Innovated Banana Fiber Nonwoven Reinforced Polymer Composites: Effects of Pre- and Post-treatments on Physical and Mechanical Properties

Abstract

Four types of nonwovens were prepared from different sections of the banana tree e.g., outer bark (OB), middle bark (MB), inner bark (IB) and midrib of leaf (MR) by wet laid web formation. They were reinforced on two different types of matrices e.g., epoxy (E) and polyester (P) to make eight variants of composites. Different concentration (5–15%) of NaOH and water repellent (WR); and different doses (100-500krd) of gamma radiation were applied in different stages of process. The properties like water absorbency, tensile strength (TS), flexural strength (FS) and elongation at break (Eb%) were investigated. OB composites were exhibited higher water absorbency, TS and FS but lower Eb% than other types of composites. Epoxy composites were found to have 16% lower water absorbency, 41.2% higher TS and 39.1% higher FS than polyester composites on an average. Alkali treatment reduced the water absorbency by 32%; improved the TS by 71%; improved the FS by 87% on an average at 15% NaOH. Water repellent treatment (on alkali treated composites) decreased the absorbency by 63% at 10% WR but increased 6.3% at 15% WR. Gamma radiation improved the TS of 30% and FS of 35% on an average at a dose of 100krd for IB and 200krd for other composites. Further increment of dose reduced both the FS and TS.

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Innovated Banana Fiber Nonwoven Reinforced
Polymer Composites: Effects of Pre- and Post-
treatments on Physical and Mechanical Properties
K.Z.M. Abdul Motaleb (  k.motaleb1@ktu.edu )
Kauno Technologijos Universitetas https://orcid.org/0000-0003-2908-9638
Abdul Ahad
BGMEA University of Fashion and Technology
Ginta Laureckiene
Kaunas University of Technology: Kauno Technologijos Universitetas
Rimvydas Milasius
Kaunas University of Technology: Kauno Technologijos Universitetas
Research Article
Keywords: Banana nonwoven, epoxy, polyester, eco-friendly composites, alkali treatment, water repellent
treatment, gamma radiation
DOI: https://doi.org/10.21203/rs.3.rs-755923/v1
License:   This work is licensed under a Creative Commons Attribution 4.0 International License. 
Read Full License

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Abstract
Four types of nonwovens were prepared from different sections of the banana tree e.g., outer bark (OB),
middle bark (MB), inner bark (IB) and midrib of leaf (MR) by wet laid web formation. They were reinforced
on two different types of matrices e.g., epoxy (E) and polyester (P) to make eight variants of composites.
Different concentration (5–15%) of NaOH and water repellent (WR); and different doses (100-500krd) of
gamma radiation were applied in different stages of process. The properties like water absorbency,
tensile strength (TS), exural strength (FS) and elongation at break (Eb%) were investigated. OB
composites were exhibited higher water absorbency, TS and FS but lower Eb% than other types of
composites. Epoxy composites were found to have 16% lower water absorbency, 41.2% higher TS and
39.1% higher FS than polyester composites on an average. Alkali treatment reduced the water absorbency
by 32%; improved the TS by 71%; improved the FS by 87% on an average at 15% NaOH. Water repellent
treatment (on alkali treated composites) decreased the absorbency by 63% at 10% WR but increased 6.3%
at 15% WR. Gamma radiation improved the TS of 30% and FS of 35% on an average at a dose of 100krd
for IB and 200krd for other composites. Further increment of dose reduced both the FS and TS.
1. Introduction
From the last century, traditional materials like wood, metal, ceramic, glass are being rapidly replaced by
the polymer matrix composite (PMC) materials with the reinforcement of synthetic bers due to a lot of
advantages like light weight, easy processing, low cost, and high productivity. However, this rapid
increase of non-biodegradable PMC also created a lot of dangerous and alarming problems like
environmental pollution from plastics, burning of fossil fuels, increasing global warming potential, etc.
Consequently, these problems are creating a harmful and unsafe environment for humans, animals, and
marine lives (Malviya et al. 2019). For these reasons, researchers are paying attention to alternative eco-
sustainable materials now-a-days. Natural ber reinforcement can be a potential alternative in polymer
composite due to their numerous advantages including biodegradability, low relative density, economical,
ease of handling, availability, light weight, high impact resistance, high exibility, low specic gravity,
recyclability, low carbon emission, good thermal and acoustic insulation and so on (Wu et al. 2018; Keya
et al. 2019; Nayak et al. 2020; Kerni et al. 2020; Santhanam et al. 2020). Natural ber reinforced
composites (NFRCs) are becoming more attractive in many areas of engineering applications with a wide
range of properties (Lot et al. 2021). Natural bers those are used as a reinforcement in NFRCs can be
obtained from plants, animals, and minerals. However, over the years, most of the natural bers
investigated as a reinforcement have been from agricultural plant, byproducts, or wastes.
There are numerous sources of plant bers all over the world especially in tropical regions. They can be
categorized by the parts of the plant from where they are extracted like leaf bers (pineapple, sisal,
abaca), bast bers (jute, banana, ax, hemp) and seed bers (cotton, coir, kapok) (Zwawi 2021). Most of
the plant bers are mainly consists of cellulose, hemicellulose, and lignin (Santhanam et al. 2020).
Banana ber is one of the cellulosic bers extracted from the stem of banana tree
(Musa acuminata).
The stem is usually known as pseudo stem is cylindrical in shape and contains plenty of long bers.

