β Silicon Carbide Coated MWCNTs Reinforced Polyetherimide Nanocomposites

Transcription

1 β Silicon Carbide Coated MWCNTs Reinforced Polyetherimide Nanocomposites β Silicon Carbide Coated MWCNTs Reinforced Polyetherimide Nanocomposites Nitin Nagar, K.N. Pandey *, Pratibha Singh, Vishal Verma, and R.M. Mishra Central Institute of Plastics Engineering and Technology, Lucknow, India Received: 29 March 2014, Accepted: 11 October 2014 Summary Polycarbosilane derived β silicon carbide coated multi wall carbon nanotubes (MWCNTs) reinforced polyetherimide (PEI) nano-composites (with 0.1 to 0.3 phr coated MWCNTs reinforcements) have been fabricated by a sigma high temperature internal mixer followed by compression. Scanning electron microscopy (SEM) shows uniform and homogeneous dispersion of the coated MWCNTs in polyetherimide matrix, due to interfacial adhesion between the coated MWCNTs and the PEI matrix. Increasing mechanical properties of coated MWCNT/PEI nanocomposites with increasing amounts of coated MWCNTs in their compositions, confirm reinforcing effect of MWCNTs in PEI matrix in coated MWCNT/PEI nanocomposites. Thermo gravimetric analysis shows that the thermal stability of coated MWCNT/PEI nanocomposites is same as of PEI. Introduction Recently carbon nanotube reinforced polymeric nanocomposites have gained a superlative degree of attention across the world due to their promising mechanical, thermal and other properties, and their potential applications. Polymer nanocomposites with single-wall and multiwall carbon nanotubes have been reviewed [1-3]. A homogenous and uniform dispersion of the nanotubes in the polymer matrix and good interfacial adhesion between the reinforcing nanotubes and the polymer matrix is a must for successful processing of a nanocomposite. Corresponding author: knpandey09@gmail.com Smithers Information Ltd., 2014 Applied Polymer Composites, Vol. 2, No. 4,

2 Nitin Nagar, K.N. Pandey, Pratibha Singh, Vishal Verma, and R.M. Mishra Aggregation and bundling of CNTs due to strong interaction among CNTs creates an obstacle in their dispersion in water and in organic solvents and therefore, in processing nanocomposites. Several methodologies have been adopted to improve the dispersion of CNTs in polymer matrix in a nanocomposite, including their functionalization. Functionalized multi walled carbon nanotubes are being investigated as reinforcement materials for polymeric nanocomposites [4]. Polyetherimide is a high performance amorphous engineering thermoplastic, having excellent mechanical properties even at elevated temperatures due to its high glass temperature (Tg~ C). The ether units provide the chain flexibility and good melt flow characteristics and the aromatic imides units provide thermal resistance and mechanical properties to PEI. However, very little work has been reported on the influence of CNTs on PEI in CNT/PEI nanocomposites. Multi-walled carbon nanotube / polyetherimide (MWCNT / PEI) nanocomposite films have been prepared by casting and imidization [5]. Carbon nanotube based nanocomposite membranes have been fabricated through solution casting by embedding multi-walled carbon nanotubes (MWCNTs) within polyetherimide (PEI) polymer host matrix [6]. Hybridizing graphitic nanoplatelets (GNP) with commercially functionalized multi-walled carbon nanotubes (MWCNTs) in a polyetherimide (PEI) matrix nanocomposite at a total loading of 0.5 wt% showed improved electrical, thermal and dynamic mechanical properties, compared to solely GNP or solely MWCNT composites at the same total loading [7]. Commercially functionalized multi-walled carbon nanotubes (MWNTs) reinforced PEI nanocomposite films showed increased electrical conductivity and increased thermal decomposition temperature [8]. Studies on mechanical, morphological and electrical properties of carbon nanofiber / polyetherimide composites developed successfully by using a Sigma high temperature internal mixer and then compression molding have been reported [9]. In view of the literature reports, this study investigates polycarbosilane derived β silicon carbide coated multi wall carbon nanotube reinforced polyetherimide nano-composites (coated MWCNTs / PEI), and their morphology, and the thermal and mechanical properties. Experimental Materials Polyetherimide (PEI) used in this study has been obtained from Sabic Innovative Plastic (Grade Ultem-1000) in pellet form. Polyetherimide is an 246 Applied Polymer Composites, Vol. 2, No. 4, 2014

