| 1. |
- Aguilar-Sanchez, Andrea, et al.
(author)
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Charged ultrafiltration membranes based on TEMPO-oxidized cellulose nanofibrils/poly(vinyl alcohol) antifouling coating
- 2021
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In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 11:12, s. 6859-6868
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Journal article (peer-reviewed)abstract
- This study reports the potential of TEMPO-oxidized cellulose nanofibrils (T-CNF)/poly(vinyl alcohol) (PVA) coatings to develop functionalized membranes in the ultrafiltration regime with outstanding antifouling performance and dimensional/pH stability. PVA acts as an anchoring phase interacting with the polyethersulfone (PES) substrate and stabilizing for the hygroscopic T-CNF via crosslinking. The T-CNF/PVA coated PES membranes showed a nano-textured surface, a change in the surface charge, and improved mechanical properties compared to the original PES substrate. A low reduction (4%) in permeance was observed for the coated membranes, attributable to the nanometric coating thickness, surface charge, and hydrophilic nature of the coated layer. The coated membranes exhibited charge specific adsorption driven by electrostatic interaction combined with rejection due to size exclusion (MWCO 530 kDa that correspond to a size of similar to 35-40 nm). Furthermore, a significant reduction in organic fouling and biofouling was found for T-CNF/PVA coated membranes when exposed to BSA and E. coli. The results demonstrate the potential of simple modifications using nanocellulose to manipulate the pore structure and surface chemistry of commercially available membranes without compromising on permeability and mechanical stability.
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| 2. |
- Aguilar-Sanchez, Andrea, et al.
(author)
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Waterborne nanocellulose coatings for improving the antifouling and antibacterial properties of polyethersulfone membranes
- 2021
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In: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 620
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Journal article (peer-reviewed)abstract
- This article presents a waterborne nanocellulose coating process to change the surface characteristics and mitigate fouling of commercially available polyethersulfone (PES) microfiltration membranes. An extensive comparative study between nanoporous and nano-textured layers composed of cellulose nanocrystals (CNC) or TEMPO-oxidized cellulose nanofibrils (T-CNF), which were coated on the PES membrane by taking advantage of the electrostatic interactions between the PES substrate, a polyallylamine hydrochloride (PAHC1) anchoring layer, and the nanocellulose functional layer. Coated PES membranes exhibited decreased surface roughness and pore sizes as well as rejection of compounds with a M-w above 150 kDa, while the water permeability and mechanical properties of remained largely unaffected. The coatings improved the wettability as confirmed by a reduction of the contact angle by up to 52% and exhibited a higher negative surface charge compared to the uncoated membranes over a pH range of 4-8. A significant reduction in organic fouling was observed for the coated membranes demonstrated by bovine serum albumin (BSA) adsorption studies on T-CNF and CNC surfaces using Quartz Crystal Microbalance with Dissipation monitoring (QCM-D), UV-vis spectroscopy and FTIR mapping after exposing the membranes to dynamic adsorption of BSA. The T-CNF coating exhibited effective antibacterial action against Escherichia coli (E. coli) attributed to the pH reduction effect induced by the carboxyl groups; while CNC coatings did not show this property. This work demonstrates a simple, green, and easy-to-scale layer-by-layer coating process to tune the membrane rejection and to improve antifouling and antibacterial properties of commercially available membranes.
