Non-isothermal Chemiluminescence Research Articles

Stability Qualification of Resins/Metallic Oxide Composites for Surface Oxidative Protection.

The accelerated degradation of alkyd resins via γ-irradiation is investigated using non-isothermal chemiluminescence. The stability qualification is possible through the comparison of emission intensities on a temperature range starting from 100 °C up to 250 °C under accelerated degradation caused by radiolysis scission. The measurements achieved in the samples of cured state resin modified by various inorganic oxides reveal the influence of metallic traces on the aging amplitude, when the thermal resistance increases as the irradiation dose is augmented. Even though the unirradiated samples present a prominent chemiluminescence intensity peak at 80 °C, the γ-processed specimens show less intense spectra under the pristine materials and the oxidation starts smoothly after 75 °C. The values of activation energies required for oxidative degradation of the sample subjected to 100 kGy are significantly higher in the composite states than in the neat resin. The degradation mechanism of polymerized resins is discussed taking into account the effects of fillers on the stability of studied epoxy resin at various temperatures when the degradation and crosslinking are in competition for the decay of free radical.

INSIGHT INTO THE OXIDATIVE DEGRADATION OF PHENOLIC RESIN DESTINED FOR THE CORROSION PROTECTION OF METALLIC SURFACES

The effects on the stability under accelerated degradation of phenolic resin used for the corrosion inhibition of metallic surfaces in aeronautical and nuclear spare parts are evaluated by nonisothermal chemiluminescence (CL) at four different heating rates: 5, 10, 15, and 20 ⁰C min-1. The simulation of the interface interaction between the metallic bodies and protection layers is achieved by the addition of metallic oxides as corrosion promoters: Gd2O3, CeO2, Pr2O3, MgO, MnO2, Cr2O3, and In2O3. These metallic atoms may be the main alloying elements that are present in the compositions of special application products. The presence of a specific peak in the CL spectra between 160 and 177°C proves the oxidation activity of filler in the connection of electronic interference. The differences between the emission intensities of the studied formulations certify the unlike contributions of alloying components. The heating rate plays also the role of oxidation factor that influences the refreshing surrounding atmosphere. The present results define the thermal technological limits of peculiar operation conditions for any metallic item subjected to a high level of warranty. The initiation of degradation in phenolic resin is done by -irradiation when free fragments are provided for the interaction with metallic structures. The development of oxidation is analyzed by the modification of CL emission intensities from room temperature to 250°C. The diminution of this process parameter over 200°C is found an essential factor for the preservation of surface integrity.

The Effect of Hollow Glass Microspheres on the Kinetics of Oxidation of Poly(ε-Caprolactone) Determined from Non-Isothermal Thermogravimetry and Chemiluminescence

The effect of hollow glass beads on poly(ε-caprolactone) (PCL) oxidative degradation has been evaluated by the non-isothermal chemiluminescence (CL) method and thermogravimetry analysis (TGA). The main goal of the research and this publication was to reduce the production costs associated with the materials for 3D printing, which would also have a low mass, excellent biocompatibility and suitable thermal properties. Experiments have clearly shown the dual effect of a filler and its extent in terms of poly(ε-caprolactone). The chosen methods demonstrate the superposition of both the pro-degradation and stabilization effects of hollow glass beads on the polymer. The former was evident above the load of 10 wt.% of filler. The non-isothermal TGA records were analyzed as being composed of three temperature-dependent processes of the first-order kinetics. A massive compensation effect between the so-called activation energy and the logarithm of pre-exponential factors for heating rates of 2.5, 5 and 10 °C/min has been shown to be typical for similar non-isothermal thermogravimetry evaluation.

