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Polymers
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Cellulose Nanomaterials
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Cellulose Nanomaterials

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Biomacromolecules, Biobased and Biodegradable Polymers".

Deadline for manuscript submissions: closed (15 July 2017) | Viewed by 126708

Special Issue Editors

Prof. Dr. Wolfgang Gindl-Altmutter

E-Mail Website
Guest Editor
Department of Material Sciences and Process Engineering, Institute of Wood Technology and Renewable Materials, BOKU—University of Natural Resources and Life Sciences, Vienna, Austria
Interests: wood science; wood composites; wood adhesion; natural fiber materials; lignin materials; cellulosic fibers; nanocellulose
Dr. Stefan Veigel

E-Mail Website
Guest Editor
Department of Material Sciences and Process Engineering, Institute of Wood Technology and Renewable Materials, BOKU—University of Natural Resources and Life Sciences, Vienna, Austria
Interests: natural fibers; nanocellulose; composite materials; wood bonding; wood surface technologies

Special Issue Information

Dear Colleagues,

This Special Issue of Polymers is dedicated to cellulose nanomaterials. During the past two decades, nanocellulose has received tremendous attention, as documented by a steadily-increasing number of patents and scientific publications. Presently, the knowledge generated here finally translates into increasing production capacities and emerging applications of this still comparably new high-performance bio-based material. Even so, important challenges with regard to a widespread utilization of nanocellulose are still to be overcome. Among those, the need for processing, transport, and storage of nanocellulose in dilute aqueous suspension, and the lack of inherent surface-chemical compatibility of nanocellulose with many widely used non-polar polymers, are probably most important. In order to reflect the current state of the art on the subject and to explore potential future developments, the present Special Issue welcomes submissions on all aspects of cellulose nanomaterials ranging from nanocellulose production and characterization to surface modification, processing, and new applications.

Prof. Dr. Wolfgang Gindl-Altmutter
Dr. Stefan Veigel
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • nanocellulose
  • nanomaterial
  • fibrillation
  • surface chemistry
  • bio-based materials
  • mechanical properties
  • applications

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Published Papers (16 papers)

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Research

1922 KiB  
Article
Reducing the Amount of Catalyst in TEMPO-Oxidized Cellulose Nanofibers: Effect on Properties and Cost
by Albert Serra, Israel González, Helena Oliver-Ortega, Quim Tarrès, Marc Delgado-Aguilar and Pere Mutjé
Polymers 2017, 9(11), 557; https://doi.org/10.3390/polym9110557 - 26 Oct 2017
Cited by 74 | Viewed by 7070
Abstract
Cellulose nanofibers (CNF) are interesting biopolymers that find numerous applications in different scientific and technological fields. However, manufacturing costs are still one of the main drawbacks for the industrial production of highly fibrillated, transparent CNF suspensions. In the present study, cellulose nanofibers were [...] Read more.
Cellulose nanofibers (CNF) are interesting biopolymers that find numerous applications in different scientific and technological fields. However, manufacturing costs are still one of the main drawbacks for the industrial production of highly fibrillated, transparent CNF suspensions. In the present study, cellulose nanofibers were produced from bleached eucalyptus pulp via TEMPO-mediated oxidation with varying amounts of NaClO and passed through a high-pressure homogenizer. The CNFs were chemically and physically characterized; cellulose nanopapers were also produced to study tensile properties. Production costs were also calculated. Results indicated that CNF properties are strongly dependent on the carboxyl content. Manufacturing costs showed that chemicals, in particular TEMPO catalyst, represent a large part of the final cost of CNFs. In order to solve this problem, a set of samples were prepared where the amount of TEMPO was gradually reduced. Characterization of samples prepared in this way showed that not only were the costs reduced, but also that the final properties of the CNFs were not significantly affected when the amount of TEMPO was reduced to half. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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2223 KiB  
Article
Imidazole, a New Tunable Reagent for Producing Nanocellulose, Part I: Xylan-Coated CNCs and CNFs
by Jia Mao, Hatem Abushammala, Hubert Hettegger, Thomas Rosenau and Marie-Pierre Laborie
Polymers 2017, 9(10), 473; https://doi.org/10.3390/polym9100473 - 27 Sep 2017
Cited by 19 | Viewed by 5436
Abstract
Imidazole is reported to be an effective reactant for the production of nanocellulose from hardwood pulp. The morphologies and surface properties of the nanocellulose can be simply tailored according to the water content in the imidazole system: with pure imidazole, cellulose nanofibrils (CNFs) [...] Read more.
