Cellulose Foam Research Articles

Water-stable cellulose fiber foam with antimicrobial properties for bio based low-density materials

New bio-based packaging materials are highly interesting for replacing conventional fossil based products for a more sustainable society. Water-stable cellulose fiber foams have been produced in a simple one-batch foam-forming process with drying under ambient conditions. The cellulose fiber foams have a low density (33–66 kg/m3) and can inhibit microbial growth; two highly valuable features for insulating packaging materials, especially in combination with stability in water. Cationic chitosan and/or polyvinylamine have been added during the foam-forming process to give the foams water-stability and antimicrobial properties. The structural and mechanical properties of the cellulose fiber foams have been studied and the antimicrobial properties have been evaluated with respect to both Escherichia coli, a common model bacteria and Aspergillus brasiliensis, a sporulating mold. The cellulose foams containing chitosan had both good water-stability and good antibacterial and antifungal properties, while the foams containing PVAm did disintegrate in water and did not inhibit fungal growth when nutrients were added to the foam, showing that it is possible to produce a bio-based foam material with the desired characters. This can be an interesting low-density packaging material for protection from both mechanical and microbial damage without using any toxic compounds.

All-natural and highly flame-resistant freeze-cast foams based on phosphorylated cellulose nanofibrils.

Pure cellulosic foams suffer from low thermal stability and high flammability, limiting their fields of application. Here, light-weight and flame-resistant nanostructured foams are produced by combining cellulose nanofibrils prepared from phosphorylated pulp fibers (P-CNF) with microfibrous sepiolite clay using the freeze-casting technique. The resultant nanocomposite foams show excellent flame-retardant properties such as self-extinguishing behavior and extremely low heat release rates in addition to high flame penetration resistance attributed mainly to the intrinsic charring ability of the phosphorylated fibrils and the capability of sepiolite to form heat-protective intumescent-like barrier on the surface of the material. Investigation of the chemical structure of the charred residue by FTIR and solid state NMR spectroscopy reveals the extensive graphitization of the carbohydrate as a result of dephosphorylation of the modified cellulose and further dehydration due to acidic catalytic effects. Originating from the nanoscale dimensions of sepiolite particles, their high specific surface area and stiffness as well as its close interaction with the phosphorylated fibrils, the incorporation of clay nanorods also significantly improves the mechanical strength and stiffness of the nanocomposite foams. The novel foams prepared in this study are expected to have great potential for application in sustainable building construction.

Modification of cellulose foam paper for use as a high-quality biocide disinfectant filter for drinking water

Development of a foam-formed cellulose filter paper with high wet strength was carried out for application as a drinking water filter. The wet strength and antimicrobial activity of cellulose foam paper against several bacteria species (Bacillus subtilis MTCC 441 (Gram +ve), B. cereus NCDC 240 (Gram +ve), Pseudomonas aeruginosa NCDC 105 (Gram −ve), Klebsiella pneumonia NCDC 138 (Gram −ve), and Escherichia coli MTCC 40 (Gram −ve)) were investigated. The morphology and structure of the cellulose foam paper were characterized using scanning electron microscopy (SEM). The results of our study confirmed that glutaraldehyde solution or 1,2,3,4-butanetetracarboxylic acid (BTCA) added to cellulose foam paper pretreated with cationic polyacrylamide (C-PAM) provided very high and stable wet strength performance together with excellent antimicrobial properties.

A bio-based composite material for water remediation from oily contaminants

In this work, a novel composite sorbent material for water remediation from oily contaminants, based on a cellulose three-dimensional fibrous scaffold treated with stearic acid and expanded graphite flakes, is presented.The pristine cellulose foams are inherently omniphilic, absorbing indiscriminately both water and oils. However, after being modified with stearic acid and graphite via drop casting, they become superhydrophobic (still preserving their superoleophilic characteristics). As a result, the foams start exhibiting a highly selective behaviour which permits to absorb different kinds of oils and organic solvents, while repelling water completely.Thermal and chemical characterizations reveal that the modification treatment is successfully performed, while the performed mechanical tests demonstrate a good recovery of elasticity after repeated deformations and confirm that the elasticity of the foam is preserved after the treatment. Although based on natural materials, the fabricated foams exhibit oil absorption rate, saturation time and capacity values comparable to those of some synthetic materials with the same aim, exhibiting a very important added value, as it is based on low cost, green and biodegradable materials, requiring, at the same time, low processing costs and providing excellent reusability properties.

