Cellulose Dissolution Process Research Articles

Microscopic dissolution process of cellulose in alkaline aqueous solvents and its application in CNFs extraction - Investigating temperature as a variable

The target of this study is to gain a deeper understanding of the micro-dissolution process of cellulose in alkaline aqueous solutions and to develop a novel method for extracting cellulose nanofibrils (CNFs). Herein, the dissolution process of cellulose in alkaline aqueous solutions will be controlled by varying the temperature, and the undissolved cellulose will be analyzed to reveal the microscopic dissolution process of cellulose, and a novel process for extracting cellulose nanofibrils (CNFs) will be developed based on the findings. The crystalline structure of cellulose was gradually disrupted as the dissolution progressed, and the crystal form of cellulose changed gradually from cellulose I to cellulose II during the dissolution process, while all undissolved cellulose crystals remained as cellulose I. Cellulose, after its structure is disrupted during the dissolution process, will inevitably decompose into CNFs, and the microscopic dissolution process of cellulose follows a “top-down” dissolution sequence. The CNFs extraction method developed in this study can extract CNFs with high yield (>60 %) in a stable manner, as well as narrow particle size distribution, high crystallinity (>77 %), and good thermal stability. This study enhances the comprehension of the dissolution process of cellulose and paves a possible way for industrialization of CNFs production.

Regenerated cellulose/polyvinyl alcohol composite films with high transparency and ultrahigh haze for multifunctional light management

In this study, cellulose composite films (CCFs) were fabricated through controllable dissolution and regeneration process of cellulose with the addition of polyvinyl alcohol (PVA). The competition of hydrogen bond site between cellulose and PVA led to partial dissolution of cellulose and maintained morphology of micron fibers with width range from 14.55 to 16.16 μm, which served as in-situ visible light scatterers. With this unique micron structure, the obtained CCF exhibited high transparency up to 90.5 % at 550 nm and ultrahigh haze up to 96 %. Interestingly, CCF could be used as hazy and flexible substrate, such as scattering lamp covers for indoor light management, anti-glare screen protectors and anti-reflection layers of solar cell devices. Among them, the efficiency of the solar cell device could be improved by 10.38 % with the help of a low-cost, excellent-performance CCF.

Dissolution mechanism of cellulose in a benzyltriethylammonium/urea deep eutectic solvent (DES): DFT-quantum modeling, molecular dynamics and experimental investigation.

In this paper, a benzyltriethylammonium/urea DES was investigated as a new green and eco-friendly medium for the progress of organic chemical reactions, particularly the dissolution and the functionalization of cellulose. In this regard, the viscosity-average molecular weight of cellulose (M̄w) during the dissolution/regeneration process was investigated, showing no significant degradation of the polymer chains. Moreover, X-ray diffraction patterns indicated that the cellulose dissolution process in the BTEAB/urea DES decreased the crystallinity index from 87% to 75%, and there was no effect on type I cellulose polymorphism. However, a drastic impact of the cosolvents (water and DMSO) on the melting point of the DES was observed. Besides, to understand the evolution of cellulose-DES interactions, the formation mechanism of the system was studied in terms of H-bond density and radial distribution function (RDF) using molecular dynamics modeling. Furthermore, density functional theory (DFT) was used to evaluate the topological characteristics of the polymeric system such as potential energy density (PED), laplacian electron density (LED), energy density, and kinetic energy density (KED) at bond critical points (BCPs) between the cellulose and the DES. The quantum theory of atoms in molecules (AIM), Bader's quantum theory (BQT), and reduced density gradient (RDG) scatter plots have been exploited to estimate and locate non-covalent interactions (NCIs). The results revealed that the dissolution process is attributed to the physical interactions, mainly the strong H-bond interactions.

