Effect of alkali treatment and nano filler addition on properties of palm/glass fiber reinforced polymer composite
P Pradeep* & J Edwin Raja Dhas
Department of Automobile Engineering, Noorul Islam Centre for Higher Education, Kumaracoil 629 180, India Received 7 June 2016; accepted 31 July 2017
Usage of natural fiber as reinforcements with polymer resins increases the physical, chemical and mechanical properties of the fabricated composites. Composites developed from natural hybrid fiber have more advantage than composites developed from individual fibers. This may be due to the limitation of one fiber which is replaced by the advantage of other.
In the proposed work hybrid palm/glass fibers with coconut shell nano filer have been used as reinforcements and its effects on mechanical properties were studied. The mechanical properties (hardness, tensile, flexural, impact strengths), thermo gravimetric analysis (TGA), Fourier transform infrared (FTIR) analyses are investigated. Composites containing hybrid fibers found to posses better mechanical properties when compared to pure palm fibers. The morphological analysis namely scanning electron microscope (SEM) is also performed. All the results indicate that introduction of natural filler added hybrid palm/glass fiber reduces the overall cost of the composites with no compromise in strength enabling green technologies.
Keywords: Polyester resin, Palm fiber, Green composite, TGA, FTIR, SEM
Composites are artificial made materials with different chemical constituents. One or more discontinuous phases therefore, are embedded in a continuous phase to form a composite. The continuous phase (matrix) requires strengthening which is imparted by the harder and stronger discontinuous phase (reinforcement). The matrix material can be metal, polymer or ceramic. The composite made of a polymer is called polymer matrix composite1,2. Composite materials have successfully substituted the traditional materials in several light weight and high strength applications.
Polymer composites are selected due to their high strength-to- weight ratio, high tensile strength at elevated temperatures, high creep resistance and high toughness3. Composite properties (e.g. stiffness, thermal expansion) are varied continuously over a broad range under the control of the designers. In many instances, polymer composites are used to produce products with complex shapes. Optimum potentials and the better results are achieved through the use of composites in conjunction with traditional materials4. The reinforcing can either be fibers or particles that are derived from plants or living species called natural-fibers and some are artificially made.
Generally reinforcing fibers carry load, while the matrix protects them from outer atmosphere. Current research findings show that in certain applications, natural fibers demonstrated competitive performance to the dominant glass fibers to reinforce thermoplastic and thermoset polymer composites5-7.
Some of the natural fibers (coconut, banana and palm fibers) are used as a reinforcing agent due to its low cost and lower density, renewable nature and biodegradability. Palm fibers possess better tensile strength and less moisture absorption which makes it as a novel fiber in preparing composite laminates8,9.
To enhance interfacial bonding and to reduce moisture absorption, surface modification of the lignocellulosic fibers was performed. Such modifications are achieved by biological, physical and chemical methods. Natural fibers are generally soaked in alkali medium (sodium hydroxide, potassium permanganate) and then cleaned with distilled water.
This mechanism increases percentage of tensile, flexural and impact strength. Alkali treatment carried out for different fibers such as Kenaf fiber, Borassus fine fiber, coconut fiber, Raffia palm fiber, Palmyra palm leaf stalk, jute fibers shows improvement in mechanical properties10,11.
Fillers are used in polymers for reducing cost, effective density control, good thermal conductivity
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*Corresponding author (E-mail: pspradeep2006@rediffmail.com)
and control over thermal expansion, retarding flame and mainly improve mechanical characters. Addition of filler considerably reduces the voids on composites12.
Some of the natural available fillers are eggshell13, fly ash14,15, barley husk, coconut shell16 and others.
Polymer composites using coconut shell as filler results with increase in mechanical properties, and reduced water absorption. Also increase in the filler content increased the tendency of filler-matrix interaction evident through scanning electron microscope17.
Most of the polymer composites are easy to fabricate as they require very less knowledge to prepare the solid components with a desired size and shape18. Unlike working with metals the casting of desired component can be offered in minutes with simple techniques like hand lay-up. Polymer composite as laminates are formed by stacking several thin layers of fibers impregnated within resin. Some properties that may be cited as improved by lamination are strength, stiffness, weight reduction, corrosion resistance, aesthetics, thermal and acoustic insulation. These are widely used in small scale industries for toy making, fiber boat making components for automobiles and others19-22.
Experimental Procedure
Materials
The composites are produced from palm fibers (Fig. 1) with polyester as resin by simple hand layup technique. The palm fiber collected from the local area is washed several times with water then soaked in 8% of KMnO4 concentrated solution for 30 min.
