Morphology and thermal degradation studies of melt-mixed poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) biodegradable polymer blend nanocomposites with TiO2 as filler

The morphology and thermal stability of melt-mixed poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) blend nanocomposites with small amounts of TiO₂ nanoparticles were investigated. The nanoparticles were mostly located in the PLA phase, with good dispersion of individual particles, although significant aggregation was also visible. The thermal stability and degradation behaviour of the different samples were studied using thermogravimetric analysis (TGA) and TGA-Fourier-transform infrared (FTIR) spectroscopy. Neat PCL showed better thermal stability than PLA, but the degradation kinetics revealed that PLA had a higher activation energy of degradation than PCL, indicating its degradation rate more strongly depends on temperature, probably because of a more complex degradation mechanism based on chain scission and re-formation. Blending of PLA and PCL reduced the thermal stabilities of both polymers, but the presence of TiO₂ nanoparticles improved their thermal stability. The nanoparticles also influenced the volatilization of the degradation products from the blend, acted as degradation catalyst and/or retarded the escape of volatile degradation products.     

The influence of silicone shell on double-layered microcapsules in intumescent flame-retardant natural rubber composites

The mechanisms of the thermal degradation of polyhedral oligomeric octaphenylsilsesquioxane (OPS), octa(nitrophenyl)silsesquioxane (ONPS), and octa(aminophenyl)silsesquioxane (OAPS) were investigated. The –NO₂ or –NH₂ substituents on the phenyl group affected the mechanism of the POSS thermal degradation. The thermal stabilities of OPS, ONPS, and OAPS were characterized by TG and FTIR. Thermal degradation of OPS included mainly the degradation of caged polyhedral oligomeric silsesquioxane structures and phenyl groups. Nitro or amino substituents decreased its thermal stability. The thermal degradation processes of OPS, ONPS, and OAPS differed. Phenyl groups and cyclobutadiene were observed in the OPS degradation products. Oxygen radicals that caused intensive CO₂ release between 350 and 450 °C were generated by the degradation of ONPS –NO₂. OAPS released mainly aminophenyl groups at 370 °C, whereas a small number of phenyl groups decomposed at 500 °C. The OAPS reactivity could enhance the thermal stability of POSS structure in the polyimide OAPS composites.     

Thermal degradation study of gadolinium and lutetium methanesulfonates

The synthesis, characterization and thermal degradation study of gadolinium and lutetium methanesulfonates is reported. The prepared salts were characterized by elemental analysis and infrared spectroscopy. The thermal degradation study was performed by using thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). By using thermogravimetric data, a kinetic study of the dehydration of Gd and Lu methanesulfonates is performed employing the Coats-Redfern and Zsakó methods. It is verified that under heating, the gadolinium and lutetium methanesulfonates suffer three main processes: dehydration, thermal degradation and oxide formation. The thermal degradation products were characterized by infrared spectroscopy and X-diffractometry. Furthermore, depending on the atmosphere nature, i.e. inert or oxidant, the thermal degradation process could be endothermic (N₂) or exothermic (air).     

Thermal degradation of poly(vinylpyridine)s

The thermal stability and the temperature at which maximum degradation yields are detected were quite similar for both poly(2-vinylpyridine) (P2VP) and poly(4-vinylpyridine) (P4VP). However, considerable differences among the thermal degradation products of both polymers were detected indicating a correlation between the polymer structure and the degradation mechanism. Direct pyrolysis mass spectrometry analyses revealed that P2VP degrades via a complex degradation mechanism, yielding mainly pyridine, monomer, and protonated oligomers, whereas depolymerization of P4VP takes place in accordance with the general thermal behaviour of vinyl polymers. The complex thermal degradation behaviour for P2VP is associated with the position of the nitrogen atom in the pyridine ring, with σ-effect.     

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.     

