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INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING-GREEN TECHNOLOGY Vol. 1, No. 3, pp. 241-246 JULY 2014 / 241
© KSPE and Springer 2014
Plasma-treated Abaca Fabric/Unsaturated Polyester
Composite Fabricated by Vacuum-assisted Resin
Transfer Molding
Marissa A. Paglicawan1,#, Byung Sun Kim2, Blessie A. Basilia1, Carlo S. Emolaga1,
Delmar D. Marasigan1, and Paul Eric C. Maglalang1
1 Department of Science and Technology, Industrial Technology Development Institute, Bicutan, Taguig City, Philippines, 1631
2 Korea Institute of Materials Science, 797 Changwongdaero, Seongsangu, Changwon, Gyeongnam, South Korea
# Corresponding Author / E-mail: mapaglicawan@yahoo.com;mapaglicawan@dost.gov.ph, TEL: +632-837-2071, FAX: +632-8373167
KEYWORDS: Abaca fiber, Composite, Vacuum assisted resin transfer, Mechanical properties
To improve the adhesion and wetting between the abaca fibers and matrix, the surface of abaca fabric was modified using plasma
polymerization. Different plasma exposure times were conducted to determine the effect of plasma treatment on the properties of the
composites. A combination of plasma and other surface modification processes was also investigated to determine whether double
treatments could further enhance the properties of these composites. Combined treatments involve plasma polymerization of the fabric
after pretreatment with one of the following surface-modification reagents: a) γ-methacrylopropyltrimethylsilane, b)
triethoxyvinylsilane, and c) 2%w/w NaOH (aq).The abaca fabric/unsaturated polyester composites were fabricated using the vacuum-
assisted resin transfer molding (VARTM) technique.SEM results showed that 10 to 20 seconds plasma treatment gave the right amount
of surface roughness for maximum fiber and matrix adhesion leading to improved mechanical properties of the composites. Longer
plasma treatment time and double treatment however resulted in composites with lower mechanical properties. Although the
composite with alkali and plasma-treated fabric showed the lowest mechanical properties it exhibited the lowest water uptake in both
distilled water and brine solution.
Manuscript received: May 6, 2014 / Revised: June 2, 2014 / Accepted: June 3, 2014
1. Introduction
The high price of synthetic fibers and the demands for environment-
friendly materials led to the search for new reinforcing materials that
are both cheap and environment-friendly. The use of natural fiber in
composites does not only help reduce dependence on non-renewable
energy/material sources but also lowers pollutant and greenhouse gas
emissions, enhances energy recovery, and end of life biodegradability
of components. The mechanical properties of natural fiber composite
can compete with that of the synthetic with better fiber treatment and
appropriate processing technique.1 The components of natural fibers
include cellulose, hemicellulose, lignin, pectin, waxes and water
soluble substances. They fall into three major types: bast fiber, core
fiber, and leaf fiber. The percent composition depends on the fiber
source. Abaca for example is composed of around 60% cellulose, 15 to
17% hemicellulose or pentosan, 7 to 9% lignin, and 3% ash.2,3
Knowledge of the chemical composition and surface bonding
properties of natural fibers is essential for developing natural fiber
reinforced composites.4-6 Tropical countries like the Philippines abound
with fibrous plants, some of which are agricultural crops.Abaca is in
fact one of the top export earners for the country. Abaca fiber, known
as Manila hemp, is extracted from the stalk of the plant Musa textiles
Nee. Abaca is similar to banana in appearance except that the leaves
are upright, pointed, narrower and more tapered than the leaves of
banana. It is considered as one of the strongest natural fibers being
three times stronger than sisal fibers. Abaca is also far more resistant
to salt water decomposition than most of the vegetable fibers. The
presence of strongly polarized hydroxyl groups in lignocellulose-
derived natural fibers make them hydrophilic. These fibers, therefore,
are inherently incompatible with hydrophobic thermoplastics and
thermosets which are the commonly used matrices for fiber-reinforced
composites. When unmodified natural fibers are used as reinforcements
in such matrices, poor interfacial adhesion between polar, hydrophilic
fiber and non-polar, hydrophobic matrix, and difficulties in mixing due
DOI: 10.1007/s40684-014-0030-3
242 / JULY 2014 INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING-GREEN TECHNOLOGY Vol. 1, No. 3
to poor wetting of the fiber with the matrix occur. This in turn leads to
composites with weak interface. In addition, poor fiber-matrix
interaction and the fiber’s low resistance to moisture have unfavorable
effect on the long term properties of the composite. On the other hand,
good fiber-matrix interaction can substantially improve the moisture
resistance of the composite.7 Several researchers have attempted to
improve the interfacial bonding between the natural fibers and the
matrix by altering the hydrophilic nature of the fibers. Several methods
to achieve this include chemical treatment,8-14 acetylation of the
hydroxyl group of the fibers,15 post-treating with urotropine and urea16
and the well-known process of alkali treatment.10,14-16 Alkali treatment
has the potential of improving fiber strength by removing lignin, hemi-
cellulose, and pectin. Chemical modification of fiber surface may
activate hydroxyl groups or introduce new moieties that can react with
hydroxyl groups of the matrix, elimination of weak boundary layers
and improvement of the wetting between the matrix and fibers. This
reduces fiber diameter resulting to an increase in aspect ratio.16 Alkali
treatment also increases fiber roughness. On the other hand, plasma
treatment using atmospheric glow discharge (AGD) with plasma source
using high voltage radio frequency (RF) was used to effect both fiber
roughness and polymerization on the fiber surface (by introducing the
appropriate monomer into the chamber).