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Banana ber contains 71.08% of cellulose, 12.61% of hemicellulose and 7.67% of lignin in their chemical
composition with a diameter of 138 µm and density of 1.28 g/cm3 (Kenned et al. 2020a). In a tropical
country like Bangladesh, banana plants are considered as agricultural crops, growing abundantly due to
favorable climate conditions. After harvesting fruits, banana plants are cut at their lower section and the
whole cutting portions are considered as a complete waste including pseudo stem and leaf those can be
utilized as a source of natural bers for the manufacturing of NFRCs, textiles, nonwoven, packaging
materials, wiping materials and so on (Adeniyi et al. 2019). Therefore, the bers can be used in the
industry without any additional expenses for the cultivation (Balaji et al. 2020). Moreover, banana bers
exhibit good mechanical properties competently with other cellulosic bers that makes them a potential
reinforcing material for varieties of engineering applications (Gholampour and Ozbakkaloglu 2020;
Komal et al. 2020; Srinivasan et al. 2020; Lot et al. 2021).
However, the performance of the NFRCs depends on ber orientation, ber content, length, shape and
their interfacial bonding with the matrix (Al-Oqla and Salit 2017). Fiber orientations are also varied with
different forms of reinforcement like chopped ber reinforcement, continuous ber (lament)
reinforcement, woven fabric reinforcement and nonwoven reinforcement. Woven fabrics are generally
produced by interlacing the yarns usually at the right angles by following a regular pattern. The strength
of woven fabrics can be increased by increasing the twist angle of the yarns up to a certain limit.
However, this twist angle plays an opposite role in case of composites. Increase of twist angle decreases
the permeability of matrix to the ber which results poor ber-matrix adhesion and low mechanical
properties (Peças et al. 2018). In case of lament reinforcement, mechanical properties are much lower in
transverse direction of bers that is also a limitation for different applications. To avoid these problems,
nonwoven reinforcement can be a great option. Nonwovens are prepared in a at structure with different
thickness without interloping or interlacing. Fibers are chopped, uniformly distributed, and bonded
together by chemical, mechanical or thermal treatment. They don’t have preferential strength direction
and can produce in large scale due to availability and low cost (Al-Oqla and Sapuan 2014).
Thermosetting resins are most widely used in the composite industry as a polymer matrix. Among them,
epoxy and polyester resin are most applied matrix in the composites. Epoxy resin, also known as poly
epoxides, have good adhesion properties with natural bers. Other key features are low moisture
absorption, high chemical resistance, low shrinkage, and simple processing. These excellent properties
make them superior in market with wide range of applications (Oliveira et al. 2019). However, unsaturated
polyester resin, also known as polyhydric alcohols, have satisfactory mechanical properties and enough
adhesion properties with the natural bers which are reported in several studies. The main advantage of
polyester resin is, they are cheaper, available and can be used in wide ranges of applications (Sreekumar
and Thomas 2008).
There is no doubt that, natural ber brings a lot of potentiality for their unique properties and
environmental friendliness, but they have some drawbacks like high moisture absorption, low
compatibility with the commercial resins, poor adhesion between ber and matrix, less homogenous like
laments, low resistance to re (Gholampour and Ozbakkaloglu 2020). However, these challenges can be

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overcome by different types of physical and chemical treatments. Chemical treatments of the bers
including alkaline, saline, acetylation, benzoylation and many more can improve the adhesion between
ber and matrix (Faruk et al. 2014). Alkali treatment is one of the simplest and cheapest method which is
easily applicable to natural bers by immersing them into the solution of NaOH. After the alkali treatment,
bers become more uniform by removing all the impurities. Therefore, physical and mechanical
properties of the composites are improved consequently (Gholampour and Ozbakkaloglu 2020). Several
studies have been reported the improvement of physical and mechanical properties of the composites by
alkali treatment of natural bers (Yan et al. 2012; Mohd Nazarudin et al. 2013; Manalo et al. 2015; Preet
Singh et al. 2017; Wijianto et al. 2019; Binti Mohd Hadz et al. 2021). To overcome the high-water
absorbency problem of NFRCs, surface treatment of natural bers with water repellent is a potential way.
The water repellent makes a coating on the ber surface and resist the water to penetrate inside. There is
no relevant study yet regarding the water repellent treatment on natural bers to improve the
hydrophobicity of NFRCs.
Physical treatments like x-ray, ultraviolet (UV) ray, gamma ray, plasma, corona are applied to the
composites to improve the ber-matrix adhesion. Due to less time consumptions, high productivity, low
environmental pollution, structural availability and easy application, gamma radiation becomes popular
day by day (Noura et al. 2018). Gamma radiation is a powerful ionizing radiation which can penetrate
inside the polymeric structure of the composites and produce reactive sites to make more oriented
polymeric structures and improve the mechanical properties of the composites (Masudur Rahman et al.
2018). Many researchers have been applied this radiation and reported the improvement of mechanical
properties of the composites (Khan et al. 2009; Haydaruzzaman et al. 2009; Masudur Rahman et al. 2018;
Martínez-Barrera et al. 2020). However, the studies also reported that, gamma radiation improves the
mechanical properties up to a certain level of gamma radiation dose after that it alters the properties.
Therefore, an optimum dose must be maintained.
Numerous studies have been noted regarding the properties of banana ber reinforced composite
materials. Majority of them used banana ber or pseudo stem mat as a reinforcing material (Jordan and
Chester 2017; Mohan and Kanny 2019; Balaji et al. 2020; Komal et al. 2020; Srinivasan et al. 2020). Only
a few of them studied about banana nonwoven reinforced composite materials. Kenned J et al. studied
thermo-mechanical and morphological characterization of needle punched nonwoven banana ber
reinforced polymer composites (Kenned et al. 2020b). The properties of needle punched nonwoven from
banana ber was also studied by Sengupta et al (Sengupta et al. 2020). Thilagavathi et. al. developed
needle punched banana nonwovens for the application of noise control car interiors (Thilagavathi et al.
2010). But no research has been reported the development of banana ber nonwoven by wet laid web
formation technique from various parts of banana tree and the properties of their reinforced composites.
Moreover, no study has been found regarding the surface modication of such nonwovens and their
composites.
The aim of this study is to develop an ecofriendly composite material from a natural source to replace the
existing environmentally destructing, carcinogenic, synthetic composites materials those are being used

