Issue 37

P. Velev et alii, Frattura ed Integrità Strutturale, 37 (2016) 272-279; DOI: 10.3221/IGF-ESIS.37.36 273 E XPERIMENTAL PART Materials and methods. Materials: nsaturated polyester resins VIAPAL VUP 4627 BEMT/56 (CYTEC, Germany), containing 44% styrene, which is previously accelerated. Cyclohexanoneperoxide (PEROXIMON K 41) Ammonia-25% solution, FeCl 2 (Acrosorganics) and FeCl 3 (Acrosorganics) have been used without purification as received. Methods: The average hydrodynamic diameter of the magnetic nanoparticles is determined using Dynamic Light Scattering (DLS) - Malvern CGS-3 equipped with Не-Ne laser with wave number 623,8 nm at temperature 25 о С and angle 90 о . The concentration of the iron in the hydrosol of γFe 2 O 3 of 9600 µg/ml is determined by atomic absorption analysis (AAA) using Perkin – Elmer spectrophotometer. The composite materials are investigated with the aid of the following methods: - Tensile strength - EN ISO 527 – 1,2 : 1996; - Impact strength - EN ISO 179 : 1993; - Flexural strength - EN ISO 178 : 1996; - Determination of specific volume and surface resistance [18]; Relatively density and degree of swelling (weight and volume) in acetone Synthesis Synthesis of hydrosol of γFe 2 O 3. Magnetic nanoparticles are prepared according to reference [19]. Briefly, 0.85 ml of 12,1 М HCl and 25 ml degassed water are mixed with 5.2 g FeCl 3 and 2 g FeCl 2 . The molar ration of Fe 2+ and Fe 3+ was Fe 2+ / Fe 3+ =0.5 at рН=11- 12. Thus prepared mixture is added dropwise into 250 ml 1.5 M NaOH solution under vigorous stirring. The last stage consists in the formation of black precipitate. The precipitate is collected in magnetic fields and added to degassed water followed by centrifugation (three times for 1 min) at 4000 rpm. After this purification, 500 ml 0.01M HCl is added to the precipitate in order to neutralized the anionic charge of the particles. The cationic colloidal nanoparticles are separated again by centrifuging and they are peptized with addition of water. The result is a clear, transparent colloid (hydrosol). The oxidation of Fe 3 O 4 to γFe 2 O 3 is based in the change in the pH of the hydrosol of Fe 3 O 4 to рН=3,5. The transparent hydrosol is stirred for 30 min at 100 о С under air. The color of the solution is changed from red to brown red. This solution is cooled to room temperature and the upper layer is collected after centrifugation for 30 min at 4000 rpm. The obtained transparent brown-red layer is a hydrosol of γFe 2 O 3 nanoparticles. Copolymerization of unsaturated polyester resin The method of preparation is described in references [17, 20]. The unsaturated polyester resin is placed in a reactor where is tempered at appropriate initial temperature. Then the initiator is added and the time of copolymerization is accounted as the reaction mixture is stirred during 30 sec. To determine the time and the maximum reached copolymerization temperature of unsaturated polyester resin at different initiator concentrations is used equipment shown in Fig. 1. 1 2 3 4 5 Figure 1: Scheme of the reactor used to study the copolymerization process: 1-lid; 2-thermocouple; 3 – orifice for the tempered fluid; 4- vessel for the investigated resin; 5 – circulating fluid. U