Characterization of kenaf bast fibre filled poly (butylene succinate) composites: mechanical, water absorption and weathering properties.
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Date
2011
Authors
Ahmad Thirmizir, Mohd Zharif
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Abstract
Characterization of kenaf bast fibre (KBF) filled poly(butylene succinate)
(PBS) composites in this study involved several stages. Firstly, the effect of KBF
loadings (l0 - 40 wt. %) on flexural and impact properties were investigated. The
flexural strength of the composites increased with increasing fibre loadings up to 30
wt. % with the highest value of about 9.4 % before decreasing with a further increase
in fibre loading. The flexural modulus of the composites increased about 87.1 - 424
% with increasing KBF loadings from 10 to 40 wt. %. This indicates that the addition
of KBF at 30 wt. % loading had resulted in a balance of performance and
processability of the composites. However, the stiff nature of the KBF resulted in the
reduction of the composites' impact strengtll. Secondly, the effect of fibre length (5,
10, 15 and 20 mm KBF) on the mechanical properties was investigated at fibre
loading of 30 wt. %. Composite with 10 mm KBF length showed the highest
increment in flexural strength and modulus of about 16.7 and 3.6%, respectively. The
inferior flexural and impact strength of the composites with 15 rom and 20 mm KBF
length could be due to the relatively longer fibres that underwent severe fibre
attrition as a result of high mechanical shearing during the compounding. This was
proven by analysis of the fibre length, diameter and aspect ratio. Third stage focused
on the improvement of fibre-matrix interfacial adhesion by an introduction of
unpurified and purified maleated PBS compatibilisers. For preparation of PBSgMA,
DCP initiator concentration was kept constant at 1 phr while MA concentration was
varied from 3 - 10 phr. The optimum enhancements in flexural and impact strength
were observed in both composites with addition of 5 wt. % unpurified and purified
compatibilisers at 5 phr MA concentration. The inferior mechanical properties of the
composites with unpurified compatibilisers to those with purified compatibilisers
probably due to the presence of unreacted MA in the unpurified compatibilisers
which could restrict the formation of complete bridging between matrix and fibres.
The last stage involved evaluation of water absorption and natural weathering
performance on both the uncompatibilised and compatibilised PBSIKBF composites.
Increment about 2.49 to 12.5 wt.% in equilibrium water content (Mm) were observed
for uncompatibilised composites with increasing fibre loading from 10 to 40 wt. %.
This was attributed to the presence of more hydrophilic KBF in the composites. On
the contrary, the Mm for the composites with purified compatibilisers at
concentrations of MA 3 - 7 phr were lower than that of uncompatibilised composite.
This may be due to the formation of a good fibre-matrix interfacial adhesion with the
presence of purified compatibiliser. The deteriorating impact of water on the
composites was proven by reduction in the flexural properties and degradation of the
composites' structure after exposed to 90 days water immersion. Exposure of both
uncompatibilised and compatibilised composites to natural weathering for a period of
6 months resulted in a decrease of the flexural properties due to severe photo- and
thermal-oxidation degradation during the exposure. However, the reduction in
flexural properties upon natural weathering observed for the composites with
purified compatibilisers was higher than the uncompatibilised composites due to the
higher content of chemical groups of the former, which were more susceptible to
undergo oxidation during weathering. The degradation of specimens upon
weathering was also proven by FTIR analysis, SEM examination and colour change
analysis.