Material Characterisation
Optical and dielectric properties of polyvinylchloride/polymethylmethacrylate blends

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Abstract

The optical and dielectric properties of prepared polyvinychloride/atactic polymethylmethacrylate (PVA/α-PMMA) blends are studied as a function of applied field frequency and PMMA content. The observed optical energy gaps and the energy gap tails were determined from the measured absorption spectra. It was found that the applied frequency and the α-PMMA concentration have some effects on the physical parameters such as the optical energy gap, the glass transition temperature (Tg), the dielectric constant, and the refractive index. Correlation between the determined optical energy gaps and the measured Tg is presented. The observed changes in these physical parameters are due to structural changes in the amorphous domains, impurities and space charge within the interfaces in the mixed phases.

Introduction

The demands of the market have pushed the development of new polymeric materials, blends, alloys, and composites. These developments run parallel with a large series of studies aimed at understanding the property–structure relationships of the materials developed. Among these, are the modified mechanical, thermal, electrical, and optical properties to fulfil the required characteristics for such goods as packaging and optical devices. The research area concerning optical and dielectric properties is particularly interesting and important for optoelectric applications [1], [2], [3].

Polymeric blends are obtained by melt blending at high temperatures and subsequent cooling to below glass or crystallization temperature. These blends may display a wide range of improved properties in comparison to the individual polymers or copolymers. The modified properties of polymer blends are governed by important and sensitive factors such as compatibility, interfacial adhesion between phases and morphology of the dispersed phases [4], [5]. Blending is basically a variation of compounding or formulating multi-component polymeric systems to meet the needs of the current markets [6]. In many cases a favourable situation, such as outstanding properties or a desired morphology, can be obtained by addition of compatibilizers or the induction of physical–chemical interactions during the blending process. For example, the homopolymer atactic polymethylmethacrylate (α-PMMA) normally added as a possible stabilizer to polyvinylchloride (PVC). The purpose of blending these polymers is to enhance the thermal stability of PVC. The miscibility of these blends and the effect of α-PMMA on the thermal stability of PVC have been investigated through glass transition predictions [7], [8], [9].

Recently, we focused our research on studying the optical and electrical properties of PEO/PVC blends through impedance and photospectroscopy techniques. Interesting effects were observed on the ac conductivity, dielectric behavior, optical transmission under different measuring conditions, such as temperature, applied field frequency, blending ratio, and molecular weight [10], [11]. This paper is concerned with the study of some optical and dielectric properties of PVC/PMMA blends. The study covers measurements of optical spectra, dielectric constant, and determination of the refractive index and the optical energy gaps of these blends as a function of blending ratio and glass transition temperature.

Section snippets

Blend preparation

Materials and the procedure of blending were reported elsewhere by Cimmino and Popovska [12]. Briefly, the PVC (Mh=8.104 Tg=77°C, DSC) and α-PMMA (Mh=1.2.106 Tg=115°C) were mixed in a Brabender apparatus at 180°C for 10 min. Sheets of PVC/α-PMMA blends with weight ratios: 100/0, 95/5, 90/10, 85/15, 50/50, 25/75, and 0/100 were prepared. The majority of these blends were used in the present study. In all blends, Irgstab 17 Mok as stabilizer (2 wt.% based on PVC), and WAX-E as lubricant (1 wt.%

Results and discussion

Studying the optical absorption spectra and the dielectric behavior of the prepared PVC/α-PMMA is interesting to characterize the blend properties through determination of some physical parameters such as the optical energy gaps, dielectric constant, and refractive index. Correlation between the determined optical energy gaps and the measured glass transition temperature Tg is useful to understand property–structure relationship.

Conclusion

Blends of two homopolymers PVC and α-PMMA were prepared. The optical absorption and dielecric behavior of these blends was investigated as a function of applied field frequency and the α-PMMA concent. Some physical quantities as the optical energy gap, dielectric constant, and the refractive index were determined. Correlation between optical energy gaps and the glass transition temperature Tg is discussed. The changes in the values of the optical energy gaps, dielectric constants, and the

Acknowledgements

The authors thank Drs S. Climmino, M. DiLorenzo, and C. Silvestre and the Institute of Research and Technology of Plastic materials in Napoli (Italy) for useful discussion and cooperation and permission to quote the Tg values of DTMA measurements. Special thanks to our Research Assistant Mr Aws Ahmad Abdo for his duty work on this research. Also thanks to colleagues in the Faculty of Pharmacy of the University of Jordan, Amman for the use of the photospectrometer. This work was carried out

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