3 β Silicon Carbide Coated MWCNTs Reinforced Polyetherimide Nanocomposites amorphous, transparent, amber color high performance thermoplastic with a glass transition temperature around o C. Polycarbosilane coated MWCNTs of diameter 2-4 nanometers, length µm and the aspect ratio of around 10,000 have been obtained from DMSRDE Kanpur, India. These coated MWCNTs have been used as reinforcement for PEI matrix to develop coated MWCNT / PEI nanocomposites. Processing of Coated MWCNT / PEI Nanocomposites PEI pellets were dried under vacuum at 80 C for at about hrs. Coated MWCNT / PEI nano-composites have been prepared in a Sigma high temperature internal mixer equipped with two counter-rotating Sigma type rotors at 320 C, with a speed of 100 rpm and a mixing time of 10 min. PEI polymer was initially melted, and then the coated MWCNT were incorporated into the molten PEI matrix. In a typical experiment, 30 gm of PEI pellets were mixed with 0.1, 0.2 or 0.3 (phr) of coated MWCNTs. Formulations of the composites are listed in Table 1. The processed coated MWCNT / PEI nanocomposites samples were dried at 80 C for hrs. The obtained composites coated MWCNT / PEI nanocomposites were compression molded under a pressure of about 20 MPa at 300 C for about 10 mins. The composite samples were cooled to room temperature under the same pressure at the rate of 2 C/min. Table 1. Composition of coated-mwcnt / PEI nanocomposites Sample No. PEI (gm) Coated MWCNTs (phr) N N N N Tensile Properties Tensile properties of PEI and the coated MWCNT / PEI nanocomposites have been evaluated according to ASTM D 638 at room temperature by Universal Testing Machine (INSTRON 3382) by using 10 KN load cell at a speed of 40 mm/min. Morphology The surface morphology of the gold coated tensile fractured coated MWCNT / PEI nanocomposites has been examined by a JEOL scanning electron microscope Model JSM-6390 LV SEM. Applied Polymer Composites, Vol. 2, No. 4,

4 Nitin Nagar, K.N. Pandey, Pratibha Singh, Vishal Verma, and R.M. Mishra Thermo-Gravimetric Analysis Thermo gravimetric analysis of the coated MWCNT / PEI nanocomposites has been conducted by a Perkin-Elmer Pyres TGA, in the temperature range of C under heating rate of 10 C/min in nitrogen atmosphere. Results and Discussion Tensile Properties Tensile properties of the coated MWCNT / PEI nanocomposites are recorded in Table 2, and Figures 1 and 2. Results indicate that the tensile modulus and the tensile strength the coated MWCNT / PEI nanocomposites increases linearly with addition of only small amounts of coated MWCNTs into the PEI matrix. The tensile modulus of PEI is 1.25 GPa. The tensile modulus of coated-mwcnt / PEI nanocomposites increases to 1.27 GPa, 1.28 GPa and 1.29 GPa respectively, with the amounts of the reinforcing coated MWCNTs in the PEI increasing to 0.1, 0.2, and 0.3 phr respectively, and the formation of the respective coated-mwcnt / PEI nanocomposites. The tensile strength of PEI is MPa. The tensile strength of coated-mwcnt / PEI nanocomposites increases to MPa, MPa and 72.8 MPa respectively, with the amounts of the reinforcing coated MWCNTs in the PEI increasing to 0.1, 0.2, and 0.3 phr respectively, and the formation of the respective coated-mwcnt / PEI nanocomposites. Table 2. Tensile properties of coated-mwcnt / PEI nanocomposites Sample Tensile Strength (MPa) Tensile Modulus (GPa) N N N N The improvement in tensile properties of coated-mwcnt / PEI nanocomposites, with increasing amounts of coated MWCNTs in them, appears due to the homogeneous and uniform dispersion of the coated MWCNTs in the PEI matrix; as well as the strong interfacial interaction between coated MWCNTs and the PEI matrix. This has been investigated by the nanocomposites morphology examined by SEM, as discussed in the next section. 248 Applied Polymer Composites, Vol. 2, No. 4, 2014

