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Markovic G.,Tigar | Marinovic-Cincovic M.,Vinča 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.,Vinča 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.


Jankovic B.,University of Belgrade | Marinovic-Cincovic M.,Vinča 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.


Jankovic B.,University of Belgrade | Marinovic-Cincovic M.,Vinča 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.


Marinovic-Cincovic M.,Vinča Institute of Nuclear Sciences | Jankovic B.,University of Belgrade | Jovanovic V.,University of Prishtina | Samarzija-Jovanovic S.,University of Prishtina | Markovic G.,Tigar
Composites Part B: Engineering | Year: 2013

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) rubbers degradations represent the complex processes, where there are conversion regions with a constant value of the apparent activation energy (Ea). It was established that 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 lnA and Ea, known as the kinetic compensation effect (KCE). The linear dependence was also established between the change of the entropy ΔS ≠ and Ea, for the formation of the activated complex from the reagents. These dependences are related to assumption that the kinetic mechanisms of the non-isothermal degradation of the NBR and EPDM samples are very similar. © 2012 Elsevier Ltd. All rights reserved.


Samarzija-Jovanovic S.,University of Prishtina | Jovanovic V.,University of Prishtina | Markovic G.,Tigar | Konstantinovic S.,University of Niš | Marinovic-Cincovic M.,Vinča 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.


Markovic G.,Tigar | Marinovic-Cincovic M.S.,Vinča Institute of Nuclear Sciences | Jovanovic V.,University of Prishtina | Samarzija-Jovanovic S.,University of Prishtina | Budinski-Simendic J.,University of Novi Sad
Composites Part B: Engineering | Year: 2012

The effect of gamma-irradiation on the acrylonitrile butadiene/ chlorosulphonated polyethylene rubber blends (NBR/CSM) based nanocomposites containing carbon black (CB) and silica filler (Si) were investigated by TG-DTG and ATR-FTIR techniques. The silica (with primary particle size of 22 nm) was added in content of 0, 10, 20 and 30 phr and carbon black (with primary particle size 40-48 nm) was added in content of 30 phr and rubber blend compounds were prepared. The obtained elastomeric materials were aging to different γ-irradiation doses (100, 200 and 400 kGy). The cure and mechanical properties of obtained nanocomposites were determined. Incorporating 20 phr of silica to the control NBR/CSM rubber blends containing 30 phr CB resulted 152% increase in tensile strength, 116%, in elongation at break and 142% modulus at 100% elongation, according to synergistic effect between the fillers. FTIR measurements of aged samples estimated the formation of alcohols, ethers and small amounts of lactones, anhydrides, esters and carboxylic acids after exposure to lower doses of γ-radiation (100 kGy). On the basis of the obtained spectra the formation of shorter polyene sequences and aromatic rings in aged elastomeric samples are assumed. The results show that 30 phr of carbon black (CB) and 20 phr of silica are needed for the best gamma aging resistance of NBR/CSM rubber nanocomposites. The result of radiation exposure is decrease in mechanical properties. The dose at which ultimate mechanical properties decreased was at 200 kGy. TG-DTG measurements estimated decrease in thermal stability of gamma-irradiated NBR/CSM rubber blend based nanocomposites. Silica reinforced NBR/CSM rubber blend had better radiation resistant than carbon black. Rough and heterogeneity of fracture surfaces has been observed for NBR/CSM rubber blends filled with silica. More uniform morphology of fracture surfaces according to high polymer-filler interaction and low filler-filler interaction has been observed for CB/Si filled NBR/CSM rubber blend. © 2011 Elsevier Ltd. All rights reserved.