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vastly in different areas like packaging, households, building materials, automobiles, technical textiles
and so on. To full the objectives, four types of banana ber nonwovens were developed from different
parts of the banana tree e.g., outer bark, middle bark, inner bark of banana stem and mid rib of banana
leaf in our previous study (Motaleb et al. 2020). This study is the continuation of the last work.
Nonwovens were prepared by following the previously developed wet laid web formation technique from
the extracted bers. The prepared four types of nonwovens were reinforced on two different types of
matrices e.g., epoxy resin and polyester resin to make eight variants of composites. Surface treatments
were applied in three stages, i) ber stage – alkali (NaOH) treatment, to improve the mechanical
properties and hydrophobicity, ii) nonwoven stage - water repellent treatment, to improve the
hydrophobicity and, iii) composites stage – gamma radiation, treatment to improve the mechanical
properties. Water absorbency of the composite samples and the improvement of hydrophobicity by the
surface modication were inspected. Mechanical properties like tensile and exural strength and the
inuence of physical and chemical treatment on those properties were also analyzed in this study. A
comparative study between the composites of epoxy matrix and polyester matrix are elaborated in
different aspects throughout the study.
2. Materials And Methods
2.1 Materials
Banana trees were collected from a banana plantation as a waste material (after harvesting banana fruit)
in Gazipur, Bangladesh. Epoxy resin, hardener HY-951, polyester resin and methylethylketone peroxide
(MEKP) were bought from a European chemical supplier. Caustic soda and water repellent (peruoroalkyl
acrylic) were purchased from Archroma International Ltd.
2.2 Methods
2.2.1 Banana Fiber Extraction
Banana trees were segregated into four different sections such as 1) outer layers of banana bark
designated as outer bark (OB), 2) middle layers of banana bark designated as middle bark (MB), 3) inner
layers of banana bark designated as inner bark (IB) and 4) middle rib of banana leaves designated as
midrib (MR). All the sections are mentioned in Fig. 1. The raw materials of each section were then pressed
by a metal tube squeezer for removing the inside water as much as possible. After that, they were dried in
sunlight for about 15 days.
The dried materials were scratched by a metal comber to make like ribbon and cut them with a length of
3 cm. For the initial ber extraction, these small pieces were taken in a big metal pot and treated with 5
(w/v) % of NaOH with a temperature of 90ºC for about 30 minutes until they became soft. They were
rinsed properly for removing unwanted materials and dried subsequently. Thus, the raw banana bers
from different parts of the banana trees were extracted.

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2.2.2 Alkali Treatment on Fibers
The extracted raw bers were still contained various impurities like fat, wax, pectens and so on. To clean
off these impurities, the bers were immersed into a solution of NaOH at different concentrations i.e., 5,
10 and 15 (w/v) % for 24 hours at a temperature of 23 ± 2ºC. The bers were rinsed and dried again after
the treatment.
2.2.3 Nonwoven Formation
Firstly, the alkali treated banana bers were blended with water to make a uniform pulp mixture. Then,
they were rinsed properly to remove the leftover of NaOH and dried once again. The prepared banana
pulp was taken in the blender again with the ber (pulp)/water ratio of 1:50. After blending, the mixture
was poured in a mold prepared with wooden frame and mesh fabric. The bers were distributed
uniformly by immersing the complete mold on a tab of water to make a sheet from the ber webs
according to the wet laid web formation technique. The sheet, usually known as nonwoven, was then
moved to a plastic plate, and pressed with wiping paper to remove extra water. Finally, they were dried in
sunlight and straighten with an electrical iron in case of rough surface. Similar procedure was followed to
make all types of banana ber nonwovens. The average thickness of the nonwovens were found 0.75 ±
0.05 mm.
2.2.4 Water Repellent Treatment on Nonwovens
Before making composites by reinforcing the nonwovens, some of them were treated with a water
repellent (WR) chemical (peruoroalkyl acrylic) to improve the hydrophobicity of the composites. WR
was applied at three different concentrations i.e., 5%, 10% and 15% to nd out the appropriate dose to
decrease the water absorbency by keeping up the strength. The nonwovens were immersed into the
solution of WR and kept for couple of minutes. The wet nonwovens were then squeezed by a padding
roller to remove excess solution. They were dried and cured in an oven with a temperature of 160–170ºC
for 30 minutes.
2.2.5 Composite Formation
The composites were prepared with hand layup technique. The already prepared nonwoven from four
different section of banana tree i.e., OB, MB, IB, MR were used as reinforcing material and two types of
resin i.e., epoxy (E) and polyester (P) were used as matrix. In total, eight variants of composites were
prepared, which are designated as OB/E, MB/E, IB/E, MR/E, OB/P, MB/P, IB/P and MR/P with all possible
combination of nonwovens and resins. Two metal plates were used as top and bottom surface of the
mold with a size of 35×35 cm. The metal plates were wrapped with Teon (PTFE) paper to avoid the
sticking diculties during the composite peel off. Three layers of nonwovens were reinforced for all types
of composites. At rst, the nonwovens were cut with a size of 30×30 cm. Three pieces of nonwoven
sheets were weighted together by a precise scale. According to the weight of nonwovens, a certain
amount of resin mixture was prepared with the addition of appropriate catalyst by maintaining a

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constant ber/resin weight ratio of 30:70 for all the composites. 10% HY951was used for epoxy resin and
2% MEKP was used for polyester resin as a hardener. The bottom metal plate was placed in a suitable at
surface. To begin the fabrication of composite, ¼ of the resin mixture was poured on the bottom metal
plate and spread them uniformly with a brush according to the size of the nonwovens. Then the rst
nonwoven layer was placed on them and pressed with a hand roller in such a way that the resin
penetrated throughout the nonwoven. Again, ¼ of the resin mixture was poured on the rst nonwoven
layer and repeated the same process to reinforce second and third nonwoven layer. The rest ¼ of the resin
mixture was poured on the third nonwoven layer, the top metal plate was placed on them to make a
complete sandwich structure. A dead weight of 20kg was laid on the top metal plate and kept them 24
hours for curing. Finally, the dead weight was removed, and the composite was separated from metal
plates. Similar procedure was followed for making all the composites. The overall thickness of the
composites was found 3 ± 0.5 mm.
2.2.6 Sampling
In total eight types of composites were prepared. Samples for each treatment or test were prepared
separately according to the prescribed standards. All types of samples are described in Table 1. Some
prepared samples for the tensile tests are presented in Fig. 2.

