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.     

Synthesis, thermal properties, and biodegradability of propyl-etherified starch

High amylose corn starch (HACS) was etherified with 1-bromopropane in dimethyl sulfoxide. The structure of the products was characterized by infra-red and ¹H-NMR spectroscopy. The degree of substitution (DS) on glucose unit calculated from ¹H-NMR spectrum was varied from 0.9 to 2.7 by changing feed ratio of 1-bromopropane to HACS. Thermogravimetric analysis reveals that the etherified HACS has a higher decomposition temperature than unmodified HACS. Differential scanning calorimetry analysis reveals that the etherified starch has a clear glass transition temperature which decreased with increasing DS, and that no melting point is observed. This result demonstrates that the etherified HACS mainly consists of amorphous region. The biodegradation rate decreases with increasing degree of etherification.     

Excellent blue fluorescent trispirobifluorenes: synthesis, optical properties and thermal behaviors

Tetraiodotrispirobifluorene (1) was synthesized through cyclization of 2,7-diiodofluorene with pentaerythrityl tetrabromide under base condition. Subsequent treatment of 1 with arylboronic acid or arylacetylene under Pd-catalyzed coupling condition led to corresponding tetraaryl trispirobifluorenes (3–8). These trispirobifluorene derivatives exhibited bright-violet to blue photoluminescence (PL) with excellent quantum efficiencies and showed high thermal stabilities. ‘Green-emission tail’ could not be detected for those tetraaryl substituted trispirobifluorenes (3–8) annealed both in N₂ and in air.     

Combustion properties and thermal degradation behavior of polylactide with an effective intumescent flame retardant

An intumescent flame retardant spirocyclic pentaerythritol bisphosphorate disphosphoryl melamine (SPDPM) has been synthesized and its structure was characterized by Fourier transformed infrared spectrometry (FTIR), ¹H and ³¹P nuclear magnetic resonances (NMR). A series of polylactide (PLA)-based flame retardant composites containing SPDPM were prepared by melt blending method. The combustion properties of PLA/SPDPM composites were evaluated through UL-94, limiting oxygen index (LOI) tests and microscale combustion calorimetry (MCC) experiments. It is found that SPDPM integrating acid, char and gas sources significantly improved the flame retardancy and anti-dripping performance of PLA. When 25 wt% flame retardant was added, the composites achieved UL-94 V0, and the LOI value was increased to 38. Thermogravimetric analysis (TGA) showed that the weight loss rate of PLA was decreased by introduction of SPDPM. In addition, the thermal degradation process and possible flame retardant mechanism of PLA composites with SPDPM were analyzed by in situ FTIR.     

Thermal properties and stability of cassava starch films cross-linked with tetraethylene glycol diacrylate

The thermal stability of starch cross-linked with tetraethylene glycol diacrylate was studied under nitrogen atmosphere by thermogravimetry (TG) and infrared spectroscopy (FTIR). The cross-linking reaction was confirmed by the increase in intensity of the absorption band at ca. 3330 cm⁻¹ indicating the reinforcement of hydrogen bonds and the appearance of a new band at 1726 cm⁻¹ associated with the carbonyl group of the cross-linking agent. After cross-linking the solubility of starch in water decreased to the range 9%-16%. The thermogravimetric curves of pure and cross-linked starches showed an initial stage of degradation (up to ca. 150 °C) associated with the loss of water. The main stage of degradation occurred in the range 250-400 °C corresponding to ca. 60%-70% mass loss. The activation energy (E) for the degradation process increased from 145 kJ mol⁻¹ (pure starch) to 195 kJ mol⁻¹ and 198 kJ mol⁻¹ for starch treated for 60 min by UV (30 °C) and at 90 °C, suggesting high stability after cross-linking. A higher value (240 kJ mol⁻¹) was obtained for starch treated by UV for 120 min. The main volatile products determined by FTIR which correspond to hydrocarbons and carbonyl groups are apparently associated with the scission of weak bonds in the chain (probably branched groups) and the scission of stronger bonds (glycosidic linkages), respectively.     

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.     

