Thermal characterization of the effect of fillers and ionic liquids on the vulcanization and properties of acrylonitrile–butadiene elastomer

Different thermal analysis techniques were used to study the effect of fillers and ionic liquids (ILs) on the vulcanization process, thermal and dynamic mechanical properties of acrylonitrile–butadiene elastomer (NBR). The products of the studies were composites of NBR filled with hydrotalcite, nanosized silica or carbon black. ILs such as 1-butyl-1-methylpyrrolidinium (BMpyrrolBF₄), 1-butyl-4-methylpyridinium (BMpyrBF₄) or 1-butyl-1-methylpiperidinium (BMpipBF₄) tetrafluoroborates were applied to improve the dispersion degree of the curatives and filler particles in the elastomer and to increase the efficiency of vulcanization. The differential scanning calorimetry results indicated that ILs reduced the vulcanization temperature of NBR compounds and increased the homogeneity of cross-link distribution in the elastomer network. NBRs filled with carbon black or silica exhibited similar thermal stabilities, whereas hydrotalcite reduced the temperature of thermal decomposition. The lowest mechanical loss factors were determined for vulcanizates filled with nanosized silica.

     

A new simple numerical model based on experimental scorch curve data fitting for the interpretation of sulphur vulcanization

Sulphur was the first agent used to vulcanize commercial elastomers (e.g. natural rubber) and allows meaningful cost reductions during the industrial process (production cost ratio between peroxides and accelerated sulphur is around 5). Therefore, accelerated sulphur vulcanization is the most popular technique for the production of polydiene and EPDM elastomers items. At present, crosslinking mechanisms are not analytically known in detail, therefore reticulation kinetic has to be deduced from mechanical properties obtained during standardized tests, as for instance the oscillating disc rheometer. In the present paper, we propose a numerical model to fit experimental rheometer data based on a simple composite three functions curve, able to describe the increase of the viscosity at successive curing times at different controlled temperature to use during the production of thick items vulcanized with sulphur. It is believed that rheometer curve is able to give an indirect information on the rubber reticulation kinetic at different temperatures, to use in a successive step to establish simplified analytical kinetic formulas to adopt in the accelerated sulphur vulcanization of polydiene and EPDM elastomers. In the model, it is necessary to collect rheometer curves at different specimen temperatures, because vulcanization in industrial practice occurs at variable temperatures during curing, with considerable differences from the core to boundary of the item. Once that rheometer curves are suitably collected in a database, they are used to predict the optimal vulcanization of real items industrially produced. Finally, a so called alternating tangent approach (AT) is implemented to determine optimal input parameters (curing external temperature T _n and rubber exposition time t) to use in the production process. Output mechanical property (objective function) to optimize is represented by the average tensile strength of the item. A meaningful example of engineering interest, consisting of a thick 2D EPDM cylinder is illustrated to validate the model proposed.     

The role of thiophosphoryl disulfide on the co‐cure of CR‐EPDM blends: effect of white fillers

Bis(diisopropyl) thiophosphoryl disulfide (DIPDIS) being a rubber accelerator has a definite role as a coupling agent in the silica filled polychloroprene rubber with ethylene propylene diene rubber (CR‐EPDM) blends. Diethylene glycol can further improve the beneficial effect of DIPDIS in silica filled CR‐EPDM blends. Two‐stage vulcanization technique further improves the physical properties of silica filled CR‐EPDM blends. The results have been compared with non‐reinforcing calcium carbonate filled systems. Scanning electron microscopy (SEM) studies further indicate the coherency and homogeneity in the silica filled CR‐EPDM blend vulcanizates obtained from this two‐stage process. Copyright © 2004 John Wiley & Sons, Ltd.     

A study of an elastomeric coating based on EPDM of cold vulcanization

Studies of the thermostability of vulcanizates of ethylene–propylene–diene rubbers (EPDM) obtained by using dinitrosogenerating systems of low-temperature vulcanization are performed. It is shown that vulcanizates retain sufficient high properties in operation up to 200°C for a long time. The use of such compositions for producing thin rubber coatings applied on a number of insulating materials allows the effect of energy saving to be obtained.     