Imidazole is reported to be an effective reactant for the production of nanocellulose from hardwood pulp. The morphologies and surface properties of the nanocellulose can be simply tailored according to the water content in the imidazole system: with pure imidazole, cellulose nanofibrils (CNFs) in a yield of 10 wt % can be produced. With 25 wt % of water in imidazole, cellulose nanocrystals (CNCs) are obtained in 20 wt % yield. Both nanocelluloses exhibit crystallinity indices in the order of 70%. Interestingly, they retain the original xylan from the pulp with ca. 9–10 wt % of residual xylan content. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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2927 KiB  
Article
Bioconversion of Waste Fiber Sludge to Bacterial Nanocellulose and Use for Reinforcement of CTMP Paper Sheets
by Genqiang Chen, Guochao Wu, Björn Alriksson, Wei Wang, Feng F. Hong and Leif J. Jönsson
Polymers 2017, 9(9), 458; https://doi.org/10.3390/polym9090458 - 18 Sep 2017
Cited by 28 | Viewed by 8010
Abstract
Utilization of bacterial nanocellulose (BNC) for large-scale applications is restricted by low productivity in static cultures and by the high cost of the medium. Fiber sludge, a waste stream from pulp and paper mills, was enzymatically hydrolyzed to sugar, which was used for [...] Read more.
Utilization of bacterial nanocellulose (BNC) for large-scale applications is restricted by low productivity in static cultures and by the high cost of the medium. Fiber sludge, a waste stream from pulp and paper mills, was enzymatically hydrolyzed to sugar, which was used for the production of BNC by the submerged cultivation of Komagataeibacter xylinus. Compared with a synthetic glucose-based medium, the productivity of purified BNC from the fiber sludge hydrolysate using shake-flasks was enhanced from 0.11 to 0.17 g/(L × d), although the average viscometric degree of polymerization (DPv) decreased from 6760 to 6050. The cultivation conditions used in stirred-tank reactors (STRs), including the stirring speed, the airflow, and the pH, were also investigated. Using STRs, the BNC productivity in fiber-sludge medium was increased to 0.32 g/(L × d) and the DPv was increased to 6650. BNC produced from the fiber sludge hydrolysate was used as an additive in papermaking based on the chemithermomechanical pulp (CTMP) of birch. The introduction of BNC resulted in a significant enhancement of the mechanical strength of the paper sheets. With 10% (w/w) BNC in the CTMP/BNC mixture, the tear resistance was enhanced by 140%. SEM images showed that the BNC cross-linked and covered the surface of the CTMP fibers, resulting in enhanced mechanical strength. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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5171 KiB  
Article
Simple Green Route to Performance Improvement of Fully Bio-Based Linseed Oil Coating Using Nanofibrillated Cellulose
by Stefan Veigel, Eva-Marieke Lems, Gerhard Grüll, Christian Hansmann, Thomas Rosenau, Tanja Zimmermann and Wolfgang Gindl-Altmutter
Polymers 2017, 9(9), 425; https://doi.org/10.3390/polym9090425 - 07 Sep 2017
Cited by 14 | Viewed by 5736
Abstract
Due to their bio-based character, oil-based coatings become more and more prevalent in wood surface finishing. These coatings impart appealing optical and haptic properties to the wood surface, but lack sufficient protection against water and mechanical influences. The present study reports a simple [...] Read more.
