Structure, Mechanical and Thermal Properties of Coconut Fiber Reinforced Polypropylene Composites with 2% MAPP as a Compatibilizer

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1 Structure, Mechanical and Thermal Properties of Coconut Fiber Reinforced Polypropylene Composites with 2% MAPP as a Compatibilizer Structure, Mechanical and Thermal Properties of Coconut Fiber Reinforced Polypropylene Composites with 2% MAPP as a Compatibilizer Anshu Anjali Singh*, Priyanka and Kishor Biswas Department of Polymer & Process Engineering, Indian Institute of Technology-Roorkee, DPPE IIT-R SRE Campus, Paper Mill Road, Saharanpur Received: 13 January 2014, Accepted: 27 April 2014 Summary Coconut fibers reinforced polypropylene composites processed by extrusion with 2% MAPP maleic anhydride grafted polypropylene as compatibilizer show about 10 to 20% improved tensile strength and tensile modulus as compared to that of the polypropylene matrix due to fiber/matrix interfacial adhesion resulting from compatibilizing effect of MAPP. Scanning electron microscopy shows coconut fibers deeply embedded in polypropylene matrix with good interfacial adhesion. The melting temperatures of the CNF/PP composites are same as that of PP and are around 170 C. Introduction Natural fibers are being used as reinforcement materials because of their environmental advantages, including renewable, recyclable, CO 2 neutral and biodegradable nature [1]. Natural fiber reinforced polymer composites are offering techno-economic advantages, for example; good mechanical and thermal properties, low cost, low energy consumption, non-abrasive to instrument and non-toxic, and are replacing conventional synthetic or inorganic fiber reinforced polymer composites in some applications [2]. * anshuanjaliiitr@gmail.com Smithers Information Ltd., 2014 Applied Polymer Composites, Vol. 2, No. 2,

2 Anshu Anjali Singh, Priyanka and Kishor Biswas Properties of natural fiber reinforced polymer composites are governed by properties, chemical composition and aspect ratio of the reinforcing fiber and properties of the polymer matrix and the interfacial adhesion between the fiber and the polymer matrix of the composite. Natural fibers are hydrophilic and hygroscopic because of the presence of cellulose, hemicelluloses, lignin, which contain hydroxyl (-OH) groups, and therefore have poor compatibility with hydrophobic thermoplastic polymer matrix in a natural fiber reinforced polymer composite [3]. This leads to the weak fiber/matrix interfacial adhesion in natural fiber reinforced thermoplastic composites and thus limits proper load transfer from the matrix to the fiber and limits the mechanical properties of the composites. Following methods have been used to improve fiber/matrix interfacial adhesion in natural fiber reinforced thermoplastic composites: (i) physical or chemical treatment for surface modification of natural fibers; (ii) use of a third component known as a compatibilizer or a coupling agent, and (iii) Palsule process based on chemically functionalized polyolefin matrix [4, 5]. This study reports processing and structure and properties of coconut fiber reinforced polypropylene (CNF/PP) composites using maleic anhydride grafted polypropylene as a compatibilizer. Coconut fiber also known as coir fiber is most commonly cultivated in the tropical countries. Several coconut fiber reinforced polypropylene composites have been processed by the chemical or physical treatment of fibers; for example; coconut fibers have been treated using, 2% NaOH solution followed by UV radiation [6], basic chromium sulphate and sodium bicarbonate salt in acidic media [7], alkali, potassium permanganate and stearic acid [8], 2%-10% NaOH [9], sodium periodate (NaIO 4 ) and 5% solution of p-aminophenol [10]. Coconut fiber reinforced chemically functionalized high density polyethylene composites have been developed by Palsule process [5]. 5%-20% lignin [11] has been used as a compatibilizer for processing coconut fiber reinforced polypropylene composites. 1% MAPP [12], 3% MAPP [13] and 4% to 8% MAPP [14] have been used as compatibilizers for processing of CNF/PP composites. However, processing and thermal and mechanical properties of coconut fiber reinforced polypropylene composites with 2% MAPP have not been evaluated. This study aims to process coconut fiber reinforced polypropylene composite by using 2% maleic anhydride grafted polypropylene as a compatibilizer and to study their thermal and mechanical properties. 110 Applied Polymer Composites, Vol. 2, No. 2, 2014

