DSC Heating Curves Research Articles

The influence of poly(maleic anhydride - co - vinyl acetate) on polylactide/wood flour/calcium carbonate composites

In this paper, polylactide (PLA)/wood flour (WF)/calcium carbonate (CC) composites with different content of poly(maleic anhydride -co- vinyl acetate) (PMAVA) were prepared. PMAVA was obtained by radical solution polymerization and identified by FTIR. The torque - time curves showed that the balance torques of PLA/WF/CC composites with PMAVA were improved by the adding of PMAVA. SEM photographs showed that after the addition of PMAVA, the compatibility and interfacial adhesion between the filler (CC or WF) and PLA in each composite were increased. DSC heating curves showed that two cold crystallization temperature (Tcc) peaks appeared in each PLA/WF/CC composite, and the Tcc peak at high temperature and Tm peak in the composite containing PMAVA were split into two peaks, showing that the effects of WF and CC on the crystal of PLA were uncorrelated, and the presence of PMAVA decreased the crystal integrity of PLA. The tensile test results showed that the tensile strength and modulus of the composite were increased with the addition of PMAVA, and the composite with 0.5 wt% of PMAVA owned the best tensile performance. The hydrolysis results showed that the use of low content of PMAVA in the composite was beneficial to improve its hydrolysis rate.

Crystallization and melting of unentangled poly(ε-caprolactone) cycles containing pendants.

The Rouse model provides a basic framework to understand the chain dynamics of polymers, which is confirmed to be more suitable for exploring the linear dynamics of unentangled polymers. The crystalline morphology governed by chain dynamics and crystallization kinetics is expected to differ in linear and cyclic polymers. Cyclic poly(ε-caprolactone)s (c-PCLs) containing two bi-anthracenyl group pendants with molecular weights close to the critical molecular weight (Mc) were synthesized to investigate the chain dynamics based crystallization and melting behavior by DSC, POM, and in situ simultaneous small-angle X-ray scattering/wide-angle X-ray scattering (SAXS/WAXS) investigations during heating of the isothermally crystallized samples. Double endothermic peaks were observed in the DSC curves with a low heating rate of c-PCLs without entanglement after isothermal crystallization, especially for c-PCLs with Mc. The structure evolution of the crystalline structures observed from the in situ investigations during the heating and double endothermic peaks in DSC heating curves of the c-PCLs indicate the role of pendants in the chain dynamics, which leads to the reorganization of the metastable structures. Banded spherulites of c-PCL without entanglement were observed for the first time, and the uneven growth of spherulites along the radial direction may be caused by the mismatch between chain dynamics and crystallization kinetics.

Influence of Cooling Rate on Ice Crystallization and Melting in Sucrose-Water System

The ice crystallization and melting in systems where the equilibrium state is difficult to reach is one of the growing areas in pharmaceutical freeze-drying research. The quality of the final freeze-dried product depends on the parameters of the cooling step, which affect the ice nucleation and growth. In this paper, we present a DSC study of ice crystallization and melting in a sucrose-water system. Using two different types of thermal cycles, we examine the influence of cooling and heating rates on the thermal behavior of sucrose-water solutions with water contents between 50 and 100 wt%.The DSC results show that low cooling rates provide crystallization at higher temperatures and lead to lower amount of non-freezing water. Consequently, the glass transition and ice melting properties observed upon heating depend on the cooling conditions in the preceding step. Based on the experimental results, we investigate the reasons for the existence of the two steps on DSC heating curves in sucrose-water systems: the glass transition step and the onset of ice melting. We show that diffusion of water can be the limiting factor for ice growth and melting in the sucrose-water system when the amorphous phase is in a liquid state. In particular, when the diffusion coefficient drops below 10−14 m2/sec, the ice crystals growth or melting becomes strongly suppressed even above the glass transition temperature. Understanding the diffusion limitations in the sucrose-water system can be used for the optimization of the freeze-drying protocols for proteins and probiotics.

