Abstract
Nowadays, due to the global warming and pollution issues, sustainable materials must be considered.
Composites materials can offer excellent mechanical performance with low weight, hence saving fuel.
However, most of the composites systems are based on petrochemicals, and natural materials may
be a better option; for example, fibre reinforcements from plant stems (bast) and bio-based resins
are becoming available commercially.
One of the major inconveniences of the NFRP is the moisture absorption in marine environments. This
problem is usually solved increasing the fibre-matrix bonding. Commercially available fibre systems
are chemically treated in order to tackle this issue, but those treatments produce environmental
burdens. This thesis seeks to develop an environmentally-friendly, commercially competitive and
easily performed treatment methodology for improving the NFRP mechanical properties.
The proposed silane-in-hardener method, adding coupling agent to the hardener, rather than direct
treatment of the fibres in solvent, can eliminate solvent use, considerably reducing environmental
burdens. This new proposal also reduces process time and improves the composite mechanical
performance, resulting in commercial competitiveness. The primary research question in this thesis is
can sensible NFRP properties be achieved with silane-in-hardener replacing prior treatment of
reinforcements?
Flax fibre and epoxy resin were selected for the experimental campaign. First, flax fibre was
mercerised in different immersion-time and concentrations conditions, and the resulting mechanical
performance of composite systems evaluated; from the campaign the best mercerised system was
selected. In a second stage, raw flax fibre and best mercerised flax fibre were silanised and resulting
composite system mechanical properties evaluated. In a third stage, silane was directly added to the
epoxy resin and the mechanical properties evaluated together with raw flax fibre. In the final stage,
the developed silane in resin method was applied to flax/bio-epoxy system and compared with the
basic system in order to evaluate its real improvement.
Aitor Hernandez Michelena PhD thesis Page vii of xxiv
Additionally, water immersion tests were performed to the silanised flax fibre/epoxy resin system in
order to evaluate whether the moisture resistance was increased or not.
From the experimental campaign, it was concluded that the fibre mercerisation process reduces the
resulting composite mechanical performance. First, whenever the flax is immersed in the NaOH
solution the fibre swells, impeding the flax fibre correct wetting, reducing as a result the composite
mechanical performance. Second, because at long immersion-times and concentrations the flax fibre
starts to degrade, reducing the composite performance. Similarly, when the flax was immersed in a
silane solution, fibre swelling was also obtained, reducing mechanical performance. In contrast when
the 1% w/w silane was added to the resin system, the swelling was avoided, and the objective
interfacial properties enhanced, getting as a result static mechanical properties improvement.
However, when the enhanced and base systems moisture ingress resistance was evaluated, the
values difference was not as representative as expected.
Date of Award | 2019 |
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Original language | English |
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Awarding Institution | |
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Supervisor | John Summerscales (Other Supervisor) |
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Natural fibre reinforced composite materials
Hernandez Michelena, A. (Author). 2019
Student thesis: PhD