Browsing by Author "Rojas, Orlando J."
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Item 3D printed manifolds for improved flow management in electrodialysis operation for desalination(Elsevier, 2021-06-01) Gonzalez-Vogel, Alvaro; Felis-Carrasco, Francisco; Rojas, Orlando J.; School services, CHEM; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; Dantec DynamicsDesalination with electrodialysis requires cell designs for optimal flow distribution. Such units include polymeric frames, electrodes, membranes and spacers. Frames are used for mechanical support of electrodes and hydraulic connectors. Their geometry needs to be customized for appropriate fluid management and hydraulic compartmentalization. Typically, such electrodialysis frames are manufactured by drilling solid plastic blocks. However, design flexibility is required to fit the increasing number of developments incorporating new materials and flow inter-connectivity. Here we propose additive manufacturing coupled with computational design to optimize flow dynamics and their coupling with physical devices. First, CAD models are proposed to incorporate major improvements in process lines, and to integrate internal manifold cavities. Even fluid flow and pressure drop distributions are verified by numerical models at given flowrates. The frames were 3D printed and assembled with electrodes and membranes to investigate their performance, and to experimentally confirm numerical predictions. Compared to conventional frames, and as a result of the even distribution of the fluids inside the cell, it was possible to reach an improved (21% higher) limiting current density while ensuring pH stability. Finally, our approach can be integrated in new designs, taking advantage of material selection and geometrical complexity of 3D-printing to add novel functionalities.Item 3D-Printed Thermoset Biocomposites Based on Forest Residues by Delayed Extrusion of Cold Masterbatch (DECMA)(AMERICAN CHEMICAL SOCIETY, 2021-10-18) Trifol, Jon; Jayaprakash, Siddharth; Baniasadi, Hossein; Ajdary, Rubina; Kretzschmar, Niklas; Rojas, Orlando J.; Partanen, Jouni; Seppälä, Jukka V.; Department of Chemical and Metallurgical Engineering; Department of Mechanical Engineering; Department of Bioproducts and Biosystems; Polymer technology; Advanced Manufacturing and Materials; Bio-based Colloids and MaterialsWe developed a 3D-printing process based on thermoset biocomposites termed Delayed Extrusion of Cold Masterbatch (DECMA). DECMA is a processing method, based on controlling the degree of curing, that takes some responsibility of the 3D printing from materials and as such can be used to 3D print otherwise unprintable materials. First, a masterbatch was produced by mixing a bio-based resin (bioepoxy) and sawdust and lignin. This paste was partially cured at room temperature until reaching an apparent viscosity suitable for extrusion (≈105 mPa·s at 1 s-1). The system was next cooled (5-10 °C) to delay subsequent hardening prior to 3D printing. The printability of the biocomposite paste was systematically investigated and the merits of the delayed extrusion, via DECMA, were assessed. It was found that DECMA allowed the revalorization of sawdust and lignin via 3D printing, as direct printing led to failed prints. Our approach afforded cost-effective, shear-thinning dopes with a high bio-based content (58-71%). The bio-based 3D-printed materials demonstrated good machinability by computer numerical control (CNC). Overall, the benefits of the introduced DECMA method are shown for processing bio-based materials and for on-demand solidification during additive manufacturing.Item Absorbent Filaments from Cellulose Nanofibril Hydrogels through Continuous Coaxial Wet Spinning(2018-08-15) Lundahl, Meri J.; Klar, Ville; Ajdary, Rubina; Norberg, Nicholas; Ago, Mariko; Cunha, Ana Gisela; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Department of Mechanical Engineering; Bio-based Colloids and Materials; Spectris plcA continuous and scalable method for the wet spinning of cellulose nanofibrils (CNFs) is introduced in a core/shell configuration. Control on the interfacial interactions was possible by the choice of the shell material and coagulant, as demonstrated here with guar gum (GG) and cellulose acetate (CA). Upon coagulation in acetone, ethanol, or water, GG and CA formed supporting polymer shells that interacted to different degrees with the CNF core. Coagulation rate was shown to markedly influence the CNF orientation in