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| 3. |
- Hooshmand, Saleh
(author)
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Process and properties of continuous fibers based on cellulose nanocrystals and nanofibers
- 2014
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Licentiate thesis (other academic/artistic)abstract
- In recent years, composites made from natural fibers based on cellulose have received increasing attention since they have a low environmental impact and good mechanical properties. However, these fibers are short and discontinuous and the conventional spinning techniques used for these fibers results in continuous yarns with mechanical properties considerably lower than that of the single fibers. The aim of this work was to prepare continuous fibers where nano-sized cellulose crystals and cellulose nanofibers were used to improve the fiber properties. Two different strategies have been used to reach this aim. In the first study, bio-based fibers of cellulose acetate butyrate (CAB) and cellulose nanocrystals (CNC) using triethyl citrate (TEC) as plasticizer were prepared by melt spinning. Two different dispersion techniques were studied. In the first technique, the water content of the CNC suspension was reduced and exchanged to ethanol using centrifugation. In the second, the water in the CNC suspension was completely exchanged to ethanol by a sol-gel process. Results showed that tensile modulus and tensile strength of the nanocomposite fibers produced with the first technique were lower than CAB-TEC fibers, but the fibers produced by the sol-gel process showed an increase in the tensile modulus and had no decrease in the strength. Optical microscopy of the fibers indicated less aggregations in the sol-gel prepared materials. The results indicate that the sol-gel process is enhancing the dispersion of cellulose nanocrystals and can be a suitable way to prepare nanocomposite fibers. The second study is an extension of the first study. Here the effect of weight concentration of CNC and fiber drawing was studied. The microscopy studies showed that the addition of CNC in CAB resulted in defect-free and smooth fiber surfaces. An addition of 10 wt% CNC enhanced the storage modulus and increased the tensile strength and Young’s modulus. Fiber drawing improved the mechanical properties further. In addition, a micromechanical model of the composite material was used to estimate the stiffness and showed that theoretical values were exceeded for the lower concentration of CNC but not reached for the higher concentration. In conclusion, this dispersion technique combined with melt spinning can be used to produce all-cellulose nanocomposites fibers and that both the increase in CNC volume fraction and the fiber drawing increased the mechanical performance. In the third study a different strategy was used. Here low cost and environmentally friendly continuous fibers of native cellulose were prepared by dry spinning an aqueous suspension of cellulose nanofibers (CNF). The CNF were extracted from banana rachis, a bio-residue from banana cultivation in Columbia. The effect of spinning rate and CNF concentration on the mechanical properties of the fibers were investigated. The results showed that there was a relationship between the spinning rate and concentration. The modulus of the fibers was increased from 7.7 to 12.6 GPa and the strength increased from 131 to 222 MPa when the lowest concentration and highest speed was used. This improvement is believed to be due to an increased orientation of the CNF in the fiber. A minimum concentration of 6.5 wt% was required for continuous fiber spinning. However, this relatively high concentration is thought to limit the orientation of the CNF in the fiber. The process used in this last study has a good potential for up-scaling providing a continuous fiber production with well-controlled speed but further work is required to increase the orientation and subsequently the mechanical properties.The results from these three studies shows that it is possible to spin continuous fibers where nanocellulose is used as a reinforcing agent. It is also shown that the dispersion and alignment of the nanocellulose plays a key role in improving the mechanical properties.
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| 4. |
- Kaldéus, Tahani
(author)
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Surface modification approaches of cellulose nanofibrils and their effect on dispersibility
- 2019
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Doctoral thesis (other academic/artistic)abstract
- In the strive to find and develop sustainable bio-based materials an increased interest for nanocellulosic materials as attractive alternatives has arisen during the past decades. This can be attributed to their abundant renewability, remarkable inherent mechanical properties and their capability to be chemically modified. Cellulose nanofibrils (CNFs) are commonly obtained from wood pulp fibres and prepared through mechanical, chemical and/or enzymatic treatments. However, due to their hydrophilic nature and tendency to self-aggregate, their surface chemistry need to be altered to fully utilise their inherent properties and enable their usage in conventional large-scale industrial processes.This thesis work focuses on elucidating the fundamental aspects of the colloidal stability of highly concentrated CNF dispersions and the redispersibility of dried CNFs. Small amounts of amine-terminated poly(ethylene glycol) (PEG) were used to sterically stabilise the CNFs at higher fibril concentrations and delay the dispersion-arrested state transition (Paper I). The redispersibility of dried CNFs was studied for differently charged CNFs as a function of redispersing agents such as carboxymethyl cellulose (CMC), PEG and lignin (Paper II).This thesis presents green, facile modification approaches as well as strategies for improved dispersibility and compatibility with polymer matrices. The commercially established carboxymethylation process was expanded with a subsequent functionality step, yielding a mild, versatile one-pot protocol for the preparation of bi-functional CNFs (Paper III). Further, reactive amphiphilic macromolecules with targeted side-chain functionalities were used to compatibilise the CNF surface by water-based approaches. In the first study, a macroinitiator was used for the development of a versatile, yet facile, protocol for the controlled polymerisation of both hydrophilic and hydrophobic monomers in water from the CNF surface (Paper IV). In the second study, a reactive macro-compatibiliser was used to molecularly engineer the interface between CNFs and a polymer matrix by reactive-melt processing, yielding nanocomposites with improved stiffness while maintaining the deformability (Paper V).
