Cellulose-based Aerogels Research Articles

Highly flame retardant zeolitic imidazole framework-8@cellulose composite aerogels as absorption materials for organic pollutants

In the current study, Zeolitic Imidazole Framework-8 (ZIF-8) was in situ grown on the surface of cellulose fibers and the ZIF-8@cellulose composite aerogels were fabricated by a freeze-drying method. The flame-retardant, thermal and mechanical characteristics of the cellulose-based aerogels were investigated. SEM images indicated that ZIF-8 was evenly deposited on the surface of the cellulose fibers in the aerogel owing to formation of hydrogen bonding with cellulose molecules. The addition of ZIF-8 enhanced thermal stability and flame retardancy of the host cellulose aerogel. The peak of heat release rate of the ZIF-8@cellulose-3 composite aerogel exhibited a drastic decline from 128 W g−1 to 63 W g−1 and the total heat release from 25.9 kJ g−1 to 14.8 kJ g−1. In the UL-94 vertical burning test, the samples showed self-extinguishing behavior. Additionally, ZIF-8 induced a dramatic enhancement in the mechanical properties of the host cellulose. Specifically, the compressive stress of the ZIF-8@cellulose composite aerogel showed a significant increase from 0.45 to 34.80 MPa. Moreover, the ZIF-8@cellulose composite aerogel can selectively remove the organic pollutants from water and adsorb a wide range of liquid oils with considerable capacities. The current study presented a feasible approach to synthesis of strong and flame-retardant cellulose-based aerogels for waste water purification.

Effect of lignin on the performance of biodegradable cellulose aerogels made from wheat straw pulp-LiCl/DMSO solution

To expound the effects of existing endogenous or exogenous lignin on the performance of cellulose-based aerogels, both the cellulose aerogels and composite aerogels were fabricated by the dissolution-regeneration process by using LiCl/DMSO solvent system. The varying content of endogenous and exogenous lignin could lead to different aggregation states of cellulose, hemicellulose and lignin, thus causing different micromorphology and mechanical properties of cellulose aerogels and composite aerogels. The increased endogenous lignin in lignocellulose restricted the dissociation of cellulose and hemicellulose in dissolving process, which led to the appearance of enlarged pores, and then resulted in the decreased mechanical strength. However, for composite aerogels, externally added exogenous lignin deposited on the cellulose chains and then restricted the movement of polymer chains. It could not only bring about the increased pore size of aerogels, but also help to improve the mechanical strength, which was different from that of cellulose aerogels. Furthermore, two types of aerogels with higher lignin content both exhibited better adsorption capacity for methylene blue, especially for composite aerogel. This study provides a feasible way to tailor the morphology and physical properties of the aerogels by controlling the existential state or content of lignin.

Cellulose-based aerogels from sugarcane bagasse for oil spill-cleaning and heat insulation applications

A promising and economic material for various applications, such as thermal insulation in construction building and oil clean-up in marine ecosystems, is successfully developed from the by-product of the sugarcane industry. Biodegradable sugarcane bagasse aerogels are produced using polyvinyl alcohol (PVA) binder, followed by a freeze-drying method. This environmental-friendly recycled aerogel has an ultra-low density ([0.016-0.112] g/cm3), a high porosity ([91.9–98.9]%), and a very low thermal conductivity ([0.031-0.042] W/mK). Its superhydrophobicity properties and its maximum oil absorption capacity (up to 25 g/g) are measured after coating aerogel samples with methyltrimethoxysilane (MTMS). The biodegradable aerogel has a Young's modulus of 88 K Pa and can be bent without breaking, demonstrating its high flexibility.

Methyltrimethoxysilane-coated recycled polyethylene terephthalate aerogels for oil spill cleaning applications

Recycled polyethylene terephthalate (rPET) aerogels are successfully developed using rPET fibers from plastic bottle wastes for oil spill cleaning applications. The rPET aerogels are formed via a freeze-drying process with polyvinyl alcohol (PVA) and glutaraldehyde (GA) crosslinking agents. After coating with methyltrimethoxysilane (MTMS), the MTMS-coated rPET aerogels exhibit hydrophobicity with a water contact angle of 133°–141° for oil absorption applications. The effects of the rPET fiber concentrations, fiber deniers and cross-linker contents on the oil absorption performance of the rPET aerogels are comprehensively quantified. The 0.5 wt% rPET aerogels show the largest oil absorption capacity of 79.4 g/g, approximately 7.0 and 3.2 times better than commercial sorbents, polypropylene pads and polypyrrole sponges, respectively and slightly larger than 0.5 wt% cellulose-based aerogels from paper waste. From the oil absorption kinetics of the rPET aerogels quantified by the pseudo-first and pseudo–second order models, the 0.5 wt% rPET aerogels can absorb oil up to 3.0 times faster than cellulose-based aerogels. In addition, rPET aerogels are also demonstrated to have a good absorption capacity for different organic solvents. These establish the novelty of the contribution and demonstrate that rPET aerogels can be promising materials for absorption applications due to their high absorption capacities, environmental-friendly and cost-effective fabrication method.