the filament and, as a result, its mechanical strength. The fastest coagulation noted for the CNF/GG core/shell system in acetone led to an orientation index of ∼0.55 (Herman's orientation parameter of 0.40), Young's modulus of ∼2.1 GPa, a tensile strength of ∼70 MPa, and a tenacity of ∼8 cN/tex. The system that underwent the slowest coagulation rate (CNF/GG in ethanol) displayed a limited CNF orientation but achieved an intermediate level of mechanical resistance, owing to the strong core/shell interfacial affinity. By using CA as the supporting shell, it was possible to spin CNF into filaments with high water absorption capacity (43 g water/g dry filament). This was explained by the fact that water (used as the coagulant for CA) limited the densification of the CNF core structure, yielding filaments with high accessible area and pore density.Item Accounting for Substrate Interactions in the Measurement of the Dimensions of Cellulose Nanofibrils(AMER CHEMICAL SOC, 2019-07) Mattos, Bruno D.; Tardy, Blaise L.; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Bio-based Colloids and MaterialsMechanically fibrillated cellulose nanofibrils (CNFs) have attracted special attention as building blocks for the development of advanced materials and composites. A correlation exists between CNF morphology and the properties of the materials they form. However, this correlation is often evaluated indirectly by process-centered approaches or by accessing a single dimensionality of CNFs adsorbed on solid supports. High-resolution imaging is currently the best approach to describe the morphological features of nanocelluloses; nevertheless, adsorption effects need to be accounted for. For instance, possible deformations of the CNFs arising from capillary forces and interactions with the substrate need to be considered in the determination of their cross-sectional dimensions. By considering soft matter imaging and adsorption effects, we provide evidence of the deformation of CNFs upon casting and drying. We determine a substantial flattening associated with the affinity of CNFs with the substrate corresponding to a highly anisotropic cross-sectional geometry (ellipsoidal) in the dried state. Negative-contrast scanning electron microscopy is also introduced as a new method to assess the dimensions of the CNFs. The images obtained by the latter, a faster imaging method, were correlated with those from atomic force microscopy. The cross-sectional area of the CNF is reconstructed by cross-correlating the widths and heights obtained by the two techniques.Item Acetylated Nanocellulose for Single-Component Bioinks and Cell Proliferation on 3D-Printed Scaffolds(AMER CHEMICAL SOC, 2019-05-22) Ajdary, Rubina; Huan, Siqi; Zanjanizadeh Ezazi, Nazanin; Xiang, Wenchao; Grande, Rafael; Santos, Hélder A.; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; University of HelsinkiNanocellulose has been demonstrated as a suitable material for cell culturing, given its similarity to extracellular matrices. Taking advantage of the shear thinning behavior, nanocellulose suits three-dimensional (3D) printing into scaffolds that support cell attachment and proliferation. Here, we propose aqueous suspensions of acetylated nanocellulose of a low degree of substitution for direct ink writing (DIW). This benefits from the heterogeneous acetylation of precursor cellulosic fibers, which eases their deconstruction and confers the characteristics required for extrusion in DIW. Accordingly, the morphology of related 3D-printed architectures and their performance during drying and rewetting as well as interactions with living cells are compared with those produced from typical unmodified and TEMPO-oxidized nanocelluloses. We find that a significantly lower concentration of acetylated nanofibrils is needed to obtain bioinks of similar performance, affording more porous structures. Together with their high surface charge and axial aspect, acetylated nanocellulose produces dimensionally stable monolithic scaffolds that support drying and rewetting, required for packaging and sterilization. Considering their potential uses in cardiac devices, we discuss the interactions of the scaffolds with cardiac myoblast cells. Attachment, proliferation, and viability for 21 days are demonstrated. Overall, the performance of acetylated nanocellulose bioinks opens the possibility for reliable and scale-up fabrication of scaffolds appropriate for studies on cellular processes and for tissue engineering.Item Adsorption and