Browsing by Author "Wang, Ling"

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  • Conductive Carbon Microfibers Derived from Wet-Spun Lignin/Nanocellulose Hydrogels
    (2019-03-18) Wang, Ling; Ago, Mariko; Borghei, Maryam; Ishaq, Amal; Papageorgiou, Anastassios C.; Lundahl, Meri; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We introduce an eco-friendly process to dramatically simplify carbon microfiber fabrication from biobased materials. The microfibers are first produced by wet-spinning in aqueous calcium chloride solution, which provides rapid coagulation of the hydrogel precursors comprising wood-derived lignin and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNF). The thermomechanical performance of the obtained lignin/TOCNF filaments is investigated as a function of cellulose nanofibril orientation (wide angle X-ray scattering (WAXS)), morphology (scanning electron microscopy (SEM)), and density. Following direct carbonization of the filaments at 900 °C, carbon microfibers (CMFs) are obtained with remarkably high yield, up to 41%, at lignin loadings of 70 wt % in the precursor microfibers (compared to 23% yield for those produced in the absence of lignin). Without any thermal stabilization or graphitization steps, the morphology, strength, and flexibility of the CMFs are retained to a large degree compared to those of the respective precursors. The electrical conductivity of the CMFs reach values as high as 103 S cm -1 , making them suitable for microelectrodes, fiber-shaped supercapacitors, and wearable electronics. Overall, the cellulose nanofibrils act as structural elements for fast, inexpensive, and environmentally sound wet-spinning while lignin endows CMFs with high carbon yield and electrical conductivity.
  • Effects of non-solvents and electrolytes on the formation and properties of cellulose I filaments
    (2019-12-01) Wang, Ling; Lundahl, Meri J.; Greca, Luiz G.; Papageorgiou, Anastassios C.; Borghei, Maryam; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Coagulation is a critical process in the assembly of cellulose nanofibrils into filaments by wet spinning; however, so far, the role of the coagulation solvent has not been systematically elucidated in this context. This work considers organic non-solvents (ethanol, acetone) and aqueous electrolyte solutions (NaCl(aq), HCl(aq), CaCl2(aq)) for the coagulation of negatively charged cellulose nanofibrils via wet spinning. The associated mechanisms of coagulation with such non-solvents resulted in different spinnability, coagulation and drying time. The properties of the achieved filaments varied depending strongly on the coagulant used: filaments obtained from electrolytes (using Ca2+ and H+ as counterions) demonstrated better water/moisture stability and thermomechanical properties. In contrast, the filaments formed from organic non-solvents (with Na+ as counterions) showed high moisture sorption and low hornification when subjected to cycles of high and low humidity (dynamic vapor sorption experiments) and swelled extensively upon immersion in water. Our observations highlight the critical role of counter-ions and non-solvents in filament formation and performance. Some of the fundamental aspects are further revealed by using quartz crystal microgravimetry with model films of nanocelluloses subjected to the respective solvent exchange.
  • Functional fibres by Wet-spinning of Bio-based Colloids
    (2020) Wang, Ling
     School of Chemical Engineering | Doctoral dissertation (article-based)
    Chitin nanofibrils (ChNF), TEMPO-oxidized cellulose nanofibrils (TOCNF), lignocellulose nanofibrils (LCNF), and lignin were isolated from marine and plant biomass. Microfibres were synthesized by wet spinning of aqueous suspensions of the respective bio-based colloid. The influence of coagulant type in wet spinning as well as the properties of the microfibers obtained from TOCNF and ChNF were studied. In general, fibres coagulated via ion exchange demonstrated better mechanical properties and water/moisture stability. Meanwhile, a clear difference was found in thermal properties: TOCNF microfibres coagulated in aqueous electrolyte presented better thermal stability compared to those coagulated in organic solvents. All the TOCNF and ChNF microfibres were biocompatible as shown by in vitro tests, which indicate prospective applications in the biomedical fields. Lignin-based fibres were manufactured from either LCNF or aqueous lignin suspensions in the presence of TOCNF. An increased lignin loading resulted in microfibres of lower mechanical strength and better thermostability. Carbon microfibres were obtained by one-step carbonization. The higher lignin content in the precursor led to carbon microfibres at higher mass yields and displaying smoother surfaces and higher electroconductivity. The measured electroconductivity (up to 103 S/cm) make them suitable for microelectrodes and wearable electronics. Moreover, the carbon microfibres developed from LCNF suspensions were demonstrated in uses as fibre-shaped supercapacitors, which showed a promising performance. A prototype system for continuous wet-spinning was developed to increase the spinning rate and to optimize the process. This work highlights the use of renewable bioresources in the production of microfibers with no need for molecular dissolution. Thus, the wet-spinning technique is shown as a feasible and versatile approach to produce microfibres, furthering their potential in functional materials. Biobased colloids are suitable alternatives for adoption in fibre production, replacing petroleum-based precursors and opening new opportunities for green processing.
