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Nanofiber networks, aerogels and biocomposites based on nanofibrillated cellulose from wood
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. (Biocomposites)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanofibrillated cellulose (NFC) from wood is an interesting material constituent of high strength and high aspect ratio, which easily forms networks through interfibril secondary bonding including hydrogen bonds. This has been exploited in preparation of new materials, which extend the range of properties for existing cellulosic materials. The objective is to explore processing-structure and structure-property relationships in NFC materials.

Dense networks of NFC, referred to as “nanopaper” having a random-in-the-plane orientation of the fibrils have been successfully prepared by a papermaking-like process involving vacuum filtration and water evaporation using laboratory papermaking equipment. Large, flat and transparent nanopaper sheets have thus been prepared in a relatively short time. Using the same preparation route, NFC was used to reinforce pulped wood fibers in dense network structures. NFC networks formed in the pore space of the wood fiber network give an interesting hierarchical structure of reduced porosity. These NFC/wood fiber biocomposites have greater strength, greater stiffness and greater strain-to-failure than reference networks of wood fibers only. In particular, the work to fracture (area under the stress-strain curve) is doubled with an NFC content of only 2%.

The papermaking preparation route was extended to prepare nanocomposites of high NFC content with a cellulose derivative matrix (hydroxyethyl cellulose, HEC) strongly associated to the NFC. Little HEC was lost during filtration. The NFC/HEC composites have high work to fracture, higher than that of any reported cellulose composite. This is related to NFC network characteristics, and HEC properties and its nanoscale distribution and association with NFC.

Higher porosity NFC nanopaper networks of high specific surface area were prepared by new routes including supercritical drying, tert-butanol freeze-drying and CO2 evaporation. Light-weight porous nanopaper materials resulted with mechanical properties similar to thermoplastics but with a much lower density and a specific surface area of up to 480 m2/g.

Freeze-drying of hydrocolloidal NFC dispersions was used to prepare ultra-high porosity foam structures. The NFC foams have a cellular foam structure of mixed open/closed cells and “nanopaper” cell wall. Control of density and mechanical properties was possible by variation of NFC concentration in the dispersion. A cellulose I foam of the highest porosity ever reported (99.5%) was prepared. The NFC foams have high ductility and toughness and may be of interest for applications involving mechanical energy absorption. Freeze-drying of NFC suspended in tert-butanol gave highly porous NFC network aerogels with a large surface area. The mechanical behavior was significantly different from NFC foams of similar density due to differences in deformation mechanisms for NFC nanofiber networks.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , 74 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:024
Keyword [en]
Nanofibrillated cellulose, nanopaper, nanofiber, biocomposites, aerogel, foam
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-32079ISBN: 978-91-7415-931-8OAI: oai:DiVA.org:kth-32079DiVA: diva2:408658
Public defence
2011-04-27, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110406Available from: 2011-04-06 Created: 2011-04-05 Last updated: 2011-11-11Bibliographically approved
List of papers
1. Fast Preparation Procedure for Large, Flat Cellulose and Cellulose/Inorganic Nanopaper Structures
Open this publication in new window or tab >>Fast Preparation Procedure for Large, Flat Cellulose and Cellulose/Inorganic Nanopaper Structures
2010 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 11, no 9, 2195-2198 p.Article in journal (Refereed) Published
Abstract [en]

Nanostructured materials are difficult to prepare rapidly and as large structures. The present study is thus significant because a rapid preparation procedure for large, flat, smooth, and optically transparent cellulose nanopaper structures is developed using a semiautomatic sheet former. Cellulose/inorganic hybrid nanopaper is also produced. The preparation procedure is compared with other approaches, and the nanopaper structures are tested in uniaxial tensile tests. Optical transparency and high tensile strength are demonstrated in 200 mm diameter nanopaper sheets, indicating well-dispersed nanofibrils. The preparation time is 1 h for a typical nanopaper thickness of 60 pm. In addition, the application of the nanopaper-making strategy to cellulose/inorganic hybrids demonstrates the potential for "green" processing of new types of nanostructured functional materials.

