High performance polymer composites such as poly (ether-ether ketone) PEEK, poly (ether imide) PEI with fillers results in unique combination of thermal and morphological properties which make then useful for various applications. By introducing suitable fillers in polymers, composite properties can be tailored to meet specific design requirements such as low density, high strength, high stiffness, high damping, chemical resistance, thermal shock resistance, high thermal conductivity, low coefficient of thermal expansion (CTE) and good electrical properties such as dielectric constant. Bulk of literature is available which documented that PEEK display excellent thermal, mechanical and electrical properties [2].

High performance engineering polymer having semicrystallinity afford a range of advantage over polymer composite due to complete cohesion between the reinforcement and the matrix.

This is so characterized because both the reinforcing crystalline phase and the mesophase are of the same material.

In polymer composites the reinforcement and matrix adhesion is brought with the help of interphasing agent which act through Vander wall’s interaction. These forces are by no means as strong as the cohesive forces which interact in a semi crystalline polymer [3]. Blending of these two polymers combines the complimentary properties of both of them and hence PEEK/PEI blends have been the subject of several investigations for more than two decades [3, 4-18] out of different composition of PEEK/PEI blend. It has found that 50:50 are the optimum composition [3]. Despite of many aspects that have also been studied the thermal decomposition studies on PEEK and PEI blends using TGA. The results mostly directed in understanding its degradation temperature, and thereby to correlate with other physical and mechanical properties [19]

Carbon nanotubes (CNTs) have been considered as an ideal reinforcement to fabricate high-performance nanocomposites due to its excellent physical properties such as high mechanical strength and electrical AND thermal conductivity [20].

However the major challenges associated with development of high-performance nanocomposites are uniform dispersion of CNT’s in the polymer matrix and developing a strong interfacial interaction which will lead to the effective load transfer from the polymer to the CNT’s. In a very recent article MWCNT coated with SiC were used to improve the dispersion of MWCNT in the polymer matrix (PEEK/LCP) [21].

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 polyphosphazene coated MWCNT nanocomposites.

MATERIALS:

Polyethetetherketone (PEEK) material of grade keta spire KT-820P, supplied by Solvay specially polymers. The polyether-imide (PEI) material of grade ULTEM 1010 was supplied by GE plastics. Multi-walled carbon nanotube ( MWCNT) and polyphosphazene (PPh) have been synthesis and supplied by DMSRDE, Kanpur are used for present investigation MWCNT having a diameter 2-4 nanometer and length 20-30 µm and the aspect ratio 10,000.

Figure-1: Chemical structure of polyetheretherketone (PEEK).

Figure- 2: Chemical structure of polyetherimide (PEI).

Figure-3 Multi-walled carbon nanotube (MWCNT)

Figure-4: Chemical structure of Polyphosphazene

Coating of polyphosphazene on MWCNT:

For the coating of polyphosphazene on MWCNT firstly we took 2 liter of tetra hydro furan (THF) and 100 gm KOH and pass it over 500 gm of Alumina beads to remove the moisture. Then after sodium pieces putted in this solution and leave the solution for two days, a bluish colour is produced. Distillation of this solution was carried out and then 100 ml of this solution mixed with 100 mg PPh. After mixing 0.4 gm MWCNT added in to 40 ml of prepared solution and reflux it for 6 to 7 hours. Then after again distillation is done at 90⁰C and obtained residue is heated to 250⁰C and then cooled to room temperature. This as a result we get PPh coated MWCNT.

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% pph coated MWCNT 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 compositions

Batches S. No.	PEEK gm	PEI gm	Polyphosphazene coat MWCNT,s (wt %)
1	15	15	0.01%
2	15	15	0.02%
3	15	15	0.03%

Characterization:

Thermo gravimetric analysis (TGA):

In the present study, the degradation pattern and thermal stability of the various nano composites were determined by Pyres TGA-1 (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.

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.

Scanning electron microscopy (SEM):

SEM analysis has been carried out with the help of JSM 6380 Model (JEOL). Prior to SEM analysis specimen gold coated with the help of gold sputtering unit to avoid the charging effect and enhance the emission of the secondary electrons.

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 5000 c/s, operated at 40 kv and 20 mA to get an explicit idea of the relative crystallinity of composites.