Matching Cure Characteristics of Automotive Rubber Compound and Polyurethane Coating

The present investigation focuses on matching cure characteristics of EPDM rubber compound and polyurethane (PU) coating using temperature modulated and pressure differential scanning calorimetry (TMDSC, PDSC). TMDSC provides a detailed and better understanding of the curing process of model rubber system as well as complex automotive rubber compounds. The low level of unsaturation present in EPDM, results in the small heat of vulcanization (2–5 J g^–1), which is difficult to accurately measure using conventional differential scanning calorimetry (DSC). Thus, curing of highly filled EPDM compound was investigated using TMDSC. The kinetics of PU curing was monitored using pressure DSC (PDSC), and heat of curing was determined as 4.2 J g^–1 at 10°C min^–1 heating rate. It is found that complex automotive compounds and the PU coating are curing simultaneously. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal analysis of kerosene with 1,2-methyl ethyl 1-methyl pyrrolidinium bis(trifluoromethanesulfonyl) amide as an additive

This paper reports the thermal characterization of kerosene fuel-doped ionic liquid (1, 2-methylethyl 1-methyl pyrrolidinium bis(trifluoromethanesulfonyl) amide) (MEMP TFSA), an antistatic additive used in jet fuel engines. The ionic liquids (ILs) samples are prepared with the mass of 5, 10 and 15% in the kerosene fuel. These fuel samples are subjected to thermal decomposition studies at different scanning rates of 5, 10 and 15 °C min^?1 using the differential scanning calorimetry (DSC) method. The onset temperatures of exothermic reactions of kerosene-doped ILs are increased from 360–465 °C, when the mass percentage of ILs increased in the kerosene fuel. The boiling point of the kerosene-doped ILs was displaced to the higher temperature when compared to the pure kerosene. This showed that the doping of antistatic additives of ILs with kerosene increased its thermal stability property than the pure kerosene fuel. The thermo-kinetic studies are also carried out using Ozawa’s Kinetic method to determine the activation energy (E_a) and pre-exponential factor (A). The FTIR analysis showed that the kerosene-doped ionic liquid forms a homogenous mixture rather than prevailing separately.

     

CO_2 absorption with ionic liquids at elevated temperatures

CO_2 capture with ionic liquids(ILs) has attracted many attentions, and most works focused on absorption ability at ambient temperatures, while seldom research was concerned at elevated temperatures.This not only limits the CO_2 absorption application at elevated temperature, but also the determination of the operation condition of the CO_2 desorption generally occurring at higher temperature. This work mainly reported CO_2 solubilities in ILs at elevated temperatures and related properties were also provided. 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide([CnMIm][Tf_2N]) ILs were selected as physical absorbents for CO_2 capture in this work due to their relative higher CO_2 absorption capacities and good thermal stabilities. The long-term stability tests showed that [CnMIm][Tf_2N] is thermally stable at 393.15 K for long time. CO_2 solubilities in [CnMIm][Tf_2N] were systematically determined at temperatures from 353.15 K to 393.15 K. It demonstrated that CO_2 solubility obviously increases with the increase of pressure while slightly decreases with increase of temperature. As the length of alkyl chain on the cation increases, CO_2 solubility in ILs increases. Additionally, the thermodynamic properties including the Gibbs free energy, enthalpy, and entropy of CO_2 were also calculated.     

Thermal study and evaluation of new menthol-based ionic liquids as polymeric additives

Thermal properties of new ionic liquids (ILs) were investigated by thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC). Chlorides, tetrafluoroborates and hexafluorophosphates of (−)mentholpyrrolidinium and (−)-mentholimidazolium cations revealed good thermal stability at air atmosphere. Morphological characteristics of poly(methyl methacrylate) (PMMA) matrices doped with 10% of these ILs were also investigated by DRX and water absorption test. Into the matrix, they exhibited a very satisfactory pattern concerning the polymer thermal stabilization. DSC results show that some of these ILs also present plasticizer features since they can lower the polymer glass transition temperature (T _g) up to 317.15 K.     

New dicationic piperidinium hexafluorophosphate ILs,synthesis, characterization and dielectric measurements

A new class of dicationic ionic liquids (ILs) were synthesized for electrochemical applications at high temperatures. The syntheses are based on a dialkylation reaction of N-alkylpiperidine followed by anion exchange. The structures of ILs, based on piperidinium combined with hexafluorophosphate anion, were identified by using ¹H, ¹³C, ¹⁹F, ³¹P NMR and FT-IR spectroscopy. ILs’ thermal properties were investigated in the temperature range from −50 to 350 °C by using differential scanning calorimetry (DSC). In the frequency of 10⁻²–10⁶ Hz range, dielectric measurements were performed on ILs’ samples at various temperatures from −80 to 20 °C, i.e. around the glass transition temperature. The peak relaxation was observed near to this temperature. Also, the conductivity was investigated and the energy activation determined. The temperature dependence of the relaxation times was shown to be governed by the Arrhenius equation.     