Versatile fabrication of anisotropic and superhydrophobic aerogels for highly selective oil absorption

Aerogels have shown great potential as oil absorbents, but they typically suffer from poor hydrophobicity and inferior mechanical property. Herein, anisotropic, superhydrophobic and superoleophilic fluorinated aerogels were prepared by directionally freeze-casting aqueous suspensions of graphene oxide and agarose in the presence of fluorine containing organosilane sol. The hydrogen bonding interactions between graphene oxide and agarose, and the directionally aligned porous structure gave the fluorinated aerogel prominent compression and recoverability properties. Due to its superoleophilicity, the fluorinated aerogel could collect a wide range of organic solvents and oils with excellent absorption capacities, which exceeded those of all cellulose-based aerogels and most carbon-based aerogels. The fluorinated aerogel also proved to be highly efficient in removing oil spills from water surface with outstanding selectivity due to its superhydrophobic and superoleophilic characteristics. Moreover, the high compression flexibility of the fluorinated aerogel facilitated fast and efficient recovery of the absorbed oil by simple mechanical squeezing, and ensured stable performance over repeated use. The present study provided a versatile method for design and fabrication of anisotropic, superhydrophobic and superoleophilic aerogels for environmental remediation and other potential applications.

Gas Permeability of Cellulose Aerogels with a Designed Dual Pore Space System.

The gas permeability of a porous material is a key property determining the impact of the material in an application such as filter/separation techniques. In the present study, aerogels of cellulose scaffolds were designed with a dual pore space system consisting of macropores with cell walls composing of mesopores and a nanofibrillar network. The gas permeability properties of these dual porous materials were compared with classical cellulose aerogels. Emulsifying the oil droplets in the hot salt–hydrate melt with a fixed amount of cellulose was performed in the presence of surfactants. The surfactants varied in physical, chemical and structural properties and a range of hydrophilic–lipophilic balance (HLB) values, 13.5 to 18. A wide range of hierarchical dual pore space systems were produced and analysed using nitrogen adsorption–desorption analysis and scanning electron microscopy. The microstructures of the dual pore system of aerogels were quantitatively characterized using image analysis methods. The gas permeability was measured and discussed with respect to the well-known model of Carman–Kozeny for open porous materials. The gas permeability values implied that the kind of the macropore channel’s size, shape, their connectivity through the neck parts and the mesoporous structures on the cell walls are significantly controlling the flow resistance of air. Adaption of this new design route for cellulose-based aerogels can be suitable for advanced filters/membranes production and also biological or catalytic supporting materials since the emulsion template method allows the tailoring of the gas permeability while the nanopores of the cell walls can act simultaneously as absorbers.

Superabsorbent food packaging bioactive cellulose-based aerogels from Arundo donax waste biomass

A.donax waste biomass has been valorized for the extraction of cellulosic fractions with different purification degrees, as well as aqueous bioactive extracts, which were then combined to develop superabsorbent bioactive aerogels. All the developed aerogels presented excellent water and oil sorption capacities; however, the presence of hemicelluloses yielded more porous and hydrophilic aerogels, capable of absorbing more water. With regards to the aqueous extracts, the hot water treatment (HW) of A. donax stems promoted the extraction of polysaccharides and polyphenols, producing the extract (S-HW) with the highest antioxidant capacity. This extract was then incorporated into the aerogels produced from the less purified stem fractions (F2A and F3A), which were chosen due to their good water sorption capacity, higher antioxidant potential and lower production costs and environmental impact. The hybrid aerogels showed a great potential to be used as bioactive pads for food packaging. In particular, the F2A + S-HW aerogel would be the most optimum choice since it provides a complete release of the extract in hydrophilic media, as demonstrated by in-vitro release and β-carotene bleaching inhibition studies, and it is able to reduce the colour loss and lipid oxidation in red meat upon refrigerated storage to a greater extent.

