Co-microencapsulate of ammonium polyphosphate and pentaerythritol and kinetics of its thermal degradation

Co-microencapsulated ammonium polyphosphate (APP) and pentaerythritol (PER) (M (A&P)) is prepared using melamine-formaldehyde (MF) resin by in situ polymerization method, and characterized by Energy dispersive spectrometer (EDS) and Fourier transform infrared (FTIR) spectra. Thermal stability of M (A&P) has been analyzed and compared with APP/PER mixture. In air atmosphere, the mass loss of M (A&P) at different heating rates was investigated using TGA. The kinetics of thermal degradation and activation energy was described using Flynn-Wall-Ozawa and Kissinger methods. It showed that there were two degradation stages. Expanded carbon structure with honeycomb was formed in the first stage between 200 and 450 °C. The second stage was the oxidation of carbon with E_a as high as 151.7 kJ/mol, so the expanded carbon had a good thermal stability. The reaction order of thermal degradation was found to be 0.935, so the mechanism of M (A&P) thermal degradation was controlled by the process of random nuclear formation and growth.     

Non-isothermal kinetics of reactions whose activation energy depends on the degree of conversion

A procedure for evaluating the non-isothermal kinetic parameters of reactions for which the activation energy depends on the degree of conversion is suggested. The procedure has been applied to the dehydration of calcium oxalate monohydrate and to the thermal degradation of poly(vinyl chloride) (PVC) and polychloroprene rubber.     

Kinetics of thermal degradation and estimation of lifetime for polypropylene particles: Effects of particle size

The thermal stability and degradation behavior of polypropylene (PP) particles having diameter varying from few micrometers to nanometers were studied by thermogravimetric analysis (TGA). The PP particles of average diameter ∼20 μm, ∼10 μm, ∼5 μm, ∼1 μm and <500 nm were studied over a range of temperature from 25 to 600 °C in N₂ atmosphere and heating rates of 5, 10 and 15 °C/min. Thermal stability of PP particles initially decreases and then increases as particle size further decreases to nanometer scale. The five single heating rate techniques such as Friedman, Freeman-Carroll, Chang, Coats-Redfern and second Kissinger; and three multiple heating rate techniques such as the first Kissinger, Kim-Park and Flynn-Wall were used to compute the kinetic parameters of degradation reaction, e.g., activation energy (E_a), order of reaction (n) and frequency factor [ln(Z)]. The lifetime of macro-, micro- and nanosized PP particles was also estimated by a method proposed by Toop. It was found that the activation energy and lifetime of nanosized PP particles are moderately high compared to the microsized PP particles. Moreover, the decomposition temperature, order of reaction (n), frequency factor [ln(Z)] not only depend on the heating rate and calculation technique but also on the particle size of polymer. The results are compared with macrosized PP.     

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

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

Thermal degradation kinetics of polystyrene/cadmium sulfide composites

The thermal degradation kinetics of polystyrene/CdS composites were studied by thermogravimetry. The samples were heated in nitrogen, with three different heating rates: 5, 20 and 40 °C min⁻¹. We calculated kinetic parameters using KAS isoconversion method. The results showed that the maximum activation energy of thermal degradation is achieved for PS/CdS composite with about 10% of the CdS filler. Higher concentration of CdS in the composite (20%) induced acceleration of the thermal degradation, approaching the rate of degradation of the pure polystyrene matrix.     

Effects of synthetic and natural zeolites on morphology and thermal degradation of poly(lactic acid) composites

Poly(lactic acid) (PLA) composites containing 5 wt% synthetic (type 4A) and natural (chabazite) zeolites were prepared using extrusion/injection molding. Morphological, structural, and thermal properties of composites were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). DSC results revealed that the glass transition and melting temperatures were not significantly changed; however, the incorporation of both type 4A and chabazite zeolites enhanced the nucleation of PLA crystallites as well as increased the percent crystallinity. Thermal degradation properties of PLA and PLA/zeolite composites were studied by non-isothermal thermogravimetric analysis (TGA) in nitrogen atmosphere. TGA results showed that at temperatures above 300 °C, PLA/type 4A synthetic zeolite composites were thermally decomposed more easily than the PLA and PLA/chabazite natural zeolite composites. The apparent activation energies of thermal degradation of PLA and PLA/zeolites composites estimated using both the Flynn-Wall-Ozawa and Kissinger methods followed the same order: PLA/type 4A < PLA/chabazite < PLA.     

