Polycaprolactone/polystyrene bioblends characterized by thermogravimetry, modulated differential scanning calorimetry and infrared photoacoustic spectroscopy

Polymer blends comprising at least one biodegradable polymer with other polymers are referred to as bioblends. Successful development of bioblends requires the biodegradable polymers to be compatible with other polymer components. Compatibility is normally assessed through the evaluation of the degree of intermolecular interactions between individual components. In this work, the degree of interaction in binary bioblends comprising biodegradable polycaprolactone (PCL) and polystyrene (PS) was investigated using thermogravimetric analysis (TGA), modulated differential scanning calorimetry (MDSC) and Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS). The TGA studies indicated that incorporation of PCL in PS results in thermal destabilization of PCL/PS bioblends. The MDSC studies showed that some parameters, such as the enthalpies of melting and crystallization, favored partial miscibility of PS in PCL, while others, such as change in the glass transition temperature, favored immiscibility. The FTIR-PAS spectra suggested the presence of intermolecular n-π interactions between PCL and PS and supported the results of TGA and MDSC analyses of PCL/PS bioblends.     

Spectroelectrochemical studies of magnesium deposition by in situ FTIR spectroscopy

Magnesium can be reversibly deposited electrochemically from solutions of ethereal solvents, with Grignard reagents (RMgX) or complexes of Mg(AX_3−nR_n+1)₂ stoichiometry as the electrolytes (A=Al, B; X=Cl, Br; R=alkyl or aryl groups). These processes are far from being simple reactions of the Mg/Mg⁺⁺ couple, since the above electrolytes in solutions have complicated structures in which the ether molecules play an important stabilization role. In addition, Mg deposition processes in all of the above solutions are accompanied by adsorption phenomena. The surface chemistry of magnesium electrodes was studied in situ by FTIR spectroscopy, using an internal reflectance mode. The electrolyte solutions studied included tetrahydrofuran (THF) solutions of the RMgX electrolytes (R=butyl, ethyl, methyl benzyl, and X=Cl, Br); Mg(AlCl₂BuEt)₂; Mg(AlCl₃Bu)₂ and Mg(BPh₂Bu₂); Bu, Et, Ph=butyl, ethyl and phenyl groups, respectively. It was clear from these studies that Mg electrodes do not develop stable passivation in these solutions (i.e. formation of surface films). The nature of the adsorbed species in the above systems is discussed, based on the spectral results.     

Human cytokines characterized by dielectric thermal analysis, thermogravimetry, and differential scanning calorimetry

Malaria affects over 500 million people worldwide leading to 1–2 million deaths each year, the majority of whom are children. Four Plasmodium species cause malaria in humans. To properly diagnose, and correctly treat malarial infections, accurate diagnosis of infection is required. Proper diagnosis of infection will result in a reduction of morbidity, mortality, and of drug resistant parasites. However, the current tests for malaria diagnosis do not efficiently identify the appropriate human and parasite biomarkers associated with disease. Detection of specific inflammatory mediators such as cytokines associated with malaria pathogenesis will aid the determination of disease progression, disease prognosis, and the early diagnosis of malaria infection. In this study, we used dielectric thermal analysis (DETA), thermogravimetric analysis, and differential scanning calorimetry (DSC) to characterize five human cytokines (IL-1α, IL-2, IL-4, IL-6, and IL-10), to demonstrate how their thermoanalytical properties can be investigated for sensor design. Analysis for DETA was performed at a frequency range of 0.1–300,000 Hz. Permittivity and loss factor measurements were used to calculate tan δ values. Peak frequencies were used to determine dielectric signatures for each cytokine. The peak frequencies were different for each cytokine analyzed. In addition, activation energies were frequency dependent for IL-2 but frequency independent for the remaining four cytokines. Cytokines were also examined using DSC which established variance in heat of crystallization and heat of fusion of solvent among the five cytokines. A noticeable differentiation was observed with IL-1α among the other four cytokines when analyzed using trend analysis. Detection of unique dielectric signals will aid development of sensitive dielectric sensors capable of detecting cytokines in various human samples.     

