Influence of the nanoparticle type on the thermal decomposition of the green starch/poly(vinyl alcohol)/montmorillonite nanocomposites

In this study, some aspects concerning the thermal decomposition of starch/poly(vinyl alcohol) (PVA)/montmorillonite (MMT) nanocomposites with 2 wt% nanoclay, prepared by melt mixing method, were studied. For these loadings, the inorganic fillers are well dispersed through the PVA/starch matrix, i.e., the nanocomposites formed are mostly intercalated hybrids. The aim of this article is to establish the effect of the nanofiller nature on the thermal decomposition of the starch/PVA/MMT nanocomposites. The thermal behavior of the 50 wt% starch/50 wt% PVA blend and its nanocomposites with 2 wt% nanoclay has been investigated by thermogravimetric analysis coupled with Fourier transform-infrared spectroscopy and mass spectrometry (MS). The volatile compounds resulting during the thermal degradation were studied by in situ vapor phase FT-IR spectroscopy and MS technique under a controlled temperature/time program. Apart from the identification of the volatile compounds, some conclusions on the nanoclays effect on the degradation mechanism and formation of the volatile compounds in accordance with the previously developed general mechanisms for PVA and starch degradation have been formulated. The clay–PVA/starch nanocomposites show completely different degradation product distribution patterns, which may be attributed to the presence of the head-to-head structures and Si–O–C linkages formed between clay and blend components.     

Thermal and structural characterization of superfine down powder

The thermal degradation of down fiber and down powder was studied using TG, DSC, TG-FTIR, and ATR-FTIR as a function of mass loss. For both down fiber and down powder, two evident mass loss stages were observed. Compared to down fiber, down powder had higher moisture and lower thermal stability. The oxygen in air weakened the mass loss of superfine down powder in the temperature range of 300–530 °C, and accelerated the oxidation–reduction reaction between oxygen and powder when the temperature was over 530 °C. The microstructures of down fiber and down powder were investigated on the analysis of DSC results. As the decrease in the average particle size of down powder, the absorbed energy of the destruction of crystallinity, rupture of crosslinks and thermal degradation of peptide bonds decreased, respectively. The gases evolved during thermal degradation of superfine down powder were inspected by in situ FTIR, and then the solid residues collected at different temperature were analyzed using ATR-FTIR. The color evaluation of superfine down powder hot-pressed at high temperature was discussed to confirm the best hot-processing condition.     

Thermal degradation of poly(siloxane-urethane) copolymers

The aim of this study was to investigate the characteristics and mechanism of the degradation of poly(siloxane-urethane) (PSiU) copolymers by thermogravimetric analysis (TGA) and TGA coupled with Fourier-transform infra-red spectroscopy (TG-FTIR). The PSiU copolymers consisted of 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butanediol (1,4-BD), and OH-terminated polydimethylsiloxane (PDMS). In TGA they exhibited a two-stage degradation at 250-650 °C. The two stages of degradation have been found to comprise eight degradation steps and two interchange reactions, as revealed by TG-FTIR analysis. The main decomposition products have been identified as CO₂, tetrahydrofuran, cyclosiloxane, and macrocyclic species. In addition, the effects of hard segment content (HSC) on the degradation and thermal stability of PSiU copolymers have been investigated by means of TG and DTG curves; notably, a stability region at 410-470 °C is caused by the cyclosiloxane, as verified by TG-FTIR.     

Thermal analysis of bis(tetraethylammonium) tetrachloroferrate(II)

Thermal decomposition of bis(tetraethylammonium) tetrachloroferrate(II) has been studied using the TG-FTIR, TG–MS and DTA techniques. The measurements were carried out in an inert atmosphere over the temperature range of 293–1073 K. The solid products of the thermal decomposition were identified by the FT-FIR, Mössbauer spectroscopy as well as the X-ray powder diffractometry. The influence of the oxidation state and the nature of a metal on thermal transformation profiles of analogous complexes have been discussed.     

聚乙烯/石墨层间化合物热降解过程的TG-FTIR研究

将含磷化合物插层石墨层间化合物(GIC)用于聚乙烯(PE)的阻燃,采用氧指数(LOI)方法评价了PE/GIC的阻燃性能,并采用热分析-红外光谱联用技术(TG-FTIR)研究了PE/GIC的热降解过程,探讨了GIC的阻燃机理。研究表明,不同含磷化合物插层GIC阻燃聚乙烯的氧指数有显著差别,其中以多聚磷酸铵-GIC的阻燃效果较好,氧指数较高。TG-FTIR研究结果表明,GIC并未显著影响PE的热降解方式,但由于GIC体积膨胀所发生的氧化还原反应导致部分PE热降解提前并发生热氧化降解,促进了后期成炭的石墨化过程。     

基于差示扫描量热技术的生物质热解两步连续反应模型研究

采用差示扫描量热分析仪对我国的一种生物质试样在空气气氛中进行了实验, 发现试样从常温到923 K高温的低速升温过程中, 经历了两步明显的放热过程. 对放热机理的分析表明, 第一步主要是由半纤维素和纤维素的有氧热解过程控制, 第二步放热过程则受木质素热解和炭的氧化反应的共同作用. 采用等转化率方法和优化计算方法, 对热解过程的动力学模型进行了研究, 结果表明, 两步连续反应机理可用于描述生物质在空气气氛中热解的放热动力学.     

