Manganese stearate initiated photo‐oxidative and thermo‐oxidative degradation of LDPE,LLDPE and their blends

This study is an attempt to investigate the effect of a representative pro‐oxidant (manganese stearate) on the degradation behavior of 70 ± 5 μ thickness films of LDPE, LLDPE and their blends. Films were prepared by film blowing technique in the presence of varying quantities of manganese stearate (0.5–1% w/w) and subsequently subjected to accelerated degradative tests: xenon arc exposure and air‐oven exposure (at 70°C). The physico–chemical changes induced as a result of aging were followed by monitoring the mechanical properties (Tensile strength and Elongation at break), carbonyl index (CI), morphology (SEM), melt flow index (MFI), oxygen content (Elemental analysis), and DSC crystallinity. The results indicate that the degradative effect of pro‐oxidant is more pronounced in LDPE than LLDPE and blends, due to the presence of larger number of weak branches in the former. The degradation was also found to be proportional to the concentration of the pro‐oxidant. Flynn‐Wall‐Ozawa iso‐conversion technique was used to determine the kinetic parameters of degradation, which were used to determine the effect of the pro‐oxidant on the theoretical lifetime of the polymer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Modeling of degradation of unstabilized and HALS‐stabilized LDPE films under thermo‐oxidation and natural weathering conditions

Mathematical models are proposed to predict degradation of unstabilized low density polyethylene (LDPE) films and those stabilized with hindered amine light stabilizers (HALS) under both thermo‐oxidation at 90°C and natural weathering conditions. The degradation was measured by change in percent elongation at break (?_r) with time. The mathematical approach developed was multiple linear regression analysis (MLRA). The reliability of the selected models was analysed using four statistical criteria, residual variance, coefficient of determination (r²), Student test and Fisher‐Snedecor test. The linear systems that resulted from the MLRA were resolved by the Cholesky method. The results obtained indicated that the polynomial models developed to predict elongation at break were reliable for both unstabilized and HALS‐stabilized samples under thermo‐oxidation at 90°C and natural weathering conditions. This was also confirmed by the comparison of the half‐life time (HLT) values predicted from the models with those observed experimentally. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3284–3292, 2001     

The impact of cupric ion on thermo‐oxidative degradation of chitosan

The thermal degradation of chitosan and chitosan–cupric ion compounds in air was studied using thermogravimetric and differential thermal analyses in the temperature range 30–600 °C. The impact of cupric ion on the thermo‐oxidative degradation of chitosan was investigated. Fourier transform infrared and X‐ray diffraction analyses were utilized to determine the microstructure of the chitosan–cupric ion compounds. Kinetic parameters such as activation energy, pre‐exponential factor, Gibbs energy, and enthalpy and entropy of activation were determined using the Coats–Redfern equation. The results show that the thermo‐oxidative degradation of chitosan and chitosan–cupric ion compounds is a two‐stage reaction. The impact of cupric ion on the thermo‐oxidative degradation of chitosan is significant, and all thermodynamic parameters indicate that the thermo‐oxidative degradation of chitosan and chitosan–cupric ion compounds is a non‐spontaneous process and proceeds via a mechanism involving nucleation and growth, with an Avrami–Erofeev function (A₄) with the integral form [?ln(1 ? α)]⁴. Copyright © 2010 Society of Chemical Industry     

Composites of ethylene‐vinyl acetate copolymers with modified magnesium hydroxide–thermo‐oxidative ageing

Flame retardant composites must perform their protective roles permanently, also under conditions of intermittent or long‐term exposure to sunlight, moisture or increased temperature. The aim of our work was characterization of the thermo‐oxidative ageing (90 °C) and the changes in flammability of ethylene‐vinyl acetate copolymer composites with 40 and 60 wt.% of magnesium hydroxide. The neat polymer and its composites were investigated for their thermal (DSC) and structural (FTIR) characteristics as well as their density, melt flow index, tensile properties and combustibility during ageing test. As FTIR results identified the different carbonyl groups in copolymer were created, the highest oxidation intensity was observed for neat copolymer. That process was accompanied by the scission of the polymer macromolecules, especially for first 700 h of thermal ageing. Thermo‐oxidative ageing resulted also in the reduction of flammability of the test materials. The highest reduction was observed for neat polymer. The changes in some properties as analysed both for the copolymer and for its composites after over 700 h of ageing were indicative for initiation of cross‐linking of copolymer molecules after that time. Copyright © 2014 John Wiley & Sons, Ltd.     