Due to their bio-based character, oil-based coatings become more and more prevalent in wood surface finishing. These coatings impart appealing optical and haptic properties to the wood surface, but lack sufficient protection against water and mechanical influences. The present study reports a simple green route to improve the performance of linseed oil coating by the addition of nanofibrillated cellulose (NFC). In order to achieve surface chemical compatibility with linseed oil, NFC was chemically modified with acetic anhydride and (2-dodecen-1-yl)succinic anhydride, respectively, using propylene carbonate as a solvent. NFC/linseed oil formulations were prepared and applied to wood substrates. The wear resistance of oil-coated wood surfaces was assessed by a newly developed test combining abrasive loading with subsequent contact angle measurement. As revealed by infrared and nuclear magnetic resonance (NMR) spectroscopy, as well as X-ray diffraction (XRD), NFC has been successfully modified without significantly affecting the structure of cellulose. In abrasion tests, all NFC-modified oil coatings performed better than the original oil. Interestingly, NFC only suspended in propylene carbonate, i.e., without chemical modification, had the strongest improvement effect on the coating’s wear resistance. This was primarily attributed to the loose network structure of this NFC variant which effectively prevents the oil from penetration into the wood surface, thus forming a protective NFC/oil composite layer on the wood surface. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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2862 KiB  
Article
The Influence of Cellulose Nanocrystals on the Hydration and Flexural Strength of Portland Cement Pastes
by Tengfei Fu, Francisco Montes, Prannoy Suraneni, Jeffrey Youngblood and Jason Weiss
Polymers 2017, 9(9), 424; https://doi.org/10.3390/polym9090424 - 07 Sep 2017
Cited by 66 | Viewed by 7036
Abstract
Recent research has shown that cellulose nanocrystals (CNCs) can be used at low dosage levels (approximately 0.2% by volume of cement) to increase the extent of hydration and to improve the flexural strength of cement pastes. However, the previous work was based on [...] Read more.
Recent research has shown that cellulose nanocrystals (CNCs) can be used at low dosage levels (approximately 0.2% by volume of cement) to increase the extent of hydration and to improve the flexural strength of cement pastes. However, the previous work was based on using a CNC made from a single source material and processing technique and was performed using only Type V cement. This work examines the influence of various raw material sources and processing techniques used to make the CNCs. In total, nine different CNCs were investigated with pastes made using Type I/II and Type V cements. Isothermal calorimetry (IC), thermogravimetric analysis (TGA) and ball-on-three-ball (B3B) flexural strength testing were used to quantify the performance of CNC-cement composites. IC and TGA results showed that CNCs increased the degree of hydration in all systems. IC results showed that the increase in total heat release was greater in the Type V than in the Type I/II cement paste systems. B3B flexural testing indicated an increase in flexural strength of up to 20% with both Type I/II and Type V systems. These results also showed that the performance of CNC-cement composites can be affected by the source and manufacturing process used to make the CNC. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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3027 KiB  
Article
Cellulose Acetate Phthalate and Antiretroviral Nanoparticle Fabrications for HIV Pre-Exposure Prophylaxis
by Subhra Mandal, Karl Khandalavala, Rachel Pham, Patrick Bruck, Marisa Varghese, Andrew Kochvar, Ashley Monaco, Pavan Kumar Prathipati, Christopher Destache and Annemarie Shibata
Polymers 2017, 9(9), 423; https://doi.org/10.3390/polym9090423 - 07 Sep 2017
Cited by 16 | Viewed by 6621
Abstract
To adequately reduce new HIV infections, development of highly effective pre-exposure prophylaxis (PrEP) against HIV infection in women is necessary. Cellulose acetate phthalate (CAP) is a pH sensitive polymer with HIV-1 entry inhibitory properties. Dolutegravir (DTG) is an integrase strand transfer inhibitor with [...] Read more.
