Thermal Oxidative Degradation Research Articles

Thermal stability and yellowing of polyamide finished with a compound anti-thermal-yellowing agent

In order to enhance the thermal stability and reduce the thermal yellowing of polyamide fabrics, a kind of compound anti-thermal-yellowing agent made up by urea, sodium hypophosphite, and adipic dihydrazide was finished to polyamide in this study. The structure change and the thermal stability of the polyamide were investigated by the analysis of TG-DSC, TG-FTIR curves, viscosity-average molecular weight, and end carboxyl group content of polyamide fibers. The anti-yellowing effect was evaluated by whiteness and yellowing index values. The results showed that the compound anti-thermal-yellowing agent could enhance the decomposition temperature and hinder the thermal-oxidative degradation of polyamide. Besides, the whiteness values of the fabrics treated by the anti-thermal-yellowing agent were distinctly higher than that of untreated fabrics and fabrics treated by Umidol UWP but the yellowing index values were lower, which supported that the thermal stability of the polyamide treated by the anti-thermal-yellowing agent became better.

Thermooxidative degradation of polyoxymethylene homo- and copolymer nanocomposites with hydroxyapatite: Kinetic and thermoanalytical study

In this paper thermooxidative degradation process of polyoxymethylene homo- and copolymer (POM)/hydroxyapatite nanocomposites has been studied. Kinetic analysis by Friedman, Ozawa–Flynn–Wall and multiple non-linear regression methods, as well as thermoanalytical studies using TG–MS and TG–FTIR method, were performed. TG results show that thermal stability of POM matrix significantly decreases with an increase of HAp nanoparticles concentration. The presence of higher HAp concentration changes mechanism of POM degradation, including its kinetics, which was demonstrated by a change of kinetic model from autocatalytic to phase-boundary or nth order reaction one. Hyphenated TG–MS and TG–FTIR data show that the main degradation product in the presence of higher amounts of HAp is formaldehyde, and formation of other degradation products – typical for POM thermoxidative degradation – is considerably diminished. Finally, mechanism of POM degradation in the presence of stoichiometric hydroxyapatite has been postulated.

Ultrahigh-performance liquid chromatography-ultraviolet absorbance detection-high-resolution-mass spectrometry combined with automated data processing for studying the kinetics of oxidative thermal degradation of thyroxine in the solid state

Levothyroxine as active pharmaceutical ingredient of formulations used for the treatment of hypothyroidism is distributed worldwide and taken by millions of people. An important issue in terms of compound stability is its capability to react with ambient oxygen, especially in case of long term compound storage at elevated temperature. In this study we demonstrate that ultrahigh-performance liquid chromatography coupled to UV spectrometry and high-resolution mass spectrometry (UHPLC-UV-HRMS) represent very useful approaches to investigate the influence of ambient oxygen on the degradation kinetics of levothyroxine in the solid state at enhanced degradation conditions. Moreover, the impurity pattern of oxidative degradation of levothyroxine is elucidated and classified with respect to degradation kinetics at different oxygen levels. Kinetic analysis of thyroxine bulk material at 100°C reveals bi-phasic degradation kinetics with a distinct change in degradation phases dependent on the availability of oxygen. The results clearly show that contact of the bulk material to ambient oxygen is a key factor for fast compound degradation. Furthermore, the combination of time-resolved HRMS data and automated data processing is shown to allow insights into the kinetics and mechanism of impurity formation on individual compound basis. By comparing degradation profiles, four main classes of profiles linked to reaction pathways of thyroxine degradation were identifiable. Finally, we show the capability of automated data processing for the matching of different stressing conditions, in order to extract information about mechanistic similarities. As a result, degradation kinetics is influenced by factors like availability of oxygen, stressing time, or stressing temperature, while the degradation mechanisms appear to be conserved.

Thermal-Oxidation Degradation and Evaluation of Non-Durable Non-Woven Fabrics

Samples of polypropylene (PP), polyethylene (PE),polyester (PET), polylactide (PLA), and viscose (CV) non-woven fabrics, were exposed to blowing hot oven at 110°C temperature conditions separately for different times. In order to determine the state of thermal oxidation degradation, samples were examined by Tensile Properties, Scanning Electron Microscopy, Fourier Transform Infrared (FTIR) spectroscopy and Differential Scanning Calovimotry (DSC). These methods can be used to study and evaluate the sample thermal oxidation degradation.

