Advances in Materials Physics and Chemistry, 2011, 1, 78-85
doi:10.4236/ampc.2011.13013 Published Online December 2011 (
Copyright © 2011 SciRes. AMPC
Effects of Fiber Weight Ratio, Structure and Fiber
Modification onto Flexural Properties of Lu ffa-Polyester
Lassaad Ghali1, Slah Msahli1, Mondher Zidi2, Faouzi Sakli1
1Textile Research Unit, ISET of Ksar Hel l al , Ksar Hellal, Tunisia
2Laboratory of Mechanical Engineering, ENIM of Monastir, Monastir, Tunisia
Received August 4, 2011; revised Se ptember 12 , 2011; accepted Sept ember 26, 2011
The effect of chemical modification, reinforcement structure and fiber weight ratio on the flexural proprieties
of Luffa-polyester composites was studied. A unsaturated polyester matrix reinforced with a mat of Luffa
external wall fibers (ComLEMat), a short Luffa external wall fibers (ComLEBC) and a short Luffa core fi-
bers (ComLCBC) was fabricated under various conditions of fibers treatments (combined process, acetylat-
ing and cyanoethylating) and fiber weight ratio. It resorts that acetylating and cyanoethylating enhance the
flexural strength and the flexural modulus. The fiber weight ratio influenced the flexural properties of com-
posites. Indeed, a maximum value of strength and strain is observed over a 10% fiber weight ratio. The uses
of various reinforcement structures were investigated. The enhancement of elongation at break and the strain
values of the composite reinforced by natural mat was proved.
Keywords: Luffa Fibers, Composite, Flexural Properties, Fiber Weight Ratio
1. Introduction
A combination of properties of some natural fibers in-
cluding low cost, low density, non-toxicity, no abrasion
during processing and recyclability has arisen more in-
terest for the manufacturing industry of low cost and low
weight composites [1-2].
The composite materials reinforced with natural fibers
are used in many fields such as automotive industry,
aeronautics and naval [3] .
Despite the advantages of cellulosic fibers reinforcing
thermoplastics, the polymer-cellulose composites mate-
rials are criticized for their low permissible processing
temperatures and highly hydrophilic property associated
with a low compatibility of hydrophobic polymers as
well as a loss of mechanical proprieties after moisture
uptake [2 -4 ].
Due to the poor compatibility, the surface of fibers
must be treated to improve the adhesion between fiber
and matrix. Beldzki et al. [1] reported many methods to
modify the surface of natural fibers for their use in com-
posite materials such as acetylation, alkali and isocy-
anates treatments. Saha et al. [5] studied the effect of
cyanoethylation on the mechanical properties of jute fi-
ber reinforced polyester composite. They noted that a
better creep resistance at lower temperatures was ob-
tained for the composite reinforced with cyanoethylated
jute fibers. According to Saha et al. [6], it has been found
that cyanoethylation of jute improved flexural strength
and modulus by 62% and 39%, respectively.
Results published in the open literature have indicated
the increase of flexural strength of the heigh-density
polyethylene (HDPE)-henequen by 36% after silane
treatment [2]. The contributio n of acetylation, propionyla-
tion, malaeic anhydride and styrene on the mechanical
properties of obtained composites was investig ated [7,8].
An increase in the interfacial shear strength between ac-
etylated fibers and hydrophobic resins was reported [9].
However, acetylation made the fibers more hydrophobic
by reacting its hydroxyl groups with acetyl groups [10].
The alkali treatments changed the mechanical proprieties
of Luffa [11] and sisal fibers [1] reinforced polyester
resin. They showed that the flexural mechanical proper-
ties increased with alkali treatment and explained this
enhancement by the incr ease of fiber roughness and con-
tact area. These results were corresponding to those ob-
tained with bagasse and bamboo fibers composites [13,
In addition, the mechanical properties of composites
reinforced with natural fibers were influenced by the
fibers ratio and the reinforcing structure. According to
Rao et al. [15], for example, and the flexural strength of
vakka, sisal, bamboo and banana reinforced composites
increased with fiber volume fraction. Good mechanical
properties of different fibers reinforced composites were
obtained for various amount of fiber ratio [15 -1 9] .
