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RESEARCH ARTICLE
Dyeability and mechanical properties of banana fiber
reinforced polypropylene composite
Shuvo Brahma
1,2
| Sk. Mohammad Raafi
3
| Sharfun Nahar Arju
3
|
Junaid ur Rehman
2
1
Department of Environmental Science
and Engineering, Bangladesh University
of Textiles, Dhaka, Bangladesh
2
College of Science and Engineering,
Materials Science, Engineering, and
Commercialization, Texas State
University, San Marcos, Texas, USA
3
Department of Wet Process Engineering,
Bangladesh University of Textiles,
Dhaka, Bangladesh
Correspondence
Sk. Mohammad Raafi, Department of Wet
Process Engineering, Bangladesh
University of Textiles, Dhaka, Bangladesh.
Email: raafi@wpe.butex.edu.bd
Abstract
Banana fibers being highly strong and biodegradable, have always been an
interesting aspect of polymer science. The research examines the pretreat-
ment process to enhance the dyeability of banana fibers with synthetic dyes,
followed by the preparation of polypropylene (PP) composites with dyed
fibers to explore their mechanical properties. Raw banana fibers were
extracted from the pseudo stems of banana plants for pretreating with
sodium hydroxide and hydrogen peroxide and further dyed in the exhaust
method using direct, basic, reactive, and vat dyes. Despite a decrease in
fiber strength, the scoured-bleached fibers appeared whiter and lustrous
compared to untreated fibers. Direct dye exhibited a higher color strength
(K/S) value of 20.7 and better wash fastness on average of 4-3 rating com-
pared to basic dye. Later polypropylene sheets were prepared using a Hot
Plate Molding Machine, and composite specimens were fabricated by sand-
wiching the fibers between PP sheets and hot pressing. Fourier Transform
Infrared Spectroscopy (FTIR) analysis revealed minor bond formations
between the dyed fibers and polypropylene matrix in composites showing
significant bonding at N H, C H, and O H regions. The composites con-
taining dyed fibers showed slight improvements in tensile strength and
modulus which is at best 2% than that of untreated fiber.
Highlights
•Direct and basic dyes were determined as the most suitable synthetic dyes.
•FTIR analysis revealed minimal bond formation between the fiber and PP
matrix.
•Composites having dyed banana fiber showed little better mechanical
features.
KEYWORDS
banana fiber, composite, mechanical properties, polypropylene, synthetic dyes
Received: 21 February 2024 Revised: 9 March 2024 Accepted: 11 March 2024
DOI: 10.1002/pls2.10129
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided
the original work is properly cited.
© 2024 The Authors. SPE Polymers published by Wiley Periodicals LLC on behalf of Society of Plastics Engineers.
SPE Polymers. 2024;5:353–365. wileyonlinelibrary.com/journal/pls2 353
1|INTRODUCTION
Composite is a material, made from two or more con-
stituents having distinct physical or chemical proper-
ties that, when combined, produce a material with
characteristics different from the individual compo-
nents.
1
Synthetic fiber composites are commonly called
conventional composites where glass and carbon fibers
are dominantly used because of their easy processing,
better productivity, and superior mechanical proper-
ties. But their higher density and non-recyclability at
the end of their life cycle become significant shortcom-
ings making them inadvisable to use. Manufacturing
these fibers consumes a huge amount of energy, an
added threat to the present era of the energy crisis.
Energy consumption also causes pollution of the envi-
ronment.
2
Hence, a relatively smart concept is to con-
sider natural fibers as a reinforcing material.
3
Natural
fibers are considered as an appropriate alternative to
synthetic fibers as they come with low cost, high
strength-to-weight ratio, stiffness, biodegradability,
reusability, and recyclability.
4–6
Among all the natural fibers, banana is abundantly
available in tropical countries like Bangladesh and India. It
is particularly interesting to use banana fibers as reinforce-
ment in the polymer matrix due to their excellent mecha-
nical properties.
7–9
Chemically, banana fiber includes
60%–65% cellulose, 19% hemicellulose, 5%–10% lignin, 3%–
5% pectin, 1%–3% ash, less than 1% wax, and 10%–11%
moisture.
9
Banana fibers having 1.35 g/cm
3
density and a
diameter between 0.08 and 0.25 mm were reported with a
tenacity of 529–759 MPa, an elastic modulus of 8–20 GPa,
and 1.0%–3.5% elongation at break.
10,11
Typically, the fibers
extracted from the pseudo-stem of the banana plant exhibit
superior mechanical strength compared to those from
other parts such as the leaves or fruit stalk. This is because
the pseudo-stem contains a higher concentration of cellu-
lose and lignin, providing greater structural integrity and
tensile strength. Regions with optimal conditions, such as
moderate temperatures, adequate rainfall, and fertile soil,
tend to produce fibers with better mechanical properties.