Table 1
Description of the samples with their designation.
Types Description Designation
01 Outer bark nonwoven reinforced epoxy composites OB/E
02 Middle bark nonwoven reinforced epoxy composites MB/E
03 Inner bark nonwoven reinforced epoxy composites IB/E
04 Midrib nonwoven reinforced epoxy composites MR/E
05 Outer bark nonwoven reinforced polyester composites OB/P
06 Middle bark nonwoven reinforced polyester composites MB/P
07 Inner bark nonwoven reinforced polyester composites IB/P
08 Midrib nonwoven reinforced polyester composites MR/P
2.2.7 Gamma Radiation on Composites

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The composite samples were irradiated with different doses of gamma radiation. A capsule type of
gamma irradiator Co-60 was used which has remote controlled electromechanical system with a capacity
of 65Kci. Five different doses of gamma radiation i.e., 100krd, 200krd, 300krd, 400krd and 500krd were
applied for each type of sample.
2.2.8 Water Absorbency
Samples were prepared and tested according to the standard ASTM D570-98. Before immersing into the
water, they were conditioned in an oven for 24 hours at 50°C, cooled in a desiccator, and weighted
immediately to have the dry weight of each sample. The conditioned samples were then put in a beaker
of water, maintained the temperature of 23 ± 2°C. The samples were taken out for maximum 2 minutes
for measuring weight after every hour for the rst four hours and then after every 4 hours over the 24
hours. Before measuring weight, the samples were wiped off every time to remove surface water. The
water absorbency by weight percentage was calculated by the following Eq.(1).
Where Ww is wet weight after water immersion and Wc is conditioned weight.
2.2.9 Mechanical Tests
Tensile properties like tensile strength (TS) and elongation at break percentage (Eb%) were tested
according to the standard ASTM D638-14. A universal testing machine (UTM) from the brand Zwick was
used for testing the samples at Laboratory of Materials Engineering, Kaunas University of Technology
(KTU), Kaunas, Lithuania. Samples were prepared with according to the standard size of 165mm×13mm.
A gauge length of 50mm was maintained. Load was applied at a constant rate of motion 10 mm/min of
grips. The tensile strength and elongation at break were calculated by the following equations (2) and (3)
respectively.
Where Fmaxis maximum load and A is cross-sectional area of the sample.
Where Δ lb is elongation at breaking point and l0 is initial length of the sample.

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Flexural property was tested with the same UTM according to the standard ASTM D790-03 to determine
the exural strength (FS) of the composites. Samples were prepared according to the standard and
placed on the two supports with a span length of 16 times the thickness of the samples. Load was
applied on the midspan with a constant deection speed of 0.10 mm/mm/min until breaking. The
exural strength was calculated by the Eq.(4).
Where
F
is breaking load,
L
is length of support span,
b
is width and
d
is thickness of the sample.
3. Results And Discussions
3.1 Water Absorbency
3.1.1 Effect of Alkali Treatment on Water Absorbency
Figure3 (a) demonstrates the water absorbency of different types of banana nonwoven composites after
24 hours of water immersion. The effect of alkali treatments on the water absorbency of the composites
are presented in Fig.3 (b). Among the untreated composites, MR/E showed the lowest water absorbency
of 15.14% and OB/P showed the highest absorbency of 28.63%. OB and MB composites exhibited higher
absorbency and MR composites exhibited lower absorbency for both polyester and epoxy matrix. In
comparison of epoxy and polyester composites, epoxy always showed lower absorbency than polyester
composites. For instance, OB/E, MB/E, IB/E and MR/E was found 20.7%, 9.28%, 25.43% and 9.45% lower
water absorbency than OB/P, MB/P, IB/P and MR/P respectively.
The water absorbency of the composite were varied with different types of banana bers. This may be
due to the different chemical compositions of the banana bers from different parts of the banana trees.
From the earlier studies, the chemical compositions of the banana stem bers are also varied notably
with different percentages of cellulose content such as 71.08% (Kenned et al. 2020b), 60–65%
(Alavudeen et al. 2015), 57.6% (Mostafa and Uddin 2016), 43.46 (Wijianto et al. 2019). The other
constituents like lignin and hemicellulose are also varied remarkably on these studied. This variation may
occur due to different species of banana trees as well different sections of banana trees. OB nonwovens
may contain more cellulose than other types. Thus, more hydrophilic sites of cellulose absorbed more
water. The composites with epoxy matrix showed less absorbency than polyester matrix. This may be
due to the better interfacial adhesion between ber and epoxy matrix than polyester (Oliveira et al. 2019).
Which results better covering of hydrophilic bers by the hydrophobic resins and make them more
watertight. Better adhesion also leads to remove the amorphous regions and porosity in the ber-matrix
interface thus, water absorbency reduces.

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Alkali treatment improves the hydrophobicity of the composite samples which are clearly visible in Fig.3
(b). The water absorbency of the composites were decreased signicantly with the concentration of
NaOH applied to the banana bers. For example, at lowest concentration of 5% NaOH treatment, water
absorbency was decreased by 12.5%, 12.9%, 17.7% and 17.9% for OB/E, MB/E, IB/E and MR/E
respectively. In the same way, 24.1%, 17.1%, 13.6% and 17.2% decreases were found for OB/P, MB/P, IB/P
and MR/P composites respectively. Even more inuence was found at 10% of NaOH treatment. For
instance, 27.5%, 24.8%, 23.7%, 25.6% decrease of water absorbency was found for OB/E, MB/E, IB/E,
MR/E composites and 32.7%, 35.2%, 25.0%, 23.7% for OB/P, MB/P, IB/P, MR/P composites respectively in
compared to untreated composites.
Water absorbency was continued to decrease at 15% NaOH as well. From all the 2nd order polynomial
curve, it is evident that, the inuence is lower in 15% than 10% concentration regarding the amount of
NaOH. Between Epoxy and Polyester composites, Polyester composites were inuenced more by the
NaOH than Epoxy composites. For example, at 10% of NaOH treatment, water absorbency was decreased
approximately 30% for Polyester composites and 22% for Epoxy composites in an average.
The hydrophobicity of the composites were improved with the various concentration of alkali treatments.
This is because, alkali treatment removes unwanted materials like pectin, oil, wax, lignin, hemi-cellulose,
and other impurities to a certain amount (Binti Mohd Hadz et al. 2021). That results better adhesion
between the ber and matrix. Therefore, the strong interfacial bonding makes the bers rmly protected
with the hydrophobic matrix and decreases the water absorbency (Mohd Nazarudin et al. 2013). The
application of NaOH also reduce the hydroxyl groups of cellulose (the main responsible group to absorb
water) by ionizing them into alkoxides (Li et al. 2007; Reddy et al. 2018).
Water absorbency ows described in Fig.4, shows that water absorbency rate is very fast in rst couple
of hours. It was observed that, approximately 40–50% water was absorbed in rst two hours of 24 hours
of complete observation. The rate can be considered medium during the time of 3–8 hours. Near about
80% water is absorbed after 8 hours of 24 hours. Then all the ows were become slow up to 20 hours and
very slow up to 24 hours.
3.1.1 Effect of Water Repellent Treatment on Water
Absorbency
The water absorbency of untreated (0% WR + 15% NaOH) composites after 24 hours of immersion into
water is presented in Fig.5 (a). OB/P composite showed the highest 15.55% and MR/E composite
showed the lowest 10.16% of water absorbency. OB composites exhibit higher absorbency than all other
three types of composites (MB, IB and MR) for both Epoxy and Polyester composites. Between the two
types of matrices, Epoxy composites showed signicantly lower water absorbency than Polyester
composites except for MB composites where the absorbency is close to each other. For instance, OB/E,
MB/E, IB/E and MR/E was found 13.44%, 0.43%, 21.16% and 17.03% lower water absorbency than OB/P,
MB/P, IB/P and MR/P respectively.

