Isothermal DSC Research Articles

Cure characterization of carbon fiber reinforced phenyl-ethynyl terminated oligoamic acid by FTIR–photoacoustic spectroscopy

Curing of phenyl-ethynyl terminated oligoamic acid resin reinforced with carbon fiber and of the neat extracted resin was investigated by FTIR–photoacoustic spectroscopy (PAS). Imidized oligoamic acid with phenylethynyl termination form the precursor for the formation of phenyl-ethynyl terminated imide (PETI), which are employed for high temperature, high performance applications. The reaction kinetics was modeled based on two-stage, first order kinetic model for the imidization process, whereas the crosslinking was modeled on a simple first order model. Our results show that the imidization is kinetically controlled, whereas the crosslinking stage exhibits kinetic and diffusion controlled phases. The activation energy for the PETI composite and resin crosslinking was calculated to be 22.6 and 23.2 kcal/mol, respectively. Variation in rates for resin and composite are discussed. The cure extent as determined by isothermal DSC and by FTIR–PAS measurements were found to be in good agreement.

Curing kinetics and mechanisms of polysulfone nanofibrous membranes toughened epoxy/amine systems using isothermal DSC and NIR

Curing kinetics and mechanisms of polysulfone nanofibrous membranes toughened TGDDM/DDS were investigated by using isothermal DSC and NIR, and compared to those of TGDDM/DDS and PSF films toughened TGDDM/DDS. At early curing stage, the curing rate of nanofibrous membranes toughened system was faster than those of other two systems, whereas the final conversion of toughened systems was lower than that of resin matrix. Most of the primary amine was consumed by gelation and the concentration of secondary amine reached the maximum around gelation. The faster consuming rates of primary and secondary amines in nanofibrous membranes toughened system resulted in higher concentration of hydroxyl groups and tertiary amines at gelation, which led to larger amounts of branching and crosslinking compared to resin matrix. The comparison of the results obtained from two methods showed that the epoxide conversion exhibited identical variations as a function of time, as well as the curing rate.

Quantitative evaluation of fractionated and homogeneous nucleation of polydisperse distributions of water-dispersed maleic anhydride-grafted-polypropylene micro- and nano-sized droplets

Abstract The nucleation processes in waterborne Maleic Anhydride-grafted-Polypropylene micro- and nano-droplet suspensions have been studied. Compared to a previous report on this topic, an extended set of samples in combination with improved particle size distribution data of the samples have been used, which are both essential for the advancement of the analysis. Self-nucleation was utilized to ensure that the observed lowered fractionated crystallization (peak) temperatures – down to the extremely low value of 34 °C – are due to a lack of seeds in the droplets, which seeds for the polypropylene system used are normally active at the heterogeneous crystallization temperature of approximately 110 °C. An unusual self-nucleation behavior was observed in case of samples having a large amount of small droplets, requiring an extremely low self-nucleation temperature in order to suppress all crystallization at the lowest temperatures. Such behavior was observed for block copolymers but has not been reported so far for droplets dispersed in an immiscible matrix, polymeric or not. Another unusual behavior was observed for some self-nucleation temperatures for which apparently two different populations of self-nuclei are created that are suggestive of the α 1 and α 2 crystal structures of isotactic polypropylene. Next, two new methods are presented to quantify various crucial parameters of the nucleation process: one estimates the density of nucleants acting at different temperatures from the combination of dynamic DSC data and particle size distribution (PSD) data, and the other one focuses on the nature of the nucleation mechanism using both isothermal DSC data and PSD data, quantifying the nucleation rate at different temperatures. For the present MA-g-PP dispersions the latter method leads to the conclusion that the lowest crystallization temperatures reflect sporadic nucleation, probably by way of volume (homogeneous) nucleation. In the field of polymer crystallization, polymer dispersions are usually treated as being monodisperse, even though that is rarely the case. This simplification is inadequate for the present calculations, which is why polydispersity has been taken into account in order to quantify the density of nucleants and the kinetics of nucleation. Though in the present study DSC data are used for the calculations, the methods developed can be easily adapted to other techniques like time-resolved X-ray, rheometry and dilatometry.