Control of Thermal-Oxidative Degradation of Natural Rubber STR 5L by Using Cysteine Encapsulated with Alginate/Chitosan Microcapsules

This research was to study the efficiency of cysteine (Cys) acted as a natural antioxidant, which was encapsulated in alginate/chitosan (AG/CS) microcapsules to control the thermal oxidative degradation of natural rubber STR 5L. The microcapsules were prepared by a combined method based on ionic gelation and electrospraying techniques. The preparation of AG/CS microcapsules were executed to find the appropriate parameters such as applying voltage and concentration of alginate and chitosan. The applied voltage achieved for controlling the particle size as well as narrow size distribution of microcapsule. The AG/CS/Cys microcapsules were found to be a spherical shape and the average size was approximately 120 μm. The percentage of cysteine encapsulated within AG/CS microcapsules was increased with the increasing of chitosan concentration and encapsulation efficiency of cysteine in the microcapsules is about 81%. Core-shell structure of the microcapsule was confirmed by confocal laser scanning microscopy. After that, the natural rubber STR 5L mixed with AG/CS/Cys microcapsules was evaluated the oxidative resistance by Wallace plasticity. Thermal aging test according to standard ASTM D1349 at 70°C of the STR 5L mixed with AG/CS/Cys microcapsules were carried out. Weight-average molecular weight (w) of the rubber sample before and after aging test was also investigated by gel permeation chromatography. Thewof rubber sample before and after aging test presented clearly results depending on the aging time. Concisely, the AG/CS/Cys microcapsules have a potential to control release Cys and can be used to control the deterioration of raw STR 5L. The model of this encapsulation is expected to be applied with other applications.

Influence of phosphazenes of various structures on the curing parameters and thermal oxidative degradation of oligomethylphenylsiloxane

Scientific and applied aspects of possible use of cyclic phosphazenes, by-products from phosphonitrilic anilide synthesis, as thermal stabilizers were considered. The solubility and thermal oxidative stability of phosphonitrile anilide trimer and tetramer were studied, the dependence of the curing parameters of oligomethylphenylsiloxane compositions (gel time, temperature intervals of curing) from the structure of the modifying additive was examined, and the resistance of compositions based on oligomethylphenylsiloxane modified with linear and cyclic oligophosphazenes to thermal oxidation at 350°C was evaluated.

The effect of carbon black reinforcement on the dynamic fatigue and creep of polyisobutylene-based biomaterials

This paper investigates the structure–property relationship of a new generation of poly(styrene-b-isobutylene-b-styrene) (SIBS) block copolymers with a branched (dendritic) polyisobutylene core with poly(isobutylene-b-para-methylstyrene) end blocks (D_IBS), and their carbon black (CB) composites. These materials display thermoplastic elastomeric (TPE) properties, and are promising new biomaterials. It is shown that CB reinforced the block copolymer TPEs, effectively delayed the oxidative thermal degradation of the D_IBS materials, and greatly improved their dynamic fatigue performance. Specifically, the dynamic creep of a CB composite was comparable to that of chemically crosslinked and silica-reinforced medical grade silicone rubber, used as a benchmark biomaterial.

Kinetic study and thermoxidative degradation of palm oil and biodiesel

Abstract This work investigated the synthesis of biodiesel from palm oil, its thermal stability using the Ozawa–Flynn–Wall and Vyazovkin kinetic models and its thermoxidation using thermogravimetry. The obtained biodiesel was in accordance with the specifications of Resolution No. 7/2008 of the ANP. The 97.4% wt conversion of palm oil to methyl esters confirmed the efficiency of the conversion of fatty acids into esters. The thermal analysis was performed on a thermobalance using heating rates of 5, 10 and 20 °C min−1. The oil exhibited two mass losses, and the biodiesel exhibited only one mass loss. The average values of the obtained apparent activation energies were 184.6 and 191.3 kJ mol−1 for palm oil and 64.1 and 65.3 kJ mol−1 for biodiesel. Additionally, the results indicate that thermal analysis can be used as a tool for monitoring the thermoxidation of biodiesel as a function of time.

Influence of antioxidant on the thermal–oxidative degradation behavior and oxidation stability of synthetic ester

The influence of pentaerythritol tetrakys 3-(3,5-ditert-butyl-4-hydroxyphenyl) propionate (1010) and octylated/butylated diphenylamine (L57) on the thermal–oxidative degradation of di-2-ethylhexyl sebacate (DEHS) was studied by using model-free thermo analysis under air atmosphere. Activation energies about the thermal–oxidative degradation of lubricants were evaluated by Kissinger–Akahira–Sunose (KAS) method. Pressure drop test (PDT) and pressurized differential scanning calorimetry (PDSC) tests were also employed to study their antioxidant performance in DEHS. The results showed that the addition of 1010 and L57 could enhance the oxidation stability of DEHS and increase the activation energy of thermal–oxidative degradation especially at the initial stage of thermal–oxidative decomposition. Meanwhile, a good corresponding relationship was found between model-free method and traditional test methods.