Rapid test methods for analyzing degradable polyolefins with a pro‐oxidant system

Chemiluminescence, size exclusion chromatography, differential scanning calorimetry, thermogravimetry, and Fourier transform infrared spectroscopy were used to assess differences in oxidation rate between two different pro‐oxidant systems in degradable low‐density polyethylene. The pro‐oxidant formulation used consisted of manganese stearate and natural rubber or manganese stearate and a synthetic, styrene‐butadiene copolymer rubber. The low‐density polyethylene containing the pro‐oxidant with natural rubber showed the highest degradation rate. Chemiluminescence and thermogravimetry were found to be the most effective techniques for establishing the differences between different pro‐oxidant systems. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2309–2316, 2001     

The effect of oxygen pressure on the kinetics of thermo‐oxidative degradation of the copolymer EVA and nitrile–butadiene rubber

The results of nonisothermal kinetic analysis of the thermo‐oxidative degradation in air and in oxygen of the copolymer EVA and nitrile–butadiene rubber (NBR) are presented. It was observed that similar processes take place at thermo‐oxidative degradation in air as well as in oxygen of both investigated polymeric materials. The first process, which leads to solid products, is followed by thermo‐oxidative degradation with the generation of volatile products. It has been shown that the first process of thermo‐oxidation occurs at lower temperatures in oxygen than in air. For this process, the nonisothermal kinetic analysis was carried out using the Kissinger method. The obtained results revealed the importance of the oxygen pressure as an accelerator in the thermo‐oxidative degradation of copolymer EVA and NBR. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1453–1457, 2000     

Pyrolysis and thermo‐oxidative degradation of polycyclopentadiene

Thermal degradation of polycyclopentadiene polymer (PCPD) was investigated by pyrolysis gas chromatography (PGC) in the temperature range of 500–950°C. The nature and composition of the pyrolyzates at various temperatures are presented, and the mechanism of degradation is explained. The activation energy of decomposition (E_a) was obtained from an Arrhenius‐type plot using the concentration of the product ethylene (C₂) at different pyrolysis temperatures and the value was found to be 138 kJ mol⁻¹. Thermo‐oxidative degradation of PCPD in the presence of ammonium perchlorate (AP), the most commonly used oxidizer for polymeric fuel binders, was studied at a pyrolysis temperature of 700°C. The compositions of the products with varying amounts of AP are given, and the exothermicity of oxidative decomposition reactions is evaluated. The energetics of the degradation processes are compared with those of polybutadiene type polymers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 635–641, 2000     

Formation and decomposition of stigmasterol hydroperoxides and secondary oxidation products during thermo‐oxidation

The oxidation mechanisms of stigmasterol at 100 and 180 °C were investigated by using the HPLC‐UV‐FL method. An overall picture of the oxidation status was achieved with a single HPLC analysis, enabling us to monitor the formation and decomposition of both primary and secondary oxidation products. The oxidation behavior of stigmasterol was different at the two temperatures. At 180 °C, the amounts of hydroperoxides increased sharply during the first 10 min and then began to decrease. At 100 °C, the amounts of hydroperoxides increased over the entire experimental period. At 180 °C, all major secondary oxidation products, except 7‐ketostigmasterol, reached a plateau after 40 min of oxidation, while at 100 °C their amounts increased constantly. The same oxidation products were formed at both temperatures, but their distribution differed. At 180 °C, the formation of free radicals at position 7 was more favorable than formation of radicals at position 25. The situation was the opposite at 100 °C; radicals formed more easily at the tertiary position 25. At 180 °C, 7‐ketostigmasterol was dominant after 40 min of oxidation, whereas at 100 °C it was the main oxidation product over the entire experiment.     

