Cellulose Foam Research Articles

Multifunctional lignin-reinforced cellulose foam for the simultaneous removal of oils, dyes, and metal ions from water

Pollutants emitted by industry pose an emerging threat to ecosystems, human health and native species, which has attracted global attention. At present, most of the biomass-based water remediation materials suffer from the poor mechanical properties, complexity of the modification process, single function and low adsorption capacity. Therefore, a high-strength lignin/cellulose foam absorbent (LCMA) with super-hydrophilic surface was developed for wastewater treatment by using lignin as the skeleton to crosslink cellulose through sol-gel method. Combined with an abundance of reactive functional groups and a highly porous structure, LCMA demonstrated a superior absorption and removal performance for cationic dyes and heavy metal ions, with separation efficiencies exceeding 99.76 % for cationic dyes and 99.85 % for heavy metal ions. Further modification of LCMA by a facile method using polydopamine (PDA) and polyethyleneimine (PEI) imparted superhydrophilicity to the foams. The developed LCMA@PDA@PEI exhibited an impressive immiscible oil-water separation performance and emulsion separation performance (Separation efficiency >99.95 % for immiscible oil-water mixtures and >99.05 % for oil-in-water emulsions). With the capabilities of simultaneous removal for dyes, heavy metal ions and oil pollutants from water, LCMA holds a broad application prospect in the water remediation, especially in the treatment of polluted water with complex components.

Efficient atmospheric water harvesting enabled by hierarchically structured cellulose foam

The sorption-based atmospheric water harvesting technique is an appealing solution for addressing the challenge of freshwater shortages. In this study, a composite foam was fabricated by confining hygroscopic salt (CaCl2) into a Cr-based metal–organic framework (MIL-101), which was then integrated into a bacterial cellulose (BC) skeleton. The hierarchical structure, which contains micron- and nanoscale pores, enhances water storage, transport, and vapor evaporation throughout the whole water capture and release process. The pore confinement effect of MIL-101 and the interconnected BC network effectively restricted the leakage of the liquefied salt solution. Interestingly, the color of the CaCl2@MIL-101@BC foam changed from light green to dark green as the amount of absorbed water increased. This moisture-induced color darkening improves the light absorption ability during the water release stage under sunlight. At 30 % relative humidity, the foam can absorb up to 0.78 g g−1 of water per cycle (8 h) and desorb quickly under solar radiation. This makes foam a promising method for water production in arid areas.

Ultrahigh-strength cellulose nanofiber foams via the synergy of freeze-casting and solvent exchange

Ultrahigh-strength and lightweight materials have found wide use. However, it is difficult for artificial materials to maintain high strength while being lightweight, as the mechanical properties of most materials are strongly dependent on density. In this study, we combined the methods of freeze casting and solvent exchange to prepare cellulose nanofiber foams with lightweight and ultrahigh strength. Freeze casting created the continuous 3D network at the microscale while solvent exchange promoted the reconstruction of cellulose nanofibers via the alkali-induced mercerization effect. The foams thus possessed an ordered hierarchical structure that contained lamellar layers at the microscale and a high density of pores at the nanoscale. A quadratic exponential positive correlation between relative modulus and relative density was identified for the foams. The maximum compressive and bending moduli of the foams were 26.09 and 42.10 MPa, respectively, while its density was 210.16 mg/cm3. The study provides a robust method for the preparation of lightweight and high-strength cellulose foams.

Low-density, water-repellent, and thermally insulating cellulose-mycelium foams

This work explored whether partial cellulose bioconversion with fungal mycelium can improve the properties of cellulose fibre-based materials. We demonstrate an efficient approach for producing cellulose-mycelium composites utilizing several cellulosic matrices and show that these materials can match fossil-derived polymeric foams on water contact angle, compression strength, thermal conductivity, and exhibit selective antimicrobial properties. Fossil-based polymeric foams commonly used for these applications are highly carbon positive, persist in soils and water, and are challenging to recycle. Bio-based alternatives to synthetic polymers could reduce GHG emissions, store carbon, and decrease plastic pollution. We explored several fungal species for the biofabrication of three kinds of cellulosic-mycelium composites and characterized the resulting materials for density, microstructure, compression strength, thermal conductivity, water contact angle, and antimicrobial properties. Foamed mycelium-cellulose samples had low densities (0.058 – 0.077 g/cm3), low thermal conductivity (0.03 – 0.06 W/m∙K at + 10 °C), and high water contact angle (118 – 140°). The recovery from compression of all samples was not affected by the mycelium addition and varied between 70 and 85%. In addition, an antiviral property against active MS-2 viruses was observed. These findings show that the biofabrication process using mycelium can provide water repellency and antiviral properties to cellulose foam materials while retaining their low density and good thermal insulation properties.Graphical

