Great interest has been generated in the use of natural fibres as environmentally
friendly reinforcing materials in polymeric composites, which do not require high
load bearing capabilities. kenaf fibres extracted from kenaf plants (hibiscus
cannabinus) have been identified as an attractive option due to its production cost
and the ability of the kenaf plants to grow in a variety of climatic conditions.
Polypropylene (PP) has a relatively low production cost, excellent corrosion
resistance, good retention of mechanical properties and less recycling challenges
in comparison to other matrix systems such as thermosets. Given the individual
advantages of kenaf fibre and polypropylene, kenaf reinforced polypropylene
composites (kenaf/PP composites) have considerable commercial interest in the
composite industry. However, limitations arise with respect to the mechanical
performance and to the resistance to moisture absorption when natural fibres are
used.
This study focuses on the improvement of the mechanical properties (e.g. tensile,
flexural, fatigue and impact properties) and the resistance to moisture absorption
of kenaf reinforced polypropylene composites by means of fibre treatments (e.g.
alkali and alkali-silane treatments) and the use of filler materials (e.g.
functionalized multi-wall carbon nanotubes). Kenaf reinforced polypropylene
composites are manufactured by a modified compression moulding using the
film–stacking technique. The crux of this technique is that kenaf mats are
impregnated with polypropylene powder in order achieve a uniform material
distribution and to lower the manufacturing temperature, thereby preventing the
thermal alteration of the composite constituents (e.g. kenaf fibres) and silano
functional groups attached to the multi-wall carbon nanotubes. Fibre treatments
including alkali treatments and alkali followed by silane treatments (alkali-silane)
are considered in order to improve the fibre-matrix interfacial adhesion. The
concentrations of the alkali solutions range from 1% to 8% in intervals of 1% by
mass. Fibre contents ranging from 20% to 35% in interval of 5% by mass are
considered for both kenaf and glass fibre reinforced plates. Functionalized multi-wall carbon nanotubes are used as filler material in order to improve the
mechanical properties of the composite plates. The concentrations of the multiwall
carbon nanotube (MWCNT) range from 0.1% to 1.25%.
Mechanical test and microscopic examination results showed that alkali
treatments improve the mechanical properties of kenaf/PP composites. However,
the improvements due to alkali-silane treatments were found to be more
significant because additional silane treatments substantially enhanced the fibrematrix
interfacial adhesion. Material failures in untreated kenaf/PP composites
and alkali treated kenaf/PP composites were mainly characterized by fibre pullouts,
whereas in alkali-silane treated kenaf/PP composites they were characterised
by fibre breakage. Alkali concentrations of 5% and 6% NaOH are found to the
optimum concentrations for both alkali treatment and alkali-silane treatment.
The use of functionalized MWCNTs as filler material improved furthermore the
mechanical properties of kenaf/PP-MWCNT composites in comparison to those
of kenaf/PP and glass/PP composites. The main contributing factors of the
improvements were found to be the enhancement of the interfacial adhesion
between the nanoparticles and the matrix, and also between the nanoparticles and
kenaf fibres. Material failures in kenaf/PP-MWCNT composites were
characterized by fibre breakage and matrix cracks. The optimum MWCNT
concentrations were found to be 0.5% and 0.75%. 30% fibre contents was found
to be the optimum fibre content for both kenaf/PP and kenaf/PP-MWCNT
composites. Test results showed that the fibre treatments, especially alkali-silane
treatment, improved the resistance to moisture absorption of the composites. Test
results also showed that the manufacturing technique, which enables the
manufacturing of composite plates with layers of different moisture diffusion
resistances, has a significant influence on the resistance of kenaf/PP composites.
The addition of multi-wall carbon nanotubes to the polypropylene matrix did not
alter the moisture absorption resistance of kenaf/PP-MWCNT composites. The
impregnation of kenaf and fibre glass mats with polypropylene powder
significantly lowered the manufacturing temperature
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/15415 |
| Date | 05 September 2014 |
| Creators | Asumani, Oscar |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf |
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