3 Structure, Mechanical and Thermal Properties of Coconut Fiber Reinforced Polypropylene Composites with 2% MAPP as a Compatibilizer Materials and Processing Materials Coconut fiber was obtained commercially from the local market in raw form, and was cut into fibers of 4-5 mm length. Polypropylene was obtained from RTP Company (USA). Maelic anhydride grafted polypropylene (MAPP) was obtained from commercial supplier, Pluss Polymer Pvt. Ltd. (New Delhi, India). Polypropylene composites with coconut fiber as reinforcement were processed with 2% maleic anhydride as a compatibilizer. Processing and Sample Preparation Coconut fiber reinforced polypropylenes (CNF/PP) composite with 2% MAPP as a compatibiliser, were processed on a Haake Rheocord and the samples for testing and characterizations were made by injection molding machine. Before compounding and injection molding of the samples, chopped coconut fibers (CNF) of length 4-5 mm were dried in an oven at 60 C overnight to remove the moisture. Calculated amount of chopped coconut fiber (on a dry basis), 2% weight MAPP compatibilizer and polypropylene (PP) granules were dried in an oven at 50 C for 2 hours. After 2 hours the CNF, MAPP and the PP were mixed manually. Table 1 shows formulation of CNF/PP composites with 2% MAPP. Table 1. Formulations of coconut fiber reinforced polypropylene (CNF/PP) composite with 2% MAPP as a compatibilizer (in weight%) CNF/PP Composites 0/100 5/95 10/90 Coconut Fiber (CNF) wt.% Polypropylene (PP) wt.% Maleic Anhydride Grafted Polypropylene (MAPP) wt.% Compounding was performed by a laboratory size internal extruder (Haake Rheocord) that enables the compounding and blending of thermoplastics and rubbers and has been used to process CNF/PP composites. CNF, MAPP and PP granules were compounded by HAAKE Pheomix 9000 at around 175 C to develop 5/95 and 10/90 CNF/PP composites. The temperatures used during the compounding process were kept relatively low to prevent thermal Applied Polymer Composites, Vol. 2, No. 2,

4 Anshu Anjali Singh, Priyanka and Kishor Biswas degradation of the coconut fiber. The zones were set at various temperatures depending on the fiber content, as follows: Zone C, Zone C, Zone C, Zone C Melt temperature C, Torque N. The screw speed was set at 60 rpm. The compounded materials were collected as strands and palletized in a standard strand pelletizer used in plastics compounding. Injection molding of the granulated PP and of the extruded 5/95 and 10/90 CNF/PP composites were performed using TEXAIR injection molding machine following ASTM standards. During the operation the heating of each zone in injection molding are: Zone C, zone C, and zone C. Testing and Characterization Mechanical Properties Tensile properties of PP matrix and of the processed 5/95 and 10/90 CNF/PP composites with 2% MAPP were evaluated following ASTM D638. The tensile tests were performed in a Universal Testing Machine, (Model 3382, INSTRON, 25 Ton Capacity) and values recorded were average of five samples each of PP matrix and of the 5/95 and 10/90 CNF/PP composite compositions tested. The cross head speed for tensile test was 50 mm/min. Morphology Analysis Field Emission Scanning Electron Microscope (FE-SEM Model Quanta 200F) with an acceleration voltage of 15kV was used to study morphology of raw coconut fiber (CNF), PP matrix, and the 5/95 and 10/90 CNF/PP composites. The specimens were coated with a thin gold layer and mounted on the Al stub for examination. Thermal Properties Thermal properties i.e; the melting temperature of the samples were evaluated by Differential Scanning Calorimeter (DSC F3 NETZSCH). The equipment was programmed to work at the temperature range between room temperature (around 30 C) and 300 C, under nitrogen flow of 50 ml/min. The heating rate was 10 C/min. The values of melting temperature (Tm) were obtained. 112 Applied Polymer Composites, Vol. 2, No. 2, 2014

