Treated Coconut Shell Reinforced Unsaturated Polyester Composites

Transcription

1 International Journal of Engineering & Technology IJET-IJENS Vol:13 No:02 94 Treated Coconut Shell Reinforced Unsaturated Polyester Composites H. Salmah, M. Marliza and P. L. Teh Abstract The effect of untreated and treated Coconut Shell (CS) reinforced Unsaturated Polyester (USP) composites were studied. Coconut shell was treated with 1% sodium hydroxide (NaOH). The results showed that the addition of CS content have increased the tensile strength, modulus of elasticity, flexural strength, flexural modulus and thermal stability whereas elongation at break of USP/CS composites decreased. The treated USP/CS composites have higher tensile strength, modulus of elasticity, flexural strength, flexural modulus and thermal stability of treated USP/CS composites compared than untreated composites. The better filler dispersion and interaction between CS and USP with alkali treatments was proven by SEM study. The FTIR spectra show that the change of functional group of treated CS with alkali treatment. Index Term unsaturated polyester, coconut shell, treatment, composites. I. INTRODUCTION THE development in science and technology required a variety of polymer with good properties and low cost. Therefore, polymer composites were considered to be among the more promising approaches to yield new materials and have been investigated extensively [1-4]. In recent years, many studies have been dedicated to utilize lignocellulosic fillers such as coconut shell, wood, pineapple leaf, palm kernel shell, etc. as fillers in order to replace synthetic fillers through utilization of natural fillers or reinforcement in thermoplastic and thermoset polymer composites in an attempt to minimize the cost, increase productivity and enhance mechanical properties of product [5-8]. Coconut shell (CS) is among the most significant lignocellulosic materials that growth in tropical countries such as Malaysia, Sri Lanka, Thailand and Indonesia. In an attempt to downsize the abundance of this industrial waste, new applications are urgently needed for CS to be more useful. Therefore, the utilization of CS as lignocellulosic fillers in polymer composites becomes more favorable due to their high strength and modulus properties [9-10]. Natural filler possess several advantages compared to inorganic fillers, that are lower density, greater deformability, abundance and low cost, less abrasiveness to equipment. More importantly, lignocellulosic-based fillers are derived from renewable resources. Although lignocellulosic fillers can offer the resulting Correspondence author: irsalmah@unimap.edu.my, Division of Polymer Engineering, School of Materials Engineering, Universiti Malaysia Perlis, Jejawi, Perlis, Malaysia; Fax: ; irsalmah@unimap.edu.my. composites many advantages, the usually polar fillers have inherently low compatibility with non-polar polymer matrices. The incompatibility may cause problem in the composites processing and material properties. Hydrogen bond may form between the hydrophilic fillers, and thus the fillers tend to agglomerates [11-12]. The moisture absorption of the lignocellulosic fillers may cause dimensional change of the resulting composites and weaken the interfacial adhesion [13-14]. Treatment of natural filler is beneficial in order to improve the water resistance of fillers, enhance the wettability of natural filler surface by polymers and promote interfacial adhesion. Assorted surface treatment techniques like alkali treatment, isocyanate treatment, acrylation, acetylation, silane treatment and peroxide treatment [15-24] have been implemented on the lignocellulosic fillers in order to enhance the mechanical and thermal properties, size and its shape and the interfacial adhesion between treated fillers and polymer composites. The aims of this work to investigate the effect of CS content and treatment with NaOH on the mechanical, thermal properties and morphology of coconut shell reinforced USP/CS composites were studied. II. EXPERIMENTAL A. Materials Unsaturated polyester (USP), grade Reversol P9509 was supplied by Echemo Trading Sdn. Bhd., Penang. The catalyst used butanox M-60 which chemical name is methyl ethyl ketone peroxide in dimethyl (MEKP) was obtained from KeumJung Akzo Nobel Peroxides Ltd., China. Sodium hydroxide supplied by ChemAR. Coconut shell (CS) used as filler in USP/CS composites was obtained from market Kangar, Malaysia. The CS was cleaned, washed and grounded to become powder. The average particle size of CS is 63 μm, analyzed using Malvern Instrument Mastersizer 2000 equipment. The formulation of untreated and treated USP/CS composites is shown in Table I. Table II shows the chemical composition of coconut shell. B. Coconut shell treatment Sodium hydroxide (NaOH) 1% (v/v) diluted in distilled water at room temperature. Then coconut shell added into solution. The mixture was mechanically stirred for 3 hours. The CS was filtered, washed with distilled water and dried in the oven at 80 ºC for 24 hours.