Assembly of Cellulosic and Lignin Colloids at Oil/Water Interfaces(AMER CHEMICAL SOC, 2019-01-22) Bai, Long; Greca, Luiz G.; Xiang, Wenchao; Lehtonen, Janika; Huan, Siqi; Nugroho, Robertus Wahyu N.; Tardy, Blaise L.; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Bio-based Colloids and MaterialsThe surface chemistry and adsorption behavior of submicrometer cellulosic and lignin particles have drawn wide-ranging interest in the scientific community. Here, we introduce their assembly at fluid/fluid interfaces in Pickering systems and discuss their role in reducing the oil/water interfacial tension, limiting flocculation and coalescence, and endowing given functional properties. We discuss the stabilization of multiphase systems by cellulosic and lignin colloids and the opportunities for their adoption. They can be used alone, as dual components, or in combination with amphiphilic molecules for the design of multiphase systems relevant to household products, paints, coatings, pharmaceutical, foodstuff, and cosmetic formulations. This invited feature article summarizes some of our work and that of colleagues to introduce the readers to this fascinating and topical area.Item Adsorption study on the formation of interfacial layers based on birch glucuronoxylans(Elsevier Science Ltd., 2024-09-01) Abik, Felix; Solin, Katariina; Hietala, Sami; Rojas, Orlando J.; Ho, Thao Minh; Mikkonen, Kirsi S.; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; University of HelsinkiGlucuronoxylans (GX), particularly crude fractions obtained by pressurized hot water extraction of birch wood, act as potent emulsifiers and stabilizers against physical separation and lipid oxidation. Herein, we studied the adsorption of GX on hydrophobic interfaces to correlate their multicomponent character towards the formation of interfacial layers in emulsions. Dynamic interfacial tension (DIFT) and quartz crystal microgravimetry with dissipation monitoring (QCM-D) were applied to various GX fractions and the results compared with those from cellulose-based emulsifiers. The roles of residual lignin and polysaccharides are discussed considering the formation of interfacial layers during emulsification. The DIFT of the different GXs reached quasi-equilibrium faster as the lignin concentration increased, implying a correlation between the rate of adsorption and the residual lignin content. The effect of NaCl addition was more pronounced in polysaccharide-rich fractions, indicating that the polysaccharide fraction modulated the effect of ionic strength. QCM-D showed that despite the fast adsorption exhibited by the lignin-rich GX extract in the DIFT curves, the adsorbed materials were lightweight, suggesting that the polysaccharide fraction built the bulk of the interfacial layer. These results provide a foundation towards understanding the role of GX in interfacial stabilization beyond traditional plant-based counterparts.Item Advanced Materials through Assembly of Nanocelluloses(WILEY-V C H VERLAG GMBH, 2018-06) Kontturi, Eero; Laaksonen, Päivi; Linder, Markus B.; Nonappa; Gröschel, André H.; Rojas, Orlando J.; Ikkala, Olli; Department of Bioproducts and Biosystems; Department of Applied Physics; Materials Chemistry of Cellulose; Nanostructures and Materials; Biomolecular Materials; Bio-based Colloids and Materials; Molecular Materials; University of Duisburg-EssenThere is an emerging quest for lightweight materials with excellent mechanical properties and economic production, while still being sustainable and functionalizable. They could form the basis of the future bioeconomy for energy and material efficiency. Cellulose has long been recognized as an abundant polymer. Modified celluloses were, in fact, among the first polymers used in technical applications; however, they were later replaced by petroleum-based synthetic polymers. Currently, there is a resurgence of interest to utilize renewable resources, where cellulose is foreseen to make again a major impact, this time in the development of advanced materials. This is because of its availability and properties, as well as economic and sustainable production. Among cellulose-based structures, cellulose nanofibrils and nanocrystals display nanoscale lateral dimensions and lengths ranging from nanometers to micrometers. Their excellent mechanical properties are, in part, due to their crystalline assembly via hydrogen bonds. Owing to their abundant surface hydroxyl groups, they can be easily modified with nanoparticles, (bio)polymers, inorganics, or