半纤维素模型化合物热解机理的理论研究

针对半纤维素模型化合物4-O-甲基葡萄糖醛酸的热解,提出了六种可能的反应路径,对各种反应路径中的反应物、产物、中间体和过渡态的结构进行了几何结构全优化,计算了各步反应的标准动力学参数。结果表明,4-O-甲基葡萄糖醛酸热解时,首先通过分子内的氢原子转移发生开环反应而形成链状中间体,然后中间体进一步分解,主要产物是甲醇、乙醇醛、2-羟基-3-甲氧基丁醛酸、乙二醛和2-羟基丁醛酸等;主要的热解竞争产物是甲酸、CO_2、CO、4-羟基-3-丁烯酮和甲基乙烯醚等。在半纤维素的热解中,CO_2是通过不饱和反应物或中间体脱羧基反应而形成,乙酸则是通过脱O-乙酰基反应而形成。     

Solubility and Thermal Degradation of Quercetin in CO2-Expanded Liquids

The solubility of quercetin and its thermal degradation was studied in CO₂-expanded ethanol and ethyl lactate. An equipment setup was constructed that enabled the separation of the products of degradation while quantifying the solubility of quercetin. Three different conditions of temperature were analyzed (308, 323, and 343 K) at 10 MPa. Higher solubility and thermal degradation of quercetin were observed for CO₂-expanded ethyl lactate in comparison with CO₂-expanded ethanol. At the same time, as the amount of CO₂ was increased in the CO₂-expanded liquids mixtures, the thermal degradation of quercetin decreased for almost all the conditions of temperature considered in this work. The importance of considering thermal degradation while performing solubility measurements of compounds that are thermally unstable such as quercetin was highlighted.     

新型侧基含磷共聚酯的阻燃和热降解动力学

利用动态热重分析法(TG)研究了聚酯(PET )及侧基含磷共聚酯(FR-PET)在不同升温速率下的热稳定性及热降解动力学, 并通过极限氧指数法(LOI)考察了FR-PET的阻燃性能; 采用Flynn-Wall-Ozawa方法分析了PET和FR-PET的热降解表观活化能; 利用Coast-Redfern方法通过对不同机理模型的选取, 确定了PET和FR-PET热降解动力学机理及其模型, 得出了主降解阶段的非等温动力学方程及热降解速率曲线图. 研究结果表明, 侧基含磷单元的引入提高了聚酯的阻燃性能, 侧基上的P—C和P—O键易断裂, 从而降低了聚酯的热稳定性. PET和FR-PET的热降解表观活化能(0.1≤α≤0.85)分别为194-227和184-209 kJ/mol; PET和FR-PET热降解反应均属于受减速形α-t曲线控制的反应级数机理, 其机理函数为f(α)=3(1-α)2/3(0.1≤α≤0.85). 侧基含磷单元的引入对PET的主降解阶段的热降解速率并无实质上的影响. 侧基含磷共聚酯的凝聚相阻燃作用有限, 可能以气相阻燃机理为主发挥阻燃作用.     

The non-oxidative thermal degradation of poly (Di-2-chloroethyl itaconate)

The non-oxidative thermal degradation of poly (di-2-chloroethyl itaconate) (PD2CEI) was studied by TG and by analysing the thermal products. The major processes occurring during thermal analysis are crosslinking, depolymerisation and carbonisation. The thermal degradation activation energy increased with increasing sample mass loss. The thermal degradation of PD2CEI was compared to that of the structurally similar poly(2-chloroethyl methacrylate) (P2CMA).     

基于DFT密度泛函理论的聚酯热降解反应机理研究

本文应用密度泛函理论（DFT）研究钛系催化剂催化聚酯热降解的反应机理。分别以Ti(OEt)4化合物以及Ti(OEt)3 阳离子化合物为催化剂,探讨了二苯甲酸乙二酯（EDB）解聚反应的Lewis酸催化热降解反应机理（M1机理）和烷氧基配位催化热降解反应机理（M2机理）。结果表明,Lewis酸催化热降解反应机理在两种催化剂下的解聚反应能垒与无催化剂反应非常相似,未表现出明显促进作用;Ti(OEt)3 催化剂在M2机理中明显降低了解聚反应能垒,是聚酯热降解反应的催化活性中心。经轨道相互作用分析发现,阳离子催化剂和反应物EDB之间存在较为明显的轨道相互作用。     

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).     

