Milena Marinović-Cincović

The effect of gamma radiation on the ageing of sulfur cured NR/CSM and NBR/CSM rubber blends reinforced by carbon black

In this work the effect of the γ-radiation dose on ageing of carbon black reinforced elastomeric materials was studied. The compounds based on natural rubber/chlorosulfonated rubber blend (NR/CSM) and butadiene acrylonitrile rubber/chlorosulfonated rubber blend (NBR/CSM) (50:50, w/w) with different loadings (0, 20, 40, 50, 60, 80 and 100 phr) of the filler with the average particle size of 40 nm were cured by sulfur. The obtained elastomeric composites were subjected to radiation doses (100, 200, 300 and 400 kGy) in the presence of oxygen. The changes of material mechanical properties were estimated after radiation accelerated ageing. By using Fourier transform infrared measurements (ATR-FTIR) it was assessed that after exposure to doses of 100 kGy alcohols, ethers, lactones, anhydrides, esters and carboxylic acids are formed in materials. The formation of shorter polyene sequences and aromatic rings in aged samples are assumed on the basis of the obtained spectra.

Magnetic and structural studies of CoFe 2 O 4 nanoparticles suspended in an organic liquid

We present a study of magnetic and structural properties of CoFe2O4 nanoparticles suspended in an organic liquid. Transmission electron microscopy shows that the nanoparticles have a narrow size distribution of average particle size 5.9 ± 1.0 nm. X-ray diffraction shows that the particles are of cubic spinel crystal structure. Dynamic light scattering measurements reveal the existence of an organic shell around the CoFe2O4 nanoparticles with an average hydrodynamic diameter of 14.4 nm. Coercive magnetic field at T = 5K is found to be 11.8 kOe. Disappearance of the coercive field and remanent magnetization at about 170K suggests that the CoFe2O4 nanoparticles are superparamagnetic at higher temperatures which is confirmed by the room temperature Mossbauer spectrum analysis. Saturation magnetization of the nanoparticles of 80.8 emu/g(CoFe2O4) at 5K reaches the value detected in the bulk material and remains very high also at room temperature. The cobalt ferrite nanoparticle system synthesized in this work exhibits magnetic properties which are very suitable for various biomedical applications.

Optical, structural and thermal characterization of gold nanoparticles – poly(vinylalcohol) composite films

We report synthesis and characterization of gold NPs/PVA composite films. Gold colloidal NPs were introduced into a PVA matrix by simple solution-casting method to obtain homogenous, transparent, and colored films. NPs and NC films with different contents of inorganic phase (0.7, 1.4, and 2.1 wt %) were characterized by UV/Vis and FTIR spectrophotometry. Dimensions of the colloidal NPs were obtained by TEM (d ∼ 15±3 nm) and compared with results obtained by AFM of NC films. Comparison of thermal properties of the pure PVA and NC films showed that thermal stability is slightly reduced. DSC measurements revealed that Tg and melting temperatures of NCs are higher compared to pure PVA films.

Synthesis and properties of novel star-shaped polyesters based on l -lactide and castor oil

The topology of biodegradable polyesters can be adjusted by incorporating multifunctional polyols into the polyester backbone to obtain branched polymers. The aim of this study was to prepare the biodegradable-branched polyester polyols based on l-lactide and castor oil using the trifluoromethanesulfonic acid as a catalyst. FTIR and 1H NMR spectroscopy measurements were used to estimate the molecular structure of the novel materials. The polyester polyol was synthesized by ‘‘core-first” method which involves a polymerization of l-lactide by using a castor oil as multifunctional initiator. Molar masses estimated by gel permeation chromatography and vapor pressure osmometry were in good correlation with calculated values based on hydroxyl number of obtained polymers. DSC measurements confirmed high crystallinity degree of the synthesized material. It was assessed that the molar masses of obtained polymers-influenced glass transition temperature significantly. The thermal stability was investigated by TG analysis, and the results have shown the dependence of weight loss on the arm length of the star-shaped polyesters. The thermal stability of star-shaped polyesters significantly decreased with degradation of polyester polyol obtained in acid solution.

The Effect of Accelerators on Curing Characteristics and Properties of Natural Rubber/Chlorosulphonated Polyethylene Rubber Blend

The aim of this work was to determine the influence of accelerator type on curing behavior and properties of sulphur vulcanized rubber blend based on natural rubber (NR) and chlorosulphonated polyethylene (CSM). In NR/CSM compounds filled with carbon black three types of accelerator were used: N-cyclohexylbenzothiazylsulphenamide (CBS), tetramethylthiuram disulphide (TMTD), and 2-mercaptobenzothiazol (MBT). The curing characteristics were estimated using oscillating disk rheometer. The results revealed that the accelerator type not only affects the cure characteristics, but also has great influence on the mechanical properties of obtained elastomers. It was determined that the tensile strength of rubber blends cured in the presence of TMTD was relatively high.

