Design of biodegradable cellulose filtration material with high efficiency and breathability.

Using respiratory protective equipment is one of the relevant preventive measures for infectious diseases, including COVID-19, and for various occupational respiratory hazards. Because experienced discomfort may result in a decrease in the utilization of respirators, it is important to enhance the material properties to resolve suboptimal usage. We combined several technologies to produce a filtration material that met requirements set by a cross-disciplinary interview study on the usability of protective equipment. Improved breathability, environmental sustainability, and comfort of the material were achieved by electrospinning poly(ethylene oxide) (PEO) nanofibers on a thin foam-formed fabric from regenerated cellulose fibers. The high filtration efficiency of sub-micron-sized diethylhexyl sebacate (DEHS) aerosol particles resulted from the small mean segment length of 0.35 µm of the nanofiber network. For a particle diameter of 0.6 µm, the filtration efficiency of a single PEO layer varied in the range of 80-97 % depending on the coat weight. The corresponding pressure drop had the level of 20-90 Pa for the airflow velocity of 5.3 cm/s. Using a multilayer structure, a very high filtration efficiency of 99.5 % was obtained with only a slightly higher pressure drop. This opens a route toward designing sustainable personal protective media with improved user experience.

Thermoresponsive Nanocellulose Films as an Optical Modulation Device: Proof-of-Concept.

Flexible optoelectronic technologies are becoming increasingly important with the advent of concepts such as smart-built environments and wearable systems, where they have found applications in displays, sensing, healthcare, and energy harvesting. Parallelly, there is also a need to make these innovations environmentally sustainable by design. In the present work, we employ nanocellulose and its excellent film-forming properties as a basis to develop a green flexible photonic device for sensing applications. Cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) were used as matrix materials along with a black thermochromic pigment to prepare thermoresponsive hybrid films. Optical properties of nanocellulose films such as transparency and haze were tuned by varying pigment loading. Nearly 90% transparent CNF and CNC films could be tuned to reduce the transmission to as low as 4 and 17%, respectively. However, the films regained transparency to up to 60% when heated above the thermochromic transition temperature (31 °C). The thermoresponsive behavior of the prepared films was exploited to demonstrate an all-optical modulation device. Continuous infrared light (1300 nm) was modulated by using a 660 nm visible diode laser. The laser intensity was sufficient to cause a localized thermochromic transition in the films. The laser was pulsed at 0.3 Hz and a uniform cyclic modulation depth of 0.3 dB was achieved. The demonstrated application of functional nanocellulose hybrid films as a light switch (modulator) could be harnessed in various thermally stimulated sensing systems such as temperature monitoring, energy-saving, and anti-counterfeiting.

Effect of Surfactant Type and Sonication Energy on the Electrical Conductivity Properties of Nanocellulose-CNT Nanocomposite Films.

We present a detailed study on the influence of sonication energy and surfactant type on the electrical conductivity of nanocellulose-carbon nanotube (NFC-CNT) nanocomposite films. The study was made using a minimum amount of processing steps, chemicals and materials, to optimize the conductivity properties of free-standing flexible nanocomposite films. In general, the NFC-CNT film preparation process is sensitive concerning the dispersing phase of CNTs into a solution with NFC. In our study, we used sonication to carry out the dispersing phase of processing in the presence of surfactant. In the final phase, the films were prepared from the dispersion using centrifugal cast molding. The solid films were analyzed regarding their electrical conductivity using a four-probe measuring technique. We also characterized how conductivity properties were enhanced when surfactant was removed from nanocomposite films; to our knowledge this has not been reported previously. The results of our study indicated that the optimization of the surfactant type clearly affected the formation of freestanding films. The effect of sonication energy was significant in terms of conductivity. Using a relatively low 16 wt. % concentration of multiwall carbon nanotubes we achieved the highest conductivity value of 8.4 S/cm for nanocellulose-CNT films ever published in the current literature. This was achieved by optimizing the surfactant type and sonication energy per dry mass. Additionally, to further increase the conductivity, we defined a preparation step to remove the used surfactant from the final nanocomposite structure.

Cyclodextrin-Functionalized Fiber Yarns Spun from Deep Eutectic Cellulose Solutions for Nonspecific Hormone Capture in Aqueous Matrices.

