Pyrolysis kinetics of ethylene–propylene (EPM) and ethylene–propylene–diene (EPDM)

The thermal degradation kinetics of several ethylene–propylene copolymers (EPM) and ethylene–propylene–diene terpolymers (EPDM), with different chemical compositions, have been studied by means of the combined kinetic analysis. Until now, attempts to establish the kinetic model for the process have been unsuccessful and previous reports suggest that a model other than a conventional nth order might be responsible. Here, a random scission kinetic model, based on the breakage and evaporation of cleavaged fragments, is found to describe the degradation of all compositions studied. The suitability of the kinetic parameters resulting from the analysis has been asserted by successfully reconstructing the experimental curves. Additionally, it has been shown that the activation energy for the pyrolysis of the EPM copolymers decreases by increasing the propylene content. An explanation for this behavior is given. A low dependence of the EPDM chemical composition on the activation energy for the pyrolysis has been reported, although the thermal stability is influenced by the composition of the diene used.     

Degradation profiles in aged EPDM water seals using focused ion beam-scanning electron microscopy

The degradation of an ethylene–propylene-diene (EPDM) rubber seal used in a water supply system was investigated using focused ion beam-scanning electron microscopy (FIB-SEM). The EPDM rubber seal was used for 3 years within the temperature range 20–40 °C in a city water system. The accretions present on the surface of the EPDM seal after use were observed by SEM and were found to consist of iron and oxygen atoms based on energy dispersive X-ray spectroscopy (EDS) analysis. A cross-sectional depth image of the EPDM rubber was obtained by FIB-SEM, after slicing the EPDM rubber with a focused Gallium ion beam. Iron and oxygen atoms in the cross-section of the EPDM rubber were detected through EDS. The distribution of iron was comparable to that of oxygen derived from the carbonyl groups generated by the degradation of EPDM, suggesting that iron ions may promote the degradation of natural rubber through catalytic effects.     

Mechanism and kinetics of the non-isothermal degradation of ethylenepropylene diene monomer (EPDM)

The thermal degradation behaviour of ethylene-propylene-diene (EPDM) elastomer, was examined under non-isothermal conditions at different heating rates (5, 7, 10 and 12 °C/min) using thermogravimetric analysis. Kinetic parameters of degradation were evaluated using the Flynn–Wall–Ozawa isoconversional method, as well as the integral method of Coats and Redfern. A comparison between the two methods showed that the degradation of EPDM follows the Avrami–Erofeev two-dimensional nucleation model. The thermodynamic parameters were also calculated and the effect of the heating rate on each was deduced.     

GMA熔融接枝EPDM的研究

以甲基丙烯酸缩水甘油酯（ＧＭＡ）为接枝单体，过氧化二异丙苯（ＤＣＰ）为引发剂，对三元乙丙胶（ＥＰＤＭ）进行了熔融接枝，在烃链上引入极性基团，以改善ＥＰＤＭ与极性聚合物的相容性。用差示扫描量热计（ＤＳＣ）研究了ＧＭＡ的聚合温度，用富里叶红外（ＦＴ－ＩＲ）、凝胶渗透色谱（ＧＰＣ）对接枝产物进行了表征。实验结果表明，产物的接枝率和凝胶量可以通过反应条件（温度、时间、反应物组成及加料方式）来控制。     

Study of the degradation of 5-azacytidine as a model of unstable drugs using a stopped-flow method and further data analysis with multivariate curve resolution

A general strategy for the study of degradation processes of drugs based on stopped-flow monitoring in a flow system is proposed. The flow system consists of a two-channel manifold for pumping sample and buffer solutions, which join and mix in a PTFE coil (57 cm × 0.7 mm i.d). The flow is stopped when the sample reaches the detection cell and, then, the corresponding kinetic processes are monitored in the spectral range 200-300 nm using a UV-vis diode array spectrophotometer. 5-Azacytidine has been chosen as a model of unstable drugs to illustrate the possibilities of the procedure. Kinetic runs have been developed at temperatures in the range 25-80 °C and pH values from 2 to 11 in order to investigate the influence of these factors on the degradation of the pharmaceutical agent. Multivariate curve resolution based on alternating least squares has been used for the data treatment in order to obtain the kinetic and spectral profiles of species involved in the degradation as well as to calculate the kinetic constants. Results indicate that 5-azacytidine is moderately stable in acid solutions while quickly decomposes in alkaline media. In addition, the degradation is dramatically accelerated with increasing temperature.     

