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4COMPARATIVE ANALYSIS OF THE STRUCTURE OF PP- AND PS-BASED NANOCOMPOSITES, OBTAINED BY INCORPORATING SILICON DIOXIDE NANOPARTICLES, IN ORDER TO EVALUATE THE APPLICATION POTENTIAL
HABIBA SHIRINOVA ASLAN
Ph.D. Department of chemical physics of nanomaterials, Baku State University,
Baku, Azerbaijan
HASANOVA MATANAT RUFAT Ph.D. student at Department of chemical physics of nanomaterials, Baku State University,
Baku, Azerbaijan
ASMAR ALIEVA NUSRAT
Master student at Department of chemical physics of nanomaterials, Baku State University,
Baku, Azerbaijan
Abstract: In the present work, the role of the polymer matrix in the formation of the unique properties of the nanocomposites was analyzed. Silicon dioxide-based polymer nanocomposites were prepared by a combination of mixing in a polymer solution and hot-pressing techniques. The UV-Vis spectrums of the PS+SiO2 and PP+SiO2 nanocomposite were investigated. The bandgap of the polymer nanocomposites was calculated according to the UV-Vis spectrum with the help of Tauc 's relation.
It can be concluded that with the addition of the silica nanoparticles into the pure polymers band gap of pure polymer increased. It can be related to surface defects of nano-sized silicon dioxide particles. Furthermore, it was shown that the addition of the amorphous silicon oxide nanoparticles into the polymers leads to the observation of broadpeaks at the 400-600 nm regions for both polymer nanocomposites. Differences in PL spectra of PS+SiO2 and PP+SiO2 nanocomposite may be associated with the differences in the polymer's electronic structure.
Key words: polystyrene, polypropylene, silica nanoparticles, silicon dioxide nanoparticles PACS: 61.43.Gt, 07.60.Rd, 78.55.-m'
1. Introduction
Various types of compounds with different sizes, compositions, and shapes can be fillers for the polymer matrix. Various types of compounds with different sizes, compositions, and shapes can be fillers for the polymer matrix. Ceramic fillers have important properties such as high thermal conductivity and electrical insulation [2]. Ceramic materials refer to chemical compounds formed due to ionic, covalent, and sometimes Van der Waals or metallic bonds [10]. Amorphous silica is a white, odorless, tasteless powder. Among the substances, amorphous silicon dioxide has the lowest thermal conductivity and dielectric constant [3]. Furthermore, amorphous silicon dioxide nanoparticles act as a multifunctional filler due to optical properties due to structural defects, dielectric nature, or good thermal conductivity [7].
However, the properties of the final material depend not only on the nature of the filler but also on the properties of the polymer matrix. In this regard, the study of nanocomposites obtained based on SiO2 nanoparticles distributed in different matrices is of great importance in terms of evaluating their application possibilities. Two crucial polymers used in a variety of commercial and industrial applications are polypropylene and polystyrene [4]. High tensile strength, elongation at break, and flexural yield strength are attributes of polypropylene (PP) [11]. Conversely, PS exhibits a poorer impact resistance and is comparatively fragile [15]. It is known that one of the main requirements for polymer nanocomposites is to optimize the balance between strength and durability as much as possible. Tensile strength, impact resistance, elasticity, hardness, and other parameters are used to evaluate nanocomposites [8].
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Another parameter that affects the formation of the properties of the polymer nanocomposite is the interaction forces between the components. Polymer and nanoparticles together show a synergistic effect, which in turn plays an essential role in the formation of the final properties of nanocomposites [6-5-9].
In the present work, the role of the polymer matrix, namely polypropylene, and polystyrene, in the formation of the unique properties of the nanocomposites was analyzed.
2. Experimental
2.1. Materials
The chemicals that were used in this study: Impact resistant HIPS ( high impact polystyrene) 7240 polystyrene. White, granular with a density of 1.04 gr/cm3(Tabriz Petrochemical Company); Isotactic PP (PP grade Moplen HF500N, homopolymer): density-0.92 g/cm3 at 25°C; Mw= 250,000; Mn=67,000; melt mass flow rate (MFR)=11.5g/10min (23°C, 2.16 kg); melting temperature =162C. Toluene (PLC); deionized water. Amorphous silicon oxide(SiO2) nanoparticles with 50nm size.
Solution blending and hot pressing methods were used for the preparation of the polymer nanocomposites [12]
2.2. Characterization.
Rigaku Mini Flex 600 XRD diffractometer; UV-VIS Spectrophotometer Specord 250 Plus; and spectrofluorometer Varian Cary Eclipse were used for sample investigation.
3. Results and discussion
The UV-Vis spectrums of the PS+SiO2 and PP+SiO2 nanocomposite are given in Figure 1. The bandgap of the polymer nanocomposites was calculated according to the UV-Vis spectrum with the help of Tauc's relation [14]. The band gap of pure PS and PP polymers is about 4eV [16] and 5eV [13], respectively. According to the table, it can be concluded that with the addition of the silica nanoparticles into the pure polymers band gap of pure polymer increased. It can be related with surface defects of nano sized silicon dioxide particles
Figure 1: Dependence of absorbance on the wavelength and the dependence of absorption
coefficient on the photon energy: a) PS+7%SiO2 b) PP+7%SiO2
Table 1
№
Sample
Thickness
Bandgap
1 PS+7%SiO2 100 |im 4.19 eV
2 PP+7%SiO2 100 |im 5.91 eV
Figure 2 shows PL spectra of distilled water and water-SiO2 system. Excitation wavelength was 391 nm. Emission spectrum shows broad bands in 450-600 nm.
450 500 550 600
Wavelength (nm)
Figure2. PL spectra of distilled water(1) and water-SiO2 system(2)
Figure 3 demonstrates emission spectra PS+SiO2 and PP+SiO2 nanocomposites. The excitation wavelength was chosen at 370 nm.
Figure3. PL spectra of (a) PS+7%SiO2 and (b) PP+7%SiO2 nanocomposites
The addition of the amorphous silicon oxide nanoparticles leads to the observation broad peaks at the 400-600 nm regions for both polymer nanocomposites. Surface oxygen-deficient centers, namely, three-coordinated silicon (=Si=O)3 Si=O*; two-coordinated silicon (=Si=O)2 Si:silanone Si=O; dioxasilyrane (=Si-O)2Si(O)2 are main sources of luminescence [8]. The interaction of the polymer and silica nanoparticles in the interface region leads to the observation of the luminescence maximum [1]. It is also known that polystyrene, unlike polypropylene, has luminescent centers. The formation of additional peaks in the PL spectrum of PS+SiO2 nanocomposites may be associated with the electronic structure of polystyrene.
Conclusion
Polymer nanocomposites based on silica nanoparticles were created by combining hot pressing with a polymer solution methods. The PS+SiO2 and PP+SiO2 nanocomposite's UV-Vis spectra were examined. Using Tauc's relation, the bandgap of the polymer nanocomposites was computed based on the UV-Vis spectra. The band gap of the pure polymer increased when silica nanoparticles were added. It might have to do with surface flaws in silicon dioxide particles that are nanoscale in size. Additionally, it was demonstrated that for both polymer nanocomposites, large peaks were observed at the 400-600 nm areas with the addition of amorphous silicon oxide nanoparticles to the polymers. Variations in the electronic structure of the polymer may be the cause of the variations in the PL spectra of the PS+SiO2 and PP+SiO2 nanocomposite with the same filler concentration.
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