RESULTS AND DISCUSSION:

It has been proposed that the polymer matrix reinforced with Polyphosphazene coated MWCNT would improve its thermal stability. TGA studies have been performed for polymer nanocomposites with varying polyphosphazene coating 0.01 to 0.03 wt %. The TGA curve of 50:50 percentage of PEEK/PEI with PPh coated MWCNT is shown in Figure 5. 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 PPh 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. Similar enhancements in the thermal stability attributed to a more homogenous distribution of the CNT have been reported for Nylon 6/MWCNT [22] and PU/MWCNT [23] composites.

Figure 5: TGA curve of PEEK/PEI 50:50 blend with PPh coated MWCNT

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

Description	On set tem(˚c)	Peak tem(˚c)	Weight loss in%	Residue at 980(˚c)
PEEK/MWCNT	450	960	51.03	48.97
PEEK/MWCNT (PPh coated)	432	960	54.12	45.88
PEEK/PEI (PPh coated MWCNT)	435	900	49.05	50.95 Residue at 900 (˚c)

In the case of melting process, thermogram in Figure-6 shown an endothermic peak for PEEK/PEI with polyphosphazene coated MWCNT at 340⁰c. But it has been cited in the literature that PEEK/PEI blend has melting point at 332⁰c [24]. 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 polyphosphazene has been incorporated. It can be attributed to improved degree of dispersion of MWCNT coated with PPh in the matrix. Another reason may be due to more perfect crystals which takes place during the heating.

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

Figure 6: DSC curve of PEEK/PEI 50:50 blend with PPh coated MWCNT

Scanning electron microscopy Figure 7 (a) AND (b) shows the phase morphology of PEEK/PEI composites with PPh coated MWCNT 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 then the uncoated MWCNT. It may be due to the dispersion of elastomeric in to polymer matrix.

Figure -7(a): SEM photograph of PEEK/PEI blend 50:50 with

uncoated MWCNT

Figure -7 (b): SEM photograph of PEEK/PEI blend 50:50 with PPh coated MWCNT

The crystalline structure of PEEK/PEI/ MWCNT coated with polyphosphazene composites has been evaluated using wide angle X-Rays diffraction. Six main peaks can be observed at 2θ = 21.2607°,23.3514°, 29.4464°, 33.7870°,39.6183°,48.069° correspond to the diffraction of various crystalline planes [25]. With d-spacing at 4.17570, 3.80636, 3.03089, 2.65078, 2.27302, and 1.89128, Å, respectively.XRD results reveal that compact crystalline structured nanocomposites have been formed at various loading of polyphosphazene coated MWCNT. These results are in good agreement with the observation obtained in DSC and TGA analysis. Thus we can say that nanocomposites with PPh coated MWCNT, s has higher thermal stability enhancement in melting point and good dispersion of the MWCNT in the matrix can be archived.

Figure -8: X-Ray Diffraction of (PEEK/PEI with PPh coated MWCNT)

CONCLUSION:

Different PEEK/PEI /PPh coated MWCNT composites at 0.01,0.02,and 0.03 wt% MWCNT content, have been prepared by melt blending an efficient dispersion of the CNT,s in the matrix was achieved by the polyphosphazene coating, as revealed by SEM micrograph of composites. TGA thermogram shown a substantial increase in the matrix degradation temperature by the incorporation of PPh coated MWCNT. Higher thermal stability is found for samples with improve CNT dispersion. 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.

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Received on 17.05.2012 Modified on 20.05.2012

Asian J. Research Chem. 5(5): May 2012; Page 650-654

Batches [MWCNT %]	Virgin-PEEK ( Melt temp- 340˚c)				PEEK/PEI(50-50) blend (Melt temp- 332˚c) PPh coated MWCNT
Batches [MWCNT %]	MWCNT		PPh coated MWCNT		PEEK/PEI(50-50) blend (Melt temp- 332˚c) PPh coated MWCNT
	Tm	∆H	Tm	∆H	Tm	∆H
0.01	340.69	3.067	340.00	7.581	336.75	5.062
0.02	339.53	4.728	338.55	6.713	337.40	14.786
0.03	338.03	5.871	337.36	5.071	339.67	15.022