treatment of fibres, and the effect of environmental conditions (Sticklen, Kamel, Hawley, & Adegbite,
1992).
The reinforcement of the matrix is also an important aspect in composites. Textile fibres from various
sources have gained a great deal of usage as reinforcement and this has led to the exploration of new plants
that can produce fibres for composites. Calotropis
is a perennial shrub found chiefly in China, India,
Malaysia, as well as in most of Asia and large parts
of Africa and South America (Yuanhui et al., 2018).
The genus Calotropis (Asclepiadaceae) comprises two
species: C. gigantea and C. procera, The plant grows
mainly in arid regions such as Tharaka Nithi, Baringo,
Makueni, Turkana and Kajiado counties in Kenya
(Muriira, Muchugi, Yu, Xu, & Liu, 2018; Yuanhui et
al., 2018). Two kinds of fibres can be obtained from the
Calotropis plant: fruit and stem/bark (Ramasamy, Obi
Reddy, & Varada Rajulu, 2018) and they can be used
for various purposes (Chen et al. 2013; Zheng et al.
2016). The feasibility study done by Ramasamy et al.
(2018) reported that both its fruit and bast fibres have
potential as reinforcement in composites. Hydroxyl
groups, hemicellulose, pectin, waxes and lignin affect
the composite strength matrix adhesion and thermal
stability of fibres during hot pressing processes.
There are various methods used in the manufacture
of composites and different researchers have investigated and used them for developing a number of
composite materials.A compression moulding method
has been found to be the better option to obtain a composite based on natural fibres in terms of mechanical
properties (Satyanarayana,Arizaga, & Wypych, 2009).
This method also uses small amounts of energy, so
the green concept is reinforced. Nevertheless, the process needs to be optimised to address issues such as
delamination and production of composites with high
fibre plies (Rubio-López, Olmedo, Díaz-Álvarez, &
Santiuste, 2015). Also, the presence of low thermally
stable fibre components such as waxes, hemicellulose
and pectin can induce thermal degradation of the fibre
at higher loadings (Elsabbagh, Steuernagel, & Ring,
2017; Santos, Mauler, & Nachtigall, 2009). Alkaline
and microwave treatment are some of the chemical
treatments of natural fibres to enhance their workability. Both alkaline treatment and microwave irradiation
treatment have a potential to modify fibre surface
through disruption of hydrogen bonding in the network structure, thereby increasing surface roughness
(Imoisili, Tonye, Victor, & Elvis, 2018). They also
remove some of the lignin, wax and oils covering the
fibre cell wall external surface, depolymerizing cellulose and exposing the short length crystallites. This can
help in reducing fibre damage by heat during hot processing by increasing the thermal stability of the fibres
and improve fibre–matrix adhesion (Mohanty, Misra,
& Hinrichsen, 2000). The thermal degradation of natural fibres is an important concern for the processing
of Natural Fibre Reinforced Composites (Gassan &
Bledzki, 2001) and therefore the treatment of fibres
has the potential to improve the thermal properties
of fibres (Kalia, Thakur, Celli, Kiechel, & Schauer,
2013). The influence of heating temperature, from
175 to 200
◦ C, was analysed through comparison tests
(Ochi, 2008). The specimens were manufactured from
10361D PLA matrix reinforced with basket weave flax
woven plies, and the applied pressure was 32 MPa.
Heating temperatures over 200
◦ C produced fibre damage due to overheating. On the other hand, the matrix
was not completely melted for heating temperatures
below 175
◦ C for short processing times. Thus, the
temperature must be high enough for matrix melting, but not so high as to cause fibres damage. In this
research, temperature of 200
◦ C was used for the fabrication of PLA sheets, the pressure was kept constant.
Ochi (Ochi, 2008) also found that natural fibres can be
degraded at temperatures higher than 180
◦ C, but if this
temperature is applied for a short time period, fibres
do not get damaged. In Rubio-López, et. Al., (2015)
work, preheating time was set to 2 minutes and heating
under pressure time to 3 minutes to compress the PLA
sheets and fibres to form a composite structure.” A
temperature of 200
◦ C was used and was kept constant
to ensure PLA melting, its homogenous distribution
in the laminate, and there was a slow application of
pressure to avoid fibre misalignment.
In this study, Calotropis procera bast fibres were
extracted manually and treated using two methods:
alkaline solution and microwave irradiation in order
to examine the applicability and sustainability of
these two methods. Microwave irradiation was used
because it affects the material thermally whereby
microwaves heat the material by interacting with the
molecules of material via the electromagnetic field
produced by microwave energy. It also affects the
material non-thermally, whereby it interacts with the
polar molecules and ions in the materials, causing
physical, chemical, and biological reactions (Thostenson & Chou, 1999). Through this treatment, the
properties of the fibres and fibre–matrix adhesion
could be improved. Biocomposite materials were also
fabricated using POLYLACTIC acid as matrix and
Calotropis procera bast fibres as reinforcement. The
heating temperature was stated at 185
◦ C to manufacture 4032D PLAbased biocomposite reinforced with
Calotropis procera bast fibres. According to Ochi
(Ochi, 2008), a pressure range between 8 and 32 MPa
can be used to produce biocomposites. Tensile strength
increases with manufacturing pressure until 8 MPa,
then there is a plateau until a manufacturing pressure
of 32 MPa, at which tensile strength decreases with
pressure causing fibre breakage, while pressure under
8 MPa means a lack of cohesion in the biocomposite.
This research focuses on the exploitation of natural
abundant resources for the benefit of humanity and
environment. The specific objectives of the current
work are as follows:
i. To extract and characterize Calotropis procera
bast fibres.
ii. To treat Calotropis procera bast fibres with alkali
solution and microwaves to modify the surface.
