Analysis of Thermodynamic Parameters of Glass Forming Polymeric Melts

The temperature dependence of the Gibbs free energy difference (ΔG), enthalpy difference (ΔH) and entropy difference (ΔS) between the undercooled meltand the corresponding equilibrium solid has been analysed for glass forming polymeric materials by calculating ΔG, ΔH and ΔS within the framework of the hole theory of liquids. The study is made for nine samples of glass forming polymeric melts; polypropylene oxide (PPO), polyamid-6 (PA-6), polytetramethylene oxide (PTMO), polyethylene oxide (PEO), polystyrene (PS), polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET) and polybutadiene (PB) and three simple organic liquids: tri-α-naphthyl benzene (tri-α-NB), o-terphenyl (o-ter) and phenyl salicylate (salol) in the entire temperature range T _m (melting temperature) to T _g (glass transition temperature). The ideal glass transition temperature (T _K) and the residual entropy (ΔS _R) of these samples have also been studied due to their important role in the study of the glass forming ability of materials. This revised version was published online in August 2006 with corrections to the Cover Date.     

Differential scanning calorimetric examination of the degenerated human palmar aponeurosis in dupuytren disease

The Dupuytren contracture - degenerative shortening of the palmar aponeurosis - is a common disease of the hand in Europe. The aetiology of the degenerative changes in the collagen structures is still not clear. To describe the clinical manifestation of the disease we use an international classification according to Iselin. Our hypothesis was that in Dupuytren disease there is a clear pathological abnormality in the tissue elements building up the palmar aponeurosis, which is responsible for the disease, and could be monitored besides the classical histological methods by differential scanning calorimetry. The thermal denaturation of different parts of human samples was monitored by a SETARAM Micro DSC-II calorimeter. All the experiments were performed between 0 and 100°C. The heating rate was 0.3 K min⁻¹. DSC scans clearly demonstrated significant differences between the different types and conditions of samples (control: T _m=63°C and ΔH _cal=4.1 J g⁻¹, stage I.: T _m= 63°C and ΔH _cal=5.1 J g⁻¹, stage II.: T _m=64°C and ΔH _cal=5.2 J g⁻¹, stage III.: T _m=60°C and ΔH _cal=5.2 J g⁻¹, stage IV.: T _m=60.2°C and ΔH _cal=5.3 J g⁻¹). The heat capacity change between native and denatured states of aponeurosis samples increased with the degree of structural alterations indicating significant water loosing. These observations could be explained with the structural alterations caused by the biochemical processes. With our investigations we could demonstrate that DSC is a useful and well applicable method for the investigation of collagen tissue of the human aponeurosis. Our results may be of clinical relevance in the future i.e. in the choice of the optimal time of surgical therapy of different clinical level Dupuytren contractures.     

Thermal properties of post-consumer PET processed in presence of phosphites

Thermal properties of recycled triphenylphosphite (TPP) chain extended poly(ethylene terephthalate) (PET) was investigated. As the TPP concentration increases, both reaction residues and molecular mass increase affecting significantly the thermal properties and crystallization behavior of the material. The presence of TPP residues did not affect the crystalline melt temperature (T _m), but modified the glass transition temperature (T _g), the crystallization temperature on heating (T _hc) and the crystallization temperature on cooling (T _cc). In the samples submitted to extraction with acetone, the properties were influenced by molecular mass changes, probably due to the presence of some insoluble reaction residue. The thermal stability of the sample purified by extraction after chain extension was comparable to that of the non-extended sample when heating was carried out under nitrogen atmosphere.This revised version was published online in November 2005 with corrections to the Cover Date.     

Calculations of thermal functions of group-III nitrides

The change of thermal functions (ΔH ⁰(T), ΔS ⁰(T), ΔG ⁰(T)) and formation functions (ΔH _f⁰(T), ΔG _f⁰(T), K _f(T)) with temperature for gallium nitride and indium nitride have been formulated based on the reliable experimental data obtained by the use the same equipment in one laboratory.     