XNBR/LDH nanocomposites: Effect of vulcanization and organic modifier on nanofiller dispersion and strain‐induced crystallization

In elastomer/organo clay nanocomposites, the morphological characteristics, and hence the mechanical properties, of the vulcanizates are strongly influenced by the organic modifier and the vulcanization process. When the elastomer itself undergoes strain‐induced crystallization, both the organic modifier and the dispersed filler particles could significantly influence the crystallization process. These phenomena are very common in case of natural rubber‐based vulcanizates. In this study, the similar effects have been demonstrated with carboxylated nitrile rubber (XNBR) and organically modified layered double hydroxide (O‐LDH)‐based nanocomposites. The effect of size of the organic modifier was obviously visible on the interlayer distance of O‐LDH and also on the morphological reorganization of the dispersed O‐LDH particles during vulcanization process. The strain‐induced crystallization of the XNBR was found to be strongly dependent on the morphological change that occurs during vulcanization process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Physicochemical characterization of nicergoline and cabergoline in its amorphous state

Formulation of poorly water-soluble crystalline drugs into their more soluble amorphous form is a common approach for improving their bioavailability. In this study, the amorphous forms of nicergoline (NIC) and cabergoline (CAB) were obtained by different methods (melting and precipitation under solvent evaporation). The physicochemical characteristics of the samples were determined by HPLC, differential scanning calorimetry (DSC), thermogravimetry, and X-ray powder diffractometry. The physical stability of the amorphous forms was investigated by DSC by considering how the onset temperature and the enthalpy content at the glass transition vary with aging time and temperature. Using the Kohlrausch–Williams–Watts equation on the data obtained from the experiments, the “mean molecular relaxation time constant” (τ) was estimated. This parameter was used to understand the stability of NIC and CAB in their glassy state at different temperatures, and results showed that their stability is adequate to enable the formulation of these drugs into solid dosage forms.     

Radiothermoluminescence. I. Radiothermoluminescence for investigation of thermal and radiation-induced crosslinking of rubber mixtures

Phase heterogeneity of vulcanizates based on cis-polybutadiene (cis-Europrene) and SBR (Europrene 1500) blends obtained by radiation, thermal, two-stage radiation-thermal, and two-stage thermal-radiation processes was investigated by the radiothermoluminescence method. Unvulcanized blends of these polymers are found to be heterogeneous, exhibiting two glass transition temperatures T_g, which coincide with the values for the initial components. Following vulcanization, the difference between the two T_g values for a polyblend decreases. The decrease is more distinct for polyblends crosslinked at high temperatures. When the vulcanization temperature exceeds 140°C and the crosslink density (or 1/M_c) exceeds 5 × 10^?5–1 × 10^?4 mole/cm³, the glass temperature ranges of the crosslinked blend are practically superimposed. Such crosslinked mixtures should be considered pseudohomogeneous in phase.     

Interfaces in Composites. Reinforcement of Elastomers by Carbon Black

Basic features of carbon black-aggregation of particles into structure, particle size and morphology, and surface activity-are reviewed. Carbon black reinforcement of vulcanizates is first examined in the example of tearing, and the influence of hysteresis is considered. The dynamic properties of vulcanizates containing two major types of reinforcing carbon black are compared.

While particle size gives the best correlation with tensile strength of vulcanizates, surface activity is shown to be the key to reinforcement. The role of these properties of carbon black in dissipating rupture energy is discussed.

The relation between work to tensile break and hysteresis to break in gum rubbers can be applied to black-reinforced vulcanizates by use of a strain amplification factor. The complication introduced by stress-softening is explained in terms of localized stress relaxation. Abrasion reinforcement can also be explained in terms of hysteresis.

The Flory-Rehner relationship of modulus of elasticity of swollen vulcanizates to physically-effective cross-linking applies to unswollen vulcanizates only after prestressing. Black-reinforced vulcanizates involve application of the strain amplification factor.

The concept of mobile linkages to rubber chains at the surface of black particles is related to the influence of strain magnification and strain rate magnification in the reinforcing mechanism. These linkages result in formation of “shell” rubber adjacent to carbon black particles. The slippage of rubber chains relative to carbon black aggregates allows stress-sharing by highly-stressed chains. Bound rubber results from reaction of elastomer free radicals generated during mastication with carbon black.

