Showing papers in "Cellulose in 2012"
TL;DR: In this paper, the influence of reaction time on the morphology, crystallinity, and thermal stability of cellulose nanocrystals (CNCs) was investigated and the optimal extraction time was found to be around 40min during hydrolysis at 45°C with 65% sulfuric acid.
Abstract: Cellulose nanocrystals (CNC) were first isolated from kenaf bast fibers and then characterized. The raw fibers were subjected to alkali treatment and bleaching treatment and subsequent hydrolysis with sulfuric acid. The influence of the reaction time on the morphology, crystallinity, and thermal stability of CNC was investigated. Fourier transform infrared spectroscopy showed that lignin and hemicellulose were almost entirely removed during the alkali and bleaching treatments. The morphology and dimensions of the fibers and acid-released CNC were characterized by field emission scanning electron microscopy and transmission electron microscopy. X-Ray diffraction analysis revealed that the crystallinity first increases upon hydrolysis and then decreases after long durations of hydrolysis. The optimal extraction time was found to be around 40 min during hydrolysis at 45 °C with 65% sulfuric acid. The thermal stability was found to decrease as the hydrolysis time increased. The electrophoretic mobility of the CNC suspensions was measured using the zeta potential, and it ranged from −8.7 to −95.3 mV.
661 citations
TL;DR: In this article, a critical analysis of the intermolecular interactions involved and mechanisms of dissolution of cellulose molecules is presented, showing that cellulose is significantly amphiphilic and hydrophobic.
Abstract: Despite being the world’s most abundant natural polymer and one of the most studied, cellulose is still challenging researchers. Cellulose is known to be insoluble in water and in many organic solvents, but can be dissolved in a number of solvents of intermediate properties, like N-methylmorpholine N-oxide and ionic liquids which, apparently, are not related. It can also be dissolved in water at extreme pHs, in particular if a cosolute of intermediate polarity is added. The insolubility in water is often referred to strong intermolecular hydrogen bonding between cellulose molecules. Revisiting some fundamental polymer physicochemical aspects (i.e. intermolecular interactions) a different picture is now revealed: cellulose is significantly amphiphilic and hydrophobic interactions are important to understand its solubility pattern. In this paper we try to provide a basis for developing novel solvents for cellulose based on a critical analysis of the intermolecular interactions involved and mechanisms of dissolution.
440 citations
TL;DR: In this article, four methods were examined to dry cellulose nanocrystal and nanofibrillated cellulose suspensions: (1) oven drying, (2) freeze drying (FD), (3) supercritical drying (SCD), and (4) spray-drying (SD).
Abstract: Increasing research activity on cellulose nanofibril-based materials provides great opportunities for novel, scalable manufacturing approaches. Cellulose nanofibrils (CNFs) are typically processed as aqueous suspensions because of their hydrophilic nature. One of the major manufacturing challenges is to obtain dry CNFs while maintaining their nano-scale dimensions. Four methods were examined to dry cellulose nanocrystal and nanofibrillated cellulose suspensions: (1) oven drying, (2) freeze drying (FD), (3) supercritical drying (SCD), and (4) spray-drying (SD). The particle size and morphology of the CNFs were determined via dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and morphological analysis. SCD preserved the nano-scale dimensions of the cellulose nanofibrils. FD formed ribbon-like structures of the CNFs with nano-scale thicknesses. Width and length were observed in tens to hundreds of microns. SD formed particles with a size distribution ranging from nanometer to several microns. Spray-drying is proposed as a technically suitable manufacturing process to dry CNF suspensions.
373 citations
TL;DR: In this paper, a novel type of sponge-like material for the separation of mixed oil and water liquids has been prepared by the vapour deposition of hydrophobic silanes on ultra-porous nanocellulose aerogels.
Abstract: A novel type of sponge-like material for the separation of mixed oil and water liquids has been prepared by the vapour deposition of hydrophobic silanes on ultra-porous nanocellulose aerogels. To achieve this, a highly porous (>99%) nanocellulose aerogel with high structural flexibility and robustness is first formed by freeze-drying an aqueous dispersion of the nanocellulose. The density, pore size distribution and wetting properties of the aerogel can be tuned by selecting the concentration of the nanocellulose dispersion before freeze-drying. The hydrophobic light- weight aerogels are almost instantly filled with the oil phase when selectively absorbing oil from water, with a capacity to absorb up to 45 times their own weight in oil. The oil can also be drained from the aerogel and the aerogel can then be reused for a second absorption cycle.