12
The novelty of using banana fibers as reinforcement in
polypropylene (PP) composites lies in their unique combi-
nation of properties, including high strength, biodegrad-
ability, and abundance as a natural resource. Additionally,
banana fibers exhibit favorable adhesion characteristics
with polymer matrices when properly treated, enhancing
the overall performance and durability of the composite
materials. The reinforcement of banana fiber in
thermoplastics was investigated by a few researchers.
13–19
Thermoplastic polymeric matrices are preferential to ther-
mosets due to the low production cycle, lower cost of pro-
cessing, and high reparability.
20
Combinations of various
hybrid composites produced using banana fiber and vari-
ous other natural or synthetic fibers in the polymer
matrixes contributed to a 30%–50% increase in all the
mechanical properties such as tensile, flexural, and impact
strength.
21
Untreated banana fibers of 30–40 mm in length
were reported to increase the tensile strength and impact
strength of polyester composites by 20% and 341%, respec-
tively.
13
Reinforcement of banana fibers in epoxy compos-
ites was found to confirm a very stable mechanical
behavior of the composites under different tests and a 90%
increase in the tensile strength compared to the raw epoxy
as well as an improvement in the impact strength by
approximately 40% were observed.
14,15
Inthecaseofintro-
ducing banana yarn into a polypropylene matrix, the ten-
sile strength and flexural strength of the composite were
increased by 294% and 72%, respectively when compared
to those of unreinforced PP.
18
Apart from other thermo-
plastic matrix materials, polypropylene (PP) is widely used
because it has some excellent characteristics like high heat
distortion temperature, transparency, flame resistance,
dimensional stability, and impact strength.
20,22
The need for chemical treatment in natural
fiber-reinforced composites, including banana fiber com-
posites, is crucial to enhance their compatibility with
polymer matrices and improve their overall performance.
Chemical treatments such as scouring and bleaching are
commonly employed to remove lignin, waxes, and other
non-cellulosic components from the natural fibers, which
not only improves their dyeing affinity but also facilitates
better interfacial bonding with the polymer matrix. The
chemically treated banana fibers were also used with PP
for preparing composites, which were detected, charac-
terized, and analyzed by many researchers.
23–28
The
incorporation of alkali and enzyme-treated banana fibers
into a polypropylene matrix was reported to improve the
tensile modulus, tensile strength, flexural modulus, and
flexural strength due to better adhesion of the fibers with
the matrix.
25,29
After alkaline treatment, the tensile, flex-
ural, and impact strength of the PP composite was
increased by 3.8%, 5.17%, and 11.50%, respectively.
26
However, it is worth noting that while chemical treat-
ment enhances fiber-matrix adhesion, it may also lead to
a reduction in fiber strength due to the removal of natu-
ral components.
30
The motivation for this study stems from the increas-
ing demand for sustainable materials in various indus-
tries and the potential of natural fibers, such as banana
fibers, to fulfill this need. While banana fibers are known
for their high strength and biodegradability, their use in
composite materials remains relatively less explored.
A gap in the research works shows that the dyeability of
banana fiber was ignored by using various synthetic dyes.
In addition, the concepts of the various dye-treated
354 BRAHMA ET AL.
banana fibers as reinforcing material were not studied.
Thus, it can be determined that dyed banana fiber with
synthetic dye as reinforced material in PP composite still
has not been taken into consideration. Therefore, the pre-
sent study was intended to address a research gap in the
comprehensive understanding of banana fiber PP com-
posites, particularly, emphasizing their dyeability and
mechanical properties. This study aims to evaluate the
suitability of banana fibers for dyeing using various syn-
thetic dyes, optimize pretreatment processes to enhance
dyeability, fabricate PP composites with dyed banana
fibers, and assess the mechanical behavior of the result-
ing composites, particularly their flexural properties.
Furthermore, the investigation seeks to characterize the
dyed banana fibers comprehensively in terms of color,
length, strength, diameter, moisture regain, and density.
The novelty of this work lies in its holistic approach
towards exploring the use of banana fibers in composite
materials, addressing both their dyeing potential and
mechanical performance, thus contributing to the advance-
ment of sustainable materials in various applications.
2|MATERIALS AND METHODS
2.1 |Preparation of raw banana fiber
Banana plants (Musa balbisiana) were collected from
Nayarhat, Savar, Bangladesh. Initially, the pseudo stem is
cut into pieces of about 60 cm in length and 7.5 cm in
width. After the stem had been separated, it was dried for
2 days for better extractions of the fiber. The slices, pre-
pared from stems are fed to the fiber-extracting machine
which is consisted of a pair of feed rollers and a beater.
The slices were fed to the beater in between the squeez-
ing roller and the scrapper roller. Thus, the pulp gets sep-
arated and fibers are extracted. After sun drying, a bunch
of fibers is mounted or clamped on a stick to facilitate
segregation. Each fiber is separated individually accord-
ing to fiber length and is grouped accordingly. About
3.5 kg of banana fiber was collected for the experimental
work which was about 25–30 cm in length. The creamy-
white-looking fibers were quite stiff, harsh, and light.