Thermal stability of porcine pepsin influenced by Al(III) ion: DSC study

Differential scanning calorimetry (DCS) has been used to determine thermodynamic profile of pepsin and the in vitro effect of Al(III) ions. Thermograms of pepsin unfolding in the presence and absence of aluminum were used to determine the binding constant, K _L, in the pepsin-aluminium model system. The thermodynamic parameters were derived from DSC profiles at different ligand concentrations (1, 5 and 10 mM). The temperatures of thermal transitions (T _m), calorimetric (ΔH ^cal) and van’t Hoff enthalpy (ΔH ^VH), Gibbs free energy, Δ(ΔG), of Al(III) binding to pepsin, as well as an average number of ligands bound to the native protein, were obtained from DSC profiles too. Temperature-dependent changes in the protein structure were also monitored by native PAGE electrophoresis. Increasing the temperature causes the decrease in electrophoretic mobility. Increase in concentration of Al(III) decelerate the migration of pepsin samples on concentration dependent manner. Analysis showed that ligand binding increases thermal stability of protein.     

DSC measurement of cartilage destruction caused by septic arthritis

Summary Treatment of a bacterial arthritis is a challenging task for a clinician as inadequate therapy can cause cartilage destruction and can result in severe osteoarthritis of the affected joint. The development of cartilage destruction in septic arthritis is not known in details. The aim of this study was to follow this process by calorimetric method. We induced experimental septic arthritis in knee joints of seven New Zealand rabbits by single inocculation of Staphylococcus aureusOKI 112001 culture (1.5 mL 8·10⁸±5% c.f.u.). The first rabbit died on the 11^thday. At that time all the other subjects were made overslept and samples were isolated from the cartilage of the femurs for calorimetric measurement. The DSC scans clearly demonstrated the development of infective structural destruction in cartilage from the first to the tenth day of incubation. In case of healthy control the melting temperatures (T_m) were: 49.7, 55 and 63.4°C and the total calorimetric enthalpy change (ΔH) was 0.55 J g^-1. After the first day the enthalpy decreased (0.375 J g^-1), the first two transition temperature shifted towards higher temperature: 57 and 63.15°C. Up to the fourth day the effect of infection culminated with T_mof 49.3, 55.9, 59.4, 62.8°C and further decrease of the ΔH. At the fifth day the effect of infection is culminated in two separable thermal denaturation events (with 55 and 63.3°C T_ms) with high jump in ΔHindicating the dramatic change of the structure of rabbit cartilage, so this time elapsed seems to be critical from the point of view of practical clinical relevance too. Between the 7^thand 11^thdays practically we had same melting temperatures (50 and 63°C) with low (~0.24 J g^-1) enthalpy.     

Studies on the thermal properties of caprolactam/long chain lactam copolymer

The thermal properties of caprolactam/long chain lactam copolymer were studied with a Perkin-Elmer DSC 7. The melting point (T _m), heat of fusion (δH _m), crystalline degree (X _c), crystallization temperature (T _c) and glass transition temperature (T _g) of the copolymers increase with decrease of the content of the log chain lactam. From the changes in the mechanical properties with corresponding changes in the thermal properties, it is clear that the copolymers are thermal plastic and elastic. In addition, it is found that the results at a heating rate of 10 deg·min^?1 are almost the same as that at 20 deg·min^?1 after thermal history is erased.     

Melting and thermodestruction processes in the poly(ethylene)-nanocrystalline nickel system

Composite materials (CM) based on poly(ethylene) (PE) and nanocrystalline nickel (Ni) have been produced. The effect of the content of nanocrystalline Ni and processes of structure formation of its particles on a melting temperature (T _m), interval of melting, true melting heat (ΔH _m), degree of crystallinity (χ) as well as characteristics of CM thermodestruction have been determined by DTA and thermogravimetry techniques. It was found that these characteristics are changed non-linearly when the content of nanocrystalline Ni increases. The most efficient influence of Ni on the above mentioned characteristics was observed for its low content (0.01 volume part of Ni). It was shown that a formation of a branched multifractal cluster of nickel above a percolation threshold favored a decrease in T _m, ΔH _m, χ of filled PE and a majority of thermal characteristics of CM thermodestruction as well. This revised version was published online in August 2006 with corrections to the Cover Date.     

