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Jankovic B.,University of Belgrade | Marinovic-Cincovic M.,Vinca Institute of Nuclear Sciences | Jovanovic V.,University of Belgrade | Samarzija-Jovanovic S.,University of Belgrade | Markovic G.,Tigar
Thermochimica Acta | Year: 2012

The non-isothermal degradation processes of acrylonitrile-butadiene/ ethylene-propylene-diene rubber blends reinforced with carbon black/silica fillers were investigated with thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG), using the different calculation procedures. Using differential and integral isoconversional methods, it was found that the NBR/EPDM 70 phr SiO 2, NBR/EPDM 35 phr carbon black/35 phr SiO 2 and NBR/EPDM 50 phr carbon black/20 phr SiO 2 degradations represent complex processes, with existing conversion regions of constant apparent activation energy (E a). It was found that the degradation process of the NBR/EPDM 70 phr SiO 2 under nitrogen atmosphere can be described by the one and a half order (n = 3/2; F3/2) kinetics, while the degradation of the NBR/EPDM 35 phr carbon black/35 phr SiO 2 and NBR/EPDM 50 phr carbon black/20 phr SiO 2 can be described with two- (D2) and three- (D3) dimensional diffusion mechanisms. For all investigated systems, an artificial compensation effect (art-CE) was found. Good agreement was observed between the experimental and calculated conversion curves, for all considered degradation processes. It was found that the sample of the polymer blend, which contains the highest carbon black content (50 phr carbon black), shows the greatest self-protective behavior. © 2012 Elsevier B.V.


Jankovic B.,University of Belgrade | Marinovic-Cincovic M.,Vinca Institute of Nuclear Sciences | Markovic G.,Tigar
Thermochimica Acta | Year: 2012

The non-isothermal degradation processes of acrylonitrile-butadiene and ethylene-propylene-ethylidenenorbornene rubber compounds were investigated with thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG), using the different calculation procedures. It was found that the acrylonitrile- butadiene (NBR) and the ethylene-propylene-diene (EPDM) rubber degradations represent the complex processes, where there are conversion regions with a constant value of the apparent activation energy (E a). It was established that the NBR and EPDM degradation under nitrogen atmosphere can be described by the one and a half order (n = 3/2) and the first order (n = 1) reaction kinetics, respectively. A linear dependence was observed between ln A and E a at every heating rate, known as the artificial compensation effect (art-CE). It was found that the calculated differential conversion curves are in good agreement with the experimental ones, for each of the observed heating rates, thus confirming the correctness of the obtained reaction models for the NBR and EPDM degradation processes. © 2011 Elsevier B.V.


Markovic G.,Tigar | Marinovic-Cincovic M.,Vinca Institute of Nuclear Sciences
Journal of Thermal Analysis and Calorimetry | Year: 2010

The properties of filled polymers depend on the properties of the matrix and the filler, the concentration of the components and their interactions. In this research we investigated the rheological and mechanical properties and thermal stability of polychloroprene/chlorosulfonated polyethylene (CR/CSM) rubber blends filled with nanoand micro-silica particles. The density of the nano-silica filled CR/CSM rubber blends was lower than that of the micro-silica filled samples but the tensile strength and elongation at break were much higher. The nano-silica filled CR/CSM rubber blend has higher V r0/Vrf values than micro-silica composites and show better polymer-filler interaction according to Kraus equation. The nano-silica filled CR/CSM rubber blends were transparent at all filler concentration, and have higher glass transition values than micro-silica filled compounds. The higher values of the glass transition temperatures for the nano-than the microfilled cross-linked systems are indicated by DMA analysis. The nano-filled cross-linked systems have a larger number of SiO-C links than micro-filled cross-linked systems and hence increased stability. © Akadémiai Kiadó, Budapest, Hungary 2010.


Markovic G.,Tigar | Marinovic-Cincovic M.,Vinca Institute of Nuclear Sciences
Journal of Thermal Analysis and Calorimetry | Year: 2011

The thermal stability of pure urea-formaldehyde resin (PR) and modified urea-formaldehyde (UF) resins with hexamethylenetetramine-HMTA (Resin 1), melamine-M (Resin 2), and ethylene urea (EU, Resin 3) including nano-SiO 2 was investigated by non-isothermal thermo-gravimetric analysis (TG), differential thermal gravimetry (DTG), and differential thermal analysis (DTA) supported by data from IR spectroscopy. Possibility of combining inorganic filler in a form of silicon dioxide with UF resins was found investigated and percentage of free formaldehyde was determined. The shift of DTG peaks to a high temperature indicates the increase of thermal stability of modified UF resin with EU (Resin 3) which is confirmed by data obtained from the FTIR study. The minimum percentage (6%) of free formaldehyde was obtained in Resin 3. © 2010 Akadémiai Kiadó, Budapest, Hungary.


Samarzija-Jovanovic S.,University of Prishtina | Jovanovic V.,University of Prishtina | Markovic G.,Tigar | Konstantinovic S.,University of Nis | Marinovic-Cincovic M.,Vinca Institute of Nuclear Sciences
Composites Part B: Engineering | Year: 2011

Rheometric characteristics, curing kinetics, mechanical properties before and after thermal aging and morphology of nanocomposites based on various network precursors (i.e., acrylonitrile-butadiene rubber (NBR), ethylene-propilene-diene monomer (EPDM) and its blend (NBR/EPDM) reinforced of nanosilica) is presented here. The ratios of EPDM and NBR as binary blend system vary significantly. The rheometric characteristics and curing kinetics of nanocomposites were determined using a rheometer with an oscillating disk, in which the network formation process was registered by the varying torque durations. The mechanical properties of the elastomeric composites were determined before and after thermal aging using an air-circulating oven. The specific interactions between the rubber and filler were characterized by Fourier transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) was employed to study the surface morphology of fractured rubber. The obtained results demonstrated a correlation between the calculated activation energies of cross linking (Eac) and reversion (Ear) and mechanical properties, which can be seen in sample EPDM/NBR = 20/80. For this blend, maximum tensile strength values and synergism were observed. Additionally, this blend exhibited a relatively co-continuous morphology, which was investigated by SEM. The differential scanning calorimetry (DSC) curves reported that the silica-reinforced EPDM/NBR rubber blends were immiscible. FTIR studies showed a strong interaction between the polymer matrix and filler, which was reflected in the peak shifts at 1441.9 and 1462.5 cm-1 to higher wave numbers. © 2011 Elsevier Ltd. All rights reserved.

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