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| 5. |
- Karim, Zoheb, et al.
(author)
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In situ TEMPO surface functionalization of nanocellulose membranes for enhanced adsorption of metal ions from aqueous medium
- 2017
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In: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 7:9, s. 5232-5241
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Journal article (peer-reviewed)abstract
- The current work demonstrates an innovative approach to develop nanocellulose based membranes with high water permeability, mechanical stability and high functionality via (1) tailoring the composition of the support layer of sludge microfibers/cellulose nanofibers (CNFSL) and (2) in situ TEMPO functionalization of the thin functional layer of cellulose nanocrystals (CNCBE) to enhance the metal ion adsorption capacity. SEM studies showed a porous network structure of the cellulose support layer and a denser functional layer with CNCBE embedded within gelatin matrix. AFM studies indicated the presence of a nanoscaled coating and increased roughness of membranes surface after TEMPO modification whereas FT-IR and conductometric titration confirmed the introduction of carboxyl groups upon TEMPO oxidation. The contact angle measurement results showed improved hydrophilic nature of membranes after in situ TEMPO functionalization. High networking potential of CNFSL made the membrane support layer tighter with a concomitant decrease in the average pore size from 6.5 to 2.0 μm. The coating with CNCBE further decreased the average pore size to 0.78 and 0.58 μm for S/CNCBE and S–CNFSL/CNCBE, respectively. In parallel, a drastic decrease in water flux (8000 to 90 L MPa−1 h−1 m−2) after coating with CNCBE was recorded but interestingly in situ functionalization of top CNCBE layer did not affect water flux significantly. The increase in adsorption capacity of ≈1.3 and ≈1.2 fold was achieved for Cu(II) and Fe(II)/Fe(III), respectively after in situ TEMPO functionalization of membranes. Biodegradation study confirmed the stability of layered membranes in model wastewater and a complete degradation of membranes was recorded after 15 days in soil.
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| 6. |
- Karim, Zoheb, et al.
(author)
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In situ TEMPO surface functionalization of nanocellulose membranes for enhanced adsorption of metal ions from aqueous medium
- 2017
-
In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 7:9, s. 5232-5241
-
Journal article (peer-reviewed)abstract
- The current work demonstrates an innovative approach to develop nanocellulose based membranes with high water permeability, mechanical stability and high functionality via (1) tailoring the composition of the support layer of sludge microfibers/cellulose nanofibers (CNFSL) and (2) in situ TEMPO functionalization of the thin functional layer of cellulose nanocrystals (CNCBE) to enhance the metal ion adsorption capacity. SEM studies showed a porous network structure of the cellulose support layer and a denser functional layer with CNCBE embedded within gelatin matrix. AFM studies indicated the presence of a nanoscaled coating and increased roughness of membranes surface after TEMPO modification whereas FT-IR and conductometric titration confirmed the introduction of carboxyl groups upon TEMPO oxidation. The contact angle measurement results showed improved hydrophilic nature of membranes after in situ TEMPO functionalization. High networking potential of CNFSL made the membrane support layer tighter with a concomitant decrease in the average pore size from 6.5 to 2.0 mm. The coating with CNCBE further decreased the average pore size to 0.78 and 0.58 mm for S/CNCBE and S-CNFSL/CNCBE, respectively. In parallel, a drastic decrease in water flux (8000 to 90 L MPa-1 h(-1) m(-2)) after coating with CNCBE was recorded but interestingly in situ functionalization of top CNCBE layer did not affect water flux significantly. The increase in adsorption capacity of approximate to 1.3 and approximate to 1.2 fold was achieved for Cu(II) and Fe(II)/Fe(III), respectively after in situ TEMPO functionalization of membranes. Biodegradation study confirmed the stability of layered membranes in model wastewater and a complete degradation of membranes was recorded after 15 days in soil.
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| 7. |
- Mautner, Andreas, et al.