329 citations
TL;DR: In this article, a review of various mechanical, chemical, and biological approaches for the preparation and separation of macro-, micro-, and nano-sized fibers from raw bamboo are summarized.
Abstract: Natural plant fibers have unequivocally contributed economic prosperity and sustainability in our daily lives. Particularly, bamboo fibers have been used for industrial applications as diverse as textiles, paper, and construction. Recent renewed interest in bamboo fiber (BF) is primarily targeted for the replacement or reduction in use of glass fiber from non-renewable resources. In this review, various mechanical, chemical, and biological approaches for the preparation and separation of macro-, micro-, and nano-sized fibers from raw bamboo are summarized. The differences in the mechanical, thermal, and other properties of fibers from different materials are linked to their size, aspect ratio, surface charge and groups, and their function in nature. Biocomposites made of BF are considered to be green, environmentally responsible eco-products. Different processing parameters such as fiber extraction, surface modification, and synthesis of the composites affect the characteristics of composites. Fiber length, orientation, concentration, dispersion, aspect ratio, selection of matrix, and chemistry of the matrix must all be considered during fabrication in order to achieve desirable functionalities and performance. Because of the hydrophilic nature of BF, different methods may be adopted to improve interfacial surface adhesion. A better understanding of the fiber structure and characteristics that influence composite performance could lead to the development of additives, coatings, binders, or sizing suitable for natural fiber and a variety of polymeric matrices.
293 citations
TL;DR: The assertion that little-recognized (or under-estimated) hydrophobic interactions have been the reason for a tardy development of cellulose solvents provides the platform for a debate in the hope that new scientific endeavors are stimulated on this important topic.
Abstract: The hypothesis advanced in this issue of CELLULOSE [Springer] by Bjorn Lindman, which asserts that the solubility or insolubility characteristics of cellulose are significantly based upon amphiphilic and hydrophobic molecular interactions, is debated by cellulose scientists with a wide range of experiences representing a variety of scientific disciplines. The hypothesis is based on the consideration of some fundamental polymer physicochemical principles and some widely recognized inconsistencies in behavior. The assertion that little-recognized (or under-estimated) hydrophobic interactions have been the reason for a tardy development of cellulose solvents provides the platform for a debate in the hope that new scientific endeavors are stimulated on this important topic.
244 citations
TL;DR: In this paper, the production of cellulose nanofibrils (CNF) from a bleached eucalyptus pulp using a commercial stone grinder was reported.
Abstract: This study reports the production of cellulose nanofibrils (CNF) from a bleached eucalyptus pulp using a commercial stone grinder Scanning electronic microscopy and transmission electronic microscopy imaging were used to reveal morphological development of CNF at micro and nano scales, respectively Two major structures were identified: (1) highly kinked, naturally helical, and untwisted fibrils that serve as backbones of CNF networks, and (2) entangled, less distinctively kinked (or curled) and twisted “soft looking” nanofibrils These two major structures appeared in different features of CNF network such as “trees”, “net”, “flower”, single fibril, etc Prolonged fibrillation can break the nanofibrils into nanowhiskers from the untwisted fibrils with high crystallinity Energy input for mechanical fibrillation is on the order of 5–30 kWh/kg The gradual reduction in network size of CNF with time may be used to fractionate CNF
239 citations
TL;DR: In this paper, the tensile index, elongation and elastic modulus of nanofibrillated cellulose (NFC) and nanopaper were compared and the effect of residual cell wall components accessed.
Abstract: Unbleached (UN), oxygen-delignified and fully-bleached (FB) birch fibers with a residual lignin content of ca. 3, 2 and <1 %, respectively, were used to produce nanofibrillated cellulose (NFC) and nanopaper by using an overpressure device. The tensile index, elongation and elastic modulus of nanopaper were compared and the effect of residual cell wall components accessed. Under similar manufacturing conditions, UN NFC produced nanopaper with a density of 0.99 g/cm3, higher than that from FB NFC (0.7 g/cm3). This translated in much lower air permeability in the case of UN nanopaper (1 and 11 mL/min for UN and FB samples, respectively). Fundamentally, these observations are ascribed to the finer fibrils produced during microfluidization of UN fibers compared to those from lower yield counterparts (AFM roughness of 8 and 17 nm and surface areas of 124 and 98 m2/g for NFC from UN and FB fibers, respectively). As a result, values of stress at break and energy absorption of nanopaper from high yield fibers are distinctively higher than those from fully bleached NFC. Interactions of water with the surface and bulk material were affected by the chemical composition and structure of the nanofibrils. While UN nanopaper presented higher water contact angles their sorption capacity (and rate of water absorption) was much higher than those measured for nanopaper from FB NFC. These and other observations provided in this contribution are proposed to be related to the mechanoradical scavenging capacity of lignin in high shear microfluidization and the presence of residual heteropolysaccharides.
