellulosic fibers (with fiber diameters in the range of 15–50 μm) . They are usually prepared by the so-called foam-forming method, which consists of incorporating air into an aqueous dispersion of fibers and surfactants followed by oven-drying the liquid foam to obtain a lightweight network with apparent densities as low as 0.005 g/cm 3 . , Recently, we introduced an alternative method to fabricate lightweight cellulosic structures by demonstrating that dispersions of partially hydrolyzed fibers can be dried in an oven without the need for surfactants or air incorporation . This method produces cellulosic matrices free of additives with a network connected by fiber entanglements.…”

“…However, these more expensive and time-consuming drying methods are normally needed to produce cellulose aerogels with extremely low density networks, with 0.0002 g/cm 3 being the lowest density reported to date . Such aerogels are often produced by solvent removal from nanocellulose gels (sometimes with cryo-templating prior to drying), as reviewed previously. − Lightweight materials containing fibers have been investigated for applications in construction, membranes, and packaging since their properties include, for example, high sound absorption, , fluid permeability suitable for aerosol filters, and resistance to compressive stress. , …”