Radiochemical ageing of epoxy coating for nuclear plants

The degradation of an epoxy-amine network exposed to gamma irradiation in oxygen atmosphere has been studied by using a variety of analytical methods, including infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and sol–gel analysis. Results show that the oxidation of epoxy systems grows with the irradiation dose. Hydroperoxides, which are species resulting from oxidation, were identified and quantified by DSC. As indicated by the sol–gel analysis, the mechanism of degradation of chain scission seems to be predominant over crosslinking. The modifications induced by irradiation reflect in a greater capacity of water absorption.     

Thermal degradation and stabilization of poly(2,6-dimethyl-1,4-phenylene oxide)

Thermal degradation and stabilization of poly(2,6-dimethyl-1,4-phenylene oxide) have been examined in air in the range 100–400°. Plots of weight-average molecular weight vs time are linear, confirming random chain scission. The breakdown process has also been studied by DTA and TGA. It was concluded that thermal analysis alone was insufficient to characterize the degradation fully so the degradation products were determined qualitatively using i.r. and NMR spectroscopy. The heats of activation for the systems have been calculated and a stabilization mechanism by bis(1-phenyl-3-α-pyridyl triazeno)Cu(II) chelate has been postulated.     

The use of TG-FTIR technique for the assessment of hydrogen bromide emissions in the combustion of BFRs

The TG-FTIR technique was used in the present study to investigate the thermal degradation behaviour of materials containing brominated flame retardants under fire conditions. Time-temperature profiles and oxygen concentrations typical of selected fire scenarios were reproduced in the thermogravimetric analyzer, while the characterization of the gaseous products generated was performed by the simultaneous FTIR analysis. FTIR analysis combined with the use of specific calibration procedures allowed the quantitative estimation of the gaseous products evolved as a function of experimental conditions. The results obtained allowed the straightforward assessment and the comparison of the quantities of hydrogen bromide formed in the oxidation and thermal degradation of pure brominated flame retardants and of flame retarded materials of industrial interest. Hydrogen bromide yields resulted dependent on the experimental conditions used, such as oxygen concentration and heating rate. Although TG-FTIR experiments only provide a representation of the actual heterogeneous combustion products in real fire conditions, the coupled TG-FTIR technique proved to be a straightforward experimental methodology allowing one to obtain reference data on the nature and quantities of the macropollutants generated in a fire. This revised version was published online in July 2006 with corrections to the Cover Date.     

Understanding of thermal/thermo-oxidative degradation kinetics of polythiophene nanoparticles

The polythiophene nanoparticles (nano-PT) were prepared with average diameter of 20–35 nm. The nanostructurals of polythiophene were confirmed by TEM and SEM analyzes. The kinetics of the thermal degradation and thermal oxidative degradation of nano-PT were investigated by thermogravimetric analysis. Kissinger method, Flynn–Wall–Ozawa method, and advanced isoconversional method have been used to determine the activation energies of nano-PT degradation. The results showed that the thermal stability of nano-PT in pure N₂ is higher than that in air atmosphere. The analyzes of the solid-state processes mechanism of nano-PT by Criado et al. method showed: the thermal degradation process of nano-PT goes to a mechanism involving second-order (F ₂ mechanism); otherwise, the thermo-oxidative degradation process of nano-PT is corresponding to a phase boundary controlled reaction mechanism (R ₂ mechanism).     

Modification of mechanical and thermal property of chitosan–starch blend films

Chitosan–starch blend films (thickness 0.2 mm) of different composition were prepared by casting and their mechanical properties were studied. To improve the properties of chitosan–starch films, glycerol and mustard oil of different composition were used. Chitosan–starch films, incorporated with glycerol and mustard oil, were further modified with monomer 2-hydroxyethyl methacrylate (HEMA) using gamma radiation. The modified films showed improvement in both tensile strength and elongation at break than the pure chitosan–starch films. Water uptake of the films reduced significantly than the pure chitosan–starch film. Thermo gravimetric analysis (TGA) and dynamic mechanical analysis (DMA) showed that the modified films experience less thermal degradation than the pure films. Scanning electron microscopy (SEM) and FTIR were used to investigate the morphology and molecular interaction of the blend film, respectively.     