Preparation and properties of silicon containing copolyamides

Copolyamides containing siloxane moieties in main chain were prepared by a melt polycondensation with 1,3-bis(3-aminopropyl)tetramethyldisiloxane (E), hexamethylenediamine (N6), and adipic acid (6). Glass transition temperature (T_g), cold crystallization temperature (T_cc), and melting temperature (T_m) were measured by differential thermal analysis (DTA). The depression of T_m for copolyamide was fitted by the Flory curve. Melting peak remarkably broadens with increasing E6 component in copolyamide. The change of T_g was fitted by the Gibbs and Dimarzio's equation in which the number of flexible bond is considered. The difference between T_g and T_cc increased with increasing E6 component. These DTA studies suggest that the crystallization of N66 component in copolyamide is hindered by the bulky siloxane moiety, while the micro-Brownian motion of amorphous segment is promoted by the flexible siloxane bond. Tensile strength and Young's modulus decreased with increasing E6 component. The solubility in various solvents increased with increasing E6 component. Permeability of oxygen and nitrogen increased with an increase of temperature and E6 component. The separation coefficient of oxygen to nitrogen rapidly increased near 50 mol% of E6 concentration and then leveled out above 70 mol%. The contact angle with water and methylene iodide increased with an introduction of the siloxane moiety into polymer chain.     

Thermal properties of poly(lactic acid)/organo-montmorillonite nanocomposites

Poly(lactic acid)/organo-montmorillonite nanocomposites were prepared by melt intercalation technique. Maleic anhydride-grafted ethylene propylene rubber (EPMgMA) was added into the PLA/OMMT in order to improve the compatibility and toughness of the nanocomposites. The samples were prepared by single screw extrusion followed by compression molding. The effect of OMMT and EPMgMA on the thermal properties of PLA was studied. The thermal properties of the PLA/OMMT nanocomposites have been investigated by using differential scanning calorimeter (DSC) and thermo-gravimetry analyzer (TG). The melting temperature (T _m), glass transition temperature (T _g), crystallization temperature (T _c), degree of crystallinity (χ_c), and thermal stability of the PLA/OMMT nanocomposites have been studied. It was found that the thermal properties of PLA were greatly influenced by the addition of OMMT and EPMgMA.     

Molar heat capacity and thermodynamic properties of 1,2-cyclohexane dicarboxylic anhydride [C8H10O3]

The molar heat capacity C _p,m of 1,2-cyclohexane dicarboxylic anhydride was measured in the temperature range from T=80 to 390 K with a small sample automated adiabatic calorimeter. The melting point T _m, the molar enthalpy Δ_fus H _m and the entropy Δ_fus S _m of fusion for the compound were determined to be 303.80 K, 14.71 kJ mol⁻¹ and 48.43 J K⁻¹ mol⁻¹, respectively. The thermodynamic functions [H _T-H _273.15] and [S _T-S _273.15] were derived in the temperature range from T=80 to 385 K with temperature interval of 5 K. The thermal stability of the compound was investigated by differential scanning calorimeter (DSC) and thermogravimetry (TG), when the process of the mass-loss was due to the evaporation, instead of its thermal decomposition.     

Molar heat capacities and standard molar enthalpy of formation of 2-amino-5-methylpyridine

The heat capacities (C _p,m) of 2-amino-5-methylpyridine (AMP) were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 398 K. A solid-liquid phase transition was found in the range from 336 to 351 K with the peak heat capacity at 350.426 K. The melting temperature (T _m), the molar enthalpy (Δ_fus H _m⁰), and the molar entropy (Δ_fus S _m⁰) of fusion were determined to be 350.431±0.018 K, 18.108 kJ mol⁻¹ and 51.676 J K⁻¹ mol⁻¹, respectively. The mole fraction purity of the sample used was determined to be 0.99734 through the Van’t Hoff equation. The thermodynamic functions (H _T-H _298.15 and S _T-S _298.15) were calculated. The molar energy of combustion and the standard molar enthalpy of combustion were determined, ΔU _c(C₆H₈N₂,cr)= −3500.15±1.51 kJ mol⁻¹ and Δ_c H _m⁰ (C₆H₈N₂,cr)= −3502.64±1.51 kJ mol⁻¹, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. The standard molar enthalpy of formation of the crystalline compound was derived, Δ_r H _m⁰ (C₆H₈N₂,cr)= −1.74±0.57 kJ mol⁻¹.     

