Open Journal of Composite Materials, 2012, 2, 133-138
http://dx.doi.org/10.4236/ojcm.2012.24016 Published Online October 2012 (http://www.SciRP.org/journal/ojcm) 133
The Effect of Curative Concentration on Thermal and
Mechanical Properties of Flexible Epoxy Coated Jute
Fabric Reinforced Polyamide 6 Composites
Smith Thitithanasarn1*, Kazushi Yamada1, Umaru S. Ishiaku2, Hiroyuki Hamada1
1Department of Advanced Fibro-Science, Kyoto Institute of Technology, Kyoto, Japan; 2Department of Textile Science and Tech-
nology, Faculty of Science, Ahmadu Bello University, Zaria, Nigeria.
Received May 25th, 2012; revised June 29th, 2012; accepted July 12th, 2012
ABSTRACT
Many researchers have shown interest in the reinforcement of commodity thermoplastic with natural fibers. However,
the drawback of natural fib ers is their low thermal processing temperatures, that border around 200˚C. In this investiga-
tion, we tried to improve the thermal stability of natural fibers with the use of flexible epoxy surface coating that could
facilitate processing with engineering thermoplastics. Jute fabric and Polyamide 6 (PA6) composites were prepared by
compression molding. The thermal decompos ition characteristics of the jute fab ric were evaluated by using thermo gra-
vimetric analysis (TGA). Mechanical analysis was conducted to evaluate tensile test and three point bending test of
composite. It was found that thermal degradation resistance of jute fabric was impro ved by coating with flexible epox y
resin. Moreover, the flexural modulus improved with increasing curative concentration. The interfacial interaction be-
tween the epoxy and PA6 was clearly indicated by the photo micrographs of the polished cross sections of the coated
and uncoated jute fabric/PA6 composites.
Keywords: Natural Fiber (Jute); Polyamine 6; Flexible Epoxy; Composites; Thermal Degradation; Mechanical
Properties
1. Introduction
In recent years, natural fibers such as sisal, hemp, abaca,
ramie, and jute have attracted the attention of researchers
because of the advantages that these fibers provide over
conventional reinforcement materials [1-5]. Natural fiber
exhibit many advanced properties such as low density,
low cost, high specific properties, recyclability and bio-
degradability [6,7]. Thus, natural fiber reinforced com-
posites have been show to yield properties suitable for
low stress application such as automotive, some part of
the air plan.
However, the disadvantages of natural fibers in ther-
moplastics are incompatibility between the hydrophilic
natural fiber and hydrophobic polymer [8-12]. Some re-
searchers have reported improvements in the mechanical
properties when compatibilizer used on the fiber were
chemically modified prior to mixing [13-16]. Rashed et
al. studied about jute fiber reinforced polypropylene. The
tensile strength was increased after alkalized treated jute
fibers [17]. Cao et al. reported 13% improvement in ten-
sile strength, 14% in flexural strength and 30% in impact
strength after fibers were treated with 1% NaOH solution
[18].
Another drawback seems to be the low thermal stabil-
ity of natural fibers, where the first degradation of natural
fiber occurs at temperatures above 200˚C [19]. Natural
fibers are therefore typically used with commodity ther-
moplastic matrix such as polypropylene (PP), polyethyl-
ene (PE), poly vinyl chloride (PVC) and polystyrene (PS)
with melting points that are lower than the degradation
temperature of the natural fibers [20].
S. C. Jana and A. Prieto [21,22] study about the de-
velopment of wood flour composites with high tempera-
ture thermoplastic polymers as the matrix resin. Wood
flour was miscible blend with curing agent for improving
thermal resistance of it. In the addition, poly (phenylene
ether) (PPE) was miscible blend with epoxy to reduce the
melting temperature of th e latter prior to incorporation of
wood flour through twin-screw extrusion. The composite
exhibited an improvement in mechanical performance
since low processing temperatures were used to prevent
extensive degradation to the wood flour whereas the ma-
trix itself exhibited high strength and stiffness. Thermo- *Corresponding a uthor.

The Effect of Curative Concentration on Thermal and Mechanical Properties of Flexible Epoxy Coated Jute Fabric
Reinforced Polyamide 6 Composites
134
setting polymers are among the most important materials
in many diverse industries and are being used increase
ingly in structural engineering applications. However,
these PPE composites indicated the lower thermal prop
erties as compared with original PPE injection molding
parts. On the other hand, we recently reported jute-fabric
reinforced engineering thermoplastic sandwich compos-
ites [23], and the jute fabric was pre-coated with thermo-
setting resin to improve their thermal resistance. As a
result, we have successfully to fabricate the high thermal
resistance natural fiber/engineering thermoplastics com
posites.