Structural Effects on the Decomposition Kinetics of EPDM Elastomers by High-Resolution TGA and Modulated TGA

Effects of ethylene content and maleated EPDM content on the thermal stability and degradation kinetics of ethylene propylene diene monomer (EPDM) have been studied using high resolution thermogravimetric analysis (Hi-Res TGA) and Modulated TGA (MTGA). Modulated TGA shows that EPDM degradation is complex, with activation energy of degradation increasing throughout the degradation. Values from both dynamic and constant heating rate experiments are in good agreement with each other and with the literature value. However, the dynamic heating rate experiment shows that if the difference of peak temperature of components in a system is less than 5°C, Hi-Res TGA does not resolve them.This revised version was published online in November 2005 with corrections to the Cover Date.     

Surface degradation of poly(ethylene-co-propylene-co-5-ethylidene-2-norbornene) terpolymer by ozone in water

Saturated olefinic rubbers have been widely used as materials for not only municipal waterworks, but also for household uses. As a sanitizing agent for water, chlorine will be replaced by ozone in the near future from an environmental point of view. However, the ozone treatment in water seriously damages saturated olefinic rubbers, which are necessary for the infrastructure of daily life. Here, we report the surface degradation of cross-linked poly(ethylene-co-propylene-co-5-ethylidene-2-norbornene) terpolymer (EPDM) by ozone treatment, both in water and air. We also discuss how the presence of water impacts the ozone oxidation of EPDM, resulting in macroscopic damage to EPDM.     

Some kinetic and thermodynamic aspects of thermal degradation of lightly stabilised elastomers

The thermal stability of ethylene–propylene elastomers in the presence of light stabilizing antioxidant (Topanol OC) is studied. The oxygen uptake method was performed for determination of thermal oxidation in air atmosphere at constant temperatures (165°C, 175°C and 185°C). The experimental unit used for oxygen uptake measurements is described. The dependence of absorbed oxygen on various oxidation times reveals marked dissimilarity between the two ethylene–propylene elastomers, because the terpolymer contains 3.5% ethylidene-norbornene. Changes in the activation energy of oxidation are evaluated over the whole process time. Free energy vs reaction time curves for all degradation experiments are presented and some remarks on entropy change for the overall process are made in order to explain oxygen-containing product accumulation. Using Arrhenius plots the durability of EPDM/Topanol OC system was calculated.     

Thermal degradation kinetics of g-HA/PLA composite

Thermal degradation behaviors of a composite constituted by poly(l-lactide) (PLA) and hydroxyapatite nanoparticle that was surface-grafted with l-lactic acid oligomer (g-HA) in a nitrogen atmosphere were studied using thermogravimetric analysis (TGA) and compared with PLA. The kinetic models and parameters of the thermal degradation of PLA and the g-HA/PLA composite were evaluated by the invariant kinetic parameters (IKP) method and Flynn–Wall–Ozawa (FWO) method based on a set of TGA data obtained at different heating rates. It was shown that the conversion functions calculated by means of the IKP method depend on a set of kinetic models. The g-HA particle slowed down the thermal degradation of PLA polymer matrix.     

Gamma irradiation degradation/modification of 5-ethylidene 2-norbornene (ENB)-based ethylene propylene diene rubber (EPDM) depending on ENB content of EPDM and type/content of peroxides used in vulcanization

In this study, the radiation degradation/modification of the vulcanized EPDM and the effects of dose rate, peroxide type/content in vulcanization system and ENB content of EPDM were studied to investigate the change in the extend of the modification/degradation of the mechanical properties of vulcanized EPDM via gamma irradiation. In addition, thermal, dynamic mechanical, ATR-FTIR, TGA, TGA-FTIR tests were carried out to understand the change of properties of vulcanized EPDM via irradiation.Samples were irradiated with two different dose rates of 1280 and 64.6 Gy/h. Total dose of irradiation was up to 184 kGy. The FTIR spectral analysis showed structural changes of EPDM via irradiation. It was observed that the dose rate changed the mechanical properties with different extends. The change of ENB content of EPDM and peroxide type and content in vulcanization system affect extend of the modification/degradation of the EPDM's properties.     

