Preparation and crystalline studies of PVDF hybrid composites Chethan P

Preparation and crystalline studies of PVDF hybrid composites
Chethan P. B., N. M. Renukappa, and Ganesh Sanjeev
Citation: AIP Conference Proceedings 1942, 050066 (2018); doi: 10.1063/1.5028697
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Published by the American Institute of Physics

Preparation and Crystalline Studies of PVDF Hybrid Composites Chethan P B1, 2 N M Renukappa3, b) and Ganesh Sanjeev1, a) 1Microtron Centre, Department of Physics, Mangalore University, Mangalagangotri-574199, Karnataka, India 2Department of Physics, Atria Institute of Technology, Bangalore-560024, Karnataka, India 3Department of Electronics and Communication Engineering, Sri Jayachamarajendra College of Engineering, Mysore-570006, Karnataka, India a)Corresponding author: ganesh [email protected] b)[email protected] Abstract. The conducting polymer composites have become increasingly important for electrical and electronic applications due to their flexibility, easy of processing, high strength and low cost. A flexible conducting polymer hybrid composite was prepared by melt mixing of nickel coated multi-walled carbon nanotubes (Ni-MWNT) and graphitized carbon nanofibres (GCNF) in Polyvinylidene fluoride (PVDF) matrix. The crystalline structures of the nano composites were studied by X-ray diffraction (XRD) method and showed characteristic peaks at 17.70, 18.50, 200 and 26.70 of 2?. The ? phase crystalline nature of the composite films , degree of crystallinity, melting temperature and crystallization behavior of the hybrid composites were studied using appropriate characterization techniques. The filler in the insulating polymer matrix plays crucial role to improve the crystallinity of the composites. I INTRODUCTION Conducting polymer composites have attracted industrial and research community due to their wide variety of electronic applications like sensors, electromagnetic interference (EMI) shielding, conductors, anti-static materials etc 1. Polyvinylidene fluoride (PVDF) is a semi crystalline fluoro-polymer, which has been extensively investigated because of its well known properties like good thermal stability, mechanical strength, flexibility, chemical stability, pyro, piezo and ferroelectric properties 2. These properties make it suitable for large scale scientific and industrial applications like sound transducers, sensors, actuators, bio-medical devices, pyroelectric detectors and electromechanical devices etc 3. PVDF can have five different crystalline phases ?, ?, ?, ? and ?. Among these, the polar ? phase crystalline nature of PVDF is more interesting crystal phase which is characterized by all-trans (TTTT) planar zigzag chain conformations 4. The technological up-gradation of the material depends on film processing methods in which the properties can be easily optimized and controlled. The crystalline nature of material plays a very crucial role for selected applications and is also affecting the physical properties of a material. The polar ? phase can be obtained from the most common technique, namely, mechanical stretching of PVDF film. But this is not suitable for composite preparation as stretching of film may cause uncontrolled orientation of fillers and the material would become fragile by limiting its applications 5. However, several researchers have shown that addition of fillers like graphene oxide, carbon nanotubes, carbon nanofibres, nanoclay can influence the formation of ? phase in PVDF 6-9. This has forced us to use Ni-MWNT and GCNF as the conductive fillers and their effect on crystalline nature of PVDF is discussed in this paper. 050066-1
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II EXPERIMENTAL Materials and preparation of composites The materials employed in the current work were commercially available Polyvinylidene fluoride (PVDF), grade Kynar 301 F, having a density 1.77 g/cc, melting temperature 1550C – 1600C was procured from M/s Arkema, France. The fillers used are the nickel coated multi-walled carbon nano tubes (Ni-MWNT) with a mean outer diameter of 10-20 nm, length of 10-30 ?m, purity 97% and Graphitized carbon nano fibre (GCNF) of diameter ~200 nm, length of 10-30 ?m and purity >90 wt% which were procured from M/s Global Nanotech Co. India, for the nano composites fabrication. The required amount of Ni-MWNTs and GCNF were added into PVDF using Haake mixer. The operating speed was 60 rpm with 2200C for 10 min. Then the resulting PVDF-Ni-MWNT-GCNF mixtures were subsequently compression molded at 2200C in order to obtain a sheet having a thickness of 0.5 mm for experimental characterizations. The fabricated composites coding are given in Table 1 for further discussions. TABLE 1. Sample coding Samples Coding Neat PVDF P PVDF+3wt%Ni-MWNT+3wt%GCNF PNG3 PVDF+5wt%Ni-MWNT+5wt%GCNF PNG5 Measurements The X-ray diffraction pattern of the samples were recorded in the range 100-500 of 2? with the scan speed of 0.020/s using Rigaku Smart Lab X-ray diffractometer using CuK? radiation (? = 1.54 Å) at 40 kV and 30 mA. The Fourier Transform Infrared (FTIR) spectroscopy analysis was carried out using Perkin Elmer spectrum-GX FT-IR spectrometer. The samples were scanned in transmission mode in the wavelength region of 400 cm-1 to 4000 cm-1. The melting behavior of the composites was determined using Differential Scanning Calorimeter, DSC-Q20 (TA instrument) apparatus. The samples weighing 8 mg were heated from ambient to 2000C at a heating rate of 100C/min under a nitrogen atmosphere. III RESULTS AND DISCUSSION X-ray Diffraction studies The X-ray diffractograms of the samples P, PNG3 and PNG5 are shown in Fig. 1. The prominent characteristic peaks for all the crystal phases were observed around 200. The peaks at 2? = 17.80, 18.50, 200 and 26.70 correspond to the ? phase of PVDF with (100), (020), (110) and (021) reflections respectively 10. FIGURE 1. X-ray diffraction patterns of P, PNG3 and PNG5 samples 050066-2