聚芳醚醚酮的热老化寿命研究

本工作用热重法(TG)研究了聚芳醚醚酮(PEEK)在空气和氮气中的热分解反应过程;确定了PEEK在这两种气氛中的热分解反应模型均符合无规引发断裂模型;在空气中PEEK的热分解显示两个过程,由此计算其在空气中第一阶段的热分解和氮气中的热分解反应活化能分别为214.7kJ/mol和232.2kJ/mol;由热分解反应动力学参数推算出热老化寿命曲线,并讨论了实验条件对结果的影响,进而以失重5%作为材料寿终指标估算出PEEK在氮气和空气中使用10年的最高温度分别为307℃和274℃。     

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).     

Influence of fullerene on the kinetics of thermal and thermo-oxidative degradation of high-density polyethylene by capturing free radicals

The influence of fullerene (C₆₀) on the thermal and thermal-oxidative degradation of high-density polyethylene (HDPE) was studied using non-isothermal thermogravimetric analysis under nitrogen (N₂) and air atmosphere. Kinetic parameters of the degradation were evaluated using the Flynn–Wall–Ozawa method, which does not require the knowledge of the reaction mechanism. The results showed that the addition of C₆₀ enhanced the thermal stability of HDPE and increased the activation energy both in N₂ and air atmosphere and especially affected the initial stage of degradation. In N₂, C₆₀-trapped carbon-centered radical originated from the degradation of HDPE to improve the thermal stability and increase the activation energy. While in air, C₆₀ trapped the alkyl radicals and alkyl peroxide radicals to inhibit the hydrogen abstraction (especially the initial stage of thermo-oxidative degradation) and form more stable species, which improved the thermal stability and increased the activation energy during the thermal degradation of HDPE. Comparing with that of pure HDPE, the changes of activation energy for HDPE/C₆₀ nanocomposites were higher in air than in N₂, especially in the initial stage.     

Copolymers of 2-Hydroxyethyl Methacrylate and Alkyl Methacrylates. Part III. Thermal Behavior

The relative thermal stability of copolymers of 2-hydroxyethyl methacrylate-ethyl methacrylate (HEMA-EMA) and HEMA-n-butyl methacrylate (HEMA-BMA) was investigated by thermogravimetry in an air/nitrogen atmosphere. The effect of molecular weight on thermal degradation was evaluated by taking five fractions of HEMA-EMA and four of HEMA-BMA copolymers. The enthalpic changes associated with the endothermic transition were evaluated by differential scanning calorimetry. The structural changes taking place in these copolymers during thermal degradation in air at 200°C were investigated by IR.     

Comparative study on thermal degradation of some new diazoaminoderivatives under air and nitrogen atmospheres

The article is devoted to a comparative study on the thermal degradation of some new diazoaminoderivatives under both air and nitrogen atmosphere by TG-FTIR analysis. The TG–DTG–DTA curves show the thermal degradation in air to present two temperature domains: an endothermic one identical to the case of the degradation under nitrogen and an exothermic one which is not to be found under nitrogen atmosphere. The identification of the gaseous species released by degradation in air within the endothermic domain made evident the presence of the same components of the degradation in nitrogen atmosphere. In the exothermic domain of the sample degradation in air, the CO₂, H₂O, SO₂ species result by the burning of the molecular residues of the first domain. The obtained results afforded a degradation mechanism to be advanced that coincide for the endothermic domain with that of degradation under nitrogen atmosphere. Due to the importance of these compounds as possible reaction initiators and also as potentially bioactive substances (herbicides, acaricides, fungicides), the study on their thermal degradation could give useful information on the environmental impact of the degradation products resulting by the thermal processing of the plants which could possible retain these compounds, when the initial degradation temperature is exceeded.     