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For the further improvement of hydrophobicity, alkali treated nonwovens were treated again with water
repellent chemical. Figure5. (b) details the effects of WR on the water absorbency of the composites. It is
evident that, water absorbency is decreased remarkably by the WR treatment for all types of composites.
For instance, only at 5% concentration of WR treatment, water absorbency is reduced by 45.7%, 53.8%,
56.3%, 49.9% for OB/E, MB/E, IB/E, MR/E composites and 48.3%, 40.4%, 43.5%, 42.4% for OB/P, MB/P,
IB/P, MR/P composites respectively in compared to untreated composites. Water absorbency was
continued to decrease at 10% WR application. An overall 60–70% decrease of water absorbency was
found at 10% WR in compared to untreated composites. However, from the 2nd order polynomial curves,
the inuence is lower at 10% WR when compared to 5% WR.
On the other hand, water absorbency started to increase at 15% WR for all the composites. The
absorbency was increased by 7.7%, 3.5%, 0.9%, 5.0% for OB/E, MB/E, IB/E, MR/E and 7.1%, 11.6%, 6.9%,
8.0% for OB/P, MB/P, IB/P, MR/P composites respectively from the absorbency at 10% WR.
WR treatment improves the hydrophobicity of the composites dramatically to a certain level of
concentration. The WR chemical which was used in this study is peruoroalkyl acrylic. This WR create a
surface coating on the materials and consequently resist water molecules to enter inside of the material.
WR may also cross-links with the cellulose to make them harder and rougher the surface. This rougher
surface of the ber creates air trap on the surface that makes them more hydrophobic (Bae et al. 2009;
Chowdhury 2018). However, at 15% WR, the water absorbency started to increase which is due to the
thicker coating of the ber surface. That weaken the interfacial ber-matrix bonding and creates porosity
between them. Therefore, water can penetrate on those perforated structures easily.
From the absorbency ows over the soaking times presented in Fig.6, water absorbency was very fast in
rst couple of hours like the absorbency ows of alkali treated composites. About 50–60% of water was
absorbed in rst two hours and about 75–85% was in rst eight hours. After that all the ows were
become very slow. Moreover, at 24 hours, they seemed quite stable and absorbed the maximum amount
of water. The main difference between the ows after alkali treatment (Fig.2) and after WR treatment
(Fig.4) is, the curves look more stable after WR treatment than after alkali treatment at 24 hours. That
gives an assumption of further water absorbency of the composites after the period of 24 hours. The
composites after alkali treatment will have the possibility to take water over a long period of time
whereas, the composites after WR treatment will have the possibility to stop taking water in a short time
after the period of 24 hours.
3.2 Mechanical Properties
Mechanical properties like Tensile Strength (TS), Flexural Strength (FS) and Elongation at Break (Eb%)
were analyzed in this study. The effects of alkali treatment, water repellent treatment and gamma
radiation on these mechanical properties were also investigated for all the composites.
3.2.1 Effects of Alkali Treatment