Near-critical CO2 in mesoporous silica studied by in situ FTIR spectroscopy

Attenuated total reflection Fourier transform infrared spectroscopy was used to correlate the band shift of the nu2 vibrational band of carbon dioxide with the density of the fluid. Upon adsorption of CO2 on mesoporous silica and a nonporous SiO2 film, additional bands were detected due to interactions of CO2 with SiO2. Near the saturation pressure for the porous samples, the absorbance of the nu2 band increased strongly, which was concluded to be caused by liquidlike CO2 inside the pores. Integration of single-beam-sample-reference spectra between bulk CO2 and CO2 adsorbing on the mesoporous silica coated on one part of the internal reflection element revealed excess adsorption type isotherms with sharp maxima at 21 degrees C. A flatter curve shape could be observed at 25 degrees C, which allowed estimating the pore critical temperature. Moreover, the density of the fluid inside and outside the pores could be compared. Over the investigated ranges of pressure, temperature, and pore size, the results evidenced that the CO2 density was always higher in the silica pores than in the bulk, even under supercritical conditions. This has important consequences on the pressure dependence of dissolution power and diffusivity of fluids in mesoporous solids. An overview is given on the influences of fluid phase behavior in the bulk and in the pores at various conditions on solubility and diffusivity.     

In situ high pressure study of ZIF-8 by FTIR spectroscopy

ZIF-8 as a promising storage material was investigated at high pressures up to ~39 GPa by in situ FTIR spectroscopy for the first time. Structural modifications are found to be reversible in a low-pressure region but irreversible in a high-pressure region. Overall, the ZIF-8 framework exhibits an unusual chemical stability even under extreme compression.     

丙三醇在Pt电极上吸附和氧化过程的原位FTIR反射光谱研究

运用电化学循环伏安(CV)和原位FTIR反射光谱方法, 研究了丙三醇在Pt电极上的氧化过程。结果指出, 丙三醇的氧化是一个复杂的表面过程。其间包括脱水、吸附、解离等步骤。根据CV和红外实验数据, 本文提出了Pt电极上丙三醇解离吸附的表面反应机理和不同电位下丙三醇氧化的分子过程。     

Hydration studies of modified OPC pastes by differential scanning calorimetry and thermogravimetry

Thermal methods are used extensively in investigating cements and effects of additives on their hydration behaviour. Calcium chloride is the most effective and widely used accelerator for cement hydration, but the result is largely dependent on the rate at which it is added. In this study the influence of calcium chloride dosage on the hydration behaviour of OPC pastes aged for different periods has been investigated by means of differential scanning calorimetry (DSC), thermogravimetry (TG) and X-ray diffraction (XRD) methods. The results are discussed in relation to the relative amounts of calcium hydroxide and total reaction product formed. Chloroaluminate was a product of hydration in the samples dosed with greater than 1% calcium chloride. XRD was unable of itself to differentiate between monochloroaluminate and the calcium aluminate hydrate C₄AH₁₃ when present in small amounts. Thermal methods proved effective in characterising the products of hydration in the presence of chloride.

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Zusammenfassung Bei der Untersuchung von Zement und des Einflusses von Additiven auf das Hydratationsverhalten von Zement finden thermoanalytische Methoden eine breite Anwendung. Der effektivste und meistbenutzte Beschleuniger für die Hydratation von Zement ist Calciumchlorid, aber die Ergebnisse hängen stark von der Dosiergeschwindigkeit ab. In vorliegender Studie wird mittels DSC-, TG- und Röntgendiffraktionsmethoden der Einflu\ der Dosierung von Calciumchlorid auf das Hydratationsverhalten von verschieden alten OPC-Zementbreiproben untersucht. Die Ergebnisse wurden in Bezug auf die relativen Mengen Calciumhydroxid und das gebildete Gesamtreaktionsprodukt gewertet.Bei Dosen von mehr als 1% Calciumchlorid konnte als Hydratationsprodukt Chloraluminat festgestellt werden. Sind Monochloraluminat und das Calciumaluminathydrat C₄AH₁₃ in geringen Mengen vorhanden, kann man zwischen den beiden mittels Röntgendiffraktion nicht unterscheiden. Thermoanalytische Methoden erwiesen sich als effektives Hilfsmittel bei der Charakterisierung der Produkte der Hydratation in Gegenwart von Chlorid.