Microfibrillated cellulose foams obtained by a straightforward freeze–thawing–drying procedure

Microfibrillated cellulose (MFC) is continuously gaining attention due to its outstanding mechanical properties, in particular high strength-to-weight ratio. Recently, more and more studies target the production of porous materials, such as foams, out of this natural resource. Commonly, an energy-consuming freeze–drying method is utilized for producing pure MFC porous structures from water-based suspensions, which renders these products particularly unattractive for industry. Although alternatives for foam production have been proposed, using either modified MFC or with various additives, the freeze–drying step is still one of the most critical bottle-neck of MFC foam production upscaling. A novel straightforward freeze–thawing–drying procedure assisted by the common additive urea was herein proposed. Such method allows the production of mechanically stable, lightweight MFC structures under low-cost ambient conditions drying. The influence of the cellulose fibril characteristics, the suspension formulation and the process parameters on the final foam properties have been studied in terms of porosity, density and mechanical properties.

Water-resistant cellulosic filter containing non-leaching antimicrobial starch for water purification and disinfection

Water-resistant cellulose foam paper was developed in this work in an attempt to improve the antimicrobial activity of cellulose foam paper for capture and deactivation of pathogenic microorganisms existed in water. Results indicated that the cellulose foam paper could significantly improve household water quality by incorporating guanidine-based polymer modified with starch or called antibacterial thermoplastic starch (ATPS) into fibre network in the presence of proper amount of fiber fines. Ring diffusion testing demonstrated that no ATPS diffused around or underneath of samples, verifying that cellulose foam filter added by ATPS were of non-leaching type. Furthermore, the viability of bacteria before and after filtering and the structure of cellulose foam paper were analyzed via fluorescence microscopy and scanning electron microscopy images. The findings further proved the effectiveness of antimicrobial cellulose foam in deactivating pathogens, E.coli in particular.

Ultra-lightweight cellulose foam material: preparation and properties

Ultra-lightweight cellulose foams were prepared by regeneration of sodium dodecyl sulfate (SDS)/cellulose/NaOH/urea blend solution via mechanical agitation and then freeze-drying. The morphology and properties of the blend solutions and foams were investigated via optical microscope, rheometer, BET and SEM. As a result, it was found that the inclusion complex structure between cellulose macromolecules and the solvent molecules was not destroyed. Moreover, the bubbles were about 20–50 μm in the solutions and larger (>100 μm) in the foams. Not only the micropores (bubbles) but also the nanopores could be observed in the wet and dried foams. The cellulose foams possessed ultra-low density of about 30 mg/cm3 and high specific surface area. The result of X-ray diffraction and Fourier transform infrared spectroscopy indicated that the cellulose foams were transited from cellulose I to cellulose II after dissolution and gelation. Bubbles inside the wet foams weakened the mechanical properties, but inversely increased the mechanical properties in the dried foams. Typical “J”-shaped curves were observed during the mechanical test, which revealed good compressive strength of dried foams. In this work, cellulose foams with ultra-lightweight and good mechanical properties were obtained, which exhibited great potentials for further development and comprehensive utilization of cellulose.

Application of Amine-Functionalized Cellulose Foam for CO2 Capture and Storage in the Brewing Industry

Application of Amine-Functionalized Cellulose Foam for CO₂ Capture and Storage in the Brewing Industry

Development of highly open polyhedral networks from vitreous carbon for orthopaedic applications

Highly open polyhedral networks were fabricated using an economical and environmentally friendly template route. Recycled cellulose foams were impregnated with a sucrose resin and then pyrolyzed in order to produce reticulated vitreous carbon foams with morphological features that closely resemble trabecular bone. Also, cell sizes ~1mm were achieved, a trait that will allow the mechanical reinforcement of such scaffolds using a biomaterial coating without compromising the pore size that favors osteoblast cell infiltration and growth (200-500µm). Moreover, initial studies showed that carbonization conditions have an effect on the mechanical properties of the synthesized foams and, therefore, such process parameters could be further evaluated towards the enhancement of the mechanical resistance of the scaffolds. The materials developed here are visualized as the porous component of a synthetic bone graft with features that could help overcome the current limitations associated with the medical treatments used for bone defect repair.