2.2 |Chemicals
Sodium hydroxide (NaOH) pellets and hydrogen peroxide
(H
2
O
2
) of 30% w/v used as the main chemicals for scour-
ing and bleaching of banana fibers were produced by
Merck Specialities Private Limited (India). Sodium meta-
silicate (Na
2
SiO
3
9H
2
O) was supplied by Qualikems Fine
Chem Pvt. Ltd. (India). Peroxide stabilizer and peroxide
killer were also of laboratory grade. For the dyeing of the
fiber anhydrous sodium carbonate, Glauber's salt, acetic
acid, tannic acid, tartar emetic, ammonium hydroxide,
sodium hydrosulphite (Na
2
S
2
O
4
), basic dye (Maxilon
®
Red GRL 200%), direct dye (Solophenyl
®
Red 9BE), reac-
tive dye (CI Reactive Red 135), vat dye (Vat Red 1), wet-
ting agent, sequestering agent, leveling agent, and
detergent were used. The dyes were collected from
Huntsman (Swiss Colours) and the rest of the chemicals
mentioned earlier were distributed by the local suppliers
of Hatkhola, Dhaka. For the preparation of the matrix,
the used polypropylene granules were claimed to be 90%
pure by the local distributor.
2.3 |Preparation of wet processed
banana fiber
2.3.1 | Pretreatment of banana fiber
Banana fiber was pretreated with a hot scouring and
bleaching process in an open bath at M:L of 1:50, in the
presence of 6% o.w.f. H
2
O
2
, 8% o.w.f. Na
2
SiO
3
, 0.7%
o.w.f. NaOH, 1 g/L detergent, 1 g/L sequestering agent,
and 3 g/L peroxide stabilizer. For the washing of the fiber
after scouring and bleaching, 1 g/L peroxide killer and
1% o.w.f. acetic acid was used in this experiment.
At the beginning of the process, the fibers were knot-
ted together with cotton yarn. The process was run with
fibers at room temperature with the required amount of
water. Then sequestering agent and detergent were added
to the bath. After a few minutes, the rest of the chemicals
were added and the temperature was raised to 80C. The
process was run at 90C temperature for 110 min. After
completing combined scouring-bleaching the liquor was
drained out from the dye bath. Then hot wash was given
shown in maintaining the same M:L with peroxide killer
at 80C for 20 min, followed by the neutralization with
acetic acid at 50C for 5 min. Finally, the fibers are rinsed
at room temperature for 10 min.
2.3.2 | Preparation of basic dyed specimen
To improve the dye fastness properties of basic dyed
banana fiber, mordanting was carried out first using 1 g/L
tannic acid. The acid and fibers were taken in the dye bath
and the temperature was raised to 100C and continued
for 2 h. After that fixation was carried out using 0.5 g/L
tartar emetic at room temperature for 30 min.
Later dyeing with the fiber was carried out with M:L
of 1:10 in a closed bath having wetting agent, sequester-
ing agent, and leveling agent, 1 g/L of each. Acetic acid
BRAHMA ET AL.355
(1 g/L) and dye solution containing 5% o.w.f. basic dye
was added to the system. The specimen was heated at
70C for 90 min. Then the bath was dropped and the
samples were separated for washing.
The dyed samples were loaded in the dye bath for
washing with water and neutralized at 60C for 10 min
with 1 g/L NH
4
OH. The bath was then dropped and a
hot wash was carried out for 10 min at 80C. 1 g/L deter-
gent involved soaping was carried out at 85C for 10 min.
The bath was then dropped and the sample was rinsed
with water at 30C for 10 min. Later the bath was
dropped and the sample was dried in a dryer.
2.3.3 | Preparation of direct dyed specimen
Banana fiber was dyed with direct dye in a closed bath
using the M:L of 1:10. 5% o.w.f. dye was pasted with 1 g/L
wetting agent. The required amount of water and 1 g/L
sequestering agent were added to the dye bath. It was then
followed by the addition of 1 g/L soda ash for complete
solubilization of the dye. Dyeing was started at room tem-
perature with slow heating up to 60Cduringwhichhalf
of Glauber's salt (15 g/L) was dosed. After reaching 60C
temperature, the rest (50%) of the salt was added and run
for 20 min. The temperature was further raised slowly to
boil (95C) for complete exhaustion of dye in 1 h.
For washing the dyed fiber, firstly neutralization was
done at 30C for 10 min with 1 g/L acetic acid. After
dropping the bath, a hot wash was given at 80C for
10 min, then dropped. Later soaping was continued at
85C for 10 min with 1 g/L detergent. After dropping the
soaping bath, the sample was rinsed with water at 30C
for 10 min. Finally, the sample was dried with a dryer
and preserved for characterization.