Remodeling of raw cotton fiber into flexible, squeezing-resistant macroporous cellulose aerogel with high oil retention capability for oil/water separation

Cellulose-based aerogels reveal great potential as sorbents for oil sorption due to their biodegradability and the renewability of raw material. Nevertheless, the widely reported aerogels are synthesized by using nanocellulose separated from natural fiber and cellulose derivative, and the relatively high cost limits their application in oil cleanup. Herein, we report a simple and low-cost route to prepare superhydrophobic cellulose aerogel by using raw cotton fiber as starting material. The as-prepared aerogel can absorb various oils and organic solvents and the sorption capacities can reach up to 19.8–41.5 times the weight of initial aerogel. The aerogels also reveal fast sorption rate, good oil-retention ability, and excellent recyclability. Especially, the superior hydrophobiciy endows the fabricated aerogel with high selectivity for oil sorption from water. Besides, the aerogels possess good chemical durability and can resist corrosive solutions and various oils. After the abrasion of 80 cycles, the resultant aerogel still can maintain its original hydrophobicity. Due to easy availability of cotton fiber, good oil sorption performance, and cost-effective preparation process, the raw cotton fiber-derived aerogel can be regarded as promising alternative for organic synthetic materials to oil spill cleanup and oily wastewater purification.

Sustainable Approach for Cellulose Aerogel Preparation from the DBU–CO2 Switchable Solvent

We report a sustainable and easy approach for the preparation of cellulose-based aerogels from the DBU–CO2 switchable solvent system via a solubilization and coagulation approach followed by freeze-drying. The easy, fast, and mild solubilization step (15 min at 30 °C) allows for a rapid preparation procedure. The effect of various processing parameters, such as cellulose concentration, coagulating solvent, and the superbase, on important aerogel characteristics including density, porosity, pore size, and morphology, were investigated. Density values obtained ranged between 0.05 and 0.12 g/cm3, with porosity values between 92% and 97%. The morphology of the obtained cellulose aerogels was studied using scanning electron microscopy (SEM) showing a random and open large macroporous cellulose network with pore sizes ranging between 1.1 and 4.5 μm, depending on the processing conditions. In addition, specific surface areas determined by N2 adsorption applying the BET equation ranged between 19 and 26 m2/g. The...

CuS‐functionalized cellulose based aerogel as biocatalyst for removal of organic dye

ABSTRACTCuS‐functionalized cellulose based aerogel (CBA) with 3D macroporous structure was synthesized by in situ deposition of visible light responsive CuS photocatalyst. Hexagonal CuS was deposited onto the outer and inner walls of CBA matrix. CuS/CBA composite catalyst has hierarchical porous structure and abundance in functional groups supporting CuS on CBA surface that enhance photodecomposition of methylene blue (MB). The CuS/CBA composite was characterized by XRD, FTIR, SEM‐EDS, Atomic Absorption Analysis, and XPS analysis. Photodegradation rate of MB by CuS/CBA composite catalyst in visible light was 94.1%, whereas, 67.4% for pure CuS. Initial MB concentration effects, pH change, and variations in CuS/CBA dosage on overall reaction kinetics were also studied. CuS/CBA composite catalyst carried out Photo‐Fenton like reactions which decomposed 97% MB within 6 min, by producing hydroxyl radicals from chemical and photocatalytic reactions. CuS/CBA composite catalyst was recycled and reused. It retained over 80% MB degradation rate even after five consecutive cycles. CuS/CBA composite can be used as biocatalyst for removal of organic dyes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47404.

Highly Compressible and Hydrophobic Anisotropic Aerogels for Selective Oil/Organic Solvent Absorption

Cellulose-based aerogels show great potential as absorbents for oil and chemical spill cleanup due to their low density and excellent absorption capacity. However, the hydrophility and inferior mechanical properties have often limited their practical applications. In this study, high-performance biomass-based aerogels were prepared by freeze-casting aqueous suspensions of polyvinyl alcohol and cellulose nanofibrils in the presence of hydrolyzed methyltrimethoxysilane sol. Successful silylation on the substrate surface was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermal stability, and water contact angle measurements. Freeze-casting successfully assembled a highly aligned interconnected porous structure, resulting in the prepared aerogels with high modulus and strength in the aligned direction (along the freezing direction) and outstanding compression flexibility in the perpendicular direction (transverse to the freezing direction). The ultralow density (10.2...