Photo‐stabilization of EPDM–clay nanocomposites: effect of antioxidant on the preparation and durability

The present study is to examine the photo‐stabilization effect of an antioxidant on the photo‐oxidation of ethylene‐propylene‐diene monomer (EPDM)–clay nanocomposites. During the preparation of EPDM–clay nanocomposites via melt processing antioxidants are usually incorporated along with clay, which allows phenolic antioxidant molecules to get adsorbed onto acidic clay platelets and their interaction with metallic impurities reduces the stabilizing efficiency of the antioxidant. The nanocomposites were obtained by solution dispersion followed by melt compounding of EPDM and organophilic montmorillonite (OMMT). The samples were characterized by conventional tools such as X‐ray diffraction (XRD), Fourier Transform Infra Red (FT‐IR) spectroscopy, and thermo‐gravimetric analysis (TGA). It was found, upon photo‐irradiation (λ > 290 nm) studies by following the changes in functional groups and surface morphology, that photo‐degradation was lowered by the antioxidant and the efficiency of the antioxidant could be improved by initial incorporation of antioxidant in the EPDM matrix. In EPDM–clay nanocomposites, a stabilizing activity of the antioxidant was observed above some threshold concentration of the antioxidant. The relationship between the nanoclay reinforcement and stabilizing efficiency in terms of photo‐oxidation and surface morphology for their applicability are discussed. The methodology adopted for this study is also justified through our observation. Copyright © 2007 John Wiley & Sons, Ltd.     

Thermal degradation studies of substituted conducting polyanilines

The synthesis of conducting polymers based on m-nitroaniline, m-chloroaniline and m-aminophenol by aniline initiated ammonium peroxydisulfate oxidation, has been attempted. The IR spectra of the polymers have been studied. Thermogravimetric analysis of the conducting polymers has been followed using a computer analysis method LOTUS PACKAGE, developed by us for assigning the degradation mechanism. A number of equations have been used to evaluate the kinetic parameters. The mechanism of degradation of the conducting polymers has been explained on the basis of their kinetic parameters.     

Thermogravimetric and wide angle X-ray diffraction analysis of thermoplastic elastomers from nylon copolymer and EPDM rubber

Nylon copolymer (PA6, 66) and ethylene propylene diene (EPDM) blends with and without compatibilizer were prepared by melt mixing using Brabender Plasticorder. The thermal stability of nylon copolymer (PA6, 66)/ethylene propylene diene rubber (EPDM) blends was studied using thermogravimetric analysis (TGA). The morphology of the blends was investigated using scanning electron microscopy (SEM). In this work, the effects of blend ratio and compatibilisation on thermal stability and crystallinity were investigated. The incorporation of EPDM rubber was found to improve the thermal stability of nylon copolymer. The kinetic parameters of the degradation process were also studied. A good correlation was observed between the thermal properties and phase morphology of the blends. By applying Coats and Redfern method, the activation energies of various blends were derived from the Thermogravimetric curves. The compatibilization of the blends using EPM-g-MA has increased the degradation temperature and decreased the weight loss. EPM-g-MA is an effective compatibilizer as it increases the decomposition temperature and thermal stability of the blends. Crystallinity of various systems has been studied using wide angle X-ray scattering (WAXS). The addition of EPDM decreases the crystallinity of the blend systems.     