  • Influence of magnetic nanoparticles on the mechano-magnetic response of wet-spun sodium alginate-nanocellulose filaments
    (2025-01) de Castro-Alves, Lisandra; Wang, Ling; González-Goméz, Manuel A.; Garcia-Acevedo, Pelayo; Arnosa-Prieto, Ángela; Borghei, Maryam; Piñeiro-Redondo, Yolanda; Rojas, Orlando J.; Rivas, José
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Hybrid filaments are of growing interest for a wide range of applications, including those that require stimuli-responsiveness. In this study we developed magnetic filaments by combining the properties of inorganic nanoparticles with the low density, flexibility and morphological features of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNF). The hybrid filaments were synthesized by wet spinning of TOCNF using sodium alginate (SA) adjuvant in a hydrogel containing magnetite (Fe3O4) nanoparticles (NPs) formed in-situ by nucleation and grow. The relationship between synthesis conditions and filament mechanical and magnetic properties were investigated at NP loading as high as 25%. Saturation magnetization of 1.60, 11.31, 19.41, and 33.25 emu/g Fe3O4 were measured at 5, 10, 15, and 25% NPs with a penalty in filament tensile strength which nevertheless reached at least 118 GPa along with low magnetite crystal orientation. Such high strength is rarely reported and found to depend on cellulose crystal orientation. The magnetic filaments were found suitable to replace traditional magnetic systems but add to the opportunity to develop flexible microwave adsorption textiles, artificial muscles, and micro-sensors.
  • Lignin effect in castor oil-based elastomers: Reaching new limits in rheological and cushioning behaviors
    (2021-02-08) Borrero Lopez, Antonio M.; Wang, Ling; Valencia, Concepción; Franco, José M.; Rojas, Orlando
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Lignin is demonstrated as an unprecedented reinforcing material that tailors the rheological and cushioning properties of castor oil-based polyurethane elastomers, expanding their viscoelastic moduli by four orders of magnitude. The tensile strain at break was triplicated in the presence of lignin while the Young modulus and the stress at break were enhanced 17- and 7-fold, respectively. Remarkably, in compression tests, lignin addition increased the stresses at break by more than 88-fold, whereas the strain at failure shifted from 50 to 93%. Dynamic mechanical compression tests indicated outstanding cushioning and resistance performance. Overall, the results demonstrate a performance not reached before for biosourced elastomeric materials, fitting the demands of a wide range of applications.
  • Lignin-Based Porous Supraparticles for Carbon Capture
    (2021-04-27) Zhao, Bin; Borghei, Maryam; Zou, Tao; Wang, Ling; Johansson, Leena-Sisko; Majoinen, Johanna; Sipponen, Mika H.; Österberg, Monika; Mattos, Bruno D.; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Multiscale carbon supraparticles (SPs) are synthesized by soft-templating lignin nano- and microbeads bound with cellulose nanofibrils (CNFs). The interparticle connectivity and nanoscale network in the SPs are studied after oxidative thermostabilization of the lignin/CNF constructs. The carbon SPs are formed by controlled sintering during carbonization and develop high mechanical strength (58 N·mm-3) and surface area (1152 m2·g-1). Given their features, the carbon SPs offer hierarchical access to adsorption sites that are well suited for CO2 capture (77 mg CO2·g-1), while presenting a relatively low pressure drop (∼33 kPa·m-1 calculated for a packed fixed-bed column). The introduced lignin-derived SPs address the limitations associated with mass transport (diffusion of adsorbates within channels) and kinetics of systems that are otherwise based on nanoparticles. Moreover, the carbon SPs do not require doping with heteroatoms (as tested for N) for effective CO2 uptake (at 1 bar CO2 and 40 °C) and are suitable for regeneration, following multiple adsorption/desorption cycles. Overall, we demonstrate porous SP carbon systems of low cost (precursor, fabrication, and processing) and superior activity (gas sorption and capture).