Novel Co-crystals and Eutectics of Febuxostat: Characterization, Mechanism of Formation, and Improved Dissolution.

Co-crystallization studies were undertaken to improve the solubility of a highly water-insoluble drug febuxostat (FXT), used in the treatment of gout and hyperuricemia. The selection of co-crystal former (CCF) molecules such as 1-hydroxy 2-naphthoic acid (1H-2NPH), 4-hydroxy benzoic acid (4-HBA), salicylic acid (SAC), 5-nitro isophthalic acid (5-NPH), isonicotinamide (ISNCT), and picolinamide (PICO) was based on the presence of complementary functional groups capable of forming hydrogen bond and the ΔpKa difference between FXT and CCF. A liquid-assisted grinding (LAG) method was successfully employed for the rapid screening of various pharmaceutical adducts. These adducts were characterized based on their unique thermal (differential scanning calorimetry) and spectroscopic (Fourier transform infrared and Raman spectroscopy) profiles. Binary phase diagrams (BPD) were plotted to establish a relationship between the thermal events and adduct formed. Powder X-ray diffraction (PXRD) studies were carried out to confirm the formation of eutectic/co-crystal. Thermogravimetric analysis (TGA) was also performed for the novel co-crystals obtained. The propensity for strong homo-synthons over weak hetero-synthons and strong hetero-synthons over weak homo-synthons during supramolecular growth resulted in the formation of eutectics and co-crystals respectively. FXT:1H-2NPH (1), FXT:4-HBA (1), FXT:SAC (1, 2), and FXT:5-NPH (2-1) gave rise to pure eutectic systems, while FXT:ISNCT (2-1) and FXT:PICO (1) gave rise to novel co-crystals with characteristic DSC heating curves and PXRD pattern. Additionally, the impact of microenvironmental pH and microspeciation profile on the improved dissolution profile of the co-crystals was discussed. Graphical Abstract.

Cold crystallization event on DSC heating curves of bitumen

Cold crystallization event on DSC heating curves of bitumen

Preparation and Characterization of Fluorine-Containing Polybenzoxazole Composite Films including Graphene Oxide as a Reinforcing Material

The fluorine-containing polyhydroxyamide (F-75-PHA) was synthesized by using low-temperature solution polycondensation of 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (BAHHFP, 75 mol%) and 3,3′-dihydroxybenzidine (DHB, 25 mol%) with terephthaloyl chloride (TPC) in N-methyl-2-pyrrolidinone (NMP) without metal salts. The F-75-PBO (polybenzoxazole)/GO (graphene oxide) composite films with different GO contents (0.01, 0.1, and 1.0 wt%, respectively) were prepared by heat-treatment of their precursors (F-75-PHA/GO composite films), and the effects of reinforcing material (GO) on the structural, thermal, and mechanical properties of them were studied systemically. FE-SEM images that the F-75-PBO matrix and GO sheets had a superior hydrogen bonding interaction and formed a three-dimensional (3D) network structure in composite films having a great bendability. FT-IR spectra indicated that the incorporation of GO in composite films could be reacting hydroxyl (−OH) groups on F-75-PHA matrix to carboxyl (−COOH) and/or −OH groups in GO sheets, and thus the O-H stretching peak (23.8 %) for F-75-PHA/GO-0.1 composite film mostly disappeared in comparison with that (100 %) of F-75-PHA film. DSC heating curves revealed that the thermal cyclization temperature (Tc) of the F-75-PHA/GO composite films decreased with an increment of GO content. Interestingly, for F-75-PHA/GO-0.1 composite film, the Tc decreased by up to 254 °C. However, despite the outstanding reinforcing effect of GO sheets, an interesting phenomenon was confirmed that 3D network structure including an excellent hydrogen bonding interaction did not largely influence the mechanical properties of F-75-PBO/GO composite films.

