ESR imaging and FTIR study of thermally treated poly(acrylonitrile-butadiene-styrene) (ABS) containing a hindered amine stabilizer: Effect of polymer morphology, and butadiene and stabilizer content

Electron spin resonance imaging (ESRI) was applied to the study of thermal degradation at 393 K of poly(acrylonitrile-butadiene-styrene) (ABS) prepared by emulsion polymerization and containing 25% wt butadiene (ABS-25B). The polymer was doped with 1 or 2% wt Tinuvin 770 as the hindered amine stabilizer (HAS). The spatial distribution of the HAS-derived nitroxide radicals, obtained by 1D ESRI, was initially homogeneous, but became heterogeneous through sample depth with increasing treatment time, t. The spatial variation of ESR line shaping with sample depth was visualized by 2D spectral-spatial ESRI. ESR spectra along the sample depth, obtained by nondestructive (“virtual”) slicing of the 2D images, were used to deduce the relative intensity of nitroxide radicals present in two dynamically distinct sites; the sites were assigned to butadiene-rich (fast component) and SAN-rich domains (slow component), respectively. 1D and 2D ESRI allowed the determination of the extent of degradation within morphologically-distinct domains as a function of sample depth and treatment time. The results from the ESRI experiments were substantiated by attenuated total reflectance (ATR)-FTIR spectroscopy of the outer layer (500 μm thick) of the polymer. Both techniques indicated faster degradation of polymer samples that contained the higher HAS content, 2% wt. Comparison with the results obtained for a parallel study of ABS prepared by mass polymerization and containing 10% wt butadiene (ABS-10B) indicated clearly that the rate of degradation of the polymer prepared by emulsion polymerization (ABS-25B) is significantly reduced. This result can be explained by the formation of cross-linked “composite” networks during emulsion polymerization, which leads to greater thermal stability.     

Thermal analysis kinetics applied to flame retardant polycarbonate

The degradation kinetics of polycarbonate with flame retardant additive was investigated by means of thermogravimetric analysis. The samples were heated from 30 to 900°C in nitrogen atmosphere, with three different heating rates: 5, 10 and 20°C min^–1. The Vyazovkin model-free kinetics method was applied to calculate the activation energy (E _a) of the degradation process as a function of conversion and temperature. The results indicated that the polycarbonate without flame retardant additive starts to loose mass slightly over 380°C and the polycarbonate with flame retardant additive, slightly over 390°C (with heating rate of 5°C min^–1). The activation energy for flame retardant polycarbonate and normal polycarbonate were 190 and 165 kJ mol^–1, respectively.     

Detection of degradation of ABS materials via DSC

ABS is a well-known and widely-used rigid engineering polymer. The mechanical properties of ABS are critical to its proper functioning in a given application, such as a medical device. It is therefore important to retain those properties during processing, fabrication, and use. To that end, thermal analysis and mechanical testing were employed to understand the origin of observed mechanical property losses. Oxidation onset temperature (OOT) testing and differential scanning calorimetry (DSC) analysis indicated a slightly lower onset temperature and a higher glass transition temperature, respectively, for parts which demonstrated a reduction in mechanical properties. It is also demonstrated that degradation of the butadiene-phase of the ABS is responsible for the mechanical property reduction, and that this degradation only proceeds at an appreciable rate at elevated temperatures in the presence of oxygen.     

基于TGA-FTIR联用技术研究ABS树脂的热氧降解行为

采用热失重-傅立叶变换红外光谱(TGA-FTIR)联用技术研究了空气气氛下ABS树脂的热稳定性及热氧降解失重情况。研究了ABS在4个不同升温速率下的失重情况;采用TGA-FTIR联用技术对10℃/min等速升温下ABS失重过程的逸出气体进行分析;采用热分解动力学方法分析ABS的热氧降解过程,计算热分解活化能。结果表明,ABS的TGA曲线有两个失重区间:第一区间是ABS的急剧氧化降解过程,活化能(Ea)为191.8~262.8 kJ.mol-1,第二区间是成炭产物的氧化,Ea约为139.7 kJ.mol-1;升温速率越小,ABS热氧降解速率越慢,交联成炭产物越多,有利于抑制ABS的降解;由FTIR测试和Ea变化发现,热氧降解反应为多步复杂反应,初期时氧化反应和氧化断链同时进行,并以氧化断链反应为主,随着分子链上产生的双键增多发生交联反应,失重率大于80%时开始炭化反应,最终交联炭层发生氧化反应生成CO2。     

Thermal Degradation and Kinetics of Poly(3-hydroxybutyrate)/Organoclay Nanocomposites

Poly(3-hydroxybutyrate)/Cloisite30B (PHB/30B) nanocomposites were prepared by solution-intercalation method. The influence of 30B content on the thermal stability of PHB was investigated. With the addition of 3 wt. % of 30B the highest thermal stability of PHB was achieved. The kinetic analysis of the non-isothermal degradation was performed using the isoconversional Friedman method and invariant kinetic parameters method.     

