Apparent Activation Energy Of Degradation Research Articles

Effect of a Reactive-Type Flame Retardant on Thermal Stability of Thiol-ene Composites

A reactive-type flame retardant, polyvinylphenylsilsesquioxane (PVP), was synthesized and incorporated into thiol-ene (TE) to prepare a flame-retardant TE (FRTE) composite. The thermal stability and thermal degradation kinetics of TE and FRTE in nitrogen were studied by thermogravimetric analysis (TGA). The effect of PVP in dynamic measurements of the kinetic parameters of TE degradation, such as apparent activation energy, was also investigated by the Kissinger and Flynn-Wall-Ozawa methods. The results of TGA showed that the addition of PVP improved the thermal stability of TE in nitrogen. The kinetic results indicated that the apparent activation energy for degradation of the FRTE composites was higher than that of neat TE, suggesting that the flame retardant PVP used in this work could promote the formation of char residue to block the heat flow and delay the thermal degradation of the TE matrix.

Synthesis and characterization of nickel oxide and evaluation of its catalytic activities for degradation of methyl orange in aqueous medium

This study focuses on synthesis of nickel oxide catalyst and exploration of its catalytic activities for degradation of methyl orange in aqueous medium. Nickel oxide was prepared sole-gel method using nickel nitrate haxahydrate and citric acid as precursor materials. X-ray diffractometry and scanning electron microscopy were used for characterization of prepared nickel oxide particles. The prepared particles were used as the catalysts for the degradation of Methyl Orange in aqueous medium. The effects of different parameters on degradation of methyl orange were investigated. The degradation of methyl orange followed the Eley-Rideal (E-R) mechanism. The apparent activation energies for degradation of methyl orange determined was found as 36.4 kJ/mol.

Nanocomposite scaffold with enhanced stability by hydrogen bonds between collagen, polyvinyl pyrrolidone and titanium dioxide

In this study, three-dimensional (3D) nanocomposite scaffolds, as potential substrates for skin tissue engineering, were fabricated by freeze drying the mixture of type I collagen extracted from porcine skin and polyvinyl pyrrolidone (PVP)-coated titanium dioxide (TiO2) nanoparticles. This procedure was performed without any cross-linker or toxic reagents to generate porosity in the scaffold. Both morphology and thermal stability of the nanocomposite scaffold were examined. The swelling behavior, mechanical properties and hydrolytic degradation of the composite scaffolds were carefully investigated. Our results revealed that collagen, PVP and TiO2 are bonded together by four main hydrogen bonds, which is an essential action for the formation of nanocomposite scaffold. Using Coasts–Redfern model, we were able to calculate the thermal degradation apparent activation energy and demonstrated that the thermal stability of nanocomposites is dependent on amount of PVP incorporated. Furthermore, SEM images showed that the collagen fibers are wrapped and stabilized on scaffolds by PVP molecules, which improve the ultimate tensile strength (UTS). The UTS of PVP-contained scaffold is four times higher than that of scaffold without PVP, whereas ultimate percentage of elongation (UPE) is decreased, and PVP can enhance the degradation resistance.

Synthesis and thermal characterization of new dumbbell shaped POSS/PS nanocomposites: Influence of the symmetrical structure of the nanoparticles on the dispersion/aggregation in the polymer matrix

A series of three novel dumbbell shaped polyhedral oligomeric silsesquioxanes (POSS)/ polystyrene (PS) nanocomposites, at different POSS contents (3%, 5% and 10% w/w), was synthesized and characterized in order to investigate the effects of this new bridged structure on the filler‐polymer interaction and then on the thermal behavior of the obtained polymer nanostructured materials (PNMs). Nanocomposites were synthesized by in situ polymerization of styrene and the actual POSS concentration in the obtained PNMs was checked by 1H NMR spectroscopy. Scanning electron microscopy (SEM) and FTIR spectroscopy evidenced, at the same time, the presence of filler‐polymer interactions and auto‐aggregation phenomena. Degradations were carried out into a thermobalance, in the scanning mode, at various heating rates in both inert and oxidative atmospheres. The characteristic parameters of thermal stability, namely temperature at 5% mass loss and the apparent activation energy of degradation, for the various nanocomposites were determined and an increase in the initial decomposition temperatures of PNMs with increasing the POSS contents was observed. The results are discussed and interpreted. POLYM. COMPOS., 36:1394–1400, 2015. © 2014 Society of Plastics Engineers

