1. INTRODUCTION:

Polymer blends are the suitable candidates for improvement of either specific property or providing materials with a full set of required properties at lesser cost and improving processability [1].Polymer blends containing Poly ether imide (PEI) are considered as one of the most advance research topic in the present scenario due to its good strength, high modulus and a high glass transition temperature (Tg). PEI also possesses good electrical properties and remains stable over a wide range of temperature. Several studies of this type of blend system have been documented in literature [2-5].

Poly (ether ether) ketone (PEEK) is a semicrystalline, high performance material with excellent mechanical properties such as elastic modulus, strength and toughness, resistance to hydrolysis and extremely high thermal stability. Because of high thermal stability, it can be used in aerospace and marine industries as a load bearing structural material [6]. PEEK has been blended with PEI to enable complimentary combination of the material properties exhibited by each component [7]. The incorporation of carbon nanofiber into the PEEK matrix enhanced its thermal and mechanical properties significantly [8-9].

Carbon nanotubes have attracted a great deal of attention for many application due to its outstanding mechanical, electrical and thermal properties [10-11], arising from the nanoscale dimension excellent physical characteristics and beyond the hope high aspect ratio of nanotubes [12-13]. However, the difficult task associated with fabrication of high performance nano composites are uniform dispersion of CNTs in the polymer matrix and creating a interfacial interaction which may result to the effective load transfer from the polymer to the CNTs. Bose et al have conducted a study on MWCNTs coated with SiC to improve the dispersion of MWCNTs in the polymer matrix [14].

In this study, the main objective is to develop PEEK/PEI/MWCNTs nanocomposite and to demonstrate the effect of MWCNTs on thermal and morphological properties of PEEK/PEI blend system. The main emphasis of the present studies is to see the effect of SiC coated MWCNTs to the dispersion in the blend system.

2. MATERIALS AND METHODS:

This section briefly introduces the material used in this study for carrying out comprehensive experimental investigations followed by brief discussions about the characterization techniques adopted for analysis of the thermal and morphological properties of PEEK/PEI with polycarbosilane coated MWCNT nanocomposites.

Materials:

Poly (ether ether)keone (PEEK) grade-keta spire KT- 820P, supplied by Solvay Chemical Company. PEEK is a semi crystalline thermoplastic with excellent mechanical and chemical properties that are retained to high temperatures having glass transition temperature Tg (145⁰C) and the melting point of 345⁰C.

Multi-walled carbon nanotube (MWCNT) and polycarbosilane (PCS) have been synthesized by DMSRDE, Kanpur. MWCNT,s possess a diameter 2-4 nanometer and length 20-30 µm and the aspect ratio 10,000.

Figure-1 Chemical structure of Poly (ether ether) ketone (PEEK)

Polyether-imide (PEI) is supplied by General Electric Company under the grade ULTEM (1010).

Polyether-imide have high glass transition temperature Tg-217⁰C.

Figure-2 Chemical structure of polyether-imide (PEI).

Figure-3 Multi-walled carbon nanotube (MWCNT)

2.2 Coating of PCS on CNT:

For the coating of polycarbosilane on MWCNT first of all we take 2 liter tetra hydro furan (THF) and 100gm KOH pass it over 500 gm Alumina to remove the moisture. Then after sodium piece putted in this solution and leave the solution for two days, a bluish colour is produced. Distillation of this solution was done and then took 100 ml of this solution in a bottle and add 100 mg PCS. After mixing 0.4 gm MWCNT added in to 40 ml of prepared solution and reflex it for 6-7 hours. Now distillation of the above solution is done at 90⁰c then the obtained residue is heated up to 250⁰c and then leave it to cool as a result we get PCS coated CNT.

2.3 Preparation of nanocomposites:

A Sigma high-temperature internal mixture equipped with counter rotating rotors were used for the preparation of PEEK/PEI composites with 0.01 to 0.03 wt% PCS coated MWCNT’s at a temperature of 3500c with a rotor speed of 100 rpm for 8 to 10 min. The batched prepared is tabulated in Table-1

Table – 1 Nanocomposite composition

Sample S.No.	PEEK gm	PEI gm	Polycarbosilane coated MWCNT,s (wt %)
1	15	15	0.01
2	15	15	0.02
3	15	15	0.03

2.4 Characterization:

2.4.1Thermogravimetric Analysis (TGA):

In the present study, the degradation pattern and thermal stability of the various nano composites were determined by Pyres TGA (Perkin Elmer, USA) thermal analyzer. The Maximum weight loss of the samples was analyzed as a function of temperature. The quantity of the sample for each

test was about 10 mg and they were heated from ambient to 900 ºC at the control heating rate of 10 ºC/ min under inert atmosphere.

2.4.2 Differential scanning calorimetry (DSC):

DSC thermogram of nanocomposite was recorded with a Perkin Elmer Pyris Diamond DSC at the heating rate of sample 10⁰C/min under nitrogen atmosphere from ambient temperature to 400⁰C.

Differential scanning calorimetry (DSC) is a thermo analytical techniques in which the difference in the amount of heat required to increase the temperature of a sample and reference are measured as a function of temperature .Both the sample and reference are maintained at very nearly the same temperature throughout the experiment. By the help of (DSC) we can determine the melting point temperature, heat of melting, glass transition temperature, curing and crystallization and identification of phase transformations.

2.4.3 Scanning electron microscopy (SEM):

Morphological studies of nanocomposites have been carried out by JEOL JSM 6380 LA Scanning Electron Microscope. Prior to SEM analysis, specimens were gold coated with the help of gold sputtering unit in order to avoid charging effect and enhance the emission of secondary electrons.