Kinetics of thermal degradation and thermal oxidative degradation of poly(p-dioxanone)

The kinetics of the thermal degradation and thermal oxidative degradation of poly(p-dioxanone) (PPDO) were investigated by thermogravimetric analysis. Kissinger method, Friedman method, Flynn-Wall-Ozawa method and Coats-Redfern method have been used to determine the activation energies of PPDO degradation. The results showed that the thermal stability of PPDO in pure nitrogen is higher than that in air atmosphere. The analyses of the solid-state processes mechanism of PPDO by Coats-Redfern method and Criado et al. method showed: the thermal degradation process of PPDO goes to a mechanism involving random nucleation with one nucleus on the individual particle (F₁ mechanism); otherwise, the thermal oxidative degradation process of PPDO is corresponding to a nucleation and growth mechanism (A₂ mechanism).     

Fabrication, morphology and thermal degradation behaviors of conductive polyaniline coated monodispersed polystyrene particles

This study describes the preparation of polyaniline (PANI) coated on the surface of monodispersed 400 nm polystyrene (PS) particles by in situ chemical oxidative polymerization. The monodispersed 400 nm PS particles served as cores were synthesized using the emulsion polymerization. Both images observed by field-emission scanning electron microscopy and transmission electron microscopy show the presence of a thin PANI layer uniformly coated on the surface of PS particle. The electrical conductivity of various amounts of PANI-coated PS particles is significantly increased about 13 orders of magnitude compared to that of the pristine PS particles. Differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) were used to investigate the thermal stability and thermal degradation behavior of PS and PANI-coated PS particles. Both DSC and TGA curves revealed that the coating of a thin PANI layer on the surface of PS can drastically increase the thermal stability of PS matrix. TGA isothermal degradation data illustrate that the activation energy of the PANI-coated PS particle is larger than that of PS. This phenomenon can be attributed to the incorporation of PANI coating on the surface of PS particle caused a decrease in the degradation rate and an increase in the residual weight for the PANI-coated PS particle.     

Influence of polycaprolactone-triol addition on thermal stability of soy protein isolate based films

The influence of polycaprolatone-triol (PCL-T) on the thermal degradation properties of soy protein isolate (SPI)-based films was studied by thermogravimetry and infrared spectroscopy under nitrogen atmosphere. The results showed that in the absence of PCL-T the thermal degradation began between 292 °C (pure SPI films) and ca. 264 °C (SPI/SDS films with more than 20% of SDS), and these values decreased further to the range 250-255 °C for SPI/SDS/PCL-T films. At the same time, the temperature of maximum degradation rate (T_max) decreased from 331 °C (pure SPI film) to ca. 280 °C for SPI/SDS/PCL-T films with 39% PCL-T content. This behavior was also confirmed by the activation energy (E) values associated with the thermal degradation process. Apparently, the low thermal stability of PCL-T as compared to other film constituents, along with its plasticizer characteristics, is responsible for the decreased stability of SPI/SDS/PCL-T films. The FTIR spectra of gas products evolved during the thermal degradation indicated the formation of OH, CO₂, NH₃ and other saturated compounds, suggesting that the reaction mechanism involved simultaneous scission of the C(O)-O polyester bonds and C-N, C(O)-NH, C(O)-NH₂ and -NH₂ bonds of the protein.     