Synergistic effect of silica nanoparticles assisted by rosemary powder in the stabilization of styrene-isoprene-styrene triblock copolymer

The synergistic efficiency in the improvement of thermal and radiation stabilities of polymer substrate (styrene-isoprene-styrene triblock copolymer) is studied by isothermal and nonisothermal chemiluminescence, when silica nanoparticles loaded in various proportions (1, 2, and 3 wt%) are coupled with rosemary in the dropping down the degradation rate. The measurements of chemiluminescence emission intensities at various degradation degrees obtained by accelerated ageing with γ-radiation provide the evidences for a synergistic action of n-silica nanoparticles/rosemary extract upon the stability of polymer matrix. The main kinetic parameter, oxidation induction time (OIT), which describes the stabilization efficiency of additives by the hindering of oxidation presents illustrative values for the co-operation factors between the two prevention components. The synergistic effect is evident: the OIT of couple action is much higher than the values that characterize component activities. This feature has much higher values than unity. The contribution of this inorganic/organic antioxidant couple is discussed based on the activation energy values calculated by Arrhenius method. The effects of silica nanoparticles on the delay of degradation is also analyzed by means of nonisothermal chemiluminescence measurements, which prove the increase of protection activity when the silica loading is enhanced from 1 to 3 wt%. The applications of this stabilization couple may be found in the areas of food handling, pharmaceutics, medical wear, dentistry, nuclear sealing, commodities, and many suitable others.

Bioactivity and Thermal Stability of Collagen-Chitosan Containing Lemongrass Essential Oil for Potential Medical Applications.

Bioactive collagen–chitosan–lemongrass (COL–CS–LG) membranes were prepared by casting method and analyzed for potential biomedical applications. For COL–CS–LG membranes, LG essential oil release, antioxidant properties, in vitro cytotoxicity and antimicrobial assessments were conducted, as well as free radical determination after gamma irradiation by chemiluminescence, and structural characteristics analysis through Attenuated Total Reflection–Fourier Transform Infrared Spectroscopy (ATR–FTIR) and Differential Scanning Calorimetry (DSC). The evaluation of non-isothermal chemiluminescence after gamma radiation exposure to COL–CS–LG membranes revealed a slowing down of the oxidation process at temperatures exceeding 200 °C, in correlation with antioxidant activity. Antimicrobial properties and minimum inhibitory concentrations were found to be in correlation with cytotoxicity limits, offering the optimum composition for designing new biomaterials.

Stability Study of the Irradiated Poly(lactic acid)/Styrene Isoprene Styrene Reinforced with Silica Nanoparticles.

In this paper, the stability improvement of poly(lactic acid) (PLA)/styrene-isoprene block copolymer (SIS) loaded with silica nanoparticles is characterized. The protection efficiency in the material of thermal stability is mainly studied by means of high accurate isothermal and nonisothermal chemiluminescence procedures. The oxidation induction times obtained in the isothermal CL determinations increase from 45 min to 312 min as the polymer is free of silica or the filler loading is about 10%, respectively. The nonisothermal measurements reveal the values of onset oxidation temperatures with about 15% when the concentration of SiO2 particles is enhanced from none to 10%. The curing assay and Charlesby–Pinner representation as well as the modifications that occurred in the FTIR carbonyl band at 1745 cm−1 are appropriate proofs for the delay of oxidation in hybrid samples. The improved efficiency of silica during the accelerated degradation of PLA/SIS 30/n-SiO2 composites is demonstrated by means of the increased values of activation energy in correlation with the augmentation of silica loading. While the pristine material is modified by the addition of 10% silica nanoparticles, the activation energy grows from 55 kJ mol−1 to 74 kJ mol−1 for nonirradiated samples and from 47 kJ mol−1 to 76 kJ mol−1 for γ-processed material at 25 kGy. The stabilizer features are associated with silica nanoparticles due to the protection of fragments generated by the scission of hydrocarbon structure of SIS, the minor component, whose degradation fragments are early converted into hydroperoxides rather than influencing depolymerization in the PLA phase. The reduction of the transmission values concerning the growing reinforcement is evidence of the capacity of SiO2 to minimize the changes in polymers subjected to high energy sterilization. The silica loading of 10 wt% may be considered a proper solution for attaining an extended lifespan under the accelerated degradation caused by the intense transfer of energy, such as radiation processing on the polymer hybrid.