To adequately reduce new HIV infections, development of highly effective pre-exposure prophylaxis (PrEP) against HIV infection in women is necessary. Cellulose acetate phthalate (CAP) is a pH sensitive polymer with HIV-1 entry inhibitory properties. Dolutegravir (DTG) is an integrase strand transfer inhibitor with potent antiretroviral activity. DTG delivered in combination with CAP may significantly improve current PrEP against HIV. In the present study, the development of DTG-loaded CAP nanoparticles incorporated in thermosensitive (TMS) gel at vaginal pH 4.2 and seminal fluid pH 7.4 is presented as proof-of-concept for improved PrEP. Water–oil–in–water homogenization was used to fabricate DTG-loaded CAP nanoparticles (DTG–CAP–NPs). Size, polydispersity, and morphological analyses illustrate that DTG–CAP–NPs were smooth and spherical, ≤200 nm in size, and monodispersed with a polydispersity index PDI ≤ 0.2. The drug encapsulation (EE%) and release profile of DTG–CAP–NPs was determined by HPLC analysis. The EE% of DTG in DTG–CAP–NPs was evaluated to be ~70%. The thermal sensitivity of the TMS gel was optimized and the pH dependency was evaluated by rheological analysis. DTG release studies in TMS gel revealed that DTG–CAP–NPs were stable in TMS gel at pH 4.2 while DTG–CAP–NPs in TMS gel at pH 7.4 rapidly release DTG (≥80% release within 1 h). Cytotoxicity studies using vaginal cell lines revealed that DTG–CAP–NPs were relatively non-cytotoxic at concentration <1 µg/mL. Confocal microscopic studies illustrate that ≥98% cells retained DTG–CAP–NPs intracellularly over seven days. Antiretroviral drug loaded nanocellulose fabrications in TMS gel delivered intravaginally may enhance both microbicidal and antiretroviral drug efficacy and may present a novel option for female PrEP against HIV. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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3176 KiB  
Article
The Effect of Moisture on Cellulose Nanocrystals Intended as a High Gas Barrier Coating on Flexible Packaging Materials
by Ghislain Fotie, Riccardo Rampazzo, Marco Aldo Ortenzi, Stefano Checchia, Dimitrios Fessas and Luciano Piergiovanni
Polymers 2017, 9(9), 415; https://doi.org/10.3390/polym9090415 - 05 Sep 2017
Cited by 34 | Viewed by 7616
Abstract
Cellulose nanocrystals (CNCs) exhibit outstanding gas barrier properties, which supports their use as a biobased and biodegradable barrier coating on flexible food packaging materials. As highly hydrophilic biopolymers, however, CNCs have a strong sensitivity to water that can be detrimental to applications with [...] Read more.
Cellulose nanocrystals (CNCs) exhibit outstanding gas barrier properties, which supports their use as a biobased and biodegradable barrier coating on flexible food packaging materials. As highly hydrophilic biopolymers, however, CNCs have a strong sensitivity to water that can be detrimental to applications with fresh foods and in moist conditions due to the loss of barrier properties. In this work, the oxygen and water vapor permeability of polyethylene terephthalate (PET) films coated with CNCs obtained from cotton linters were measured at varying levels of relative humidity, both in adsorption and desorption, and from these data, the diffusion and solubility coefficients were estimated. Therefore, the characterization of CNCs was aimed at understanding the fundamentals of the water-CNCs interaction and proposing counteractions. The CNCs’ moisture absorption and desorption isotherms at 25 °C were collected in the range of relative humidity 0–97% using different techniques and analyzed through GAB (Guggenheim-Anderson-de Boer) and Oswin models. The effects of moisture on the water status, following the freezable water index, and on the crystal structure of CNCs were investigated by Differential Scanning Calorimetry and by X-ray Powder Diffraction, respectively. These findings point to the opportunity of coupling CNCs with hydrophobic layers in order to boost their capabilities as barrier packaging materials. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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3937 KiB  
Article
Dry-Spun Neat Cellulose Nanofibril Filaments: Influence of Drying Temperature and Nanofibril Structure on Filament Properties
by Shokoofeh Ghasemi, Mehdi Tajvidi, Douglas W. Bousfield, Douglas J. Gardner and William M. Gramlich
Polymers 2017, 9(9), 392; https://doi.org/10.3390/polym9090392 - 25 Aug 2017
Cited by 35 | Viewed by 6365
Abstract
Cellulose nanofibrils (CNF) were spun into filaments directly from suspension without the aid of solvents. The influence of starting material properties and drying temperature on the properties of filaments produced from three different CNF suspensions was studied. Refiner-produced CNF was ground using a [...] Read more.
