Characterisation of polysilanes by thermal analysis methods

Polysilanes have been synthesised as potential precursors for silicon carbide fibres. One critical property of these precursors is the ceramic yield obtained on pyrolysis. This is determined by TG and typical curves are shown. A second important property is the suitability for spinning a fine, flexible fibre. The characterisation of ‘spinnability’ is subjective but one of the aims of this work has been to define more precisely the temperature at which to attempt spinning. This has involved the use of TMA and DSC.     

Industrial standardization of thermal analysis in Japan

To satisfy the needs for industrial standards for thermal analysis in the Japanese polymer industry, round-robin tests of differential scanning calorimetry (DSC), thermogravimetry (TG), thermomechanical analysis (TMA) and thermodilatometry (TD) have been carried out recently. The results are discussed in this short review. The DSC applications tested were not only for determination of transition temperature but also for measurements of the transition heat and heat capacity. The TG task group did not aim at longterm thermal endurance studies, but relative thermal stability in molding and estimation of filler content, residual solvent content, etc. TMA was found to be a useful tool for measuring softening temperature and heat distortion temperature, especially for high-temperature engineering plastics, instead of the Vicat test which has temperature limitations. For temperature calibration of DSC and TG, ICTA-NIST certified reference materials were used together with other potential temperature standards; some inorganic substances and alloys were not found to be preferable to pure metals. For TMA and TD metal plates were found to be very useful for temperature calibration. Analysis of the round-robin test results also clarified present status of practical applications of thermal analysis, such as reproducibility and causes of errors. Plenary lecture     

Thermomechanical analysis (TMA) correlated to differential scanning calorimetry (DSC) for ageing study of some metallic glasses

To characterize the ageing of some metallic glasses, a correlated study of the differential scanning calorimetry method (DSC) and of the thermomechanical analysis (TMA) emphasizes the specificity of the latter. We analyzed metallic glasses which have been produced either by chemical methods or by melt spinning techniques. Using TMA and DSC, we have established that the relaxation of metallic glasses is strongly dependent on treatment applied: either thermal or mechanical history. Conversely, we do not observe large differences between DSC and TMA analysis for the crystallisation. From experimental data, we try to modelize the behaviour of this type of materials under operating conditions.The authors wish to thank Dr. H. Warlimont, Dr. Hilzinger and Dr. G. Herzer of Vaccumschmelze GmbH (Hanau F.R.G), Dr. E. Illekova and Dr. P. Duhaj of Institute of Physics (Bratislava, Tchecoslovaquie) for the scientific collaboration during which the melt spinned metallic glasses were supplied.     

Thermal properties of a polyimide fiber

A commercially available polyimide fiber was investigated as a possible precursor for the formation of carbon fibers. The thermal response of the fiber was thoroughly investigated using DSC, TMA and TG. These responses were dependent on the atmosphere and tension during scanning. The fiber was stabilized at high temperatures both in inert and oxidative environments and the effect of these stabilization treatments on the structure and properties of the fiber was carefully followed. During heating, the fiber showed shrinkage tendency at small tensions, but at higher tensions the fibers could be stretched. Among the two environments investigated, air was more effective than nitrogen in getting a more stable fiber.The authors would like to acknowledge the Graduate School of the University of Tennessee, Knoxville for financially supporting this work and Lenzing USA Corporation for providing the fiber samples.     

Application of thermal analysis methods for characterization of polymer/montmorillonite nanocomposites

Thermal analysis is a useful tool for investigating the properties of polymer/clay nanocomposites and mechanisms of improvement of thermal properties. This review work presents examples of applications of differential scanning calorimetry (DSC), modulated temperature differential scanning calorimetry (MT-DSC), dynamic mechanical thermal analysis (DMA), thermal mechanical analysis (TMA), thermogravimeric analysis (TG) and thermoanalytical methods i.e. TG coupled with Fourier transformation infrared spectroscopy (TG-FTIR) and mass spectroscopy (TG-MS) in characterization of nanocomposite materials. Complex behavior of different polymeric matrices upon modification with montmorillonite is briefly discussed.     

Modification of wool fiber using steam explosion

Wool fiber was modified by steam explosion in this study. SEM results show that some scales on the fiber surface were cleaved and tiny grooves generated during the explosion. FTIR results suggest no evident changes in the chemical composition of the fiber after the explosion treatment. However, the crystallinity of the fiber decreased slightly as the steam pressure increased based on the X-ray results. In the thermal analysis, DSC results show that the temperature corresponding to vaporization of absorbed water and cleavage of disulfide bonds respectively decreased as the steam pressure increased. The reduction in thermal decomposition energy of the treated fiber indicates that steam explosion might have destroyed some crystals and crosslinks of macromolecular chains in the fiber. The treatment also led to some alterations of the fiber properties, including reduction in strength, moisture regain and solubility in caustic solution.     

