The application potential of cellulose nanofibril (CNF) aerogels has been hindered by the slow and costly freeze-or supercritical drying methods. Here, CNF aerogel membranes with attractive mechanical, optical and gas transport properties are prepared in ambient conditions with a facile and scalable process. Aqueous CNF dispersions are vacuum-filtered and solvent exchanged to 2-propanol and further to octane, followed by ambient drying. The resulting CNF aerogel membranes are characterized by high transparency (> 90 % transmittance), stiffness (6 GPa Young's modulus, 10 GPa . cm 3 /g specific modulus), strength (97 MPa tensile strength, 161 MPa . m 3 /kg specific strength), mesoporosity (pore diameter 10-30 nm, 208 m 2 /g specific surface area) and low density (~0.6 g/cm 3 ). They are gas-permeable thus enabling collection of nanoparticles (for example, single-walled carbon nanotubes, SWCNT) from aerosols under pressure gradients. The membranes with deposited SWCNT can be further compacted to transparent, conductive and flexible conducting films (90% specular transmittance at 550 nm 1 and 300 Ω/ □ sheet resistance with AuCl3-salt doping). Overall, the developed aerogel membranes pave way towards use in gas filtration and transparent, flexible devices.

Nanocomposite materials made from cellulose show a great potential as future high-performance and sustainable materials. We show how high aspect ratio cellulose nanofibrils can be efficiently aligned in extrusion to fibers, leading to increased modulus of toughness (area under the stress-strain curve), Young’s modulus, and yield strength by increasing the extrusion capillary length, decreasing its diameter, and increasing the flow rate. The materials showed significant property combinations, manifesting as high modulus of toughness (~28–31 MJ/m3) vs. high stiffness (~19–20 GPa), and vs. high yield strength (~130–150 MPa). Wide angle X-ray scattering confirmed that the enhanced mechanical properties directly correlated with increased alignment. The achieved moduli of toughness are approximately double or more when compared to values reported in the literature for corresponding strength and stiffness. Our results highlight a possibly general pathway that can be integrated to gel-spinning process, suggesting the hypothesis that that high stiffness, strength and toughness can be achieved simultaneously, if the alignment is induced while the CNF are in the free-flowing state during the extrusion step by shear at relatively low concentration and in pure water, after which they can be coagulated.

ABSTRACT. One of the major, but often overlooked, challenges towards high end applications of nanocelluloses is to maintain their mechanical stability under hydrated conditions. As such, permanent covalent crosslinking or surface hydrophobization are viable solutions provided that neither processability nor interfibrillar bonding is compromised. Here we show an alternative based on physical crosslinking of nanofibrillated cellulose (NFC, also denoted as microfibrillated cellulose, MFC, and cellulose nanofibers, CNF) with chitosan for the preparation of transparent films. Transparency (~ 80 % throughout the visible spectrum) is achieved by suppressing aggregation and carefully controlling the mixing conditions: Chitosan dissolves in aqueous medium at low pH and under these conditions the NFC/chitosan mixtures form easily processable hydrogels.A simple change in the environmental conditions (i.e. an increase of pH) reduces hydration of chitosan promoting multivalent physical interactions between NFC and chitosan over those with water, resulting effectively in crosslinking. Films of NFC/chitosan 80/20 w/w show excellent mechanical properties in the wet state, with a tensile modulus of 4 and 14 GPa at low (0.5 %) and large (16 %) strains, respectively and an ultimate strength of 100 MPa (with corresponding maximum strain of 28 %). Remarkably, a strength of 200 MPa (with maximum strain of 8%) is measured at 50 % air relative humidity. We expect that the proposed, simple concept opens new pathways toward NFC-based material utilization in wet or humid conditions, a challenge that has remained unresolved.

The understanding of the interaction between light and complex, random structures is the key for designing and tailoring the optical appearance and performance of many materials that surround us, ranging from everyday consumer products, such as those for personal care, paints, and paper, to light diffusers used in the LED-lamps and solar cells. Here, it is demonstrated that the light transport in membranes of pure cellulose nanofibrils (CNFs) can be controlled to achieve bright whiteness in structures only a few micrometers thick. This is in contrast to other materials, such as paper, which require hundreds of micrometers to achieve a comparable appearance. The diffusion of light in the CNF membranes is shown to become anomalous by tuning the porosity and morphological features. Considering also their strong mechanical properties and biocompatibility, such white coatings are proposed as a new application for cellulose nanofibrils.

ABSTRACT. Fiber spinning of anionic TEMPO-oxidized cellulose (TOCN) nanofibrils with polycations by interfacial polyelectrolyte complexation is demonstrated. The formed fibers were mostly composed of cellulose nanofibrils and the polycations were a minor constituent, leading to yield and ultimate strengths of ca. 100 MPa and ca. 200 MPa, and Young's modulus of ca. 15 GPa.Stretching of the as-formed wet filaments of TOCN/polycation by 20 % increased the Young's modulus, yield strength, and ultimate tensile strength by approximately 45, 36 and 26 %, respectively. Importantly, feasibility of compartmentalized wound bicomponent fibers by simultaneous spinning of two fibers of different compositions and entwining them together was shown. This possibility was further exploited to demonstrate reversible shape change of a bicomponent fiber directly by humidity change, and indirectly by temperature changes based on thermally dependent humidity absorption.The demonstrated route for TOCN-based fiber preparation is expected to open up new avenues in the application of nanocelluloses in advanced fibrous materials, crimping, and responsive smart textiles.

A novel, objective, and rapid computed motility inhibition (CMI) assay was developed to identify and assess sublethal injury in toxin-exposed boar spermatozoa and compared with a subjective visual motility inhibition (VMI) assay. The CMI values were calculated from digital micrographic videos using a custom MATLAB® script by contrasting the motility index values of each experiment with those of the background and control experiments. Following a comparison of the CMI and VMI assays results, it was determined that their agreement depended on the shape of the dose-response curve. Toxins that exhibited a steep slope were indicative of good agreement between the assays. Those depicted by a gentle decline in the slope of the dose-response curve, the CMI assay were shown to be two times more sensitive than the VMI assay. The CMI assay was highly sensitive to the inhibition of mitochondrial function and glucose transport activity by sublethal doses of toxins and to disruption of cellular cation homeostasis by carrier ionophoric toxins, when compared to the cytotoxicity and lethal toxicity assays (i.e., that evaluated the inhibition of cell proliferation in somatic cell lines (FL, PK-15, and MNA cells)) and disruption to spermatozoa membrane integrity. The CMI assay recognized subtle sublethal toxicity changes in metabolism, manifested as a decrease in boar spermatozoa motility. Thus, it was feasible to effectively compare the objectively-measured numerical values for motility inhibition using the CMI assay against those reflecting lethal damage in the spermatozoa cells and somatic cell lines using a cytotoxicity assay.

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