A wood based yarn platform for capturing pharmaceutical molecules from water was developed. Cellulose fiber yarns were modified with cyclodextrins, and the capture of 17α-ethinyl estradiol (EE2), a synthetic estrogen hormone used as contraceptive, from water was tested. The yarns were prepared by spinning a deep eutectic solution (DES) of cellulose in choline chloride-urea. Despite their high porosity and water sorption capacity (5 g/g), the spun fiber yarns displayed high wet strength, up to 60% of that recorded in dry condition (128 MPa with 17% strain at break). Cyclodextrin irreversible attachment on the yarns was achieved with adsorbed chitosan and the conjugation reactions and capture of EE2 by the cyclodextrin-modified cellulose were confirmed via online detection with Surface Plasmon Resonance (SPR). The facile synthesis of the bioactive yarns and EE2 binding capacity from aqueous matrices (as high as 2.5 mg/g) indicate excellent prospects for inexpensive platforms in disposable affinity filtration. The study presents a strategy to produce a wood fiber based yarn to be used as a platform for human and veterinary pharmaceutical hormone capture.

Spinning Approach for Cellulose Fiber Yarn Using a Deep Eutectic Solvent and an Inclined Channel.

We developed a spinning approach for a dope produced by treating softwood pulp with a deep eutectic solvent (DES). The DES enables formation of a sufficiently viscous spinnable gel-like suspension of fibers, which solidifies upon the removal of the DES. This solidification, however, requires a longer time compared to most conventional wet spinning processes. Consequently, the continuity of the spinning process has been constrained in previous work. Moreover, the ability to draw the incipient yarn to increase orientation has been limited. Here we present a continuous spinning approach where the fiber yarn properties and processability can be improved using an inclined channel. A combination of an air gap and an inclined ethanol stream transports and draws the incipient fiber yarn during spinning. The influence of syringe tip diameter, angle of the channel, ethanol flow rate, and twisting were studied experimentally. The improvements in the spinning process resulted in an increase in load bearing capability and ability to reduce the linear density of the fiber yarn.

The effect of cellulose molar mass on the properties of palmitate esters.

Nowadays one of the growing trends is to replace oil-based products with cellulose-based materials. Currently most cellulose esters require a huge excess of chemicals and have therefore, not been broadly used in the industry. Here, we show that decreasing the molar mass of cellulose by ozone hydrolysis provides cellulose functionalization with less chemical consumption. To reveal the differences in reactivity and chemical consumption, we showed esterification of both native cellulose and ozone treated hydrolyzed cellulose. Based on the results, the molar mass of the starting cellulose has a significant effect on the end product's degree of substitution and properties. Furthermore, molar mass controlled palmitate esters form mechanically strong, flexible and optically transparent films with excellent water barrier properties. We anticipate that molar mass controlled cellulose will provide a starting point for the greater use of cellulose based materials, in various application, such as films and composites.

Hydrothermal carbonization of pulp mill streams.

The progress of the conversion, the yield, the structure and the morphology of the produced carbonaceous materials as a function of time were systematically studied with pyrolysis-GC/FID and FESEM microscope. The conversion of galactoglucomannan, bleached kraft pulp and TEMPO oxidized cellulose nanofibrils followed the reaction route of glucose being slower though with fibrous material, higher molar mass and viscosity. The conversion of kraft lignin was minor following completely different reaction route. Carbonaceous particles of different shape and size were produced with yields between 23% and 73% after 4h with being higher for lignin than carbohydrates. According to the results, potential pulp mill streams represent lignocellulosic resources for generation of carbonaceous materials.

Simultaneous bench scale production of dissolving grade pulp and valuable hemicelluloses from softwood kraft pulp by ionic liquid extraction.

Ionic liquid extraction of wood pulp has been highlighted as a highly potential new process for dissolving pulp production. Coproduction with a polymeric hemicellulose fraction was demonstrated in bench scale from softwood kraft pulp using extraction with the ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIM OAc) and water. In total, the recovered pulp and hemicellulose fraction together yielded 95.5 wt.% of the pulp input. The extracted pulp had a remarkably high purity with an R18-value of 97.8%. The hemicellulose fraction consisted of galactoglucomannan, arabinoxylan and some cellulose and was precipitated from the ionic liquid-water mixture. After hydroxypropylation of the hemicellulose fraction, films were prepared and barrier and strength properties were compared to films from other polysaccharides. Reduced oxygen and water vapor permeation and good strength properties were demonstrated when compared to corresponding films from hydroxypropylated xylan from cold caustic extraction. The films have potential for applications in food packaging and edible films.

Production and applications of carbohydrate-derived sugar acids as generic biobased chemicals.

