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Nanostructured biocomposites based on unsaturated polyester resin and a cellulose nanofiber network
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.ORCID iD: 0000-0001-7870-6327
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.ORCID iD: 0000-0001-5818-2378
2015 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 117, 298-306 p.Article in journal (Refereed) Published
Abstract [en]

Biocomposites reinforced by natural plant fibers tend to be brittle, moisture sensitive and have limited strength. Wood cellulose nanofibers (CNF) were therefore used to reinforce an unsaturated polyester matrix (UP) without the need of coupling agents or CNF surface modification. The nanostructured CNF network reinforcement strongly improves modulus and strength of UP but also ductility and toughness. A template-based prepreg processing approach of industrial potential is adopted, which combines high CNF content (up to 45 vol%) with nanoscale CNF dispersion. The CNF/UP composites are subjected to moisture sorption, dynamic thermal analysis, tensile tests at different humidities, fracture toughness tests and fractography. The glass transition temperature (T-g) increases substantially with CNF content. Modulus and strength of UP increase about 3 times at 45 vol% CNF whereas ductility and apparent fracture toughness are doubled. Tensile properties at high humidity are compared with other bio-composites and interpreted based on differences in molecular interactions at the interface.

Place, publisher, year, edition, pages
Pergamon Press, 2015. Vol. 117, 298-306 p.
National Category
Polymer Technologies Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-176037DOI: 10.1016/j.compscitech.2015.07.004ISI: 000362132900037Scopus ID: 2-s2.0-84937901929OAI: oai:DiVA.org:kth-176037DiVA: diva2:865621
Funder
VINNOVAKnut and Alice Wallenberg Foundation
Note

QC 20151029

Available from: 2015-10-28 Created: 2015-10-28 Last updated: 2017-12-01Bibliographically 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)
Opponent
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

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