Cellulose nanofiber powered interface engineering strategy to manufacture mechanically stable, moldable, recyclable, and biodegradable cellulose foam

In this work, an ingenious and energy-efficient interface engineering strategy is developed to manufacture pulp cellulose foam via incorporating cellulose nanofiber/alkyl ketene dimer (CNF/AKD) Pickering emulsions. In this strategy, CNF/AKD emulsion can uniformly anchor onto pulp microfiber surface, not only achieving interfacial exoskeleton reinforcement, but also enabling low energy surface, which facilitates the direct and large-scale production of lightweight pulp/CNF/AKD (PCA) foam by oven drying without requiring any harmful crosslinking chemistries. By simply regulating the mass fractions of CNF and AKD in emulsion, the prepared PCA foams can achieve excellent and tunable 3D porous structure, mechanical performance, water resistance and wet stability. The dry compressive modulus and wet compressive modulus underwater of PCA foams with low density of 0.09 g/cm3 can reach 0.67 and 0.57 MPa, respectively. Even 1 week in water, the compressive modulus still retains 76.2 % of initial modulus. Notably, the proposed interface engineering strategy provides remarkable formability, moldability and structural designability, enabling cellulose foam to be customized into complex and delicate 3D macroscopic structures for different scenarios. Furthermore, the PCA foam displays economically feasible closed-loop recyclability by easy hot-water disintegration and natural biodegradability in soil. Therefore, this work proves a cost-effective and viable interface engineering strategy for scalable production of lightweight, mechanically stable, recyclable, biodegradable cellulose foams with high environmental benefits and low petrochemical consumption.

Bio‐Based Foams to Function as Future Plastic Substitutes by Biomimicry: Inducing Hydrophobicity with Lignin

To replace common plastics, bio‐based alternatives are needed. Cellulose foams, as plant‐based materials, are the most attractive solution, being often biodegradable and inexpensive and having the potential for distributed production. Cellulose and its derivatives, as raw materials, present a fundamental challenge, as they are hydrophilic. Herein, this problem is solved by drawing inspiration from the hydrophobic barrier that lignin creates in wood and applying lignin to methylcellulose (MC) foams. The lignin (0.0–1.0 wt% being the range studied here) is applied directly to the suspension consisting of water and MC (1.8 wt%), which is then foamed and solidified to a dry 3D porous structure. By comparing different types of lignin and the resulting surface morphologies, it is shown that organosolv lignin (OL) most strongly self‐assembles to the air–foam interfaces, achieving area fractions up to 27%. Using different concentrations of OL, how hydrophobicity—described by the initial water contact angle and its time evolution—increases with increasing lignin concentration is then shown. Thus, significantly increased water resistance (up to 91 times higher compared to the pure MC foam), a crucial property for developing novel bio‐based materials that can compete with traditional plastics, is able to be achieved.

Imbibition of water into a cellulose foam: The kinetics

Cellulose foams are representative of many porous engineering solids that can absorb a large quantity of fluid such as water. Experiments are reported to give insight into water rise in cellulose foams and the underlying mechanisms. The water rise characteristic of water height h versus time t displays a distinct knee on a log-log plot; this knee separates an initial regime where h scales as t1/2 from a subsequent regime where h scales as t1/4. The rate of water rise below the knee is consistent with the Washburn law of water rise in a single dominant capillary, and the knee in the h(t) curve suggests that the Jurin height of this large capillary has been attained. Water rise in the foam above the knee of the h(t) curve is interpreted as water rise in a population of small capillaries with a wide range of radius that feed off the dominant capillary. A series of critical experiments support this interpretation, including water rise in inclined columns, and water rise from a limited reservoir of water. A simple analytical model is used to provide a physical explanation for the observations. Additionally, X-ray computer tomography is used to deduce the probability density function of the small capillaries. The experimental findings are in support of the hypothesis that water rise in the cellulose foam is driven by capillary action and not by diffusion.