Solid fraction analysis with DSC in semi-solid metal processing

Solid fraction at the forming temperature is a key parameter in semi-solid processing as it affects the slurry viscosity and the subsequent mould filling at the forming stage. The type as well as the rate of scanning in the DSC experiment impacts the solid fraction analysis. Hence, the DSC experiment for solid fraction analysis must be designed carefully to avoid over- or underestimation of the forming temperatures. Thixoforming involves heating into the semi-solid temperature range followed invariably by an isothermal step and uses a melting scan while the rheo route employs controlled cooling from the liquid state and must rely on a solidification scan. Isothermal as well as conventional scanning DSC experiments were performed in order to better approximate the heating and cooling routines employed in industrial scale semi-solid forming operations. Heating below 2.5 K min −1 and cooling at 0.5 K min −1 produced melting and solidification curves which are in reasonable agreement with the isothermal DSC experiments.

The kinetics of two-stage formation of TiAl 3 in multilayered Ti/Al foils prepared by accumulative roll bonding

The solid-state reactions of Ti/Al multilayered samples produced by Accumulative Roll Bonding (ARB) have been investigated using differential scanning calorimetry, X-ray diffraction and scanning electron microscopy. The kinetics of the formation of the intermetallic compound TiAl 3 was highlighted. Experimental evidence and analysis of the data shows that, there was a two-stage process in the formation of TiAl 3 in the ARB Ti/Al reactive multilayered samples. Calorimetric and microstructural analyses also suggest that the interdiffusion of Al and Ti which led to solid solutions preceded the formation of intermetallic compounds. Despite the apparent chaos in the thickness of the ARB multilayered samples, the distribution of layer spacing did not become broad enough to lose the main features of the double exothermal behaviour. Isothermal DSC shows a larger Avarami constant in ARB Ti/Al multilayered structures than was found in Ti/Al thin films. A modified model based on thin films was set up to describe the kinetic characteristics of the formation of the intermetallic compound TiAl 3 in ARB samples.

Crystallization kinetics and phase transformation in superionic lithium metaphosphate(Li2O–P2O5) glass system

The ionic conductivity of mol%50Li2O–50P2O5 melt quenched glass shows an anomalous increase after its glass transition temperature(Tg) around590 K. On further increasing the temperature gradually, the conductivity decreases owing to the devitrificationof Li2O–P2O5 glass. The evolution of devitrified crystallites was evidenced by XRD patterns. To understand thedevitrification process, isothermal and non-isothermal DSC studies have been carried out on mol%50Li2O–50P2O5 glass.Tg aswell as Tc values are found to increase monotonically with increasing heating rates. Variation ofTg as a function of heating rates has been investigated to evaluate the lower limiting temperature ofTg and the activation energy for structural relaxation. Results of the DSC studies indicate(i) single-stage bulk crystallization of the glass, with DSC traces exhibiting a single transition, (ii) an order parameter (Avrami constant) of2.8 ± 0.1,suggesting internal (bulk) crystallization of the glass, (iii) an activation energy for crystallization equalto 121.7 kJ mol−1 and (iv) the activation energy for structural relaxation,Eg, tobe 558.8 kJ mol−1. The crystallization mechanism is closely associated with the JMA model and theexperimental dataset have been fitted to a non-isothermal Avrami expression and theobtained parameters confirm the experimental results.

Curing kinetics of alkyd/melamine resin mixtures

Alkyd resins are the most popular and useful synthetic resins applied as the binder in protective coatings. Frequently they are not used alone but are modified with other synthetic resins in the manufacture of the coatings. An alkyd/melamine resin mixture is the usual composition for the preparation of coating called 'baking enamel' and it is cured through functional groups of resins at high temperatures. In this paper, curing kinetics of alkyd resins based on castor oil and dehydrated castor oil with melamine resin, has been studied by DSC method with programmed heating and in isothermal mode. The results determined from dynamic DSC curves were mathematically transformed using the Ozawa isoconversional method for obtaining the isothermal data. These results, degree of curing versus time, are in good agreement with those determined by the isothermal DSC experiments. By applying the Ozawa method it is possible to calculate the isothermal kinetic parameters for the alkyd/melamine resin mixtures curing using only calorimetric data obtained by dynamic DSC runs. Depending on the alkyd resin type and ratio in mixtures the values of activation energies of curing process of resin mixtures are from 51.3 to 114 kJ mol-1. The rate constant of curing increases with increasing the content of melamine resin in the mixture and with curing temperature. The reaction order varies from 1.12 to 1.37 for alkyd based on dehydrated castor oil/melamine resin mixtures and from 1.74 to 2.03 for mixtures with alkyd based on castor oil. Based on the results obtained, we propose that dehydrated castor oil alkyd/melamine resin mixtures can be used in practice (curing temperatures from 120 to 160?C).