Comparison of thermo‐oxidative treatments for the anaerobic digestion of sewage sludge

BACKGROUND: In this study, various thermo‐oxidative treatments were examined and compared with the aim of overcoming the disadvantages of thermal treatment and enhancing the anaerobic digestion of sewage sludge. RESULTS: Oxygen, hydrogen peroxide and ozone were selected as oxidant, accompanied with the addition of either acid (HCl) or alkali (Na₂CO₃) for oxygen. The temperature and duration were fixed at 170 °C and 1 h, respectively. Anaerobically digested sludge was used as the substrate, to see the effects on the refractory part of sewage sludge. A batch methanogenesis test using 120 mL serum bottles was run at 35 °C for 20 days, and methane production, solids reduction, dewaterability and color intensity were measured. As the strength of the oxidants was increased, methane production tended to decrease, whereas solids reduction was increased. The dewaterability of the sludges and the color in the filtrates became worse for thermo‐oxidative treatment with oxygen and alkali. On the other hand, the dewaterability was improved significantly and color generation was restricted the most for the thermo‐oxidative treatment with oxygen and acid. CONCLUSION: Lowering the pH of thermo‐oxidative treatment is advantageous with respect to the dewaterability and color generation of digested sludge. Based on evaluation of the overall performance, thermo‐oxidative treatment with acid is considered the best among the thermo‐oxidative treatments examined. Copyright © 2008 Society of Chemical Industry     

The effects of e‐beam crosslinking of LDPE on the permeation of hydrocarbons

Polyethylene is a useful material in numerous applications, such as packaging, fuel tanks as well as oil and gas pipes. However, it must be considered that polyethylene is permeable to gases and liquids. Small molecules, such as hydrocarbons, may permeate through the material and cause environmental problems. Consequently, a particular aspect of polymer materials is the requirement of a high permeation resistance against low‐molecular‐weight hydrocarbons. Modifications of the commonly used polyethylene material are necessary to achieve adjusted permeation properties. In this contribution, the effect of electron‐beam crosslinking of polyethylene on the resulting permeation characteristics was investigated. Polyethylene sheets were processed and crosslinked by irradiation with high energy electrons. The formation of a network structure was characterized by gel content determination and by rheological measurements. The permeation properties of the polymer sheets were assessed by a gravimetric method. It is demonstrated that—as a result of the crosslinking process—the permeation of low molecular weight hydrocarbon through polyethylene is reduced with respect to the chain length of the aliphatic substances. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44968.     

Study of ultraviolet photooxidative degradation of LDPE film containing cerium carboxylate photosensitizer

The carbonyl indices (CI) of photooxidation of low-density polyethylene (LDPE) films containing cerium carboxylate (CeCar₃) with/without aromatic ketones (AK) were determined by infrared (IR) spectroscopy. The effects of these photosensitizers on the rates of ultraviolet (UV) photooxidation of LDPE films and their mechanism in sensitizing photooxidative degradation are studied. Results show that CeCar₃ can cause the accelerated photooxidative degradation of LDPE films, but CeCar₃ in combination with AK may bring about the accelerated or retarded photooxidative degradation of LDPE films to varying degrees. After UV irradiation, followed by long duration storage, LDPE films containing these photosensitizers continued storage oxidative degradation at the storage oxidative rates similar to the past, except for the Michler ketone.     