There is a relation between bound rubber and reinforcement which is fully developed only after vulcanization. Formation of bound rubber results from the surface activity of carbon black rather than its structure. Its contribution to reinforcement of the vulcanizate may be as important as cross-linking.     

Reinforcement effect of MAA on nano‐CaCo3‐filled EPDM vulcanizates and possible mechanism

Methacrylic acid (MAA) was used as in situ surface modifier to improve the interface interaction between nano‐CaCO₃ particle and ethylene–propylene–diene monomer (EPDM) matrix, and hence the mechanical properties of nano‐CaCO₃‐filled EPDM vulcanizates. The results showed that the incorporation of MAA improved the filler–matrix interaction, which was proved by Fourier transformation infrared spectrometer (FTIR), Kraus equation, crosslink density determination, and scanning electron microscope (SEM). The formation of carboxylate and the participation of MAA in the crosslinking of EPDM indicated the strong filler–matrix interaction from the aspect of chemical reaction. The results of Kraus equation showed that the presence of MAA enhanced the reinforcement extent of nano‐CaCO₃ on EPDM vulcanizates. Crosslink density determination proved the formation of the ionic crosslinks in EPDM vulcanizates with the existence of MAA. The filler particles on tensile fracture were embedded in the matrix and could not be observed obviously, indicating that a strong interfacial interaction between the filler and the matrix had been achieved with the incorporation of MAA. Meanwhile, the presence of MAA remarkably increased the modulus and tensile strength of the vulcanizates, without negative effect on the high elongation at break. Furthermore, the ionic bond was thought to be formed only on filler surface because of the absolute deficiency of MAA, which resulted in the possible structure where filler particles were considered as crosslink points. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1226–1236, 2006     

Influence of the nature of a curing agent on the peculiarities of formation of vulcanization networks in polysulfide sealants

The molecular mobility of vulkanizates of liquid thiokols cured with various vulcanizing agents was studied by the NMR method in a wide temperature interval. The influence of the nature of vulcanizing agents and the structure of the forming vulcanization network on the change in the character of molecular mobility in vulcanizates of polysulfide oligomers was established. The correlation of effective (υ_eff) and chemical (υ_ch) densities of vulcanization networks of thiokol sealants with parameters of the NMR spectrum of the latter was found. The influence of the nature of a curing agent on the peculiarities of the formation of vulcanization networks of polysulfide oligomers is discussed.     

Foaming of trans‐polyisoprene using N2 as the blowing agent

Foaming of trans‐1,4‐polyisoprene (TPI) polymer was carried out through a batch process using nitrogen (N₂) as the blowing agent. TPI vulcanizates having varying crosslink densities were prepared by varying crosslinking agent content and curing time. The vulcanizates were then saturated with N₂ inside a pressure vessel at a pressure of 14 MPa and varying temperatures for 5 hours before effecting the foaming by rapidly quenching the pressure. The effects of varying the crosslinking agent content, silica filler content, and precuring time of the vulcanizates and the effects of varying the gas saturation temperature of foaming on the cell characteristics and physical properties of the foam prepared were investigated. The cells of the TPI foams had a spherical, closed structure. The density, expansion ratio, cell size, cell density, and tensile properties of the foams varied with varying crosslink density of the TPI vulcanizates as well as the saturation temperature of foaming. The important effects of crosslink density and saturation temperature on the N₂ solubility in the TPI matrix and thus on the foam expansion were discussed. The silica filler was found to be acting as a cell nucleating agent and reinforcing filler for the TPI foams.     

A DSC study of miscibility and phase separation in crystalline polymer blends of phenolphthalein poly(ether ether sulfone) and poly(ethylene oxide)

The miscibility of blends of phenolphthalein poly(ether ether sulfone) (PES-C) and poly(ethylene oxide) (PEO) was established on the basis of the thermal analysis results. Differential scanning calorimetry (DSC) studies showed that the PES-C/PEO blends prepared by casting from N,N-dimethylformamide (DMF) possessed a single, composition-dependent glass transition temperature (T_g), and thus that PES-C and PEO are miscible in the amorphous state at all compositions at lower temperature. At higher temperature, the blends underwent phase separation, and the PES-C/PEO blend system was found to display a lower critical solution temperature (LCST) behavior. The phase separation process in the blends has also been investigated by using DSC. Annealed at high temperatures, the PES-C/PEO blends exhibited significant changes of thermal properties, such as the enthalpy of crystallization and fusion, temperatures of crystallization and melting, depending on blend composition when phase separation occurred. These changes reflect different characteristics of phase structure in the blends, and were taken as probes to determine phase boundary. From both the thermal analysis and optical microscopy, the phase diagram of the blend system was established. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1383–1392, 1997     