2 International Journal of Engineering & Technology IJET-IJENS Vol:13 No:02 95 C. Composites preparation Mixing of the USP/CS composites was carried out using casting technique. The first, unsaturated polyester was mixed with coconut shell until it is homogeneously mixed before the catalyst is added inside to initiate the polymerization reaction. The composites are poured into the mold. The total mixing of composites is about 10 minutes. The compression molding machine was used in order to give some heat to speed up the process of crosslinking of composites. The composites were compression molded under a pressure of 100 kg/m 2 at 70 ºC for 5 minutes. D. Mechanical properties Tensile test and flexural test were carried out according to ASTM D 638 and ASTM D 790, respectively by using Instron Machine Model Composite samples with 3 mm x 15 mm x 150 mm were cut from the molded sheet using cutter machine. A cross- head speed of tensile test was used 5 mm/min and flexural test 3 mm/min and test was performed at 25 ± 3 0 C. Tensile strength, elongation at break and modulus of elasticity, flexural strength and flexural modulus were recorded and automatically calculated by the instrument software. E. Morphology study The morphology of the tensile fracture surface of unsaturated polyester/coconut shell composites are carried out by using a scanning electron microscope model JEOL JSM LA (SEM). The fractured surfaces of specimens were mounted on aluminum stubs and sputter coated with a thin layer of palladium to avoid electrostatic charging during examination. F. Thermal properties Thermogravimetric analysis (TGA) of composites was carried out using Perkin Elmer analyzer equipments. The sample weights between mg were scanned from 25 ºC to 850 ºC using a nitrogen air flow 50 ml/min and at heating rate 20 ºC/min. G. Fourier transform infrared spectroscopy analysis (FTIR) FT-IR spectroscopic analysis of the untreated and treated of CS was carried out in a Perkin Elmer Spectrometer 2000 FT- IR. KBr pellet technique was applied. Scanned range was cm -1 and resolution for all the infrared spectra was 4 cm -1. III. RESULTS AND DISCUSSION A. Tensile properties Fig.1 shows the effect of filler content on tensile strength of untreated and treated USP/CS composites. It can be seen that the tensile strength of both untreated and treated USP/CS composites increased as filler content increases. The increase of tensile strength is due to the ability of the CS filler to support stress transfer from the USP matrix. It is clearly indicate that inclusion of CS filler improved the load bearing capability of the USP/CS composites. The higher tensile strength of composites value was result of the capability of the filler to sustain stresses transmitted from polymer matrix. Other factor that contributes to increase in tensile strength is higher in lignin content in CS filler. Lignin not jus t binds the lignocellulosic materials together, yet as well behaves as a stiffening agent for the cellulose molecules inside the lignocellulosic cell wall [25]. Lignin consist of polar hydroxyl groups, benzene rings and nonpolar hydrocarbon [26] which it is predicted capable to enhance the adhesion between the two constituents of the composite between hydrophilic natural filler reinforcement and hydrophobic matrix polymer. The treated USP/CS composites exhibit higher tensile strength compared to untreated USP/CS composites. The increases of tensile strength due to removal of noncellulosic filler components and increased surface roughness which leading to better bonding of treated CS fillers with USP resin. The increase surface roughness would also increase mechanical interlocking with unsaturated polyester resin. It is well acknowledged that sodium hydroxide represents the most normally utilized chemical for bleaching or cleaning the surface of plant fillers [27]. The chemical treatment of fillers through sodium hydroxide aqueous solution would lead to the partially removal of bonding material, consequently exposing dissociate individual cellular elements on the filler surface. The surface modification by utilizing the sodium hydroxide comprises of the disruption of hydrogen bonding in the network structure and henceforth increases the roughness of the lignocellulosic filler surface Fig. 2 shows the effect of filler content on elongation at break of untreated and treated USP/CS composites with NaOH. It can be seen that the elongation at break of both untreated and treated USP/CS composites decreased with increasing filler content. The results match greatly with the results obtained from the modulus of elasticity of USP/CS composites where those composites with high modulus exhibit lower elongation at break. As a rigidity of the composites increases, it decreased the deformability of a rigid interface between CS filler and the USP matrix material. The CS particles act as barrier against the mobility of dislocations. The inclusion of rigid filler to polymer composites substantially diminishes the elongation at break through reducing the quantity of material that accessible to deform. The elongation at break decreased upon filler addition for composites regardless the nature of the filler. At higher filler content, the domination of filler-matrix interaction can be expectable to subside and being substituted by filler-filler interaction. The elongation at break for treated USP/CS composites lower than untreated USP/CS composites. This due to improve the adhesion between filler and matrix where it increases the number of filler bonded on matrix hence increase the stiffness of the composites. The surface treatment of CS using NaOH has enhanced wettability of the fillers, which consequently reduce the elongation at break of the treated USP/CS composites. The effect of filler content on modulus of elasticity of