Structural configuration-radiation stability relationship in the degradation of dumbbelled POSSs

The stability of the inorganic filler, polyhedral oligomeric sisesquioxane (POSS) powders modified as dumbbelled structures is analyzed. This study was conducted by γ-irradiation at four γ-doses, when the degradation of compounds was accomplished. The radiochemical stability was investigated by nonisothermal chemiluminescence. This procedure allowed to establish the sequence of radiation resistance as a characteristic feature in their applications as hybrid filler. The activation energies required for the delaying oxidation in the minor component were calculated. The consequences of defined molecular structure are discussed in the relation of the initiation of the material ageing in the formulation they would be included. The shown stabilization property is closely related to the activation energies that is required for the oxidation. The radiochemical modification occurred in dumbbell POSSs is characterized by the resistance of internal bridges rather than the degradation strength of spatial polyhedral configuration. The degradation profiles resulting from nonisothermal CL measurements are conditioned by the structural reasons and the diffusion of fed oxygen which maintains the spontaneous ageing of polymers, where these fillers would be added. The present results are appropriate proofs for the utilization of dumbbelled POSSs as suitable stabilizers for polymer materials subjected to radiation sterilization.

Stability Effect of Metallic Traces in the Degradation of Materials

AbstractThe electrical devices, where alkyd resin is used as insulation material must have an improved thermal stability. The added filler, inorganic oxide compounds, have various contributions on the resin durability because of their differences in the electronic distribution. The PbTiO3 doped with Mn, Ce, In, Gd, Nb, Pr, and Nd atoms possessing certain features of stabilization played the role of protector during material oxidation. The investigations by isothermal and nonisothermal chemiluminescence revealed the effect of filler in the alkyd resin matrices subjected to the accelerated degradation by γ‐irradiation. The influence of doping atoms is discussed and the stabilization consequences are evaluated.

Evaluation of thermal and radiation stability of EPDM in the presence of some algal powders

In this paper, ecological-friendly materials based on ethylene–propylene–diene terpolymer (EPDM) with improved thermal and radiation stabilities by Chlorella vulgaris (CV) and Spirulina platensis (SP) powders were investigated by complementary procedures: FTIR spectroscopy and isothermal and nonisothermal chemiluminescence (CL). The stabilization potential of microalgae was evaluated at several degrees of γ-radiolysis by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, while the polymer resistances were studied on a large range of algal concentrations (1, 3, 5 and 10 mass%). The carbonyl and hydroxyl indices of all degraded EPDM formulations were found to be two times smaller in the presence of algal powders, if compared to the pristine material. Some dissimilarities between the oxidation development in pristine and modified EPDM appeared, especially in unirradiated samples. The activation energies required for the oxidation of EPDM and the lifetime of these samples at various temperatures between room temperature and 100 °C were calculated. The antioxidant compounds existing in the studied microalgae proved a significant influence on the stability of EPDM, mainly in the presence of SP, which was confirmed by the activation energies calculated from our CL results. The investigation of cycling thermal degradation revealed the obvious contribution of additives towards delaying EPDM ageing.

Improvement of thermal stability of EPDM by radiation cross-linking for space applications

The investigation of radiation effects on ethylene–propylene–diene terpolymer (EPDM) loaded with trifunctional monomer (trimethylolpropane triacrylate, TMPTA) at three concentrations (0, 2.5 and 5 phr) was accomplished by isothermal and nonisothermal chemiluminescence spectroscopies, thermal analysis, mechanical testing and scanning electron microscopy. All these investigations indicate the contribution of monomer to the improvement of degradation strength and the possible extension of improved material over the space and nuclear ranges. The monomer loading of 2.5 phr and 50 kGy exposure dose is the optimal conditions for the improvement in thermal strength of polymer. The radiation effect is related to the cross-linking, but the contribution of radiolysis on the thermal stability at 100 kGy must not be discarded. The modified EPDM presents satisfactory functional features related to the material durability. The oxidative degradation and cross-linking, the main ways to high material performances, are the competitive processes through which EPDM is qualified for special operation purposes.