Keyword
High-tensile strength, Large structures, Nano-fibrils, Nano-structured, Optical transparency, Preparation procedures, Uniaxial tensile test, Well-dispersed, Cellulose, Functional materials, Tensile testing
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-26699 (URN)10.1021/bm100490s (DOI)000281629600001 ()2-s2.0-77956524317 (ScopusID)
Note
QC 20101129Available from: 2010-11-29 Created: 2010-11-26 Last updated: 2011-04-06Bibliographically approved
2. Wood cellulose biocomposites with fibrous structures at micro- and nanoscale
Open this publication in new window or tab >>Wood cellulose biocomposites with fibrous structures at micro- and nanoscale
2011 (English)In: Composites Science And Technology, ISSN 0266-3538, Vol. 71, no 3, 382-387 p.Article in journal (Refereed) Published
Abstract [en]

High-strength composites from wood fiber and nanofibrillated cellulose (NFC) were prepared in a semiautomatic sheet former. The composites were characterized by tensile tests, dynamic mechanical thermal analysis, field-emission scanning electron microscopy, and porosity measurements. The tensile strength increased from 98 MPa to 160 MPa and the work to fracture was more than doubled with the addition of 10% NFC to wood fibers. A hierarchical structure was obtained in the composites in the form of a micro-scale wood fiber network and an additional NFC nanofiber network linking wood fibers and also occupying some of the micro-scale porosity. Deformation mechanisms are discussed as well as possible applications of this biocomposites concept. (C) 2010 Published by Elsevier Ltd.

Keyword
Nanofibrillated cellulose (NFC), Fibers, Nano composites, Mechanical properties, Scanning electron microscopy (SEM)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-31014 (URN)10.1016/j.compscitech.2010.12.007 (DOI)000287288200016 ()2-s2.0-78751622635 (ScopusID)
Note
QC 20110318Available from: 2011-03-18 Created: 2011-03-07 Last updated: 2011-04-06Bibliographically approved
3. Nanostructured biocomposites of high toughness-a wood cellulose nanofiber network in ductile hydroxyethylcellulose matrix
Open this publication in new window or tab >>Nanostructured biocomposites of high toughness-a wood cellulose nanofiber network in ductile hydroxyethylcellulose matrix
2011 (English)In: Soft Matter, ISSN 1744-683X, Vol. 7, no 16, 7342-7350 p.Article in journal (Refereed) Published
Abstract [en]

Nanopaper from wood-based nanofibrillated cellulose (NFC) offers vastly improved strength and strain-to-failure compared with plant fiber-based paper and plant fiber biocomposites. In the present study, unique nanostructural toughening effects are reported in cellulose nanofiber/hydroxyethylcellulose (HEC) biocomposites. HEC is an amorphous cellulose derivative of high molar mass and toughness. A previously developed preparation route inspired by paper-making is used. It is "green", scalable, and allows high reinforcement content. In the present concept, nanostructural control of polymer matrix distribution is exercised as the polymer associates with the reinforcement. This results in nanocomposites of a soft HEC matrix surrounding nanofibrillated cellulose forming a laminated structure at the submicron scale, as observed by FE-SEM. We study the effect of NFC volume fraction on tensile properties, thermomechanical stability, creep properties and moisture sorption of the nanocomposites. The results show strong property improvements with NFC content due to the load-carrying ability of the NFC network. At an NFC volume fraction of 45%, the toughness was more than doubled compared with cellulose nanopaper. The present nanocomposite is located in previously unoccupied space in a strength versus strain-to-failure property chart, outside the regions occupied by microscale composites and engineering polymers. The results emphasize the potential for extended composites mechanical property range offered by nanostructured biocomposites based on high volume fraction nanofiber networks.

National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-32097 (URN)10.1039/c1sm05325f (DOI)000293412900028 ()2-s2.0-79961132459 (ScopusID)
Available from: 2011-04-06 Created: 2011-04-06 Last updated: 2011-09-05Bibliographically approved
4. Strong and Tough Cellulose Nanopaper with High Specific Surface Area and Porosity
Open this publication in new window or tab >>Strong and Tough Cellulose Nanopaper with High Specific Surface Area and Porosity
2011 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 10, 3638-3644 p.Article in journal (Refereed) Published
Abstract [en]

In order to better understand nanostructured fiber networks, effects from high specific surface area of nanofibers are important to explore. For cellulose networks, this has so far only been achieved in nonfibrous regenerated cellulose aerogels. Here, nanofibrillated cellulose (NFC) is used to prepare high surface area nanopaper structures, and the mechanical properties are measured in tensile tests. The water in NFC hydrogels is exchanged to liquid CO(2), supercritical CO(2), and tert-butanol, followed by evaporation, supercritical drying, and sublimation, respectively. The porosity range is 40-86%. The nanofiber network structure in nanopaper is characterized by FE-SEM and nitrogen adsorption, and specific surface area is determined. High-porosity TEMPO-oxidized NFC nanopaper (56% porosity) prepared by critical point drying has a specific surface area as high as 48(2) m(2) g(-1). The mechanical properties of this nanopaper structure are better than for many thermoplastics, but at a significantly lower density of only 640 kg m(-3). The modulus is 1.4 GPa, tensile strength 84 MPa, and strain-to-failure 17%. Compared with water-dried nanopaper, the material is softer with substantially different deformation behavior.