Rate equations in the study of the DSC kinetics of epoxy-amine reactions in an excess of epoxy

We show in this work that the heat flow signal as acquired applying DSC to systems in an excess of epoxy must be proportional to the rate of consumption of the excess component but not to the rate of reaction. The rate equations reasoning from this finding have been analysed. According to the model, a DSC data set monitoring the reaction progress of an epoxy excess system must be identical to that exhibiting the reaction advance of the formulation at stoichiometry. Experimental data confirming the proposed methodology have been presented. Both non-isothermal and isothermal DSC experiments support adequately the model. The non-linear transform from the excess component measurement into the reaction rate expression has been also commented in the study from the point of view of the kinetics.

Evaluation of the phase composition of amylose by FTIR and isothermal immersion heats

Amylose, a linear component of starch, has been shown to be directly responsible for many of starch's physical properties. In this study isothermal DSC assisted by FTIR spectroscopy was used to determine the phase composition of amylose under various pH conditions and while shear was used to disrupt chain–chain interactions. The analysis was based on a three-phase model consisting of crystalline (type B and single helices), amorphous, and network (physical entanglements and hydrogen bonds related) environments. Varying the pH of the water present in the samples enables the detection of the presence of the networks. Such networks, preferentially located in the amorphous phase, were found to be more reactive to chemical and probably thermal modifications. However, when chain entanglements or hydrogen bond networks are found near or in the helix of the crystalline phase, the polymer becomes more resistant to chemical and physical modification. Furthermore, it was observed that pH and shear could be used to control the morphology, orientation and phase content of amylose, which had a significant impact on the biodegradability of the treated samples.

Theoretical Prediction and Experimental Measurement of the Degree of Cure of Anisotropic Conductive Films (ACFs) for Chip-On-Flex (COF) Applications

The degree-of-cure of an anisotropic conductive film (ACF) was theoretically predicted and experimentally measured to investigate the effect of the degree-of-cure of the ACF on the electrical and mechanical stability of ACF joints and the reliability of COF assemblies. The cure reaction of the ACF observed by isothermal DSC analysis followed an autocatalytic cure mechanism, and the degree-of-cure of the ACF as functions of time and temperature was mathematically derived from an autocatalytic cure kinetics model. To accurately simulate the ACF temperature field during COF bonding process, the thermal properties of the ACF such as thermal diffusivity (alpha), specific heat capacity (Cp), and thermal conductivity (lambda) were experimentally characterized. The degree-of-cures of the ACF as a function of bonding times during COF bonding process were theoretically predicted by the incorporation of the autocatalytic kinetics modeling and the ACF temperature simulation. The predicted degree-of-cures of the ACF were well matched with the experimental data measured by an ATR/FT-IR analysis. The contact resistances of ACF joints and the peel adhesion strengths of COF assemblies were measured to evaluate the electrical and mechanical interconnection stability. According to the results, the contact resistances decreased and the peel adhesion strength increased as the degree-of-cure increased. In addition, to investigate the effect of the degree-of-cure of the ACF on the reliability of COF assemblies, the 85degC and 85% relative humidity (85degC/85% RH) test was performed. The results showed that the reliability of COF assemblies also strongly depends on the degree-of-cure of the ACF.