2.3.4 | Preparation of reactive dyed
specimen
For reactive dyeing of the fiber, 5% o.w.f. dye was taken
into consideration. The M:L ratio was set to 1:10 and
1 g/L wetting agent, 30 g/L Glauber's salt, and 1 g/L
sequestering agent were used. Soda ash of 20 g/L was
used for dye fixation.
31
The process of dyeing started by taking the fiber in
the dye bath. The auxiliary chemicals and the dye were
added next. Half of the salt was added before raising the
temperature of the bath to 60C. After that, the rest of
thesaltandthesodawereaddedandthedyeingtook
place for 50 min.
Later the dye bath was rinsed and the fiber was
taken for washing. The washing cycle is identical to
that used in the direct dyeing of banana fibers, as
stated earlier.
2.3.5 | Preparation of vat dyed specimen
The vat dyeing of banana fiber was started with the vat-
ting of 5% o.w.f. dye, in presence of 5 g/L Na
2
S
2
O
4
and
20% o.w.f. NaOH at M:L ratio of 1:10. That reduction
and solubilization process was continued for 20 min at
60C. After the vatting was completed, 20 g/L salt, 1 g/L
leveling agent, and 1 g/L sequestering agent were added
and the temperature was raised to 70C and maintained
for 30 min. Later, the dyed fiber was taken outside of the
dye bath for 10-min-long air oxidation. Finally, after per-
forming the same washing cycle as used in the direct dye-
ing of banana fibers, the sample was dried with a dryer
and stored for characterization.
2.4 |Preparation of polypropylene sheet
The polypropylene (PP) sheets of 0.10–0.15 cm thickness
were prepared using the Hot Plate Molding Machine
(Figure 1A) of the Yarn Engineering Laboratory of
Bangladesh University of Textiles (BUTEX) and manu-
factured by Carver.
The PP granules (Figure 1C)wereplacedonthebottom
plate inside the holder (Figure 1B). The thickness of the
holder was about 1 mm. Later the second plate was placed
on top and the steady increase of temperature was fixed at
180Cfor10minunderapressureof510
8
Pa. The plate
was cooled and the PP sheet was obtained (Figure 1D).
2.5 |Fabrication of composite
Banana fibers of approximately 8 cm cut-length were
used to prepare four (4) types of polymer composite
specimens comprising 90% PP/10% Raw Banana fiber
(RBPP), 90% PP/10% Scoured-Bleached Banana fiber
(SBBPP), 90% PP/10% Basic Dyed Banana fiber (BBPP),
and 90% PP/10% Direct Dyed Banana fiber (DBPP).
The banana fiber, with the specific length, was
arranged in continuous order in the direction of the
mold by the hand layup method.
Composites were prepared by sandwiching one layer
of banana fiber between two layers of pre-weighted PP
sheets as shown in Figure 2and pressed at 190C for
10 min between two steel plates under a pressure of
510
8
Pa in the Carver Laboratory Press Machine. Then
composite containing steel mold was cooled to room tem-
perature and cut to the desired size.
356 BRAHMA ET AL.
2.6 |Characterization
2.6.1 | Color
Raw banana fiber obtained from the fiber-extracting
machine was taken as a sample. The fiber was taken to a
light box and color was accessed in D65 daylight.
2.6.2 | Length
The measured length of the obtained raw banana fiber
was calculated. The average length of the fiber was calcu-
lated using the common scale.
2.6.3 | Strength
The banana fiber used in this experiment has gone
through a series of wet processing methods which have
affected its bundle strength. Due to this the fiber strength
has been determined in terms of gram/tex. The Stelometer
of the BUTEX Quality Testing Laboratory has been
utilized for this purpose.
2.6.4 | Diameter of the Fiber
The diameter of the raw banana fiber was also deter-
mined by the screw gauge. Five of the fiber specimens
(V1, V2, V3, V4, and V5) were taken and the average
diameter of the fiber was calculated by using the
formula (I):
Diameter ¼Main scale reading
þLeast count Circular Scale readingðÞ:ðIÞ
2.6.5 | Moisture regain
The moisture regain of the raw banana fiber (from V1 to
V5) is measured with the help of oven dry weight (D)of
the sample along with the weight of the water (W) in the
FIGURE 1 (A) Hot plate machine,
(B) steel plate and the holder,
(C) polypropylene granules, and
(D) prepared PP sheet.
FIGURE 2 Fabrication of composite.
BRAHMA ET AL.357
sample. Later the moisture regain percentage was calcu-
lated using the formula (II):
Moisture Regain,R¼W
D100:ðIIÞ
2.6.6 | Density
The density of the raw banana fiber is easily measured by
calculating the volume (V) using the screw gauge and
later obtaining the mass of the sample (M).
The volume of the sample, V=πd
2
l/4 (where
d=diameter of the fiber and l=length of the fiber).