Thermal stability of polydiphenylamine synthesized through oxidative polymerization of diphenylamine

The thermal stability of polydiphenylamine synthesized through the oxidative polymerization of diphenylamine has been studied. It has been established that the main processes of thermal and thermooxidative degradation of polydiphenylamine begin at 600–650 and 450°C, respectively. It has been shown that, in the course of thermal oxidation of the doped polydiphenylamine, the elimination of a dopant takes place first. With a further increase in temperature, the behavior of this material becomes similar to that of the neutral polymer.     

Thermal degradation of biodegradable edible films based on xanthan and starches from different sources

Films based on xanthan/wheat starch and xanthan/maize starch were prepared in different proportions and analysed in terms of thermal stability in relation to the degradation reaction in an inert atmosphere. The main gaseous decomposition products were identified by infrared spectroscopy. Xanthan was found to be less thermally stable than starch from different sources. The starch addition to xanthan induced an increase in the film thermal stabilities. The thermal degradation mechanism of xanthan starts with scission of the side chain groups with subsequent scission of the main chain. Starches from maize and wheat presented a constant mechanism of thermal degradation. The proportion of xanthan/starch (50/50) presented a synergistic behaviour which may be associated with changes in the mechanism of the thermal degradation process. The FTIR spectra of the gaseous products during thermal degradation of xanthan showed a broad absorption in the 2750–3300 cm⁻¹ region, probably indicating decomposition of β-d-mannopyranosyl groups, present in xanthan side chains. For pure starches, absorptions related to alcohol O–H stretching (3500–3750 cm⁻¹), CO stretching of CO₂, CO and carbonyl compounds (2361, 2177 and 1743 cm⁻¹, respectively) were observed. For xanthan/starch mixtures (50/50) the same compounds as those for the pure polymer degradation were evolved. However, a shift of the CO to higher wavenumber values indicates that new carbonyl compounds are being formed due to changes in the thermal degradation mechanism.     

Stepwise thermal degradation of a polybenzimidazole foam

The stepwise thermal degradation of a polybenzimidazole (PBI) foam, prepared from 3,3′-diaminobenzidine and isophthaldiamide, has been studied under conditions of pyrolysis and nonflaming oxidative degradation in a thermal analyzer using gas and liquid chromatographic separation and mass spectrometric and infrared detection techniques. The recoveries of sample weight, as degradation products, were quantitative over the entire temperature ranges studied (100–300, 300–570, 570–700, and 700–1000°C for pyrolysis; and 100–570 and 570–900°C for nonflaming oxidation). In pyrolysis, 17 volatile compounds were identified with NH₃ and CH₄ accounting for 94 and 57 mole % of the total mass loss between 300–570 and 570–700°C, respectively. Above 700°C, HCN and H₂ were formed from degradation of arylnitrile-containing oligomers. The thermal and oxidative degradation of three substituted benzimidazole monomers was also studied, and the relative ratios of N₂, NH₃, and HCN that were produced from each, when compared with PBI, support a mechanism for degradation that favors cleavages that least alter the conjugation of the polymer backbone. In the presence of air, PBI formed stable oxygen-containing residues that decomposed at high temperatures to N₂, CO₂, and H₂O almost exclusively. Large quantities of H₂ and N₂ from model compounds support results from PBI that suggest that degradation begins with total erosion of the imide ring at 570°C and the formation of more condensed heterocyclic species. These quantitative techniques are generally applicable to the study of all polymeric materials.     

Mechanistic study on the thermal decomposition of polybenzoxazines: Effects of aliphatic amines

The thermal degradation of a series of polybenzoxazines based on bisphenol A and various aliphatic amines has been studied. Using the hyphenated techniques of thermogravimetric analysis-Fourier transform infrared spectroscopy (TGA-FTIR), and gas chromatography-mass spectrometry (GC-MS), the mechanisms of thermal decomposition have been proposed. It is also proposed that the Mannich base in polybenzoxazines plays a significant role in the thermal degradation of polybenzoxazines. The contribution of hydrogen bonding to the degradation mechanism of the Mannich base has been examined. The proposed mechanisms have also been supported through the thermal degradation study of benzoxazine model dimers. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1935–1946, 1998     

Correlation of thermal degradation mechanisms: Polyacetylene and vinyl and vinylidene polymers

The thermal degradation of poly(vinyl bromide) (PVB), poly(vinyl chloride) (PVC), poly(vinyl alcohol) (PVA), poly(vinyl acetate) (PVAc), poly(vinyl fluoride) (PVF), poly(vinylidene chloride) (PVC₂), and poly(vinylidene fluoride) (PVF₂) has been studied by direct pyrolysis–mass spectrometry (DP-MS) and flash pyrolysis–gas chromatography–mass spectrometry techniques. Vinyl and vinylidene polymers exhibit two competitive thermal degradation processes: (1) HX elimination with formation of polyene sequences which undergo further moleculaar rearrangements, and (2) main-chain cleavage with formation of halogenated or oxigenated compounds. The overall thermal degradation process depends on the prevailing decomposition reaction in each polymer; therefore, different behaviors are observed. The thermal degradation of polyacetylene (PA) has also been studied and found important for the elucidation of the thermal decomposition mechanism of the title polymers.     