Reactive Compatibilization of Polyethylene/Ground Tire Rubber Inhomogeneous Blends via Interactions of Pre-Functionalized Polymers in Interface

Summary: Reactive compatibilization of recycled low- or high-density polyethylenes (LDPE and HDPE, respectively) and ground tire rubber (GTR) via chemical interactions of pre-functionalized components in their blend interface has been carried out. Polyethylene component was functionalized with maleic anhydride (MAH) as well as the rubber component was modified via functionalization with MAH or acrylamide (AAm) using chemically or irradiation (γ-rays) induced grafting techniques. The grafting degree and molecular mass distribution of the functionalized polymers have been measured via FTIR and Size Exclusion Chromatography (SEC) analyses, respectively. Thermoplastic elastomer (TPE) materials based on synthesized reactive polyethylenes and GTR as well as ethylene-propylene-diene rubber, EPDM were prepared by dynamic vulcanization of the rubber phase inside thermoplastic (polyethylene) matrix and their phase structure, and main properties have been studied using DSC and mechanical testing. As a final result, the high performance TPE with improved mechanical properties have been developed.     

Fracture morphology and mechanical properties of ethylene/vinyl acetate rubber vulcanizates reinforced by in situ prepared sodium methacrylate

Ethylene/vinyl acetate rubber (EVM) was reinforced by sodium methacrylate (NaMAA) that was in situ prepared through the neutralization of sodium hydroxide and methacrylic acid in EVM during mixing. The mechanical properties of EVM vulcanizates with different NaMAA loadings and at different crosslink densities were studied and compared with those of high abrasion furnace carbon black (HAF) filled EVM vulcanizates. The fracture surfaces of gum and filled EVM vulcanizates were observed with scanning electron microscopy. The results showed that NaMAA‐reinforced EVM vulcanizates had better mechanical properties than HAF/EVM vulcanizates. When the NaMAA loading was 50 phr, the tensile strength of the NaMAA/EVM vulcanizate was 30 MPa, the tear strength was 102 kN/m, and the elongation at break was over 400%. Fourier transform infrared analysis confirmed that NaMAA formed in the compounding process and underwent polymerization during vulcanization. Scanning probe microscopy analysis revealed that nanoscale particles dispersed in the NaMAA/EVM vulcanizates. The mechanical properties were correlated with the fracture morphology of all the vulcanizates. The tensile rupture of NaMAA‐filled EVM vulcanizates occurred through tearing from a crack in the bulk of the samples. Tear deviation occurred with the addition of NaMAA and resulted in a rough surface, leading to an improvement in the tear strength of NaMAA‐filled EVM vulcanizates. The micrographs of the tear surfaces of the vulcanizates indicated that the different fracture modes depended on the NaMAA loading and the crosslink density. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1715–1724, 2004     

Thermal stability of acrylonitrile/chlorosulphonated polyethylene rubber blend

The properties of chlorosulphonated polyethylene (CSM) rubber, acrylonitrile rubber (NBR) and their blend (50/50 w/w) were studied. Fourier transform infrared (FTIR) studies supported that CSM/NBR rubber blend is self curable, when cross-linking takes place between acrylonitrile groups of NBR and –SO₂Cl groups or in situ generated allyl chloride moieties of CSM. The thermal stability of vulcanizates was analyzed in nitrogen by thermogravimetry. It was found that the initial degradation temperature of elastomer based on CSM rubber is lower than of pure NBR rubber. By adding NBR to CSM rubbers, the degradation temperature of crosslinked material increased, indicating higher thermal stability. The activation energy for the degradation are determined using the Arrhenius equation The activation energies for the rubber blends are higher than for elastomers based on pure rubbers. It was found that the mass loss of the blends at any temperature was between those of the pure rubbers. The differential scanning calorimetry (DSC) was used for the glass transition temperature determination. It is estimated thermodynamic immiscibility of NBR/CSM blend based on noticed two different glass transition temperatures, corresponding to CSM and NBR rubbers.