198 citations
TL;DR: In this article, aqueous suspensions of cellulose nano-crystals (CNCs) were fabricated from both native and mercerized cotton fibers by sulfuric acid hydrolysis, followed by high-pressure homogenization.
Abstract: Stable aqueous suspensions of cellulose nano-crystals (CNCs) were fabricated from both native and mercerized cotton fibers by sulfuric acid hydrolysis, followed by high-pressure homogenization. Fourier transform infrared spectrometry and wide-angle X-ray diffraction data showed that the fibers had been transformed from cellulose I (native) to cellulose II (mercerized) crystal structure, and these polymorphs were retained in the nanocrystals, giving CNC-I and CNC-II. Transmission electron microscopy showed rod-like crystal morphology for both types of crystals under the given processing conditions with CNC-II having similar width but reduced length. Freeze-dried agglomerates of CNC-II had a much higher bulk density than that of CNC-I. Thermo-gravimetric analysis showed that CNC-II had better thermal stability. The storage moduli of CNC-II suspensions at all temperatures were substantially larger than those of CNC-I suspensions at the same concentration level. CNC-II suspensions and gels were more stable in response to temperature increases. Films of CNC and Poly(ethylene oxide) were tested. Both CNC-I/PEO and CNC-II/PEO composites showed increased tensile strength and elongation at break compared to pure PEO. However, composites with CNC-II had higher strength and elongation than composites with CNC-I.
197 citations
TL;DR: In this article, a SEM examination of the fracture surface of a slowly-dried cellulose film showed a surprisingly regular fan-like pattern which was shown to be characteristic of cross-sections of the left-handed helicoidal arrangement of nanocrystals, where the helicoidal axis was almost perpendicular to the film surfaces.
Abstract: The chiral nematic self-assembly of aqueous suspensions of cellulose nanocrystals is partially preserved on evaporation of water, but the ordering of the rod-like nanoparticles may become distorted by changes in volume, ionic strength and surface and convective forces during evaporation, thus affecting the morphology and optical properties of the dried film. Proposed applications for these solids with chiral nematic order require confirmation of their structure. A SEM examination of the fracture surface of a slowly-dried film showed a surprisingly regular fan-like pattern which is shown to be characteristic of cross-sections of the left-handed helicoidal arrangement of nanocrystals, where the helicoidal axis was almost perpendicular to the film surfaces. Superimposed on this pattern was what appeared to be a regular porosity, which is postulated to result from pull-out of the nanocrystals oriented orthogonal to the fracture surface.
192 citations
TL;DR: In this article, a comparative analysis of the morphology and structure between the obtained microcrystalline cellulose (MCC) and SNCC was carried out, which indicated that the SNCC suspension exhibited higher stability than the MCC suspension.
Abstract: Microcrystalline cellulose (MCC) and spherical nanocrystalline cellulose (SNCC) were successfully prepared from waste cotton fabrics through acid hydrolysis. The comparative analysis of the morphology and structure between the obtained MCC and SNCC was carried out. The SNCC suspension exhibited higher stability than the MCC suspension. Transmission electron microscopy in combination with atomic force microscopy showed that the cellulose nanospheres with average size of 35 nm were achieved, while the average particle size of MCC was 49 μm. The MCC and SNCC had similar functional groups and crystalline structure as confirmed by Fourier transform infrared spectroscopy and X-ray diffraction analysis, respectively. Viscometric average molecular weight measurement and thermo gravimetric analysis indicated that the degree of polymerization and thermal stability of SNCC was lower than that of MCC. These results should improve understanding of the characteristics of MCC and SNCC derived from waste cotton fabrics and lead to many new applications.
TL;DR: In this article, the surface charge of the nanocrystals was determined by conductometric titration and zeta potential measurements, and the influence of the reaction parameters on the CNC characteristics was discussed and compared with the data reported in the literature.
Abstract: Bamboo cellulose nanocrystals (CNCs) were successfully prepared from the sulfuric acid hydrolysis of bamboo bleached fibers. Reaction parameters such as temperature, acid-to-pulp ratio and hydrolysis time were varied over a limited range and conditions for the preparation of individual bamboo nanorods with a yield of 30 % were identified. The characteristics of bamboo CNCs were compared with those of CNCs obtained from three other sources, namely eucalyptus, sisal and curaua, prepared using already reported conditions. The shape and size of all four types of CNCs were investigated by complementary techniques, namely transmission electron microscopy, atomic force microscopy, dynamic light scattering and X-ray diffraction. The surface charge of the nanocrystals was determined by conductometric titration and zeta potential measurements. In all cases, negatively charged ribbon-like nanoparticles constituted of a few laterally associated elementary crystallites were observed. The influence of the reaction parameters on the CNC characteristics was discussed and compared with the data reported in the literature.