     

Investigation of lithium niobate composition by optical spectroscopy methods

Indirect methods of investigation of composition and defect structures of lithium niobate (LiNbO₃) single crystals with different compositions are discussed. The analysis of two methods for the determination of the Li/Nb ratio in the samples is carried out, viz., the fundamental UV absorption edge and IR vibrational spectra of the OH⁻ group defects. Intrinsic defect concentrations in lithium niobate crystals (lithium vacancies, $ V_{Li^ - } $ V_{Li^ - } and defects, $ Nb_{Li^{4 + } } $ Nb_{Li^{4 + } } ) as a function of the Li/Nb ratio in the samples are given. The results obtained can serve as an effective way of express non-destructive composition analysis in a mass production of parallel-plane plates.     

Characterization of the surface hydrolysis of kevlar-49 fibers by diffuse reflectance FTIR spectroscopy

A modified diffuse reflectance technique is used to characterize the surface hydrolysis of Kevlar-49 fibers. Treatment with 10 wt% NaOH solution produces carboxylate groups on the surface which increase rapidly up to treatment times of about 20 min at room temperature or 50 min in boiling solution. After this maximum the carboxylate groups decrease and then level out. This behavior can be explained by considering the increase as due to hydrolysis of the surface amide groups, competing with the decrease due to removal of the extensively hydrolyzed, fragmented molecules into the treatment solution. Our results shows that mild conditions (10 wt% NaOH and room temperature) as well as relatively small treatment times (less than 20 min) can be used for modifying the surface of the Kevlar-49 fiber without destroying the skin and thus deteriorating the mechanical properties of the fiber.     

Investigation of biodeteriorated historical textiles by conventional and synchrotron radiation FTIR spectroscopy

We have examined specimens of historical biodeteriorated cellulose textiles using synchrotron radiation and conventional source FTIR spectroscopy. The main aim of our research was to investigate structural changes caused by ageing and biodeterioration in different types of cellulose fibres. We compared the results, obtained with both methods regarding spectral quality and information obtained with each method. Additionally, we obtained mapping images of the cross sections of the investigated specimens using synchrotron FTIR in order to analyze structural changes in cross sections, caused due to biodeterioration.     

Thermal investigations of the structure of two humic acid salts by in situ FTIR spectroscopy

Diffuse reflectance infrared Fourier-transformed (DRIFT) spectra of two humic sodium salts (ALDRICH, SERVA) have been recorded to study structural changes caused by heating. In situ investigations during the heating process has been accomplished by using a reaction chamber. The equilibrium of carbonate species dissolved in pore water (HCO ₃ ^– , CO ₃ ^2– ) has been studied. Decreasing OH and C=O band intensities and the formation of CO₂ and CH₄ have been observed. An increasing absorption of the band at 2170 cm^–1 indicates changes of nitrogen linkages in the molecule. Observable amounts of nitrile groups have been formed only at temperatures around 400°C.Dedicated to Professor Dr. H. Kriegsmann on the occasion of his 70th birthday     

Investigation of restriction endonuclease EcoRII complex with DNA in solution by FTIR spectroscopy

The X-ray structure of type IIE EcoRII restriction endonuclease has been solved but the structure of the R.EcoRII-DNA complex is still unknown. We report here on the structure of the pre-reactive R.EcoRII-DNA-Ca²⁺ complex in solution examined by FTIR spectroscopy. The secondary structure of R.EcoRII as well as the structure of the target DNA in the R.EcoRII-DNA-Ca²⁺ complex was characterized. It was shown that the R.EcoRII-DNA-Ca²⁺ complex formation is accompanied by changes in the spectrum of both DNA bases and DNA sugar-phosphate backbone that suggest contacts of the enzyme with different groups of atoms in DNA. The change of the R.EcoRII secondary structure in the R.EcoRII-DNA-Ca²⁺ complex is also observed.     