112
1992).
The reinforcement of the matrix is also an important aspect in composites. Textile fibres from various
sources have gained a great deal of usage as reinforcement and this has led to the exploration of new plants
that can produce fibres for composites. Calotropis
is a perennial shrub found chiefly in China, India,
Malaysia, as well as in most of Asia and large parts
of Africa and South America (Yuanhui et al., 2018).
The genus Calotropis (Asclepiadaceae) comprises two
species: C. gigantea and C. procera, The plant grows
mainly in arid regions such as Tharaka Nithi, Baringo,
Makueni, Turkana and Kajiado counties in Kenya
(Muriira, Muchugi, Yu, Xu, & Liu, 2018; Yuanhui et
al., 2018). Two kinds of fibres can be obtained from the
Calotropis plant: fruit and stem/bark (Ramasamy, Obi
Reddy, & Varada Rajulu, 2018) and they can be used
for various purposes (Chen et al. 2013; Zheng et al.
2016). The feasibility study done by Ramasamy et al.
(2018) reported that both its fruit and bast fibres have
potential as reinforcement in composites. Hydroxyl
groups, hemicellulose, pectin, waxes and lignin affect
the composite strength matrix adhesion and thermal
stability of fibres during hot pressing processes.
There are various methods used in the manufacture
of composites and different researchers have investigated and used them for developing a number of
composite materials.A compression moulding method
has been found to be the better option to obtain a composite based on natural fibres in terms of mechanical
properties (Satyanarayana,Arizaga, & Wypych, 2009).
This method also uses small amounts of energy, so
the green concept is reinforced. Nevertheless, the process needs to be optimised to address issues such as
delamination and production of composites with high
fibre plies (Rubio-López, Olmedo, Díaz-Álvarez, &
Santiuste, 2015). Also, the presence of low thermally
stable fibre components such as waxes, hemicellulose
and pectin can induce thermal degradation of the fibre
at higher loadings (Elsabbagh, Steuernagel, & Ring,
2017; Santos, Mauler, & Nachtigall, 2009). Alkaline
and microwave treatment are some of the chemical
treatments of natural fibres to enhance their workability. Both alkaline treatment and microwave irradiation
treatment have a potential to modify fibre surface
through disruption of hydrogen bonding in the network structure, thereby increasing surface roughness
(Imoisili, Tonye, Victor, & Elvis, 2018). They also
remove some of the lignin, wax and oils covering the
fibre cell wall external surface, depolymerizing cellulose and exposing the short length crystallites. This can
help in reducing fibre damage by heat during hot processing by increasing the thermal stability of the fibres
and improve fibre–matrix adhesion (Mohanty, Misra,
& Hinrichsen, 2000). The thermal degradation of natural fibres is an important concern for the processing
of Natural Fibre Reinforced Composites (Gassan &
Bledzki, 2001) and therefore the treatment of fibres
has the potential to improve the thermal properties
of fibres (Kalia, Thakur, Celli, Kiechel, & Schauer,
2013). The influence of heating temperature, from
175 to 200
◦ C, was analysed through comparison tests
(Ochi, 2008). The specimens were manufactured from
10361D PLA matrix reinforced with basket weave flax
woven plies, and the applied pressure was 32 MPa.
Heating temperatures over 200
◦ C produced fibre damage due to overheating. On the other hand, the matrix
was not completely melted for heating temperatures
below 175
◦ C for short processing times. Thus, the
temperature must be high enough for matrix melting, but not so high as to cause fibres damage. In this
research, temperature of 200
◦ C was used for the fabrication of PLA sheets, the pressure was kept constant.
Ochi (Ochi, 2008) also found that natural fibres can be
degraded at temperatures higher than 180
◦ C, but if this
temperature is applied for a short time period, fibres
do not get damaged. In Rubio-López, et. Al., (2015)
work, preheating time was set to 2 minutes and heating
under pressure time to 3 minutes to compress the PLA
sheets and fibres to form a composite structure.” A
temperature of 200
◦ C was used and was kept constant
to ensure PLA melting, its homogenous distribution
in the laminate, and there was a slow application of
pressure to avoid fibre misalignment.
In this study, Calotropis procera bast fibres were
extracted manually and treated using two methods:
alkaline solution and microwave irradiation in order
to examine the applicability and sustainability of
these two methods. Microwave irradiation was used
because it affects the material thermally whereby
microwaves heat the material by interacting with the
molecules of material via the electromagnetic field
produced by microwave energy. It also affects the
material non-thermally, whereby it interacts with the
polar molecules and ions in the materials, causing
physical, chemical, and biological reactions (Thostenson & Chou, 1999). Through this treatment, the
properties of the fibres and fibre–matrix adhesion
could be improved. Biocomposite materials were also
fabricated using POLYLACTIC acid as matrix and
Calotropis procera bast fibres as reinforcement. The
heating temperature was stated at 185
◦ C to manufacture 4032D PLAbased biocomposite reinforced with
Calotropis procera bast fibres. According to Ochi
(Ochi, 2008), a pressure range between 8 and 32 MPa
can be used to produce biocomposites. Tensile strength
increases with manufacturing pressure until 8 MPa,
then there is a plateau until a manufacturing pressure
of 32 MPa, at which tensile strength decreases with
pressure causing fibre breakage, while pressure under
8 MPa means a lack of cohesion in the biocomposite.
This research focuses on the exploitation of natural
abundant resources for the benefit of humanity and
environment. The specific objectives of the current
work are as follows:
i. To extract and characterize Calotropis procera
bast fibres.
ii. To treat Calotropis procera bast fibres with alkali
solution and microwaves to modify the surface.
112