The thermal degradation kinetics of dextran and pullulan

The effect of molar mass and, in the case of dextran, of the degree of branching on the thermal degradation kinetics of dextran and pullulan was studied in the presence and absence of oxygen. Although the initial mass loss of the dextran samples occurred at higher temperatures than that of the pullulan samples, the overall thermal degradation activation energies were lower for dextran than for pullulan. In the case of dextran the thermal stability was found to decrease with molar mass and degree of branching. The molar mass of pullulan, in the range of 10⁴ to 10⁵ g/mol, appeared to have no significant influence on the thermal characteristics of the samples.     

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.     

Synthesis and thermal degradation kinetics of cellulose esters

Polymers that are biodegradable currently achieve high interest in material science since they offer reductions of landfill space during waste management as well as new end-user benefits in various fields of applications. In this work, cellulose esters such as cellulose benzoate, cellulose succinate and cellulose cinnamate were prepared using dimethylaminopyridine along with dimethylaminopyridine-p-toluene sulfonic acid catalyst. Films of cellulose esters were cast from solution. Cellulose esters were characterized by spectral methods such as infrared, nuclear magnetic resonance, thermal method such as thermogravimetric analysis. Various methods of kinetic analysis were compared in the case of thermal degradation of the cellulose and cellulose esters. Copyright­© 2003 John Wiley & Sons, Ltd.     

Synthesis and kinetics of non-isothermal degradation of amide grafted high density polyethylene

The grafted structures from the reaction of high density polyethylene with maleic anhydride (PEgMA) was reacted further with 1,4-diaminobutane to synthesize amide grafted polyethylenes. Grafted amic-acids were partially converted to imide groups during the reaction. Grafted products were identified by titration, elemental analysis and FTIR. DSC analysis indicated that C_p for amide grafted product increased about 47% with respect to PEgMA, its crystallinity increased 50% with respect to PE and 18% with respect to PEgMA. Analysis of kinetics of degradation was performed by thermogravimetry; degradation kinetic parameters of these amide grafted products have not been evaluated or reported. The degradation of Amide grafted polyethylene is similar to HDPE but with smaller activation energy indicating that it is the most stable product. F_n and A_n kinetic models seemed more suitable than diffusion models.     

Preparation of telechelic oligomers by thermal degradation of propylene copolymers

The reactive end groups of nonvolatile oligomers obtained by controlled thermal degradation of poly(propylene-ran-ethylene) and poly(propylene-ran-1-butene) were determined by ¹H and ¹³C NMR spectroscopy. The molar ratio of unsaturated to saturated end groups was found to be about 9:1. The average number of unsaturated end groups per molecule was between 1.6 and 1.8, indicating that 60–80 mol% of the oligomer molecules were telechelic, having two terminal unsaturated end groups. These oligomers had a lower polydispersity than the raw material, despite their lower molecular weight and melting temperature. Although the end groups resulting from each monomer unit could be detected by ¹³C NMR, the end group composition differed from that of the main chains of the raw materials. The end group composition was satisfactorily explained by the differences in bond dissociation energy and activation energy of elementary reactions that occurred during thermal degradation, based on the monomer composition of the raw materials.     

Aging and thermal degradation of poly(N-methylaniline)

The conductivity aging and thermal stability of poly(N-methylaniline) are reported. Poly(N-methylaniline) doped with chloride ion was electrochemically synthesized. The conductivity data obtained in the temperature range between 118 and 483 K are analysed by Arrhenius and Mott models to elucidate the conduction mechanism. The thermal degradation of both doped and dedoped samples of poly(N-methylaniline) in air and nitrogen atmosphere has been followed using thermogravimetric and differential thermal analysis techniques. The polymer is heat-aged at various temperatures and the aged samples are analysed by FT-IR, SEM and XRD. The thermogravimetric data are further analysed by three different methods: Horowitz and Metzger [Anal. Chem. 35 (1963) 1464], Coats and Redfern [Nature 201 (1964) 68], Chan et al. [Synth. Met. 31 (1989) 95] to evaluate the energy of activation. The applicability of the three methods for the evaluation of kinetic parameters is discussed.     