The role of glycerol in manufacturing freeze-dried chitosan and cellulose foams for mechanically stable scaffolds in skin tissue engineering

Various strategies have extensively explored enhancing the physical and biological properties of chitosan and cellulose scaffolds for skin tissue engineering. This study presents a straightforward method involving the addition of glycerol into highly porous structures of two polysaccharide complexes: chitosan/carboxymethyl cellulose (Chit/CMC) and chitosan/oxidized cellulose (Chit/OC); during a one-step freeze-drying process. Adding glycerol, especially to Chit/CMC, significantly increased stability, prevented degradation, and improved mechanical strength by nearly 50%. Importantly, after 21 days of incubation in enzymatic medium Chit/CMC scaffold has almost completely decomposed, while foams reinforced with glycerol exhibited only 40% mass loss. It is possible due to differences in multivalent cations and polymer chain contraction, resulting in varied hydrogen bonding and, consequently, distinct physicochemical outcomes. Additionally, the scaffolds with glycerol improved the cellular activities resulting in over 40% higher proliferation of fibroblast after 21 days of incubation. It was achieved by imparting water resistance to the highly absorbent material and aiding in achieving a balance between hydrophilic and hydrophobic properties. This study clearly indicates the possible elimination of additional crosslinkers and multiple fabrication steps that can reduce the cost of scaffold production for skin tissue engineering applications while tailoring mechanical strength and degradation.

Ultralight reduced graphene oxide based foam with excellent electromagnetic interference shielding and superior mechanical properties

Reduced graphene oxide/carboxymethyl cellulose (RGO/CMC) foams with ultra-lightweight, excellent EMI shielding and mechanical robustness are fabricated based on a facile solution method and regulation of thermal reduction conditions. Results indicate that the two-step heating mode is good to obtain better EMI shielding properties. By introducing only 10 wt% of CMC, high electrical conductivity up to 34.7 S/m and EMI shieling effectiveness (SE) up to 34.6 dB are obtained. In addition, due to the connection effect of CMC, superior compressive strength and modulus as high as 8.3 KPa and 29.2 KPa are achieved, corresponding to an increase of 388.2% and 378.7%, respectively, compared to that of the RGO foam without CMC. Moreover, due to the ultralow density (∼4.1 mg/cm3) and high EMI SE of RGO/CMC, excellent specific shielding efficiency as high as 42195 dB.cm2/g is obtained, way much superior to that of other metal-, graphene-, and CNT-based carbon foams. This work will have great significance for facile fabricating efficient EMI shielding materials towards electronics and aerospace applications.

Lightweight, mechanically robust and scalable cellulose-based foam enabled by organic-inorganic network and air drying

Lightweight and high-strength cellulose-based foams have gained increasing momentum due to their combination of sustainability and high performance. However, complex modification to cellulose fibers can sacrifice the environmental friendliness and further limit productional scalability. Here, we engineer lightweight yet strong cellulose-based foams made from mechanically treated microfibrillated cellulose (MFC), reinforced by organic-inorganic network, and scaled by surfactant foaming combined with air drying. Consisting of strong coordination and extensive secondary interaction within the organic-inorganic network, the resulting cellulose composite foams achieve both a high compressive modulus of 451.3 kPa and a yield strength of 25.1 kPa at a low density of 32.9 mg cm−3, which exceed other MFC-based foams based on surfactant foaming. In addition, the incorporation of the organic-inorganic network has no negative effect on the scalability, recyclability, or biodegradability of cellulose composites foam, making closed-loop material recycling possible. The life-cycle assessment reveals that replacing petroleum-based foams with our cellulose composite foams result in substantial reductions in carbon emissions. The structural design and manufacturing of our cellulose-based foam can stimulate market interest for cellulose foam and the development of the bioeconomy.