(author)
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Cellulose nanopapers as tight aqueous ultra-filtration membranes
- 2015
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In: Reactive & functional polymers. - : Elsevier BV. - 1381-5148 .- 1873-166X. ; 86, s. 209-214
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Journal article (peer-reviewed)abstract
- Recently, we have demonstrated the use of wood-derived nanocellulose papers, herein termed nanopapers, for organic solvent nanofiltration applications. In this study, we extend the use of these nanopapers to tight ultrafiltration (UF) membranes. The feasibility of such nanopaper-based UF membranes intended for use in water purification is shown. Four types of nanocelluloses, namely bacterial cellulose, wood-derived nanocellulose, TEMPO-oxidized cellulose nanofibrils and cellulose nanocrystals, were used as raw materials for the production of these nanopaper-based membranes. The resulting nanopapers exhibit a transmembrane permeance in the range of commercially available tight UF membranes with molecular weight cut-offs ranging from 6 to 25 kDa, which depends on the type of nanocellulose used. These molecular weight cut-offs correspond to average pore sizes of a few nanometres. The rejection performance of the nanopapers is on the border of nanofiltration and UF. We demonstrate that the pore size of the nanopapers can be controlled by using different types of nanocellulose fibrils.
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| 8. |
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| 9. |
- Penttilä, Paavo A., et al.
(author)
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Xylan as limiting factor in enzymatic hydrolysis of nanocellulose
- 2013
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In: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 129, s. 135-141
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Journal article (peer-reviewed)abstract
- The role of xylan as a limiting factor in the enzymatic hydrolysis of cellulose was studied by hydrolysing nanocellulose samples prepared by mechanical fibrillation of birch pulp with varying xylan content. Analyzing the nanocelluloses and their hydrolysis residues with dynamic FT-IR spectroscopy revealed that a certain fraction of xylan remained tightly attached to cellulose fibrils despite partial hydrolysis of xylan with xylanase prior to pulp fibrillation and that this fraction remained in the structure during the hydrolysis of nanocellulose with cellulase mixture as well. Thus, a loosely bound fraction of xylan was predicted to have been more likely removed by purified xylanase. The presence of loosely bound xylan seemed to limit the hydrolysis of crystalline cellulose, indicated by an increase in cellulose crystallinity and by preserved crystal width measured with wide-angle X-ray scattering. Removing loosely bound xylan led to a proportional hydrolysis of xylan and cellulose with the cellulase mixture.
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| 10. |
- Pöhler, Tiina, et al.
(author)
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Pilot-scale modification of polyethersulfone membrane with a size and charge selective nanocellulose layer
- 2022
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In: Separation and Purification Technology. - : Elsevier BV. - 1383-5866 .- 1873-3794. ; 285
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Journal article (peer-reviewed)abstract
- The utilisation of plant-derived nanoscale cellulosic materials (cellulose nanofibrils, CNF) in tailoring water purification membranes is constantly gaining interest in the context of green-functionalised membrane solutions. However, most of the existing approaches based on renewable and biobased materials suffer from the lack of efficient and scalable processing strategies. Here, we introduce a roll-to-roll membrane modification approach based on thin submicron nanocellulose coatings (400–800 nm) to manufacture anti-biofouling membranes with size and charge dependent selectivity using unit operations compatible with existing industrial lines. We turned a commercial polymeric polyethersulfone (PES) microfiltration membrane into highly hydrophilic and tight membrane structure by applying thin and water-durable cellulose nanofibril layers using cast or spray coating methods. Nanocellulose coated membranes exhibited water permeance values of 80 – 100 LMH/MPa with the highest rejection levels of > 90% for Cytochrome C. Furthermore, the nanocellulose layers were able to withstand relatively high filtration pressure levels of 1 MPa, indicating that the selected procedures to improve mechanical integrity i.e. polyethylene imine-based anchoring and acid induced CNF cross-linking were successful. The coated membranes with the thinnest nanocellulose layer exhibited a molecular weight cut-off (MWCO) of 2 kDa for negatively charged polystyrene sulfonate and 14 kDa for neutral dextrane indicating charge selective behaviour. It can be concluded that our nanocellulose coated PES membranes represent nanofiltration membranes and lower boundary of ultrafiltration membranes with clear anti-biofouling performance directly evidenced via systematic bovine serum albumin (BSA) adsorption investigations. Our approach paves the way towards tunable and sustainable water treatment technologies simultaneously opening space for novel biobased solutions in membrane sector.
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