In this study, plasma polymerization and plasma polymerization in
combination with other surface modification processes (pretreatment of
fiber with alkali and silane coupling agents) was applied to abaca
fabrics. The mechanical properties and water absorption of the surface-
modified abaca fabric reinforced composites were then investigated.
The interfacial adhesion between the fiber and the matrix was
determined from the morphology of the fractured surface of the
composites. It is also the aim of the study to determine the mechanical
performance of composites fabricated by Vacuum Assisted Resin
Transfer Molding (VARTM) since in our knowledge this technique has
never been applied to unsaturated polyester and natural fiber.
2. Materials and Methods
2.1 Materials
The abaca fibers used in this study were selected from the variety
coded as S-2 and S-3 from Bicol region of the Philippines (Fig. 1(a)).
The fibers were weaved into fabrics in 0/90 orientation with 3-ply in 0
degree (welf) and 1 ply in 90 degree (warp) as shown in Fig. 1 (b)&(c).
The matrix used in this study is the unsaturated polyester resin (RGP-
10-103) with styrene monomer, cobalt napthanate and methyl ethyl
ketone peroxide (MEKP). All of these reagents were purchased from
Polymer Products Inc, Philippines. The silane coupling agents used
for surface treatment, triethoxyvinylsilane (trisilane) and γ-
methacrylopropyltrimethylsilane (methasilane), were purchased from
Japan. Other chemicals such as sodium hydroxide and acrylic acid were
used without further purification.
2.2 Surface Modification
2.2.1 Alkali Treatment
The abaca fabric was soaked in 2% w/w NaOH (aq) solution for 30
minutes at room temperature. This condition was established after
optimizing the alkali solution concentration, soaking time, and soaking
condition (room temperature or boiling temperature) in the preliminary
experiments. The alkali-treated fabric was then rinsed repeatedly with
distilled water until the rinsingreaches pH 7 as monitored by pH meter.
The alkaline treated fabric was air-dried for 2 to 3 days and stored in
zip lock bags. The moisture content of the fabricas determined by
digital moisture meter (Denver IR-60) was about 5-7%.
2.3 Silane Coupling Agent Treatment
Two types of silane coupling agent were used to modify the surface
of abaca fabric: triethoxyvinylsilane (referred here as tri-silane) and γ-
methacrylopropyltrimethylsilane (referred here as metha-silane). The
abaca fabric was washed with water for several times and then dried
prior to treatment. Both silane treatments follow the following steps: 1)
0.8 g silane was added to 20 mL of solution of acetone/acidified water
(95:5 v/v, pH 3) to form a hydrolyzed silane solution. The solution was
left for 15 minutes; 2) The pre-dried fibers were immersed in the
solution, and 3) the treated fabric was air dried for 24 hours and oven
dried at 60oC for 24 hours.
2.4 Plasma Polymerization Treatment
Plasma treatment was generated in glow discharge manner which
was operated in closed and semi-automatic system. The sample was
placed on the ground electrode in the middle of the reactor. As shown
in Fig. 2, the abaca woven fabric was placed between the electrode
plates where the plasma polymerization takes place. Helium was used
as purging gas and as carrier gas of the acrylic acid monomer that will
create a thin hydrophobic layer on the surface of the fabric during
plasma-initiated polymerization.17 The frequency and voltage were
20 kHz and 3 kV, respectively. The fabric was exposed to plasma at
different duration (10 seconds, 20 seconds, 30 seconds, 60 seconds, and
120 seconds). Another set of fabrics which were previously treated
with 2 wt% NaOH for 30 minutes, 1% triethoxyvinylsilane, and 1% γ-
Fig. 1 Digital photo of abaca (a) fiber and (b) woven fabric, and (c)
schematic representation of the weave orientation of the fabric
Fig. 2 Plasma polymerization set-up. (a) schematic diagram of the set-
up and (b) placing the fabric inside the chamber
INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING-GREEN TECHNOLOGY Vol. 1, No. 3 JULY 2014 / 243
methacrylopropyltrimethylsilane were also subjected to plasma
polymerization for 10 seconds to see whether the double treatment
results to some synergistic effect on the mechanical properties of abaca
fiber-reinforced composites.