Crystallization of Mechanically Alloyed Ni50Ti50 and Ti50Ni25Cu25 Shape Memory Alloys

The Ni50Ti50 and Ti50Ni25Cu25 alloys were produced in the form of powder using the high-energy ball milling. In the as-milled state, both alloys revealed presence of an amorphous state with a small amount of nanocrystalline areas. The non-isothermal DSC heating curves were used to investigate the crystallization process. Temperatures and activation energy of crystallization were determined. In both alloys, the crystallization occurred at temperatures range from 777 to 813 K, dependently on the heating rate. The activation energy values determined by the Kissinger and Ozawa method were comparable for both alloys and ranged from 410 to 429 kJ/mol.

Effect of the clay nanomaterial laponite on the crystallization characteristics of nanocomposites TPP/laponite

Influence of nanoparticles of the clay nanomaterial laponite on the crystallization process of various polymorphic phases of the composite TPP/laponite was studied by infrared spectroscopy and differential scanning calorimetry method. It was shown that the presence of clay nanoparticles leads to the formation of a new crystalline phase of the composite stable at room temperature, which melts at 306.8 K. It was also shown that in this stable phase conformers of TPP molecule dominate, different from the conformers realized in other metastable phases of the composite. The glass transition temperature, as derived from the DSC heating curves, is found to be only minor influenced by the clay addition.

Largely enhanced transcrystalline formation and properties of polypropylene on the surface of glass fiber as induced by PEI-CNT and PEI-GO modification

Interfacial performances of fibers/thermoplastic composites are crucial to their mechanical behaviors and application. In this work, isotactic polypropylene (iPP)/various modified glass fibers (GFs) micro composites were prepared under quiescent field and shear field respectively for investigating the interfacial crystallization and mechanical properties. The polyethyleneimine (PEI) modified carbon nanotubes (PEI-CNT) and graphene oxide (PEI-GO) were coated on the GFs surface to form a homogeneous and dense coating layer. Under quiescent field, transcrystallization (TC) structure was easily formed at the interface of iPP/PEI-CNT-GF and iPP/PEI-GO-GF due to the high nucleating ability of PEI-CNT and PEI-GO. The total crystallinity (Xc) increased by 33.0% and 26.8% in comparison to iPP/raw GF. The interfacial shear strength (IFSS) and SEM morphologies of interface after micro-droplet test were adopted to evaluate the interfacial adhesion. The IFSS results improved by 39.5% and 34.5% respectively, which indicated that the sufficient TC structure was beneficial to enhancing interfacial adhesion. In practical production, the preparation process of fibers/thermoplastic composites is under shear condition. It is worthy to study the transcrystallization under shear filed and we researched it further. After pulling fiber at the rate of 50 μm/s, the denser TC structure was formed, and the β-form crystals could be observed, particularly in iPP/PEI-CNT-GF and iPP/PEI-GO-GF micro composites, which was verified by DSC heating curves and selective melting experiment at 158 °C. The dense β-form crystals formation led to higher Xc (51.6% and 49.1%, respectively) and IFSS values (17.9 MPa and 17.5 MPa, respectively) in iPP/PEI-CNT-GF and iPP/PEI-GO-GF. In this work, an effective method was provided to introduce a coating layer of high nucleating capacity on the GFs surface and further construct the different TC structure at the interface of GFs/iPP composites under quiescent field and shear field respectively, which improved the interfacial performance dramatically. It would provide guidance for practical industrial production effectively.

Temperature range definition of phase transformation in experimental biocompatible Ti-Nb-Zr system alloys by various methods