Radiochemical stability and lifetime of HDPE-based flexible composite filled with Ce-doped PbZrTiO3

This paper presents the stabilization effects of inorganic filler, cerium-doped lead zirconate titanate on high-density polyethylene. The filler was loaded in two concentrations (1 and 3 wt%). The dopant contents in PbZrO3 were 0, 0.05, 0.075, 0.1 and 0.125 mol%. The degradation of hybrid samples was accomplished by γ-irradiation at various doses up to 200 kGy. The isothermal and nonisothermal chemiluminescence (CL) and thermal analysis (TG-DSC) were applied for the thermal stability characterization of modified HDPE samples. The mechanistic considerations and radiochemical consequences caused by the variation of filler concentration and doping level are discussed. The results demonstrate that the filler acts efficiently as stabilizer at low concentration of additive when the lower filler amount is present. The start of degradation precedes melting by four processes through which the chain scission and radical oxidation represent the essential degradation stage. The filler concentration influences the degradation due to the intimate interaction between solid-state defects and free radicals. The polymer protection against oxidation is based on the scavenging of radicals by the doping elements, that is, they trap and block radicals delaying material aging. The present results open a new perspective in the quality amelioration of organic products toward high durability.

Alkyd hybrid coatings for electrical rotating machines

Alkyd hybrid systems containing antioxidants (IRGANOX 1010, IRGANOX 1076, and SANTONOX R), titania and alumina were subjected to thermal and radiation degradation for their application in the electrical engineering. For the characterization of thermal stability of hybrid compositions, crystallinity evolution in nanostructured organic polymers, and structure changes, due to different thermal treatment isothermal and nonisothermal chemiluminescence, X-ray diffraction, infrared absorption spectroscopy with Fourier transforming infrared spectrometer and Raman spectroscopy were, respectively, used. It was found that the oxidation protector IRGANOX 1010 and TiO2 filler increased the thermal stability proved by chemiluminescence. The long-term heating characterized by temperature index demonstrated that the modified alkyd–melamine–epoxy resin is a suitable treatment for polyester laminates used in the electrical rotating machines. The superior thermal performances of cured polyester laminates were also demonstrated by the evaluation of swelling degree that is placed at half or lower values in modified materials than in neat resin. The interaction between formulation components is revealed by the improvement of thermal strength whose level is increased due to the cage effects promoted by additive and filler.

Thermal stability of gamma-irradiated polyurethane/POSS hybrid materials

In this work, new version: we report essential data on the stability of gamma-irradiated polyurethanes chemically modified by octa(3-hydroxy-3-methylbutylmethylsiloxy) POSS (o-POSS) which varies from 2, 4, 6, 8 to 10 mass%. These hybrid materials were tested by isothermal (190 °C) and nonisothermal (β = 2, 3.7, 5 and 10 K min−1) chemiluminescence, and the thermal stability of gamma-radiation-aged samples was correlated with the change in the nanofiller loading and absorbed dose. The compositions where inorganic phase is less than 6% show an increasing thermal strength as o-POSS concentration enhances. The other samples with higher nanoparticle content present less stability in respect of inferior homologous composition. The nonisothermal chemiluminescence profiles are changing from one type of sample to the other where nanofiller induces different effects. The considerations on mechanistic aspects are discussed, too.

Aerobic Biodegradation of Aromatic Aliphatic Copolyester Induced by Bacteria Obtained from Different Environments