TL;DR: In this paper, composites of nanofibrillated cellulose (NFC) and Ag nanoparticles (NP) were prepared for the first time via the electrostatic assembly of Ag NP (aqueous colloids) onto NFC.
Abstract: Nanofibrillated cellulose offers new technological solutions for the development of paper products. Here, composites of nanofibrillated cellulose (NFC) and Ag nanoparticles (NP) were prepared for the first time via the electrostatic assembly of Ag NP (aqueous colloids) onto NFC. Distinct polyelectrolytes have been investigated as macromolecular linkers in order to evaluate their effects on the building-up of Ag modified NFC and also on the final properties of the NFC/Ag composite materials. The NFC/Ag nanocomposites were first investigated for their antibacterial properties towards S. aureus and K. pneumoniae microorganisms as compared to NFC modified by polyelectrolytes linkers without Ag. Subsequently, the antibacterial NFC/Ag nanocomposites were used as fillers in starch based coating formulations for Eucalyptus globulus-based paper sheets. The potential of this approach to produce antimicrobial paper products will be discussed on the basis of complementary optical, air barrier and mechanical data.
TL;DR: In this article, the potential of simultaneously recovering cellulosic solid residues (CSR) and producing cellulose nanocrystals (CNCs) by strong sulfuric acid hydrolysis to minimize cellulose loss to near zero was demonstrated.
Abstract: This study demonstrated the potential of simultaneously recovering cellulosic solid residues (CSR) and producing cellulose nanocrystals (CNCs) by strong sulfuric acid hydrolysis to minimize cellulose loss to near zero. A set of slightly milder acid hydrolysis conditions than that considered as “optimal” were used to significantly minimize the degradation of cellulose into soluble sugars that cannot be economically recovered, but resulted in CSR that is easily recoverable through conventional centrifuge. It was found that the window for simultaneous recoveries of CSR and producing high yield CNC in strong acid hydrolysis was extremely narrow. However, we achieved significant CSR yield with near zero cellulose loss but without sacrificing CNC yield compared with that obtained at “optimal condition”. The resultant CSR contains sulfate ester groups that facilitated subsequent mechanical nano-fibrillation to cellulose nanofibrils (CNFs), a potential high value nanocellulosic material for a variety of applications.
TL;DR: In this paper, the rheological properties of microfibrillated cellulose suspensions under stepped flow and constant shear were studied using a combination of rotational dynamic rheometer and digital imaging.
Abstract: In this work, the rheological properties of microfibrillated cellulose suspensions under stepped flow and constant shear were studied using a combination of rotational dynamic rheometer and digital imaging. During each rheological measurement, the structure of the suspension was monitored through a transparent outer cylinder with a digital camera. This enabled simultaneous analysis of the suspension floc size distribution and traditional rheological characterization. In stepped flow conditions, a good correlation between suspension floc structure and flow curve measurement was found. At constant shear, the suspension structure was dependent on the shear rate and concentration of the suspension. A low shear rate resulted in heterogeneous floc structure, which was also detected by an increase in the ratio of the viscous component to elastic component in the rheological measurement. At low concentrations and 0.5 s−1 shear rate, flow induced a formation of floc cylinders between the rotating cylinder and stationary cup surface.
TL;DR: In this article, the authors analyzed how the charge content of cellulose nanofibers influences the mechanical energy needed to disintegrate a cellulose fiber and developed an efficient and energetically friendly production process that overcomes the extensive energy consumption of shear-based existing processes.
Abstract: Cellulose nanofibers have a bright future ahead as components of nano-engineered materials, as they are an abundant, renewable and sustainable resource with outstanding mechanical properties. However, before considering real-world applications, an efficient and energetically friendly production process needs to be developed that overcomes the extensive energy consumption of shear-based existing processes. This paper analyses how the charge content influences the mechanical energy that is needed to disintegrate a cellulose fiber. The introduction of charge groups (carboxylate) is achieved through periodate oxidation followed by chlorite oxidation reactions, carried out to different extents. Modified samples are then subjected to different levels of controlled mechanical energy and the yields of three different fractions, separated by size, are obtained. The process produces highly functionalized cellulose nanofibers based almost exclusively on chemical reactions, thus avoiding the use of intensive mechanical energy in the process and consequently reducing drastically the energy consumption.