5 β Silicon Carbide Coated MWCNTs Reinforced Polyetherimide Nanocomposites Figure 1. Tensile modulus of PEI and the coated-mwcnt / PEI nanocomposites Figure 2. Tensile strength of PEI and the coated-mwcnt / PEI nanocomposites Morphology Figure 3 shows the SEM micrographs of the fractured surface of the PEI matrix (Figure 3a) and of the phr coated - MWCNT / PEI nanocomposites (Figure 3b,c,d). The fractured surface of PEI (Figure 3a) is relatively smooth compared to that of the coated MWCNT / PEI nanocomposites (Figure 3b,c,d). The rougher surface of the coated MWCNT / PEI nanocomposites is due to the interactions between the reinforcing coated MWCNT and the PEI matrix. Applied Polymer Composites, Vol. 2, No. 4,

6 Nitin Nagar, K.N. Pandey, Pratibha Singh, Vishal Verma, and R.M. Mishra Figure 3b shows that the coated MWCNTs may be identified as aligned in the direction of stretching of the nanocomposites during tensile fracture. However, it is known that, in general, it is a very difficult to entirely unfold and de-bundle all nanotubes into individual tubes. Figure 3. SEM images of PEI and the coated-mwcnt / PEI nanocomposites Thermo-Gravimetric Analysis The TGA (thermo gravimetric analysis) plots for PEI and the coated MWCNT / PEI nanocomposites are shown in Figure 4. Degradation of PEI begins at 520 C. Degradation of 0.1, 0.2, 0.3 phr coated MWCNT / PEI nanocomposites also starts at 520 C. Thus the addition of coated MWCNT as reinforcement does not alter the thermal stability of the PEI polymer matrix. Conclusions Polycarbosilane derived β silicon carbide coated multi wall carbon nanotubes (MWCNTs) reinforced polyetherimide (PEI) nano-composites (with 0.1 to 0.3 phr coated MWCNTs reinforcements) have been successfully fabricated by a sigma high temperature internal mixer followed by compression. The coating has been advantageous for dispersion of MWCNTs in PEI matrix in the coated MWCNT / PEI nanocomposites. The increasing amounts of coated MWCNTs in the coated MWCNT / PEI nanocomposites result in increasing 250 Applied Polymer Composites, Vol. 2, No. 4, 2014

7 β Silicon Carbide Coated MWCNTs Reinforced Polyetherimide Nanocomposites Figure 4. TGA graph of PEI and the coated-mwcnt / PEI nanocomposites tensile modulus and tensile strengths of the resulting coated MWCNT / PEI nanocomposites. This appears due to bonding between coated MWCNTs and PEI in the coated MWCNT / PEI nanocomposites. Thermal stability of coated MWCNT / PEI nanocomposites is almost the same as that of PEI. References 1. Thostensona E.T., Renb Z., a T-W. Composites Science and Technology 61(13), , (2001). 2. Moniruzzaman M., Winey K.I., Macromolecules, 39(16), , (2006) 3. Spitalsky Z., Tasis D., Papagelis K., Galiotis C., Progress in Polymer Science, 35(3), , (2010) 4. Ma P.C., Siddiqui N.A., Marom G., Kim J.K., Composites Part A: Applied Science and Manufacturing 41(10), (2010) 5. Liu T., Tong Y., Zang W-D., Composite Science & Technology, 67(3-4), (2007) 6. Goh P.S., Ng B.C., Ismail A.F., Aziz M.S.M., Solid State Sciences, 12(12), Applied Polymer Composites, Vol. 2, No. 4,

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