In this study the biodegradation characteristics of aromatic aliphatic copolyester Ecoflex was assayed with five different bacterial strains isolated from different kinds of environments and living at diverse optimum of temperature. The biodegradation properties of selected strains (Brevibacterium luteolum, Bacillus thuringiensis, Aeromonas media, Geobacillus kaustophilus and Serratia sp.) were assessed through several plate assays oriented to their proteolytic, lipolytic, esterolytic and cellulolytic abilities; catalase activities were measured too. In addition the bacterial hydrolytic abilities for polyhydroxybutyrate, polylactic acid and polybutyrate adipate terephthalate were obtained using specific culture media including also a specific Ecoflex agar. The biodegradation dynamics of selected strains were evaluated mainly by the incubation of Ecoflex foils with a specific bacterium during a period from 3 days until 16 weeks and the change of the degradability of the Ecoflex surface in nitrogen has been assessed by nonisothermal chemiluminescence measurements from 40 to 250 °C. Scanning electron microscope observation of inoculated foils was applied too. The comparison of the results showed the complexity of biodegradation phenomena. The concentration of oxygenated products measured by reached the maximum after 2 weeks of cultivation for strains G. kaustophilus and B. thurigiensis, after 4 weeks of cultivation for strain B. luteolum, and 8 weeks of cultivation for strains Serratia sp. and A. media. Each strain evidenced its own hydrolytic optimum at different periods, but almost all tested strains demonstrated a decline of hydrolysis up to 16 weeks of incubation. This study demonstrated that nonisothermal chemiluminescence examining momentaneous oxidation state of the polymer surface is a valuable technique to follow the biodegradation dynamics on polymeric film, while the Ecoflex agar is able to select useful polymer-degrading bacteria.

Structural characterization and thermal behaviour of some azomethine compounds derived from pyridoxal and 4-aminoantipyrine

Eight azomethine-type compounds (1–8) derived from pyridoxal (3-hydroxy-5-(hydroxymethyl)-2-methylpyridine-4-carbaldehyde) and 4-aminoantipyrine, respectively, were prepared and thoroughly characterized from structural and thermal perspective. The structures of the compounds were studied based on IR, 1H and 13C NMR spectroscopy and electrospray ionization mass spectrometry. The formation of the azomethine derivatives is confirmed by the occurence of signals typical for the imine bond. Compounds 6 and 8 feature a high crystallinity, and their structures were resolved by single-crystal X-ray diffraction. The thermal behaviour of all the compounds was studied by non-isothermal chemiluminescence in static air atmosphere at different heating rates. The pattern of the oxidation process is described. Moreover, thermo-gravimetric and differential scanning calorimetry experiments were conducted in order to assess the thermal oxidation stability. The onset oxidation temperatures show a high thermal stability for all the tested azomethine compounds. The crystallinity degree was comparatively evaluated on the basis of melting enthalpy values and discussed in connection with the molecular structure. Compounds 6–8 show the higher thermal stability and crystallinity degree.

Study on radiation aging of PA6/EPDM blends

The modification in the stability of polyamide-6 (PA6)/ethylene-propylene diene copolymer (EPDM) was studied by isothermal and non-isothermal chemiluminescence and FTIR spectroscopy. The compositions of the blends consisted of PA-6 as basic component and EPDM as the second component at different loadings (0, 10, 20, and 30 wt %). The exposure to γ-radiation (137Cs) was performed in air at room temperature at five total doses of 10, 25, 50, 100 and 160 kGy and dose rate of 0.4 kGy h−1. The different oxidation rates were correlated with the elastomer concentration according to the dissimilarity between the radiation resistance of the components. The maximum CL intensities attained at 210 °C corresponded to the highest oxidation rates in non-isothermal CL spectra. The delayed oxidation was due to the presence of elastomer which was noticed in the non-isothermal CL intensities of all compositions. The isothermal CL determinations revealed the contribution of elastomer to the oxidative strengths of PA-6/EPDM compounds. The non-isothermal chemiluminescence determinations confirmed that the main source of radicals along the γ-radiation exposure was EPDM component. The slight shift of the temperature peaks, characterizing the maximum oxidation levels, was noticeable by higher EPDM concentrations. The propagation of oxidation was likely supported by the intermediates appeared in elastomeric phase which could split at tertiary carbon atoms easier. FTIR records highlight the contribution of each component in oxidation process.