In the case of Luffa fibers composites, Demir et al. [20]
had studied the influence of chemical modification by
silane coupling reagents on Luffa fiber reinforced poly-
propylene composites. Boynard et al. [11] studied also
the flexural properties of Luffa fibers reinforced polyes-
ter composite. They noticed that the flexural modulus
increased by 14% after fibers Alkali treatment. In an-
other study, Tanobe et al. [21] characterized the chemi-
cally modified Luffa fibers with methacrylamide and
NaOH. However, other chemical modifications, rein-
forcing structure and fiber weight ratio onto Luffa fibers
composite were still not investigated. Therefore the aim
of this study is to explain the variations of the flexural
proprieties of the composites Luffa-polyester with those
of fibers weight ratio, structure (short fibers and mat) and
treatments (acetylation and cyanoetylation).
2. Materials and Methods
2.1. Fibers Extraction
In this experimental study, many structures of Luffa fi-
bers were used. These fibers can be extracted from the
external wall of sponge (LE) or from its core (LC). The
external wall Luffa fibers were used as a vascular fibrous
network (LEMat) or shelled and cut fibers (LEBC). A
Shirley analyser instrument was used to shell the fibrous
network. The core Luffa fibers were also shelled and cut
(LCBC) to be used as short fibers reinforced polyester
The Shirley Analyzer uses a cleaning technique com-
bining mechanical and airflow actions as follows:
Luffa fibers are taken by a feed roller to be presented
to the following parts of the machine;
The taker-in with the help of its needles opens the mass
of the fibers so that it can be cleaned later in the machine;
A variable airflow separates used fibers and dust and
trash by the use of performed roller.
Finally, the guard fibers and waste are collected in the
trash tray and used fibers are recovered in the fibers box.
The various forms of Luffa fibers were chemically ex-
tracted using an optimized solution containing 4% of
sodium hydroxide and 10% of hydrogen peroxide at
100˚C during 2 hours. Samples were then washed and
dried. This treatment is called a combined process [22].
It was used to remove waxy and gummy substances such
as lignin and hemicellulose.
2.2. Surface Modification of Fibers
The first modification method of Luffa fibers is the ac-
etylating. Samples of Luffa fibers treated with combined
process were added to a round bottomed flask with suffi-
cient acetic anhydride and brought to the desired reaction
temperature of 100˚C for 3 hours [7]. The fibers were
washed using acetone in ambient temperature to ensure a
good removal of acetic anhydride.
The second method used in this study is the cyano-
ethylating. The Luffa fibers were dried for 4 h at 80˚C. A
2 g of Luffa fibers were impregnated with a sodium hy-
droxide solution for 2 min at ambient temperature. The
fibers were hydro extracted to about 90% wet pickup.
The alkali soaked fibers were then put in round bottomed
flask containing acrylonitrile solution. The fiber weight
to acrylonitrile solution ratio of 1:20 was maintained. In
this study toluene was chosen as a diluent for a series of
experiments in which the concentration of acrylonitrile
was fixed at 50%. The alkali concentration, temperature
and time reaction were kept unchanged, i.e., 4%, 60˚C
and 60 min were considered [23]. After a stipulated time
of reaction, the fibers were thoroughly washed with 5%
acetic acid solution and finally with distilled water. The
fibers were then dried at 80˚C until constant weight was
To identify the chemical modifications at fiber surface,
infrared spectroscopy analysis of treated and untreated
fibers was conducted using an IR-840 SHIMADZU
spectrometer. A mixture of 5 mg of dried fibers and 200
mg of KBr was pressed into a disk for FTIR measure-
ments. 100 scans were collected for each measurement
over the spectral range between 400 - 4000 cm–1. All the
IR spectra presented in this work were obtained in an
absorbance mode.