TL;DR: In this article, the stabilizing role of carboxymethyl groups on conformal deposition of Ag NPs over cellulosic fibers was elucidated while developing a method for the deposition of silver nanoparticles (NPs) on cellulose acetate (CA), cellulose and partially carboxylicated cellulose (CMC) electrospun fibers.
Abstract: The stabilizing role of carboxymethyl groups on the conformal deposition of Ag NPs over cellulosic fibers was elucidated while developing a method for the deposition of silver nanoparticles (NPs) on cellulose acetate (CA), cellulose and partially carboxymethylated cellulose (CMC) electrospun fibers. CMC fibers were prepared through judicious anionization of deacetylated cellulose acetate fibers. Ag NPs were chemically reduced from silver nitrate using sodium borohydride and further stabilized using citrate. Ag NPs were directly deposited onto CA, cellulose and CMC electrospun fibers at pH conditions ranging from 2.5 to 9.0. The resulting composites of Ag/fiber were characterized by field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX). The results revealed that the amount of Ag agglomerates and NPs deposited on CMC fibers was higher than that deposited on cellulose fibers at similar pH conditions, and that barely any Ag agglomerates or NPs were deposited on the CA fibers. These results implied that functional groups on the cellulose backbone played two important roles in the deposition of NPs as follows: (1) Hydrogen bonding was the main driving force for agglomeration of NPs when the medium pH was below 4.4, which corresponds to the pKa of carboxylic acid groups; (2) Carboxymethyl groups could replace citrate groups as stabilizers allowing the fabrication of a uniform and evenly distributed Ag NPs layer over CMC fibers at higher pH values. This report also highlights the importance of the substrate’s surface charge and that of the pH of the medium used, on the deposition of NPs. The composite of Ag NPs on CMC electrospun fibers appears to be a promising candidate for wound dressing applications due to its superior antibacterial properties originated by the uniform and even distribution of Ag NPs on the surface of the fibers and the wound healing aptness of the CMC fibers.
TL;DR: A mechanism for chemical attachment and growth of a Cu-BTC Metal-Organic Framework, also known as MOF-199 or HKUST-1, onto cellulosic substrates is reported in this paper.
Abstract: A mechanism for chemical attachment and growth of a Cu-BTC Metal–Organic Framework, also known as MOF-199 or HKUST-1, onto cellulosic substrates is reported. Four different experimental procedures were attempted in order to elucidate the role of carboxylate groups on the anionic cellulose’s surface. The order of addition of Cu(OAc)2—copper acetate, BTH3, 1,3,5-benzenetricarboxylic acid and TEA—Triethylamine was found to be a critical factor for the attachment and growth of the MOF-199 crystals onto anionic cellulose. The presence of MOF-199 crystals was probed using XRD and XPS spectra and a strong chemical interaction to the carboxymethylated cellulose fibers was confirmed by intense and vigorous washing of the specimens with water, DMF and methanol. Based on the recognized ability of MOF-199 to capture gases and toxic chemicals, combined with the availability of cellulose-based fibrous materials, the described procedure provides the basis for future fabrication of functionalized fibers and active filtration media.
TL;DR: In this paper, the effect of hybrid organic-inorganic coatings containing ammonium polyphosphate (APP), chitosan and silica has been evaluated on polyester-cotton blends (PET-CO), exploiting the layer by layer assembly.
Abstract: Hybrid organic–inorganic coatings containing ammonium polyphosphate (APP), chitosan and silica have been deposited on polyester-cotton blends (PET-CO), exploiting the layer by layer assembly. To this aim, two different complex architectures (namely, chitosan/APP bilayers plus silica/silica bilayers or silica/silica/chitosan/APP quadlayers) have been thoroughly investigated. The effect of their morphologies on the flame retardancy properties of the fabrics (flammability and combustion behaviour) has been assessed. More specifically, some of the above complex architectures exhibited significant enhancements concerning flammability (i.e. the suppression of afterglow, together with a considerable final residue increase) and combustion behaviour as evidenced by cone calorimeter tests. A close relationship between the overall flame retardancy properties of the blends and the level of dishomogeneity of the LbL architectures has been shown.
TL;DR: In this paper, a free-standing films of bacterial cellulose and polyaniline (PAni) composites with high electrical conductivity values (0.9 S cm−1) and good mechanical properties (40 MPa) were prepared through in situ oxidative chemical polymerization of aniline on the surface of synthesized BC nanofibers by using FeCl3·6H2O, as oxidant.