In this study, we try to enhance the thermal resistance
of jute fabric in order to facilitate their usage with engi
neering thermoplastics, i.e. polyamide 6. The jute fabrics
were coated with flexible epoxy resin to improve their
thermal resistance prior to molding of the composites. In
addition, the effect of the amount of curing agent to react
with jute fabric and epoxy resin was discussed. The
thermal decomposition characteristics of the jute fabrics
before and after coating were evaluated by using thermal
gravimetric analysis (TGA) while mechanical tests were
also performed to evaluate the performance of the com-
posites.
2. Experimental
2.1. Materials
The matrix resins used in this study was Polyamide 6
(PA6) (grade CM 1056) supplied by Toray Co., Ltd. The
flexible epoxy resin (grade PB 3600) and curing agent
(grade B 0231) were supplied by Daicel Chemical. Co.,
Ltd. Recycled woven jute coffee bags with a thickness of
approximately 0.5 mm provided by a coffee company in
Japan were us ed as the reinforcement.
2.2. Sample Preparation Methods
2.2.1. Pr e paration of Matrix Resin Sheet
PA6 pellets were dried at 120˚C for 8 hours. These pel-
lets were then used to form matrix sheets by compression
molding at 270˚C under a constant pressure of 10 MPa.
The pellets were pre-heated for 3 min while molding time
was 2 min. The molded sheets were then cooled for 3 min
prior to the release of pressure.
2.2.2. Surface Coating by Using Flexible Epoxy Resin
The jute fabrics were dried at 80˚C for 24 hours prior to
immersion in flexible epoxy. The flexible epoxy was
dissolved in acetone before using. The volume ratio be
tween flexible epoxy and acetone was 1:1. The concen
trations of curing agent for the flexible epoxy were varied
at 0, 5, 10, 15, and 20 wt%. After 2 minutes immersion,
the jute fabric were hung up and allowed to cure at 80˚C
for 2 hours in the oven. The thickness of the resin coating
was determined to be approximately 0.15 mm. The
weight content of each material was showed in Table 1.
2.2.3. Composites Fabricatio n
TGA measurements were carried out on the uncoated and
coated jute fabrics by using a thermo gravimetric ana-
lyzer (TGA) (TA Instruments 2950) over temperature
range of 40˚C to 600˚C at a heating rate of 50˚C/min.
Measurements were performed in air. The weight of all
samples was maintained around 5 mg.
2.3. Characterization
2.3.1. Thermogravimetric Analysis (TGA)
TGA measurements were carried out on the uncoated and
coated jute fabrics by using a thermo gravimetric ana
lyzer (TGA) (TA Instruments 2950) over temperature
range of 40˚C to 600˚C at a heating rate of 50˚C/min.
Measurements were performed in air. The weight of all
samples was maintained around 5 mg.
2.3.2. Fl ex ural Tes ting
The specimens were cut into strips in order to perform
3-point flexural test (ASTM D790) by using an Instron
4206 universal testing machine at 28˚C. Specimens of
125 mm length, 10 mm wide and 3 mm thickness were
cut from the composite such the jute warp oriented along
the length of the specimen. The flexural tests were con
ducted at a crosshead speed of 1 mm/min. Span length
was 48 mm. Tensile test was performed by the Instron
4206 universal testing machine at a crosshead speed of 1
mm/min. At least five composite specimens were test for
each condition.
2.3.3. Tensile Testing
Tensile testing was carried out with an Instron 4206 ma-
chine at 28˚C, according to ASTM D 3039, at a cross
head speed of 1 mm/min. At least five composite speci-
mens were test for each condition.
2.3.4. Morpho l ogy Studi es
A scanning electron microscope (JEOL, JSM5200) was
used for morphology studies of the gold sputtered frac
ture surfaces of the composites. The polished cross-sec-
tions of the composites were observed by using a digital
microscope (Keyence VH-S30). The specimens were
finely polished to a mirror finish by gradually changing
the roughness of the polishing medium from coarse to
fine (i.e. polishing paper index from 200 to 400, 800,
1200, and 2000) with constant water flow over the
specimen and polishing papers to prevent the specimens

The Effect of Curative Concentration on Thermal and Mechanical Properties of Flexible Epoxy Coated Jute Fabric
Reinforced Polyamide 6 Composites 135
Table 1. Weight content of each material.
