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Cellulose nanopaper structures of high toughness
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0001-5818-2378
Solid Mechanics Department, Mid Sweden University, Sundsvall.
STFI-Packforsk AB.
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2008 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 9, no 6, 1579-1585 p.Article in journal (Refereed) Published
Abstract [en]

Cellulose nanofibrils offer interesting potential as a native fibrous constituent of mechanical performance exceeding the plant fibers in current use for commercial products. In the present study, wood nanofibrils are used to prepare porous cellulose nanopaper of remarkably high toughness. Nanopapers of different porosities and from nanofibrils of different molar mass are prepared. Uniaxial tensile tests are performed and structure-property relationships are discussed. The high toughness of highly porous nanopaper is related to the nanofibrillar network structure and high mechanical nanofibril performance. Also, molar mass correlates with tensile strength. This indicates that nanofibril fracture controls ultimate strength. Furthermore, the large strain-to-failure means that mechanisms, such as interfibril slippage, also contributes to inelastic deformation in addition to deformation of the nanofibrils themselves.

Place, publisher, year, edition, pages
2008. Vol. 9, no 6, 1579-1585 p.
Keyword [en]
Cellulose; Deformation; Fibers; Fracture fixation; Molar mass; Petroleum products; Tensile strength; Tensile testing; American Chemical Society (ACS); Commercial products; High toughness; Inelastic deformations; Large strains; mechanical performances; Nano-fibrils; Nanofibrillar; Network structures; Plant fibers; Strength (IGC: D5/D6); Structure property relationships; ultimate strength; Uniaxial tensile testing
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-7910DOI: 10.1021/bm800038nISI: 000256635100011ScopusID: 2-s2.0-46849094688OAI: diva2:13080
QC 20100810. Uppdaterad från submitted till published (20100810).Available from: 2008-01-21 Created: 2008-01-21 Last updated: 2010-08-10Bibliographically approved
In thesis
1. Cellulose Nanofibril Networks and Composites: Preparation, Structure and Properties
Open this publication in new window or tab >>Cellulose Nanofibril Networks and Composites: Preparation, Structure and Properties
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [sv]

Träbaserade cellulosananofibriller är intressanta som förstärkande fas i polymera nanokompositer; detta främst på grund av den kristallina cellulosans höga styvhet och på grund av nanofibrillernas förmåga att bilda nätverk. Cellulosananofibriller kan användas i form av mikrokristallin cellulosa, MCC, som har lågt längd/diameter förhållande, eller i form av mikrofibrillerad cellulosa, MFC, med högt längd/diameter förhållande. Målet med det här arbetet är att studera struktur-egenskapsförhållanden för nanofibrillnätverk och kompositer.

Nanokompositer baserade på MCC och termoplastisk polyuretan tillverkades genom in-situ polymerisation. Cellulosafibrillerna var väl dispergerade i matrisfasen och kompositen visade ökad styvhet, styrka samt brottöjning. Dessa förbättningar antas bero på stark interaktion mellan polyuretan och cellulosananofibrillerna.

En metod som underlättar mikrofibrillering av massafiberns cellvägg under homogenisering har utvecklats. Massan förbehandlades med ett enzym innan homogenisering. Den här metoden förenklade mikrofibrilleringen och mekanismerna diskuteras. De resulterande MFC-nanofibrillerna hade högt längd/diameter förhållande.

Filmer har tillverkats av MFC-nanofibriller och filmernas struktur samt mekaniska egenskaper har studerats. Röntgendiffraktion och SEM visar att nanofibrilerna är mer orienterade i planet än i rymden. SEM och densitetsmätningar visar även att filmerna har en porös struktur. Resultaten från dragprovning visade att filmernas brottstyrka är beroende av molekylvikten för cellulosan. Nanofibrillerna med högst molekylvikt visade en E-modul på 13.2 GPa, brottstyrkan var 214 MPa och brottöjningen 10.1%.

Kompositer med hög fiberhalt har tillverkats genom tillsats av melaminformaldehyd till MFC-filmer. Dessa kompositer visar ökad styvhet och styrka på bekostnad av brottöjningen. Kompositer har också tillverkats genom impregnering av MFC-nätverk med en hyperförgrenad polymer som tvärbands. DMA visar två Tg för kompositerna med 0.26 och 0.43 volymfraktion nanofibriller; matrisens Tg samt ytterligare ett Tg vid högre temperatur. Detta motsvarar molekyler med lägre mobilitet på grund av ökad interaktion med nanofibrillernas ytor.

Abstract [en]

The cellulose nanofibril from wood is an interesting new material constituent that can provide strong reinforcement in polymer nanocomposites due to the high stiffness of the cellulose crystals and the network formation characteristics of the nanofibrils. Cellulose nanofibrils can be used either in the form of low aspect ratio microcrystalline cellulose, MCC, or as high aspect ratio microfibrillated cellulose, MFC. The objective is to study structure-property relationships for cellulose nanofibril networks and composites.

Nanocomposites based on MCC and thermoplastic polyurethane were prepared by in-situ polymerization. The cellulose nanofibrils were successfully dispersed in the matrix and the composites showed improvements in stiffness, strength, as well as in strain-to-failure. Cellulose nanofibrils reinforce the physical rubber network by strong molecular interaction with the rubber.

A method that facilitates microfibrillation of the pulp cell wall during homogenization has been developed. The pulps were treated with a combination of beating and enzymatic treatment prior to homogenization. The enzymatic pretreatment was found to facilitate the microfibrillation and the mechanisms are discussed. The resulting MFC nanofibrils were of high aspect ratio.

Cellulose nanofibril networks of high toughness were prepared from MFC and studied with respect to the structure and mechanical properties. These films have a porous structure and the nanofibrils are more in-plane than in-space oriented. Tensile testing showed that the strength is dependent on the average molecular weight of the cellulose. The MFC of the highest molecular weight showed a modulus of 13.2 GPa, tensile strength as high as 214 MPa and 10.1% strain-to-failure, at a porosity of 28%.

Composites of high fiber content have been prepared by addition of melamine formaldehyde to MFC films. These composites show increased stiffness and strength, at the cost of strain-to-failure. Composites were also prepared by impregnating MFC nanofibril networks with a hyperbranched polymer. The matrix was crosslinked and strong interactions with the nanofibrils were formed. By DMA two Tg’s were observed for the composites with 0.26 and 0.43 volume fraction nanofibrils. The Tg of the matrix was observed as well as a Tg at higher temperatures. This corresponds to molecules with constrained mobility by increased interactions with the cellulose nanofibril surfaces.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 51 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2008:3
cellulose nanocomposites, microfibrillated cellulose, nanofibrils, biofibers, mechanical properties, deformation mechanisms, molar mass, endoglucanase
National Category
Materials Engineering
urn:nbn:se:kth:diva-4610 (URN)978-91-7178-849-8 (ISBN)
Public defence
2008-02-08, F3, F-byggnaden, Lindstedtsvägen 26, Stockholm, 10:00
QC 20100810Available from: 2008-01-21 Created: 2008-01-21 Last updated: 2010-08-10Bibliographically approved

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