Standard enthalpy of formation of 3,4,5-trimethoxybenzoic acid

The energy of combustion of crystalline 3,4,5-trimethoxybenzoic acid in oxygen at T=298.15 K was determined to be -4795.9±1.3 kJ mol^-1 using combustion calorimetry. The derived standard molar enthalpies of formation of 3,4,5-trimethoxybenzoic acid in crystalline and gaseous states at T=298.15 K, Δ_fH_m ^Θ (cr) and Δ_fH_m ^Θ (g), were -852.9±1.9 and -721.7±2.0 kJ mol^-1, respectively. The reliability of the results obtained was commented upon and compared with literature values. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phase transition of locust bean gum-, tara gum- and guar gum-water systems

Phase transition behaviour of neutral galactomannans, i.e., locust bean gum (LBG), tara gum (Tara-G) and guar gum (GG)-water systems is investigated. In this study, water content {W_c=(gram of water)/(gram of dry sample)} of these systems was varied from 0.2 to 3.6 g g^-1. In the DSC heating curves, glass transition (T_g), cold crystallization (T_cc) and melting (T_m) were observed in all three samples. In addition, liquid crystal transition (T*) was observed in GG-water systems at a temperature higher than Tm. Using T_g, T_cc, Tm and T*, phase diagrams of each system were established. From the melting enthalpy of ice in the systems, three types of water, non-freezing water (W_nf), freezing bound water (W_fb) and free water were calculated. The maximum amount of Wnf was observed at Wc=0.7 g g-1, where Tg showed the lowest temperature. The amount of Wnf in LBG and GG is higher than that of Tara-G, whereas the highest amount of Wfb is found in GG. T* was only observed in GG-water systems. It is concluded that frequency of the side chains in the repeating unit of the main chains of these three galactomannan affects the frozen structure of the glassy state in the presence of water. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of thermal parameters of glasses from the system Bix(As2S3)100?x based on DSC curves

Thermal properties of glasses from the system Bi _x (As₂S₃)_100−x were studied by differential scanning calorimetry of a representative series of samples with x = 0.5, 2, 4, 6, 8, and 10 at.% Bi by determining the characteristic temperatures (T _g, T _onset, T _c, T _m) and enthalpies (H _c, H _m) of the processes taking place in the samples during their thermal treatment. Analysis of DSC recordings for the samples at the same heating rate allowed characterization of the phase transition temperature T _g as a function of the content of doping atoms in accordance with the criteria of chemical bonds formation in amorphous materials. Samples with 4 and 6 at.% Bi were thermally treated at different heating rates with the aim of determining, among the others, the parameters of their thermal stability. The assessment was done based on three different criteria. A higher tendency toward crystallization was observed with the glasses having a higher Bi content. Also, a trend of T _g shifting toward higher values, observed with increase in the heating rate, is in concordance with the Lasocka equation.     

Calorimetric study and thermal analysis of crystalline nicotinic acid

As one primary component of Vitamin B₃, nicotinic acid [pyridine 3-carboxylic acid] was synthesized, and calorimetric study and thermal analysis for this compound were performed. The low-temperature heat capacity of nicotinic acid was measured with a precise automated adiabatic calorimeter over the temperature rang from 79 to 368 K. No thermal anomaly or phase transition was observed in this temperature range. A solid-to-solid transition at T _trs=451.4 K, a solid-to-liquid transition at T _fus=509.1 K and a thermal decomposition at T _d=538.8 K were found through the DSC and TG-DTG techniques. The molar enthalpies of these transitions were determined to be Δ_trs H _m=0.81 kJ mol^-1, Δ_fus H _m=27.57 kJ mol^-1 and Δ_d H _m=62.38 kJ mol^-1, respectively, by the integrals of the peak areas of the DSC curves. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal properties of globulin from buckwheat (<Emphasis Type="Italic">Fagopyrum esculentum</Emphasis> Moench)

