Studies on thermal degradation of benzylidene malononitriles

Thermal decomposition studies have been carried out using flash vacuum thermolysis (FVT) to find out the decomposition temperature for benzylidene malononitriles (BMNs) including 2-chlorobenzylidene malononitrile (cs), a widely used riot control agent. The FVT studies have been carried out in a specially designed all glass assembly at various temperatures ranging from 300 to 600°C. A number of rearranged products along with hydrogen cyanide were obtained as major decomposition products. The products were analysed and the structures were confirmed by GC/MS. the thermal behaviour of BMNs has also been investigated by TG under nitrogen atmosphere. These studies show that the pyrotechnic mixture for tear gas munitions should not have burst temperature above 300°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fuel cell catalyst degradation on the nanoscale

A newly developed methodology for examining fuel cell catalyst degradation is introduced. In contrast to the conventional, destructive TEM investigation procedure, this methodology enables the observation of corrosion processes of the same catalyst region repeatedly. In particular we demonstrate the impact of a potential cycling treatment on a carbon-supported platinum catalyst, and propose a new corrosion mechanism for fuel cell catalyst degradation. Under the applied harsh conditions, whole Pt particles detach from the support and dissolve into the electrolyte without re-deposition.     

The effect of fullerene on the resistance to thermal degradation of polymers with different degradation processes

Investigations were made about the effect of fullerene (C₆₀) on the resistance to thermal degradation of high density polyethylene (HDPE), polypropylene (PP), polymethyl methacrylate (PMMA), and bisphenol A polycarbonate (PC) matrix by using thermogravimetric analysis coupled to Fourier transform infrared spectroscopy. The results showed that the influences of C₆₀ on the resistance to the thermal degradation of different polymers were dependent on their thermal degradation mechanism. The resistance to the thermal degradation of HDPE, PP, and PMMA were improved with the addition of C₆₀, especially for HDPE matrix, which indicated that the radical trapping played a dominant role. PP and PMMA released more gaseous products at high temperature by the random scission of C–C backbone; owing to the lower bond dissociation energy of C–C in the backbone for the existence of side chains. Meanwhile, the steric hindrance of side chains also made the radicals hard to recombine with each other and accelerated the random scission, leading to the less effect on the resistance to the thermal degradation of PP and PMMA. However, few changes of resistance to the thermal degradation were found in PC matrix with the addition of C₆₀ for its non-radical degradation mechanism.     

Thermal degradation of polyimides—I. Investigation of the role of isoimide structure on degradation process

The structures of isoimide cycles in polyimides were elucidated from i.r. and ¹³C NMR spectra of N-phenylphthalimide and N-phenylphthalisoimide. Using i.r. and gas-chromatographic data, conversion of isoimide cycles to the imide form was studied as a function of temperature. This process is irreversible, precluding the presence of the isoimide form at high temperature.     

Study on oxidative degradation behaviors of polyesterurethane network

In this study H₂O₂/CoCl₂ system was used as an oxidative environment to investigate the in vitro degradation behavior of a crosslinked polyesterurethane network. Weight loss, water absorption, mechanical properties, swelling degree and gel content were determined as a function of degradation time. The results showed that the H₂O₂/CoCl₂ system could effectively accelerate the degradation of the polyurethanes. The samples had almost completely degraded after 84 days of incubation in a 3% H₂O₂/2% CoCl₂ solution at 37 °C. The weight loss process could be approximately divided into three major phases: the weight decreased slowly during an induction phase (1), which was followed by a phase characterized by accelerated weight loss (2), and finally by a phase showing slow linear weight loss until complete erosion (3). The attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra of degraded polyurethane networks showed that the polyurethane underwent chain scission of the copolyester segment chains, and the joints of copolyester and 2,2,4- and 2,4,4-trimethylhexamethylene during degradation in the oxidative environment. The glass transition temperature of degraded polyesterurethane networks decreased significantly with increasing degradation time. From these results the H₂O₂/CoCl₂ system can be used as an oxidative condition to evaluate the in vitro degradability of polyesterurethane.     

超声波降解吡啶溶液

焦化厂的排污水中含有酚、氰、杂环化合物(吡啶、吲哚、喹啉等)等有害物质[1]。利用超声波的声空化作用降解有机污染物,是一种清洁、高效的新型处理方法[2]。本文研究了超声波降解吡啶模拟焦化废水。探讨了吡啶初始浓度、溶液pH、超声辐射时间及处理温度等对降解效果的影响及规律。1　实验部分1 1　实验仪器及试剂KQ 100型超声波发生器,昆山市超声波仪器厂;SG 600W型超声波清洗器,张家港超声仪器有限公司;PHS 3C型酸度计,萧山市凯利科学仪器有限公司;751G紫外/可见分光光度计,上海分析仪器厂;DDS 11A型电导率仪,上海雷磁新泾仪器…     

Thermal degradation studies on some metal hydrazinic complexes

The paper deals with the characterization of three hydrazinic complexes with Ni, Cu and Cr respectively, by means of non-isothermal thermal methods, TG, DTG and DTA, under nitrogen atmosphere in order to investigate the structure-thermostability-thermal degradation mechanism correlation. The thermal analysis made evident the degradation mechanisms characteristic of every sample in accordance with the chemical structure. The quantitative analysis by TG-DTG afforded the estimation of the metal amount in the complex on the basis of the resulting metallic oxide nature as well as of some aspects of the thermal degradation mechanism supported by mass spectral measurements. The melting points given by DTA and confirmed by the Boetius method and the initial temperatures of thermal degradation from TG-DTG-DTA afforded to ascertain the temperature range proper for using and storing the complexes under study which show potential practical applications as drugs.     