2.5 Vacuum-assisted Resin Transfer Molding (VARTM)
VARTM has been used in many applications because of its
capability of fabricating composites with good quality at a shorter time
and at a relatively low cost. The basic steps in the VARTM fabrication
process include: 1) Mold preparation and fabric lay-up; 2) Sealing the
mold and creating a vacuum; 3) Preparation and degassing of the resin;
4) Resin transfer; 5) Curing of the composite.
2.6 Characterization
The morphology of the fiber was examined using a Table Top SEM
(Hitachi TM 3000). The images were taken at magnification of 180x
and 500x. The morphology of the composites and interfacial bonding
between the fiber and the unsaturated polyester matrix was examined
using a Field Emission Scanning Electron Microscope (Helios
NanoLab 600i) to study the changes in the fractured surfaces of the
composites. The samples were taken at magnification of 100x. The
infrared spectra of raw and treated abaca were recorded on a Perkin
Elmer Spectrum RX1 at a scan range of 4000-500 cm-1 to characterize
any chemical change upon treatment of abaca with NaOH, plasma, and
other surface treatments.
2.7 Mechanical Testing
The tensile tests after conditioning at 25oC were carried on universal
testing machine model Instron 5882 equipped with a 5-kg load cell.
The tests were performed in accordance with ASTM standards D3039.
The crosshead speed used was 5 mm/min for tensile testing. For the
flexural test (three-point bending), specimens with nominal dimensions
of 50 mm ×25 mm ×2.5 mm, a span length of 90 mm and a crosshead
speed of 0.7100 mm/min were used. The tests were performed in
accordance with ASTM standards D790-07. The izod impact test was
performed in accordance with ASTM D 256. The dimensions of the
specimen are 63.5 mm ×12.7 mm ×3 mm. All the samples were cut in
welf direction. The average values of the mechanical properties were
obtained from 6 specimens.
2.8 Water Absorption
The dried and weighed specimens were immersed in distilled water
for 24 hours and 144 hours in accordance with ASTM D5229. The
specimens were cut into 25.5 ×25.5 ×2mm
3. Prior to absorption
experiments, five specimens for each treatment were dried in an oven
for 24 hours at 102±3oC. For each measurement, specimens were
removed from the water and the surface water was wiped off using
blotting paper. Weight change measurements were made using a micro-
balance. The values of water absorption in percentage were calculated
as follows:
WA ( %)t=(Mc −Mo)/Mo×100
where WA (t) is the water absorption at time t, Mo is the mass of the
dried specimen and Mc is the mass of the specimen as a function of
immersion time.
3. Results and Discussion
3.1 Mechanical Properties
The duration of plasma treatment on the abaca fabric affects the
mechanical properties of the resulting composite (Fig. 4). Plasma
treatment of the abaca fabric for 10 to 20 seconds resulted to
composites with the highest tensile strength while plasma treatment at
an extended period tends to lower the tensile strength of the abaca-
unsaturated polyester composite.The figure also shows that extending
the treatment for up to two minutes diminishes the reinforcing effect of
Fig. 3 Vacuum assisted resin transfer molding (VARTM). (a) actual
set-up with abaca fabric, and (b) schematic representation of the
different layers of the VARTM set-up
Fig. 4 Tensile and flexural properties of abaca fabric unsaturated
polyester composites using abaca fabric of different plasma treatment
times
244 / JULY 2014 INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING-GREEN TECHNOLOGY Vol. 1, No. 3
plasma treatment. The unfavorable effect of extending the plasma
treatment beyond twenty (20) seconds was also evident in the result of
the Izod impact test of the composites (Fig. 5). Abaca fabric exposed
to plasma polymerization for only 10 to 20 seconds again resulted to
composites with improved impact strength while composites with
abaca fabric that are plasma-treated for a longer period even performed
worse than the composite with untreated fabric.
Several studies have reported improvement in the tensile strength of
composites containing natural fibers modified by several surface
modification techniques (e.g. alkali and various silane treatments), as
shown in Table 1. In this study, plasma treatment was performed on
abaca fabric pretreated with silane (methasilane and trisilane ) and 2%
NaOH (aq) to see if there is further improvement in the tensile strength
of the composite if two surface modification processes were combined.
Fig. 6 shows that coupling plasma and silane or alkali treatment did not
lead to further improvement in the tensile strength of the composite. In
fact, the tensile strength of the composite tends to decrease especially for
the one involving abaca treated with both alkali and plasma.
The SEM image of the composite with the combined alkali and
plasma treatment (Fig. 7(f)) may not provide enough information to
account for its noticeably low tensile strength. One possibility is that
the double treatment may have affected the integrity of the fiber itself.