Cellulose Aerogels for Thermal Insulation in Buildings: Trends and Challenges

Cellulose-based aerogels hold the potential to become a cost-effective bio-based solution for thermal insulation in buildings. Low thermal conductivities (<0.025 W·m−1·K−1) are achieved through a decrease in gaseous phase contribution, exploiting the Knudsen effect. However, several challenges need to be overcome: production energy demand and cost, moisture sensitivity, flammability, and thermal stability. Herein, a description and discussion of current trends and challenges in cellulose aerogel research for thermal insulation are presented, gathered from studies reported within the last five years. The text is divided into three main sections: (i) an overview of thermal performance of cellulose aerogels, (ii) an identification of challenges and possible solutions for cellulose aerogel thermal insulation, and (iii) a brief description of cellulose/silica aerogels.

A facile approach to light weight, high porosity cellulose aerogels

This work reported a facile approach to make cellulose-based aerogels in NaOH/urea aqueous solution via freeze-drying hydrogels, which were obtained by mixing N,N′-methylene bisacrylamide (MBA) with cellulose solution at room temperature. The cellulose solution showed pronounced MBA-induced gelation behaviors. The obtained cellulose aerogels possessed a three dimensional network with macroporous structure (20–600 μm), low density (0.0820–0.0083 g/cm3), high porosity (90.3%–99.02%), moderate thermal stability (275 °C) and certain absorbency to Cu (II) (85 mg/g) and methylene blue (MB) (115 mg/g). Cellulose aerogels with different morphologies can be obtained by adjusting the cross-linking degree and the concentration of cellulose. This kind of aerogel provides an excellent matrix for the functionalization of cellulose-based aerogel.

Kinetic, isotherm, and thermodynamic studies of the adsorption of dyes from aqueous solution by cellulose-based adsorbents

In this study, a highly efficient and eco-friendly porous cellulose-based aerogel was synthesized by grafting polyethyleneimine onto quaternized cellulose (PQC) to remove the anionic dye Congo Red (CR). The prepared aerogel had a good flexibility and formability. The adsorbents were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and elemental analysis. The results showed that there were many amino groups on CE/PQC aerogel and the structure was porous, which increased the adsorption capacity. The effects of initial concentration, adsorbent dose, contact time, temperature, and pH on the dye sorption were all investigated. The adsorption mechanism was also explored, including adsorption kinetics, adsorption isotherms and thermodynamic studies of adsorption. The results showed that the adsorption kinetics and isotherms fitted the pseudo-second-order kinetic model and Langmuir isotherm, respectively. The Langmuir isotherm revealed that the maximum theoretical adsorption capacity of the aerogels for CR was 518.403 mg g-1. The thermodynamic parameters including Gibbs free energy change (ΔG0), enthalpy change (ΔH0) and entropy change (ΔS0), showed the adsorption process was exothermic and spontaneous. These results imply that this new absorbent can be universally and effectively used for the removal of dyes from industrial textile wastewater.

Mechanically Resistant and Sustainable Cellulose-Based Composite Aerogels with Excellent Flame Retardant, Sound-Absorption, and Superantiwetting Ability for Advanced Engineering Materials

The production of cellulose-based aerogels from the conversion of cheap and rich precursors using environmentally friendly techniques is a very attractive subject in materials chemistry. In this work, we report a facile strategy to construct flame retardant, sound-adsorption, and mechanical enhancement cellulose-based composite aerogels by the incorporation of aluminum hydroxide nanoparticles (AH NPs) into cellulose gels via an in situ sol–gel process, followed by freeze-drying to coat AH NPs on cellulose composite aerogels (AH NPs@cellulose composite aerogels). The results demonstrated that the AH NP homogeneous dispersion within cellulose aerogels and the presence of AH NPs did not have a remarkable influence on the homogeneous porous structure of cellulose aerogels when compared with cellulose aerogels prepared from the NaOH/urea/thiourea solution. The prepared composite cellulose aerogels showed excellent flame retardancy, the peak of heat release rate (PHRR) of the composite aerogels decreased signif...