Enhanced ultrasonic degradation of acetaminophen and naproxen in the presence of powdered activated carbon and biochar adsorbents

This study investigated the degradation of pharmaceuticals (PhACs), acetaminophen (AAP) and naproxen (NPX), via treatment under ultrasonic (US) conditions. The most efficient frequency based on the rate of PhACs degradation and hydrogen peroxide (H2O2) production was found to be 580kHz when 28, 580, and 1000kHz frequencies were applied. Additionally, the degradation of PhACs at 580kHz could be improved by increasing the US-power density and solution temperature. The apparent activation energy of degradation was determined via Arrhenius law to be 10.3 and 11.2kJmol−1 for AAP and NPX, respectively, wherein the most favorable degradation pH was acidic. Density functional theory based calculations demonstrated that NPX has 8 barrierless points of reaction compared to AAP having 1 barrierless point. This molecular modeling analysis result explains the faster kinetics of NPX degradation. Additionally, a maximum rate of PhACs degradation was observed when the H2O2 concentration was 5μM. The degradation of PhACs was strongly inhibited by the presence of tert-butanol when compared to methanol, indicating that the degradation of AAP and NPX was dependent on the presence of OH. Based on the synergistic index and Langmuir–Hinshelwood model, biochar was more efficient for treating PhACs than powdered activated carbon under US irradiation, degrading PhACs mainly via a combination of adsorption onto the absorbents and reaction with OH under US irradiation with absorbent particles providing nucleation sites. This method shows great potential in providing a viable catalyst toward degrading PhACs within catalytic industrial processes.

Degradation Kinetics and Aqueous Degradation Pathway of Cloxacillin Sodium

AbstractThe degradation kinetics of cloxacillin sodium (CS) under real production conditions was determined using high‐performance liquid chromatography (HPLC). Degradation in methanol (MeOH) follows zero‐order kinetics. The introduction of water kept the degradation order but decreased the rate constant, while butyl acetate (BA) accelerated the degradation and shifted the kinetics to first order. In the MeOH/BA system, the pH‐dependent degradation rate generally increased when increasing the pH, except for a distinct drop at about pH 6.5. In aqueous solution, the effect of temperature was determined and the apparent activation energy of degradation was found to be 80.34 ± 5.88 kJ mol–1. The degradation products were analyzed using HPLC, mass spectrometry, and infrared spectroscopy, and a pathway toward cloxalloic acid via cloxacilloic acid as intermediate is proposed.

Characterization and thermal‐oxidative degradation behavior of poly(ethylene terephthalate‐co‐4,4′‐bibenzoate) prepared via direct esterification technique

AbstractA series of poly(ethylene terephthalate‐co‐4,4′‐bibenzoate)s (PETBBs) were prepared via direct esterification from the monomers of terephthalic acid (TPA), 4,4′‐biphenyl dicarboxylic acid (BPDA), and ethylene glycol (EG) with different molar ratios. The chemical compositions of the obtained PETBBs, investigated by H1‐NMR, were identical with the feed ratio, and the high molecular weights of PETBBs were confirmed by GPC analysis. The glass transition, crystallization, and melting behavior of them were measured by DSC; the results indicated that, in the range of 5–25 mol% of BPDA addition, the glass transition temperature (Tg) increased almost linearly and the melting temperature (Tm) decreased with increasing content of BPDA unit. As expected, the crystallization of PETBB became difficult with increasing introduction of BPDA, explained by higher crystallization temperature and smaller crystallization enthalpy from the glassy state. This decrease of crystallization rate may be beneficial to film processing. Moreover, owing to the introduction of rigid‐rod BPDA unit, the initial and maximum thermal‐oxidative decomposition temperatures were enhanced. The kinetic analysis of the thermal‐oxidative degradation indicated that the apparent activation energies of degradation for these PETBBs became higher than that of PET. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Preparation of nano poly(phenylsilsesquioxane) spheres and the influence of nano-PPSQ on the thermal stability of poly(methyl methacrylate)