nanocarbons to form functional fibers, films, bulk matter, and porous aerogels and foams. Here, some of the recent progress in the development of advanced materials within this rapidly growing field is reviewed.Item Advancing bio-based materials for sustainable solutions to food packaging(Nature Publishing Group, 2023-04) Tardy, Blaise L.; Richardson, Joseph J.; Greca, Luiz G.; Guo, Junling; Bras, Julien; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; University of Tokyo; Sichuan University; Université Grenoble AlpesThe unprecedented accumulation of plastic waste forms a serious threat to the biosphere, and current recycling efforts are not living up to their promise. Replacements for synthetic plastics are therefore critically needed, which has led to a rapid growth in research surrounding the development of sustainable materials, such as bioproducts. Still, commercialization has been limited, as knowledge gaps separating publicly funded research from industrial implementation need to be overcome. The food-packaging sector is currently undergoing drastic transformations in phasing out plastics and can therefore provide a blueprint for catalysing the adoption of bioproducts that could be applicable to other sectors.Item Agave tequilana Bagasse as Source of Cellulose Nanocrystals via Organosolv Treatment(2018) Hernandez, Javier; Romero, Victor; Escalante, Alfredo; Toriz, Guillermo; Rojas, Orlando J.; Sulbaran, Belkis; Universidad de Guadalajara; Department of Bioproducts and BiosystemsCellulose nanocrystals (CNCs) were isolated from Agave tequilana residues derived from ethanol production. Hemicelluloses and lignin extraction from agave bagasse was carried out via organosolv (ethanol/acetic) digestion followed by conventional sulfuric acid hydrolysis. The ethanol/acetic acid treatment resulted in cellulose yields of approximately 67% after lignin and ash removal. Compared to soda and sodium chlorite treatments with organosolv, the time and chemical load needed for delignification were remarkably reduced. The morphology of the cellulose fiber obtained in the three treatments was between 0.55 and 0.62 mm, with which CNC was obtained in the order of 83 to 195 nm in length. It is noteworthy that the longest cellulose fibers and nanocrystals were obtained from organosolv cellulose. The organosolv treatment led to a high purity cellulose, derived CNCs with a minimum energy consumption and mild chemical usage, and also considered the use of material streams associated with distillation processes.Thus, a viable alternative is suggested for the production of high quality CNC from widely available residual biomass that otherwise poses environmental and health-related risks.Item All-Aqueous Bicontinuous Structured Liquid Crystal Emulsion through Intraphase Trapping of Cellulose Nanoparticles(AMERICAN CHEMICAL SOCIETY, 2023-01-09) Guo, Shasha; Tao, Han; Gao, Guang; Mhatre, Sameer; Lu, Yi; Takagi, Ayako; Li, Jun; Mo, Lihuan; Rojas, Orlando J.; Chu, Guang; Department of Bioproducts and Biosystems; Materials Chemistry of Cellulose; Bio-based Colloids and Materials; University of British Columbia; South China University of TechnologyHere, we describe the all-aqueous bicontinuous emulsions with cholesteric liquid crystal domains through hierarchical colloidal self-assembly of nanoparticles. This is achieved by homogenization of a rod-like cellulose nanocrystal (CNC) with two immiscible, phase separating polyethylene glycol (PEG) and dextran polymer solutions. The dispersed CNCs exhibit unequal affinity for the binary polymer mixtures that depends on the balance of osmotic and chemical potential between the two phases. Once at the critical concentration, CNC particles are constrained within one component of the polymer phases and self-assemble into a cholesteric organization. The obtained liquid crystal emulsion demonstrates a confined three-dimensional percolating bicontinuous network with cholesteric self-assembly of CNC within the PEG phase; meanwhile, the nanoparticles in the dextran phase remain isotropic instead. Our results provide an alternative way to arrest bicontinuous structures through intraphase trapping and assembling of nanoparticles, which is a viable and flexible route to extend for a wide range of colloidal systems.Item All-Aqueous Liquid Crystal Nanocellulose Emulsions with Permeable Interfacial Assembly(AMERICAN CHEMICAL SOCIETY, 2020-10-27) Bai, Long; Huan, Siqi; Zhao, Bin; Zhu, Ya; Esquena, Jordi; Chen, Feng; Gao, Guang; Zussman, Eyal; Chu, Guang; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; Center