Reactivity of fly ash in cement paste studied by means of thermogravimetry and isothermal calorimetry

Four paste mixtures with varying replacement level of the cement content by fly ash have been studied. Due to fly ash, the acceleration period decreased and a third hydration peak was noticed with isothermal calorimetry. The total heat after 7 days increased with increasing fly ash content. From 1 to 7 days, thermogravimetry showed a higher chemically bound water and Ca(OH)₂-content for the pastes with fly ash. Between 7 and 14 days the calcium hydroxide started to be depleted due to the pozzolanic reaction. A unique relation was found between calcium hydroxide and total heat development.     

Study of the hydration of Portland cement blended with blast-furnace slag by calorimetry and thermogravimetry

The hydration of ordinary Portland cement (OPC) blended with blast-furnace slag (BFS) is a complex process since both materials have their own reactions which are, however, influenced by each other. Moreover, the effect of the slag on the hydration process is still not entirely known and little research concerning the separation of both reactions can be found in the literature. Therefore, this article presents an investigation of the hydration process of mixes in which 0–85% of the OPC is replaced by BFS. At early ages, isothermal, semi-adiabatic and adiabatic calorimetric measurements were performed to determine the heat of hydration. At later ages, thermogravimetric (TG) analyses are more suitable to follow up the hydration by assessment of the bound water content w _b. In addition, the microstructure development was visualized by backscattered electron (BSE) microscopy. Isothermal calorimetric test results show an enhancement of the cement hydration and an additional hydration peak in the presence of BFS, whilst (semi-)adiabatic calorimetric measurements clearly indicate a decreasing temperature rise with increasing BFS content. Based on the cumulative heat production curves, the OPC and BFS reactions were separated to determine the reaction degree Q(t)/Q _∞ (Q = cumulative heat production) of the cement, slag and total binder. Moreover, thermogravimetry also allowed to calculate the reaction degree by w _b(t)/w _b∞. The reaction degrees w _b(t)/w _b∞, Q(t)/Q _∞ and the hydration degrees determined by BSE-image analysis showed quite good correspondence.     

Thermal decomposition study of chloride-containing complex ammonium nitrate-based fertilizers by thermogravimetry and differential scanning calorimetry

Thermogravimetry and differential scanning calorimetry were used to study the thermal properties of chloride-containing complex ammonium nitrate-based fertilizers produced with various degrees of phosphoric acid ammonization on the basis of ammonium nitrate. Isoconversion integral methods were used to calculate the dependence of the activation energy on the degree of exothermic decomposition. It was shown that the exothermic decomposition process occurs in several stages. A conclusion was made on the basis of the results obtained that the thermal decomposition of these types of fertilizers is affected by the degree of ammonization and by the component ratio.     

Study of the clay effect on crude oil combustion by thermogravimetry and differential scanning calorimetry

Thermogravimetry (TG) and differential scanning calorimetry (DSC) were used to study the effect of sand, silica and kaolinite on crude oil combustion. Three distinct regions, namely distillation and two combustion/cracking regions were observed on all TG curves. Thermogravimetric curves were analyzed using an Arrhenius-type kinetic model and a ratio method to obtain kinetic parameters. Activation energy and reaction order were obtained from this analysis. The reaction order seemed to be insensitive to the presence of granular materials. However, a significant reduction of activation energy was caused by addition of kaolinite to the crude oil, indicating that the kaolinite had a catalytic and surface area effect on crude oil combustion/cracking reactions.     