A thermal analysis investigation of new insulator compositions based on EPDM and phenolic resin

New rocket insulator compositions have been studied by adding various types and amounts of fillers, such as graphite and asbestos fibres, Al₂O₃, MgZrO₂, Cr₂O₃, SiC, carbon powders and phenolic resin to the base EPDM gum and graphite, kevlar,E type glass fibres to the base phenolic resin in order to improve thermal and ablative efficiency. The degradation of the insulators has been investigated by thermogravimetry (TG) analysis to 900°C and DSC analysis to 500°C. Conversion curves of the insulators at different heating rates were performed and maximum degradation temperatures were found as 646 and 661°C for EPDM P and phenolic resin, respectively. The kinetic parameters for degradation have been evaluated and the lifetime of the rocket insulators has been estimated. Thermal analysis has been conducted on the insulators and the indepth temperature distribution was evaluated in order to find optimum insulation thickness.     

Chemical ageing effects on the mechanical behaviour of ethylene-propylene diene monomer

Ethylene-propylene diene monomer (EPDM) elastomer diaphragm failures due to material degradation pose a major risk in the biopharmaceutical industry, as they can result in long periods of production downtime. It is suspected that a key cause of this EPDM degradation is due to the chemical solutions used in equipment cleaning processes. However this has never been empirically investigated in the public domain. Twenty four virgin samples were utilised for testing, twelve of which were subject to common chemical cleaning solutions used in the biopharmaceutical sector. The chemical solutions under investigation were aqueous solutions of NaOH, NaClO, H₃PO₄, and the interaction between 100 °C H₂O and NaClO. The characterisation of the degradation process was conducted by mechanical testing. The results show that degradation of the polymer bulk proceeds predominantly via crosslinking for all exposure types. NaOH and H₃PO₄ exposure results in an accelerated rate of crosslinking compared to NaClO in the early stages of exposure.     

Nanosize and microsize clay effects on the kinetics of the thermal degradation of polylactides

Polylactide (PLA)-montmorillonite (MMT) micro- and nanocomposites based on semicrystalline and amorphous polymers and unmodified or organomodified clays at 5 wt% content were produced by melt mixing. Based on the three different test methods that were used to follow thermal degradation, different conclusions were obtained. During melt processing, thermomechanical degradation was more pronounced in the presence of all fillers, which apparently acted catalytically, but to different degrees. During isothermal degradation in air from 180 °C to 200 °C, degradation rate constants were calculated from novel equations incorporating changes in intrinsic viscosity (IV). Results show that the thermal degradation rate constants of the amorphous PLA and its composites are lower than those of the semicrystalline PLA and its composites. Due to better filler dispersion in the polymer matrix, the thermal degradation rate constants of the nanocomposites are significantly lower than those of the unfilled polymers and their microcomposites under air. As per dynamic TGA data and thermal kinetic analysis from weight losses and activation energy calculations, organomodified nanofillers have a complex effect on the polymer thermal stability; the unmodified fillers, however, reduce polymer thermal stability. These TGA data and kinetic analysis results also support the findings that the thermal stability of the amorphous PLA and its composites is higher than that of the semicrystalline polymer and its composites and the thermal stability of the nanocomposites is higher than that of the microcomposites. In general, mathematical modeling based on random thermal scission equations was satisfactory for fitting the TGA experimental data.     

Effect of ZnO nanoparticles on kinetics of thermal degradation and final properties of ethylene–propylene–diene rubber systems

The morphology, thermal degradation behavior in addition to static and dynamic mechanical properties of various ethylene?Cpropylene?Cdiene (EPDM) rubber compounds containing nano-zinc oxide (NZnO) were investigated compared to those of EPDM with ordinary-sized ZnO (OSZnO). The field-emission scanning electron microscopy studies showed that unlike the conventional system, the formation of large size ZnO agglomerates was discouraged for NZnO filled systems. Thermogravimetric analysis (TG) revealed that the thermal degradation of EPDM system was delayed upon the inclusion of NZnO instead of OSZnO in the compound. The kinetic analysis of TG data based on Friedman and Kissinger methods showed that the nanocomposite samples exhibited higher activation energy (E _a ) and lower order of reaction (n) over the conventional system, suggesting the enhancement of thermal stability upon decreasing ZnO particle size. The results obtained from dynamic mechanical analysis and static mechanical characterizations in terms of hardness, resilience, and abrasion tests interestingly indicated that NZnO not merely could act as a thermal insulator, but also could perform as a nano-filler to improve the final performance of EPDM elastomers.     