A molecular dynamics (MD) simulation of the solubility behaviours of cellulose in aqueous cuprammonium hydroxide solution

The dissolution of cellulose in cuprammonium hydroxide solution (CUAM) was studied using an MD simulation method under specific conditions. By monitoring the deformation in the geometry of the cellulose chains over the simulation time, we explained how the solvent dissolves the cellulose chains. We also investigated the behaviour of the solvent components (anions and cations) by a radial distribution function study, which showed that Na + ions play an important role in the cellulose dissolution process. The variation in the number of hydrogen bonds between cellulose chains was studied by counting the instantaneous hydrogen bonds during the simulation. On the other hand, the data collected indicated that the geometries of the cellulose chains have changed significantly and become less likely to be organized in parallel arrangements due to the formation of cellulose cuprammonium complexes.

A novel strategy to intensify the dissolution of cellulose in deep eutectic solvents by partial chemical bonding

The relatively low solubility of cellulose in choline chloride-based deep eutectic solvents (DESs) restricts their practical application in the production industry. Here, cellulose was slightly oxidized into dialdehyde cellulose (DAC) at first, and then partial chemical bonding was introduced to intensify the dissolution process of cellulose in (choline chloride-resorcinol) DES. In this process, the solubility of cellulose in DES increased 10-fold, and the crystallinity of cellulose decreased over 24% while the oxidation level was lower than 20%. An intensified hydrogen bond network was revealed, which implied that cellulose components mainly acted as hydrogen bond donor after dissolution. A new class of DES containing cellulose was thus preliminarily established. The cellulose chains and the intensive hydrogen bond network also resulted in an increased viscosity and a conversion from Newtonian behavior to non-Newtonian behavior of dissolved samples. The phase transition behaviors of dissolved samples were gradually converted from crystallization to cool crystallization. The proposed and performed strategy is novel and scalable and will open a fresh perspective to achieve higher efficient dissolution of cellulose in DES and establish a new partially derivatized cellulose/DES system.

The solution state and dissolution process of cellulose in ionic-liquid-based solvents with different hydrogen-bonding basicity and microstructures

We demonstrated a clear and comprehensive description of the solution state, dissolution process, and regulation principle of cellulose in ionic liquids (ILs) and IL/co-solvent systems.

NMR study on the cellulose dissolution mechanism in CaCl2·6H2O-LiCl molten salt hydrate.

As there is a rising interest in upgrading cellulose to high-performance bio-products, the studies on innovative reaction media and processes have been leaping forward. Green solvents in terms of cellulose dissolution and brief processes for upgrading are critical to green chemistry. However, most solvent systems generally exhibit defects in harsh pH operating windows with limited temperature ranges, environmental pollution, long reaction times, complicated processes, etc. In this work, we have provided a novel molten salt hydrate (CaCl2·6H2O-LiCl) as a green solvent and investigated the role of hydrated molten salts in the dissolution process via the solid state nuclear magnetic resonance (NMR) technique. The cellulose could be dissolved in CaCl2·6H2O-LiCl molten salt hydrated at 120 °C with 3.0% solubility and regenerated in-situ by cooling down to ambient temperature. The regenerated cellulose exhibited a high solubility and excellent stability. From 7Li single pulse NMR experiments, it was observed that two types of Li+ existed in the cellulose dissolution, and the Li+ significantly impacted the dissolving process and the dissolution ability of cellulose. This work would provide an environmental-friendly strategy to prepare cellulose solutions for biocompatible cellulose materials.

Antibacterial Fibers Containing Nanosilica with Immobilized Silver Nanoparticles

Abstract The main aim of the presented research was to obtain antibacterial fibers containing nanosilica with immobilized silver nanoparticles. The nanomodifier in an amount of 250 ppm, 500 ppm, 1,000 ppm, and 2,000 ppm were introduced into the cellulose fiber matrix during the cellulose dissolution process. In order to assess the influence of the nanomodifier's amount in the fiber on the antibacterial activity of modified fiber, a quantitative test of the antibacterial activity of the fibers was performed. The basic parameters of modified fibers, such as the mechanical and hygroscopic, were estimated. The size and shape of the nanomodifier in the selected fibers, as well as microanalysis of the polymer matrix, were examined. The investigations were conducted by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy Dispersive Spectrometry (EDS). The obtained results allowed the selection of optimal fibers with strong antibacterial properties that can be potentially used for personal protection or medical purposes.

