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The enthalpies of crystallization of NaCl, KCl, LiCl·H2O, MgCl2·6H2O, CaCl2·6H2O and BaCl2·2H2O from aqueous solution were determined by means of different calculation methods on the basis of the earlier-measured differential and integral enthalpies of solution of the above salts. The obtained crystallization enthalpies are discussed and compared with the appropriate literature data.

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Abstract  

The direct measurements of differential enthalpies of solution Δsol H 2, of LiCl·H2O, NaCl, KCl, MgCl2·6H2O, CaCl2·6H2O and BaCl2·2H2O, as the function of molality,m, in the region of concentrated solutions were performed. On this basis the enthalpies of crystallization, Δcryst H m, were calculated and compared to the appropriate literature data.

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New polyurethanes with mesogenic units in the main chain due to the use of a liquid crystalline chain extender were synthesized from 4,4'-methylenebis(cyclohexyl isocyanate) (HMDI)using diisocyanates of different trans, trans isomer content, a low molecular diol4,4'-bis(6-hydroxyhexoxy)biphenyl (BHHBP) and a high molecular poly(hexyleneadipate)diol (PHA). The growth of trans, trans isomer content in HMDI used to syntheses of PU induces monotonic growth of melting point, rectilinear growth of crystallization temperatures and the growth of crystallization enthalpy, both for hard segment polyurethanes and block polyurethanes. The increase of trans, trans isomer content in HMDI increases also glass transition temperatures and dynamic storage modulus of the polyurethanes.

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An analysis of the crystallization behaviour of a new poly(aryl-ether-ether-ketone-ketone), PK99, by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) is presented. Isothermal crystallization TG were obtained in the whole range between the glass transition temperature (T g) and the melting temperature (T m) as a consequence of the slow crystallization kinetics stemming from the closeness of these transitions. The calorimetric results, compared with WAXD data, were applied to determine the theoretical melting temperature and crystallization enthalpy. The DSC and WAXD data were combined in order to calculate the total amount of the crystallizable fraction of the polymer, and a model was proposed to explain the difference between the fractions of crystallinity observed with these techniques. The thermal and X-ray data were also correlated with different lamellar morphologies arising from the crystallization conditions. Finally, DSC experiments on the crystallized sample were used to detect the presence of a rigid amorphous phase which does not relax at T g.

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The poly(1,4-butylene terephthalate-co-DL-lactide) (BLA) copolymers were successfully prepared by the melt reaction between poly(1,4-butylene terephthalate) (PBT) and DL-oligo(lactic acid) (OLA) in the presence of 1,4-butanediol (BDO) without any catalysts. The transesterification between butylenes terephthalate (BT), 1,4-butanediol and lactide (LA) segments during the reaction was confirmed by the 1H NMR analysis. The chemical structure of the copolymers was further investigated by the 13C NMR and two-dimensional 1H–13C HMQC (heteronuclear multiple quantum correlation) technique. The effect of reaction temperatures and the starting feed ratios on the molecular microstructures, molecular weights, solubility and thermal stability of the copolyesters was extensively studied. The sequence length of BT (NBT) was found to play a vital role on the solubility and thermal behaviors of the resulting copolyesters. The copolyesters with NBT in the range of 2.8 and 7.3 were soluble in chloroform. The B10LA40 copolyester with the shortest NBT of 2.8 exhibited almost the lowest glass-transition temperature (Tg), crystallization temperature (Tc), melting temperature (Tm), crystallization enthalpy (ΔHc) and melting enthalpy (ΔHm) as compared with the other copolyesters. The copolyester of B10LA40 was able to hydrolytically degrade and the fabricated scaffold that showed good biocompatibility towards the human bone marrow stromal cells.

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The DSC curve of freeze-dried amorphous sucrose shows the glass transition, the crystallization and the melting (just before decomposition) of the sample. Sucrose crystallization occurs below 100°C: this phenomenon can therefore be observed with the microcalorimeter Setaram Micro-DSC used in the scanning mode. Mixtures of amorphous and crystalline sucrose in known proportions were used to calibrate the instrument. Low level amorphism (down to about 0.5%) could be detected and quantitatively evaluated on the basis of the crystallization enthalpies determined. The calibration curve obtained can be applied to determine the degree of amorphism in milled sucrose. A simple gravimetric method, based on the desorption of water induced by recrystallization of the amorphous layer can be used to obtain similar data more rapidly. This simple method is particularly useful for controlling the amorphism on line during a process, and is also briefly described.

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g ), thermal stability (Δ T ), and crystallization enthalpy (Δ H c ) In non-isothermal kinetics analysis, the results obtained from the thermogram are represented in terms of the crystallized volume fraction ( α

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released in the total heat released (crystallization enthalpy), the amount of precipitated wax at different temperatures can be determined by dividing the accumulated heat released by the heat of crystallization as has been reported in literature [ 7 , 8

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crystallization enthalpy values, consequently additionally crystallization occurs at 130 °C between the isothermal step and the melting of the sample. The deviation is significant especially in the case of the early stage of crystallization. Consequently, the

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the basis of the crystallization curves, by designation the crystallization enthalpy. Crystallisation enthalpy was determined from the area under the crystallisation curve. On account of curves crystal conversion versus time, the half-time of

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