Markovic G.,Tigar | Marinovic-Cincovic M.,Vinča Institute of Nuclear Sciences | Jovanovic V.,University of Prishtina | Samarzija-Jovanovic S.,University of Prishtina | Budinski-Simendic J.,University of Novi Sad
Composites Part B: Engineering | Year: 2013

Biogenic silica (BSi) was added at different ratios to some polymer blends of polyisoprene rubber (NR) and chlorosulphonated polyethylene rubber (CSM) cured by conventional sulfur system. The reinforcing performance of the filler was investigated using rheometric, mechanical and swelling measurements, differential scanning calorimetry (DSC), thermogravimetric (TGA) and scanning electron microscopy (SEM) analysis. There was a remarkable decrease in the optimum cure time (tc90) and the scorch time (ts2), which was associated with an increase in the cure rate index (CRI), with filler loading up to 30 phr in the different blend ratios. The tensile strength and hardness was 4-5 Sh-A higher in the case for the different blend compositions, while the resistance to swelling in toluene became higher. SEM photographs show that the filler is located at the interface between the different polymers which induces compatibilization in the immiscible blends. DSC scans of the filled blends showed shifts in the glass transition temperatures Tg which can be attributed to the improve interfacial bonding between filler and NR/CSM matrix. A higher thermal stability of NR/CSM/BSi composites was detected. © 2013 Elsevier B.V. All rights reserved.


Markovic G.,Tigar | Veljkovic O.,Tigar | Marinovic-Cincovic M.,Vinča Institute of Nuclear Sciences | Jovanovic V.,University of Prishtina | And 2 more authors.
Composites Part B: Engineering | Year: 2013

Blend of polybutadiene (BR) rubber with varying ratios of chlorosulphonated polyethylene rubber (CSM), BR/CSM, keeping the total waste rubber powder (WRP) content constant at 50 phr (parts per 100 rubber) have been prepared on a laboratory-size (300 × 600 mm) two-roll mixing mill maintained at 40 ± 5 °C. The mechanical properties, namely tensile strength (TS), tensile modulus at 100% elongation (M100), elongation at break (Eb%) and hardness have been followed up as a function of irradiation dose (dose rate of 10 kGy h-1 and total absorbed dose of 100, 200, 300 and 400 kGy) as well as blend composition. The results indicated that the addition of CSM has improved the properties of BR/CSM rubber blends waste rubber powder filled composites. The improvement in mechanical properties of the BR/CSM/WRP (50/50/50) rubber blends is in correlation with homogenous WRP distribution which has been assigned by scanning electron microscopy. Also BR/CSM rubber blends waste rubber powder filled composites are thermally and irradiation more stable than BR and CSM rubbers alone. © 2012 Elsevier Ltd. All rights reserved.


Jovanovic V.,University of Prishtina | Samarzija-Jovanovic S.,University of Prishtina | Budinski-Simendic J.,University of Novi Sad | Markovic G.,Tigar | Marinovic-Cincovic M.,Vinča Institute of Nuclear Sciences
Composites Part B: Engineering | Year: 2013

This paper investigates the effect of carbon black filler (CB) (loading 60-100 phr) on the cure kinetics, mechanical properties, morphology and thermal stability of acrylonitrile-butadiene/ethylene-propylene-diene (NBR/EPDM) rubber blends. The determination of cure characteristics was estimated by Monsanto Oscillating Disc Rheometer R-100. Mechanical properties such as tensile strength, elongation at break, modulus at 200% and 300% elongation, hardness, have been measured at room temperature on an electric tensile testing machine (Zwick 1425) according to ASTM D 412. Morphology of the cross linked system was carried out by scanning electron microscope (SEM). The cure kinetics were determined from three temperature rheokinetic curves (T1 = 160 °C, T2 = 180 °C and T3 = 190 °C). From obtained results of NBR/EPDM/CB (80/20/70) composite, a correlation between mechanical properties and calculated activation energy of cross link (E ac) and reversion (Ear) process can be concluded. Maximum tensile strength values and synergism for this blend has been observed. The apparent activation energy values (Ea) of degradation were determined by the Kissinger method for NBR, EPDM and NBR/EPDM/CB rubber blend. E a for the NBR/EPDM/CB rubber blend composite is lower (45.1 kJ/mol) compared to Ea for the rubber based on NBR (156 kJ/mol) and EPDM (75 kJ/mol), which indicates easier formation of rubber blend. © 2012 Elsevier Ltd. All rights reserved.

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