A comparative study of structure,thermal degradation,and combustion behavior of starch from different plant sources

The present study investigated the structure, degradation properties, and combustion behavior of starch from maize, sweet potato, lotus root, and tobacco. Compared with other plant starches, tobacco starch had the smallest size, the highest amylose content and the least crystallinity. Microscale combustion calorimetry (MCC) experiment demonstrated that sweet potato starch showed the maximum peak heat release rate value (888.0 W g^?1) while tobacco starch showed the minimum value (316.0 W g^?1) and thermogravimetric analysis coupled with Fourier transform infrared spectrometer (TG-FTIR) results showed tobacco starch had good char formability (residue mass: 15.6%) and released more incombustible gaseous products, such as H₂O and CO₂. These results suggest that the thermal properties of plant starches were mainly influenced by the structural features and amylose content, especially the amylose ratio, and tobacco starch was very promising for application in green flame-retardant material.     

Silver-layered double hydroxides self-assemblies

New inorganic ensembles type layered double hydroxides enriched with silver ions were investigated in terms of thermal behavior and structural evolution by means of TG-FTIR analysis. The studies were focused on two classes of layered precursors, actually distinguished only by the nature of the divalent metal ions, in order to correlate the influence of the clay structure with the thermal behavior of the silver-anionic clay ensembles. The understanding of the thermal degradation mechanism, which is essential to advance the potential applications, requires supplementary characterization techniques such as XRD and FTIR analyses. The thermal analysis performed at three different heating rates revealed the three thermal degradation stages typical for LDHs structure, but different from sample to sample as a consequence of the different interactions between the clay layers and the interlayer anions. The interpretation of the 3D FTIR spectra of the gaseous species resulting in each stage of the thermal degradation process, by means of standard IR spectra, indicates CO₂ and H₂O as main evolved gasses. Moreover, the evolution curves of the gaseous species released by the thermal degradation in air of the studied anionic clays point out that the two gaseous components are eliminated into the temperature ranges corresponding to those given by TG–DTG. The comparative study of the silver-LDH ensembles from the perspective of the structural evolution during the controlled heating suggest a better response from the ensemble with structure consisting of magnesium as divalent cation in the clay network, meaning a better thermal stability.     

LC–MS/MS method for the characterization of the forced degradation products of Entecavir

A rapid, specific, and reliable isocratic LC–MS/MS method has been developed and validated for the identification and characterization of the stressed degradation products of Entecavir (ETV). ETV, an antiviral drug, was subjected to hydrolysis (acidic, alkaline, and neutral), oxidation, photolysis and thermal stress, as per the international conference on harmonization specified conditions. The drug showed extensive degradation under oxidative and acid hydrolysis stress conditions. However, it was stable to thermal, acidic, neutral, and photolysis stress conditions. A total of five degradation products were observed and the chromatographic separation of the drug and its degradation products were achieved on a Waters Symmetry C₁₈ (250 mm × 4.6 mm, id, 5 μm) column using 20 mM ammonium acetate (pH 3)/acetonitrile (50:50, v/v) as a mobile phase. The degradation products were characterized by LC–MS/MS and its fragmentation pathways were proposed. The LC–MS method was validated with respect to specificity, linearity, accuracy, and precision. No previous reports were found in the literature regarding the degradation behavior of ETV.     

Synthesis and thermal properties of cellulose-based polycaprolactones

Cellulose-based polycaprolactone (CAPCL) sheets were prepared from cellulose acetate (CA) and ϵ-caprolactone (CL). Thermal properties of the obtained CAPCL's were studied by differential scanning calorimetry (DSC), thermogravimetry (TG) and TG-Fourier transform infrared spectrometry (TG-FTIR). The glass transition temperatures (T_g 's) of CAPCL decreased with increasing CL/OH ratio, until CL/OH ratio reached 15 and then increased above that ratio. Melting of CAPCL was observed when CL/OH ratio was over 10. The thermal degradation temperatures (T_d 's) of CAPCL increased from ca. 350 °C to 390 °C with increasing CL/OH ratio. The results obtained by TG-FTIR analysis of CAPCL showed that gases with OH, CH, C=O, C-O-C groups evolved by thermal degradation.