Effect of hydroxy propyl cellulose grade and foam quality on foam granulation of a high drug load formulation

Foam granulation is a relatively newer wet granulation process whereby foamed binder solutions are added to the powders in the mixer to reduce localized over-wetting encountered during the wet granulation. This study is the first to investigate the effect of binder grade and foam quality on foam granulation process and granule properties of a high drug load formulation. Two different HPC grades, HPC LF (two times more viscous) and HPC EXF at an equivalent 7.4%w/w solution concentration, and foam quality of 50%, 90% and binder solution dripped were added to a high drug load (81%w/w) formulation for wet granulation. The granules were evaluated for compactibility and resultant compact strengths. The 50% foam quality of either HPC LF and HPC EXF resulted in lowest impeller power reading and water activity compared to 90% foam quality or dripped HPC solution. Granules prepared with 50% foam quality also exhibited smaller granule size, wider size distribution and higher specific surface area, resulting in higher compactibility. Whilst the granules prepared with different foamed HPC grades were not significantly different in compression behavior, they were higher in compact strengths, suggesting that foam mixing was more efficient in binder distribution compared to binder liquid penetration and distribution.

Multifunctional Bagasse Foam with Improved Thermal Insulation and Flame Retardancy by a Borax-Induced Self-Assembly and Ambient Pressure Drying Technique.

Cellulose foams are considered an effective alternative to plastic foam, because of their advantages of low density, high porosity, low thermal conductivity, and renewable nature. However, they still suffer from complex processing, poor mechanical properties, and flammability. As an agricultural waste, bagasse is rich in cellulose, which has attracted much attention. Inspired by the fact that borate ions can effectively enhance the strength of plant tissue by their cross-linking with polysaccharides, the present work designs and fabricates a series of multifunctional bagasse foams with robust strength and improved thermal insulation and flame retardancy via a unique borax-induced self-assembly and atmospheric pressure drying route using bagasse as a raw material, borate as a cross-linking agent, and chitosan as an additive. As a result, the optimized foam exhibits a high porosity (93.5%), a high hydrophobic water contact angle (150.4°), a low thermal conductivity (63.4 mW/(m·K) at 25 °C), and an outstanding flame retardancy. The present study provides a novel and inspiring idea for large-scale production of cellulose foams through an environmentally friendly and cost-effective approach.

Mechanically robust, thermal insulating sustainable foams fully derived from bamboo fibers through high temperature drying

The development of lignocellulosic foams has been gaining momentum due to their sustainability and biodegradability. However, lignocellulosic foams often have low preparation efficiency and poor mechanical properties, especially compression performance. Here, we constructed mechanically robust and thermal insulating cellulosic foams through high-temperature drying, in which all bamboo-sourced lignin-containing pulp fibers (LPF) and steam explosion fibers (SEF) were chosen as a skeleton and high solid fibrillated cellulose (HSFC) as a binder. This study aimed to investigate the effects of the characteristics of bamboo fibers and the HSFC addition on the formation, and mechanical- and thermal insulation performances of the resulting foams. The HSFC incorporation endowed the foams with excellent mechanical performance, the stress at 10 % strain and compressive modulus were 0.29 MPa and 4.4 MPa, respectively, which were 10-fold and 44-fold compared to LPF foam without HSFC. The LPF/HSFC possessed excellent energy absorption capacity (170 kJ/m3 under 40 % strain) as well as good thermal insulating performance (0.054 W/(m·K)). The LPF/HSFC foam with a much more homogeneous cellular structure outperformed the SEF/HSFC foam. This work suggests that the developed bamboo fiber foams hold promise for use in protective packaging and thermal insulation applications.