So, density =M/V.
2.6.7 | Evaluation of color strength
Color coordinate value is the position of the color in color
space through tristimulus value. CIE L*a*b*methodwas
applied here to determine the color coordinate values of
all samples through the Datacolor SF 600 reflectance spec-
trophotometer of the Wet Process Laboratory of BUTEX.
The reflectance percentage of the dyed samples, for
example, basic dye and direct dye treated banana fiber
were measured by using Datacolor 650 Spectrophotome-
ter. For the strength of the dyestuffs related to absorption
property, Kubelka-Munk gives the following relation (III)
between reflectance and absorbance.
32,33
K=S¼1RðÞ
2=2R,ðIIIÞ
where, Ris the reflectance, Kis the absorbance, and Sis
the scattering.
2.6.8 | Evaluation of color fastness
The color fastness to wash, color fastness to rubbing, and
color fastness to light of the samples were evaluated
according to ISO 105-C10:2006, ISO 105 X12:2016, and
ISO 105 B02:2014 test standards.
34–36
2.6.9 | Fourier transform infrared (FTIR)
spectroscopy analysis
In this study, the infrared spectrum of the untreated
banana fibers and dye-treated banana PP composite was
recorded by IR Prestige 21, Shimadzu instrument at a res-
olution of 2 cm
1
. An average of 30 scans were recorded
in absorbance units from 4000 to 400 cm
1
.
2.6.10 | Mechanical properties of composites
The tensile tests were performed according to ASTM
D638-14 with a Universal Testing Machine (model H50
KS-0404, Hounsfield Series S, United Kingdom) at a cross-
head speed of 5 mm/min.
37
The static flexural tests of the
composites were carried out by a Three-point Bending Test
machine that was used for the tensile test only by changing
the attachment. Different dimensions of the flexural test
specimen are L=100 mm, b=10 mm, and h=2.5 mm.
Flexural tests were conducted following the ASTM
D790-17 standard at a cross-head speed determined by the
following Equation (IV).
38
R¼ZS2=6h, ðIVÞ
where, R=rate of cross-head motion =1.749 mm/min,
h=thickness =4.1 mm, S=support span =16 h =16
2.5 mm =40 mm, and Z=rate constant of straining of
the outer fiber =0.01.
To perform the flexural test, operating conditions
were similar to that of the tensile test. Three specimens
of each composition were tested and the average values
were reported. The flexural strength (σ
f
) and flexural
modulus (E
b
) were obtained by using QMAT software in
a computer interfaced with the Hounsfield UTM
machine. The following two equations (Vand VI) were
used in the QMAT software to calculate the flexural
strength σ
f
and flexural modulus E
b
, respectively.
Flexural strength,σf¼3FS=2bh2,ðVÞ
Flexural modulus,Eb¼S3m=4bh3,ðVIÞ
where, F=maximum load in N, and m=slope of the
tangent to the initial straight portion of the load-
deflection in N/mm.
For the mechanical tests, five (5) samples from each
type of composite were taken. The allowable error for the
tests ASTM D638-14 and ASTM D790-17 typically ranges
from ±1% to ±5%.
3|RESULTS AND DISCUSSION
3.1 |Fiber characterization
Raw banana fiber obtained from the mechanical extruder
is the considered sample. The following properties
(Table 1) of the fiber have been analyzed after the fiber is
separated. The color of the fiber is assessed in the color
matching cabinet at the 45table under D65 daylight.
358 BRAHMA ET AL.
The length of the fiber is assessed by a common scale and
the diameter is measured via a screw gauge.
3.1.1 | Color
Raw banana fiber is light yellowish and, cannot be uti-
lized in dyeing because of the lignin, oil wax, and other
impurities present in the fiber. To make the fiber suit-
able for further treatment and dyeing it must be scoured
and bleached. The scoured bleached fiber is compara-
tively whiter and lustrous when perceived by the
naked eye.
Moreover, Figure 3indicates that the whiteness of the
fiber jumped from 84.48 to 71.82 after the scouring and
bleaching. This suggests that the fibers have become
more lustrous and brighter. The tint of the fiber refers to
a negative value. But the tint of the raw banana fiber is
more negative than that of the scoured-bleached ones
suggesting that the fiber has become less yellow with the
scoured-bleached treatment. Lastly, the yellowness index
(YI) of the samples exhibits that the raw banana fiber is
much yellowish and duller. Combined scouring-
bleaching has made the fiber much whiter and the YI
index also decreased to a greater extent accordingly.
3.1.2 | Strength
Table 2shows the fiber strength of the banana fiber in
different stages of the experiment. The fiber exhibits bun-
dle strength at an average of 26.243 g/tex without being
treated but strength significantly falls to 19.68 g/tex when
the fiber is scoured and bleached. The direct dye-treated
fiber shows an even lower bundle strength of 19.4 g/tex
while the basic dye-treated fiber shows the lowest bundle
strength of 18.88 g/tex. Possible causes of the loss of bun-
dle strength are the continuous loss of lignin from the
fiber interface and the loss of weight of the fiber as being
treated. The strength of vat dye and reactive dye-treated
fibers is not measured since their K/Svalues explained in
the following discussion were not satisfactory.