Enhanced thermal stability of poly(vinyl alcohol) in presence of melanin

A novel method was developed to enhance the thermal stability of PVA by using natural and synthetic melanins from oxidation of dopamine. Thermogravimetric (TG) curves indicated that the synthetic melanin changed the thermal degradation behaviors of PVA and largely improved the decomposed temperature by 80–110 °C in nitrogen when incorporation of synthetic melanin with low content (0.5–2 mass%). The thermal degradation kinetics suggested the activation energies of PVA/synthetic melanin blends were much higher than these of pure PVA. Isothermal TG curves conformed that the PVA/synthetic melanin blends exhibited more thermal stability than pure PVA. Moreover, the chemical structure changes of macromolecular after degradation were characterized by using fourier transform infrared and the results suggested that elimination reaction on the first degradation step did not took place for the PVA/synthetic melanin blends at 270 °C.     

A comparative study on thermal and catalytic degradation of polybutylene terephthalate

A comparative study on the thermal and catalytic degradation of polybutylene terephthalate (PBT) at atmospheric pressure was conducted. The weight loss of PBT under thermal degradation was significantly influenced by the temperature between 360 °C and 380 °C, but little affected by the PBT particle size. Four groups of catalysts include metal chloride, metal oxide, metal acetate, and metal copper powder were used to test PBT degradation activity. Copper (II) chloride is the most active one for increasing the percentage PBT weight loss more than 100% in comparison with the result of thermal degradation at a temperature of 360 °C for 30 min. PBT and catalyst mixtures can be prepared by impregnation and physical method, the former resulted in a better PBT degradation. The percentage PBT weight loss in the presence of CuCl₂ increased steadily between 320 °C and 380 °C which was different from the results of thermal degradation. The time for obtaining a same percentage PBT weight loss reduced effectively when compared to the catalytic to thermal degradation. The weight ratio of CuCl₂/PBT was tested between 0 and 0.2 and the optimal ratio was 0.1. The gaseous product distribution analyzed by GC/MS for PBT thermal and catalytic degradation revealed almost the same and the major products were ethane, carbon monoxide, carbon dioxide, 1-butene, 2-butene, 1,3-butadiene, and butadiene dimmer. But the relative abundance of major products was changed, especially for 1,3-butadiene increased dramatically, and a new chlorocompound was produced in catalytic degradation. In condensed liquid product, both the number and the molar mass of components were more and greater than that of in gaseous product and 4-heptylacetophenone was the most abundance product. In PBT catalytic degradation, 4-heptylacetophenone and some products were decreased and some even disappeared completely while the abundance of benzoic acid increased and three new products were generated.     

紫外光照射对皮胶原热降解活化能的影响

将皮胶原经不同时间的紫外光照射,采用热重法(TG)和微分热重分析(DTG)研究了照射前后皮胶原的热降解行为,用Horowitz-Metzger法和Coats-Redfern法计算了其热降解活化能,得到了未照射皮胶原和经过不同紫外线照射时间处理后的皮胶原的热降解活化能。研究发现,在较短时间(0~4h)的照射后,皮胶原的热降解活化能略有增大;在较长时间(8~64h)的照射后,皮胶原的热降解活化能大幅降低。这可能是由于在紫外光照射的过程中,皮胶原分子链发生了以交联为主和以断链为主的复杂光化学反应。     

Thermal stability and degradation products analysis of benzocyclobutene-terminated imide polymers

Benzocyclobutene-terminated imides were prepared and fully characterized with ¹H NMR, MS, and FT-IR. The thermal degradation of polymers was investigated by using thermogravimetric analyzer (TGA) and high-resolution pyrolysis-gas chromatography–mass spectrometry (HR-Py-GC–MS). TGA showed that thermal degradation of the polymer was a single-stage process in N₂, whereas a three-stage degradation in air atmosphere. The major involved products were found to be CO₂, naphthalene and naphthalene derivatives. Degradation mechanism of the polymer was suggested and the relationship between structures of the polymer and degradation products was also discussed.