Preparation and characterization of thermo- and pH dual-responsive 3D cellulose-based aerogel for oil/water separation

Oily wastewater caused by industrial production and crude oil leakage has attracted worldwide attention. Here, a thermo- and pH dual-responsive biodegradable cellulose-based aerogel for oil–water separation was designed and prepared via surface-initiated atom transfer radical polymerization (ATRP) of non-fluorine-containing 2-dimethylaminoethyl methacrylate (DMAEMA). The cellulose-based aerogel exhibit switchable superhydrophilicity with a water contact angle (WCA) of 0° and hydrophobicity (WCA 130°) by modulating pH or temperature. The functionalized cellulose-based aerogels could be used to absorb the water under 60 °C (pH 7.0) and pH is 1.0 (T = 25 °C), while absorb oil underwater when the temperature is above 60 °C (pH 7.0) or pH is 13.0 (T = 25 °C). So this adsorbent were suitable for the separation of water-rich or oil-rich oil/water mixtures, and it could adsorb oil over ten times its own weight, and had a good reusability. What’s more, the cellulose-based aerogel is green, low cost, and environmental friendly, which makes it a promising candidate to be used for oil–water separation.

Nanocellulose Aerogels Inspired by Frozen Tofu

Cellulose-based aerogels are reported that were generated using cellulose nanofibril (CNF) gels in an ambient drying process. These nancellulose aerogels were inspired by the preparation of a traditional Chinese food, frozen tofu, which undergoes significant toughening after freezing and thawing. It is this toughening mechanism that allows for the formation of nanocellulose aerogels which ordinarily would collapse upon ambient drying. By freezing hydrated CNF gel dispersions, solvent exchanging, and drying at ambient pressure, monolithic nanocellulose aerogels with high porosity (>98%), low density (as low as 0.018 g cm–3), and high surface area (>30 m2 g–1) were readily generated. Moreover, since no special reactors are required, these structures can be easily created over large areas. For example, a hydrated CNF gel was frozen at −72 °C, and then, the frozen gel was immersed directly in a 2-propanol bath to allow solvent exchange. The resulting alcohol-infused gel was dried at ambient pressure to fabric...

Thermal conductivity of Kelvin cell cellulosic aerogels: analytical and Monte Carlo approaches

New organic aerogel using cellulose derivatives as precursors have promising insulating properties even at atmospheric pressure. In order to go further in the knowledge of their thermal behaviour, a relevant numerical model for estimating the phonon thermal conductivity of cellulose-based aerogels has been developed. The model accounts for the characteristic solid matrix at the local scale by using Kelvin cell representation of the porous structure. The cell size varies between 57 and 500 nm. The phonon heat transfer in the solid phase is treated by solving numerically the Boltzmann equation. The numerical results are confronted with previous analytical model and experimental measurements of the conductivity conducted on suitable aerogel samples.

Resource recovery of Eichhornia crassipes as oil superabsorbent

The elastic cellulose-based aerogels (CBAs) with highly porous (99.56%) and low-density (0.0065gcm−1) were prepared using Eichhornia crassipes as cellulose source and polyvinyl alcohol directly as cross-linker via a facile and environment-friendly process. The prepared CBAs exhibited excellent oil/solvent sorption capacities (60.33–152.21gg−1), super-hydrophobicity (water contact angle of 156.7°) as well as remarkable reusability. More importantly, the absorbed oil could be quickly recovered by simple squeezing without significantly structure damage (at least 16 times). All these merits make CBAs very promising materials for oil spillage cleaning.

APLICAÇÃO DE AEROGÉIS PARA REMOÇÃO DE PITCH NA INDÚSTRIA DE CELULOSE E PAPEL

O licor negro formado na polpação da indústria de celulose e papel contém pitchs, materiais resinosos em estado coloidal, derivados da madeira, que se acumulam nos maquinários da indústria, danificando-os ou o produto final. O objetivo do trabalho foi estudar o uso de aerogéis à base de celulose na remoção dos pitchs, função exercida pelo talco na maioria das indústrias. Os aerogéis são sólidos porosos, produzidos a partir de liofilização de uma suspensão coloidal de celulose nanofibrilada e xilanas, em diferentes proporções, e resina PAE - poliamina-epiclorohidrina. A contagem dos pitchs foi feita com uma câmara de Neubauer. Todos os aerogéis apresentaram poder de adsorção, de modo que quanto maior o teor de CNF-Celulose Nanofibrilada, melhor o adsorvente. De modo geral, os aerogéis 100:0 (CNF:Xilana) são melhores adsorventes que os aerogéis 30:70. Não foi observada uma proporção entre massa e capacidade de adsorção, sugerindo a existência de quantidades específicas para cada aerogel.