5 DISCUSSION OF RESULTS
The effect of varying the percentage of sisal/cattail
fibres in the polyester hybrid composites at a constant hybrid fibre weight fraction of 15 wt.% on the
thermal conductivity of the composites is given in
Table 1. Thermal conductivity of the hybrid composites increased with increase in the percentage of sisal
fibres in the hybrid from 0 to 100%. This behaviour
could be due to the fact that as sisal fibre content
in the hybrid increased (0 to 100%) and the cattail
fibre decreased (100 to 0%). The former increased
thermal conductivity as they have a relatively better
thermal conductivity compared to cattail fibres with
good insulation properties (Colbers et al. 2017). A
low mean thermal conductivity of 0.309 ± 0.09 W/mK
was reported at 0/100 sisal/cattail fibre blend while
the highest mean thermal conductivity of the composites (0.666 ± 0.046 W/mK) was reported at 100/0
sisal/cattail fibre blend. Statistical analysis indicated
that there was a significant difference (p = 0.023) in
the mean thermal conductivities of the hybrid composites. The results of the study were similar to
previous reports. Alsina et al. (2005) reported thermal conductivities between 0.19 and 0.237 W/mK and
0.19 and 0.22 W/mK for jute/cotton hybrid polyester
and ramie/cotton hybrid polyester composites, respectively. Further, Ramanaiah et al. (2011) concluded that
the thermal conductivity of cattail-reinforced polyester
composites were 0.32–0.385 W/mK at a fibre volume fraction of 0.15–0.32. A comparable thermal
conductivity value of 0.163 W/mK at 85% clay was
reported by Dieye, Sambou, Faye, Thiam, and Adj et
al. (2017) while investigating the effect of the binder
(clay) weight on the thermal conductivity of cattail
fibre-reinforced composites.
The effects of varying the hybrid fibre weight fraction while the percentage of sisal/cattail fibres in the
hybrid was kept at 50/50 is illustrated in Figure 2.
Thermal conductivity of the composites decreased
as the hybrid fibre loading increased from 5 to 25
wt.% with a minimum mean thermal conductivity
of 0.5024 ± 0.04 W/mK. The thermal conductivity
of the hybrid composites dropped by 2.93%, 23.4%,
4.31%, and 20.39% for 5–10, 10–15, 15–20, and
20–25 wt.% hybrid fibre loadings, respectively. Significant differences (p = 0.001) between the means of
various composites at different hybrid fibre weight
loadings were recorded. This could be due to the presence of cattail fibres in the hybrid as well as their
increment in the composite as hybrid fibre weight
fraction was increased from 5 to 25 wt.%. Cattail
fibres generally have lower thermal conductivity due
to the presence of aerenchyma tissues (Figure 3) (Colbers et al. 2017). Similar trends have been reported
by previous studies. Ramanaiah et al. (2013), studying the effect of fibre weight fraction on thermal
conductivity of fish tail palm tree fibre-reinforced
polyester composites, reported a decrease in thermal
conductivity with increase in fibre content from 0.1 to
0.4. Similarly, Ramanaiah et al. (2011) inferred that
thermal conductivity of Typha angustifolia-reinforced
composites decreased with increase in fibre loading.
Thermal insulation properties reported in this paper (at
25 wt.%) were found to be better than those reported
by Colbers et al. (2017) for cattail fibres.
The effect of composite density on thermal conductivity of sisal/cattail polyester hybrid composites
at 50/50 sisal/cattail fibre content in the hybrid are
shown in Figure 4. Thermal conductivity was directly
proportional to the hybrid composite density where
at high composite density, high thermal conductivity values were reported. This may be due to the
fact that, as the density of the hybrid composite
decreases, available voids between the fibres in the
composite increases. It is these air-filled voids that
result in lower thermal conductivity of the hybrid
composites (Luamkanchanaphan, Chotikaprakhan, &
Jarusombati 2012). The same behaviour was reported
by Sair et al. (2018) investigating the effect of
density on thermal behaviour of hemp/polyurethane
composites.
6 CONCLUSION
At constant fibre blend ratio of 1:1 and 15 wt.% hybrid
fibre weight fraction, composite density was reported
to be directly proportional to its thermal conductivity and an optimal thermal insulation property was
reported at a fibre weight fraction of 25 wt.%. Further,
low thermal conductivity was reported as the ratio of
cattail fibres increased from 0–100% in the hybrid at
a constant hybrid fibre weight fraction of 15wt%. The
composites produced, can be used in non-structural
applications such as ceiling board and electronic and
food packaging among many other applications where
heat conservation is required.
Further studies on the physical properties for the
resultant composite, i.e., water absorption, flammability, and biodegradability tests should be done. Additionally, further research should be done to examine
the effect of using a woven blend of sisal/cattail fibres
on thermal conductivity properties of the resultant
composite.
REFERENCES
Alsina, O. L. S., De Carvalho, L. H., Filho, F. G. R.,
& Almeida, J. R. M. (2005). Thermal properties of
hybrid lignocellulosic fabric-reinforced polyester matrix
composites Polymer Testing, 24, 81–85.
Bongomin, O., Ocen, G. G., Nganyi, E. O., Musinguzi, A.,
& Omara, T. (2020). Exponential Disruptive Technologies and the Required Skills of Industry 4.0. Journal of
Engineering, 2020, 1–17.
Colbers, B., Cornelis, S., Geraets, E., Gutiérrez-Valdés, N.,
Tran, L. M., Moreno-Giménez, E., & Ramírez-Gaona, M.
(2017). A feasibility study on the usage of cattail (Typha
spp.) for the production of insulation materials and bioadhesives Wageningen University and Research Centre,
1–71.