Convolutional Neural Networks‐Motivated High‐Performance Multi‐Functional Electronic Skin for Intelligent Human‐Computer Interaction

A multi-functional electronic skin (e-skin) with high sensitivity and wide response range is crucial for intelligent human-computer interaction (HCI) system. Here, a multi-functional hybrid e-skin (TPES) integrated by a piezo-capacitive pressure sensor (PCPS) and a triboelectric nanogenerator (TENG) is reported. An ion-gel electrospinning doped with MXene is combined with a micro-structured ion-gel to enrich the structural variations of the overall device, enabling TPES to achieve a high sensitivity of 616.42 kPa−1, a broad response range of 0.6 Pa–1 MPa, and a fast response time of 5.6 ms. The vast surface area of the mixed cellulose foam layer effectively enhances the electrical output of the TENG, making TPES’s application scenarios become more flexible. By further integrating the different functionalities of the TPES with one-dimensional convolutional neural networks and HCI module, a gesture recognition and material perception HCI system is realized. Additionally, benefiting from the excellent performance of the PCPS and TENG, a multi-information recognition HCI system is established, capable of simultaneously recognizing the pressure and surface material of the balls and enabling real-time interaction with a virtual character. In summary, the proposed work offers a novel avenue for practical intelligent HCI system in virtual reality field.

Eco-friendly bamboo pulp foam enabled by chitosan and phytic acid interfacial assembly of halloysite nanotubes: Toward flame retardancy, thermal insulation, and sound absorption

Lightweight, porous cellulose foam is an attractive alternative to traditional petroleum-based products, but the intrinsic flammability impedes its use in construction. Herein, an environmentally friendly strategy for scalable fabrication of flame-retardant bamboo pulp foam (BPF) using a foam-forming technique followed by low-cost ambient drying is reported. In the process, a hierarchical structure of halloysite nanotubes (HNT) was decorated onto bamboo pulp fibers through layer-by-layer assembling of chitosan (CS) and phytic acid (PA). This modification retained the highly porous microcellular structure of the resultant BPF (92 %–98 %). It improved its compressive strength by 228.01 % at 50 % strain, endowing this foam with desired thermal insulation properties and sound absorption coefficient comparable to commercial products. More importantly, this foam possessed exceptional flame retardancy (47.05 % reduction in the total heat release and 95.24 % reduction in the total smoke production) in cone calorimetry, and it showed excellent extinguishing performance, indicating considerably enhanced fire safety. These encouraging results suggest that the flame retardant BPF has the potential to serve as a renewable and cost-effective alternative to traditional foam for applications in acoustic and thermal insulation.

Efficient defluoridation of water by employing hybrid nanosized cerium oxides embedded within cross-linked cellulose foam

Efficient defluoridation utilizing current hybrid nano-oxides remains a great challenge because of low loading capacity and hindered nucleation during immobilization. In this study, a new adsorbent for defluoridation was developed by encapsulating nanosized cerium oxides within a cross-linked network of cellulose foam using an embedding method. The controllable structure, uniform dispersion, and high content of NCO endowed the composite with high efficiency for fluoride removal. The batch adsorption experiments exhibited a broad pH range (2.0–6.0) for optimal fluoride adsorption and confirmed that NCO@CF had a maximum adsorption capacity of 109.88 mg·g−1 at pH 4.0, which was much higher than that of other materials. Exceptional adsorption selectivity was also observed, indicating strong attraction between NCO@CF and fluoride ions, even at high concentrations of competing ions. X-ray photoelectron spectrogram and the Fourier transform infrared spectra analyses suggested that the defluoridation mechanism involved ligand exchange and inner-sphere complexation between NCO@CF and fluoride. Batch adsorption–regeneration cycles demonstrated that NCO@CF could be effectively and consistently regenerated using an alkaline solution. In fixed-bed adsorption experiments, remarkable working capacities of 1782 and 480 bed volume were observed for NCO@CF at pH 4.0 and 6.0, respectively. The findings of this study provide insights into the practical application of hybrid NCO in efficient defluoridation from water.

Applications of Xylan Derivatives to Improve the Functional Properties of Cellulose Foams for Noise Insulation.

Cellulose-based foams present a high potential for noise insulation applications. These materials are bio-degradable, eco-friendly by both embedded components and manufacturing process, have low density and high porosity, and are able to provide good noise insulation characteristics compared with available petroleum-based foams currently used on a large scale. This paper presents the results of some investigations performed by the authors in order to improve the functional characteristics in terms of free surface wettability and structural integrity. Native xylan and xylan-based derivatives (in terms of acetylated and hydrophobized xylan) were taken into account for surface treatment of cellulose foams, suggesting that hemicelluloses represent by-products of pulp and paper industry, and xylan polysaccharides are the most abundant hemicelluloses type. The investigations were mainly conducted in order to evaluate the level to which surface treatments have affected the noise insulation properties of basic cellulose foams. The results indicate that surface treatments with xylan derivatives have slowly affected the soundproofing characteristics of foams, but these clearly have to be taken into account because of their high decrease in wettability level and improving structural integrity.