for Biomedical Research Network (CIBER); University of British Columbia; Technion - Israel Institute of Technology; Northeast Forestry UniversityWe report on the formation of water-in-water liquid crystal emulsions with permeable colloidal assemblies. Rodlike cellulose nanocrystals (CNC) spontaneously self-assemble into a helical arrangement with the coexistence of nonionic, hydrophilic polyethylene glycol (PEG) and dextran, whereas the two polymer solutions are thermodynamically incompatible. Stable water-in-water emulsions are easily prepared by mixing the respective CNC/polymer solutions, showing micrometric CNC/PEG dispersed droplets and a continuous CNC/dextran phase. With time, the resulting emulsion demixes into an upper, droplet-lean isotropic phase and a bottom, droplet-rich cholesteric phase. Owing to the osmotic pressure gradient between PEG and dextran phases, target transfer of cellulose nanoparticles occurs across the water/water interface to reassemble into a liquid crystal-in-liquid crystal emulsion with global cholesteric organization. The observed structural, optical, and temporal evolution confirm that the colloidal particles in the two immiscible phases experience short-range interactions and form long-range assemblies across the interface.Item Alternative chemo-enzymatic treatment for homogeneous and heterogeneous acetylation of wood fibers(SPRINGER, 2018-09) Quintana, Elisabet; Ago, Mariko; Valls, Cristina; Roncero, M. Blanca; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; Polytechnic University of Catalonia; BarcelonaTechA new chemo-enzymatic treatment is proposed to produce cellulosic fibers suitable for heterogeneous- or homogeneous-phase acetylation. The procedure included enzymatic (laccase–violuric acid) lignin removal from the precursor fibers (unbleached sulfite pulp) followed by hydrogen peroxide treatment. An optional intermediate stage included partial hydrolysis (endoglucanase) to increase fiber reactivity. The obtained “biobleached” fibers were acetylated in the heterogeneous phase with acetic anhydride in nonpolar solvents, yielding various acetyl group contents, depending on the severity of the reaction. The degree of acetylation was highly sensitive to the treatment conditions, mainly the acetic anhydride activity in the system. The results were compared to those obtained after acetylation of commercial, dissolving-grade fibers, used as reference. The effect of the inherent nature of the fibers tested were elucidated as far as hemicellulose content, fiber length, fine content and crystallinity. Acetyl group content of up to 24% were determined after heterogeneous reaction with the chemoenzymatic fibers. The substitution of hydroxyl groups by acetyl moieties resulted in a lower hydrophilicity, as assessed by measurement of the water contact angle. Homogeneous acetylation of the chemo-enzymatic and reference fibers resulted in relatively similar acetyl group content (up to 36 and 33%, respectively). These samples were soluble in acetone and produced transparent films (via solvent casting), with enhanced dry strength and lower hydrophilicity. Overall, it is concluded that the proposed chemo-enzymatic treatment is a feasible alternative for the production of fibers that are suitable for efficient acetylation.Item Alternative proton exchange membrane based on a bicomponent anionic nanocellulose system(Elsevier Science Ltd., 2024-09-15) Brito dos Santos, Fernanda; Kaschuk, Joice; Banvillet, Gabriel; Jalaee, Adel; Rojas, Orlando J.; Foster, E. Johan; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; University of British ColumbiaAs integral parts of fuel cells, polymer electrolyte membranes (PEM) facilitate the conversion of hydrogen's chemical energy into electricity and water. Unfortunately, commercial PEMs are associated with high costs, limited durability, variable electrochemical performance and are based on perfluorinated polymers that persist in the environment. Nanocellulose-based PEMs have emerged as alternative options given their renewability, thermal and mechanical stability, low-cost, and hydrophilicity. These PEMs take advantage of the anionic nature of most nanocelluloses, as well as their facile modification with conductive functional groups, for instance, to endow ionic and electron conductivity. Herein, we incorporated for the first time two nanocellulose types, TEMPO-oxidized and sulfonated, to produce a fully bio-based