Influence of intensified cellulose dissolution process on spinning and properties of lyocell fibres

Effect of intensification of cellulose dissolution process on the spinning of lyocell fibers and their physical properties was systematically investigated. The cellulose dissolution process was intensified by pre-swelling of the pulps that benefited in bringing down the conventional process temperature of 75 °C to 50 °C as well as by assisting in good dissolution and formation of homogeneous dope. Further, effect of dopes prepared from pre-swelled and un-swelled pulps at a lower temperature (i.e. 50 °C) on spinnability and fiber properties, was thoroughly investigated and compared with dopes prepared at 75 °C. The resultant fibers were morphologically and structurally analyzed using SEM and XRD and correlated with their physical properties. It was observed that fibers regenerated from pre-swelled dope, showed increased overall molecular orientation (measured by birefringence) as well as high amorphous orientation that resulted in improved tenacity of the fibers. Finally, it has been observed that cellulose dissolution using pre-swelled method is an energy-efficient technique over un-swelled method (almost 35% at 50 °C and ∼20% at 75 °C of energy saving). Present work makes lyocell process more sustainable and simultaneously enhance fiber properties.

Regenerated Cellulose/Graphene Composite Fibers with Electroconductive Properties

Abstract Conductive cellulose fibers may find application in producing antistatic materials and fibrous electronic elements for smart textiles (textronics). In this paper, we present a method of fabrication of cellulose fibers modified with the reduced graphene oxide (rGO) and graphene oxide (GO). The fibers were obtained by using N-methylmorpholine-N-oxide (NMMO) as a direct solvent, adding dispersion of GO during the cellulose dissolution process. In the next step, the GO enclosed in the fibers was reduced for ca. half an hour at 90°C with the excess of water solution of hydrazine to obtain fibers containing rGO. The viscosity of the spinning solution increased when GO was added; however, the difference is important at low shearing rates but decreases at high shearing rates, similar to that used in the process of fiber spinning. Cellulose fibers containing 3, 4, 6, and 10% w/w of rGO were obtained. Fiber morphology was studied using electron microscopy. The results of the electrical properties’ measurements showed that the conductivity of modified fibers strongly depends on the concentration of rGO. At 10% rGO conductivity was 9 x 10−3 S/cm. The mechanical properties of the obtained fibers were slightly changed by the presence of GO and rGO. Tenacity and elongation at break decreased with the increase in the content of GO and rGO in the fibers but remain at an acceptable level from the textiles processing point of view.

Pre-service chemistry teachers’ conceptions of ionic liquids as ionic solvents on the cellulose dissolution process

This study examines pre-service chemistry teachers’ understanding of concepts related to ionic liquids as cellulose solvents which include knowledge of cellulose, ionic compounds, and ionic liquids. This study used a descriptive method and involved 35 pre-service chemistry teachers from 6th semester who enrolled in the High School Chemistry unit. The research instruments of an open-ended questions which related to the concepts of ionic compounds, ionic liquids and cellulose. The results show that pre-service chemistry teachers have limited conceptions about of the concepts related to the dissolution of cellulose in ionic liquids. Based on the analysis of student answers to open-ended questions, students’ conceptions about definition of cellulose are quite good, but student have no sufficient knowledge about the structure and benefits of cellulose. Furthermore, students’ conceptions related to ionic compounds and ionic liquids are not good enough because student have not been able to mention the differences between ionic compounds and ionic liquids based on the structure, properties, and the constituent particles. This is because ionic liquids as cellulose solvents and the concepts related are not taught directly in the classroom so that it becomes an unfamiliar concept to student.

Revisiting the Dissolution of Cellulose in NaOH as "Seen" by X-rays.

