Influence of CdS-filler on the thermal properties of poly(methyl methacrylate)

Abstract

Nowadays, polymer composites are widely used in many fields of technology. Among them a significant roles play polymers containing semiconductor particles, especially for the manufacturing of electronic devices [1]. Therefore, it is important to understand the effects of these fillers on the properties of composites. The properties of composites mostly depend on size and shape of filler particles, their concentration as well as the type of interaction with polymer matrix. Poly(methyl methacrylate) (PMMA) is an important thermoplastic material with excellent transparency. However, its lower thermal stability restrains it from applications in higher temperature region. To improve the thermal properties of PMMA, fillers such as silica, titania, zirconia and alumina [2–8], as well as clay [9] were introduced into the PMMA. Recently, we showed significant improvement of the thermal stability of the polystyrene matrix filled up to a few mass% with the CdS nanoparticles (the mean particle diameter was 50 A) [10]. This effect is a consequence of high surface to bulk ratio of the CdS nanofiller and the presence of large number of dangling bonds that lead to the formation of chemical bonds between surface atoms of the CdS nanoparticles and the polymer chains. However, the synthetic route for preparation of nanocomposites is quite complex involving transfer of nanoparticles from water to organic phase. Because of that, simplified synthetic route for preparation of the polystyrene–CdS composite was developed based on mixing the CdS-filler in micrometer size range with the polymer melt [11]. In the present study, we synthesized new composite using PMMA as a matrix and submicronic CdS particles as a filler. The composite was characterized using structural techniques and the influence of the CdS-filler on the thermal properties of the PMMA–CdS composite was discussed in detail. The CdS-filler particles were prepared by mixing 500 mL of aqueous solutions containing 7.0 · 10 M Cd(NO3)2 (Merck) and 1.0 · 10 M Na2S (Fluka) at 90 C. Precipitate was washed out several times with water. In order to make surface of CdS-filler particles hydrophobic 150 (L of castor oil (Akzo Chemie) was added. Finally, colloidal dispersion was filtered, and precipitate was dried. The PMMA–CdS composite was prepared by dissolving appropriate amount of CdS in solution of PMMA (Diakon CMG314V)) in xylene, and consequent evaporation of solvent. The contents of inorganic phase were chosen to be 1.5, 3.0 and 6.0 wt%. In order to characterize morphology of the PMMA–CdS composite atomic force microscopy (AFM) was performed using Quesant Universal SPM instrument operating in noncontact (intermittent) mode. Measurements were performed in air using Si probes. Typical AFM image of the PMMA–CdS composite is shown in Fig. 1. Non-agglomerated spherical CdS particles in the size range from 0.2 to 0.35 lm in the PMMA matrix can be noticed. The X-ray diffraction (XRD) spectra of the PMMA–CdS composites were obtained by using Philips PW 1710 diffractometer. A typical XRD spectrum of the PMMA–CdS composite is shown in Fig. 2. The XRD peaks corresponding to 1 1 1, 2 2 0 and 3 1 1 crystallographic planes indicate that CdS is in a cubic phase (12] The CdS XRD peaks are very broad due to the small crystalline domains in the particles. The Scherrer diffraction formula was used to estimate the crystalline domain size (D) J. Kuljanin-Jakovljevic AE Z. Stojanovic AE J. M. Nedeljkovic (&) Vinca Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade, Serbia and Montenegro e-mail: jovned@vin.bg.ac.yu J Mater Sci (2006) 41:5014–5016 DOI 10.1007/s10853-006-0111-y