PEM and studied their contribution separately and when mixed in a PEM matrix. Sulfonated nanocellulose-based PEMs are shown to perform similarly to commercial and bio-based membranes, demonstrating good thermal-oxidative stability (up to 190 °C), mechanical robustness (Young's modulus as high as 1.15 GPa and storage moduli >13 GPa), and high moisture-uptake capacity (ca. 6330 % after 48 h). The introduced nanocellulose membranes are shown as promising materials for proton-exchange material applications, as required in fuel cells.Item Ambient-Dried Cellulose Nanofibril Aerogel Membranes with High Tensile Strength and Their Use for Aerosol Collection and Templates for Transparent, Flexible Devices(2015) Toivonen, Matti S.; Kaskela, Antti; Rojas, Orlando J.; Kauppinen, Esko I.; Ikkala, Olli; Department of Forest Products Technology; Department of Applied Physics; Department of Bioproducts and Biosystems; Molecular MaterialsThe 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 cm3 g−1 specific modulus), strength (97 MPa tensile strength, 161 MPa m3 kg−1 specific strength), mesoporosity (pore diameter 10–30 nm, 208 m2 g−1 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, SWNT) from aerosols under pressure gradients. The membranes with deposited SWNT can be further compacted to transparent, conductive, and flexible conducting films (90% specular transmittance at 550 nm and 300 Ω ◻−1 sheet resistance with AuCl3-salt doping). Overall, the developed aerogel membranes pave way toward use in gas filtration and transparent, flexible devices.Item Anion-Specific Water Interactions with Nanochitin: Donnan and Osmotic Pressure Effects as Revealed by Quartz Microgravimetry(AMERICAN CHEMICAL SOCIETY, 2021-09-28) Jin, Soo Ah; Khan, Saad A.; Spontak, Richard J.; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; North Carolina State UniversityThe development of new materials emphasizes greater use of sustainable and eco-friendly resources, including those that take advantage of the unique properties of nanopolysaccharides. Advances in this area, however, necessarily require a thorough understanding of interactions with water. Our contribution to this important topic pertains to the swelling behavior of partially deacetylated nanochitin (NCh), which has been studied here by quartz crystal microgravimetry. Ultrathin films of NCh supported on gold-coated resonators have been equilibrated in aqueous electrolyte solutions (containing NaF, NaCl, NaBr, NaNO3, Na2SO4, Na2SO3, or Na3PO4) at different ionic strengths. As anticipated, NCh displays contrasting swelling/deswelling responses, depending on the ionic affinities and valences of the counterions. The extent of water uptake induced by halide anions, for instance, follows a modified Hofmeister series with F- producing the highest swelling. In marked contrast, Cl- induces film dehydration. We conclude that larger anions promote deswelling such that water losses increase with increasing anion valence. Results such as the ones reported here are critical to ongoing efforts designed to dry chitin nanomaterials and develop bio-based and sustainable materials, including particles, films, coatings, and other nanostructured assemblies, for various devices and applications.Item Anomalous-Diffusion-Assisted Brightness in White Cellulose Nanofibril Membranes(WILEY-V C H VERLAG GMBH, 2018-04) Toivonen, Matti S.; Onelli, Olimpia D.; Jacucci, Gianni; Lovikka, Ville; Rojas, Orlando J.; Ikkala, Olli; Vignolini, Silvia; Department of Applied Physics; School services, CHEM; Department of Bioproducts and Biosystems; Molecular Materials; Bio-based Colloids and Materials; University of CambridgeThe 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.Item Assembling Native Elementary Cellulose Nanofibrils via a Reversible and Regioselective Surface Functionalization(AMERICAN CHEMICAL SOCIETY, 2021-10-20) Beaumont, Marco; Tardy, Blaise L.; Reyes, Guillermo; Koso, Tetyana V.; Schaubmayr, Elisabeth; Jusner, Paul; King, Alistair W.T.; Dagastine, Raymond R.; Potthast, Antje; Rojas, Orlando J.; Rosenau, Thomas; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; University of Helsinki; University of Natural Resources and Life Sciences, Vienna; University of MelbourneSelective surface modification of biobased fibers affords effective individualization and functionalization into nanomaterials, as exemplified by the TEMPO-mediated oxidation. However, such a route leads to changes of the native surface chemistry, affecting interparticle