Cotton production is reaching a global limit, leading to a growing demand for bio-based textile fibers produced by other means. Textile fibers based on regenerated cellulose from wood holds great potential, but in order to produce fibers, the components need to be dissolved in suitable solvents. Furthermore, the dissolution process of cellulose is not yet fully understood. In this study, we investigated the dissolution state of microcrystalline cellulose in aqueous NaOH by using primarily scattering methods. Contrary to previous findings, this study indicated that cellulose concentrations of up to 2 wt % are completely molecularly dissolved in 8 wt % NaOH. Scattering data furthermore revealed the presence of semi-flexible cylinders with stiff segments. In order to improve the dissolution capability of NaOH, the effects of different additives have been of interest. In this study, scattering data indicated that the addition of ZnO decreased the formation of aggregates, while the addition of PEG did not improve the dissolution properties significantly, although preliminary NMR data did suggest a weak attraction between PEG and cellulose. Overall, this study sheds further light on the dissolution of cellulose in NaOH and highlights the use of scattering methods to assess solvent quality.

Intensification of lyocell dissolution process and dope characteristics using pre-swelled cellulosic pulp

Transformation of pulp into regenerated lyocell fibre involves a critical step of cellulose dissolution in aqueous NMMO solution. The objective of this work is to investigate the effect of using pre-swelled pulps derived from hardwood kraft sulphate (H-KS) and softwood kraft sulphate (S-KS) process, on cellulose dissolution. Pre-swelling at temperatures follows from 30 °C to 75 °C results in lowering of pulp crystallinity, and hence, was hypothesized to form a homogeneous solution with lower power consumption during the dissolution process. Experimental torque moments (proportional to power consumption) of the un-swelled and pre-swelled pulps at different temperatures were compared and correlated with the cellulose dissolution process. Further, a time based morphological study of cellulose dissolution was performed with the help of a microscopic investigation method. The quality of the dissolved dope was evaluated by optical image analysis, refractive index (RI), dope composition and thermal analysis (TGA/DSC). It was observed that by using pre-swelled pulps, homogeneous cellulose solution could be formed at lower processing temperature, consuming less time and power thereby making the lyocell process more energy-efficient and sustainable.

The potential of magnetisation transfer NMR to monitor the dissolution process of cellulose in cold alkali

Cellulose is the most important biopolymer on earth and, when derived from e.g. wood, a promising alternative to for example cotton, which exhibits a large environmental burden. The replacement depends, however, on an efficient dissolution process of cellulose. Cold aqueous alkali systems are attractive but these solvents have peculiarities, which might be overcome by understanding the acting mechanisms. Proposed dissolution mechanisms are for example the breakage of hydrophobic interactions and partly deprotonation of the cellulose hydroxyl groups. Here, we performed a mechanistic study using equimolar aqueous solutions of LiOH, NaOH and KOH to elucidate the dissolution process of microcrystalline cellulose (MCC). The pH was the highest for KOH(aq) followed by NaOH(aq) and LiOH(aq). We used a combination of conventional and advanced solution-state NMR methods to monitor the dissolution process of MCC by solely increasing the temperature from − 10 to 5 °C. KOH(aq) dissolved roughly 25% of the maximum amount of MCC while NaOH(aq) and LiOH(aq) dissolved up to 70%. Water motions on nanoscale timescales present in non-frozen water, remained unaffected on the addition of MCC. Magnetisation transfer (MT) NMR experiments monitored the semi-rigid MCC as a function of temperature. Interestingly, although NaOH(aq) and LiOH(aq) were able to dissolve a similar amount at 5 °C, MT spectra revealed differences with increasing temperature, suggesting a difference in the swollen state of MCC in LiOH(aq) already at − 10 °C. Furthermore, MT NMR shows a great potential to study the water exchange dynamics with the swollen and semi-rigid MCC fraction in these systems, which might give valuable insights into the dissolution mechanism in cold alkali.

Cellulose Degradation by Calcium Thiocyanate.