Materials Weight content (wt% of composites )
Jute Fabric 10.73
Flexible Epoxy 8.72
PA 6 80.53
Figure 1. Schematic representation of the compression
molding process.
from being damaged by heat and also to flush away the
debris. Further polishing using graded alumina suspen-
sions in water was performed. The alumina practice size
was gradually changed from 1.0 to 0.1 and finally 0.05
µm (3 min for each polishing stage). The polished speci-
mens were thoroughly washed to discard any residue by
immersing the specimens into an ultrasonic cleanser
filled with clean water for 15 minutes.
3. Result and Discussion
3.1. Thermal Degradation Resistance of Jute
Fabric
Figure 2 shows the TGA thermograms of uncoated and
coated jute fabrics containing 5 wt% of curing agent. It
can be seen that uncoated jute fabrics started to degrade
considerably after 270˚C. Meanwhile, the fabrics coated
with flexible epoxy resin recorded an onset degradation
temperature of 355˚C. This indicates that the thermal
degradation resistance of jute fabric can be significantly
improved with the flexible epo xy coating.
The effect of curing agent concentration on thermal
degradation resistance of flexible epoxy coated jute fibers
is shown in Figure 3 Although the thermal degradation
resistances of all epoxy coated jute fibers were higher
than the uncoated fibers, the onset degradation tempera
ture decreased with increasing curing agent content. Thus
indicating that 5 wt% of curing agent is the optimum
concentration as thermal degradation resistance decreased
at higher curing agent concentrations. The lower degra
dation temperature at high curing agent contents could be
due to the presence of flammable residue from the curing
Temperature (˚C)
Figure 2. TGA thermograms of flexible epoxy, uncoated and
flexible epoxy coated jute fabrics.
Figure 3. Onset degradation temperatures of uncoated and
coated jute fabrics with flexible epoxy.
agent. However, the incorporation of curing agent is un-
avoidable since it is important for the epoxy coating on
the jute fibers to solidify prior to composite fabrication.
Therefore, it is thought that the usage of 5 wt% curing
agent is sufficient for curing of the resin as it provides
good thermal stability to the ju te fibers.
3.2. Effect of Surface Coating on Mechanical
Properties
The flexural moduli of composites of uncoated and
coated jute fabrics as compared to neat PA6 are elabo-
rated in Figure 4. The flexural modulus of the matrix and
uncoated jute fabric are found to be 2.35 and 2.65 GPa,
respectively. For the coated jute fabric, the flexural
modulus increased with increasing curing agent content.
This indicates that the flexural modulus can be improved
when curing agent content increased due to the increased
stiffness of the fabric after coating with flexible epoxy.
Figure 5 shows the flexural strength of the compo-
sites as compared with neat PA6. The flexural strength of
neat PA6 and uncoated jute composites are similar, with
the coated composites showing lower to higher values
with increasing curative concentration. The Low flexural

The Effect of Curative Concentration on Thermal and Mechanical Properties of Flexible Epoxy Coated Jute Fabric
Reinforced Polyamide 6 Composites
136
strength of coated jute composites at lower curative con-
tent could be due to incomplete curing of the epoxy.
However, the flexural strength increased with increasing
curing agent concentration that could be attributed to
high crosslinking of flexible epoxy resulting in improved
strength of the fabric and consequently affected on rein-
forcement of the matrix.
Figure 6 elaborates the tensile modulus of composites
Figure 4. Effect of curing agent concentration on the flex-
ural modulus of PA6 reinforced with flexible epoxy coated
and uncoated jute fabric.
Figure 5. The effect of curing agent concentration on the
flexural strength of PA6 reinforced with flexible epoxy
coated and uncoated jute fabric.
Figure 6. Effect of curing agent concentration on the Tensile
modulus of PA6 reinforced with flexible epoxy coated and
uncoated jute fabric.
of uncoated and coated jute fabric as compared to neat
PA6. The tensile modulus of the uncoated jute composite
and neat PA6 are found to be 1.38 and 1.21 GPa, respec-
tively. It is obvious that the uncoated jute fabric shows
superior tensile modulus as compared to the coated com-
posites with the exception of the 20 wt% concentratio n. It
should be noted that PA6 is not a hydrophobic matrix
[6-10] and therefore good interfacial interaction is ex-
pected to arise from hydrogen bonding between jute sur-
face and PA6. For the coated jute fabric, the tensile
modulus of the composites is lower than the uncoated
jute albeit the tensile moduli of coated jute increased
slightly with increasing curing agent content. It can be
seen that tensile modulus can be slightly improved by
flexible epoxy when curing agent content increased.