Comparative thermal analysis study of two biopolymers, starch and cellulose

The degradation of cellulose and starch samples in air and nitrogen has been investigated by thermal analysis techniques. The techniques employed were differential thermal analysis, rising temperature and temperature jump thermogravimetry. Rate data were obtained from these experiments and Arrhenius parameters calculated from these values. This data was used to determine the mechanism by which the cellulose and starch samples degraded. The Arrhenius parameters were also calculated. The behavior of starch and cellulose upon thermal analysis were compared and are reported.E _act for corn starch was found to be 474 kJ mol^–1 and for a cellulose 242 kJ mol^–1.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

Synthesis,characterization and thermal studies of new polyhydrazides and its poly-1,3,4-oxadiazoles based on dihydro-9,10-ethanoanthracene in the main chain

New interesting class of new polyhydrazides having inherent viscosities in the range 0.45–0.71 dI/g were prepared by polymerizing a series of diacid chlorides, e.g., sebacoyl, isophthaloyl or terphthaloyl with 9,10-dihydro-9,10-ethanoanthracene-11,12-dihydrazide I in polar aprotic solvent and by the low-temperature polycondensation technique. In order to characterize the polymers, a model compound II was synthesized from I and benzoyl chloride. All the hydrazide polymers are semi crystalline in nature and are readily soluble in various polar solvents such as N-methyl pyrrolidine (NMP) and dimethylsulfoxide (DMSO). Their T_gs were recorded in the range of 78–95 °C and could be thermally dehydrated into the corresponding polyoxadiazoles in the region of 310–20 °C, as evidenced by the DTA thermograms. The oxadiazole polymers showed a dramatically decreased in solubility and higher T_g when compared to their respective hydrazide prepolymers. The morphology of polyhydrazide V was examined by SEM.     

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.     

Thermal degradation studies of alkyl-imidazolium salts and their application in nanocomposites

Increasing the thermal stability of organically-modified layered silicates is one of the key points in the successful technical application of polymer-layered silicate nanocomposites on the industrial scale. To circumvent the detrimental effect of the lower thermal stability of alkyl ammonium-treated montmorillonite, a series of alkyl-imidazolium molten salts were prepared and characterized by elemental analysis, thermogravimetry (TGA) and thermal desorption mass spectroscopy (TDMS). The effect of counter ion, alkyl chain length and structural isomerism on the thermal stability of the imidazolium salts was investigated. Alkyl-imidazolium-treated montmorillonite clays were prepared by ion exchange of the imidazolium salts with Na-montmorillonite. These organically-modified clays were characterized by X-ray diffraction (XRD), TDMS and thermogravimetry coupled with Fourier transform infrared spectroscopy (TGA-FTIR), and compared to the conventional quaternary alkyl ammonium montmorillonite. Results indicate that the counter ion has an effect on the thermal stability of the imidazolium salts, and that imidazolium salts with PF₆⁻, N(SO₂CF₃)₂⁻ and BF₄⁻ anions are thermally more stable than the halide salts. A relationship was observed between the chain length of the alkyl group and the thermo-oxidative stability; as the chain length increased from propyl, butyl, decyl, hexadecyl, octadecyl to eicosyl, the stability decreased. The results also show that the imidazolium-treated montmorillonite has greater thermal stability compared to the imidazolium halide. Analysis of the decomposition products by FTIR provides an insight about the decomposition products which are water, carbon dioxide and hydrocarbons.     

Synthesis, characterization and kinetics of thermal decomposition of dimeric peroxycarbamates

Several dimeric peroxycarbamates (PCs) have been synthesized by using cycloaliphatic and aromatic diisocyanates with mono- and di-hydroperoxides. The reactions were carried out under suitable conditions either in the presence of T-12 (dibutyltin dilaurate) as catalyst or in the absence of this catalyst. The products were characterized by IR-spectra and molecular weight measurements from isocyanate and peroxygen analyses. Thermal decomposition kinetics of these PCs were studied in THF solution at 80, 90 and 100 °C; the reactions were found to be first-order and decomposition rate constants (k_d) were found. Activation energies and frequency factors for the decomposition were calculated. Activation energies were found to be in the range 67-121 kJ mol⁻¹ and frequency factors were of the order of 10¹¹-10¹⁵ s⁻¹ depending on the structure of the PC. The results for the PCs agree well with literature values.     

Effect of preparation conditions on the thermal stability of an epoxy-functional inorganic-organic hybrid material system doped with Zr

An inorganic-organic hybrid material system consisting of (3-glycidyloxypropyl)trimethoxysilane, dimethyldimethoxysilane and zirconium(IV) n-propoxide was prepared by the sol-gel method. The influence of processing parameters including Zr content, UV irradiation and sol ageing on the thermal stability of the resultant thin films was characterised by thermogravimetry. It was demonstrated that the crosslinking of epoxy groups in the structure was the primary reason for variation in the thermal stability of the system. As Zr and/or UV irradiation may be employed to crosslink the epoxy groups in the structure, the thermal stability of the system can be tuned by the optimal combination of these two crosslinking methods.     