The dissolution process of cellulose aerogels is an important part of their production. However, if the cellulose is severely degraded during the dissolution process, the quality may be low. To evaluate the degradation of cellulose during the dissolution process using calcium thiocyanate, the hydrolysis and oxidation of cellulose were evaluated by the change in absolute molecular weight and by the changes in the content of carboxyl and carbonyl groups introduced into the cellulose hydroxyl group, respectively. A noteworthy hydrolysis phenomenon was found in the cellulose dissolution process. The rate of hydrolysis increased as the number of hydrates in calcium thiocyanate decreased and as the reaction temperature increased. In the case of the reaction with calcium thiocyanate containing six hydrates, the time to reach a 50% loss of the degree of polymerization of cellulose reduced from 196 to 47 min as the reaction temperature was increased from 100 to 120 °C; however, the effect on oxidation was not significant. The Brunauer–Emmett–Teller (BET) surface area reduced as the degree of cellulose polymerization decreased. Therefore, it is necessary to consider how the cellulose degradation occurring during the cellulosic dissolution process can affect the quality of the final cellulose aerogels.

Thermal hazard analysis of a biomass pretreatment process using ionic liquids

Ionic liquids (ILs) may have various applications as less hazardous solvents because of their thermal stabilities and low vapor pressures. However, it is challenging to remove heat from large amount because of IL’s high viscosity and low vapor pressure when cooling failure or abnormal reaction occurs. Because chemical processes using ILs on an industrial scale are still in the early phase of development, it is important to assess the associated thermal hazards of chemical process using ILs. This work proposes a systematic approach of analyzing thermal hazards of chemical process using ILs, based on the approach proposed by Stoessel and analyze the cellulose dissolution process using ILs containing impurities as a test case. Copper oxide, which might be contaminated from wood chips, was chosen as a model impurity. To analyze the thermal hazards of cellulose dissolution process using ILs, thermal analysis using small-scale reaction calorimeter, differential scanning calorimeter and thermogravimetry–differential thermal analysis–mass spectrometry were performed. From these results, reaction heat and heat value of ILs and its mixture were low, while CuO lowers the decomposition temperature of ILs and produces flammable gases. From these trials, exothermal reaction was not observed, while flammable gaseous products might be produced in vapor phase in the reactor.

Dissolution and Regeneration of the Produced Nano Bacterial Cellulose of Food Industries Wastewaters by a Cost-Benefit Method

This paper applied a simple and cost-benefit method for the production of regenerated bacterial cellulose. The inexpensive production of cellulose with complex media derived from wastewater from food industries such as molasses adds a lot of contaminants to the produced bacterial cellulose, which puts a lot of challenges in cellulose purification. Therefore, the present study aimed to develop an inexpensive strategy for the complete dissolution of the very dirty cellulose produced from the low-cost medium containing molasses and corn steep liquor, and the reconstruction of pure bacterial cellulose that can be used for all types of cellulose. The bacterial cellulose was produced by Gluconacetobacter xylinus BRP2001 in an effective and inexpensive culture media including a mixture of molasses and corn steep liquor, then cuprammonium rayon method as a cost effective approach was modified for quick and complete dissolution of the bacterial cellulose. The main parameters in cuprammonium method such as the value of sodium hydroxide and copper sulfate, the water removal method and dissolution process were optimized by irregular fraction design. In addition to cost, the time of dissolution process of bacterial cellulose was reduced to less than 1 hour which is unprecedented in comparison with other conventional methods. Regeneration of bacterial cellulose for the fabrication of novel regenerated bacterial cellulose was carried out using dilute sulfuric acid. Under the optimum rayon method comprising 3 wt% NaOH/ 6 wt% copper sulfate solution, the diameter of the nanofibers of bacterial cellulose and regenerated bacterial cellulose ranged between 20-80 nm and 60-120 nm, respectively. Also, the crystal sizes of bacterial and regenerated bacterial cellulose were estimated at about 59.74nm and 6.13nm and the crystallinity indexes of bacterial cellulose and regenerated bacterial cellulose were calculated as 89% and 64%, respectively. The mechanical modulus and crystallinity of regenerated bacterial cellulose were significantly reduced because of the disruption of the hydrogen bond.