2.3. Composites Preparation
The treated and untreated Luffa fibers were used to rein-
force an unsaturated polyester matrix. The composites
were manufactured manually by placing the mixture of
fibers and resin inside a mould. In order to remove en-
trapped air bubbles and also enabled manufacturing all
uniform thickness composites, the mould was closed and
2.4. Flexural Test
After composite material preparation, test samples hav-
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Copyright © 2011 SciRes. AMPC
ing dimensions of (80 × 15 × 4) mm3 were cut for the
mechanical characterization with the three-point bend ing
flexure test according to the standard EN ISO 14125
pure polyester specimen (PES), polyester reinforced by
untreated Luffa fibers, polyester reinforced by Luffa fi-
bers treated with combined treatment, polyester rein-
forced by acetylated Luffa fibers and polyester rein-
forced with cyanoethylated Luffa fibers.
The flexural properties of polyester samples and poly-
ester reinforced by treated and untreated Luffa fibers
were made using a universal testing machine LLOYD
with a 10 mm/mn test speed. The flexural strength (
the flexural modulus (
E) and the surface elongation at
break (
) are calculated respectively by:
Table 1 shows the results of three points bending
flexural test of polyester matrix reinforced with the ex-
ternal wall Luffa fibers.
It can be noted from Table 1 that the reinfo rcement of
polyester matrix with external wall Luffa fibers changes
the flexural proprieties of composite material. In fact, the
initial flexural modulus decreased from 3.4 GPa for the
unreinforced polyester matrix to 2.45 GPa for the Com-
LEMat treated with combined process. The stress and
deformation at break were increased with the addition of
fibers mat. Thus, the flexural stress increased slightly
from 41.3 MPa for unreinforced polyester matrix to 42.79
MPa for the untreated Luffa fibers reinforced polyester
matrix. We can notice also the decrease of the mechani-
cal properties of the composite reinforced with Luffa
fibers treated with co mbined process. This decrease could
be due to a degradation of fibers during the chemical
treatment or to a low cohesion between fiber and matrix.
In fact, the SEM micrographs of Luffa fibers treated with
combined process showed an opened structure (Figure 1).
Ebh w
where F is the maximum load (N), L the range (mm), h
the specimen thickness (mm), b the specimen width (mm)
and w indicates the defection (mm).
3. Results and Discussions
The three point bending flexure tests were carried out on
Table 1. Flexural proprieties of ComLEMat.
Specimen Fiber treatment Fiber weight ratio (%) f
E (GPa) f
ComLEMat Combined process 5.03 2.45 34.17 1.47
ComLEMat Acetylating 5.04 3.29 52.3 1.79
ComLEMat Cyanoethylating 5.27 2.55 41.81 1.72
ComLEMat Untreated 4.93 3.05 42.79 1.61
PES - - 3.4 41.3 1.38
Figure 1. SEM micrographs of Luffa fibers extracted with combined process.
Copyright © 2011 SciRes. AMPC
This opened structure showed the ultimate Luffa fibers.
This individualization lost the technical Luffa fibers its
cohesion therefore its strength.
The weak interface between fiber and matrix was im-
proved by acetylation and cyanoethylation of Luffa fi-
bers. Thus, the properties of the composite reinforced
with surfaces treated fibers increased. The composites
became more deformable and resistant. The infrared spec-
tra examination presented by Figures 2(b)-(c) confirmed
that the Luffa fibers extracted with combined process
were modified by acetylation and cyanoethylation.
Moreover, the treatment of Luffa fibers with acetic an-
hydride led to the appearance of an absorbance peak in
the regions o f 1743 and 1 243 c m–1. Th e pe ak obs erved at
2254 cm–1 confirmed the apparition of acrylonitrile
groups on the surface of Luffa fibers.
It’s important to indicate that the good cohesion be-
tween fibers and matrix is governed by many parameters
such as the surface area, the roughness and the surface
tensile of fibers. In fact, the acetylation and cyanoethyla-
tion made the fibers more hydrophobic by the substitu-
tion of hydroxyls groups with acetyls and cyanoethyls
groups [6,7].
The SEM micrographs of the fracture surface of com-
posite specimens reinforced with treated and untreated
Luffa fibers presented in Figure 3 showed that adhesion
between fiber and matrix enhances with the chemical
treatments. In fact, as shown in Figure 3(a), before
modification, the wettability between Luffa fibers and
unsaturated polyester matrix seemed to be poor because
of the presence of a gap between the two componements.