Material properties of the cell walls in nanofibrillar cellulose foams from finite element modelling of tomography scans

The mechanical properties of the nanofibrillar cellulose foam depend on the microstructure of the foam and on the constituent solid properties. The latter are hard to extract experimentally due to difficulties in performing the experiments on the micro-scale. The aim of this work is to provide methodology for doing it indirectly using extracted geometry of the microstructure. X-ray computed tomography scans are used to reconstruct the microstructure of a nanofibrillar cellulose foam sample. By varying the levels of thresholding, structure of differing porosities of the same foam structure are obtained and their macroscopic properties of the uni-axial compression are computed by finite element simulations. A power law relation, equivalent to classical foam scaling laws, are fit to the data obtained from simulation at different relative densities for the same structure. The relation thus obtained, is used to determine the cell wall material properties, viz. elastic modulus and yield strength, by extrapolating it to the experimental porosity and using the measured response at this porosity. The simulations also provide qualitative insights into the nature of irreversible deformations, not only corroborating the experimental results, but also providing possible explanation to the mechanisms responsible for crushable behaviour of the nanofibrillar cellulose foams in compression.

Modeling Growth Kinetics of Gas Hydrate in Porous Media: Experimental Validation

In this contribution, a rigorous kinetic model is proposed for carbon dioxide (CO2) based gas hydrate formation in porous media in the presence of a promoter. This model introduces the difference in chemical potential between the water in hydrate phase and liquid phase as the driving force. The effective surface area of porous material is proposed for the growth of CO2 hydrate, and this parameter plays a major role in making the model different with the existing kinetic models. A parameter set is identified for each of the porous materials used involving a system with various components at a reasonably high pressure. The proposed kinetic model is finally evaluated for four different porous materials (cellulose foam, silica gel, silica sand, and polyurethane foam) by comparing it with the available models with reference to the experimental data sets taken from the literature. It is investigated that this kinetic model consistently outperforms the existing models for a wide variety of conditions.

Crystalline structure and morphological properties of porous cellulose/clay composites: The effect of water and ethanol as coagulants

In this study, cellulose foams incorporated with surface-modified montmorillonite (SM-MMT) were prepared following NaOH dissolution and regeneration into water and ethanol. According to the SEM images, the type of coagulating agent significantly affected the morphological properties of composite foams. The crystalline parameters were evaluated using wide-angle X-ray diffraction (WAXD), which showed an increase in crystal size as the effect of SM-MMT; however, the crystal size decreased for the samples treated with ethanol. The distribution of hydrogen bond types was also investigated using Fourier transform infrared (FTIR). Resolving the hydrogen-bonded OH stretching band at around 3340 into five bands indicated that presence of SM-MMT caused the shift of OH-stretching vibration band to lower wave number due to new hydrogen bonds between cellulose and SM-MMT. In general, the results indicated a change in the contents of the intra- and inter-molecular hydrogen bonds when the coagulant was changed or SM-MMT was incorporated.

Development of PLA/cellulosic fiber composite foams using injection molding: Crystallization and foaming behaviors

Poly(lactic acid) (PLA) and northern bleached softwood kraft (NBSK) or black spruce medium density fiberboard (MDF) fibers were melt compounded using a co-rotating twin screw extruder and subsequently microcellular injection molded. Poly(ethlylene glycol) (PEG) was used as a lubricant. The microcellular structure, thermal properties, and crystallization behaviors were characterized using scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and wide angle X-ray diffraction. Results show that cellulosic fibers, acting as crystal nucleating agents, increased the crystallization temperature and the crystallinity and decreased the crystallization half time. The dissolved N2, the shear stress, and biaxial stretching during foaming also enhanced the crystallinity of PLA. Compared to PLA/PEG, a finer and more uniform cell structure was achieved in the cellulosic fiber composite foams. The improved foam morphology was attributed to the cell nucleating effects of the fibers and the increased melt strength by the addition of cellulosic fibers and by the gas- and fiber- induced crystallization.