Characterization and thermal stability of poly(vinyl chloride) plasticized with epoxidized soybean oil for food packaging

The use of phthalates in plasticized poly(vinyl chloride) (PVC) formulations has been questioned by their potential toxicity and high migration to foodstuff. Phthalates can be replaced by other harmless and environmentally friendly plasticizers, such as epoxidized soybean oil (ESBO), which has been also proved an efficient stabilizer for PVC helping to prevent degradation during processing. Formulations based on PVC with different amounts of ESBO (from 30 to 50 wt%) were fully characterized showing good compatibility and a clear increase in thermal stability. An evaluation of the use of ESBO for PVC stabilization in commercial lids was carried out by using thermogravimetric analysis (TGA). ESBO was detected in all materials and their thermal stability was highly dependent on the plasticizer concentration. Most of them showed a significant increase in thermal degradation temperatures, permitting their use in food processing at high temperatures without risk of degradation.     

Application of a validated stability-indicating densitometric thin-layer chromatographic method to stress degradation studies on moxifloxacin

A simple, sensitive, selective, precise and stability-indicating high-performance thin-layer chromatographic (HPTLC) method for densitometric determination of moxifloxacin both as a bulk drug and from pharmaceutical formulation was developed and validated as per the International Conference on Harmonization (ICH) guidelines. The method employed TLC aluminium plates pre-coated with silica gel 60F-254 as the stationary phase and the mobile phase consisted of n-propanol-ethanol-6 M ammonia solution (4:1:2, v/v/v). Densitometric analysis of moxifloxacin was carried out in the absorbance mode at 298 nm. Compact spots for moxifloxacin were found at R_f value of 0.58 ± 0.02. The linear regression analysis data for the calibration plots showed good linear relationship with r = 0.9925 in the working concentration range of 100-800 ng spot⁻¹. The method was validated for precision, accuracy, ruggedness, robustness, specificity, recovery, limit of detection (LOD) and limit of quantitation (LOQ). The LOD and LOQ were 3.90 and 11.83 ng spot⁻¹, respectively. Drug was subjected to acid and alkali hydrolysis, oxidation, dry heat, wet heat treatment and photodegradation. All the peaks of degradation products were well resolved from the standard drug with significantly different R_f values. Statistical analysis proves that the developed HPTLC method is reproducible and selective. As the method could effectively separate the drug from its degradation products, it can be employed as stability-indicating one. Moreover, the proposed HPTLC method was utilized to investigate the kinetics of the acidic and alkaline degradation processes at different temperatures. Arrhenius plot was constructed and apparent pseudo-first-order rate constant, half-life and activation energy were calculated. In addition the pH-rate profile for degradation of moxifloxacin in constant ionic strength buffer solutions within the pH range 1.2-10.8 was studied.     

Studies on grafting of tris(2‐methoxyethoxy)vinylsilane onto ethylene‐propylene‐diene terpolymer

New graft copolymer was prepared by incorporating tris(2‐methoxyethoxy)vinylsilane (TMEVS) on ethylene‐propylene‐diene terpolymer (EPDM) by using dicumyl peroxide (DCP) as initiator, in Haake Rheocord 90 torque rheometer. The effect of EPDM concentration, TMEVS concentration, reaction time, reaction temperature and initiator concentration on the graft co polymerization was studied. The grafting efficiency of TMEVS on EPDM was confirmed by Fourier Transform infrared (FT‐IR) spectroscopy. The grafting efficiency increased with increase in the silane concentration upto 6% by weight. The grafting efficiency decreased beyond 6% by weight due to homopolymerization of TMEVS and non‐availability of carbon–carbon double bond in the EPDM terpolymer. The thermal properties of peroxide cured EPDM and hot water cured EPDM‐g‐TMEVS were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis. The results show thermal properties like degradation tempertature and glass transition temperature of the EPDM‐g‐TMEVS were increased due to introduction of TMEVS on to EPDM terpolymer as well as the formation of thermally stable three‐dimensional network. Copyright © 2004 John Wiley & Sons, Ltd.