聚苯乙烯热降解机理的理论研究

采用密度泛函理论B3LYP/6-311G（d）方法,对聚苯乙烯（PS）热降解反应机理进行了研究。PS热降解的主要产物是苯乙烯,其次是甲苯、α-甲基苯乙烯、乙苯和二聚体等芳烃化合物。PS热降解反应主要包括主链C-C键均裂、β-断裂、氢转移和自由基终止等反应。针对以上各类反应进行了路径设计和理论计算分析,对参与反应的分子的几何结构进行了优化和频率计算,获得了各热降解路径的标准动力学和热力学参数。计算结果表明,苯乙烯主要由自由基的链端β-断裂反应形成;二聚体主要由分子内1,3氢转移的反应形成;α-甲基苯乙烯由分子内的1,2氢转移后进行β-断裂形成;甲苯由苯甲基自由基夺取主链上的氢原子形成;乙苯由苯乙基自由基夺取氢原子形成。动力学分析表明,苯乙烯形成所需要的能垒低于其他产物形成所需要的能垒,故苯乙烯为主要的热降解产物;这与相关实验结果基本一致。     

Boundary effect on the thermal degradation of copolymers

The mechanism of thermal degradation of vinyl-type copolymers at high temperatures was investigated theoretically and experimentally. A parameter β was proposed to account for the boundary effect. Values of β for acrylonitrile–styrene and methyl methacrylate–styrene copolymers were determined experimentally. It was ascertained that the value of β was independent of the distribution of monomer sequence lengths in a copolymer, but dependent on the pyrolysis temperature and on the nature of the copolymer. The boundary effect is attributed to differences in the dissociation energies of C? C bonds connecting terminal monomer units to adjacent monomer units in copolymer chain radicals.     

Effect of clay organomodifiers on degradation of polyhydroxyalkanoates

Ammonium surfactants are commonly used as clay organomodifiers in nanocomposites. Their effect on the thermal- and thermo-mechanical degradation of polyhydroxyalkanoates (PHAs) is reported. Two poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) grades were tested and compared to polyhydroxybutyrate (PHB). Thermal stabilities were determined from thermogravimetric data and determination of molecular weight changes after processing was performed. The data revealed that all surfactants enhance the PHBV degradation. The results also highlight the preponderant effect of the initial M_w rather than the HV content on the thermal stability. The thermo-mechanical study confirmed the role of surfactants and their different behaviour towards PHBV degradation. This study demonstrates that all surfactants enhance the PHA degradation since their decomposition products most likely act as catalytic agents.     

光电催化降解模拟工业染色废水的研究

印染废水毒性大、组分比较复杂、可生化性差,大部分有机物质多具有致癌、致畸、致突变的作用[1-5],常规的处理方法对印染废水的处理效果并不理想[6].     

New findings on thermal degradation properties of fluoropolymers

In this paper, the thermal degradation properties of Viton A and Fluorel are investigated by both isoconversional and combined kinetic analysis methods using non-isothermal thermogravimetry technique. It has been found that the heating rate has little affect on the degradation residue of Fluorel and Viton A, where around 1.3% char was formed for Fluorel and 3.5% for Viton A. Different from the literature, the decomposition of Viton A should be considered as an overlapped dehydrofluorination and carbon chain scission process, with activation energy of 214 ± 11 and 268 ± 13 kJ mol^?1, respectively. The effect of dehydrofluorination on degradation of Fluorel is not so significant due to low content of H, and hence, it could be considered as a single-step mechanism with average activation energy of 264 ± 14 kJ mol^?1. The thermal stability of Fluorel is much better than that of Viton A, and the predicted half-life is around 218 min for Fluorel and 49 min for Viton A at 420 °C, which are consistent with experimental values. If using a single-step model as in the literature for Viton A, its half-life at 420 °C would be underestimated for >20%.     

Thermal degradation of polyurethanes based on xylylene diisocyanates

Polyurethanes derived from xylylene diisocyanates and trans-1,4-cyclohexanedimethanol were thermally degraded by using the techniques of thermogravimetry and pyrolysis at atmospheric pressure. Quantitative determination of the pyrolysis products such as CO₂, diamine, olefin, and starting diol showed that these polyurethanes follow the typical mechanism of degradation via dissociation into starting diol and diisocyanate. Kinetic parameters for the overall degradation reaction were determined using four different methods. The results showed the influence of the experimental technique used when making a comparison of the thermal stability of polymers, as determined by the kinetic parameters of the degradation reactions.     