The soaked fibers are cleaned in water and dried.
Thus clean fibers are obtained. Glass fiber is used to sandwich these palm fibers, Coconut shell prepared as nano powder is mixed uniformly with polyester resin.
Table 1 shows the properties of materials used in this work.
Preparation of composites
The composite in form of laminates are fabricated by hand lay up technique. Polyester resin with hardener mixed with weight percentage ratio of 10:1
and is used to prepare the composites. The fibers in pre determined length (3 cm) are rolled as mat prior to reinforcement. Wax is applied on mould box surface, the proportionate mixture is taken and is poured into the mould to form a uniform layer. After that fibers are placed as another layer and resin with hardener mixture is poured over it. The same procedure is repeated until desired thickness is obtained. The specimens prepared are properly cured at room temperature for one day.
Table 2 shows the combinations of polyester resin,
Fig. 1a — Palm fiber spotted on a palm tree
Fig. 1b — Extracted palm leaf stalk fiber Table 2 — Combination of polyester resin and the natural
fiber in wt%
Specimen Combinations Weight
% (g)
A Polyester resin+ 70 1050
Pure or raw palm leaf stalk fiber
mat, E-glass fiber mat. 30 450
B Polyester resin+ 70 1050
8% KMnO4 treated palm leaf stalk fiber mat, E-glass fiber mat, Coconut shell nano filler
30 450
Table 1 — Properties of materials used Materials/ Properties Appearance Density
(g/cm3)
Size Elongation (%)
Tensile strength (MPa)
Young’s modulus (GPa)
Polyester resin Yellowish 1.2-1.5 --- 2 40-90 2-4.5
E-glass Colourless 2.5 5-26 µm 3.2 2000-3500 70
Palm leaf stalk Yellowish brown 1-1.2 10-20 µm 2-4.50 97-196 2.50-5.40
Coconut shell nanopowder Clear light brown 0.9 2-50nm 2 --- ---
fibers and filler materials in weight percentage. Stages of manufacturing the proposed composite are shown in Fig. 2. The composite plates A and B are fabricated in this combination.
Mechanical and morphological properties
The mechanical properties such as hardness, tensile, flexural and impact strengths as per ASTM standards23 were analyzed. TGA was used to investigate the thermal stability of the composite An FTIR was conducted to analyze the chemical changes if any on the composites. Also the morphological analysis SEM was made to verify uniformity in composites.
Ultimate tensile strength (UTS)
UTS of raw and 8% KMnO4, treated palm leaf stalk fiber/sandwiched glass fiber mat /filled coconut shell nano filler reinforced polymer composites are found by testing the samples of each material on a computerized servo controlled Universal Testing machine (UTM) with specimen standard ASTM D 638 (Fig. 3). The samples are placed in the grips of the UTM, the gauge length and cross head speeds are fixed to 50 mm and 2 mm/min respectively and pulled apart for measuring strength and elongation until the specimen got fractured.
Flexural strength
The flexural strength of treated and untreated samples of palm leaf stalk fiber/sandwiched glass fiber mat/filled coconut shell nano filler reinforced polymer composites were measured by conducting flexural test on computerized UTM using special attachment with specimen standard ASTM D 790 (Fig. 4).
Impact strength
The impact strength of both composites are measured using a charpy impact tester with specimen standards ASTM D 6110 (Fig. 5). The energy absorbed by cross-sectional area of the specimen was noted.
Hardness value observation
The hardness test was conducted on both specimens using a Rockwell hardness tester as per specimen standard ASTM D 785 (Fig. 6). A load of 60 kg was applied for 15 s and the hardness was measured.
Thermo gravimetric analysis
The thermal degradation for measuring weight loss was done using thermo gravimetric analyzer. Powder samples of 10 mg were analyzed under the
Fig. 2 — Stages of manufacturing composite
Fig. 3 — Specimen for tensile test
Fig. 4 — Specimen for flexural test
temperature range of 30-600°C at a heating rate of 10°C/min with nitrogen gas flow rate of 50 mL/min.
FTIR spectroscopy
The infrared spectra were obtained on a FTIR spectrometer Perkin Elmer spectrum 2000 instrument with the diamond attenuated total reflectance (ATR) techniques. The data were recorded in a wave number range of 4000-280 cm-1. Approximately 10 mg of composite powder as samples was analyzed for this purpose.
Surface electron microscopy
The surface morphology of the samples was examined by using a scanning electron microscope.
The fractured samples were mounted onto SEM holder using double sided electrically conducting carbon adhesive tapes to prevent surface charge on the specimens when exposed to the electron beam for a voltage of 3 kV with two different magnifications X300, 50 µm and X500, 50 µm.