Keyword
tempo-mediated oxidation, composite membranes, native cellulose, nanofibers, aerogels, polymer, nanoparticles, density, liquid
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-46853 (URN)10.1021/bm2008907 (DOI)000295602600031 ()2-s2.0-80053988282 (ScopusID)
Note
QC 20111107. Uppdaterad från Manuskript till Artikel (20111111)Available from: 2011-11-07 Created: 2011-11-07 Last updated: 2011-11-11Bibliographically approved
5. Mechanical performance tailoring of tough ultra-high porosity foams prepared from cellulose I nanofiber suspensions
Open this publication in new window or tab >>Mechanical performance tailoring of tough ultra-high porosity foams prepared from cellulose I nanofiber suspensions
2010 (English)In: Soft Matter, ISSN 1744-683X, Vol. 6, no 8, 1824-1832 p.Article in journal (Refereed) Published
Abstract [en]

Low-density structures of mechanical function in plants, arthropods and other organisms, are often based on high- strength cellulose or chitin nanofibers and show an interesting combination of flexibility and toughness. Here, a series of plant-inspired tough and mechanically very robust cellular biopolymer foams with porosities as high as 99.5% (porosity range 93.1-99.5%) were therefore prepared by solvent-free freeze-drying from cellulose I wood nanofiber water suspensions. A wide range of mechanical properties was obtained by controlling density and nanofiber interaction in the foams, and density property relationships were modeled and compared with those for inorganic aerogels. Inspired by cellulose-xyloglucan (XG) interaction in plant cell walls, XG was added during preparation of the toughest foams. For the cellulose-XG nanocomposite foams in particular, the mechanical properties at comparable densities were superior to those reported in the literature for clay aerogel/cellulose whisker nanocomposites, epoxy/clay aerogels, polymer/clay/nanotube aerogels, and polymer/silica aerogels. The foam structure was characterized by high-resolution field-emission scanning electron microscopy and the specific surface area was measured by nitrogen physisorption. Dynamic mechanical thermal analysis and uniaxial compression tests were performed. The foam was thermally stable up to 275 degrees C where cellulose started to degrade.

Keyword
Density structures, Dynamic mechanical thermal analysis, Field emission scanning electron microscopy, Foam structure, High resolution, High-strength, In-plants, Mechanical functions, Mechanical performance, Nanocomposite foams, Solvent free, Thermally stable, Ultra-high, Uniaxial compression tests, Water suspensions, Xyloglucans, Aerogels, Cellulose, Ceramic materials, Compression testing, Density (specific gravity), Dynamic mechanical analysis, Foams, High resolution electron microscopy, Nanocomposites, Nanofibers, Physisorption, Plant cell culture, Porosity, Scanning electron microscopy, Thermoanalysis
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-19383 (URN)10.1039/b927505c (DOI)000276469300027 ()2-s2.0-77950854066 (ScopusID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-04-06Bibliographically approved
6. High-porosity aerogels of high specific surface area prepared from nanofibrillated cellulose (NFC)
Open this publication in new window or tab >>High-porosity aerogels of high specific surface area prepared from nanofibrillated cellulose (NFC)
2011 (English)In: Composites Science And Technology, ISSN 0266-3538, Vol. 71, no 13, 1593-1599 p.Article in journal (Refereed) Published
Abstract [en]

Low-density aerogels based on nanofibrillated cellulose (NFC) from wood pulp were prepared from NFC aqueous dispersions using solvent exchange from water to tert-butanol followed by tert-butanol freeze-drying. In the present study, the dispersion of NFC nanofibers in the hydrocolloid was very well preserved in the aerogels. The "effective" diameter of the NFC nanofibers in the aerogels is around 10-18 nm corresponding to specific surface areas as high as 153-284 m(2) g(-1). Aerogels based on different NFC nanofibers were studied by FE-SEM, BET analysis (nitrogen gas adsorption), and mechanical properties were measured in compression for different densities of aerogels. The properties are compared with polymer foams and inorganic aerogels. Compared with cellular NFC foams, the present nanofibrous aerogels have lower modulus and show lower stress in compression for a given strain. Tert-butanol freeze-drying can therefore be used to create "soft" aerogels.

Keyword
Mechanical properties, Nano composites, Cellulose nanofibers, Freeze drying
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-45601 (URN)10.1016/j.compscitech.2011.07.003 (DOI)000295864000010 ()2-s2.0-80051939439 (ScopusID)
Note
QC 20111107 This article is a revised version of the manuscript "High-porosity aerogels of high specific surface area prepared by new routeusing nanofibrillated cellulose (NFC) disintegrated from the wood cell wall" which is a part of the thesis "Nanofiber networks, aerogels and biocomposites based on nanofibrillated cellulose from wood"Available from: 2011-11-07 Created: 2011-10-31 Last updated: 2011-11-11Bibliographically approved

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