New synthesis and thermal studies of palladacycloalkanes and their precursors

A series of new palladacycloalkanes of formula cis-[PdL₂(CH₂)_n] (9. n = 6, L = PPh₃; 10. n = 6, L₂ = dppe; 11. n = 8, L = PPh₃; 12. n = 8, L₂ = dppe) have been prepared by two routes. In the first route, the precursor bis(1-alkenyl) complexes cis-[PdL₂((CH₂)_nCHCH₂)₂] (1. n = 2, L = PPh₃, 2. n = 2, L₂ = dppe, 3. n = 3, L = PPh₃, 4. n = 3, L₂ = dppe) were allowed to react with Grubb’s 2nd generation catalyst to give the palladacycloalkenes, cis-[PdL₂(CH₂)_nCHCH(CH₂)_n] (5. n = 2, L = PPh₃, 6. n = 2, L₂ = dppe, 7. n = 3, L = PPh₃, 8. n = 3, L₂ = dppe), which were then hydrogenated to the palladacycloalkanes, 9-12. In the second route, the di-Grignard reagents BrMg(CH₂)_nMgBr (n = 6, 8) were reacted with the palladium complex [PdCl₂(COD)] followed by immediate ligand displacement to form the respective palladacycloalkanes 10 and 12. The complexes obtained were characterized by a range of spectroscopic and analytical techniques. Thermal decomposition studies were carried out on the palladacycloalkanes 9-12 and the main organic products shown to be 1-alkenes and 2-alkenes.     

Effect of preparation conditions on the thermal stability of an epoxy-functional inorganic-organic hybrid material system with phenyl side group

A hybrid material system consisting of (3-glycidyloxypropyl)trimethoxysilane and dimethyldimethoxysilane as matrix materials and diphenyldimethoxysilane (DPDMS) as both a matrix material and a potential thermal stabiliser by the sol-gel method. A detailed thermogravimetric analysis study of the influence of processing parameters, including DPDMS content, UV irradiation and sol ageing, on the thermal stability of the resultant thin films was presented. FT-IR spectroscopy was used to monitor the changes in the relative amount of epoxy rings in the system during processing. It was demonstrated that the crosslinking of epoxy groups in the structure is the primary reason for changes in the thermal stability of the system. It was also shown that the thermal stability, in terms of 10% mass loss, of the material system could be improved up to 280 °C, by adjusting the preparation conditions, compatible with several subsequent high temperature optoelectronic integration processes.     

Structure, morphology, thermal stability and carbonization mechanism studies of electrospun PA6/Fe-OMT nanocomposite fibers

In the present work, Fe-montmorillonite (Fe-MMT) was synthesized by hydrothermal method, and then was modified by cetyltrimethyl ammonium bromide (CTAB). The polyamide 6 (PA6)/organic-modified Fe-montmorillonite (Fe-OMT) nanocomposite fibers were prepared by a facile compounding and electrospinning. The catalyzing carbonization studies of the Fe-OMT based on PA6 nanocomposite fibers were performed. It was found from High-resolution electron microscopic (HREM) observations that the silicate clay layers were well dispersed within the nanocomposite fibers and was oriented along the fiber axis. The Scanning electron microscopic (SEM) images indicated that the nanofibers were randomly distributed to form the fibrous web and the Fe-OMT additives decreased the diameters of nanocomposite fibers. The Thermogravimetric analyses (TGA) revealed that the loading of the Fe-OMT led to the crosslinking of the PA6, promoted the charred residue yield and catalytic graphitization effect. The structure and morphology of the purified charred residue, characterized by XRD, HREM, Selected area electron diffraction (SAED) and Laser Raman spectroscopic (LR), approved further the presence of graphite sheets. The possible catalyzing carbonization mechanisms included: (1) catalyzing effect of the Fe³⁺, which promoted the crosslinking of polymer, (2) Hofmann degradation of the Fe-OMT, whose degraded products had also positive role in promoting crosslinking reactions, (3) gas barrier properties of the nano-dispersed silicate clay layers stopped or reduced the releases of the pyrolytic products, which was dehydrogenated and aromatized to form graphite.     