This review considers the chemical and biotechnological synthesis of acids that are obtained by direct oxidation of mono- or oligosaccharide, referred to as sugar acids. It focuses on sugar acids which can be readily derived from plant biomass sources and their current and future applications. The three main classes of sugar acids are aldonic, aldaric and uronic acids. Interest in organic acids derived from sugars has recently increased, as part of the interest to develop biorefineries which produce not only biofuels, but also chemicals to replace those currently derived from petroleum. More than half of the most desirable biologically produced platform chemicals are organic acids. Currently, the only sugar acid with high commercial production is d-gluconic acid. However, other sugar acids such as d-glucaric and meso-galactaric acids are being produced at a lower scale. The sugar acids have application as sequestering agents and binders, corrosion inhibitors, biodegradable chelators for pharmaceuticals and pH regulators. There is also considerable interest in the use of these molecules in the production of synthetic polymers, including polyamides, polyesters and hydrogels. Further development of these sugar acids will lead to higher volume production of the appropriate sugar acids and will help support the next generation of biorefineries.

Fabrication of electrospun poly(D,L lactide-co-glycolide)80/20 scaffolds loaded with diclofenac sodium for tissue engineering.

BACKGROUND: Adaptation of nanotechnology into materials science has also advanced tissue engineering research. Tissues are basically composed of nanoscale structures hence making nanofibrous materials closely resemble natural fibers. Adding a drug release function to such material may further advance their use in tissue repair. METHODS: In the current study, bioabsorbable poly(D,L lactide-co-glycolide)80/20 (PDLGA80/20) was dissolved in a mixture of acetone/dimethylformamide. Twenty percent of diclofenac sodium was added to the solution. Nanofibers were manufactured using electrospinning. The morphology of the obtained scaffolds was analyzed by scanning electron microscopy (SEM). The release of the diclofenac sodium was assessed by UV/Vis spectroscopy. Mouse fibroblasts (MC3T3) were seeded on the scaffolds, and the cell attachment was evaluated with fluorescent microscopy. RESULTS: The thickness of electrospun nanomats was about 1 mm. SEM analysis showed that polymeric nanofibers containing drug particles formed very interconnected porous nanostructures. The average diameter of the nanofibers was 500 nm. Drug release was measured by means of UV/Vis spectroscopy. After a high start peak, the release rate decreased considerably during 11 days and lasted about 60 days. During the evaluation of the release kinetics, a material degradation process was observed. MC3T3 cells attached to the diclofenac sodium-loaded scaffold. CONCLUSIONS: The nanofibrous porous structure made of PDLGA polymer loaded with diclofenac sodium is feasible to develop, and it may help to improve biomaterial properties for controlled tissue repair and regeneration.

Synthesis and characterization of copolyanhydrides of carbohydrate-based galactaric acid and adipic acid.

A series of copolyanhydrides, consisting of 2,3,4,5-tetra-O-acetylgalactaric acid (AGA) and adipic acid (AA) as monomer units, was polymerized. Synthesis of AGA monomer consisted of two steps. First, O-acetylation of galactaric acid secondary hydroxyl groups was performed using acetic anhydride as a reagent. Acetic anhydride was then further used as a reagent in the synthesis of diacetyl mixed anhydride of AGA. Polymerizations were conducted as bulk condensation polymerization at 150 °C. Thermal properties of the copolymers varied depending on monomer composition. Increase in the AGA content had a clear increasing effect on the Tg. A similar increasing effect was observed in Tm. The degree of crystallinity decreased as AGA content increased. There was a slightly lowering tendency in the molecular weights of the obtained polymers when the AGA content in the polymerization mixtures increased. The described synthesis route shows that bio-based aldaric acid monomers are potential candidates for the adjustment of thermal properties of polyanhydrides.

Nanofibrous chitosan-polyethylene oxide engineered scaffolds: a comparative study between simulated structural characteristics and cells viability.

3D nanofibrous chitosan-polyethylene oxide (PEO) scaffolds were fabricated by electrospinning at different processing parameters. The structural characteristics, such as pore size, overall porosity, pore interconnectivity, and scaffold percolative efficiency (SPE), were simulated by a robust image analysis. Mouse fibroblast cells (L929) were cultured in RPMI for 2 days in the presence of various samples of nanofibrous chitosan/PEO scaffolds. Cell attachments and corresponding mean viability were enhanced from 50% to 110% compared to that belonging to a control even at packed morphologies of scaffolds constituted from pores with nanoscale diameter. To elucidate the correlation between structural characteristics within the depth of the scaffolds' profile and cell viability, a comparative analysis was proposed. This analysis revealed that larger fiber diameters and pore sizes can enhance cell viability. On the contrary, increasing the other structural elements such as overall porosity and interconnectivity due to a simultaneous reduction in fiber diameter and pore size through the electrospinning process can reduce the viability of cells. In addition, it was found that manipulation of the processing parameters in electrospinning can compensate for the effects of packed morphologies of nanofibrous scaffolds and can thus potentially improve the infiltration and viability of cells.

Wood-derived olefins by steam cracking of hydrodeoxygenated tall oils.