Abstract The calculated dependences of the α- and β-phases volume fractions change in the 300–600 °C temperature range and thermodynamic equilibrium temperatures of polymorphic α + β-β-transformations (β-transus temperature, Tβ) for biocompatible alloys of the Ti-39%Nb-xZr system, where x ≈ 5; 7; 9 wt% were defined by thermodynamic calculations using ThermoCalc software package. It is established the zirconium in Ti-Nb-Zr system behaves as a β-stabilizer rather than a neutral element, and provides a Tβ decreasing with an increase of its content in the alloy. An equation is proposed for calculating Tβ in ternary alloys of the Ti-Nb-Zr system, where Ci – chemical element concentration, at.%: Tβ = 882.5 − 12.68CNb − 5.56CZr. The equation was obtained from the data on the change of Tβ in the equilibrium binary Ti-Nb, Ti-Zr systems. The Tβ values, calculated according to this equation, were close to those obtained by thermodynamic calculation (the difference does not exceed 4 °C). It was shown that the temperature of the endothermic peak minimum on the DSC heating curves of the Ti-Nb-Zr system alloys caused by the α + β-β-transformation corresponds to the Tβ determined using the ThermoCalc software. The endothermic peak intensity was found to decrease with an increase of the zirconium content, which additionally confirms the β-stabilizing effect of zirconium.

In search of an optimized electrolyte for Na-ion batteries

Electrolytes are essential for the proper functioning of any battery technology and the emerging Na-ion technology is no exception. Hence, a major focus on battery research is to identify the most appropriate formulation so as to minimize interface reactions and enhance both cell performances and safety aspects. In order to identify suitable electrolyte formulations for Na-ion chemistry we benchmarked various electrolytes containing diverse solvent mixtures (cyclic, acyclic carbonates, glymes) and Na-based salts having either F-based or perchlorate anions and measured viscosity, ionic conductivity, and thermal and electrochemical stability. The binary EC:PC solvent mixture has emerged as the best solvent formulation and has been used to test the performance of Na/hard carbon cells with both NaClO4 and NaPF6 as dissolved salts. Hard carbon electrodes having reversible capacities of 200 mA h g−1 with decent rate capability and excellent capacity retention (>180 cycles) were demonstrated. Moreover, DSC heating curves demonstrated that fully sodiated hard carbon cycled in NaPF6–EC:PC exhibits the highest exothermic onset temperature and nearly the lowest enthalpy of reaction, thus making this electrolyte most attractive for the development of Na-ion batteries.

Effect of nanoclay on the thermal, mechanical, and crystallization behavior of nanofiber webs of nylon-6

Nylon-6 and nanoclay/nylon-6 composite nanofibers were prepared by electrospinning technique, in which formic acid was used as a solvent for good solubility of nylon-6. The diameter of nylon-6 and nanoclay/nylon-6 nanofibers was below 350 nm and had smooth surfaces. The DSC heating curves of nylon-6 and composites nanofibers show two endotherm behaviors, Tm1 (about 214°C) and Tm2 (about 220°C), corresponding to the melting events of γ-form and α-form crystals, respectively. The WAXs study showed that the γ-crystalline phase predominantly present in both nylon-6 and nanoclay/nylon-6 nanofibers. The mechanical properties of the nanoclay/nylon-6 composite nanofibers were higher than neat nylon-6 electrospun nanofibers, which was decreased as the quantity of the clay increased. It might be due to the aggregation of nanoclay at high concentration. The thermal properties of the composite nanofibers were higher than neat nylon-6 nanofibers. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers

Effect of Solvent Evaporation Rate on Order-to-Disorder Phase Transition Behavior of Regioregular Poly(3-butylthiophene)

The effect of solvent evaporation rate on the crystal modification and the thermal stability of solution cast regioregular poly(3-butylthiophene) (P3BT) film was investigated by WAXD, DSC, and FTIR. It is found that, independent of the solvent evaporation rates, the P3BT films prepared from chloroform solution demonstrate essentially the same interlayer distance, which is very close to the reported value of form I′, rather than the conventional form I. However, in the DSC heating curves, it is interesting to find that a single “melting” peak and a double one in the temperature region of 45–100 °C can be observed respectively for P3BT films prepared with fast and extremely slow solvent evaporation rates. The double melting behavior of P3BT in this low-temperature region has never been discussed in the literature. By temperature-dependent infrared spectroscopy, it is shown that these low-temperature “melting” peaks are related to the order-to-disorder phase transition (form I′ to form I) of P3BT. Furthermor...