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3.2.1.1 Effect of Alkali Treatment on Tensile Strength
Tensile strength of the untreated (0% NaOH) composites are illustrated in Fig.7 (a). It is shown that, OB/E
exhibits the highest TS (15.78 MPa) and IB/P exhibits the lowest TS (8.45 MPa) among all types of
composites. Study revealed that, there was an inuence of different ber types which were used for
making the nonwovens and composites subsequently. Among them, tensile strength was found with a
sequence of OB > MB > MR > IB for both epoxy and polyester matrix composites where, 15.78 MPa, 14.56
MPa, 13.78 MPa, 12.23 MPa was found for OB/E, MB/E, MR/E, IB/E and 12.25 MPa, 10.11 MPa, 9.35
MPa, 8.45 MPa was found for OB/P, MB/P, IB/P, MR/P composites respectively. Among two types of
matrices, epoxy composites demonstrated higher tensile strength than polyester composites. It is evident
that, OB/E, MB/E, IB/E and MR/E composites were found 28.8%, 44.1%, 44.7% and 47.4% higher TS than
OB/P, MB/P, IB/P and MR/P composites respectively.
There is apparent inuence of alkali treatment on the tensile strength of the composites which is
presented in Fig.7 (b). It is evident that, TS was increased with the increase of NaOH concentration. At 5%
of NaOH treatment, TS was increased by about 35% where, about 60% increase was found at 10% NaOH
and 75% increase was found at 15% NaOH treatment in an average for all types of composites. For
instance, at maximum 15% NaOH treatment, TS were increased by 71.4%, 67.1%, 74.8%, 72.9% for OB/E,
MB/E, IB/E, MR/E composites and 63.3%, 75.7%, 69.5%, 75.8% for OB/P, MB/P, IB/P, MR/P composites
respectively. The 2nd order polynomial curves prove that the impact of alkali is more in 5% and 10% than
that of 15% of NaOH concentration.
3.2.1.2 Effect of Alkali Treatment on Flexural Strength
Figure8 (a) shows the exural strengths (FS) of the untreated composites and the effect of alkali
treatment on exural strengths are shown in Fig.8 (b). Flexural strength was found in a sequence of OB >
MB > MR > IB for both epoxy and polyester matrix composites. The highest 29.47 MPa FS was found from
OB/E composite and the lowest 13.32 MPa FS was found from IB/P composite. Study revealed that,
OB/E composites exhibited 56.1% higher FS than IB/E and OB/P composites exhibited 60.1% higher FS
than IB/P composites for instance. That clearly denes the effects of ber types from different parts of
banana trees on the FS of the composites. Like TS, epoxy composites showed better FS than polyester
composites. OB/E, MB/E, IB/E and MR/E composites were found 37.5%, 42.4%, 41.7% and 34.7% higher
TS than OB/P, MB/P, IB/P and MR/P composite respectively.
The effect of alkali treatment on exural properties of the composites followed the similar trend as tensile
properties described earlier. Flexural strength was increased with increase of NaOH concentration. For
example, FS were improved by 47.3%, 63.3%, 80.8%, 64.1% for OB/E, MB/E, IB/E, MR/E composites and
72.4%, 80.8%, 85.2% 65.2% for OB/P, MB/P, IB/P, MR/P composites respectively at a concentration of 10%
NaOH than untreated composites. The improvement was even more at a concentration of 15% NaOH.
From the 2nd order polynomial curve, impact is more at 10% NaOH than 15% by considering the amount
of NaOH.

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3.2.1.3 Effect of Alkali Treatment on Elongation at Break
Elongation properties of the composites shows exactly opposite trend of TS and FS which is presented in
Fig.9 (a). The highest Eb% was found from IB/P and lowest was from OB/E. In comparison of different
nonwoven reinforcements, OB always showed lowest and IB always showed highest Eb% where MB and
MR exhibited medium Eb% for both polyester and epoxy matrix composites. The composite with
polyester matrix showed higher Eb% than epoxy matrix. Study found that, OB/P, MB/P, IB/P and MR/P
demonstrated 11.8%, 32.1%, 25.8% and 29.5% of higher Eb% than OB/E, MB/E, IB/E and MR/E
composites respectively.
The effects of NaOH on Eb% of the composites are illustrated in Fig.9 (b). Alkali treatment reduces the
Eb% to a small extent. The maximum 21.0%, 19.8%, 20.2%, 20.1% reduction of Eb% were found for OB/E,
MB/E, IB/E, MR/E composites and 19.9%, 22.5%, 18.5%, 18.1% for OB/P, MB/P, IB/P, MR/P composites
respectively at a concentration of 15% NaOH.
After analyzing the mechanical properties i.e., TS, FS and Eb% of the composites, the results can be
summarized as, OB composites showed higher mechanical properties like TS and FS but lower Eb% than
other type of nonwoven composites. Where IB composite exhibited lower TS and FS but higher Eb%. MB
and MR can be considered medium in all the case. As discussed above, there may be a variation of
chemical compositions of different types of banana bers. OB nonwoven may contain higher
percentages of cellulose that leads them to achieve better mechanical properties. The cellulose
percentage may gradually decrease from the outer bark (OB) to the inner bark (IB) of the banana tree. As
a result, lower cellulose content makes the IB bers weaker and consequently lower mechanical
properties in composites. Also, outer bark of the banana tree is found harder as a raw material that can
make stronger materials than other layers of the banana stem. The midrib also found harder but
surprisingly became soft after chemical extraction. The previous study also proved the higher mechanical
properties of OB as a nonwoven material (Motaleb et al. 2020). Epoxy composite always found higher
mechanical properties i.e., higher value of TS and FS but lower Eb% than polyester composites. This
because of better interfacial bonding between ber and epoxy that leads very good adhesion between
them. As a result, the applied load can be distributed properly though the ber and matrix which leads to
bear higher loads. Similar results were found in some earlier studies (Rohen et al. 2018; Oliveira et al.
2019; Sivakandhan et al. 2020).
The alkali treatment demonstrated the improvement of mechanical properties like TS and FS but
decrease the Eb%. As discussed above, alkali treatment eliminates some unwanted materials including
lignin and hemicellulose. This elimination creates rough ber surface that helps better mechanical
interlocking among the bers. By cleaning the impurities, the cellulose content of the bers is increased
which may increase the reactive sites and create strong bonding with the matrix. Therefore, the
mechanical properties like TS and FS were improved. Due to the same reason, Eb% of the composites
were decreased. As better as the adhesion between the ber and matrix, the material become more solid