The nano poly(phenylsilsesquioxane) spheres (nano-PPSQ) were prepared by the sol–gel method and incorporated into poly(methyl methacrylate) (PMMA) by in situ bulk polymerization of methyl methacrylate. The structure of nano-PPSQ was confirmed by transmission electron microscope and thermogravimetry analysis (TG). The interaction between nano-PPSQ and PMMA was investigated by Fourier transform infrared spectra (FT-IR). The influence of nano-PPSQ on the thermal stability of PMMA was investigated by TG and differential scanning calorimetry (DSC) measurements. The results indicated that nano-PPSQ enhanced the thermal stability and the temperatures of glass transition (T g) of nanocomposites. The effect of the heating rate in dynamic measurements (5–30 °C min−1) on kinetic parameters such as activation energy by TG both in nitrogen and air was investigated. The Kissinger method was used to determine the apparent activation energy for the degradation of pure PMMA and nanocomposites. The kinetic results showed that the apparent activation energy for degradation of nanocomposites was higher than that of pure PMMA under air.

The influence of sulfonation degree on the thermal behaviour of sulfonated poly(arylene ethersulfone)s

Initial decomposition temperature ( T i), apparent activation energy of degradation ( E a) and glass transition temperature ( T g) of some low molar mass ( M n ≈ 8000 g mol −1) sulfonated poly(arylene ethersulfone)s s-(PAES) s were determined to check their dependence on sulfonation degree ( SD ). The results obtained were compared with those for unsulfonated poly(arylene ethersulfone) PAES. In order to have an accurate control of the chemical structure, a pre-sulfonation route was followed for the preparation of sulfonated compounds. The thermal behaviour of the investigated s-(PAES) s as well as that of PAES appears not to be influenced by the environment (flowing nitrogen or static air atmosphere) of degradation. Both T i and T g values of s-(PAES) s were higher than those of PAES and increased quite linearly as a function of sulfonation degree. An analogous linear trend was observed for the apparent degradation energy of s-(PAES) s, but the values found were largely lower than those of unsulfonated homopolymer. The results are discussed and interpreted.

Crosslink density dependence of polymer degradation kinetics: Photocrosslinked acrylates

A series of crosslinked polyurethane acrylate films with glass transition temperatures ranging from −49 °C to +65 °C was prepared by photopolymerization of solvent-free resins. The kinetics of thermo-oxidative (in air) and thermal (in N 2) degradation of these crosslinked acrylate networks at temperatures from 100 °C to 400 °C was monitored thermogravimetricly as a function of crosslink density. Initial degradation rate of polyurethane network decreased with the increase of crosslink density. Apparent activation energies of degradation were found to be temperature and crsosslink density dependent and ranged from 12.6 kJ mol −1 to 25.1 kJ mol −1 in 200–300 °C interval and 33.5 kJ mol −1 to 58.6 kJ mol −1 in 300–400 °C interval. The polyacrylate thermal stability increase with crosslinking was correlated with decreased chain segments mobility leading to the reduced oxygen and volatile products diffusion rate, rate of cyclic decarboxylation, and increased radical's recombination in a cage. Data indicated that the cyclic decarboxylation, rather than oxygen uptake or volatile products escape rate control the thermal degradation kinetics.

The influence of chain rigidity on the thermal properties of some novel random copolyethersulfones

Some random low molar mass ( M n ≈ 9000 g mol −1) poly(ethersulfoneethersulfone)/poly(ethersulfoneethersulfonebiphenylsulfone) P(ESES)/P(ESESBS) copolymers, with various (25%, 50% and 75%) ESESBS units contents, were synthesized to obtain compounds with higher chain rigidity than PES. The thermal characterization of the prepared copolymers, as well as that of corresponding P(ESES) and P(ESESBS) homopolymers, was performed, and all investigated parameters showed strong dependence on polymer composition. The glass transition temperature ( T g) was calorimetrically determined by DSC technique, and the obtained values increased linearly as function of ESESBS units percentage, thus indicating an increasing chain rigidity. Degradations were carried out in dynamic heating conditions, from 35 °C to 700 °C, in both flowing nitrogen and static air atmosphere, and the characteristic parameters of degradation were determined in order to draw useful information about the overall thermal stability of the studied compounds. The apparent activation energy of degradation ( E a) was obtained by the Kissinger method, and the values found increased linearly as a function of ESESBS content, while the temperature values at 5% mass loss ( T 5%) showed an opposite linear trend. The results are discussed and interpreted.