Effect of the Cooling Rate on the Nucleation Kinetics of Poly(l-Lactic Acid) and Its Influence on Morphology

Although the crystallization kinetics of PLLA is slow enough to allow one to obtain amorphous samples by cooling from the melt at moderate rates, surprisingly, at the same time, the formation of crystallization nuclei is difficult to avoid. Their amount depends on the cooling rate from the melt: the higher the cooling rate, the lower the amount of available nuclei after reaching the glass state. Cooling at controlled rates of 5−300 °C/min was performed by making use of a relatively new high-speed calorimetry technology, high-performance DSC (HPer DSC). Subsequent isothermal cold crystallization of amorphous PLLA, at different temperatures distributed across the bell-shaped crystal growth curve, was shown to depend on the rate at which the glass state was attained, reflecting the number of nuclei formed. However, (only) after complete cold crystallization, the DSC heating curves and the resulting morphology measured by optical microscopy and AFM were shown to be independent of the previous cooling rate into the glass, i.e., of the number of nuclei formed during the cooling process. In cases where the DSC heating curves subsequent to isothermal cold crystallization show two melting peaks, their origin, recrystallization, was clarified by heating at rates varying from 10 to 300 °C/min. The morphologies of the cold crystallized systems have been assessed by AFM and were correlated with the calorimetric results. Using HPer DSC, isothermal cold and hot crystallization at the same temperature has been studied successfully.

The way to measure quantitatively full dissolution and crystallization of polyamides in water up to 200 °C and above by DSC

The way to measure quantitatively full dissolution and crystallization of polyamides in water up to 200 °C and above by DSC is described. Stainless-steel high-pressure pans enable research on fully dissolving polyamides in water under vapor pressure. The results show clearly that polyamide 6 (PA6) is soluble in water under vapor pressure in the whole concentration range and that water acts as a crystallization and melting point suppressor. The maximum temperature depression is approximately 60 °C. This depression of the transitions is independent of concentration over a large range (10–70 mass% PA6 in water). When PA6 dissolves in water during heating, the polymer often sets to the sides of the DSC sample pan. Because of this the contact between the sample and the bottom of the pan reduces during measurement and therefore DSC heating curves are frequently curved. Adding steel wool to these stainless-steel high-pressure pans improves the measurements by increasing the thermal conductivity between the sample and pan bottom, and as a result the DSC curves become less curved. The interpretation of the measurements improves and the possibility of reproducible peak area calculations also in heating comes in sight.

Synthesis and properties of copolyesters of p,p′‐bibenzoic acid, dimer acid, and alkylene glycol

AbstractCopolyesters of p,p′‐bibenzoic acid, dimer acid, and an alkylene glycol are prepared by melt polycondensation of of dimethyl p,p′‐bibenzoate, dimer acid, and an alkylene glycol. The copolyesters are characterized by the inherent viscosity, FTIR, proton NMR, DSC, polarized microscopy, and X‐ray diffraction. The polymer composition and sequence distribution of the copolyesters can be seen from the NMR spectra. The copolyesters exhibit a degree of randomness of about 1, indicating that they are random copolymers. The glass‐transition temperature (Tg) and the melting point (Tm) of the copolyesters are found from the DSC heating curves. When the content of the flexible dimer acid unit increases, the Tg of the copolyesters decreases significantly. The copolymerization effect decreases the crystallinity and the Tm of the copolyesters. It can be seen from the DSC, polarized microscopy, and X‐ray diffraction data that some copolyesters derived from 1,6‐hexanediol and 1,5‐pentanediol exhibit a monotropic smectic phase. As the molar content of the dimer acid unit increases, the isotropic–mectic transition temperature and the smectic order decreases significantly. The liquid crystallinity is completely destroyed at certain molar contents of the dimer acid unit. The smectic order of the copolyesters derived from 1,6‐hexanediol is significantly higher than that of the copolyesters derived from 1,5‐pentanediol, and it is described as an odd–even effect. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 750–758, 2003