123
The effect of varying the percentage of sisal/cattail
fibres in the polyester hybrid composites at a constant hybrid fibre weight fraction of 15 wt.% on the
thermal conductivity of the composites is given in
Table 1. Thermal conductivity of the hybrid composites increased with increase in the percentage of sisal
fibres in the hybrid from 0 to 100%. This behaviour
could be due to the fact that as sisal fibre content
in the hybrid increased (0 to 100%) and the cattail
fibre decreased (100 to 0%). The former increased
thermal conductivity as they have a relatively better
thermal conductivity compared to cattail fibres with
good insulation properties (Colbers et al. 2017). A
low mean thermal conductivity of 0.309 ± 0.09 W/mK
was reported at 0/100 sisal/cattail fibre blend while
the highest mean thermal conductivity of the composites (0.666 ± 0.046 W/mK) was reported at 100/0
sisal/cattail fibre blend. Statistical analysis indicated
that there was a significant difference (p = 0.023) in
the mean thermal conductivities of the hybrid composites. The results of the study were similar to
previous reports. Alsina et al. (2005) reported thermal conductivities between 0.19 and 0.237 W/mK and
0.19 and 0.22 W/mK for jute/cotton hybrid polyester
and ramie/cotton hybrid polyester composites, respectively. Further, Ramanaiah et al. (2011) concluded that
the thermal conductivity of cattail-reinforced polyester
composites were 0.32–0.385 W/mK at a fibre volume fraction of 0.15–0.32. A comparable thermal
conductivity value of 0.163 W/mK at 85% clay was
reported by Dieye, Sambou, Faye, Thiam, and Adj et
al. (2017) while investigating the effect of the binder
(clay) weight on the thermal conductivity of cattail
fibre-reinforced composites.
The effects of varying the hybrid fibre weight fraction while the percentage of sisal/cattail fibres in the
hybrid was kept at 50/50 is illustrated in Figure 2.
Thermal conductivity of the composites decreased
as the hybrid fibre loading increased from 5 to 25
wt.% with a minimum mean thermal conductivity
of 0.5024 ± 0.04 W/mK. The thermal conductivity
of the hybrid composites dropped by 2.93%, 23.4%,
4.31%, and 20.39% for 5–10, 10–15, 15–20, and
20–25 wt.% hybrid fibre loadings, respectively. Significant differences (p = 0.001) between the means of
various composites at different hybrid fibre weight
loadings were recorded. This could be due to the presence of cattail fibres in the hybrid as well as their
increment in the composite as hybrid fibre weight
fraction was increased from 5 to 25 wt.%. Cattail
fibres generally have lower thermal conductivity due
to the presence of aerenchyma tissues (Figure 3) (Colbers et al. 2017). Similar trends have been reported
by previous studies. Ramanaiah et al. (2013), studying the effect of fibre weight fraction on thermal
conductivity of fish tail palm tree fibre-reinforced
polyester composites, reported a decrease in thermal
conductivity with increase in fibre content from 0.1 to
0.4. Similarly, Ramanaiah et al. (2011) inferred that
thermal conductivity of Typha angustifolia-reinforced
composites decreased with increase in fibre loading.
Thermal insulation properties reported in this paper (at
25 wt.%) were found to be better than those reported
by Colbers et al. (2017) for cattail fibres.
The effect of composite density on thermal conductivity of sisal/cattail polyester hybrid composites
at 50/50 sisal/cattail fibre content in the hybrid are
shown in Figure 4. Thermal conductivity was directly
proportional to the hybrid composite density where
at high composite density, high thermal conductivity values were reported. This may be due to the
fact that, as the density of the hybrid composite
decreases, available voids between the fibres in the
composite increases. It is these air-filled voids that
result in lower thermal conductivity of the hybrid
composites (Luamkanchanaphan, Chotikaprakhan, &
Jarusombati 2012). The same behaviour was reported
by Sair et al. (2018) investigating the effect of
density on thermal behaviour of hemp/polyurethane
composites.
6 CONCLUSION
At constant fibre blend ratio of 1:1 and 15 wt.% hybrid
fibre weight fraction, composite density was reported
to be directly proportional to its thermal conductivity and an optimal thermal insulation property was
reported at a fibre weight fraction of 25 wt.%. Further,
low thermal conductivity was reported as the ratio of
cattail fibres increased from 0–100% in the hybrid at
a constant hybrid fibre weight fraction of 15wt%. The
composites produced, can be used in non-structural
applications such as ceiling board and electronic and
food packaging among many other applications where
heat conservation is required.
Further studies on the physical properties for the
resultant composite, i.e., water absorption, flammability, and biodegradability tests should be done. Additionally, further research should be done to examine
the effect of using a woven blend of sisal/cattail fibres
on thermal conductivity properties of the resultant
composite.
REFERENCES
Alsina, O. L. S., De Carvalho, L. H., Filho, F. G. R.,
& Almeida, J. R. M. (2005). Thermal properties of
hybrid lignocellulosic fabric-reinforced polyester matrix
composites Polymer Testing, 24, 81–85.
Bongomin, O., Ocen, G. G., Nganyi, E. O., Musinguzi, A.,
& Omara, T. (2020). Exponential Disruptive Technologies and the Required Skills of Industry 4.0. Journal of
Engineering, 2020, 1–17.
Colbers, B., Cornelis, S., Geraets, E., Gutiérrez-Valdés, N.,
Tran, L. M., Moreno-Giménez, E., & Ramírez-Gaona, M.
(2017). A feasibility study on the usage of cattail (Typha
spp.) for the production of insulation materials and bioadhesives Wageningen University and Research Centre,
1–71.
123