Photo-crosslinked acrylates degradation kinetics

A series of crosslinked polyurethane acrylate solids with glass transition temperatures ranging from –49 to +65 °C was prepared by photopolymerization of specially formulated solvent-free resins. The kinetics of thermooxidative and thermal (in N2) degradation of these crosslinked acrylate networks at temperatures ranging from 100 to 400 °C was studied as a function of crosslink density using thermogravimetry. The polyacrylate network degradation rate decreased with the increase of crosslink density, while apparent activation energy of degradation increased. Polyacrylate thermal stability increase with crosslinking was explained by decreased rate of oxygen and volatile products diffusion and/or slowing of depolymerization due to increased radical recombination rate, and decreased chain segments mobility in systems with higher crosslink density.

Influence of iron content on thermal stability of magnetic polyurethane foams

Magnetorheological (MR) materials are a group of smart materials which have the controllable magnetic properties with an external magnetic field. Magnetic foams, a specific type of MR solids, were synthesized from flexible polyurethane (PU) foams and carbonyl iron particles. Effects of the carbonyl iron particles on the thermal stability of the magnetic foams have been studied. Thermogravimetric analysis (TGA) was applied to characterize the thermal degradation process of the magnetic foams and then the apparent activation energy of degradation was calculated by using Ozawa's method [Ozawa T. A new method of analyzing thermogravimetric data. Bulletin of the Chemical Society of Japan 1965; 38: 1881–1886.]. The carbonyl iron particles were found to improve the thermal stability of magnetic foams in nitrogen by showing higher 10 wt% loss temperature, slower weight loss rate and higher apparent activation energy than pure PU foams. But the magnetic foams were observed to have slightly worse thermal stability in air than pure PU foams at the earlier degradation stage. At the later degradation stage, the magnetic foams exhibited the higher activation energy than pure PU foams in air.

Kinetic study of the thermal degradation of PS/MMT nanocomposites preparedwith imidazolium surfactants

Styrene and montmorillonite organically modified with imidazolium surfactants (MMT) at various alkyl chain lengths (C12, C16 and C18) were used to prepare the corresponding PS/MMT/C12, PS/MMT/C16 and PS/MMT/C18 nanocomposites by in situ polymerization. XRD and TEM analyses evidenced the formation of both intercalated and exfoliated structures. The glass transition temperatures (Tg) of nanocomposites, as well as that of neat PS, were obtained by DSC measurements. The thermal degradations were carried out in the scanning mode, in both inert and oxidative environments, and the initial temperatures of decomposition (Ti) and the apparent activation energies of degradation (Ea) were determined. Due to an oxidative degradation mechanism, the Ti and Ea values in air atmosphere were lower than those under nitrogen.

Copolymerization kinetics of poly(acrylonitrile‐ran‐2‐ethenyl‐pyridine) and its degradation apparent activation energy

Abstract2‐Ethenyl‐pyridine (EPD) was first used to successfully copolymerize with acrylonitrile (AN) in a H2O/dimethyl formamide (DMF) mixture by using azobisisobutyronitrile as the initiator. Kinetics of copolymerization and degradation of poly(AN‐ran‐EPD) were discussed. The kinetic equation of copolymerization and the apparent activation energy of degradation of poly(AN‐ran‐EPD) were obtained. In H2O‐rich reaction medium, copolymerization followed the suspension polymerization more, but in DMF‐rich reaction medium, copolymerization followed the solution polymerization more. Increase in DMF concentration in the solvent mixture lead to a rapid increase in the degradation apparent activation energy. The apparent activation energy decreased quickly with an increase in EPD concentration, and such a change became less prominent as the molar ratio of EPD/AN went beyond 3/100. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Degradation kinetics of acrylonitrile/methyl vinyl ketone copolymers

AbstractMethyl vinyl ketone (MVK) was first used to successfully copolymerize with acrylonitrile (AN). This was achieved by using azobisisobutyronitrile as the initiator. Differential scanning calorimetry results of the degradation of AN/MVK copolymers in air are presented. The apparent activation energy of degradation of the copolymers was calculated with Kissinger method. Effects of copolymerization conditions on the apparent activation energy of the copolymers were studied. It has been found that increasing dimethyl sulfoxide concentration in the solvent mixture leads to a rapid increase in the degradation apparent activation energy of AN/MVK copolymers. The apparent activation energy decreases quickly along with increase in the comononer MVK concentration, and this change becomes less prominent as the weight ratio of MVK/AN goes beyond 7/93. The apparent activation energy shows a trend of increase as the copolymerization temperature increases. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1386–1390, 2007