Tall oil fractions obtained from Norwegian spruce pulping were hydrodeoxygenated (HDO) at pilot scale using a commercial NiMo hydrotreating catalyst. Comprehensive two dimensional gas chromatography (GC×GC) showed that HDO of both tall oil fatty acids (TOFA) and distilled tall oil (DTO) produced highly paraffinic hydrocarbon liquids. The hydrotreated fractions also contained fatty acid methyl esters and norabietane and norabietatriene isomers. Steam cracking of HDO-TOFA in a pilot plant revealed that high light olefin yields can be obtained, with 35.4 wt.% of ethene and 18.2 wt.% of propene at a coil outlet pressure (COP) of 1.7 bara, a dilution of 0.45 kg(steam)/kg(HDO-TOFA) and a coil outlet temperature (COT) of 820 °C. A pilot plant coking experiment indicated that cracking of HDO-TOFA at a COT of 850 °C results in limited fouling in the reactor. Co-cracking of HDO tall oil fractions with a typical fossil-based naphtha showed improved selectivity to desired light olefins, further demonstrating the potential of large scale olefin production from hydrotreated tall oil fractions in conventional crackers.

The use of N,N'-diallylaldardiamides as cross-linkers in xylan derivatives-based hydrogels.

N,N'-Diallylaldardiamides (DA) were synthesized from galactaric, xylaric, and arabinaric acids, and used as cross-linkers together with xylan (X) derivatives to create new bio-based hydrogels. Birch pulp extracted xylan was derivatized to different degrees of substitution of 1-allyloxy-2-hydroxy-propyl (A) groups combined with 1-butyloxy-2-hydroxy-propyl (B) and/or hydroxypropyl (HP) groups. The hydrogels were prepared in water solution by UV induced free-radical cross-linking polymerization of derivatized xylan polymers without DA cross-linker (xylan derivative hydrogel) or in the presence of 1 or 5 wt% of DA cross-linker (DA hydrogel). Commercially available cross-linker (+)-N,N'-diallyltartardiamide (DAT) was also used. The degree of substitution (DS) of A, B, and HP groups in xylan derivatives was analyzed according to (1)H NMR spectra. The DS values for the cross-linkable A groups of the derivatized xylans were 0.4 (HPX-A), 0.2 (HPX-BA), and 0.4 (X-BA). The hydrogels were examined with FT-IR and elemental analysis which proved the cross-linking successful. Water absorption of the hydrogels was examined in deionized water. Swelling degrees up to 350% were observed. The swollen morphology of the hydrogels was assessed by scanning electron microscopy (SEM). The presence of cross-linkers in DA hydrogels had only a small impact on the water absorbency when compared to xylan derivative hydrogels but a more uniform pore structure was achieved.

Tailoring of the hierarchical structure within electrospun fibers due to supramolecular comb-coil block copolymers: polystyrene-block-poly(4-vinyl pyridine) plasticized by hydrogen bonded pentadecylphenol.

Previously we demonstrated hierarchical self-assembly and mesoporosity in electrospun fibers using selected polystyrene--poly(4-vinylpyridine) (PS--P4VP) diblock copolymers with hydrogen-bonded 3--pentadecylphenol (PDP), which rendered distorted spherical P4VP(PDP) domains within the PS matrix, internal lamellar order within the P4VP(PDP) domains, and allowed distorted spherical pores by removing PDP (. 2005, , 1048). Here we study whether the internal structure of electrospun fibers can be systematically tailored by varying the compositions of PS--P4VP(PDP). We expect these complexes to be feasible choices to combine electrospinning and self-assembly, as relatively high molecular weight block copolymers are useful for electrospinning, and enhanced structure formation due to plasticization by the amphiphilic PDP was expected. Not surprisingly, the self-assembled structures of the as-prepared fibers were less perfect than those in the corresponding well-annealed bulk materials. Compositions that show spherical self-assembly of P4VP(PDP) within the PS matrix in bulk lead to distinct and elongated worm-like P4VP(PDP) domains within the PS matrix in electrospun fibers. More symmetric compositions, which showed lamellar self-assembly in bulk, lead to structures where both PS and P4VP(PDP) domains were worm-like and elongated in a relatively symmetric manner. Finally, compositions which in bulk showed self-assembly of PS spheres within the P4VP(PDP) matrix, lead to separate distorted PS domains in the P4VP(PDP) matrix. Additionally, SAXS measurements suggest a lamellar structure within the P4VP(PDP) domains. As electrospinning is a facile method to prepare mesoscale fibers, and it is known that the amphiphiles can be removed from the hierarchical assemblies, the present method offers the potential to tune the internal porosity of the fibers for release and absorption purposes.