Dissolution and Hydrolysis of Bleached Kraft Pulp Using Ionic Liquids.

Forestry industries in Chile are facing an important challenge—diversifying their products using green technologies. In this study, the potential use of Ionic Liquids (ILs) to dissolve and hydrolyze eucalyptus wood (mix of Eucalyptus nitens and Eucalyptus globulus) kraft pulp was studied. The Bleached Hardwood Kraft Pulp (BHKP) from a Chilean pulp mill was used together with five different ILs: 1-butyl-3-methylimidazolium chloride [bmim][Cl], 1-butyl-3-methylimidazolium acetate [bmim][Ac], 1-butyl-3-methylimidazolium hydrogen sulfate [bmim][HSO4], 1-ethyl-3-methylimidazolium chloride [emim][Cl], 1-ethyl-3-methylimidazolium acetate [emim][Ac]. Experimentally, one vacuum reactor was designed to study the dissolution/hydrolysis process for each ILs; particularly, the cellulose dissolution process using [bmim][Cl] was studied proposing one molecular dynamic model. Experimental characterization using Atomic Force Microscopy, conductometric titration, among other techniques suggest that all ILs are capable of cellulose dissolution at different levels; in some cases, the dissolution evolved to partial hydrolysis appearing cellulose nanocrystals (CNC) in the form of spherical aggregates with a diameter of 40–120 nm. Molecular dynamics simulations showed that the [bmim][Cl] anions tend to interact actively with cellulose sites and water molecules in the dissolution process. The results showed the potential of some ILs to dissolve/hydrolyze the cellulose from Chilean Eucalyptus, maintaining reactive forms.

Dissolution of Cellulosic Fibers: Impact of Crystallinity and Fiber Diameter.

With the aim of informing the selection of biomass pretreatment options and to assist in interpreting experimental results from different biomass/solvent combinations, this study addresses the impact of crystallinity and size on the kinetics of semicrystalline cellulose fiber swelling and dissolution. To this end, a newly developed phenomenological model is utilized that accounts for the role of decrystallization and disentanglement as two rate-determinant steps in the cellulose dissolution process. Although fibers with lower crystallinity swell more and faster, the degree of crystallinity does not affect the dissolution rate. Fibers of smaller diameter swell more and become amorphous faster. When decrystallization is important, the solubility of thinner fibers increases more with a reduction in the crystallinity compared to the diameter. However, when the dissolution is controlled by chain disentanglement, or in the case of dissolution of fibers having larger diameters, milling the fibers to reduce the particle size could increase the solubility.

Preparation and characterization of transparent cellulose films using an improved cellulose dissolution process

ABSTRACTEffective dissolution of cellulosic macromolecules is the first predominant step to prepare functional bio‐based materials with desirable properties. In this study, we developed an improved dissolution process using a freeze‐drying pretreatment to promote the dissolution of cellulose. Rheological measurements of cellulose solutions and physicochemical characterization of regenerated cellulose films (scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, and thermogravimetric analysis) were performed. Cellulose solution prepared from 5% microcrystalline cellulose (w:v) in the solvent exhibits a Newtonian fluid character while cellulose solutions at higher concentrations show a pseudo‐plastic fluid behavior. Results from physicochemical characterization indicate that a freeze‐drying pretreatment step of cellulose leads to a complete dissolution at 5% concentration while only part of cellulose is dissolved at 10% and 15% concentrations. The results obtained indicated that the use of a freeze‐drying pretreatment step under mild conditions lead to a complete dissolution of cellulose at 5% concentration. The cellulose films prepared from 5% concentration exhibited desirable properties such as good optical transparency, crystallinity, and thermal stability. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44871.