Page 14/32
and hard thus the elongation property is declined (Li et al. 2007; Mohd Nazarudin et al. 2013; Manalo et
al. 2015; Preet Singh et al. 2017).
3.2.2 Effects of Water Repellent
3.2.2.1 Effect of Water Repellent Treatment on Tensile
Strength
Figure10 reveals the effects of WR on the tensile strength of the composites. There is no doubt that, the
hydrophobicity of the composites were improved to a great extent by the WR treatment. On the other
hand, this treatment drew a negative effect on the tensile properties of the composites. Study found that,
the maximum 27.3%, 25.1%, 31.4% and 25.4% decrease of TS were found for OB/E, MB/E, IB/E and MR/E
composites where, 67.5%, 59.4%, 67.3% and 67.5% for OB/P, MB/P, IB/P and MR/P composites in
compared to untreated composites respectively. However, the deterioration is very low (about 4–14%) at
5% WR concentration. For instance, the TS of OB/E, MB/E, IB/E and MR/E composites were decreased by
5.3%, 4.4%, 7.0% and 6.2% where, the TS of OB/P, MB/P, IB/P and MR/P composites were decreased by
6.7%, 6.0%, 12.9% and 13.2% respectively at a concentration of 5% WR. At 10% WR, the TS of epoxy
composites were reduced by approx. 10% where the TS of polyester composites were reduced by approx.
34% in an average. Likewise, at 15% WR, polyester composites were also showed higher reduction
(approx. 65%) than epoxy composites (approx. 27%) in an average.
3.2.2.2 Effects of Water Repellent Treatment on Flexural
Strength
Effect of WR on the exural properties are evident in Fig.11. Similar negative trend was found for all the
composites like TS as it declined the FS to a large extent of about 40–50% (in an average) after treating
with 15% WR in compared to untreated composites. But the effect was much lower at 5% and 10% WR.
For examples, the FS of OB/E, MB/E, IB/E and MR/E composites were declined by 4.4%, 3.9%, 7.5% and
6.0% while, the FS of OB/P, MB/P, IB/P and MR/P composites were declined by 4.1%, 2.6%, 11.0% and
8.8% respectively at 5% WR in compared to untreated composites.
3.2.2.3 Effects of Water Repellent Treatment on Elongation
at Break
Elongation of the composites were increased with the increase of WR% that is clearly dened in Fig.12.
The maximum increases of Eb% were found at 15% WR. For example, OB/E, MB/E, IB/E and MR/E
composite exhibited 63.8%, 66.7%, 62.0% and 61.3% of increment at 15% WR than untreated composites.
At 10% WR, the effect was lower, Eb% were increased by 25% (approx.) on an average considering all
types of composites. Furthermore, at 5%WR, the effect was very low as Eb% was increased by about 10%
maximum from the untreated composites. The 2nd order polynomial curves also prove this trend.
The application of WR on the nonwoven surface, declined the mechanical properties like TS and FS but
increased the Eb%. This was expected because, WR creates coating on the ber surface and resist water

Page 15/32
to penetrate inside the ber thus improve the hydrophobicity. However, because of this coating or polymer
blockage, mechanical properties can be reduced. The ber-matrix interface can be disrupted by this type
of coating that results poor adhesion between the ber and matrix thus the poor mechanical properties of
the composites. The good thing is, this effect is negligible at lower concentration like 5% WR. Study
revealed that the deterioration of TS and FS in about 10% maximum for all types of composites at a
concentration of 5% WR. Whereas the hydrophobicity was increased by 40–50% (in an average) at the
same concentration of WR. Therefore, it is recommended to apply the WR with a concentration of 5% to
balance the water absorbency and mechanical properties.
3.2.3 Effects of Gamma Radiation
Effects of gamma radiation on mechanical properties like tensile strength, exural strength and
elongation at break were investigated in this study. The results are described in 2nd order polynomial
curves because the mechanical properties were inuenced by gamma radiation in two opposite factors.
3.2.3.1 Effect of Gamma Radiation on Tensile Strength
Figure13 depicts the inuence of gamma radiation on tensile properties of the composites. All the curves
demonstrate that, gamma radiation improves the mechanical properties signicantly to a certain level of
dose. The TS of OB/E, MB/E and MR/E composites were improved by maximum 31.2%, 33.3% and 37.7%
at a gamma radiation dose of 200krd where, the TS of IB/E was improved by 20.1% at a dose of 100krd
respectively in compared to non-irradiated composites. However, the TS of the composites were
decreased to a large extent by further increasing of gamma radiation dose. For instance, the TS of OB/E,
MB/E, MR/E composites were decreased by 8.5%, 16.3%, 13.1% at 300krd and the TS of IB/E was
decreased by 7.4% at 200krd respectively from the maximum value. Similar trend was found for Polyester
composites as increased the TS by 37.7%, 41.4%, 30.0% for OB/P, MB/P, MR/P composites at 200krd and
24.9% for IB/P composite at 100krd but after that the TS was decreased with the increase of radiation
dose. At higher dose like 500krd, TS was drastically by 60% in an average for all types of composites
from the maximum value of TS, which is even less than half of the TS of nonirradiated composites. Both
the polyester and epoxy composites were inuenced by the gamma radiation in the same ways though
the TS of epoxy composites were improved slightly higher in percentage than polyester composites.
3.2.3.2 Effect of Gamma Radiation on Flexural Strength
The effect of gamma radiation on the exural strength of the composites are presented in Fig.14. Similar
tendency like TS was found in this case as well; the FS of the composites were enhanced noticeably to a
certain level of dose and reduced to a large amount after that certain level. It is evident that, FS were
improved by 37.8%, 39.2%, 39.8% for OB/E, MB/E, MR/E composites and 37.3%, 34.4%, 40.8% for OB/P,
MB/P, MR/P respectively at a gamma radiation dose of 200krd. IB composite such as IB/E and IB/P
showed the maximum 21.1% and 31.2% improvement of FS at a radiation dose of 100krd. Further
increment of gamma dose, for example at 300krd, FS were decreased by 12.9%, 14.5%, 25.0%, 17.6% for
OB/E, MB/E, IB/E, MR/E composites and 22.3%, 17.2%, 29.4%, 14.3% for OB/P, MB/P, IB/P, MR/P