2.4.4 X-Ray Diffraction (XRD):

X-Ray Diffraction study was carried out on PW 1840 X-ray diffractrometer with Cu- kα (1.54 Å)targets at 2mm slits at a scanning rate of 0.050 2θ / sec. chart speed 10mm/2 θ range 5000c/s, operated at 40 KV and 20mA to get an explicit idea of the relative crystallinity of composites.

3. RESULTS AND DISCUSSION:

It has been proposed that the polymer matrix reinforced with Polycarbosilane coated MWCNT would improve its thermal stability. TGA studies have been performed for polymer nanocomposites with varying polycarbosilane coating 0.01 to 0.03 wt %. The TGA curve of 50:50 percentage of PEEK/PEI with PCS coated MWCNT is shown in Figure 4. From the Figure it can be revealed that when the temperature was raised from room temperature to 900⁰c the residue was about 48 wt % only one weight loss step was observed shown by as broad peak in the TGA curve. The weight loss range in PEEK/PEI with modified CNT is 450 to 900⁰c. The results (tabulated in Table-2) indicate that the product has good thermal stability. This can be attributed to the incorporation of coated MWCNT with PCS which reduces the chain mobility of the polymer matrix by imposing vast number of restriction sites which reduces the thermal vibration of C-C bond. So the nanocomposites require more thermal energy for the degradation of the polymer matrix which in turn increases thermal stability.

Figure-4: TGA curve of PEEK/PEI 50:50 blend with PCS coated MWCNT

In the case of melting process, thermogram in Figure-5 shown an endothermic peak for PEEK/PEI with polycarbosilane coated MWCNT at 340⁰c. But it has been cited in the literature that PEEK/PEI blend has melting point at 332⁰c [15]. Thus these observation revealed that there is an enhancement of 8⁰c in the melting point of PEEK/PEI blend when multi-walled carbon nanotube coated with polycarbosilane has been incorporated. It can be attributed to improved degree of dispersion of MWCNT coated with PCS in the matrix. Another reason may be due to more perfect crystals which takes place during the heating.

Table -2: TGA Result of PEEK/PEI with PCS coated MWCNT

Description	On set tem(˚c)	Peak tem(˚c)	Weight loss (%)	Residue at 980(˚c)
PEEK/MWCNT	450	960	51.03	48.97
PEEK/MWCNT (PCS coated)	433	960	53.12	46.88
PEEK/PEI (PCS coated MWCNT)	437	900	47.609	52.391 Residue at 900 (˚c)

The result of Differential Scanning Calorimetry (DSC) thermogram of PEEK/PEI composite with PCS coated MWCNT and compared with PEEK nanocomposite PCS coated and uncoated MWCNT shown in Table - 3.

Figure 5: DSC curve of PEEK/PEI 50:50 blend with PCS coated MWCNT

Table-3: DSC Results of PEEK/PEI blends with PCS coated MWCNT

Batches [MWCNT %]	Virgin-PEEK ( Melt temp- 340˚c)				PEEK/PEI(50-50) blend (Melt temp- 332˚c) PCS coated MWCNT
	MWCNT		PCS coated MWCNT		PEEK/PEI(50-50) blend (Melt temp- 332˚c) PCS coated MWCNT
	Tm (⁰C)	∆H (j/g)	Tm (⁰C)	∆H (j/g)	Tm (⁰C)	∆H (j/g)
0.01	340.69	3.067	340.00	7.581	337.00	2.571
0.02	339.53	4.728	338.55	6.713	337.03	7.195
0.03	338.03	5.871	337.36	5.071	339.34	2.861

SEM micrographs as shown in Figure 6 (a) and (b) depict the phase morphology of PEEK/PEI composites with PCS coated and uncoated MWCNT. The scanning micrograph shows that the MWCNT homogeneously dispersed with the polymer matrix. It is observed that the coated MWCNT filled composite gives better dispersion of MWCNT than the uncoated MWCNT. It may be due to the dispersion of elastomeric phase polymer matrix.

Figure -6 (a): SEM photograph of PEEK/PEI blend 50:50 with uncoated MWCNT

Figure -6 (b): SEM photograph of PEEK/PEI blend 50:50 with PCS coated MWCNT

The crystalline structure of PEEK/PEI/ MWCNT coated with polycarbosilane composites has been evaluated using wide angle X-Rays diffraction. Three main peaks can be observed at 2θ = 20.9733⁰, 23.0487⁰, 29.2389⁰ correspond to the diffraction of various crystalline with d-spacing at 4.23225, 3.85565, 3.05193, Å, respectively. XRD results reveal that compact crystalline structured nanocomposites have been formed at various loading of polycarbosilane coated MWCNT. These results are in good agreement with the observation obtained in DSC and TGA analysis. Thus we can say that nanocomposites with PCS coated MWCNT,s has higher thermal stability enhanced and good dispersion of the MWCNT in the matrix can be achieved.

4. CONCLUSION:

Various compositions of the PEEK/PEI nanocomposites were taken and PEEK/PEI nanocomposites were fabricated by melt blending in S.C. Dey extruder. Studies of high performance PEEK/PEI nanocomposites were investigated.

Thermogravimetric analysis (TGA) shows the improved thermal stability of the PEEK/PEI nanocomposites on increasing the percentage of PCS coated MWCNT’S (.01, .02, .03)% content into the matrix material. . DSC experiments indicate an increase in the melting temperature with increasing MWCNT,s content. XRD results indicate a compact crystalline structure of the composite. MWCNT restrict molecular mobility. In the matrix of PEEK/PEI dispersion was achieved by the polycarbosilane coating, as revealed by SEM micrograph of composite.

Figure -7: X-Ray Diffraction of (PEEK/PEI with PCS coated MWCNT)

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Received on 25.05.2012 Modified on 05.06.2012

Asian J. Research Chem. 5(6): June 2012; Page 703-706