Thermal stability of γ-irradiated chlorinated isobutylene–isoprene copolymer/chlorosulphonated polyethylene rubber blend/carbon black nanocomposites

In this study, the effect of γ-rays on the mechanical and thermal properties of polymer composites based on chlorinated isobutylene–isoprene rubber/chlorosulphonated polyethylene rubber blend with varying contents of carbon black (CB) filler was investigated. The samples were irradiated at ambient conditions with 100, 200 and 400 kGy radiation doses. Tensile strength and hardness are increasing with CB content and radiation dose is increasing, while elongation at break is decreasing. Loss of mass of 0.5, 10 and 30% was calculated for the samples from their respective thermogravimetric curves. The thermal stability of the nanocomposites was improved by both the degree of loading with filler and the cross-linking induced by γ-irradiation.

Characterization of composites based on chlorosulfonated polyethylene rubber/chlorinated natural rubber/waste rubber powder rubber blends

Chlorosulfonated polyethylene rubber (CSM) was blended with chlorinated natural rubber (CNR) with various formulations and blend ratios (CSM/CNR: 100/0; 75/25; 50/50; 25/75; 0/100) keeping the total waste rubber powder (WRP) content constant at 50 phr (parts per 100 rubber). Rheological, mechanical, dynamic mechanical and thermal aging properties as well as irradiation resistance were used as characterization of the blends. The amount of CNR in blends significantly affected the properties of the blends. The CSM/CNR/WRP rubber blend (50/50/50) possessed higher tensile strength compared with pure CSM and CNR rubber even after irradiation or thermal aging. Modulus, tensile strength and hardness of the blends appeared to increase, but elongation at break decreased progressively with increasing CNR content. These properties decreased in rubber blends after thermal aging. After irradiation, hardness, modulus and tensile strength increased up to 200 kGy and then decreased significantly for the blends with high CNR content, whereas no change in modulus was observed. CNR and CSM showed damping peaks at about 65 and −45°C, respectively, and these values correlate with the glass transition temperatures (T gs) of CNR and CSM, respectively. The shift in the T g values was observed after blending, suggesting an interfacial interaction between the two phases probably caused by the covulcanization in CSM/CNR blends.

Radiation stability of nanosilica-based urea–formaldehyde composite materials:

Three types of nanosilica-based urea–formaldehyde (UF) hybrid composite materials with a formaldehyde-to-urea (F/U) ratio of 0.8 were synthesized (UF with SiO2—Resin 1, UF + SiO2 + thiourea [TU]—Resin 2 and UF + SiO2 + thiosemicarbazide [TSC]—Resin 3). The thermal behavior of obtained materials was studied by nonisothermal thermogravimetric analysis (TGA), differential thermal gravimetry (DTG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) and supported by data from Fourier transform infrared spectroscopy (FTIR). Nanosilica-based UF hybrid composites have been irradiated (50 kGy) and after that their radiation stability was evaluated on the basis of thermal behavior. The percentage of free formaldehyde in all prepared samples was determined. DTG peaks of unmodified nanosilica-based UF resin (UF with SiO2) are shifted to a high temperature. The minimum percentage values of free formaldehyde (3%) for samples based on UF with SiO2 and UF + SiO2 + TSC after irradiation dose of 50 kGy are detected.

PMMA/Zn 2 SiO 4 :Eu 3+ (Mn 2+ ) Composites: Preparation, Optical, and Thermal Properties

Luminescent composites of poly(methylmethacrylate) (PMMA) and nanophosphors (Zn2SiO4:Mn2+, Zn2SiO4:Eu3+) were prepared by dispersion casting method. It was found that nanoparticles embedded in PMMA matrix preserve their typical phosphorescence emission. The influence of Zn2SiO4 nanofillers on thermal properties of PMMA was also investigated. A shift towards higher glass transition temperatures and slight improvements in thermal stability of the nanocomposites compared to pure PMMA were observed and are discussed herein.

Structural and optical investigation of gadolinia-doped ceria powders prepared by polymer complex solution method

Abstract We present a polymer complex solution method using a modified combustion synthesis procedure, for the production of well crystalline, sub-micron gadolinia-doped ceria powders of Ce0.9Gd0.1O1.95 composition. Polyethylene glycol of two different molecular weights (200 and 20000) was used as both fuel for the combustion and nucleating agent for the crystallization process. The synthesized materials were characterized using X-ray diffraction, thermal analysis, scanning electron microscopy, and optical and photoluminescence spectroscopy. The powders are quite similar, fully crystallized in a cubic fluorite-type phase with average crystallite size of about 70 nm and average particle size in the range 220–240 nm. UV-vis absorption spectra show the absorption edge at 3.26 eV. The presence of oxygen vacancies, confirmed indirectly by clear violet emission observed at 428 nm, originated from the 5D1 → 4F1 transition of Ce3+ions.