Poly(ether ether ketone)/poly(aryl ether sulphone) blends: thermal degradation behaviour

The thermodegradative behaviour of blends of poly(ether ether ketone) (PEEK) and poly(aryl ether sulphone) (PES) was studied by dynamic thermogravimetry in order to analyze their thermal stability. The Freeman-Carrol differential approach was used to determine the kinetic parameters i.e. the apparent activation energy (E_a) and order of reaction (n), of the degradation process. The results indicate that the presence of one component influences the thermal stability of the other. Both, temperature for 5% weight loss (T₅) and E_a for blends show a negative deviation from the linear behaviour, which signifies a lowering of thermal stability compared to homopolymers. The decrease in the thermal stability at low concentration of PES in PEEK has been explained on the basis of chemical interactions of the degradation products of PES, which has lower induction temperature for degradation, with PEEK and also on the reduction of viscosity of the medium. But the decrease in thermal stability at low concentration of PEEK in PES is unusual and at present, without the complete elucidation of degradation mechanism in these blends, is difficult to explain.     

Kinetics of thermal degradation in non-isothermal conditions of some phosphorus-containing polyesters and polyesterimides

The thermal decomposition behavior of some phosphorus-containing polyesters and a polyesterimide was studied using thermogravimetric analysis in air at several heating rates between 5 °C/min and 20 °C/min. The results of this study, realized for polymers with phosphorus linkage as pendant group, were compared with the behavior of some polymers having the same backbone structure, with phosphorus in the main chain, respectively, without phosphorus. The kinetic processing of data was carried out using the Coats-Redfern, Reich-Levi, Flynn-Wall-Ozawa and Kissinger methods.     

Global kinetics of thermal degradation of flame-retarded epoxy resin formulations

A predictive mathematical model to describe mass loss profiles of flame-retardant (FR) containing epoxy resin formulations is proposed. Mass loss is due to thermal degradation of the constituent components and can be described by a generic kinetic scheme with a given set of thermokinetic constants in the form of ordinary differential equations. The scope of this work is to determine the kinetic parameters of the thermal degradation of a known flame-retarded epoxy resin composition by using thermogravimetric analysis and using the acquired data to predict the degradation profiles for other formulations. The mass loss profiles of Visil and intumescent epoxy resin containing formulations were predicted by solving coupled systems of ordinary differential equations and then using Powell minimisation to find the optimal Arrhenius parameters, taking into account the mass ratio of the components in the mixture. The calculated kinetic constants for one formulation (85% resin-15% FR additives) are used to predict the mass loss profiles for other formulations (80% resin-20% FR additives and 90% resin-10% FR additives) with the assumption that the degradation mechanism does not change. The predicted thermal degradation profiles are compared with experimental data acquired using standard laboratory equipment in order to validate the proposed mechanisms. The kinetic parameters obtained adequately describe mass loss history of composite materials studied, even when extremely simplified kinetic schemes have been used.     

Eco-friendly fast synthesis and thermal degradation of optically active polyamides under microwave accelerating conditions

<正>An optically active bulky aromatic diacid chiral monomer,(2S)-4-[(4-methyl-2-phthalimidylpentanoyl-amino) benzoylamino]isophthalic acid(1),containing a rigid phthalimide and flexible L-leucine pendent group was synthesized in five steps.A fast and clean method for direct polyamidation reaction of monomer 1 with various aromatic diamines under microwave irradiation and conventional heating was performed.The polymerization reactions provided optically active polyamides with high yields and inherent viscosities in the range of 0.36-0.74 dL/g.Their thermal properties were evaluated by thermogravimetric analysis(TGA) and differential scanning calorimetry.TGA thermograms show that the polymers are thermally stable,10%weight loss temperatures are in excess of 385℃,and char yields at 800℃are higher than 56%.The data obtained from TGA were used to study the kinetics of thermal decomposition of the resulting polymers. The interpretation of kinetic parameters(E,ΔH,ΔS andΔG) of thermal decomposition stages was evaluated using Coats and Redfern equation.