interactions and limiting the development of potential supermaterials. Here we introduce a methodology to extract elementary cellulose fibrils by treatment of biomass with N-succinylimidazole, achieving regioselective surface modification of C6-OH, which can be reverted using mild post-treatments. No polymer degradation, cross-linking, nor changes in crystallinity occur under the mild processing conditions, yielding cellulose nanofibrils bearing carboxyl moieties, which can be removed by saponification. The latter offers a significant opportunity in the reconstitution of the chemical and structural interfaces associated with the native states. Consequently, 3D structuring of native elementary cellulose nanofibrils is made possible with the same supramolecular features as the biosynthesized fibers, which is required to unlock the full potential of cellulose as a sustainable building block.Item Associative structures formed from cellulose nanofibrils and nanochitins are pH-responsive and exhibit tunable rheology(ACADEMIC PRESS INC ELSEVIER SCIENCE, 2021-04-15) Facchine, Emily G.; Bai, Long; Rojas, Orlando J.; Khan, Saad A.; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; North Carolina State UniversityHypothesis: Nanocellulose and nanochitin are both biobased materials with complementary structures and properties. Both exhibit pH-dependent surface charges which are opposite in sign. Hence, it should be possible to manipulate them to form complexed structures via ionic bond formation at prescribed pH conditions. Experiment: Nanocellulose and nanochitin were mixed after exposure to acidic or neutral conditions to influence their ionization state. The heat of interaction during the introduction of nanochitin to nanocellulose was monitored via isothermal titration calorimetry. The strength and gel properties of the resulting structures were characterized via rheological measurement. Findings: The resultant gel properties in the designed hybrid systems were found to depend directly on the charge state of the starting materials, which was dictated by pH adjustment. Different interparticle interactions including ionic attraction, hydrophobic associations, and physical entanglement were identified in the systems and the influence of each was elucidated for different conditions of pH, concentration, and ratio of nanochitin to nanocellulose. Hydrophobic associations between neutralized nanochitin particles were found to contribute strongly to increased elastic modulus values. Ionic complex formation was found to provide enhanced stability under broader pH conditions, while physical entanglement of cellulose nanofibers was a substantial thickening mechanism in all systems.Item Asymmetric bipolar switch device for electrochemical processes(AMER INST PHYSICS, 2019-08-01) Gonzalez-Vogel, Alvaro; Rojas, Orlando J.; Biohybrid Materials; Department of Bioproducts and BiosystemsNew strategies for the intensification of industrial electromembrane processes are needed, especially to reduce equipment size and operational costs. To intensify those processes and to decrease fouling and scale occurrence in such systems, we propose operation with very short asymmetric pulses (order of microseconds) of alternating polarity. Hence, a custom made Asymmetric Bipolar Switch was designed and built, operating with pulse widths in the 10-5-10-2 s range. Compared to traditional systems, we demonstrate the possibility of applying pulses with high intensities, up to three times higher than normal operation, using a frequency range between 0 (continuous operation) and 102 Hz. The proposed device was coupled to an electrodialysis cell for desalting a brine solution. When switching in desalination, a Back Electrochemical Force was identified, which could affect the integrity of the electronic systems due to spikes of reverse voltage. Hence, mitigation strategies were applied by changing the switching logic and incorporating new elements in the circuitry, similar to those in breaking methods in electrical motors. While desalting in electrodialysis, the experiments showed a limited power loss, up to 0.6% of the total power applied, attributed mainly to electrical disturbance (conduction and switching losses in the electronic components were minor at this scale). No significant variation in the desalination performance was observed at low current densities. The designed Asymmetric Bipolar Switch opens new possibilities for the operation with electromembranes and other electrochemical processes.
