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Hierarchical wood cellulose fiber/epoxy biocomposites: Materials design of fiber porosity and nanostructure
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.ORCID iD: 0000-0001-7870-6327
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.ORCID iD: 0000-0001-5818-2378
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2015 (English)In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 74, 60-68 p.Article in journal (Refereed) Published
Abstract [en]

Delignified chemical wood pulp fibers can be designed to have a controlled structure of cellulose fibril aggregates to serve as porous templates in biocomposites with unique properties. The potential of these fibers as reinforcement for an epoxy matrix (EP) was investigated in this work. Networks of porous wood fibers were impregnated with monomeric epoxy and cured. Microscopy images from ultramicrotomed cross sections and tensile fractured surfaces were used to study the distribution of matrix inside and around the fibers - at two different length scales. Mechanical characterization at different relative humidity showed much improved mechanical properties of biocomposites based on epoxy-impregnated fibers and they were rather insensitive to surrounding humidity. Furthermore, the mechanical properties of cellulose-fiber biocomposites were compared with those of cellulose-nanofibril (CNF) composites; strong similarities were found between the two materials. The reasons for this, some limitations and the role of specific surface area of the fiber are discussed.

Place, publisher, year, edition, pages
2015. Vol. 74, 60-68 p.
Keyword [en]
A. Nano-structures, B. Interface, D. Fractography, Moisture stability, Cellulose, Characterization, Composite materials, Fibers, Fracture mechanics, Mechanical properties, Nanostructures, Pulp materials, Textile fibers, Wood products, Cellulose fibrils, Controlled structures, Different length scale, Fractured surfaces, Mechanical characterizations, Microscopy images, Wood cellulose fibers, Wood, Moisture, Pulps, Stability, Surfaces
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-167694DOI: 10.1016/j.compositesa.2015.03.024Scopus ID: 2-s2.0-84927161110OAI: oai:DiVA.org:kth-167694DiVA: diva2:816061
Note

QC 20150602

Available from: 2015-06-02 Created: 2015-05-22 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Nanostructured Cellulose Biocomposites: Effects from dispersion, network and interface
Open this publication in new window or tab >>Nanostructured Cellulose Biocomposites: Effects from dispersion, network and interface
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The major load bearing component in native wood, cellulose nanofibrils, are potential candidates for use as reinforcement in polymer matrices. This study is based on nanocellulose composites and attempts to prepare and characterize biocomposites with high nanocellulose content and investigate the influence of nanostructure on macroscopic properties.

In an initial study, effects from cellulose nanocrystal (CNC) dispersion on optical and mechanical properties of CNC composites are studied in a model system using polyvinylacetate (PVAc) as the polymer. CNC surface modification is used as an aid to improve dispersion, and nanocomposites with up to 20 wt% of modified and unmodified CNC are characterized. Strong influence of CNC as reinforcement and on polymer matrix characteristics were observed with well-dispersed CNCs, resulting in nanocomposites with significantly improved mechanical properties.

In the subsequent parts, an impregnation-based processing strategy is used to prepare cellulose nanofibril (CNF) based thermoset (epoxy and unsaturated polyester) composites with high CNF content (15 - 50 vol%). Influence of CNF surface hydroxyls on epoxy curing is discussed. A mono-epoxy compound is used to confirm covalent epoxy/CNF reaction and the implications of this modification on mechanical properties of wet CNF network are illustrated. Mechanical properties of thermoset composites are characterized at different relative humidities to evaluate their hygromechanical stability. The role of the CNF-thermoset interface is investigated by comparing composites with epoxy and unsaturated polyester matrices. Unique effects due to the nanostructure of composites are discussed with respect to CNF dispersion, CNF network characteristics and CNF/matrix interface. Additionally, pulp fiber composites, where the fiber wall itself is impregnated with resin, are designed and differences between nanocellulose (nanoscale network) and pulp fibers (microscale diameter) as reinforcements are analyzed.

Abstract [sv]

Trä och träbaserade material erbjuder ett hållbart alternativ till petroleumbaserade material. Mikrofibriller, eller som de också kallas i materialsammanhang, nanofibriller från cellulosa (CNF) är den huvudsakliga lastbärande komponenten i trä. Den har stor potential som förstärkande tillsats i polymerer. Denna studie handlar om kompositer baserade på nanocellulosa. Biokompositer med företrädesvis hög andel nanocellulosa framställs och karakteriseras. Huvudsyftet är att förklara inverkan av nanostruktur på makroskopiska egenskaper.

I en första studie används polyvinylacetat (PVAc) som modellpolymer för att undersöka effekten av dispergeringgrad hos cellulosa-nanokristaller (CNC) för optiska och mekaniska egenskaper. En miljövänlig form av modifiering av CNC används för att förbättra dispergeringsgraden. Nanokompositer med upp till 20 vikts-% modifierad eller icke modifierad CNC studerades. Nanokompositer med väldispergerad CNC visade dramatiskt förbättrade egenskaper, eftersom nanopartiklarna kraftigt påskyndade fysikalisk åldring av PVAc så att den fick högre E-modul och hållfasthet.

I avhandlingens andra del framställdes härdplastkompositer genom harts-impregnering av porösa CNF-nätverk, följt av härdning. Epoxi (EP) och omättade polyester (UP) användes som härdplaster. Volymsfraktionen CNF var mellan 15-50%. Reaktionshastigheten under härdning ökade kraftigt i närvaro av nanocellulosa med hög specifik yta. Troligen reagerade epoxigrupper med hydroxylgrupper på cellulosaytan, under förutsättning att katalytiska aminföreningar fanns tillgängliga. Hypotesen fick ytterligare stöd i en studie av monoepoxi + nanocellulosa. Den modifieringen visade sig också göra CNF-nätverket mindre hygroskopiskt, så att de hygromekaniska egenskaperna förbättrades. Mekaniska egenskaper hos EP- och UP-kompositer bestämdes med hjälp av dragprov vid olika luftfuktighet. EP-kompositerna visade bättre egenskaper vid hög fuktighet, främst pga de kovalenta bindningarna mellan EP och CNF. Effekter av CNF-Dispergering, CNF-nätverkets egenskaper och gränsytan CNF-härdplast analyserades. Slutligen jämfördes EP-kompositer baserade på CNF med kompositer från blekta massafibrer. CNF-kompositerna hade högre hållfasthet till följd av den låga diametern (inga problem med fiber-matris separation och sprickbildning vid låga töjningar) och kraftigt töjningshårdnande orsakad av CNF nätverket.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2016:19
Keyword
Wood, cellulose nanofibrils, hygromechanical properties, network structure, thermoset, polymer matrix composites, natural fiber composites, pulp fiber, strain hardening, humidity
National Category
Materials Engineering
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-185723 (URN)978-91-7595-924-5 (ISBN)
Public defence
2016-05-25, F3, Lindstedtsvägen 26, Stockholm, 09:00 (English)
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Supervisors
Note

Qc 20160427

Available from: 2016-04-27 Created: 2016-04-25 Last updated: 2016-04-29Bibliographically approved

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Ansari, FarhanBerglund, Lars A.Wågberg, Lars

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