Autonomous damage initiated healing in a thermo‐responsive ionomer

The partially neutralised poly[ethylene‐co‐(methacrylic acid)] copolymer Surlyn 8940^® (DuPont) ionomer exhibits damage‐initiated healing during high‐energy impact. This is attributed to the hierarchical structure of ionomers, arising from the presence of ionic aggregates and hydrogen bonding. This work investigates the mechanism of this process using novel techniques developed here. The ionomer's response to penetration has been found to consist of three consecutive events: an initial elastic response, an anelastic response and pseudo‐brittle failure. In addition, the ultimate level of healing has been shown to be dependent upon the elastic response during impact as well as post‐failure viscous flow. Increasing the local temperature at impact consistently increases elastic healing, although further improvements in healing are minor once the local temperature increases beyond the melting point. Below the order‐to‐disorder transition, microscopic investigations reveal severe plastic deformation while the lack of shape memory reduces the comparative level of elastic healing. Above this temperature, healing is facilitated by elastomeric behaviour at the impact site, while above the melting point a combination of elastomeric and viscous flow dominates. This work provides for the first time evidence of the consecutive healing events occurring during high‐impact penetration for ionomers. The hierarchical structure of ionomers and its impact upon the microstructure have been shown to be critical to the process. Comparison of the mechanical response during impact with that of non‐ionic polymers further highlights this. In addition, slow relaxational processes occurring post‐impact are found to facilitate further recovery in mechanical properties. Copyright © 2010 Society of Chemical Industry     

Kinetic study of polypropylene nanocomposite thermo‐oxidative degradation

Polypropylene (PP) has wide acceptance for use in many application areas. However, low thermal resistance complicates its general practice. The new approach in thermal stabilization of PP is based on the synthesis of PP nanocomposites. This paper discusses new advances in the study of the thermo‐oxidative degradation of PP nanocomposite. The observed results are interpreted by a proposed kinetic model, and the predominant role of the one‐dimensional diffusion type reaction. According to the kinetic analysis, PP nanocomposites had superior thermal and fireproof behaviour compared with neat PP. Copyright © 2005 Society of Chemical Industry     

Preparation and thermal and thermo‐oxidative stability of vinylidene chloride‐co‐vinyl chloride copolymer/synthetic hectorite nanocomposites

Poly(vinylidene chloride‐co‐vinylchloride)/organically modified hectorite (VDC‐VC/SPN) nanocomposites were prepared by melt blending VDC‐VC copolymer with SPN in the presence of dioctyl phthalate, which acted as a plasticizer. As a result, the exfoliated structure was found in the VDC‐VC/SPN nanocomposites. In nitrogen atmosphere, VDC‐VC/SPN nanocomposites exhibited a single‐step thermal degradation. The thermal stability of VDC‐VC/SPN nanocomposites is significantly influenced by the SPN, which was modified with long alkyl ternary ammonium salt. In air atmosphere, VDC‐VC/SPN nanocomposites revealed a two‐step thermo‐oxidative degradation behavior. At the first degradation stage, the weight loss pattern is similar to that of VDC‐VC composites in nitrogen, in which the thermo‐oxidative stability of VDC‐VC/SPN nanocomposites is affected by the ternary ammonium salt and oxygen rather than its morphology. At the second degradation stage, both the enhanced thermo‐oxidative stability and the flame‐retardation ability of VDC‐VC composites are strongly and closely related to the morphology of nanocomposites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci ,2009     

Preparation of coated thermo‐regulating textiles using Rubitherm‐RT31 microcapsules

Spherical microcapsules with a 49 wt % of Rubitherm^® RT31 were successfully synthesized by means of suspension‐like polymerization to be used for textile applications in summer conditions. Microcapsules were fixed into seven fabric substrates for different textile applications by a coating technique without deteriorating original functionalities of the textiles. Thermal performance of different coated textiles with 35 wt % of microcapsules was evaluated by differential scanning calorimetry (DSC) and infrared thermography (IR) techniques and the physical characteristics of textiles with thermo‐regulating properties were examined by environmental scanning electron microscopy (ESEM). It was observed that all treated textile substrates allow to obtain thermo‐regulating properties with acceptable latent heat storage capacities. Results also indicated that the presence of microcapsules containing Rubitherm^® RT31 produces a significant thermal insulation effect during a cold to warm transition (20–45°C). Thus, this kind of microcapsules can be used to obtain textiles with thermal comfort‐related properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and catalytic oxidation properties of polymer‐bound cobalt complexes