Results and Discussion
Alkali treatment caused fibrillation, i.e., breaking of fiber bundles into smaller fibers which would
increase the effective surface area available for wetting by the matrix material. After fibrillation due to the reduced diameter of fibers, the aspect ratio of fibers increases and yields a better fiber-matrix interface adhesion. The addition of nano coconut shell filler material got filled on the gaps and considerably decreased the voids formed during polymerization.
Specimen vs UTS
Figure 7 illustrates the plot of UTS in N/mm2 versus specimens combinations, it is seen that the untreated palm leaf stalk fiber/sandwiched glass fiber/filled coconut shell nano filler reinforced polymer composite (specimen A) yielded 85.38 MPa and 8% alkali-treated palm leaf stalk fiber/sandwiched glass fiber /filled coconut shell nano filler reinforced polymer composite (specimen B) yielded 90.28 MPa.
The results are compared with standard coir composite24 and are shown in Fig. 7 as Specimen C.
Specimen vs flexural strength
Figure 8 shows the variation of flexural strength for the specimens with and without alkali treatment. The specimen B recorded increase in flexural strength than the specimen A. This was due to high fiber-matrix compatibility, good fiber-matrix interaction and wetting. The results are compared with standard coir composite [24] and are shown in Fig. 9 as Specimen C.
Specimen vs impact strength
Figure 9 shows the variation of impact strength for the specimens with and without alkali treatment. The specimen B recorded increase in impact strength than the specimen A which results in obtaining the enhanced impact properties. The results are compared with standard coir composite24 and are shown in Fig. 9 as Specimen C.
Specimen vs hardness
The variation of hardness for the specimens with and without alkali treatment is shown in Fig. 10.
The specimen A recorded increase in hardness than the specimen B due to the presence of impurities.
TGA study
TGA curves (Fig. 11) of the pure polyester and palm fiber reinforced composites were recorded under nitrogen at 10°C/min from 50°C to 600°C.
Also, it is noted that the palm fiber reinforced polyester composite starts loosing weight attributing higher moisture content of untreated moisture
Fig. 5 — Specimen for impact test
Fig. 6 — Specimen for hardness test
evaporates from the fibers starting at 80°C. At 600°C the weight loss reflects the amount of residues left before degradation. It is seen that pure polyester has
decomposition temperature 345.5ºC while adding palm fibers shifted the curves to higher temperatures.
From this study, the alkali treated palm fiber based polyester composite becomes more stable at higher temperatures contributing enhanced thermal stability.
FTIR
According to the FTIR curves (Fig. 12), the functional groups of palm fiber reinforced polyester composite showed one extra alcohol/phenol OH stretch and one less alkyl CH stretch and aromatic CH bending functional group which confirms
Fig. 7 — Comparison of UTS
Fig. 8 — Comparison of flexural strength
Fig. 9 — Comparison of impact strength
Fig. 10 — Comparison of hardness value
Fig. 11 — TGA curves of the composites
Fig. 12 — FTIR curves of the composites
the presence and better adhesion of palm fibers in pure resin.
From FTIR curves on palm fiber it can be seen that one alcohol/phenol OH stretch, one alkyl CH stretch, two amide CO stretch and two aromatic CH bending functional groups were present. From FTIR test on palm reinforced polyester resin composite, the graph shows the same functional groups as that of palm fiber FTIR test along with one extra alkyl CH stretch.
SEM morphology
SEM micrographs of the treated composites were presented (Figs 13(a) and (b)). As seen from the micrographs, the large amount of resin adhered to the fiber surface and fewer gaps between resin and the fibers were observed. It is also indicated that the adhesion between resin and the fibers improved. Also the fiber pullout shows the improved tensile strength. This result was in agreement with those from mechanical tests.
The observation reveals the fiber resin and coconut shell powder are uniformly dispersed in the composite.
Conclusions
Un-utilized palm fibers and coconut shell nano filler are used for the successful fabrication of hybrid polymer composites. Mechanical, structural and thermal characteristics of the developed composites
are evaluated. Mechanical property observations reveal that the strength of alkali treated palm fiber with nano filler added polymer composites shows appreciable results. TGA, FTIR and SEM analysis validates the results of various tests. It is concluded that the developed composites can be used as eco friendly and low cost composite in manufacturing sectors like automobile, marine, etc for preparing components like car bonnet, fiber boat and others.
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Fig. 13 — SEM micrographs of the treated composite at (a) 300X magnification and (b) 500X magnification