Experimental characterisation of nanofibrillated cellulose foams

There is a growing interest in applications for nanofibrillated cellulose based materials owing to their exceptional mechanical properties. Nanofibrillated cellulose (NFC) foam is one such derivative which has potential applications in a wide array of fields. Here, we characterise the mechanical properties of two particular high porosity NFC foams (98.13 and 98.96 %) prepared by a freeze drying process. We evaluate their behaviour in uni-axial and bi-axial compression with cyclic loading. The secondary loading cycles reveal complete irreversible damage of the microstructure, with the secondary loading path being characterised by near zero plateau stress. In force controlled tests, negligible hysteresis corroborates the idea that there is no energy dissipation owing to near complete microstructural damage. Furthermore, we observe no indications of preferential orientation of the microstructure in these tests. The stress responses in mutually perpendicular directions are seen to be identical, within statistical considerations. We then utilise the “pseudo-elastic” model developed and adopt it to the case of highly compressible Ogden strain energy formulation with a modified neo-Hookean for the unloading, with a view of fitting a continuum hyperelastic model to the experimental data. The material parameters obtained from uni-axial data are seen to be insufficient to describe the more general bi-axial deformation. The parameters obtained from the bi-axial test describe uni-axial deformation up to stretches of ~0.5 but overestimate the stress levels beyond that point.

Nano‐crystalline cellulose, chemical blowing agent, and mold temperature effect on morphological, physical/mechanical properties of polypropylene

ABSTRACTPolypropylene (PP)/nano‐crystalline cellulose (NCC) composites and foams were produced through extrusion compounding combined with injection molding. From the samples produced, a complete morphological, physical, and mechanical analysis was performed to study the effect of NCC concentration (0–5wt %), foaming agent content (0 to 2wt %) and mold temperature (30°C and 80°C). NCC was very effective to reduce cell size (42–71%) and increase cell density (5–37 times) of the foams, while slightly increasing the overall density (2–7%). The results showed that NCC addition increased the specific tensile modulus (15–22%), specific tensile strength (1–14%) and specific flexural modulus (13–26%) of PP, but decreased specific impact strength (10–20%) and specific elongation at break (50–96%). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42845.

CO2 capture using the clathrate hydrate process employing cellulose foam as a porous media

A new biodegradable porous medium has been employed in this work for the hydrate-based gas separation (HBGS) process to capture carbon dioxide in a fixed bed column from a precombustion stream. Propane (2.5 mol%) was added as a promoter to reduce the operating pressure of the HBGS process. Experiments were conducted at 6 MPa and 274.2 K at different water saturation levels (50% and 100%) in a cellulose foam bed. It was found that a normalized rate of hydrate formation was more than double for 50% as compared to 100% water-saturated level. In addition, kinetic modelling of hydrate formation in porous media has been carried out using Avrami model by utilizing the experimental gas uptake data from current and published works. The Avrami model was found to fit the hydrate growth kinetics very well, up to 40 min of hydrate growth for different porous media like silica sand, polyurethane foam, and cellulose foam, and for different guest gas and gas mixtures.

Structure and liquid handling properties of water-insoluble carboxymethyl cellulose foam

A sodium carboxymethyl cellulose (Na-CMC) foam was obtained by lyophilization of aqueous Na-CMC solution and chemically treated with citric acid in order to control the water-solubility and liquid handling properties. The objective of this study was to prepare the water-insoluble CMC (H-CMC) foams and to investigate the liquid handling properties and their applicability to wound management materials. The chemical structure was analyzed by FT-IR, ICP, TGA, and XRD. The structural analyses revealed that the substitution of sodium atom in Na-CMC to hydrogen atom during the acid treatment resulted in more hydrogen bonding in the molecular structure. Acid concentration and treatment time influenced liquid handling properties of the foam. The increase in the amount of acid and treatment time decreased the liquid absorption capacities of the H-CMC foams. The expansion ratio and the liquid handling properties of compressed foam were affected by the compression temperature. The expansion ratio and the liquid absorption capacity decreased above 80 ℃ of compression temperature. The cytotoxicity test result confirmed the cell viability of extracted solution. This approach for controlling the shape stability and liquid handling properties by acid treatment of Na-CMC foam is expected to find useful applications in the development of novel moisture wound dressing materials.