Kinetic study of template removal of MCM-41 nanostructured material

The siliceous MCM-41 molecular sieve was synthesized starting from a hydrogel with the following molar composition: 4.58SiO₂:0.437Na₂O:1CTMABr:200H₂O. The cetyltetramethylammonium bromide (CTMABr) was used as structure template. A kinetic study of template removal after the syntheses was performed by Vyazovkin model-free kinetic method obtaining apparent activation energy of 166±8.2 kJ mol^-1. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Thermal Degradation of Alkaline Earth Metal Salts of Poly(Itaconic Acid)

The Mg-, Ca- and Ba-salts of poly(itaconic acid) (PIA) were prepared by treating the aqueous solution of the polyacid with the corresponding metal oxide or hydroxide. The resulting polysalts were analysed by FTIR spectroscopy and thermogravimetry. The results indicate that the polysalts are thermally more stable than the parent PIA, they all degrade in a similar manner, the Ba-salt being the most stable. This revised version was published online in August 2006 with corrections to the Cover Date.     

芳基乙炔聚合物热分解动力学研究

利用ＴＧ－ＤＴＧ方法研究了聚（ｐ－ＤＥＢ）在氮气和空气气氛中的热分解过程和动力学。实验发现,在氮气中其热分解反应为一步反应,热分解速率较低,热分解４温度随升温速率β的增加而线性增加,在７３０℃下残碳率高达８７％;而在空气中其热分解反应则由多步组成,热分解速率较快,热分解温度低,升温速率对热分解温度影响不大,在６００℃下聚合物已完全分解。在氦气和空气中聚合物的热分解反应均为一级速率对热分解温度不大,     

Poly(dialkoxyethyl itaconates)

The oxidative and non-oxidative degradation of poly(di-methoxy-), poly(di-ethoxy-), poly(di-iso-propoxy-) and poly(di-n-butoxyethyl itaconate) were investigated by thermogravimetry. Characteristic degradation temperatures and apparent activation energies of degradation were determined for the non-oxidative degradation of all the investigated polymers. It was not possible to determine these characteristics in the presence of oxygen as the degradation was accompanied by a secondary exothermic reaction. Based on examination of the monomers, it is supposed that the exothermic reaction is a repolymerisation of the monomers released during the earlier stages of polymer degradation.     

Synthesis and kinetic analysis of isothermal and non-isothermal decomposition of ammonium dinitramide prills

Ammonium dinitramide (ADN) prills were prepared by emulsion crystallization and characterized by optical microscopic, thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques. The isothermal and non-isothermal decomposition kinetics of ADN prills were studied by TG. The differential isoconversional method of Friedman (FR) and integral isoconversional method of Vyazovkin were used to investigate the dependence of activation energy (E _a) with conversion (α) and the results were compared with literature data. The dependence of activation energy was also derived from isothermal data. A strong dependence of E _a with α is observed for the ADN prills. All the methods showed an initial increase in E _a up to α=∼0.2 and later decreases over the rest of conversion. The apparent E _a values of FR method are higher than that of Vyazovkin method up to α=∼0.45. The calculated mean E _a values by FR, Vyazovkin and standard isoconversional method for α between 0.05 and 0.95 were 211.0, 203.9 and 156.9 kJ mol⁻¹, respectively.     

EGA/MS Investigations on the Thermal Degradation of Diammoniumhexachloroplatinate

The thermal degradation of diammoniumhexachloroplatinate (NH₄)₂PtCl₆ is used in technical scale for the production of the pure platinum metal [1] and for this reason of great interest. Our investigations have been focused on the influence of the different atmospheres (oxidizing, inert or reducing) used in the technical processes towards the degradation mechanism and the evolved volatile degradation products. The second main aspect of our investigations was the evolution of volatile platinum species. Regarding the different frequencies of platinum allergies related to the different technical processes, the evolution of volatile platinum species is of great importance, due to the supposed allergic potential of this substances [2–4]. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal decomposition of enalapril maleate studied by dynamic isoconversional method

Summary The aspartame is an artificial sweetener was discovered accidentally in the United States by J. M. Schlatter in 1965. In this work the kinetic of the thermal decomposition of sweetener, containing aspartame as sweetening agent, by means isothermal TG method was studied. The comparison of thermogravimetric data to the reference profiles of standard aspartame and lactose suggests an interaction between the two components in the sweetener, due to the decrease in the thermal stability of sweetener and of the overlapping processes. In the isothermal kinetic study the sweetener exhibited lower activation energy values, indicating a lower stability corroborating the thermoanalytical data. In case of the sweetener, the lower activation energy can be related to the interactions which took place between its components.     

Application of complex reaction kinetic models in thermal analysis

The complexity of the phenomena which arise during the heating of the various substances seldom can be described by a single reaction kinetic equation. As a consequence, sophisticated models with several unknown parameters have to be developed. The determination of the unknown parameters and the validation of the models requires the simultaneous evaluation of whole series of experiments. We can accept a model and its parameters if, and only if we get a reasonable fit to several experiments carried out at different experimental conditions. In the field of the thermal analysis the method of least squares alone seldom can select abest model or abest set of parameter values. Nevertheless, the careful evaluation of the experiments may help in the discerning between various chemical or physical assumptions by the quality of the corresponding fit between the experimental and the simulated date. The problem is illustrated by the thermal de-composition of cellulose under various experimental conditions.This research program was funded by the National Science Foundation (grant INT 8914934), the US Hungarian Science and Technology Joint Fund (grants 90b-22 and 93b-375), the Hungarian National Research Fund (OTKA, grant 3077/91) and the Coral Industries Endowment.     