5 Structure, Mechanical and Thermal Properties of Coconut Fiber Reinforced Polypropylene Composites with 2% MAPP as a Compatibilizer Results and Discussions Mechanical properties of a composite material are governed by properties, aspect ratio and amount of the reinforcing fiber, properties of the matrix, and the interfacial adhesion between the reinforcing fiber and the matrix. Five samples of PP matrix and five samples of each of the 5/95 and 10/90 CNF/PP composite compositions were tested for evaluation of mechanical properties and the results have been recorded as an average of five values. Tensile Properties Table 2 indicates that in absolute terms, 5/95 and 10/90 CNF/PP composites with 2% MAPP as a compatibilizer, respectively have a tensile modulus of 2.87 GPa and 3.01 GPa; that are higher than the tensile modulus of PP matrix that has a value 2.62 GPa. In relative terms, compared to the modulus of the PP matrix, the tensile modulus of 5/95 and 10/90 CNF/PP composite compositions are higher by 10% and 15% respectively. Figure 1 shows the effect of increasing CNF content on tensile modulus of all the CNF/PP composite compositions with 2% MAPP. The vertical line in the Figure 1 indicates the deviations in the values. Table 2. Tensile modulus and tensile strength of PP and 5/95 and 10/90 CNF/PP composites Sample Tensile Modulus (GPa) Tensile Strength (MPa) Polypropylene (PP) /95 CNF/PP / Similarly, Table 2 indicates that in absolute terms 5/95 and 10/90 CNF/PP composites with 2% MAPP as a compatibilizer, respectively have tensile strength of MPa and MPa respectively; that are higher than the tensile strength of PP matrix that has a value of 20 MPa. In relative terms, compared to the tensile strength of the PP matrix, the tensile strength of 5/95 and 10/90 CNF/PP composite compositions are higher by 15%, and 23% respectively. Figure 1 shows the effect of increasing CNF content on tensile strength of all the CF/PP composite compositions. The vertical line in the Figure 1 indicates the deviations in the values. This significant increase in the tensile strength and tensile modulus of the CNF/ PP composites with 2% MAPP as a compatibilizer, comparing to PP matrix, is attributed to the reinforcing effect of coconut fibers due to their adhesion Applied Polymer Composites, Vol. 2, No. 2,

6 Anshu Anjali Singh, Priyanka and Kishor Biswas Figure 1. Effect of increasing coconut fiber content on the tensile modulus and tensile strength of CNF/PP composites with polypropylene composite resulting from compatibilizing effect of 2% MAPP used as a compatibilizer. The improvement in the tensile properties of the composites as a function of increasing coconut fiber content is due to the increased stress transfer from the matrix to the fibers. Morphology Scanning electron micrograph of coconut fibers (CNF) and of the PP matrix and of the 5/95 and 10/90 CNF/PP composite compositions with 2% MAPP as a compatibilizer, are shown in Figure 2a-d. The micrographs of the CNF/ PP composites composition (Figure 2c-d) show the reinforcing coconut fibers (CNF) deeply embedded in, and covered with PP matrix with no noticeable voids and gaps, confirming proper adhesion between CNF and PP matrix due to the presence of 2% MAPP as a compatibilizer. Thermal Characterization Figures 3 and 4 show melting temperatures of polypropylene (PP) matrix and of the 10/90 CNF/PP composite respectively. The melting temperature of the PP matrix and of 10/90 CNF/PP composites are recorded in Figures 2 and 3 respectively. The peak melting temperature (T m ) of PP matrix and of the 10/90 CNF/PP composites evaluated from the DSC curves indicate that the melting temperature of the PP is C and of the 10/90 CNF/PP is C. This indicates that the T m of the composite are not exactly the same (170.2 C) as that of the PP matrix, but are within the limits of experimental errors, 114 Applied Polymer Composites, Vol. 2, No. 2, 2014