The Fourier Transform Infrared (FTIR) spectra and SEM images of
abaca fiber that underwent similar treatments may support this claim.
Fig. 8 shows the FTIR spectra of abaca fiber exposed to plasma and
a combination of alkali and plasma treatments. Comparing the FTIR
spectra of the untreated and plasma-treated fibers, it can be deduced
that plasma treatment did not result to noticeable structural changes in
the abaca fiber. Alkali treatment on the other hand resulted to the
disappearance of the absorption band at 1732 cm-1(Fig. 9, encircled).
This vibration frequency is attributed to C = O group of the carbonyl or
carboxyl structure.18 The disappearance of this particular band/peak in
the alkali-treated fiber indicates the removal of lignin, waxes and oils
on the external surface of the fibrils. It also depolymerizes cellulose
Fig. 5 Izod impact strength of abaca fabric-unsaturated polyester
Table 1 Tensile strength of composite using different surface- modified
abaca fibers
Surface treatment Tensile strength, MPa
Unsaturated polyester abaca fibers composite by Hand-lay up technique
1% γ- methacrylopropyl
trimethylsilane 49.44 (±2.77)
1 % triethoxyvinylsilane 61.79(±13.61)
10% Peroxide 64.79 (±10.54)
3% NaOH 40.48 (±12.05)
Epoxy abaca fiber composite by Vacuum Assisted Resin
Transfer Molding
2% NaOH 105.10 (±5.84)
3% NaOH 93.92 (±10.28)
4% NaOH 56.13(±7.36)
Fig. 6 Boxplot of the tensile strength of composites using various
surface-modified abaca fabric
Fig. 7 SEM images of abaca fabric reinforced unsaturated polyester
containing (a) untreated fiber (b) plasma treated for 10 sec (c) plasma
treated for 20 sec and with pretreatment prior to plasma treatment for 10 sec
(d) triethoxyvinylsilane (e)γ-methacrylopropyltrimethylsilane (f) 2% NaOH
INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING-GREEN TECHNOLOGY Vol. 1, No. 3 JULY 2014 / 245
and exposes the short length crystallites.4 This change in the
components of the alkali-treated fiber makes it easily etched by plasma
treatment. Fig. 9(d) clearly shows this effect. The combined treatment
resulted to an etched surface as well as disintegration of principal
strands and microcracks. This surface roughness may contribute to
increased interfacial adhesion but may have also lowered the strength
of the fabric, resulting to fiber breakage and/or splitting.
3.1 Water Absorption
The water immersion test was done to evaluate the effect of plasma
treatment and double treatment on the water uptake of abaca fabric
reinforced unsaturated polyester composite. Fig. 10 shows the
percentage of water uptake of the different composites in distilled water
and brine solution as a function of square root of time. It shows that for
both media, the moisture uptake increased with time indicating that the
water molecules penetrate into the composites resulting to an increase
in the composite weight. Initially, the weight increases abruptly due to
the rapid water penetration into the composites. The figures show sharp
increase and continue to increase gradually in time. In distilled water,
the composite with fabric plasma treated for 30 seconds exhibited
lower water uptake in two different media than the one with the fabric
plasma-treated for only 10 seconds. Of the silane-plasma treated fabric/
unsaturated polyester composites, the one with metha-silane has the
higher water uptake than the composite with tri-silane/plasma treated
fabric. This was also observed in brine solution. The combination of
2% NaOH (aq) and 10 seconds plasma treatment has the lowest water
uptake both in distilled water and brine solution.
4. Conclusions
Plasma polymerization of abaca fabric leads to enhancement of
adhesion and wetting of the fiber and the unsaturated polyester matrix.
Effective plasma treatment must be limited to 10 to 20 seconds to achieve
maximum improvement in the tensile properties of the composite. Combining
plasma treatment and other surface modification processes such as γ-
methacrylopropyltrimethylsilane (methasilane), triethoxyvinylsilane (trisilane),
and 2%w/w NaOH (aq), does not further improve the tensile properties of
the abaca-unsaturated polyester composite. The composite made from
abaca fabric treated with both alkali and plasma treatment in fact showed
a noticeably low tensile strength. However, despite its low tensile strength,
it exhibited the lowest water uptake in both distilled water and brine
solution. The poor mechanical performance of the composites maybe
attributed to volatization during curing of unsaturated polyester which led
to the formation of voids.
ACKNOWLEDGEMENT
The authors would like to thank Korea Institute of Materials Science
for the financial support as part of collaborative research work on
Plasma Treated Abaca Fiber Reinforced Composite for Industrial
Application under the Korea-Asean Program on Materials Science.
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Fig. 10 Water uptake of composites (a) & (b) in distilled water (c) &
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