Moreover, tensile strengths of coated jute composites
as shown in Figure 7 are all weaker than the uncoated
jute composite. This result is contrary to expectation as
natural fibers are known to have good interfacial interac-
tion with epoxy [6-10] while the epoxy is expected also
to serve as a good compatibilizer between jute and PA6
matrix since it is situated in between them and it interacts
positively with bo th. This contradiction in tensile proper-
ties can be explained by the fact that the epoxy has been
cured prior to the composite fabrication stage. As epoxy
is a thermoset that becomes intractable when cured, sub-
stantial chemical interaction failed to occur during the
composite fabrication so the interface between the flexi-
ble epoxy and PA6 is weak and that could be the source
of the weakness of the coated composites. This notion is
clarified by the polished cross sections of the composites
as discussed later.
3.3. Morphology Studies
Figures 8(a)-(c) show the SEM micrographs of the ten-
sile fracture surfaces of uncoated and coated jute fibers. It
can be seen from Figure 8(a) that the fiber/matrix inter-
facial bonding between jute an d PA6 is quite strong. Th is
is indicated by the lack of fiber pull out and the fact that
the matrix and fibers fractured on the same plane. The
strong interfacial interaction could be due to hydrogen
bonding between the jute fibers and PA6. Similarly
strong interfacial bonding is displayed by the flexible
epoxy coating and jute fibers in Figures 8(b) and (c) for
the 0 wt% and 20 wt% curative contents respectively.
This is expected as epox y is known to have good interfa-
cial interaction with natural fibers. However, the poor
mechanical properties of the epoxy coated jute/PA6
composites could be traced to the poo r interfacial interac-
tion between the fully cured epoxy and PA6 as revealed
by the photo micrograph of the polished cross section of
the epoxy coated jute/PA6 composites.
Figure 9(a) elaborates the photo micrograph of the

The Effect of Curative Concentration on Thermal and Mechanical Properties of Flexible Epoxy Coated Jute Fabric
Reinforced Polyamide 6 Composites 137
polished cross section of the uncoated jute fabric/PA6
composite. The fiber bundles in the warp and weft direc-
tions are clearly indicated with adequate wetting by the
matrix and free from imperfections. However, Figure 9(b)
shows a lot of distortions and cracks along the interface
between flexible epoxy and the PA6 matrix. Even though
positive interaction is predicted between the epoxy and
PA6 matrix, imperfections arose from the inability of the
already cured epoxy to adequately interact with PA6.
Being a thermoset, epoxy becomes intractable when
cured and so it could not melt and interact with PA6 dur-
ing the composite fabrication stage. This accounts for the
poor interfacial interaction between epoxy and PA6 and
Figure 7. Effect of curing agent concentration on the tensile
strength of PA6 reinforced with flexible epoxy coated and
uncoated jute fabric.
Figure 8. SEM micrograph of the tensile fracture surface of
jute fabric/PA6 composite; (a) Uncoated; (b) Curing agent 0
wt%; (c) Curing agent 20 wt%.
Figure 9. Photo micrograph of the polished cross section of
jute fabric/PA6 Composite; (a) Uncoated jute fabric; (b)
Coated jute fabric.
hence the poor tensile properties of the epoxy coated
jute/PA6 composites.
4. Conclusion
This paper investigation intended to improve the thermal
stability of natural fibers with the use of surface treat-
ments i.e. flexible epoxy so that the natural fiber can be
processed with high temperature engineering thermoplas-
tics. It was found that the flexible epoxy coating was able
to improve the thermal degradation resistance of jute fi-
bers with the best result given by 5 wt% curative concen-
tration. However, flexural properties improved continu-
ously with increasing curative concentration. The epoxy
coated jute fabric composites showed inferior tensile
properties as compared to the uncoated jute fabric com-
posite albeit the properties increased with increasing
curative content. SEM studies revealed strong fiber/
matrix interfacial bonding for both coated and uncoated
jute fabric composites. The inferior tensile properties of
the resin coated jute compo sites could be attributed to the
poor interfacial interaction between the flexible epoxy
coating and the PA6.
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