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Biocomposites Based on Core-Shell Cellulose Nanofibers: Preparation, Structure, and Properties
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cellulose nanofibers (CNFs) are of interest as load-bearing components for polymer matrix nanocomposites. A wide range of nanostructured materials including nanopaper/films, foams, aerogels, and hydrogels can be prepared from CNFs. The material performance can be fine-tuned when CNFs are combined with different polymer matrices. The main idea of the present study is to test the hypothesis that the concept of Core-shell CNFs can provide processing and performance advantages for nanocomposites through improved nanostructural control.

The problems of matrix distribution and interface structure at nanoscale are investigated. The first part of this thesis (Paper I-III) describes an alternative preparation procedure for biocomposites based on the Core-shell concept. Inspired by the structural framework and mechanical function of the primary cell wall in plants, Core-shell CNFs are formed by coating wood CNFs with a polysaccharide matrix, and are subsequently used for fabrication of biocomposite films. The nanostructure of Core-shell CNFs and their nanocomposites is characterized. Mechanical properties of the biocomposites at various hydration conditions are investigated. A study on molecular water mobility and moisture stability of the materials is conducted. In the present thesis, three different biological polysaccharides including amylopectin, xyloglucan and galactoglucomannan have been used for man-made nanocomposites based on Core-shell nanofibers.

The later sections of the thesis (Paper IV-V) describe an alternative method to disintegrate holocellulose nanofibers from wood chips. These CNFs based on holocellulose possess Core-shell structure with native hemicelluloses as “shell”. Peracetic acid pretreatment is used for the preparation of holocellulose. This procedure is a promising single-step pulping as preparation for nanofibrillation. The nanostructure of the holocellulose nanofibers are characterized, and compared with CNFs prepared from enzymatic pretreatment. The holocellulose nanofibers are used for preparation of films and porous materials. The influence of nanostructural characteristics of two different nanofibers (CNFs from enzymatic pretreatment vs holocellulose nanofibers from peracetic acid pretreatment) on final properties of the nanocomposites is clarified. 

Favorable characteristics of Core-shell fibrils are reported in terms of colloidal stability, controlled matrix distribution, improved interface characteristics, and improved hygromechanical properties of the biocomposites. In both a scientific and industrial context, the Core-shell nanofiber concept thus offers great potential for the materials design of new cellulose nanomaterials with unique characteristics.

Abstract [sv]

Nanofibrer från cellulosa (CNF) är av stort intresse som lastbärande komponent i nanokompositer och ett flertal nanostrukturerade material såsom nanopapper, nanoskum, aerogeler eller hydrogeler kan framställas från CNF. Materialegenskaperna kan finjusteras då CNF tillsätts till en polymermatris. Avhandlingen handlar om ett koncept för att kontrollera matrisfördelning och gränsyta mellan CNF och polymermatrisen, i form av sk ”Core-shell”-CNF. Första delen (artikel I-III) handlar om ”Core-shell”-CNF framställda genom att adsorbera en polysackarid på ytan av CNF. Nanostrukturen hos ”Core-shell”-CNF och dess kompositmaterial undersöks, liksom mekaniska egenskaper vid olika hydreringstillstånd. Molekylrörlighet hos vatten studeras med NMR. Tre olika polysackarider undersöks; amylopektin, xyloglukan och galaktoglukomannan. Avhandlingens andra del (artikel IV och V) handlar om CNF från holocellulosa, med vedflis som råvara. Holocellulosa innebär att huvudsakligen lignin har extraherats från veden, medan cellulosa och hemicellulosa är välbevarade. Denna CNF har också ”Core-shell”-struktur med hemicellulosa som ytskikt. Perättiksyra används som en mild framställningsmetod. Det innebär en process i ett enda steg för att framställa massa med bevarad cellulosastruktur. Nanostruktur och kemisk sammansättning karakteriseras och jämförs med enzymatiskt framställd CNF från sulfitmassa. CNF från båda typerna av nanocellulosa (holocellulosa och enzymatisk CNF) används för att framställa kompositer och porösa material (honeycombs och skum). Sambanden mellan struktur och materialegenskaper klarläggs, liksom effekterna från olika typer av CNF.  Avhandlingen visar att ”Core-shell”-CNF är ett fungerande koncept för nanostrukturerade kompositer genom påvisande av ett flertal lovande och fördelaktiga egenskaper såsom kolloidal stabilitet, kontrollerad matrisfördelning och förbättrade gränsyte- samt hygromekaniska egenskaper. Såväl vetenskapligt som industriellt kan ”Core-shell”-CNF bidra till utvecklingen av nya nanomaterial baserade på cellulosa.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , 83 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:18
Keyword [en]
biocomposites, cellulose nanofibers, polysaccharides, holocellulose, nanostructure, dispersion, mechanical properties, hygromechanical properties, moisture stability, film, porous material
National Category
Composite Science and Engineering Paper, Pulp and Fiber Technology
Research subject
Fibre and Polymer Science
Identifiers
URN: urn:nbn:se:kth:diva-166177ISBN: 978-91-7595-513-1 (print)OAI: oai:DiVA.org:kth-166177DiVA: diva2:809595
Public defence
2015-05-26, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150506

Available from: 2015-05-06 Created: 2015-05-04 Last updated: 2015-05-06Bibliographically approved
List of papers
1. High-Performance and Moisture-Stable Cellulose-Starch Nanocomposites Based on Bioinspired Core-Shell Nanofibers
Open this publication in new window or tab >>High-Performance and Moisture-Stable Cellulose-Starch Nanocomposites Based on Bioinspired Core-Shell Nanofibers
2015 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, no 3, 904-912 p.Article in journal (Refereed) Published
Abstract [en]