Antagonism of Natural Anti- and Pro-Oxidants in Synthetic Polyisoprene Rubber Vulcanizates

This research was to elucidate the antagonism of natural anti-and pro-oxidants in synthetic polyisoprene rubber (IR) grade 2200 as a model system. Alanine and linoleic acid was chosen as natural anti-and pro-oxidants, respectively. These two amino acids were directly added into the rubber by mixing in two-roll mill. Peroxide vulcanization and three types of the sulfur curing system, i.e., conventional vulcanization (C.V.), efficient vulcanization (E.V.) and semi-E.V. have been studied. Cure properties of the rubber compounds were characterized with moving die rheometer (MDR) at 150 and 170°C for sulfur and peroxide vulcanizing systems, respectively. The compounded rubbers were divided into two parts. The former was pressed on a hydraulic hot press machine and cut to a dumbbell specimen according to ASTM D412 type C. Then, the rubber specimens were subjecting to accelerate the thermal oxidative degradation at 100°C under air-circulating oven with various times. The deterioration of the aged rubber specimens was determined by tensile test. The latter was shaped and characterized by ozone resistance in accordance with ISO 1431/1. For tensile test, the results showed that only the C.V. system of the sulfur cure, the tensile stress at 200% strain of IR comprised alanine and linoleic acid with the ratio of 1:1 was higher predominantly than that of the cured IR control. In addition, the peroxide cured IR mixed with alanine and linoleic acid cannot be passed the heat aging for 96 h. For the ozone resistance, the results exhibited that all specimens appeared uncountable number of crack but only the IR cured by peroxide presented the length of crack less than 1 mm (C-3). It might be concluded from the experiment that anti-oxidative activity of the alanine plays a vital role in the rubber vulcanizate only for C.V. system. However, the existing of both alanine and linoleic acid in the sulfur cured IR was not outstandingly changed for the ozone resistance but not that for the peroxide cured IR.

Effect and mechanism of iron oxide modified carbon nanotubes on thermal oxidative stability of silicone rubber

Abstract To investigate the effects of iron (III) oxide attached on carbon nanotubes (CNTs) surface on the thermal oxidative stability of silicone rubber (SR), a series of iron oxide modified carbon nanotubes (γ-Fe 2 O 3 –CNTs) with different sizes or loadings of γ-Fe 2 O 3 were prepared. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were performed to characterize the additives; by comparing the mechanical properties of SR composites after aging, the optimal experimental group was obtained. Besides, the action mechanism of γ-Fe 2 O 3 –CNTs on the thermal oxidative degradation of SR composite was studied by measuring the average molecular weight between crosslinking points ( M c ) of SR before and after aging, as well as by detecting the degradation products of SR by thermogravimetric analysis/infrared spectrometry (TG–IR). The results indicated that γ-Fe 2 O 3 –CNTs could not only increase the initial formation temperatures of degradation products, but also decrease the concentrations of products from the oxidation and fracture of side chains of SR. All the above influences contributed to the improvement of the thermal oxidative stability of SR.

Thermal–oxidative degradation and accelerated aging behavior of polyamide 6/epoxy resin‐modified montmorillonite nanocomposites

ABSTRACTPolyamide 6 (PA6) nanocomposites based on epoxy resin‐modified montmorillonite (EP‐MMT) were prepared by melt processing using a typical twin‐screw extruder. X‐ray diffraction combined with transmission electron microscopy was applied to elucidate the structure and morphology of PA6/EP‐MMT nanocomposites, suggesting a nearly exfoliated structure in the nanocomposite with 2 wt % EP‐MMT (PA6/2EP‐MMT) and a partial exfoliated‐partial intercalated structure in PA6/4 wt %EP‐MMT nanocomposite (PA6/4EP‐MMT). The thermogravimetric analysis under air atmosphere was conducted to characterize the thermal–oxidative degradation behavior of the material, and the result indicated that the presence of EP‐MMT could inhibit the thermal‐oxidative degradation of PA6 effectively. Accelerated heat aging in an air circulating oven at 150°C was applied to assess the thermal–oxidative stability of PA6 nanocomposites through investigation of reduced viscosity, tensile properties, and chemical structure at various time intervals. The results indicated that the incorporation of EP‐MMT effectively enhanced the thermal–oxidative stability of PA6, resulting in the high retention of reduced viscosity and tensile strength, and the low ratio of terminal carboxyl group to amino group. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40825.

Effect of the antioxidants on the stability of poly(vinyl butyral) and kinetic analysis

The effect of several kinds of antioxidants on the stability of poly(vinyl butyral) (PVB) under air atmosphere is studied by thermogravimetry–differential scanning calorimetry method and kinetic analysis. After mixed with antioxidants, the thermal oxidative stability of PVB increases significantly, because the antioxidants could inhibit the oxidation of copolymer (stage I). The thermal oxidative stability increases in the following order: PVB < PVB/1010 < PVB/B215 < PVB/1098. However, the thermal oxidative degradation rate of PVB increases markedly after 320 °C, due to the loss of chemical activity for antioxidants gradually. The thermal stability of antioxidants increases in the following order: B215 < 1010 < 1098.