3.2 |Analysis of dyed fiber
3.2.1 | Color strength (K/Svalue)
The K/Svalues of the dyed sample for 5% of dye concen-
tration are represented in Figure 4. It is visible that the
color strength of the direct dye is the best. The depth of
the color is best obtained for direct and later followed by
basic, vat, and reactive dye respectively. The reason
TABLE 1 Physical properties of raw banana fiber.
Properties Identifications
Color Dull yellowish
Length of the fiber 25–30 cm
Diameter 0.22–0.29 mm
Moisture regain % 10.5
Density 780–800 kg/m
3
-84.48
-23.59
50.7
71.82
-0.56
4.88
-100
-80
-60
-40
-20
0
20
40
60
80
IYTNITIW
Values
Attributes of Whiteness
Raw Scoured-Bleached
FIGURE 3 The Whiteness Index
(WI), Tint, and Yellowness Index (YI) of
the raw and scoured-bleached banana
fiber.
TABLE 2 Assessment of fiber strength.
Status of banana fiber Strength (g/tex)
Raw 26.243
Scoured-bleached 19.68
Basic dye-treated 18.88
Direct dye-treated 19.40
BRAHMA ET AL.359
behind having high color strength of the direct dye is
because of its anionic nature and attraction to the cellu-
lose fiber. The basic dye has also given a significant color
strength value due to its greater attraction to hemicellu-
lose thus yielding a better bridge with the fiber interface.
Vat dye has shown a lower K/Svalue but with accepted
status. Since vat dye has comparatively bigger molecules
its absorption on banana fiber was satisfactory but not
excellent. Reactive dye exhibited the least color strength
value due to the lower amount of cellulose in banana
fiber compared to other cellulosic fibers. Therefore, the
reactive dye has not been able to form significant bonds
and is deprived of higher color strength values. From the
above status, direct dye and basic dye can be selected as
the best dyes and the characterization as well as the later
test results have been performed on these samples.
3.2.2 | Color values
Figure 5has been depicted to identify some quantitative
values for the dyed fiber. The L* of the basic dye is
greater along with the a* and b* values when compared
with those of the direct dye. It means the basic dye-
treated fiber is much whiter as well as more reddish and
yellowish while the direct dye-treated fiber is much dar-
ker, much greener, and blueish. Besides, the chromatic
value of direct dye is lesser than that of the basic dye,
indicating the comparatively greater vividness of the
color of the basic dye.
39
However, the color value can be
increased with mercerization in the cellulose fiber.
40
3.2.3 | Colorfastness to wash
Figure 6shows the comparative analysis of the wash fast-
ness rating of the dye-treated fibers. The average wash
fastness rating of the direct dye-treated fiber is between
4-3 which is good whereas the wash fastness rating of the
basic dye-treated fiber is in the rating of 3 which is within
the range of good to fair. In the case of the degree of stain-
ing, direct dye shows higher values than basic dye of an
average of 4-3 over 2 and 4 over 2 in diacetate (DA) and
acetate (AC) fibers respectively. The average same degree
of staining of 3 and 4 are observed respectively in the case
of cotton (CO) and polyester (PET) fiber for both the dyes.
In polyamide (PA) fiber the staining of basic is more than
that of the direct dye. In wool (WL), the staining of the
basic dye was much higher than that of the direct dye. In
conclusion, it can be summarized that the wash fastness
and the staining values of the direct dye have given
higher values than that of the basic dye.
3.2.4 | Colorfastness to rubbing
Table 3shows the comparative analysis of the
rubbing fastness of both the dye-treated fiber in dry and
14.5
20.7
4.96
7.6
0
5
10
15
20
25
Basic Direct Reactive Vat
K/S
Classes of Dyes
FIGURE 4 K/Svalues of banana fiber dyed with
different dyes.
30.09
43.87
-2.57
43.95
37.38
47.3
3.33
47.42
-5
0
5
10
15
20
25
30
35
40
45
50
La*b*c*
Values
Attributes of Color
Direct d
y
ed Basic d
y
ed
FIGURE 5 Color values of the dyed
fiber.
360 BRAHMA ET AL.
wet conditions respectively. Colorfastness to rubbing of
direct dye was good about 4-3 in dry condition and fair
to poor about 3-2 in wet condition, whereas the fastness
rating of the basic dye was excellent to good about 5-4
in dry media and good to fair about 4-3 in the wet
medium.
3.2.5 | Colorfastness to light
Both the direct dye and basic dye treated samples
have been found to score the rating of 7–8 indicating
their excellent withstands of light upon exposure.