Thermal analysis of the rice and by-products

The thermogravimetry (TG) is a technique used in the quality control of foods. In this work the moisture and ash contents in the rice and by-products (bran and husk), the thermal stability and the gelatinization process by conventional, thermogravimetric and calorimetric methods were studied. The moisture and ash contents obtained by TG and conventional methods did not present significant differences. The rice presented higher starch content, while the bran presented higher protein content. The thermogravimetric data presented the following thermal stability order: rice>bran>husk. The calorimetric curves indicated the gelatinization of the starch. The kinetic parameters were compatible. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermoanalytical characterisation of modified keratin fibres

In the wool textile industry, several processes serve to improve the commercial properties of the fibres such as fineness, softness, length, strength and lustrous. For example, wool is chemically treated with reductive agents then stretched and set. This leads to modifications of the original protein structure causing changes in thermal behaviour, dyeing, colouristic and wet resistance properties. A multidisciplinary approach was used to investigate treated and untreated wools, with the aim of exploiting the nature of the structural changes. SEM and TEM revealed changes on the cuticle and cortical cell morphology; structure modification were studied by FT-IR and DSC. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal transitions in PHEA hydrogels by thermomechanical analysis. A comparison with DSC data

The thermal transitions observed in hydrogels are frequently explained by invoking the existence of different kinds of water such as ‘bound’ and ‘free’ water. However these interpretations are intuitive and do not consider neither the thermodynamics of phase equilibrium nor kinetic aspects. Alternatively, the complicated experimental DSC thermograms have been simply explained in a thermodynamic framework with the help of a transitions diagram where the temperature of the transitions is plotted versus water concentration in the gel. In this work we further support the interpretation of the DSC thermograms on the basis of this diagram by comparing those thermograms with TMA results. The volume changes in the cooling and heating scans can be correlated with the enthalpy changes in the material and can be explained with the transition diagram.     

Modulated-Temperature Thermomechanical Analysis of Fibres

The application of modulated temperature programming to thermomechanical analysis affords a method for measuring the ‘true’ thermal expansion coefficients of materials that deform irreversibly during normal TMA. This may arise from creep under the applied load or changes in dimensions due to relaxation of orientation. Acrylic fibres made with various degrees of orientation shrink to different extents on heating but all show the same ‘true’ thermal expansion coefficients using this approach. The application of modulated temperature programming to Dynamic Mechanical Analysis is also discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

正二十二烷醇的热力学性质

用精密自动绝热量热仪测定了广谱抗病毒药物正二十二烷醇在78-400 K温区的热容. 根据实验测定的热容数据, 用最小二乘法拟合计算出热容对温度的多项式方程, 得到其相变温度、相变焓、相变熵分别为340.844 K、85.07 kJ·mol-1、249.6 J·K-1·mol-1. 根据热力学函数关系式计算了其在80-400 K温区每隔5 K的热力学函数[HT-H298.15]和[ST-298.15]. 用DSC、TG热分析技术进一步考查了该物质在400-900 K的热稳定性.     

Fractional analysis of technical polyoxaalkyl borates by TG

Results of preliminary thermoanalytical investigations (DSC/TG) of polyoxaalkyl esters of boric acid are presented. One aim of these investigations was the development of a method of characterization of the technical esterificate. The optimum parameters of quantitative thermogravimetric analysis of boric acid esters and the excess of polyoxaalkanols were assumed. The precision and accuracy of the developed method are discussed.     

生物降解材料胆酸-乳酸共聚物的热性能研究

通过直接熔融共聚法合成了系列的不同乳酸／胆酸组成比（LA／CA）的胆酸．乳酸共聚物,用DSC、TG等手段研究生物降解材料胆酸-乳酸共聚物的热性能。结果表明,共聚物的热性能与其组成、结构有关。LA／CA小的多核共聚物无明显熔融峰,热失重分两步进行;LA／CA大的单核共聚物出现明显双头熔融峰,其热失重一步进行,其Tg随着LA／CA增加而升高。     

Effect of the air-jet and the false-twist texturing processes on the thermomechanical behaviour of polyamide 6.6 yarns

Polyamide 6.6 multifilament yarns are converted to crimped fibres by texturing in order to simulate the properties of natural staple fibre yarns for textile applications. Texturing is carried out by mechanical stresses (turbulences or twisting) in different atmospheres which affect crystallinity and thermal stability of yarns. Two polyamide yarns with the same linear density but consisting of filaments of different fineness were textured by the air-jet and the false-twist procedures. The influence of texturing conditions and filament fineness on crystallinity and thermomechanical behaviour and dimensional stability were studied by TMA and DSC. The air-jet texturing procedure leads to a slight increase in crystallinity of yarns whereas the false-twist texturing procedure was more effective especially when thicker filaments were textured. The inflection point of the shrinkage curve before melting was a good estimator of the effective temperature of yarn texturing.     

