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Surface Treatment of Softwood Lignin Based Carbon Fibers for Enhanced Interfacial Adhesion: Effects of Plasma Treatment Parameters on the Creation of Surface Groups
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. (Polymeric Composite Materials)
2017 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Lightweight design is an essential part of lowering CO2 emission, which is one of the mostimportant challenges that the automotive industry is facing today. Carbon fiber reinforcedplastics offer an enormous potential for replacing heavier structural materials like steel andaluminum, however due to their high cost and scarcity, carbon fibers are not a very feasibleoption to use in high volume production applications. It is thought that the introduction of arenewable, low-cost raw material, like lignin, as the carbon fiber precursor would not onlylower the cost but also increase supply compared to its PAN based counterparts. Properties ofthe fiber/matrix interface play a crucial role in governing the overall performance of thecomposite material. Good adhesion between the fiber and the matrix must be ensured in orderto maximize performance. In this study, plasma treatment of softwood lignin based carbonfibers was performed in order to increase the interfacial adhesion between the fiber and thematrix by incorporating functional groups onto the fiber surface. Plasma treatment time,plasma power, chamber pressure and plasma gas type were varied in order to investigate theireffects on the functionalization of the surface by various visual, chemical and mechanicalcharacterization methods. Observations with optical and scanning electron microscopiesshowed the cleaning effects of plasma treatment on the fiber surface by removal of flakes andsmoothing of the fiber surface. The smoothing effect of plasma treatment was later supportedby the subtle increase in the tensile strength of the plasma treated fibers and this wasattributed to the elimination of crack initiators on the surface by a so-called “polishing” effect.Contact angle measurements of the lignin based fibers showed that all plasma gases achieve acertain level of decrease in the contact angle values thus lowering the surface tension. X-rayphotoelectron spectroscopy (XPS) results were analyzed using a design of experimentssoftware with a PLS fit. For the highest amount of surface functionality to be achieved, it wasconcluded that oxygen plasma should be used with high plasma power, low pressure and ahigh treatment time. Detection of Na and S elements combined with unusually lowmechanical properties for all lignin based carbon fibers indicated insufficient carbonization ormolecular orientation for the softwood lignin based carbon fibers used in this study.

Place, publisher, year, edition, pages
2017. , p. 76
Keywords [en]
Lignin, adhesion, surface, carbon, fiber
National Category
Composite Science and Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-61766OAI: oai:DiVA.org:ltu-61766DiVA, id: diva2:1070528
External cooperation
Swerea Sicomp
Subject / course
Student thesis, at least 30 credits
Educational program
Materials Engineering, master's level (120 credits)
Presentation
2016-12-16, Lokal E246, LTU, Luleå, 08:30 (English)
Supervisors
Examiners
Projects
GreenLightAvailable from: 2017-02-20 Created: 2017-02-08 Last updated: 2017-02-20Bibliographically approved

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CiteExportLink to record
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