3.3 |Analysis of FTIR of the composite
To determine the bond nature of the fiber within the
composite, Fourier Transform Infrared Radiation
(FTIR)hasbeendone.Thebondnatureofthefiber
and composites will differ intermsoftheirtreatment
and interactions with the PP matrix. The curves in
Figure 7indicate the transmission percentage of the
bond being absorbed specifically when exposed to
wave number. The scoured-bleached banana fiber
composite (SBBPP) is represented by a dotted line,
the direct dyed banana fiber composite (DBPP) by a
solid line and the basic dyed banana composite
(BBPP) by a dashed line. The analysis indicates no
bond formation between the fiber and PP composite.
The FTIR results of the SBBPP conform to satisfactory
removal of the lignin from the raw banana fibers since
no absorption peak was found between 1730 and
1740 cm
1
, and 1600 and 1636 cm
1
.
41
The major groups
obtained in the absorption and transmission spectrum
are N H, C H, C O, C C, CH
3
, and C N for DBPP
at the spectrum zone of absorption frequency of 3439.08,
2885.51, 1724, 1591, 1419, 1280, 920.05, 885.33, and
773.46 cm
1
, respectively.
42
The N H bond found in the
spectrum of 3439.08 cm
1
absorption frequency indicates
the common functional group of the direct dye in the
composites. The weak detection of the absorbance band
at 1419 cm
1
is assigned to CH
3
asymmetric deforma-
tions of lignin indicating the removal of the lignin after
the pretreatment.
43
BBPP shows that the major group
obtained in the absorption and transmission spectrum
are at C H, O H, C H, C O, C C, C N region in
the absorption spectrum of 2881.65, 2698.41, 1897.95,
1720.5, 1600.92, 1286.52, 920.05, and 763.81 cm
1
,
respectively. The C N bond implies the bond associated
within the fiber with the chromophore part of the
dye inside the composite matrix. The absorption peaks
from 763.81 to 920.05 cm
1
indicate that carbon impuri-
ties are present.
19
Table 4summarizes the constituents
of functional groups at corresponding peaks found in
this study.
From the above discussion, it can be concluded that
the composite materials do not give any significant
bond with fiber and PP matrix in the absorption spec-
trum. However, some minor bond formation was visi-
ble in the case of dyed composite, for example, the
OH bond. The bond formation with the dyes like
CN for basic dye and N H for direct dye with the
fiber interface is also visible in the absorption spectrum
of the sample.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Degree of
Shade
Change
DA CO PA PET AC WL
Rating
Degree of Staining
Direct d
y
ed Basic d
y
ed
FIGURE 6 Analysis of colorfastness
to wash.
TABLE 3 Analysis of color fastness to rubbing.
Status of banana fiber
Degree of staining
Dry media Wet media
Direct dyed 4-3 3-2
Basic dyed 5-4 4-3
BRAHMA ET AL.361
3.4 |Mechanical properties of composite
3.4.1 | Tensile strength
The tensile strength of PP composites of untreated
banana composite, direct dye-treated banana compos-
ite, and the basic dye-treated banana composite are
analyzed. From Figure 8it is visible that the samples
DBPP and BBPP have better tensile strengths of
33.50 and 33.04 MPa respectively, in comparison to
RBPP. There is a very negligible strength variation
between the three samples but a little increase in
strength may suggest the association of some weak
Vander Waals force in the dyed fiber and the PP
matrix.
3.4.2 | Tensile modulus
Figure 9shows the tensile modulus of the specimen. It is
visible that the sample DBPP has the highest tensile mod-
ulus of 2.488 GPa and RBPP has the lowest tensile modu-
lus of 2.418 GPa. The composite shows an increase of
about 2.895% in tensile modulus for the DBPP sample.
For BBPP composite the increase in tensile modulus is
about 2.77%.
FIGURE 7 FTIR spectra of banana
fiber reinforced composites.
TABLE 4 Assignment of the infrared absorption of the banana
fiber reinforced composites.
Wavenumber (cm
1
) Functional group
3439.08 N H
2885.51 and 2881.65 C H
2698.41 O H
1897.95 C H
1724 and 1720.5 C O
1600.92 and 1591 C C
1419 CH
3
1286.52 and 1280 C N
32
32.2
32.4
32.6
32.8
33
33.2
33.4
33.6
33.8
RBPP BBPP DBPP
Tensile Strength (MPa)
Status of Composites
FIGURE 8 Tensile strength of composites.
362 BRAHMA ET AL.
3.4.3 | Flexural strength
Flexural strength obtained for the composite RBPP,
DBPP, and BBPP are 41.81, 42.97, and 42.94 MPa, respec-
tively as shown in Figure 10. The samples DBPP and
BBPP have a close match in flexural strength and the
RBPP sample has the lowest flexural strength. An
increase of 2.774% in flexural strength is visible for the
DBPP sample whereas the 2.70% increase in strength is
visible for the BBPP sample when compared with the
RBPP sample.