Abstract: Free-standing films of bacterial cellulose (BC) and polyaniline (PAni) (BC/PAni) composites with high electrical conductivity values (0.9 S cm−1) and good mechanical properties (40 MPa) were prepared through in situ oxidative chemical polymerization of aniline (Ani) on the surface of synthesized BC nanofibers by using FeCl3·6H2O, as oxidant. The influence of polymerization conditions such as oxidant content, protonic acid, and reaction time on electrical conductivity, morphological, tensile properties and thermal stability of the BC/PAni composites was investigated. Electrical conductivities of BC/PAni composites increased with increasing reaction time due to the formation of a continuous layer that completely coated the nanofiber surface. FTIR spectra of BC/PAni composites produced with and without protonic acid exhibited overlapped absorption bands of both BC and PAni, except for quinoid and benzoid bending modes of PAni. The in situ oxidative chemical polymerization gives rise to conducting membranes with the surface constituted by different PAni content, as indicated through CHN elemental analysis. The crystalline structure of BC was not affected by the incorporation of PAni. Scanning electron microscopy analysis of the composites revealed that PAni consisted of nanoparticles around 70 nm in mean size to form a continuous coating that encapsulates the BC nanofibers. The BC/PAni composites obtained by the method described in this work have interesting properties that may find important technological applications such as sensors, electronic devices, intelligent clothes, flexible electrodes and tissue engineering scaffolds.
TL;DR: In this article, a set of experiments were performed to evaluate the influence of some factors such as NaAc/starch mass ratio, crosslinker, and nanowhiskers amount in the swelling capacity and swelling kinetics.
Abstract: Superabsorbents hydrogel nanocomposites based on starch-g-poly(sodium acrylate) and cellulose nanowhiskers (CNWs) were synthesized. A set of experiments was performed to evaluate the influence of some factors such as NaAc/starch mass ratio, crosslinker, and nanowhiskers amount in the swelling capacity and swelling kinetics. Increasing the NaAc/starch mass ratio up to 7 leads to an increase in the water uptake at a maximum value, however, higher ratios decreased that value due to the increase of crosslinking points. Similarly, the incorporation of CNWs up to 10 wt% provided an improvement in the swelling due to the hydrophilic groups from cellobiose units. Further, the incorporation of CNWs diminishes the water uptake. Besides, the CNWs improved the mechanical properties. SEM images showed that CNWs increase the average porous size of composites. The composites presented good responsive behavior in relation to pH and salt presence allowing those materials suitable for many potential applications.
TL;DR: In this article, a rotational rheometer and a transparent cylindrical measuring system were used to characterize the suspension rheology of microfibrillated cellulose in relation to flocculation of the cellulose fibrils.
Abstract: Our aim was to characterise the suspension rheology of microfibrillated cellulose (MFC) in relation to flocculation of the cellulose fibrils. Measurements were carried out using a rotational rheometer and a transparent cylindrical measuring system that allows combining visual information to rheological parameters. The photographs were analyzed for their floc size distribution. Conclusions were drawn by comparing the photographs and data obtained from measurements. Variables selected for examination of MFC suspensions were degree of disintegration of fibres into microfibrils, the gap between the cylinders, sodium chloride concentration, and the effects of changing shear rate during the measurement. We studied changes in floc size under different conditions and during network structure decomposition. At rest, the suspension consisted of flocs sintered together into a network. With shearing, the network separated first into chain-like floc formations and, upon further shear rate increase, into individual spherical flocs. The size of these spherical flocs was inversely proportional to the shear rate. Investigations also confirmed that floc size depends on the geometry gap, and it affects the measured shear stress. Furthermore, suspension photographs revealed an increasing tendency to aggregation and wall depletion with sodium chloride concentration of 10−3 M and higher.
TL;DR: In this paper, α-cellulose and cellulose II powders for use in the pharmaceutical industry can be derived from maize cob α-Cellulose was extracted from an agricultural residue (maize cobs) using a non-dissolving method based on inorganic substances.