Cellulose nanofibrils (CNF) were spun into filaments directly from suspension without the aid of solvents. The influence of starting material properties and drying temperature on the properties of filaments produced from three different CNF suspensions was studied. Refiner-produced CNF was ground using a microgrinder at grinding times of 50 and 100 minutes. Filament spinning was performed using a syringe pump-heat gun setting at three drying temperatures of 210 °C, 320 °C and 430 °C. The structure of starting CNF materials was first evaluated using a combination of optical and atomic force microscopy (AFM) techniques. Surface free energy analysis and attenuated total reflectance—Fourier transform infrared spectroscopy (ATR–FTIR) were used to study changes in hydrophobicity due to grinding. Morphology of the filaments was studied using SEM micrographs. The influence of different drying temperatures and grinding times on mechanical properties of the CNF filaments were further investigated through tensile tests and results were compared using statistical analysis .It was observed that drying temperature did not significantly influence the tensile properties of the filaments while cellulose nanofiber suspension type (grinding time) had a significant influence and improved mechanical properties. FTIR results confirmed an increase in crystallinity index and decrease in hydroxyl group availability due to grinding. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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8710 KiB  
Article
Use of Bacterial Cellulose and Crosslinked Cellulose Nanofibers Membranes for Removal of Oil from Oil-in-Water Emulsions
by Enas Hassan, Mohammad Hassan, Ragab Abou-zeid, Linn Berglund and Kristiina Oksman
Polymers 2017, 9(9), 388; https://doi.org/10.3390/polym9090388 - 23 Aug 2017
Cited by 46 | Viewed by 8258
Abstract
Abstract: Never-dried bacterial cellulose (BC) and crosslinked cellulose nanofibers (CNF) were used for the removal of oil from stabilized and non-stabilized oil-in-water emulsions with droplet sizes less than 1 µm. The CNF membranes were exchanged with isopropyl alcohol before drying. The microscopic [...] Read more.
Abstract: Never-dried bacterial cellulose (BC) and crosslinked cellulose nanofibers (CNF) were used for the removal of oil from stabilized and non-stabilized oil-in-water emulsions with droplet sizes less than 1 µm. The CNF membranes were exchanged with isopropyl alcohol before drying. The microscopic structure of the prepared membranes was evaluated using scanning electron microscopy (SEM); the water flux and the rejection of oil were evaluated using a dead-end filtration cell. BC harvested after different incubation time periods (2 to 10 days) did not show a change in the width of the nanofibers, but only the thickness of the membranes was increased. Pure water flux was not affected as a result of increasing thicknesses of BC membranes harvested after 4–10 days while BC harvested after two days had significantly higher water flux than the others. BC showed a higher flux and efficiency in removing oil from oil emulsions than CNF membranes. Removal of oil by the different membranes from the non-stabilized oil emulsion was more efficient than from the stabilized one. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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8197 KiB  
Article
Bacterial Nanocellulose from Side-Streams of Kombucha Beverages Production: Preparation and Physical-Chemical Properties
by Stefan-Ovidiu Dima, Denis-Mihaela Panaitescu, Csongor Orban, Marius Ghiurea, Sanda-Maria Doncea, Radu Claudiu Fierascu, Cristina Lavinia Nistor, Elvira Alexandrescu, Cristian-Andi Nicolae, Bogdan Trică, Angela Moraru and Florin Oancea
Polymers 2017, 9(8), 374; https://doi.org/10.3390/polym9080374 - 18 Aug 2017
Cited by 92 | Viewed by 15698
Abstract
We focused on preparing cellulose nanofibrils by purification, separation, and mechanical treatment of Kombucha membranes (KM) resulted as secondary product from beverage production by fermentation of tea broth with symbiotic culture of bacteria and yeast (SCOBY). We purified KM using two alkaline solutions, [...] Read more.