3.4.4 | Flexural modulus
Figure 11 shows the comparative flexural modulus of the
samples. The sample DBPP has the highest and RBPP
has the lowest flexural modulus. The flexural modulus of
the sample RBPP, DBPP, and BBPP are found to be as
3.28, 3.33, and 3.32 GPa, respectively. A small increase of
1.524% in flexural modulus is visible for the DBPP sample
and an increase of 1.219% in flexural modulus is shown
in the case of the BBPP sample respectively.
4|CONCLUSIONS
Banana fiber, post-scouring,andbleachingtreatments,
exhibit remarkable dye absorption properties, with direct
and basic dyes showcasing superior color strength on the
fiberinterface.Directdye-treatedbananafiberdemonstrates
higher values of wash (4-3), and rubbing (4-3) fastness com-
pared to basic dye-treated fiber (3), although both exhibit
comparable light fastness ratings. The fiber's strength
undergoes a continuous decrease with chemical treatment,
with basic dye treatment resulting in a more pronounced
decline (bundle strength: 18.88 g/tex). FTIR analysis reveals
an increase in the OH band within the fiber post-
treatment, with no observable bond formation between the
fiber and PP matrix, though unique bonds are detected in
the fiber due to dye attachment. The mechanical behavior
of composites improves significantly compared to both raw
banana fiber (tensile strength: 33.50 MPa, flexural strength:
41.81 MPa) and dye-treated counterparts, with increased
tensile strength (direct dye-treated: 33.04 MPa, basic dye-
treated: 33.50 MPa) and enhanced flexural modulus (direct
dye-treated: 3.33 GPa, basic dye-treated: 3.32 GPa). These
findings suggest promising applications across various
industries, including automotive components, construction
materials, and eco-friendly packaging solutions, where bio-
degradable, sustainable materials with improved mechani-
cal properties are highly sought after.
5|FUTURE SCOPE
The study lays a solid foundation for further exploration
and development in several areas. Future research
endeavors could focus on optimizing the dyeing process to
enhance the color strength and fastness properties of
banana fiber composites. Investigating alternative dyeing
techniques or exploring novel dye formulations could con-
tribute to achieving even better results. Additionally, there
2.36
2.38
2.4
2.42
2.44
2.46
2.48
2.5
RBPP BBPP DBPP
Tensile Modulus (GPa)
Status of Composites
FIGURE 9 Tensile modulus of composites.
41
41.2
41.4
41.6
41.8
42
42.2
42.4
42.6
42.8
43
43.2
RBPP BBPP DBPP
Flexural Strength (MPa)
Status of Composites
FIGURE 10 Flexural strength of composites.
3.22
3.24
3.26
3.28
3.3
3.32
3.34
3.36
RBPP BBPP DBPP
Flexural Modulus (GPa)
Status of Composites
FIGURE 11 Flexural modulus of composites.
BRAHMA ET AL.363
is scope for studying the impact of different pretreatment
methods on fiber strength retention to mitigate the
observed decline post-treatment, particularly in the case of
basic dye treatment. Further analysis using advanced spec-
troscopic techniques could provide deeper insights into the
bonding mechanisms between dyed fibers and the PP
matrix, paving the way for tailored composite formulations
with enhanced mechanical performance. Moreover, explor-
ing the potential of incorporating additives or modifiers to
improve the compatibility between banana fibers and the
polymer matrix could lead to the development of high-
performance composite materials. Finally, scaling up pro-
duction processes and conducting life cycle assessments to
evaluate the environmental sustainability of banana fiber
composites on a larger scale would be valuable for asses-
sing their viability and impact in real-world applications.
AUTHOR CONTRIBUTIONS
Shuvo Brahma: Conceptualization; methodology; inves-
tigation; writing—original draft. Sk. Mohammad Raafi:
Methodology; investigation; writing—original draft;
writing—review and editing. Sharfun Nahar Arju:
Supervision. Junaid ur Rehman: Writing—review and
editing. All authors have read and agreed to the pub-
lished version of the manuscript.
CONFLICT OF INTEREST STATEMENT
The authors declared no potential conflicts of interest
concerning the research, authorship, and/or publication
of this article.
DATA AVAILABILITY STATEMENT
The datasets supporting the conclusions of this study are
available upon request to the corresponding author,
Sk. Mohammad Raafi (E-mail: raafi@wpe.butex.edu.bd).
ORCID
Sk. Mohammad Raafi https://orcid.org/0000-0002-
1978-842X
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How to cite this article: Brahma S, Raafi SM,
Arju SN, Rehman Ju. Dyeability and mechanical
properties of banana fiber reinforced
polypropylene composite. SPE Polym. 2024;5(3):
353‐365. doi:10.1002/pls2.10129
BRAHMA ET AL.365
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