Calorimetric study of the component steps of oscillating chemical reactions

An influence of inorganic compounds (Fe₂O₃, ZnO, PbO, CaCO₃ and K₂CO₃) on the blast furnace coke thermal oxidation in the air and in the CO₂atmosphere was investigated by means of thermal analysis. A catalytic effect showed itself at the oxidation in the air, especially with PbO and K₂CO₃. These compounds bring the oxidation starting temperature and activation energy down and increase the reaction rate constant most distinctly. The PbO and K₂CO₃ actions differ in their mechanisms. K₂CO₃ accelerates particularly the amorphous coke fractions oxidation. In the CO₂ atmosphere an important catalytic effect occurred only with K₂CO₃. The PbO catalytic influence is less distinct. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enhancement of PUR/PIR foam thermal stability after addition of Zostera marina biomass component investigated via thermal analysis and isoconversional kinetics

In the present work, a thorough thermogravimetric (TG) analysis of bio-based polyurethane–polyisocyanurate (PUR–PIR) foams in both nitrogen and oxygen atmosphere is performed. A sustainable element of the foam is a biopolyol obtained via acid-catalyzed liquefaction of Zostera marina and Enteromorpha Algae biomass. Based on isoconversional analysis and apparent activation energies, several conclusions are obtained. In contradiction to the common understanding, biopolyol based foams exhibit enhanced stability in both oxidative atmosphere and in nitrogen compared to purely petrochemical foams. Relationships between thermal stability and structure of the foams are established. Enhanced stability of bio-based foams in oxygen is attributed to two factors. First is an increased cross-linking density due to higher hydroxyl number of biopolyol compared to petrochemical one. Possibly the presence of more amount of aromatic compounds in the structure of polyols that come from lignin or aromatic ketones contribute to further enhancement of thermal stability. Those results suggest that the studied biobased foams are prospective alternatives to standard petrochemical PUR foams.     

Degradation mechanism of diethylene glycol units in a terephthalate polymer

Diethylene glycol (DEG) is incorporated into poly(ethylene terephthalate) (PET) during industrial synthesis in order to control crystallisation kinetics. DEG is known to be a weak point in the thermal degradation of PET, which is problematic during the recycling of the polymer.Studies on the thermal decomposition of the model polymer poly(diethylene glycol terephthalate) (PDEGT) have been performed using TG, DSC, TVA and spectroscopic techniques. They revealed a degradation behaviour with two distinct steps, where the first step initiates some 100 K below the degradation temperature of PET. The second step is similar to the behaviour of PET.Based on our observations, a new degradation mechanism specific to DEG units is proposed, where random ether groups along the backbone can back-bite and form cyclic oligomers. These cyclic species, containing ether moieties, are evolved at 245 °C and constitute the first of the two steps of degradation observed for PDEGT.     

Evaluation of four ABS resins by thermal analysis

Four new commercial grades of rubber toughened ABS (acrylonitrile-butadienestyrene) terpolymers were characterized by differential scanning calorimetry (DSC), mechanical analysis and gel permeation chromatography (GPC). These rubber toughened ABS molding compounds were manufactured by a new blended technology to yield resins which offer a broad range of flow properties and levels of toughness. Based upon DSC estimates of the level of rubber included, the four ABS compounds can be divided into two groups; the first has about 11 wt.% butadiene and the second near 18 wt.%. In addition, two styrene-acrylonitrile copolymers with different average molecular weights were found blended within each ABS group. By this blending process four resins are produced with impact strengths ranging from below three to near seven ft-lb in^–1. These analytical results show that a resin's impact strength is enhanced not only by increasing the level of rubber particles in a given ABS compound but also by raising the molecular weight of the SAN which is blended into the terpolymer.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThe authors acknowledge useful discussions with L. L. Blyler, Jr., X. Quan and L. Shepherd and A. Hale for his scanning electron microscopy results. GPC results were carried out by Jordi Associates.     

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℃。     

Some Aspects About Kinetics of Isothermal Degradation of Layered Hydrous Titanate Intercalated with n-Alkyldiamines

Thermogravimetric data were used to calculate the kinetics of isothermal degradation of layered tetratitanate intercalated with n-alkyldiamines H₂N(CH₂)_nNH₂ (n=2, 3, 4, 6 or 8). The hydrous matrix showed two mass loss steps from the thermogravimetric curve, corresponding to the release of physisorbed and lattice water molecules. For the intercalated matrices a third mass loss was observed due to the release of organic moiety. From these values, the amine intercalated matrices can be ordered in the following sequence of thermal stability; C4>C2>C3≅C6>C8. Kinetic studies were carried out to the release of lattice water molecules. The kinetic model that best adjusted the experimental isothermal TG data was the diffusion mechanism controlling process. This revised version was published online in July 2006 with corrections to the Cover Date.