Studies on degradation of PET in mechanical recycling

PET Poly(ethylene terephthalate) was processed repeatedly in a twin extruder. Effect of reprocessing on molecular structure of PET was evaluated in terms of reduction in molecular weight and mechanical properties. This study shows that weight-average molecular weight M_w drops more notably compared with mechanical properties. Mechanical blending of virgin polymer with recycled PET was studied. The results of mechanical testings indicate that there is only slight loss in mechanical properties. The results suggest that mechanical recycling is a suitable method for recycling of PET for economic and environmental purposes.     

Theoretical studies on the degradation of ladder polymers

The random degradation of four- and six-membered ring ladder polymers was simulated on a digital computer by utilizing a Monte Carlo model. The degradation was compared with that of a single-chain linear polymer undergoing an identical degradation reaction. Significant differences in the change in molecular weight as a function of time were noted between the ladder polymer and the single chain polymer. Similar studies were conducted with imperfect ladder polymers which had occasional missing bonds in the ladder structure. These imperfections produced a marked drop in molecular weight at a given time compared with the perfect ladder polymer.     

The effects of microbial degradation on ignitable liquids

The identification of ignitable liquid residues in fire debris is a key finding for determining the cause and origin of a suspicious fire. However, the complex mixtures of organic compounds that comprise ignitable liquids are susceptible to microbiological attack following collection of the sample. Biodegradation can result in selective removal of many of the compounds required for identification of an ignitable liquid. Such degradation has been found to occur rapidly in substrates such as soil, rotting wood, or other organic matter. Furthermore, fire debris evidence must often be stored for extended periods at room temperature prior to analysis due to case backlogs and available evidence storage. Hence, extensive damage to ignitable liquid residues by microbes poses a significant threat to subsequent laboratory work. In this work, the effects of microbial degradation of ignitable liquids in soil have been evaluated as a function of time. Key findings include the loss of n-alkanes, particularly C₉–C₁₆, which showed the most dramatic decrease in gasoline as well as the petroleum distillates, while branched alkanes remained unchanged. Monosubstituted benzenes also showed the most dramatic loss in gasoline. In the heavy petroleum distillates, n-alkanes with even carbon numbers were degraded more than n-alkanes with odd carbon numbers. Figure A “fully involved” house fire in Indianapolis, IN

Isothermal degradation and thermooxidative degradation of an epoxy powder coating

Summary Thermogravimetry was used to study the kinetics of isothermal degradation of an epoxy thermoset powder coating in a nitrogen atmosphere and in oxidizing atmospheres of air and pure oxygen. An integral isoconversional procedure was used to analyse how the activation energy varies depending on the degree of conversion and depending on the atmospheres used. In the case of degradation in a nitrogen atmosphere, in addition to the activation energy, the kinetic triplet was completed using an Avrami reaction model and the pre-exponential factor. With this atmosphere, the conclusion was reached that the isothermal and non-isothermal kinetics are equivalent. It was shown that the thermooxidative degradation process is more complex and consists of a two-stage process. The first stage of degradation is similar whether nitrogen, oxygen or air are present. Chain scission occurs and it seems that there is formation of thermally more stable compounds. The second stage of degradation, involving several phenomena, occurs only in the presence of oxygen or air and leads to the total disappearance of the organic material by thermooxidation. These stages are very similar under non-isothermal or isothermal conditions.     

A degradation study of waterborne polyurethane based on TDI

The thermal degradation of synthetic waterborne polyurethane (PU) based on toluenediisocyanate (TDI) was investigated by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermogravimetry (TG). The degradation profiles of cast films obtained from dispersions were evaluated. More than 20 characteristic volatile pyrolyzates reflecting the structure and pyrolysis mechanisms of the polymer have been identified by on-line MS. The synthesized products of polyurethane were pyrolyzed at 350, 450, 550, 650 and 750 °C respectively, and the analysis results revealed that the pyrolyzates distribution of the polyurethane depends strongly on the pyrolysis temperature. The aqueous polyurethane thermogravimetric measurements were used to study the kinetics of thermal degradation.     

Studies on simulated ageing of paper by photochemical degradation

The study of the ageing of two paper types was performed on monitoring it during a simulated process by means of the measure of the photocatalytic degradation of the paper cellulose. Such evaluation was possible due to the combined responses of a photosensor based on titanium dioxide in suspension, of an enzymatic biosensor based on superoxide dismutase (SOD), of a specific conductivity sensor and of an enzymatic biosensor based on glucose oxidase.     

Effect of fungal degradation on mechanical properties of cellophane

Changes in dynamic mechanical properties of cellophane films due either to fungal attack or to hydrochloric acid hydrolysis have been measured. It appears that damage caused by cellulase enzymes that are released from a fungal overgrowth is localized in noncrystalline regions. These effects include a substantial reduction in elastic modulus, a reduction in temperature at which relaxation processes involving chain segmental mobility occur, and a broadening of loss tangent peaks due to segmental mobility and to rotations of methylol groups. Comparing results obtained from cellulase hydrolysis with those obtained from acid hydrolysis, it is clear that enryme attack proceeds by a characteristic and selective process. Implications regarding the embrittlement often seen to accompany biodegradation are discussed.