The thermal properties of buckwheat (Fagopyrum esculentum Moench) proteins with different lipid contents (2.5, 6.5 and 17.8%) were studied by differential scanning calorimetry (DSC) under various medium conditions. From DSC curves, many DSC characteristics including denaturation temperature (T _d), enthalpy change (ΔH) and the width at half peak height (ΔT _1/2) of endothermic peaks were obtained and evaluated. The DSC curves of various buckwheat proteins (BWPs) in the 0.05 M phosphate buffer (pH 7.0) showed a major endotherm at about 102°C and a minor endotherm at about 80°C, attributed to thermal transitions of 13S and 8S globulins, respectively. T _d and ΔH of the globulins of BWPs were independent of their lipid contents, while the presence of high lipid content (17.8%) to some extent increased the ΔT _1/2. The progressive increase in T _d of 13S globulins with increase in NaCl concentration, suggests a more compact conformation with higher thermal stability. The influence of chaotropic salts on the DSC characteristics of 13S globulins was also independent of their lipid contents. Thermal analysis of the 13S globulins in the presence of protein perturbants (including urea, sodium dodecyl sulfate, ethylene glycol, dithiothreitol and N-ethylmaleimide) indicated that hydrophobic and hydrogen bondings are the major interactions for stabilizing protein conformation of buckwheat 13S globulins and the SS-SH interchange also attributes to the stabilization of the protein conformation.     

Thermal stability of lysozyme and myoglobin in the presence of anionic surfactants

The interactions of lysozyme and myoglobin with anionic surfactants (hydrogenated and fluorinated), at surfactant concentrations below the critical micelle concentration, in aqueous solution were studied using spectroscopic techniques. The temperature conformational transition of globular proteins by anionic surfactants was analysed as a function of denaturant concentration through absorbance measurements at 280 nm. Changes in absorbance of protein-surfactant system with temperature were used to determine the unfolding thermodynamics parameters, melting temperature, T _m, enthalpy, ΔH _m, entropy, ΔS _m and the heat capacity change, ΔC _p, between the native and denatured states.     

Thermal properties of polylactides

A thermal analysis of a series of polylactides (PLA) was carried out based on the number of average molecular mass (M _n), and the nature of isomer (D, L and DL). It is confirmed that the glass transition temperature (T _g) of PLA increased as a function of molecular mass irrespective of isomer type except sample with a high polydispersity index. The melting temperature (T _m) and enthalpy of crystal fusion (ΔH _f) of L-isomer increased as the M _n was increased from 1100 to 27500. The degree of crystallinity (χ_c%) increased as a function of molecular mass. However no crystallization peak was detected in the lower molecular mass range (550–1400). The non-isothermal crystallization behavior of the PLA melt was significantly influenced by the cooling rate. Both D and L isomers exhibited insignificant difference in thermal properties and DL lactides exhibited amorphous behavior at identical molecular masses. Change in microstructure showed significant difference between two isomers. Analysis of the FTIR spectra of these PLA samples in the range of 1200–1230 cm⁻¹ supported DSC observation on crystallinity.     

Film formation stages for poly(vinyl acetate) latex particles: a photon transmission study

Photon transmission technique was used to monitor the evolution of transparency during film formation from poly(vinyl acetate) (PVAc) latex particles. The latex films were prepared below the glass transition temperature (T _g) of PVAc. These films were annealed at elevated temperatures in various time intervals above the T _g of PVAc. It is observed that transmitted photon intensity (I _tr) from these films increased as the annealing temperature is increased. It is seen from I _tr curves that there are two film formation stages. These successive stages are named void closure (viscous flow) and interdiffusion. The activation energies for viscous flow (ΔH) and backbone motion (ΔE _b) were obtained by using well-defined models. The averaged values of the backbone (ΔE _b) and the viscous flow activation energies (ΔH) were found to be 188.6 and 5.6 kcal/mol, respectively. The minimum film formation (τ _M,T _M) and healing points (τ _H,T _H) were determined. Minimum film formation (ΔE _M) and healing activation energies (ΔE _H) were measured using these time–temperature pairs. ΔE _M and ΔE _H were found to be 32.5 and 28.3 kcal/mol, respectively.