We focused on preparing cellulose nanofibrils by purification, separation, and mechanical treatment of Kombucha membranes (KM) resulted as secondary product from beverage production by fermentation of tea broth with symbiotic culture of bacteria and yeast (SCOBY). We purified KM using two alkaline solutions, 1 and 4 M NaOH, which afterwards were subjected to various mechanical treatments. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic light scattering (DLS), X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) were employed to evaluate the purification degree, the size and aspect of cellulose fibrils after each treatment step, the physical-chemical properties of intermediary and final product, and for comparison with micro-crystalline cellulose from wooden sources. We determined that 1 M NaOH solution leads to approx. 85% purification, while a higher concentration assures almost 97% impurities removal. XRD analysis evidenced an increase in crystallinity from 37% to 87% after purification, the characteristic diffractograms of Iα and Iβ cellulose allomorphs, and a further decrease in crystallinity to 46% after microfluidization, fact correlated with a drastically decrease in fibrils’ size. FTIR analysis evidenced the appearance of new chain ends by specific transmission bands at 2941 and 2843cm−1. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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4455 KiB  
Article
Pulp Fines—Characterization, Sheet Formation, and Comparison to Microfibrillated Cellulose
by Wolfgang Johann Fischer, Melanie Mayr, Stefan Spirk, David Reishofer, Lukas Andreas Jagiello, Romana Schmiedt, Jerome Colson, Armin Zankel and Wolfgang Bauer
Polymers 2017, 9(8), 366; https://doi.org/10.3390/polym9080366 - 17 Aug 2017
Cited by 51 | Viewed by 7531
Abstract
In the pulp and paper industry different types of pulp or fiber fines are generated during the pulping (primary fines, mechanical fines), and/or the refining process (secondary fines). Besides fibers, these cellulosic microparticles are a further component of the paper network. Fines, which [...] Read more.
In the pulp and paper industry different types of pulp or fiber fines are generated during the pulping (primary fines, mechanical fines), and/or the refining process (secondary fines). Besides fibers, these cellulosic microparticles are a further component of the paper network. Fines, which are defined as the fraction of pulp that is able to pass through a mesh screen or a perforated plate having a hole diameter of 76 μm, are known to influence the properties of the final paper product. To better understand the effect and properties of this material, fines have to be separated from the pulp and investigated as an independent material. In the present study, fines are isolated from the pulp fraction by means of a laboratory pressure screen. To allow for further processing, the solids content of the produced fines suspension was increased using dissolved air flotation. Morphological properties of different types of fines and other cellulosic microparticles, such as microfibrillated celluloses (MFC) are determined and compared to each other. Furthermore, handsheets are prepared from these materials and properties, such as apparent density, contact angle, modulus of elasticity, and strain are measured giving similar results for the analyzed types of fines in comparison to the tested MFC grades. The analysis of the properties of fiber fines contributes on the one hand to a better understanding of how these materials influences the final paper products, and on the other hand, helps in identifying other potential applications of this material. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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2981 KiB  
Article
Development of Synergistic Antimicrobial Coating of p-Aramid Fibers Using Ag Nanoparticles and Glycidyltrimethylammonium Chloride (GTAC) without the Aid of a Cross-Linking Agent
by Chankyu Kang, Dajeong Ahn, Changhyun Roh, Sam Soo Kim and Jaewoong Lee
Polymers 2017, 9(8), 357; https://doi.org/10.3390/polym9080357 - 11 Aug 2017
Cited by 10 | Viewed by 5187
Abstract
Functional p-aramid fibers that can express antimicrobial activity were produced by simple processing of silver nanoparticles (AgNPs), which are well known as antimicrobial agents, by using glycidyltrimethylammonium chloride (GTAC), a quaternary ammonium salt. P-aramid fibers were treated with GTAC by the pad-dry-cure process [...] Read more.