3 International Journal of Engineering & Technology IJET-IJENS Vol:13 No:02 96 untreated and treated of USP/CS composites with NaOH is shown in Fig. 3. From the Figure, modulus of elasticity of both untreated and treated USP/CS composites increased with increasing of filler content. Modulus of elasticity is an indication of the relative stiffness of composites. The addition of CS filler increased the modulus of elasticity of polymer composites. The incorporation of filler restrains the motion of the matrix phase in the proximity of each particle which consequently contributes the enhancement in modulus and stiffness. At similar filler content, treated USP/CS composites exhibit higher modulus of elasticity compared to untreated USP/CS composites. This increment indicated that the USP resins with CS reinforcement behave stiffer and could withstand higher stress at the same strain portion after the treatment using NaOH. B. Flexural properties The effect of surface treatment using sodium hydroxide on flexural properties of USP/CS composites are shown in Figs Figures show the effect of filler content on flexural strength and flexural modulus of untreated and treated USP/CS composites. Results show that the flexural strength and flexural modulus of both untreated and treated USP/CS composites increased with increasing of filler content. At similar filler content, treated USP/CS composites exhibit higher flexural strength and flexural modulus compared to untreated USP/CS composites. This is caused by the enhancement of interfacial adhesion induced through surface modification of the CS filler with NaOH. The better wetting between the CS filler and the USP matrix are achieved thus improving the level of adhesion. C. Morphology study The scanning electron microscope (SEM) was used to examine the tensile fracture surface of untreated and treated USP/CS composites at 30 and 60 php of filler content as shown in Figs The both of micrograph of untreated composites show some detachment of filler from matrix. This indicated the insufficient bonding between USP and CS filler and less adhesion occurred between them. The micrograph of treated composites in Figs. 8 and 9 exhibits CS is better dispersed in the unsaturated polyester matrix. Figure indicates that the presence of NaOH resulted less detachment and agglomeration of CS in USP matrix, thus enhanced wettability between CS and USP. The effect of improve interfacial bonding between the filler and the matrix is indicated in the enhancement of the tensile and flexural properties of the treated USP/CS composites. D. Thermogravimetric analysis (TGA) The comparison of thermogravimetric analysis curves of untreated and treated USP/CS composites with NaOH at 0 and 30 php of USP/CS is shown in Fig. 10. Table III summarized the percentage of weight loss of untreated and treated USP/CS composites. It can be seen that the total weight loss of USP/CS composites decreased as a filler content increases. This indicates that higher CS content has better thermal stability. The results also show the treated composites have lower total weight loss than untreated composites. This result indicates that the treated composites higher thermal stability compared untreated composites. The betel thermal stability of treated USP/CS is due to enhanced interfacial interaction between CS and USP matrix with alkali treatment. E. Fourier infrared spectroscopy analysis (FTIR) Fig. 11 shows the FTIR spectrum of untreated and treated CS with NaOH. The peak at 3479 cm -1 is assigned to the stretching vibrations of hydroxyl groups of CS. In the double bond region, a shoulder peak at 1735 cm -1 are assigned to the carbonyl (C=O) stretching from ester linkage of cellulose, hemicelluloses or lignin. The peaks at 1638 cm -1 are reflected for amide I. The bands at 1384 cm -1 is due to the bending vibration of C-H 3 groups. The peaks in the range of 1262 cm -1 to 1165cm -1 assigned to the C-O stretching vibration of esters while the peaks at 1121 cm -1 and 1043 cm -1 assigned to C-O stretching in secondary alcohol and aliphatic ether. The peak range from 897cm -1 to 610 cm -1 represents of C-H bending vibrations. For treated CS with NaOH show the peak change from 3479 cm -1 to 3414 cm -1 due to the interaction of hydroxyl groups of CS with NaOH to form hydrogen bond. As can be seen in this Fig. 11, the peak at 1735 cm -1 disappeared after the treatment with NaOH. This peak is assigned to C=O unconjugated stretching of carboxylic acid or ester of the hemicelluloses. The wavenumber was reduced from 1262 cm -1 to 1239 cm -1 indicated that C-O stretch of the acetyl group of lignin and is reduced with alkali treatment. Fig. 12 shows the schematic reaction of coconut shell with sodium hydroxide. IV. CONCLUSION The alkali treatment with sodium hydroxide has enhanced the mechanical and thermal properties of USP/CS composites. The treated USP/CS composites indicate higher tensile strength, modulus of elasticity, flexural strength, flexural modulus and thermal stability compared to untreated composites. SEM study exhibit that wettability and interfacial interaction enhanced between CS and USP matrix with presence alkali treatment was proven by FTIR spectra studied. REFERENCES [1] P. Threepopnatkul, N. Kaerkitcha, N. Athipongarporn. (2009). Effect of surface treatment on performance of pineapple leaf fiberpolycarbonate composites. 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Journal of Composites Science and Technology, 63, pp TABLE I T HE FORMULATION OF UNTREATED AND T REATED Materials Untreated Composites Treated Composites Untreated polyester (php a ) Coconut shell (php) 0, 15, 30, 45, 60 15, 30, 45, 60 MEKP (php) 2 2 NaOH (%)* 0 1 a php = parts per hundreds of total polymer *1% from weight filler TABLE II CHEMICAL COMPOSITION OF COCONUL SHELL Composition Lignin 29.4 Pentosans 27.7 Cellulose 26.6 Moisture 8 Solvent extractives 4.2 Uronic anhydrides 3.5 Ash 0.6 Wt.% TABLE III PERCENTAGE WEIGHT LOSS OF UNTREATED AND T REATED USP/CS COMPOSITES AT DIFFERENT T EMPERATURES Temperature (ºC) Weight loss (%) Untreated USP/CS composites with NaOH Treated USP/CS composites with NaOH 100/0 100/30 100/60 100/30 100/ Total