Abstract: Suitable α-cellulose and cellulose II powders for use in the pharmaceutical industry can be derived from maize cob α-Cellulose was extracted from an agricultural residue (maize cobs) using a non-dissolving method based on inorganic substances Modification of this α-cellulose was carried out by its dissolution in the ionic liquid 1-butyl-3-methylimidazolium chloride ([C4mim]Cl), and subsequent regeneration by addition of either water or acetone at room temperature, or of boiling water X-ray diffraction and infrared spectroscopy results showed that the regenerated celluloses had lower crystallinity, and proved that the treatment with [C4mim]Cl led to the conversion of the crystalline structure of α-cellulose from cellulose I to cellulose II Thermogravimetric analysis and differential scanning calorimetry data showed quite similar thermal behavior for all cellulose samples, although with somewhat lower stability for the regenerated celluloses, as expected The comparison of physicochemical properties of the regenerated celluloses and the native cellulose mainly suggests that the regenerated ones might have better flow properties For some of the characterizations carried out, it was generally observed that the sample regenerated with boiling water had more similar characteristics to the α-cellulose sample, evidencing an influence of the regeneration strategy on the resulting powder after the ionic liquid treatment
TL;DR: In this paper, a cellulose/silver nanoparticles (Ag NPs) composites were prepared and their catalytic performance was evaluated by optical microscopy, UV-visible spectroscopy, WXRD, SEM, TEM and TG.
Abstract: Cellulose/silver nanoparticles (Ag NPs) composites were prepared and their catalytic performance was evaluated. Porous cellulose microspheres, fabricated from NaOH/thiourea aqueous solution by a sol–gel transition processing, were served as supports for Ag NPs synthesis by an eco-friendly hydrothermal method. The regenerated cellulose microspheres were designed as reducing reagent for hydrothermal reduction and also micro-reactors for controlling growth of Ag NPs. The structure and properties of obtained composite microspheres were characterized by Optical microscopy, UV–visible spectroscopy, WXRD, SEM, TEM and TG. The results indicated that Ag NPs were integrated successfully and dispersed uniformly in the cellulose matrix. Their size (8.3–18.6 nm), size distribution (3.4–7.7 nm), and content (1.1–4.9 wt%) were tunable by tailoring of the initial concentration of AgNO3. Moreover, the shape, integrity and thermal stability were firmly preserved for the obtained composite microspheres. The catalytic performance of the as-prepared cellulose/Ag composite microspheres was examined through a model reaction of 4-nitrophenol reduction in the presence of NaBH4. The composites microspheres exhibited good catalytic activity, which is much high than that of hydrogel/Ag NPs composites and comparable with polymer core–shell particles loading Ag NPs.
TL;DR: The preparation of high-strength hydrogels from plant-based cellulose nanofibers by simple alkaline treatment is described in this article, where two types of hydrogel sheet with different crystal forms (celluloses I and II) in 9 and 15 wt% aqueous sodium hydroxide solutions were obtained.
Abstract: The preparation of high-strength hydrogels from plant-based cellulose nanofibers by simple alkaline treatment is described herein. We isolated the cellulose nanofibers with a uniform width of approximately 15 nm from wood and we prepared two types of hydrogel sheet with different crystal forms (celluloses I and II) in 9 and 15 wt% aqueous sodium hydroxide solutions. Both of the hydrogels exhibited high tensile properties because of the crystalline network in the gels. Especially, the nanofiber hydrogel with a cellulose II crystal structure with the swelling degree of 13.4 achieved a Young’s modulus and tensile strength in excess of 35 and 5 MPa respectively, because it had a continuous and strong nano-network formed via the interdigitation of the neighboring nanofibers during mercerization.
TL;DR: In this paper, four different cellulose nanofibers samples were prepared from northern bleached softwood kraft fibers, and fiber diameter distributions from SEM images were measured from fiber suspension sedimentation measurements.
Abstract: Four different cellulose nanofibers samples were prepared from northern bleached softwood kraft fibers. Fiber diameter distributions were measured from SEM images. Fiber aspect ratios ranging from 84 to 146 were estimated from fiber suspension sedimentation measurements. Three samples had heterogeneous distributions of fiber diameters, while one sample was more homogeneous. Sheet forming experiments using filters with pores ranging from 150 to 5 μm showed that the samples with a heterogeneous distribution of fiber dimensions could be easily formed into sheets at 0.2% initial solids concentration with all filter openings. On the other hand, sheets could only be formed from the homogenous sample by using 0.5% or more initial solids content and a lower applied vacuum and smaller filter openings. The forming data and estimated aspect ratios show reasonable agreement with the predictions of the crowding number and percolation theories for the connectivity and rigidity thresholds for fiber suspensions.
TL;DR: In this article, the effect of solvent composition, polymer concentration, and flow rate on electrospinning of cellulose acetate (CA) mat was investigated in relation to factors of solvent compositions and flow rates.