Functional p-aramid fibers that can express antimicrobial activity were produced by simple processing of silver nanoparticles (AgNPs), which are well known as antimicrobial agents, by using glycidyltrimethylammonium chloride (GTAC), a quaternary ammonium salt. P-aramid fibers were treated with GTAC by the pad-dry-cure process and put into an Ag colloid solution for reactions at 40 °C for 90 min to prepare GTAC/AgNPs-treated p-aramid fibers. Through these processes, GTAC was used as a substitute for existing cross-linking agents. The changes in the degree of attachment of AgNPs to the surface of p-aramid fibers were determined using a scanning electron microscope according to parameters such as GTAC concentration, Ag colloid concentration, and reaction temperature. Through this study, the following results were obtained: (i) The tensile strength of AgNPs/GTAC-treated p-aramid fibers was found to be about 80% of that of untreated p-aramid fibers; (ii) Thermogravimetric analysis showed that the thermal stability of p-aramid fibers did not change much after GTAC/AgNPs treatment and (iii) Antimicrobial activity analysis showed that AgNPs/GTAC-treated p-aramid fibers exhibited superior antibacterial properties compared to untreated p-aramid fibers, which may or may not be the effect of GTAC or AgNPs, or both. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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4689 KiB  
Article
Isolation and Characterization of Cellulose Nanocrystals from Oil Palm Mesocarp Fiber
by Buong Woei Chieng, Syn Huey Lee, Nor Azowa Ibrahim, Yoon Yee Then and Yuet Ying Loo
Polymers 2017, 9(8), 355; https://doi.org/10.3390/polym9080355 - 11 Aug 2017
Cited by 166 | Viewed by 10083
Abstract
The aim was to explore the utilization of oil palm mesocarp fiber (OPMF) as a source for the production of cellulose nanocrystals (CNC). OPMF was first treated with alkali and then bleached before the production of CNC by acid hydrolysis (H2SO [...] Read more.
The aim was to explore the utilization of oil palm mesocarp fiber (OPMF) as a source for the production of cellulose nanocrystals (CNC). OPMF was first treated with alkali and then bleached before the production of CNC by acid hydrolysis (H2SO4). The produced materials were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), a scanning electron microscope (SEM) and a transmission electron microscope (TEM). It was proven that acid hydrolysis can increase the crystallinity of bleached OPMF and reduce the dimension of cellulose to nano scale. Changes in the peaks of the FTIR spectrum at 2852 (C-H stretching), 1732 (C=O stretching) and 1234 cm−1 (C-O stretching) indicated that the alkali treatment completely removed hemicelluloses and lignin from the fiber surface. This can be seen from the thermogram obtained from the TGA characterization. Morphological characterization clearly showed the formation of rod-shaped CNCs. The promising results prove that OPMF is a valuable source for the production of CNC. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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4214 KiB  
Article
Characterization of Type-II Acetylated Cellulose Nanocrystals with Various Degree of Substitution and Its Compatibility in PLA Films
by Feng Dong, Meiling Yan, Chunde Jin and Shujun Li
Polymers 2017, 9(8), 346; https://doi.org/10.3390/polym9080346 - 06 Aug 2017
Cited by 39 | Viewed by 7548
Abstract
In order to decrease the self-agglomeration and improve the hydrophobic properties of type-II acetylated cellulose nanocrystals (ACNC II), various degree of substitution (DS) values of ACNCs were successfully prepared by a single-step method from microcrystalline cellulose with anhydrous phosphoric acid as the solvent, [...] Read more.
In order to decrease the self-agglomeration and improve the hydrophobic properties of type-II acetylated cellulose nanocrystals (ACNC II), various degree of substitution (DS) values of ACNCs were successfully prepared by a single-step method from microcrystalline cellulose with anhydrous phosphoric acid as the solvent, and acetic anhydride as the acetylation reagent, under different reaction temperatures (20–40 °C). To thoroughly investigate the DS values of ACNC II, analyses were performed using Fourier transform infrared spectroscopy (FT-IR), 13C cross polarization-magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS). At a reaction temperature of 40°C, the highest DS value was successfully obtained. XRD proved that the crystal structure of ACNC II with various DS values was maintained after acetylation. TEM showed the threadlike shape for ACNC II with various DS values. The ACNC II with various DS values was introduced into a polylactic acid (PLA) matrix to produce PLA/ACNC composite films, which showed improved rheological and thermal properties. This improvement was primarily attributed to good dispersion of the ACNC II, and the interfacial compatibility between ACNC II and the PLA matrix. This study aims to analyze the compatibility of ACNC II with various DS values in the PLA matrix by microstructure, crystallization, and rheological and thermal tests. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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16915 KiB  
Article
Membranes Based on Cellulose Nanofibers and Activated Carbon for Removal of Escherichia coli Bacteria from Water
by Mohammad Hassan, Ragab Abou-Zeid, Enas Hassan, Linn Berglund, Yvonne Aitomäki and Kristiina Oksman
Polymers 2017, 9(8), 335; https://doi.org/10.3390/polym9080335 - 03 Aug 2017
Cited by 68 | Viewed by 11713
Abstract
Cellulosic nanomaterials are potential candidates in different areas, especially in water treatment. In the current work, palm fruit stalks cellulose nanofibers (CNF), TEMPO-oxidized CNF (OCNF), and activated carbon (AC) were used to make thin film membranes for removal of E. coli bacteria from [...] Read more.