  • Mesoporous Carbon Microfibers for Electroactive Materials Derived from Lignocellulose Nanofibrils
    (2020-06-15) Wang, Ling; Borghei, Maryam; Ishfaq, Amal; Lahtinen, Panu; Ago, Mariko; Papageorgiou, Anastassios C.; Lundahl, Meri J.; Johansson, Leena Sisko; Kallio, Tanja; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The growing adoption of biobased materials for electronic, energy conversion, and storage devices has relied on high-grade or refined cellulosic compositions. Herein, lignocellulose nanofibrils (LCNF), obtained from simple mechanical fibrillation of wood, are proposed as a source of continuous carbon microfibers obtained by wet spinning followed by single-step carbonization at 900 °C. The high lignin content of LCNF (∼28% based on dry mass), similar to that of the original wood, allowed the synthesis of carbon microfibers with a high carbon yield (29%) and electrical conductivity (66 S cm-1). The incorporation of anionic cellulose nanofibrils (TOCNF) enhanced the spinnability and the porous morphology of the carbon microfibers, making them suitable platforms for electrochemical double layer capacitance (EDLC). The increased loading of LCNF in the spinning dope resulted in carbon microfibers of enhanced carbon yield and conductivity. Meanwhile, TOCNF influenced the pore evolution and specific surface area after carbonization, which significantly improved the electrochemical double layer capacitance. When the carbon microfibers were directly applied as fiber-shaped supercapacitors (25 F cm-3), they displayed a remarkably long-term electrochemical stability (>93% of the initial capacitance after 10 000 cycles). Solid-state symmetric fiber supercapacitors were assembled using a PVA/H2SO4 gel electrolyte and resulted in an energy and power density of 0.25 mW h cm-3 and 65.1 mW cm-3, respectively. Overall, the results indicate a green and facile route to convert wood into carbon microfibers suitable for integration in wearables and energy storage devices and for potential applications in the field of bioelectronics.
  • Microfibers synthesized by wet-spinning of chitin nanomaterials : Mechanical, structural and cell proliferation properties
    (2020-08-11) Wang, Ling; Ezazi, Nazanin Zanjanizadeh; Liu, Liang; Ajdary, Rubina; Xiang, Wenchao; Borghei, Maryam; Santos, Helder A.; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Partially deacetylated chitin nanofibers (ChNF) were isolated from shell residues derived from crab biomass and used to prepare hydrogels, which were easily transformed into continuous microfibers by wet-spinning. We investigated the effect of ChNF solid content, extrusion rate and coagulant type, which included organic (acetone) and alkaline (NaOH and ammonia) solutions, on wet spinning. The properties of the microfibers and associated phenomena were assessed by tensile strength, quartz crystal microgravimetry, dynamic vapor sorption (DVS), thermogravimetric analysis and wide-angle X-ray scattering (WAXS). The as-spun microfibers (14 GPa stiffness) comprised hierarchical structures with fibrils aligned in the lateral direction. The microfibers exhibited a remarkable water sorption capacity (up to 22 g g(-1)), while being stable in the wet state (50% of dry strength), which warrants consideration as biobased absorbent systems. In addition, according to cell proliferation and viability of rat cardiac myoblast H9c2 and mouse bone osteoblast K7M2, the wet-spun ChNF microfibers showed excellent results and can be considered as fully safe for biomedical uses, such as in sutures, wound healing patches and cell culturing.
  • Nanoarchitectonics of Nanocellulose Filament Electrodes by Femtosecond Pulse Laser Deposition of ZnO and In Situ Conjugation of Conductive Polymers
    (2024-05-01) Nguyen, Duong Tuan Anh; Wang, Ling; Imae, Toyoko; Su, Chun-Jen; Jeng, U-Ser; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Electroactive filament electrodes were synthesized by wet-spinning of cellulose nanofibrils (CNF) followed by femtosecond pulse laser deposition of ZnO (CNF@ZnO). A layer of conducting conjugated polymers was further adsorbed by in situ polymerization of either pyrrole or aniline, yielding systems optimized for electron conduction. The resultant hybrid filaments were thoroughly characterized by imaging, spectroscopy, electrochemical impedance, and small- and wide-angle X-ray scattering. For the filaments using polyaniline, the measured conductivity was a result of the synergy between the inorganic and organic layers, while the contribution was additive in the case of the systems containing polypyrrole. This observation is rationalized by the occurrence of charge transfer between ZnO and polyaniline but not that with polypyrrole. The introduced conductive hybrid filaments displayed a performance that competes with that of metallic counterparts, offering great promise for next-generation filament electrodes based on renewable nanocellulose.