7 Structure, Mechanical and Thermal Properties of Coconut Fiber Reinforced Polypropylene Composites with 2% MAPP as a Compatibilizer (a) (b) (c) (d) Figure 2. Scanning electron micrograph of (a) coconut fiber, (b) PP matrix, (c) 5/95 CNF/PP, (d) 10/90 CNF/PP composites probably, either because of the measurement limitations of the instrument, or probably because of some very minor interference of the fiber with the polymer matrix structure. Thus, there is no appreciable change in the melting temperature of the CNF/PP composites, as compared to PP matrix, because in principle, the PP is the only component of CNF/PP composite that actually melts, and the CNF would not melt, but would degrade. Almost negligible change was observed in melting temperature of matrix upon formation of a composite with 10/90 CNF/PP composites with 2% maleic anhydride grafted polypropylene as compatibilizer. Applied Polymer Composites, Vol. 2, No. 2,

8 Anshu Anjali Singh, Priyanka and Kishor Biswas Figure 3. Graph showing Tm of PP Figure 4. Graph showing Tm of 10/90 CNF/PP composites 116 Applied Polymer Composites, Vol. 2, No. 2, 2014

9 Structure, Mechanical and Thermal Properties of Coconut Fiber Reinforced Polypropylene Composites with 2% MAPP as a Compatibilizer Conclusions Coconut fibers reinforced polypropylene (CNF/PP) composites have been successfully processed by extrusion with 2% MAPP maleic anhydride grafted polypropylene as compatibilizer. CNF/PP composites show up to 15% improved tensile modulus and unto 23% improved tensile strength as compared to that of the polypropylene matrix due to fiber/matrix interfacial adhesion resulting from compatibilizing effect of MAPP that is evident from the scanning electron micrographs showing coconut fibers deeply embedded in polypropylene matrix with good interfacial adhesion. The melting temperatures of the CNF/PP composites are same as that of PP and are around 170 C. References 1. Mohanty A.K., Misra M., and Drzal L.T., Journal of Polymer and Environment, 10(1-2) (2002) Paul Wambua, Jan Ivens, and Ignaas Verpoest. Composites Science and Technology, 63 (2003) Bledzki A.K. and Gassan J., Progress in Polymer Science, 24 (1999) Priyanka, Palsule, Sanjay, Composite Interfaces, 20(5) 2013 DOI: / Singh A.A. and Palsule Sanjay, Journal of Composite Materials, December 10, 2013 doi: / Gelfuso M.V., Silva P.V.G.D., and Thomazini D., Materials Research, 14(3) (2011) Mir S.S., Nafsin N., Hasan M., Hasan N., and Hassan A., Materials and Design, 52 (2013) Lai C.Y., Sapuan S.M., Ahmad M., Yahya N., and Dahlan K.Z.H.M., Polymer- Plastic Technology and Engineering, 44 (2005) Huang Gu., Materials and Design, 30 (2009) Arrakhiz F.Z., Malha M., Bouhfid R., Benmoussa K., and Qaiss A., Composites Part B: Engineering, 47 (2013) Rozman H.D., Tan K.W., Kumar R.N., Abubakar A., Ishak Z.A.M., and Ismail H., European Polymer Journal, 36 (2000) Ishizaki M.H., Maciel P.D.M.C., Visconte L.L.Y., Furtado C.R.G., and Leblanc J.L., International Journal of Polymeric Materials, 58 (2009) Ayrilmis N., Jarusombuti S., Fueangvivat V., Bauchongkol P., and White R.H., Fiber and Polymers, 12(7) (2011) Applied Polymer Composites, Vol. 2, No. 2,

10 Anshu Anjali Singh, Priyanka and Kishor Biswas 14. Bettini S.H.P., Bicudo A.B.L., Augusto I.S., Antunes L.A., Morassi P.L., Condotta R., and Bonse B.C., Journal of Applied Polymer Science, 118 (2010) Applied Polymer Composites, Vol. 2, No. 2, 2014