Cellulosic nanomaterials are potential candidates in different areas, especially in water treatment. In the current work, palm fruit stalks cellulose nanofibers (CNF), TEMPO-oxidized CNF (OCNF), and activated carbon (AC) were used to make thin film membranes for removal of E. coli bacteria from water. Two types of layered membranes were produced: a single layer setup of crosslinked CNF and a two-layer setup of AC/OCNF (bottom) and crosslinked CNF (up) on hardened filter paper. The prepared membranes were evaluated regarding their microstructure and layers thickness using scanning electron microscopy (SEM). Water flux and rejection of E. coli bacteria was tested using dead end stirred cells at 1 MPa pressure. Thickness of the cosslinked CNF layer in both types of membranes was about 0.75 micron. The results showed that exchanging water by isopropyl alcohol before drying increased porosity of membranes, and thus resulted in increasing pure water flux and flux of bacteria suspension. The two-layer AC/OCNF/CNF membrane had much higher water flux than the single layer CNF due to higher porosity seen on the surface of the former. Both types of membranes showed high capability of removing E. coli bacteria (rejection ~96–99%) with slightly higher efficiency for the AC/OCNF/CNF membrane than CNF membrane. AC/OCNF/CNF membrane also showed resistance against growth of E. coli and S. aureus bacteria on the upper CNF surface while the single layer CNF membrane did not show resistance against growth of the aforementioned bacteria. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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Article
Nanopaper Properties and Adhesive Performance of Microfibrillated Cellulose from Different (Ligno-)Cellulosic Raw Materials
by Stefan Pinkl, Stefan Veigel, Jérôme Colson and Wolfgang Gindl-Altmutter
Polymers 2017, 9(8), 326; https://doi.org/10.3390/polym9080326 - 31 Jul 2017
Cited by 12 | Viewed by 5866
Abstract
The self-adhesive potential of nanocellulose from aqueous cellulosic suspensions is of interest with regard to a potential replacement of synthetic adhesives. In order to evaluate the performance of microfibrillated cellulose from different (ligno-)cellulosic raw materials for this purpose, softwood and hardwood powder were [...] Read more.
The self-adhesive potential of nanocellulose from aqueous cellulosic suspensions is of interest with regard to a potential replacement of synthetic adhesives. In order to evaluate the performance of microfibrillated cellulose from different (ligno-)cellulosic raw materials for this purpose, softwood and hardwood powder were fibrillated and compared to sugar beet pulp as a representative non-wood cellulose resource, and conventional microfibrillated cellulose produced from bleached pulp. An alkali pre-treatment of woody and sugar beet raw materials enhanced the degree of fibrillation achieved, same as TEMPO-mediated oxidation of microfibrillated cellulose. Nanopapers produced from fibrillated material showed highly variable density and mechanical performance, demonstrating that properties may be tuned by the choice of raw material. While nanopaper strength was highest for TEMPO-oxidated microfibrillated cellulose, fibrillated untreated sugar beet pulp showed the best adhesive performance. Different microscopic methods (AFM, SEM, light microscopy) examined the interface between wood and fibrillated material, showing particular distinctions to commercial adhesives. It is proposed that fibrillated material suspensions, which achieve bond strength up to 60% of commercial urea-formaldehyde adhesive, may provide a viable solution to bio-based adhesives in certain applications where wet-strength is not an issue. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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