Fe/Mn oxide-based foams via geopolymerization process as novel catalysts for tar removal in biomass gasification

Novel ceramic foams loaded with Fe and Fe/Mn oxides were developed via geopolymerization process as catalysts for tar removal in syngas cleaning operations. The foams were realized through polymer scaffold template replica, by impregnating polyurethane or cellulose foams with a metakaolin based geopolymer slurry loaded with 19 wt% powdered Fe2O3 and Mn2O3 metal oxides. A thermal treatment up to 900 °C was applied to vitrify and partially crystallize into leucite the geopolymer binder. Foams from cellulose showed better structural properties compared to those from polyurethane. Preliminary test in real gasification conditions were carried out on a lab scale double fixed bed reactor. In working conditions, vitrified phases derived from geopolymer binder promoted the formation of mixed phases of (Fe, Mn) oxides and silicates, beneficial for improving the catalytic activity. Furthermore, foams loaded with mixed Fe-Mn oxides were more effective than granules in reducing the produced tar.

Multiscale Design for Robust, Thermal Insulating, and Flame Self-Extinguishing Cellulose Foam.

Cellulose foams are in high demand in an era of prioritizing environmental consciousness. Yet, transferring the exceptional mechanical properties of cellulose fibers into a cellulose network remains a significant challenge. To address this challenge, an innovative multiscale design is developed for producing cellulose foam with exceptional network integrity. Specifically, this design relies on a combination of physical cross-linking of the microfibrillated cellulose (MFC) networks by cellulose nanofibril (CNF) and aluminum ion (Al3+), as well as self-densification of the cellulose induced by ice-crystal templating, physical cross-linking, solvent exchange, and evaporation. The resultant cellulose foam demonstrates a low density of 40.7mg cm-3, a high porosity of 97.3%, and a robust network with high compressive modulus of 1211.5 ± 60.6kPa and energy absorption of 77.8 ± 1.9kJ m-3. The introduction of CNF network and Al3+ cross-linking into foam also confers excellent wet stability and flame self-extinguish ability. Furthermore, the foam can be easily biodegraded in natural environments , re-entering the ecosystem's carbon cycle. This strategy yields a cellulose foam with a robust network and outstanding environmental durability, opening new possibilities for the advancement of high-performance foam materials.

Lightweight hydrophobic cellulose foam material with low density and high porosity applications in Cu (II) adsorption

AbstractCellulose foam, renowned for its lightweight properties and exceptional adsorption capacity, has emerged as a significant material of interest. In our study, a distinct functionalized cellulose foam adsorbent was developed using N,N‐methylenebisacrylamide (MBA) as a cross‐linker. This foam was further chemically tailored with 3‐aminopropyltriethoxysilane (APTES) and tannic acid (TA) to optimize its affinity for Cu (II). Utilizing a green and efficient procedure at ambient temperature, MBA was directly crosslinked with MCC sol, the resultant foam features a distinguished three‐dimensional, multi‐walled porous configuration, marked by a strikingly low average density of 0.0306 g/cm3 and an impressive average porosity surpassing 97%. Subsequently, more amino and oxygen‐containing groups were introduced by simple impregnation. The rich functional groups and unique structure enabled the adsorption of Cu (II) up to 93 mg/g, demonstrating an increasing trend in line with rising Cu (II) concentrations. Furthermore, this composite cellulose foam displayed commendable hydrophobic characteristics, evident from a hydrophobic angle surpassing 120°. From both environmental and economic perspectives, this chemically‐modified cellulose material epitomizes an ideal adsorbent, showcasing unparalleled adsorption capacity coupled with robust chemical and structural integrity. As such, it presents a viable option for the efficient sequestration of Cu (II) in wastewater treatments.