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Characterisation of amino-resin composites reinforced with unidirectional flax fibres
2000 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Melamine-formaldehyde and urea-formaldehyde composites reinforced with two different kinds of flax fibres are studied in this paper. The main objective was to find the combination matrix/fibres providing the best mechanical properties and resistance to moisture. Tensile properties were determined using monotonic tensile tests, and the fracture surfaces were observed to characterise the interaction between fibres and matrix. Different humidity tests were performed to find out the influence of humidity on the tensile properties of the specimens and to calculate the diffusion coefficient of water in the composite. Melamine-formaldehyde composites reinforced with unidirectional flax fibres present good mechanical properties in the fibre direction: tensile modulus of 20 to 28GPa, tensile strength of 104 to 154GPa and strain at break of 0.54 to 0.75%. Their major drawbacks are a lack of thermal stability due to different thermal expansion coefficients between the resin and the fibres, which leads to twisted plates of composites after pressing, and a high sensitivity to environmental humidity. The flax fibre-reinforced composites studied absorbed up to 13wt% of water at a relative humidity of 90%, leading to swelling of the fibres in the radial direction. The absorption of humidity had a limited effect on the mechanical properties of the composite in the fibre direction. Water absorption and desorption lowered the tensile modulus of flax fibre-reinforced composites, but this did not really affect their tensile strength, and the strain at break of the composite was even improved. The composites having the best tensile properties in the fibre direction were manufactured by dry impregnation of flax fibres with powder MF resin. Unfortunately, these composites are very sensitive to environmental humidity because they contain many chemical sites able to form hydrogen bonds with water, and their properties were dramatically lowered after humidity cycles.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Composites, natural fibres, flax, melamine-formaldehyde, urea-formaldehyde, humidity
Keyword [sv]
URN: urn:nbn:se:ltu:diva-46748ISRN: LTU-EX--00/193--SELocal ID: 45dd0f2a-bdfd-4ba7-bdd0-1ffa1e2293b1OAI: diva2:1020063
Subject / course
Student thesis, at least 30 credits
Educational program
Civil Engineering programmes 1997-2000, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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