Polymer‐bound 2,2′‐bipyridine cobalt complexes PSBPY‐Co, PSBPY‐Co‐bipy, PSBPY‐Co‐oxine, and PSBPY‐Co‐phen (where PSBPY: polystyrene bound‐2,2′‐bipyridine; bipy: 2,2′‐bipyridine; phen: 1,10‐phenanthroline) were synthesized and investigated by IR, X‐ray photoelectric spectroscopy, thermogravimetry–differential thermal analysis, inductively coupled plasma atomic emission spectrometry, and elemental analysis. The complexes were found to be catalysts for the oxidation of alkylbenzenes and cyclohexene in the presence of molecular oxygen in the absence of solvent. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1068–1074, 2000     

Thermal and thermo‐oxidative degradation properties of poly(benzimidazole amide imide) copolymers

In this study, 3,3′‐dinitrobenzidine was first reacted with excess isophthaloyl chloride to form a monomer with dicarboxylic acid end groups. Two types of aromatic dianhydride, [viz., pyromellitic dianhydride (PMDA) and 3,3′,4,4′‐sulfonyldiphthalic anhydride (DSDA)] also were reacted with excess 4,4′‐diphenyl‐ methane diisocyanate (MDI) to form polyimide prepolymers terminated with isocyanate groups. The prepolymers were reacted further with the diacid monomer to form a nitro group–containing aromatic poly(amide imide) copolymers. The nitro groups in these copolymers were hydrogenated to form amine groups and cyclized at 180°C to form the poly(benzimidazole amide imide) copolymers in polyphosphoric acid (PPA), which acts as a cyclization agent. From the viscosity measurements, copolymer appeared to be a reasonably high molecular weight. From the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) measurements it was shown that the glass transition temperature of copolymers was in the range of ～270–322°C. The 10% weight loss temperatures were in the range of 460 ～ 541°C in nitrogen and ～441–529°C in air, respectively. The activated energy and the integration parameter of degradation temperature of the copolymers were evaluated with the Doyle‐Ozawa method. It indicated that these copolymers have good thermal and thermo‐oxidative stability with the increase in imide content. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2072–2081, 2004     

Study of novel biodegradable thermo‐sensitive hydrogels of methoxy‐poly(ethylene glycol)‐block‐polyester diblock copolymers

A series of biodegradable thermo‐sensitive hydrogels were synthesized by ring‐opening polymerization of methoxy‐poly(ethylene glycol) (mPEG) and various ester monomers, i.e. D ,L ‐lactide, glycolide, β‐propiolactone, δ‐valerolactone and ε‐caprolactone. The copolymers were characterized using ¹H NMR spectroscopy and gel permeation chromatography. The micelle properties were also measured. The results indicated that the diblock copolymers formed nano‐micelles at low concentrations in aqueous phase. The lower critical solution temperatures of the diblock copolymers were above 35 °C at 1 wt%. As the temperature increased above room temperature, the diblock copolymer solutions underwent a sol‐to‐gel phase transition, which was manifested in viscosity increases, indicative of the formation of a gel. The mPEG–polyester diblock copolymer solutions exhibited sol‐gel transition behavior as a function of temperature and polymer concentration. Copyright © 2010 Society of Chemical Industry     

Synthesis and characterization of novel thermo‐ and pH‐responsive copolymers based on amphiphilic polyaspartamides

Novel amphiphilic, thermo‐ and pH‐responsive polyaspartamides showing both double‐responsive (pH and temperature) behavior and a sol‐gel transition were prepared and characterized. The polyaspartamide derivatives were synthesized by the successive aminolysis reactions of polysuccinimide using both hydrophobic N‐alkylamine (laurylamine, octylamine, hexylamine) and hydrophilic N‐isopropylethylenediamine. The composition of each component was analyzed by ¹H NMR. At the intermediate composition range, the system showed a lower critical solution temperature behavior in water. The transition temperature (pH dependent) could be modulated by changing the alkyl chain length and graft composition. The temperature dependence of the nanoparticle size distribution of the polyaspartamide derivatives was also examined. The critical micelle concentration of the copolymers in a phosphate‐buffered saline (pH 7.4) solution ranged from 6 to 20 μg/L. In addition, physical gelation, i.e., a sol‐gel transition, was observed in a concentrated solution. These novel double‐responsive and injectable hydrogels have potential biomedical applications such as drug delivery systems and tissue engineering. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009