Effect of Microwave Radiations on Electrical, Mechanical and Thermal Properties of Poly (Vinyl Alcohol) Nano Composite Films
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Saudi Digital Library
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Modification of polymer nanocomposite properties using radiations is gaining wide interest and acceptance by the researchers both in academia and industry. Laser, Electron beam, gamma, UV, X-rays, and microwave are the common radiations being used to alter the properties of the polymers. Comparing to the other types, microwave radiation is easier to use, cheaper, and safer technology.
Poly (vinyl alcohol) (PVA) is a polymer that has been received significant interest from researchers who are working with films and packaging materials. In our research groups, we have studied and reported different systems of PVA blends [1-15]. Significant improvement in the properties of PVA was reported by reinforcing it with CNT and graphene [7-14]. Among a number of different Nano fillers, Graphene and CNT have emerged as promising fillers for polymer composites in the last two decades. The main advantage of adding nano filler in the weak polymer matrix as poly (vinyl alcohol) is to give extraordinary properties enhancement favourable for different applications. The development of PVA nano composites with graphene was an important aim of current applied research work for use in the electric field. As electrical and electronic devices are used everywhere in our life. Their usage has been increased remarkably and we cannot imagine our modern life without using these important instruments. However, the electromagnetic radiations emitted from these instruments overlap with one another leading to damage or malfunctioning of the adjacent equipment. Consequently, the need of reliable and effective electromagnetic interference (EMI) shielding materials is essential. Recently, polymer based conductive composites have been attracted a considerable amount of attention by researchers owing to their low cost, low density, durability, good mechanical properties and a wide range of applications. PVA being a water soluble polymer is well known for its biocompatibility and non-toxicity. In recent years, graphene has gone one step ahead among the other nano fillers due to its unique characteristics. Graphene combines the layered structure of clays with excellent mechanical, thermal and electrical properties of carbon nanotubes, which eventually provides unique functional properties for the final products.
In this applied research work, we exposed the prepared films to microwave radiation to investigate the effect of irradiation on electrical, mechanical, thermal and morphological properties. Poly (vinyl alcohol) / graphene nanocomposites were prepared using solution casting technique. Samples were subjected to microwave radiations for 5, 10 and 15 min at a constant power of 200 watts. The nanocomposites were characterized before and after irradiation by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Reduction in crystallinity and thermal stability of PVA was observed with incorporation of graphene due to restricted dynamic movement of chains and synergistic instability respectively. Microwave irradiation for 5 min improved the crystallinity from 46% to 55% and thermal stability (activation energy increased from 122 kJ mole-1 to 128 kJ mole-1) of the nanocomposites. Further irradiation caused a decreased in the crystallinity as well as in the thermal stability due to degradation. Furthermore, the isothermal crystallization kinetics were studied by employing the well-known Avrami model. An increase in the crystallization rate was observed with graphene incorporation. The thermal degradation kinetics were also studied by the help of TGA analysis. All the nanocomposites followed nth order reaction mechanism and no change in degradation was observed due to the addition of graphene or the microwave irradiation except the changes in the kinetic parameters such as activation energy (E) and frequency factor (ko). Moreover, increase in electrical conductivity from 0.021 S/cm to 3.55 S/cm was observed in 1% and 10% graphene incorporation in PVA matrix respectively. Composites acquired percolation threshold at 5% graphene incorporation with 2.17 S/cm DC conductivity. Bueche model and Scarisbrick model were applied for the prediction of electrical conductivity and the close match was found between experimental and theoretical conductivity using Scarisbrick model at geometrical factor (C) value 0.1. Vector network analyzer (VNA) was engaged in measuring the electromagnetic inference shielding effectiveness (EMI SE). EMI SE found to increase along with an increase in graphene contents. Improvement in both electrical properties, electrical conductivity, and EMI SE, was achieved after microwave irradiation. The decrease in tensile properties was found with the incorporation of graphene especially at higher percentage due to agglomeration. Moreover, at higher graphene percentage the thickness of filler enrich side increased in bi-layered films which result in decrease of tensile strength.