Moisture stability and brittleness are challenges for plant fiber biocomposites intended for load-bearing applications, for instance those based on an amylopectin-rich (AP) starch matrix. Core-shell amylopectin-coated cellulose nanofibers and nanocomposites are prepared to investigate effects from the distribution of AP matrix. The core-shell nanocomposites are compared with nanocomposites with more irregular amylopectin (AP) distribution. Colloidal properties (DLS), AP adsorption, nanofiber dimensions (atomic force microscopy), and nanocomposite structure (transmission electron microscopy) are analyzed. Tensile tests are performed at different moisture contents. The core-shell nanofibers result in exceptionally moisture stable, ductile, and strong nanocomposites, much superior to reference CNF/AP nanocomposites with more irregular AP distribution. The reduction in AP properties is less pronounced as the AP forms a favorable interphase around individual CNF nanofibers.

National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-164463 (URN)10.1021/bm5018194 (DOI)000350841100025 ()25650787 (PubMedID)2-s2.0-84924368353 (Scopus ID)
Note

QC 20150422

Available from: 2015-04-22 Created: 2015-04-17 Last updated: 2017-12-04Bibliographically approved
2. Core-shell cellulose nanofibers for biocomposites: Nanostructural effects in hydrated state
Open this publication in new window or tab >>Core-shell cellulose nanofibers for biocomposites: Nanostructural effects in hydrated state
Show others...
2015 (English)In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 125, 92-102 p.Article in journal (Refereed) Published
Abstract [en]

Core-shell wood cellulose nanofibers (CNF) coated by an XG hemicellulose polymer are prepared and used to make biocomposites. CNF/XG biocomposites have interest as packaging materials and as hydrated CNF/XG plant cell wall analogues. Structure and properties are compared between Core-shell CNF/XG and more inhomogeneous CNF/XG. Experiments include XG sorption, dynamic light scattering of CNF nanoparticle suspensions, FE-SEM of nanostructure, moisture sorption, tensile testing in moist conditions and dynamic mechanical analysis. (2)H NMR relaxometry is performed on materials containing sorbed (2)H2O2 in order to assess water molecular dynamics in different materials. The results clarify the roles of CNF, XG and the CNF/XG interface in the biocomposites, both in terms of moisture sorption mechanisms and mechanical properties in moist state. The concept of core-shell nanofiber network biocomposites, prepared by filtering of colloids, provides improved control of polymer matrix distribution and interface structure. Also, present mechanical properties are much superior to comparable plant fiber biocomposites.

Keyword
Xyloglucan, Cellulose nanofibers, H-2 NMR relaxometry, Biocomposites, Moisture sorption, Mechanical properties
National Category
Polymer Technologies Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-164410 (URN)10.1016/j.carbpol.2015.02.059 (DOI)000353604200012 ()25857964 (PubMedID)2-s2.0-84925652982 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20150427

Available from: 2015-04-27 Created: 2015-04-17 Last updated: 2017-12-04Bibliographically approved
3. Strong effects from galactoglucomannan hemicellulose on mechanical behavior of wet cellulose nanofiber gels
Open this publication in new window or tab >>Strong effects from galactoglucomannan hemicellulose on mechanical behavior of wet cellulose nanofiber gels
(English)Manuscript (preprint) (Other academic)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-166253 (URN)
Note

QS 2015

Available from: 2015-05-06 Created: 2015-05-06 Last updated: 2015-05-06Bibliographically approved
4. Holocellulose nanofibers of high molar mass and small diameter for high-strength nanopaper
Open this publication in new window or tab >>Holocellulose nanofibers of high molar mass and small diameter for high-strength nanopaper
2015 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, no 8, 2427-2435 p.Article in journal (Refereed) Published
Abstract [en]

Wood cellulose nanofibers (CNFs) based on bleached pulp are different from the cellulose microfibrils in the plant cell wall in terms of larger diameter, lower cellulose molar mass, and modified cellulose topochemistry. Also, CNF isolation often requires high-energy mechanical disintegration. Here, a new type of CNFs is reported based on a mild peracetic acid delignification process for spruce and aspen fibers, followed by low-energy mechanical disintegration. Resulting CNFs are characterized with respect to geometry (AFM, TEM), molar mass (SEC), and polysaccharide composition. Cellulose nanopaper films are prepared by filtration and characterized by UV-vis spectrometry for optical transparency and uniaxial tensile tests. These CNFs are unique in terms of high molar mass and cellulose-hemicellulose core-shell structure. Furthermore, the corresponding nanopaper structures exhibit exceptionally high optical transparency and the highest mechanical properties reported for comparable CNF nanopaper structures.

National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-166254 (URN)10.1021/acs.biomac.5b00678 (DOI)000359499500020 ()2-s2.0-84938887804 (Scopus ID)
Note

Updated from manuscript to article.

QC 20150909

Available from: 2015-05-06 Created: 2015-05-06 Last updated: 2017-12-04Bibliographically approved
5. Mechanical performance and architecture of biocomposite honeycombs and foams from core-shell holocellulose nanofibers
Open this publication in new window or tab >>Mechanical performance and architecture of biocomposite honeycombs and foams from core-shell holocellulose nanofibers
(English)Manuscript (preprint) (Other academic)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-166255 (URN)
Note

QS 2015

Available from: 2015-05-06 Created: 2015-05-06 Last updated: 2015-05-06Bibliographically approved

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