Study on thermal degradation and combustion behaviors of PC/POSS hybrids

Polycarbonate/polyhedral oligomeric silsesquioxane hybrids were prepared based on bisphenol A polycarbonate (PC) and trisilanolphenyl-POSS (TPOSS) by the melt blending method. Investigation of transmission electronic microscopy and Fourier transform infrared spectroscopy confirms that the nanoscale TPOSS particles were well dispersed in the PC matrix and there is no chemical reaction between the TPOSS particles and PC matrix during the melt blending. The thermal degradation behaviors of the PC/TPOSS hybrids were investigated. The presence of TPOSS significantly affects the thermal degradation process of PC. The combustion behaviors of the hybrids were evaluated by cone calorimetry experiments. The addition of TPOSS significantly decreased the value of peak heat release rate of the hybrids. Moreover, the addition of TPOSS at 2 wt% leads to the maximum decrease of the PHRR. And scanning electron microscopy and X-ray photoelectron spectroscopy were used to explore the char residues of the pure PC and the hybrids.     

The comparison of thermal stability of some hydrofluoroethers and hydrofluoropolyethers

The thermal stability of representative hydrofluoropolyether (HFPE) and hydrofluoroether (HFE) compounds has been evaluated. The observed stability order appears to be correlated with the nature of the hydrogenated chain ends; in particular, molecules having fully hydrogenated chain ends (OCH₃ and OC₂H₅) show a significantly lower stability compared with the OCF₂H terminated compounds. The main degradation products suggest, however, that the same primary reaction is responsible for the decomposition of all the compounds examined; this reaction involves the fragmentation of the R_fOC_xH_yF_z bond with fluorine transfer between the two carbon atoms close to the oxygen, leading to the formation of a hydrofluorocarbon C_xH_yF_(z+1) and an acyl fluoride or a ketone.     

Synthesis,crystal structures,thermal properties,and DNA-binding studies of transition metal complexes with imidazole ligands

A new series of complexes of transition metal (Cu, Zn, Ni) perchlorate with imidazole have been synthesized and characterized by elemental analysis, infrared (IR), UV-Vis spectroscopy, and single-crystal X-ray diffraction. Based on elemental and spectral data, the complexes are M(C₃H₄N₂) _x (ClO₄)₂ (M?=?Cu, Zn, x?=?4; M?=?Ni, x?=?6; C₃H₄N₂?=?imidazole). The crystal structures of Cu(C₃H₄N₂)₄(ClO₄)₂ (1) and Zn(C₃H₄N₂)₄(ClO₄)₂ (2) show metals surrounded by four nitrogens of imidazole, while the nickel complex Ni(C₃H₄N₂)₆(ClO₄)₂ (3) has six nitrogens of imidazole. Intra- and inter-molecular hydrogen bonds exist between hydrogen of imidazole and oxygen of perchlorate. The thermal stabilities of 1, 2, and 3 at different heating rates (β?=?5°C?min^?1, 10°C?min^?1, and 15°C?min^?1) show that all the complexes exhibit two thermal decomposition stages; the sequence of thermal stability is 2?>?1?>?3. 1, 2, 3, and imidazole display DNA binding ability, ascertained by UV-Vis titration.     

Structure,thermal conductivity,and thermal stability of bromobutyl rubber nanocomposites with ionic liquid modified graphene oxide

In this report, we demonstrate that both the thermal stability and the thermal conductivity of bromobutyl rubber (BIIR) nanocomposites could be improved by incorporating the ionic liquids (ILs) modified graphene oxide (GO-ILs) using a solution compounding method. The structure, thermal stability and thermal conductivity of this newly modified BIIR nanocomposites were systematically analyzed and studied. The X-ray diffraction (XRD) analysis of GO-ILs showed that ILs had been effectively intercalated into the interlayer of GO, which was found to be able to raise the exfoliation degree of GO. The increased exfoliation degree facilitated a good dispersion of GO-ILs in the BIIR matrix, as revealed by the scanning electron microscope (SEM) images. The glass transition temperatures (T_g) of the GO-ILs/BIIR nanocomposites were also raised by the addition of GO-ILs, which indicates the strong interfacial adhesion between GO-ILs and the rubber. Most importantly, the incorporation of GO-ILs in the BIIR matrix could effectively improve the thermal stability of the rubber nanocomposites according to our thermogravimetric analysis (TGA). The activation energy (E_a) of thermal decomposition of GO-ILs/BIIR nanocomposites increases with the addition of GO-ILs. Besides, the thermal conductivity of GO-ILs/BIIR nanocomposite with 4 wt% of GO-ILs had 1.3-fold improvement compared to that of unfilled BIIR.