Thermomechanical Analysis of Polysaccharide Hydrogels in Water

Application of thermomechanometry to the measurement of hydrogels containing a large amount of water was carried out by static and dynamic methods. A thermomechanical analyzer (TMA) equipped with a quartz compression probe immersed in water was used. Polysaccharide hydrogels containing ca 98% water were measured. Creep of hydrogels in water was analyzed in a stress range from 1.04⋅10³ to 5.2⋅10³ Pa and loading rate from 0.3⋅10³ to 3.0⋅10³ Pa min⁻¹.Stress relaxation was measured in compressed ratio range from 0.02 to 0.45 m m⁻¹ and in compressing rate was 0.09 to 0.15 m m⁻¹ min⁻¹. Dynamic viscoelasticity was measured by TMA when dynamic Young’s modulus which was larger than 1⋅10⁴ Pa in frequencies ranging from 0.02~0.2 Hz. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal analysis of polyesters containing oxirane groups

The preliminary studies of the thermal behaviour of polyester obtained in polycondensation process of cyclohex-4-ene-1,2-dicarboxylic anhydride and ethylene glycol and its new epoxidized form have been performed. The thermal characterization of initial polyester and its completely oxidized form was done by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The non-isothermal DSC was applied to determine the influence of time and the temperature on the chemical modification of initial polyester using 38-40% solution of peracetic acid. On the basis of DSC profiles it has been found that the endothermic transition, due to the degradation process of initial polyester was characteristic feature under controlled heating program. The two characteristic transitions for the new epoxidized polyester, the exothermic peak corresponded to the thermal crosslinking of epoxidized polyester (322.8–336.4°C) and the endothermic decomposition peak of the cured material (363.8–388.9°C) were observed. The peak maximum temperatures (Tmax) and the heat of cross-linking reaction (ΔH_c) for epoxypolyester prepared at 20–60°C under 1–4 h were evaluated. The Tmax1 were almost independent from epoxidation conditions, while, the values of ΔH_c were dependent from conditions of synthesis. The ΔH_c values of this process decreased when time of oxidation increased. The highest values of ΔH_c at 40°C were obtained. Additionally, TG experiments confirmed two separated degradation steps of the new epoxidized polyester indicating the ester (370–380°C) and ether (450–460°C) bond breakdown.     

Thermal Characteristics of Australian Sedimentary Opals

Naturally occurring opals from three different regions in Australia were studied for their thermal characteristics. All the opals showed initial expansion followed by contraction in thermomechanical analysis (TMA) although the temperature at which the change from expansion to contraction occurred depended on their provenance. Thermogravimetric analysis (TG) revealed different rates and temperatures of dehydration for these opals. A general correlation between the temperature at which there was a zero thermal expansion and that of the maximum rate of dehydration was observed. A dehydration–sintering mechanism is proposed with the effect of sintering being more pronounced following total dehydration. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal analysis study of the effect of coal-burning additives on the combustion of coals

Thermal analysis is widely used in combustion research for both fundamental and practical investigations. Efficient combustion of coals in cement industry is very important and necessary. In this research, the effects of three coal-burning additives on burning behaviour of bituminous coal and anthracite were studied with the help of thermogravimetry (TG) and differential scanning calorimetric (DSC) analysis. The kinetic study was carried out and the results were presented. The results showed that the coal-burning additives especially LSZ can reduce the ignition temperature, increase the ignition index D _i, combustion ending index D _f and affect the activation energy of the coal samples studied. The coal-burning additives especially LSZ can improve coal combustion effectiveness.     

Thermal analysis of goethite

Differential scanning calorimetry shows two endotherms at 75 and 225°C for synthetic goethite. The latter endotherm is strongly asymmetric on the low temperature side. The endotherms were attributed to the loss of water and the dehydroxylation of the goethite. The temperature of the endotherms and the enthalpy of the phase change were found to be linear functions of the percentage of aluminium substitution into the goethite. High-resolution thermogravimetric analysis of goethite showed three mass loss steps, occurring at ~175, 196 and 263°C. The temperatures of these mass loss steps and the percentage of mass loss were also linearly related to the degree of Al substitution. The use of infrared emission spectroscopy confirmed the temperature of dehydroxylation. The observation of the low temperature dehydroxylation of goethite and its relation to ancient aboriginal cave art is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Melting behaviour and evolved gas analysis of xylose

Two enantiomeric forms of xylose were identified as α-D-xylopyranose and α-L-xylopyranose by powder diffraction. Their melting behaviour was studied with conventional DSC and StepScan DSC method, the decomposition was studied with TG and evolved gases were analyzed with combined TG-FTIR technique. The measurements were performed at different heating rates. The decomposition of xylose samples took place in four steps and the main evolved gases were H₂O, CO₂ and furans. The initial temperature of TG measurements and the onset and peak temperatures of DSC measurements were moved to higher temperatures as heating rates were increased. The decomposition of L-xylose started at slightly higher temperatures than that of D-xylose and L-xylose melted at higher temperatures than D-xylose. The differences were more obvious at low heating rates. There were also differences in the melting temperatures among different samples of the same sugar. The StepScan measurements showed that the kinetic part of melting was considerable. The melting of xylose was anomalous because, besides the melting, also partial thermal decomposition and mutarotation occurred. The melting points are affected by both the method of determination and the origin and quality of samples. Melting point analysis with a standardized method appears to be a good measure of the quality of crystalline xylose. However, the melting point alone cannot be used for the identification of xylose samples in all cases.