MnSt2-kaolin-polyethylene film: An eco-friendly polyethylene composite film and its thermo- and biodegradable research

A novel thermo- and biodegradable MnSt2–kaolin–polyethylene (signed as MKPE) composite film was prepared through a melt blending technique. Manganese stearate and common kaolin were employed as thermo-degradable additives and biodegradable promoter to improve the degradable efficiency of the waste PE. Thermo-oxidative testing was carried out in an air oven maintained at 70°C simulating a compost temperature. The biodegradation of the aging films was also investigated by analysis of evolved carbon dioxide of films in aquatic test systems according to the International Standards ISO 14852 (1999). The composite film was characterized by electronic universal testing machine, scanning electron microscopy, energy-dispersive X-ray spectroscopy, attenuated total reflection-flourier transformed infrared spectroscopy and thermo gravimetric analysis. These results showed that the MKPE film exhibited a high degree of susceptibility to thermo-oxidation and biodegradation. After thermal aging for 30 days, the mechanical properties of MKPE films reduced quickly and oxygen groups were introduced into the polymer chains. The kaolin particles wrapped in polymers were exposed gradually because of the rupture of polymer chains by thermal aging. The biodegradation degree reached 24.26% after incubation in an aqueous medium for 60 days. A possible mechanism for thermal oxidative degradation and biodegradation was also discussed. POLYM. COMPOS., 36:939–945, 2015. © 2014 Society of Plastics Engineers

Characterization of scraper-shaped defects on 4H-SiC epitaxial film surfaces

We have found undiscovered defects on a 4H-SiC epitaxial layer, the shape of which resembles a scraper in images taken by confocal differential interference contrast optical microscopy. The surface morphological structure and formation mechanism of the scraper-shaped defects were investigated by atomic force microscopy and grazing incidence monochromatic synchrotron X-ray topography, respectively. The scraper-shaped defects were surface morphological defects consisting of surface asperity and were caused by the migration of interfacial dislocations. The evaluation of the thermal oxide reliability of metal–oxide–semiconductor capacitors fabricated on these defects was performed by time-dependent dielectric breakdown measurement. The degradation of thermal oxide occurred only on the downstream line of the scraper-shaped defects. The thickness of the oxide layer on these defects was also investigated using cross-sectional transmission electron microscopy.

THERMAL OXIDATIVE DEGRADATION KINETICS OF NANOCOMPOSITE ALKYD-MELAMINE FORMALDEHYDE RESIN CONTAINING MODIFIED SILICA

□ Thermal oxidative degradation kinetics of a nanocomposite alkyd-melamine formaldehyde resin containing surface-modified silica were investigated by thermogravimetric analysis. For this goal, the surface of the silica nanoparticles was modified with glycidoxypropyl trimethoxysilane. Afterwards, a nanocomposite alkyd-melamine formaldehyde resin containing 3% (wt.) ratio of surface modified silica was prepared by an in situ polymerization method. The degradation kinetics of this resin were investigated using different methods. The activation energies of different mechanism models were determined by the Coats-Redfern method. It was concluded that the actual reaction mechanism obeyed three-dimensional diffusion compared with the values obtained from the Kissinger and Flynn-Wall-Ozawa methods.

Influence of coatings geocement activation energy of thermal oxidative degradation wood

The influence geocement coating on the activation energy thermal-oxidative degradation of wood. These thermogravimetric parameters give ability to determine the rate of thermal decomposition of materials at a predetermined temperature and oxygen concentration in the environment and therefore show a qualitative evaluation of thermal effects and determine the activation energy of thermal degradation. The results of studies of thermal timber and cover, set temperature schedule that wood is 230 oC and the mass loss of samples on which the calculated activation energy, which for heotsementnoho coverage increased 3 times. A study to determine the flammability of wood modified group coverage and set efficiency - lowering the temperature of the flue gases by 1.5 times and mass loss during the test about 8 times.

A tensiometric study of magnetorheological suspensions' stability

Surface free energy and sedimentation of composite particles with unchanged magnetorheological properties and improved resistance against thermal oxidation and chemical degradation is determined via tensiometry.

FT-IRイメージング法を用いたポリエチレンの熱酸化劣化解析

FT-IRイメージング法を用いたポリエチレンの熱酸化劣化解析

Study on Generalized Evaluation Method of Thermal Oxidation Degradation of Polymers by Using Time-Temperature Superposition Principle

Study on Generalized Evaluation Method of Thermal Oxidation Degradation of Polymers by Using Time-Temperature Superposition Principle