Abstract: Electrospinning of cellulose acetate (CA) was studied in relation to factors of solvent composition, polymer concentration, and flow rate to elucidate how the processing parameters impact electrospun CA structure. Fibrous cellulose-based mats were produced from electrospinning cellulose acetate (CA, Mn = 30,000, DS = 2.45) in acetone, acetone/isopropanol (2:1), and acetone/dimethylacetamide (DMAc) (2:1) solutions. The effect of CA concentration and flow rate was evaluated in acetone/DMAc (2:1) solution. The morphology of electrospun CA mats was impacted by solvent system, polymer concentration, and solution flow rate. Fibers produced from acetone and the mixture of acetone/isopropanol (2:1) exhibited a ribbon structure, while acetone/DMAc (2:1) system produced the common cylindrical fiber shape. It was determined that the electrospinning of 17 % CA solution in acetone/DMAc (2:1, w/w) produced fibers with an average fiber diameter in the submicron range and the lowest size distribution among the solvents tested. The solution flow rate had a power law relationship of 0.26 with the CA fiber size for 17 % CA in acetone/DMAc (2:1). Solvent composition and flow rate also impacted the stability of the network structure of the electrospun fibers. Only samples from acetone/DMAc (2:1) at solution flow rates equal or higher than 1 mL/h produced fibrous meshes that were able to preserve their original network structure after deacetylation. These samples after regeneration showed no residual DMAc and exhibited no cytotoxic effects on mammalian cells.
TL;DR: In this article, the authors investigated the effect of drying on the elastic modulus of nanopaper and found that the drying effect alone cannot explain the relatively low elastic properties of the nanopaper.
Abstract: Nanopaper is a transparent film made of network-forming nanocellulose fibers. These fibers are several micrometers long with a diameter of 4–50 nm. The reported elastic modulus of nanopaper often falls short of even conservative theoretical predictions based on the modulus of crystalline cellulose, although such predictions usually perform well for other fiber composite materials. We investigate this inconsistency and suggest explanations by identifying the critical factors affecting the stiffness of nanopaper. A similar inconsistency is found when predicting the stiffness of conventional paper, and it is usually explained by the effects introduced during drying. We found that the effect of the drying cannot solely explain the relatively low elastic modulus of nanopaper. Among the factors that showed the most influence are the presence of non-crystalline regions along the length of the nanofibers, initial strains and the three-dimensional structure of individual bonds.
TL;DR: Recently-discovered lignocellulosic solvent, 8% (w/w) lithium chloride/dimethyl sulfoxide (LiCl/DMSO), was found to dissolve cellulose of varied crystal forms and degree of polymerization.
Abstract: Recently-discovered lignocellulosic solvent, 8%(w/w) lithium chloride/dimethyl sulfoxide (LiCl/DMSO), was found to dissolve cellulose of varied crystal forms and degree of polymerization Cellulose samples could be activated for dissolution by complexation with ethylenediamine (EDA), giving EDA contents of 20–23% (w/w) in the complex irrespective of the cellulose type The cellulose solution gave well-resolved 13C NMR spectrum, confirming molecular dispersion Cellulose could be coagulated by ethanol to give translucent cellulose gels, which could be converted to highly porous aerogels via solvent exchange drying Nitrogen adsorption analysis gave their specific surface areas of 190–213 m2/g, with typical mesopore sizes of 10–60 nm Scanning electron microscopy revealed the network structure of aerogel composed of relatively straight fibril segments, approx 20 nm wide and 100–1,000 nm long X-ray diffraction showed that the material is poorly crystalline cellulose II
TL;DR: In this paper, a simple green approach was used by casting water-based suspensions of pullulan and bacterial cellulose and characterized by TGA, RDX, tensile assays, SEM and AFM.
Abstract: Bionanocomposites with improved properties based on two microbial polysaccharides, pullulan and bacterial cellulose, were prepared and characterized. The novel materials were obtained through a simple green approach by casting water-based suspensions of pullulan and bacterial cellulose and characterized by TGA, RDX, tensile assays, SEM and AFM. The effect of the addition of glycerol, as a plasticizer, on the properties of the materials was also evaluated. All bionanocomposites showed considerable improvement in thermal stability and mechanical properties, compared to the unfilled pullulan films, evidenced by the significant increase in the degradation temperature (up to 40 °C) and on both Young’s modulus and tensile strength (increments of up to 100 and 50%, for films without glycerol and up to 8,000 and 7,000% for those plasticized with glycerol). Moreover, these bionanocomposite films are highly translucent and could be labelled as sustainable materials since they were prepared entirely from renewable resources and could find applications in areas as organic electronics, dry food packaging and in the biomedical field.