  • Nanocellulose, pectin and lignin biomimetic composite filaments by wet spinning
    (2016-02-02) Wang, Ling
     Kemian tekniikan korkeakoulu | Master's thesis
    Bio-based materials are central components for the success of the future bio-economy and to fulfil product demands, for example, those derived from wood components, including cellulose, hemicellulose, lignin, extractives, etc. In turn, they can potentially address many current societal needs. An effort within the field of biomimetics of wood fibres, as presented in this thesis, is the use of TEMPO-oxidized nanocellulose (TOCNF), pectin and alkaline lignin to synthesize composite filaments. Such effort is aimed to the development of high performance products with low environmental impact. The composite water-based dope, containing the cell wall components along with calcium salts, displayed shear thinning properties and their spinnability was in some ways related to the apparent viscosity that need to be further proved. It was shown that pectin gelation was necessary for producing filaments by the wet spinning technology. In order to gellify pectin, two types of calcium salts (CaCO3 and CaCl2) were applied. It was found that acetone as coagulation medium afforded better spinnability compared to ethanol. In addition, the mechanical properties of the obtained filaments were compromised if excess calcium carbonate was used. It turned out that filaments obtained by using CaCO3 for in-situ gelation showed similar mechanical properties as those from TOCNF. In contrast, CaCl2 applied for ex-situ gelation made the filaments to become elastic. Remarkably, regardless the type of pectin gelation used, lignin improved the mechanical properties of TOCNF-based filament, in both the dry and wet state. SEM imaging was used to determine the surface morphology of the filaments. Filaments from in-situ gelation had similar surface features as those from neat TOCNF while those from ex-situ gelation were different. Polyhedral particles from CaCl2 salts were identified on the surface of filaments obtained from ex-situ gelation. Finally, quartz crystal microgravimetry was applied to understand the interaction mechanism between TOCNF, pectin and lignin.
  • Nanochitins of Varying Aspect Ratio and Properties of Microfibers Produced by Interfacial Complexation with Seaweed Alginate
    (2020-01-21) Grande, Rafael; Bai, Long; Wang, Ling; Xiang, Wenchao; Ikkala, Olli; Carvalho, Antonio J.F.; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We introduce chitin nanofibers, nanochitin (ChNF), the cationic groups of which electrostatically complex in aqueous media with the anionic groups of a polyanion, seaweed alginate (SA). This allows the formation of continuous microfibers after drawing contacting suspensions. We elucidate the effect of the nanofiber aspect ratio (15, 25, and >60) on the mechanical performance of the composite microfibers after considering variables such as concentration, pH, and drawing rate. An automatic collector facilitated a constant spinning velocity of 30 mm/s upon interfacial complexation from aqueous media (using 0.3 to 1 wt % as mass fraction for each component and a pH between 4 and 7). The composite microfibers showed a core-shell structure in which ChNFs were preferentially axially aligned in the center and more randomly oriented in the shell. The degree of ChNF alignment in the core increased with the aspect ratio, as resolved by WAXS diffractograms. Consequently, ChNF with the largest aspect ratio (>60) was readily spun into microfibers that displayed the highest Young's modulus (4.5 GPa), almost double that measured for the shortest ChNF. The latter, however, presented the highest strain and flexibility and allowed continuous fiber spinning. Distinctively, tensile tests revealed mechanically stable microfibers even in wet conditions, with a strength loss of less than 50% and strain gains of up to 35%. The amino and carboxyl groups in the microfibers offer possibilities for functionalization, expanding their potential beyond that related to wound healing and antibacterial applications. Overall, we provide a new perspective toward dry spinning via interfacial complexation of biobased components and the effect of a particle's morphology on the detailed structuring of microfibers, which display a particular assembly that is discussed here for the first time.