Page 16/32
composites respectively. FS were fallen dramatically at higher dose like 500krd. FS were found 32.89,
27.69, 14.34 and 23.92 MPa for OB/E, MB/E, IB/E and MR/E composites; 22.38, 20.79, 6.67 and 18.36
MPa for OB/P, MB/P, IB/P and MR/P composites respectively at a gamma dose of 500krd which is
almost half of the FS of nonirradiated composites.
The improvement of TS and FS through gamma radiation is mainly due to the improvement of polymeric
bonding among the intra-chain of ber and matrix by cross-linking each other. Which leads more oriented
polymeric structures and better ber-matrix adhesion, therefore increase the mechanical properties like TS
and FS (Masudur Rahman et al. 2018; Gnatowski et al. 2020). Gamma radiation is a powerful ionizing
radiation which has an ability to penetrate the materials and inuence the polymeric structure by
producing reactive sites like free radicals, ions, and peroxides. Consequently, these reactive species can
cross-link or, bind to each other to form long polymeric chains or, large molecules and leads to change the
mechanical properties of the materials. It is also evident from several studies that, gamma radiation can
break the C = C bond and generate free radicals, subsequently improve the mechanical properties
(Haydaruzzaman et al. 2009; Masudur Rahman et al. 2018; Martínez-Barrera et al. 2020). Gamma
radiation may also extract the inside moisture of the composites which is also a possible reason for
improving the properties (Khan et al. 2009; Martínez-Barrera et al. 2020).
In spite of that, mechanical properties like TS and FS were started to decrease after a certain level of
dose. This reduction is because of another aspect, usually known as chain scission or, chain degradation
which is completely opposite of chain cross-linking. At higher gamma radiation dose, the main polymeric
chains are destroyed into small particles. Thus, the mechanical properties like TS and FS are decreased
(Masudur Rahman et al. 2018).
3.2.3.3 Effect of Gamma Radiation Treatment on Elongation
at Break
Effect of gamma radiation on Eb% of the composites are revealed in Fig.15. The Eb% was reduced by the
gamma radiation to a small amount up to a certain level of irradiation then increased gradually. At a dose
of 200krad, Eb% were decreased by 20% (maximum) from the nonirradiated composites, considering all
types of composites except IB composites. They were exhibited the lowest Eb% at 100krd. After this
certain level of doses, EB% were increased with the increment of gamma radiation doses. The highest
Eb% were found at a radiation dose of 500krd as 1.59, 1.78, 2.18 and 1.92% for OB/E, MB/E, IB/E and
MR/E composites while, 1.66, 1.94, 2.86 and 2.57% for OB/P, MB/P, IB/P and MR/P composites
respectively, the values are 80–90% higher than nonirradiated composites.
As described above, gamma radiation leads strong cross-linking among the intra-chains of bers and
matrices that ensures better adhesion between them. The resultant polymeric structures become more
crystalline and limit the movement of polymer chains which leads lower Eb% of the materials (EL-Zayat et
al. 2019). In other words, the more oriented structure makes the materials more solid and harder that
reduce the elongation properties. However, at higher dose the main polymer chains and ber-matrix

Page 17/32
bonding may destroy into small pieces. That results severe disorder of polymeric structure which leads
higher elongation.
4. Conclusions
The current study reveals the developments of an innovative natural composite materials by reinforcing
different banana ber nonwovens which were developed by a special manual technique of wet laid web
formation. The outcome of this study can be summarized by the following points.
1. OB composites showed higher mechanical properties (TS and FS) and higher water absorbency than
other nonwoven composites. Between the two matrices, polyester composites exhibited higher
absorbency and lower mechanical properties than epoxy composites.
2. The hydrophobicity and mechanical properties of the composites were improved signicantly by the
alkali treatment due to the better ber-matrix adhesion which is achieved by removing unwanted
materials from the bers through this treatment. For instance, about 32% decrease of water
absorbency, 71% increase of TS and 87% increase of FS was found on an average at a concentration
of 15% NaOH.
3. The hydrophobicity was continued to improve remarkably by the water repellent treatment on the
nonwovens by creating a surface coating on the materials. On the other hand, the mechanical
properties were decreased by disrupting the ber matrix bonding through this treatment. But the good
thing is, this declination is less than 10% approximately at a concentration of 5% WR with the
signicant improvement of hydrophobicity by 47.5% on an average. Therefore, this study
recommends applying the WR with the maximum concentration of 5% to balance the water
absorbency and mechanical properties.
4. Gamma Radiation improved the mechanical properties like TS, FS and decreased Eb% due to more
oriented polymeric structure achieved by this radiation. Maximum 30% of TS and 35% of FS were
increased at a radiation dose of 200krd but further increasing of dose decreased the properties due
to breaking of main polymeric chains at higher radiation. Thus, this study recommends gamma
radiation dose of maximum 200krd.
Based on the achieved results, it is evident that, banana ber nonwoven reinforced composites are well
developed by different physical and chemical treatments on their pre and post manufacturing stages.
The developed material demonstrates excellent hydrophobicity and comparable mechanical properties
which can replace the existing non-biodegradable, carcinogenic and synthetic materials on the market.
5. Declarations
Funding Not applicable.
Conicts of interest  The authors declare that they have no conicts of interest.
Ethics approval  Not applicable.

Page 18/32
Consent to participate Not applicable.
Consent for publication Not applicable.
Availability of data and material Not applicable.
Code availability Not applicable.
Permission for collecting samplesThe authors clarify that the plant samples were collected with
appropriate permissions from the owner of the plant.
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Figures

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Figure 1
Banana tree and cross-section of banana stem.

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Figure 2
Prepared composite samples for the tensile test (from the left: OB/P, OB/E, MB/P, MB/E, IB/P, IB/E, MR/P
and MR/E).
Figure 3

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Water absorbency percentage of composites after 24 h water immersion, (a) Water absorbency of
untreated (0% NaOH) composite samples; (b) Effect of alkali treatment on the water absorbency of the
composite samples.
Figure 4
Water absorbency ows of 15% NaOH treated composite samples by the soaking time up to 24 hours.
Figure 5

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Water absorbency percentage of composites after 24 h water immersion, (a) Water absorbency of
untreated (0% WR, 15% NaOH) composites; (b) Effect of WR treatment on the water absorbency of the
composites.
Figure 6
Water absorbency ows of 10% WR treated composite samples by the soaking time up to 24 hours.
Figure 7

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(a) Tensile strength of untreated (0% NaOH) composites; (b) Effect of alkali treatment on the tensile
strength of the composites.
Figure 8
(a) Flexural strength of untreated (0% NaOH) composites; (b) Effect of alkali treatment on exural
strength of the composites.
Figure 9
(a) Eb% of untreated (0% NaOH) composites; (b) Effect of alkali treatment on Eb% of the composites.

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Figure 10
Effect of water repellent on tensile strength of the composites.

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Figure 11
Effect of water repellent on exural strength of the composites.

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Figure 12
Effect of water repellent on exural strength of the composites.

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Figure 13
Effect of gamma radiation on tensile strength of the composites.

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Figure 14
Effect of gamma radiation on exural strength of the composites.

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Figure 15
Effect of gamma radiation on elongation at break (%) of the composites.
Supplementary Files
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