Oxidative Decomposition of Polylactide Fiber by Ultraviolet Light Irradiation in Ozone-oxygen Atmosphere

The oxidative decomposition of polylactide fabrics irradiated with ultraviolet light in an ozone-oxygen atmosphere was investigated. The tensile strength of irradiated yarn remained almost constant up to 70 s of irradiation time, but it decreased steeply in the range of 70 to 300 s and did slowly above 600 s. The elongation discontinuously decreased in the range of 300 to 600 s, because the cold drawing did not occurred in the region of more than 600 s. In the DSC heating curves of irradiated fabrics, the double melting behavior remarkably changed in shape above 150 s and the peak temperatures shifted to the low-temperature side with increasing irradiation time. This result suggested that the melting-recrystallization-remelting behavior had changed since tie molecules had been decomposed. The enthalpy data of melting proved that the crystallites of samples irradiated for more than 600 s had been partially destroyed. When the carboxylic groups were analyzed by absorption of basic dye molecules on the sample surfaces, it was suggested that the oxidative decomposition is retarded on the surface of polylactide fiber.

Crystallization and Relaxation Behavior of Partially Disentangled Poly(vinyl chloride) Prepared from Large Molecule Solvent Dioctyl Phthalate

Poly(vinyl chloride) (PVC) samples for the conformation and structural relaxation studies were prepared by freeze-extracting the solutions in various solvents and with varying concentrations. The partially disentangled PVC samples could be obtained by freeze-extracting very dilute PVC/tetrahydrofuran (THF) and PVC/dimethyl phthalate (DMP) solution (0.05 wt %), while the PVC sample remains in an entangled state after freeze-extracting the concentrated solutions in THF and in DMP. Surprisingly, the extent of interpenetration of PVC chain decreases, even in concentrated solution in dioctyl phthalate (DOP) (5 wt %), which is contrary to accepted theories. DSC and infrared spectroscopic studies showed that a higher ordered conformation could be achieved for the disentangled specimens recovered from concentrated solution in DOP than for the entangled samples prepared from THF and DMP. DSC heating curves showed strong and sharp endothermal peaks for the disentangled polymer after sub-Tg annealing. The structural relaxation behavior of the disentangled PVC freeze-extracted from DOP solutions is more predominant, which is in good agreement with the modeling predictions.

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 {Wc=(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 (Tg), cold crystallization (Tcc) and melting (Tm) 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 Tg, Tcc, 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 (Wnf), freezing bound water (Wfb) 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.

Synthesis and Characterization of the β-Diketone Based Side Chain Liquid Crystalline Random Copolyphenylsilsesquioxane and Its Metal Complex

The attachment of low molecular weight β-diketone compound to random copolyphenylhydrosilsesquioxane (abbr. as Ph-T) backbone gave rise to the formation of β-diketone based side chain liquid crystalline copolyphenylsilsesquioxane (abbr. as Ph-DK). Its copper complexes (abbr. as Ph-DK-Cu) were prepared following a heterogeneous reaction procedure. The structures of the Ph-DK and their copper complexes were well characterized by IR. NMR and GPC. The DSC heating curves of the Ph-DK-Cu show three endothermic transitions. The first transitions are from crystalline state to liquid crystalline state (I), the second transitions are from liquid crystalline state (I) to liquid crystalline state (II), and the third transitions are from liquid crystalline state to the isotropic liquid. The Ph-DK-Cu are thermotropic liquid crystalline polymers. Their clearing temperature and mesophase range ΔT are lower than those of the corresponding Cu-coordinated β-diketone based copolymethylsilsesquioxane liquid crystalline polymers. The influence of the content of the Cu2+ on the Ph-DK-Cu has been discussed. The chemical incorporation of metal ion into polysilsesquioxane molecule can change the liquid crystal molecular arrangement and the transition temperature.