5 International Journal of Engineering & Technology IJET-IJENS Vol:13 No:02 98 Fig. 1.The effect of filler content on tensile strength of untreated and treated USP/CS composites. Fig. 2. The effect of filler content on elongation at break of untreated and treated USP/CS composites

6 International Journal of Engineering & Technology IJET-IJENS Vol:13 No:02 99 Fig. 3. The effect of filler content on modulus of elasticity of untreated and treated USP/CS composites Fig. 4. The effect of filler content on flexural strength of untreated and treated USP/CS composites

7 International Journal of Engineering & Technology IJET-IJENS Vol:13 No: Fig. 5. The effect of filler content on flexural modulus of untreated and treated USP/CS composites Fig. 6. Scanning electron micrograph of tensile fracture surface of untreated USP/CS composite (30 php CS).

8 International Journal of Engineering & Technology IJET-IJENS Vol:13 No: Fig. 7. Scanning electron micrograph of tensile fracture surface of untreated USP/CS composite (60 php CS). Fig. 8. Scanning electron micrograph of tensile fracture surface of treated USP/CS composite (30 php CS).

9 International Journal of Engineering & Technology IJET-IJENS Vol:13 No: Fig. 9. Scanning electron micrograph of tensile fracture surface of treated USP/CS compo site (60 php CS). Fig. 10. Comparison of thermogravimetric analysis curves of untreated and treated USP/CS composites.

10 International Journal of Engineering & Technology IJET-IJENS Vol:13 No: Fig. 11. FTIR spectra of coconut shell with sodium hydroxide. Fig. 12. Schematic reaction of coconut shell with sodium hydroxide.