  • Oleogels and reverse emulsions stabilized by acetylated Kraft lignins
    (2023-07-01) Borrero-López, Antonio M.; Wang, Ling; Li, Haiming; Lourençon, Tainise V.; Valencia, Concepción; Franco, José M.; Rojas, Orlando J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Acetylated Kraft lignins were evaluated for their ability of structuring vegetable oils into oleogels. Microwave-assisted acetylation was used to adjust lignin's degree of substitution according to reaction temperature (130 to 160 °C), and its effect in improving the viscoelasticity of the oleogels, which was related to the hydroxyl group content. The results were compared with those obtained by Kraft lignins acetylated using conventional methods at room temperature. A higher microwave temperature resulted in gel-like oil dispersions with improved viscoelastic properties, and stronger shear-thinning character, along with enhanced long-term stability. Lignin nanoparticles structured castor oil by enhancing hydrogen bonding between the hydroxyl groups of the oil and the nanoparticles. The oil structuring capacity of the modified lignins enhanced the stability of water-in-oil Pickering emulsions that resulted from low-energy mixing.
  • Spinning of Cellulose Nanofibrils into Filaments: A Review
    (2017) Lundahl, Meri; Klar, Ville; Wang, Ling; Ago, Mariko; Rojas Gaona, Orlando
     A2 Katsausartikkeli tieteellisessä aikakauslehdessä
    Spinning of cellulose nanofibrils (CNF) offers promising opportunities to develop renewable fibers and filaments with strong, aligned structure. This review introduces recent findings on the relationship between the properties of CNF hydrogels, the spinning conditions and the performance of filaments obtained by dry- and wet-spinning. For example, the filament Young’s modulus correlates with CNF structural factors, such as slenderness and crystallinity. Furthermore, high shear rates and extensional flow strengthen the filament, mainly by improving structural uniformity and partly by effectively orienting the fibrils. However, other less obvious factors, such as those associated with coagulation and drying, play critical roles in filament performance. These and other details related to this timely application of CNF are presented here for the benefit of researchers and users of fibers and filaments for composites, textiles and others.
  • Synthesis of cellulose filament for recycled fiber reinforcement
    (2016-08-23) Laocharoen, Nikorn
     Kemian tekniikan korkeakoulu | Master's thesis
    The objective of this master’ thesis was to develop techniques for recycled fiber pre-treatments in order to produce both continuous cellulosic filaments as well as other nanocellulose structures. This exploratory work, therefore, investigated the properties of these materials in applications such as technical filaments and strength enhancers for use in papermaking, respectively. Recycled fibers obtained from old cardboard was chemically pre-treated by either TEMPO oxidation or carboxymethylation and subsequently disintegrated into cellulose nanofibrils by using both homogenization and microfluidization. The surface hydroxyl groups (-OH) of the recycled, cellulosic fibers were successfully converted to carboxylic (-COOH) groups to different extent. The presence of carboxylic functional groups was confirmed by FTIR and conductometric titration. Homogenization and microfluidization were used in order to deconstruct the pretreated cellulosic fibers into small fibrils. The carboxymethylated fibers required higher mechanical energy than the TEMPO-oxidized ones. This was explained by the lower carboxylic group content introduced onto the fiber surface in the former system. The cellulose nanofibrils were examined via Scanning Electron Microscopy (SEM) and their size was assessed by the Atomic Force Microscopy (AFM). The nanofibrils were found to be 10-50 nm in width and several microns in length. From these efforts, it was concluded that nanofibrils can be obtained relatively easily from recycled fibers. Two potential applications of the isolated cellulosic nanofibrils were addressed in this thesis. First, the production of continuous filaments by wet spinning and, secondly, the development of fibrils for deployment as additives for enhancing the mechanical strength of paper by addi-tion in the wet-end. The filaments produced from cellulosic nanofibrils from recycled cardboard displayed slightly lower tensile strength compared to those from cellulose nanofibrils obtained from bleached virgin fibers. The addition 0f a co-adjuvant to the fibril hydrogel dope, namely, poly vinylalcohol, improved the dry and wet tensile strength properties of the filaments. More remarkably, however, was our finding in relation to paper strength enhance-ment: a significant improvement in mechanical strength (tensile strength, stiffness, and TEA) was observed upon addition of the nanofibrils to fibrt disperions followed by drainage and drying. In addition, lower paper surface porosity was measured. Provided the negative effects realized in dewatering are minimized, the results indicate a new potentially promising use for recycled fibers.
  • Throughput and Coverage Evaluation for Radio Network Planning with EDGE
    (2000) Yang, Yongzhao
     Helsinki University of Technology | Master's thesis