Mechanisms behind the stabilizing action of cellulose nanofibrils in wet-stable cellulose foams.

The principal purpose of the investigation was to clarify the mechanisms behind the stabilizing action of cellulose nanofibrils (CNFs) in wet-stable cellulose foams. Following the basic theories for particle-stabilized foams, the investigation was focused on how the surface energy of the stabilizing CNF particles, their aspect ratio and charge density, and the concentration of CNF particles at the air-water interface affect the foam stability and the mechanical properties of a particle-stabilized air-liquid interface. The foam stability was evaluated from how the foam height changed over time, and the mechanical properties of the interface were evaluated as the complex viscoelastic modulus of the interface using the pendant drop method. The most important results and conclusions are that CNFs can be used as stabilizing particles for aqueous foams already at a concentration as low as 5 g/L. The major reasons for this were the small dimensions of the CNF and their high aspect ratio, which is important for gel-formation and the complex viscoelastic modulus of the particle-filled air-water interface. The influence of the aspect ratio was also demonstrated by a much higher foam stability of foams stabilized with CNFs than of foams stabilized by cellulose nanocrystals (CNC) with the same chemical composition. The charge density of the CNFs affects the level of liberation within larger aggregates and hence also the number of contact points at the interface and the gel formation and complex viscoelastic modulus of the air-water interface. The charges also result in a disjoining pressure related to the long-range repulsive electrostatic pressure between particle-stabilized bubbles and hence contribute to foam stability.

Nanoporous cellulose nanocomposite foams as high insulated food packaging materials

• Nanocomposite foam-like materials were prepared based on cellulose/SM-MMT. • The presence of SM-MMT improved the insulation performance of cellulose matrix by reducing the cell sizes. • The dispersed SM-MMT particles cooperated on the improvement of thermal, mechanical and barrier properties of cellulose matrix. In this study, cellulose nanocomposite foams incorporated with surface-modified montmorillonite (SM-MMT) were developed using high shear homogenizer method which can substantially delaminate clay platelets. The goal of this study was to improve the properties of cellulose matrix as well as reducing the bubble sizes to prepare nanofoams in order to enhance mechanical and barrier properties, and thermal insulation performance. Several methods were used to characterize the prepared foam materials including scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal conductivity, mechanical and barrier analysis. Raman spectroscopy was also used to evaluate structural differences between microcrystalline cellulose and nanocomposite foams. The results of thermal conductivity and morphology indicated that presence of SM-MMT improved thermal insulating properties due to reduction of average cell size. Thermal, mechanical and barrier properties were significantly enhanced for the nanocomposites filled with low content of SM-MMT compared to pure cellulose foam. The properties of these materials allow their use as a possible alternative to expanded polystyrene (EPS) foam trays for dry food packaging. Additional studies would be needed to improve the properties to use these materials with moist foods. The thermal conductivity values obtained for cellulose foams make them suitable to use for chilled chains.

Analysis of the compressive response of Nano Fibrillar Cellulose foams

Nano Fibrillar Cellulose (NFC) is fast emerging as a biomaterial with promising applications, one of which is cellular foam. The inner structure of the foam can take various shapes and hierarchical micro-structures depending on the manufacturing parameters. The compressive response of foams developed from these materials is currently a primary criterion for the material development. In this work, we focus on the connection between the non-linear part of the response and the inner structure of the material. We study the effect of internal contact and its contribution to gradual stiffening in the energy absorbing region and accelerated stiffening in the densification region of the large strain compressive response. We use the finite element method in this study and discuss the applicability and efficiency of different modelling techniques by considering well defined geometries and available experimental data. The relative contribution of internal contact is singled out and mapped onto the overall compressive response of the material. The effect of initial non-straightness of the cell walls is studied through superposing differing percentages of the buckling modes on the initial geometry. The initial non-straightness is seen to have a significant effect for only strains up to 1%. The secant modulus measured at slightly higher strains of 4%, demonstrates lesser effect from the non-straightness of cell walls. The simulations capture the compressive response well into the densification regime and there is an order of magnitude agreement in between simulations and experiments. We observed that internal contact is crucial for capturing the trend of compressive response.