甲醇是极氧化的现场FTIR透射差谱研究

利用现场透射红外差谱方法研究了在无水1mol/LiClO~4甲醇溶液中甲醇在Pt电极上的阳极氧化。实验采用了细网格Pt电极和薄层电解池。各电位下的FTIR透射差谱反映了溶液中电极反应的变化。结果表明甲醇可被氧化成甲醛,且随电位的提高可进一步氧化成甲酸甲酯。     

原位FTIR及探针反应法研究Pt与L沸石的相互作用

本文报道了一种适合催化研究的金属原位IR池,Pt分散在NH~4L沸石上呈缺电子性,在异丙醇分解反应中不显示脱氢活性,但通过加氢抗结炭作用保护着沸石上的酸位,从而增强了NH~4L沸石的酸性催化作用,负载在碱性KL沸石上的Pt呈富电子性,在反应中极易被噻吩中毒(Pt/KL+NH~4L)混合样品在预处理和反应的过程中Pt从KL 向NH~4L沸石上迁移,导致其催化性能相似于Pt/NH~4L,实验证明:Pt与L 沸石载体之间存在着明显的相互作用,由于Pt易给出电子而不易接受电子,因此与酸位的相互作用强于与碱位的相互作用.     

Temperature programmed decomposition of polypropylene: in situ FTIR coupled with mass spectroscopy study

The temperature-programmed reaction (TPR) technique coupled with the in situ infrared (IR)/mass spectroscopy (MS) analysis has been employed to study the thermal decomposition of polypropylene. These techniques, especially when coupled with a gas chromatograph (GC), are effective for determining thermal stability, product distribution and product evolution as a function of temperature. The polymer decomposes at approximately 475 K yielding hydrocarbons in the C₁–C₇ range, with propylene, C₅ and C₆ composing the majority of gaseous products. Decomposition over alumina and 5 wt% Ni/Al₂O₃ with and without the presence of hydrogen does not affect thermal stability. Also, decomposition over alumina with and without the presence of hydrogen does not affect the depolymerization pathway. The popular β-scission/backbiting mechanism cannot fully explain observations from this study. Possible alternatives are explored.     

Investigation of surface phenomena on solid catalysts by thermogravimetry

Thermogravimetry was applied to the investigation of the phenomena of adsorption, chemisorption, desorption and surface reactions on solid catalysts. The measurements were carried out with 13 NaX and NaY type zeolites and with silica gels treated with sodium hydroxide, in the presence of cumene and methanol. On the basis of the quantitative results it is possible to give an interpretation of surface phenomena and to establish the existence of various active centres on the surface of the catalysts.

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Zusammenfassung Adsorptions-, Chemisorptions- und Desorptionserscheinungen, sowie Oberflächenreaktionen an festen Katalysatoren wurden thermogravimetrisch untersucht. Die Messungen wurden an Zeoliten der Typen 13 NaX und NaY und an mit Natriumhydroxid behandelten Silikagelen in Gegenwart von Cumol und Methanol durchgeführt. Aufgrund der quantitativen Ergebnisse war es möglich, die Oberflächenerscheinungen zu deuten und das Vorhandensein von verschiedenen aktiven Zentren an der Katalysatoroberfläche nachzuweisen.

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Résumé On a appliqué la méthode thermogravimétrique à l'étude des phénomènes d'adsorption, de chemisorption et de désorption ainsi qu'aux réactions de surface sur des catalyseurs solides. Les mesures ont été effectuées sur zéolites de type 13 NaX et NaY et sur des silicagels traités par la soude en présence de cumène et de méthanol. Des résultats quantitatifs permettent de donner une interprétation des phénomènes de surface et d'établir l'existence de divers centres actifs à la surface des catalyseurs.

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The authors express their gratitude to Prof. S. Malinowski for help and discussion and to Mr. W. Dziklinski for his technical help.