Thermal oxidative degradation kinetics of PP and PP/mg (OH)2 flame‐retardant composites

AbstractThe thermal stability and thermal oxidative degradation kinetics of polypropylene (PP) and flame‐retardant PP composites filled with untreated and treated magnesium hydroxide (MH) in air were studied by thermogravimetric analysis (TGA). The effect of the heating rate in dynamic measurements (5°C–30°C/min) on kinetic parameters such as activation energy was also investigated. The Kissinger and Flynn–Wall–Ozawa methods were used to determine the apparent activation energy for the degradation of neat PP and flame‐retardant PP composites. The results of TGA showed that the addition of untreated or treated MH improved the thermal oxidative stability of PP in air. The kinetic results showed that the apparent activation energy for degradation of flame‐retardant PP composites was much higher than that of neat PP, suggesting that the flame retardant used in this work had a great effect on the mechanisms of pyrolysis and combustion of PP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1978–1984, 2007

Thermal and rheological behaviours of some random aromatic amino-ended polyethersulfone/polyetherethersulfone copolymers

The thermal and rheological characterizations of seven random, low molecular weight ( M n ≅ 9500 g mol −1), H 2N-ended polyethersulfone/polyetherethersulfone (PES/PEES) copolymers, at various PES/PEES ratios, were performed. The glass transition temperatures ( T g) were determined by DSC. Degradations were carried out in a thermobalance, under flowing nitrogen, in dynamic heating conditions from 35 °C to 650 °C. The initial decomposition temperatures ( T i) and the half decomposition temperatures ( T 1/2) were directly determined by TG curves, while the apparent activation energies of degradation ( E a) were obtained by the Kissinger method. In addition, the complex viscosities ( η ∗) of the molten polymers were determined in experimental conditions of linear viscoelasticity. T g, E a and η ∗ values increased linearly with PES% content, while T i and T 1/2 values showed opposite behaviour. In every case both PES and PEES homopolymers felt outside linearity. The results obtained are discussed and interpreted, and compared with those of corresponding Cl-ended copolymers previously studied.

Determination of the degradation apparent activation energy of acrylonitrile/acrylic acid copolymers

AbstractAcrylonitrile/acrylic acid copolymers were prepared by H2O/dimethyl formamide suspension polymerization technique. Differential scanning calorimetry was used to investigate the degradation of acrylonitrile/acrylic acid copolymers in air. The apparent activation energy of degradation of the copolymer was calculated with the Kissinger method. Effects of copolymerization conditions on the apparent activation energy of copolymer were studied. It has been found that increasing the dimethyl formamide concentration in the solvent mixture led to a gradual increase (97.3–149.4 kJ mol−1) in the apparent activation energy of degradation of the acrylonitrile/acrylic acid copolymers. The apparent activation energy decreases with increase in acrylic acid concentration, and this change became less prominent as the acrylic acid/acrylonitrile weight ratio is more than 5/95. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4668–4671, 2006

Degradation kinetics of acrylonitrile/ammonium acrylate copolymers

Abstractacrylonitrile (AN)/ammonium acrylate (AAT) copolymers were prepared by H2O/dimethyl formamide suspension polymerization technique. Differential scanning calorimetry results of the degradation of AN/AAT copolymers in air are presented. The apparent activation energy of degradation of the copolymer was calculated by using Kissinger method. Effects of copolymerization conditions on the apparent activation energy of copolymer were studied. It has been found that increasing dimethyl formamide concentration in the solvent mixture leads to a rapid increase in the degradation apparent activation energy of AN/AAT copolymer. The value of the degradation apparent activation energy of the copolymer synthesized in dimethyl formamide solvent increases up to 141.7 kJ mol−1. The apparent activation energy decreases quickly, along with increase in AAT concentration, and this change becomes less prominent as the weight ratio of AAT/AN goes beyond 6/94. The apparent activation energy shows a trend of increase with increasing copolymerization temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4649–4653, 2006