With the addition of fillers, the peak intensities in PNG3 and PNG5 samples decrease and a new diffraction peak around 2? = 20.80 was observed indicating the formation of ? phase with (110)/(200) reflections 11. The peak position at 2? = 17.80 and 26.70 in PNG3 and PNG5 samples are diminished with decrease in intensities compared to that of neat PVDF. Further, It is also evident that the ? phase peak intensities were considerably suppressed. This clearly reflects the formation of ? phase in composite films. FTIR Studies The magnified IR spectra of P, PNG3 and PNG5 samples are shown in Fig. 2 (a). The absorption peaks at 613 cm-1, 763 cm-1, 974 cm-1, 1180 cm-1 and 1381 cm-1 correspond to the ? phase of PVDF whereas the peaks at 511 cm-1, 841 cm-1 and 1276 cm-1 represents the ? phase respectively 12. The formation of ? phase was clearly observed with the addition of Ni-MWNT and GCNF into the neat PVDF. The fillers enhancing the formation of polar crystal phase (? phase) by suppressing ? phase peaks. The relative percentage of ? phase F(?) in each sample is calculated 13 and the results were shown in Fig. 2 (b). A maximum value of 35% is obtained for PNG5 sample. Thus, the ? phase crystallization in PNG3 and PNG5 samples is confirmed and fillers may be acting as nucleating agents for accelerating the polar ? phase formation in PVDF . (a) (b) FIGURE 2. (a) FTIR Spectra (b) Relative percentage of ? phase F(?) in P, PNG3 and PNG5 samples Thermal Studies Figure 3 illustrates the second heating and second cooling DSC thermograms of neat PVDF and Ni-MWNT-GCNF-PVDF composite films. From the results it can be cleared that nanofillers has the effect of marginal increase in the melting temperature and thereby increasing the rate of crystallization in the polymer which results in higher thermal stability of the composites. It is evident from Fig. 3(a) that the neat PVDF exhibits a melting temperature of 160.540C whereas PNG3 and PNG5 samples melt at higher temperature and the melting peaks can be observed at 161.510C and 161.740C respectively. This indicates that the composite samples becoming more polar that melt at higher temperature. The cooling thermograms of neat PVDF and Ni-MWNT-GCNF-PVDF composites were shown in Fig. 3 (b). For neat PVDF there exist a multiple melting peaks may be due to the different crystal phase and re-melting of crystallites formed during heating 14. It can be observed that the crystallization temperature is 1310C, 1390C and 1400C respectively. Interestingly, the crystallization peaks of PNG3 and PNG5 samples were narrower and the crystallization temperature TC is shifted to higher temperatures (~100C) compared to that of neat PVDF. The increase in the crystallization temperature with the addition of fillers suggests that they promote overall melt crystallization of PVDF by acting as nucleating agents. The narrower crystallization peaks implies a narrower crystallite size distribution 15. The degree of crystallinity XC is calculated 14, The melting (Tm) and crystallization (TC) temperature along with melting enthalpies are reported in Table 2. The trends are encouraging the results of the heating scans and the tendency for the enthalpy to decrease with addition of fillers. The Ni-MWNT and GCNF enhances the nucleation efficiency of the neat PVDF and the crystallinity decreases in both the composites. These results complement the results obtained using XRD and FTIR techniques. 050066-3

(a) (b
URE 3.
DSC thermograms of (a) Second heating (b) Second cooling scans of neat PVDF and Ni-MWNT-GCNF-PVDF
nano composites
TABLE 2. Melting, Crystallization peak temperatures and Enthalpies of neat PVDF and Ni-MWNT-GCNF nano composites
Sample T
(0C) ?
(0C) XC
P 16

0.54 52.13 130.69 49.88

NG3 161.51 41.79 139.59 39.99
PNG5 161.74 47.93 140.15 45.88
the present study PVDF-Ni-MWNT-GCNF hybrid nano composites were prepared by well known melt
mixing method. The crystalline structure and melting/crystallization behavior of the nano composites were
investigated. XRD and FTIR studies clearly indicate the presence of Ni-MWNT and GCNF and their involvement in
the formation of polar ? phase in hybrid nano composites. DSC measurements reveal that Ni-MWNT and GCNF
stimulate the overall crystallization rates of the hybrid nano composites by enhancing the formation of ? phase
crystals. The Ni-MWNT and GCNF are acting as the nucleating agents and show a decrease trend in the crystallinity
of nano composites.
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