Thermal and spectroscopic analysis of stabilization effect of copper complexes in EPDM

The thermal stabilization effect of copper complexes on ethylene-propylene-diene terpolymer (EPDM) is studied during an accelerated degradation of polymer samples by their exposure to γ(137Cs)-radiation. These complexes of Cu(II) with two Schiff base ligands provided an efficient improvement in the stabilization of basic polymer. For the evaluation of improvement action of inorganic additive on thermal behavior of EPDM, the calculation of carbonyl and hydroxyl indexes and the radiochemical yields of corresponding radiolysis products prove the long-term stability of EPDM. Isothermal and nonisothermal chemiluminescence investigations were also accomplished, and the protection proficiencies of studied additives are compared by means of kinetic features of degradation. The activation energies required by the oxidation of polymer substrate were calculated, and their values are significant higher in comparison with the similar value found for pristine EPDM. The stabilized polymer is assisted by the interaction between mobile protons of ligands and hydrocarbon free radicals.

Comparison of the UV stabilisation effect of commercially available processing stabilizers Irganox HP 136 and Irganox 1010

Infrared and UV spectroscopy were used for estimation and mutual comparison of action of Irganox HP 136 and Irganox 1010 in UV stabilisation of polypropylene films. The instantaneous stability state of polypropylene after the different time of UV treatment was also tested by the non-isothermal chemiluminescence so that the actual resistance of sample against the thermal oxidation has been established. It was ascertained that Irganox HP 136 as a weak thermo-oxidation stabiliser is an excellent UV stabiliser of polypropylene, the fact that was not described in the literature until now. This stabilising efficiency was proposed to be provided by photochemical transformation of Irganox HP 136 to 2-hydroxy benzophenone moieties, the compound with ability to absorb the light as well as efficiently scavenge reactive free radicals.

Radiation effects in polyisobutylene succinic anhydride modified with silica and magnetite nanoparticles

Polyisobutylene succinic anhydride (PIBSA) was modified with nanoparticles of magnetite and silica for the appraising the modification in the thermal stability of organic component after gamma irradiation. Pristine anhydride was loaded with different amounts of nanofiller (1, 2 and 5 wt% of each oxide). Gamma exposure was performed in air at several doses: 10, 20, 50 and 100 kGy. The stability determinations were carried out by nonisothermal chemiluminescence in stationary air atmosphere. The presence of these oxides induces an increase in the oxidation level corresponding to their chemical availability as the filler amounts and exposure doses are enhanced. The oxidation takes essentially place on quaternary carbon atoms and double bonds, which was demonstrated by the presence of two chemiluminescence intensity peaks. The comparative analysis on the radiation oxidation of PIBSA modified with Fe3O4 and SiO2 is presented.

Thermally and UV initiated degradation of polypropylene in the presence of 2,5 bis(2-furylmethylene) cyclopentanone and heterogeneous distribution of hydroperoxides assessed by non-isothermal chemiluminescence in nitrogen

Abstract 2,5 bis(2-furylmethylene) cyclopentanone (F 2 C) has been shown to be a good inhibitor of thermal oxidation of polypropylene (PP). F 2 C structure, namely of cyclopentanone moiety linking two furan rings via conjugated system of double bonds performs captodative properties towards free radicals that may be the potential reason of its thermo-oxidation stabilization effect on polypropylene. When F 2 C is UV irradiated it acts as a weak photo-sensitizer probably due to carbonyl group in cyclopentanone, however, the original structure of F 2 C is converted fast to the products losing photo-sensitizing effect but still keeping some residual antioxidant effect on thermal oxidation of polypropylene that is probably due to 335 nm UV band. The changes of non-isothermal chemiluminescence runs in nitrogen and in oxygen and development of FTIR spectra for 0.3% of F 2 C in polypropylene were compared with pure polypropylene and polypropylene containing 0.3 wt. % of Irganox 1010. New observation has been presented namely that non-isothermal chemiluminescence runs in nitrogen shows the peak around 145 °C attributed to the decomposition of hydroperoxides superimposed with an additional peak appearing around the temperature of melting of polypropylene crystallites. This appears to be brought about by accelerated decomposition of hydroperoxides due to their higher concentration in heterogenous zones formed in the previous oxidation and to their increased mobility when polymer melts.