This gap is much less visible in the case were the fibers
were treated with combined process (Figure 3(b)).
In the other cases (Figures 3(c)-(d)) we can remark
that the matrix surrounding the fibers led to a good adhe-
sion. This result confirmed the enhancement of me-
chanical proprieties of composite reinforced with acety-
lated and cyanoethylated fibers. Thus, when the Luffa
fibers were treated with acetic anhydride and acryloni-
trile, the gap is much less pronounced and an improved
interface corroborated well the enhancement of the pre-
viously mechanical properties observed in Table 1.
Figure 4 shows the variation of the flexural modulus
and the flexural strength of the composite LCBC treated
with combined process—polyester with the increase of
the fiber weight ratio. The curves present two variation
zones. In the first zone, the flexural modulus and the
ultimate strength reached a maximum values at about
8.5% and 11% of Luffa fibers content, respectively.
Thereafter, the two flexural proprieties appear to de-
crease steadily. Similar results were reported elsewhere
[24], indicating this is a typical characteristic of fiber
composites since higher fiber weight ratio often results in
more defects owing to fiber contacts.
For the case of the composite LEBC fiber treated with
combined process-polyester matrix (ComLEBC com-
bined), the Figure 5 shows the variation of flexural
modulus and strength with the variation of fiber weight
ratio. We can note that the flexural strength and modulus
increase to reach a maximum at about 8% of Luffa fiber
weight ratio. Thereafter, the flexural modulus decreased
steadily and the flexural strength falls slightly.
Figure 2. Infrared spectra of Luffa fibers (a) treated with combined process; (b) acetylated; and (c) cyanoethylated.
Figure 3. SEM micrographs of fracture surface of: (a) ComLEBC untreated; (b) ComLEBC combined; (c) ComLEBC acety-
lating; (d) ComLEBC cyanoethylating.
Figure 4. Influence of Luffa fibers weight ratio onto mechanical proprieties of ComLCBC combined.
The effect of fiber weight ratio on the flexural elonga-
tion at break of various Luffa composites is shown in
Figure 6. The elongation at break values of the compos-
ite ComLEMat are higher than the results obtained with
composites reinforced with short Luffa fibers (Com-
LEBC and ComLCBC).
Copyright © 2011 SciRes. AMPC
This result indicates the variation of the mechanical
behaviour with the change of the reinforcement structure.
In the first step, the flexural elongation at break in-
creased and reached a maximum for a fiber weight ratio
at about 10% for the composite reinforced with mat of
Luffa fibers. In the second step, the elongation at break
dropped off steadily. For the polyester composites rein-
forced with short Luffa fibers, the elongation at break
increases to maxima at about 11% of fiber weight ratio.
Thereafter, the elongation at break decreases slightly.
As shown also in Figure 5 that the two curves of elon-
gation at break for the polyester composites reinforced
with short Luffa fibers have the same shape. The elonga-
tions at break values of ComLCBC combined are higher
Figure 5. Influence of Luffa fibers weight ratio onto mechanical proprieties of ComLEBC combined.
Figure 6. Relationship between the reinforcement structures and elongation at break of Luffa-polyester composite.
Copyright © 2011 SciRes. AMPC
Copyright © 2011 SciRes. AMPC
than those of ComLEBC combined.
4. Conclusions
In this study the influence of fiber modification and the
reinforcement structure on the flexural proprieties of
Luffa-polyester composite were investigated. The varia-
tion of these properties with the rise of fiber weight ratio
was also studied. It is clear that the acetylating and
cyanoethylating treatments of Luffa fibers enhanced the
adhesion between fiber and matrix. Those treatments
replaced the free hydroxyl groups of cellulose structure
by acetyl and cyanoethyl groups respectively. Neverthe-
less the combined process treatment decreased the flex-
ural proprieties of composite compared to the composite
reinforced with untreated fibers. This result is due to the
fiber degradation under several chemical conditions.
The uses of various reinforcement structures were in-
vestigated. The enhancement of elongation at break of
the composite reinforced by natural mat was proved.
The study of the relationship between fiber weight ra-
tio and the flexural proprieties of Luffa-polyester com-
posites is confirmed by many research reported else-
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