A multi-peak transformation kinetics model and its application to the isothermal crystallization of Mg 65Cu 25Y 10 amorphous alloy

Transformation kinetic analytical model plays an important role in the prediction of the microstructural evolution. In this paper, a simple formula has been developed for isothermal mixed nucleation transformation as the kinetic parameters of its JMAK-form formula vary upon time. The explored multi-peak transformation kinetics shows that each peak can be treated as a JMAK case, which is consistent with the classical JMAK model in only one peak case. Thereafter, a method has been developed to deal with the isothermal DSC data of multi-peak overlapping transformation. The isothermal crystallization process of Mg 65Cu 25Y 10 amorphous alloy has been explored and fitted well with the multi-peak kinetics model, which indicates a continuous nucleation, three dimensional interface-controlled growth mechanism with three crystallization peaks overlapping each other.

Crystallization kinetic characteristics of oxygen-induced I-phase and Zr 2Cu phase in Zr 65Cu 27.5Al 7.5 glassy alloy

Based on the construction of TTT diagrams by isothermal DSC measurements, the thermal stabilities of Zr 65Cu 27.5Al 7.5 glassy alloys containing 0.68% and 0.06% [O] (molar fraction) were compared. The changing tendencies of the thermal stabilities reflected in the TTT-diagrams were validated by XRD analyses and TEM observations. The crystallization kinetic characteristics of oxygen-induced I-phase and Zr 2Cu phase in Zr 65Cu 27.5Al 7.5 glassy alloy were discussed. It is found that oxygen promotes the precipitation of I-phase and retards the formation of Zr 2Cu phase. If the pre-crystallization event for oxygen-induced I-phase is permitted and the main-crystallization event for Zr 2Cu phase is taken as the thermal stability criterion, the alloy with higher oxygen content has longer onset time for crystallization within a rather large supercooling temperature range. The possibility for the preparation of Zr 65Cu 27.5Al 7.5 glassy alloy-based composite containing oxygen-induced I-phase was also forecasted.

Thermomechanical and Rheological Properties of High‐Molecular‐Weight Poly(ethylene oxide)/Novolac Blends

AbstractBlends of poly(ethylene oxide) (PEO) and novolac‐type phenolic resin were investigated for potential use as a crystallizable switching component for shape‐memory polymer systems with adjustable switching temperature. High‐molecular‐weight PEO and novolac blends with low novolac content were studied. Dynamic and isothermal DSC studies indicated a significant decrease in the crystallization temperature as a result of incorporation of novolac. We investigated the spherulitic morphology using a cross‐polarized optical microscopy and found a decrease in size and regularity of the spherulites with increasing novolac content. The rheological and mechanical properties corroborated the existence of strong interactions through H‐bonding in the amorphous phase.magnified image

パルス圧力付加オリフィス噴射法による球形単分散 Fe-Co 系金属ガラス粒子の作製

Metallic glasses are potentially applied for accurate micro parts because of their good formability and transferability as well as high mechanical properties and excellent magnetic properties. So the raw materials that the volume is precisely controlled are needed for a highly accurate processing. In this study, mono-sized spherical particles of Fe-Co-based metallic glass were prepared by Pulsated Orifice Ejection Method (POEM) and the capabilities of their micro-forming process in the glass transition temperature were investigated. Mono-sized spherical particles of Fe-Co-based metallic glass particles with 200-500 μm of diameter have been obtained by Pulsated Orifice Ejection Method (POEM). The XRD pattern of the particles shows only broad peaks without any crystalline peak. A bright field TEM image of the particles and the selected area diffraction patterns shows only halo patterns that indicate fully amorphous phase. DSC curve shows that supercooled liquid region was ΔT=48 K and a TTT curve can be constructed by isothermal DSC.

示差走査熱量計による昇温法と等温法の測定値の精度検討と劣化検出

The initial oxidation temperature, which can be measured by DSC using dynamic temperature ramp method, is an index which can be obtained rapidly and with high sensitivity, for quantification of degradation of polymeric materials. On the other hand, there are isothermal DSC methods specified in regulatory methods, such as ASTM D3895 and JWWA K144, mainly for evaluation of thermal stability of polyolefins. However, one of the disadvantages of these isothermal methods is that their measurement times are long.Here, we have studied the features of both dynamic and isothermal methods, to investigate the usefulness of the methods for determining degradation of polymers. We compared the accuracy of the results using both methods, with four different polymer samples: polypropylene, high-density polyethylene, poly-4-methyl-1-pentene, and chloroprene rubber.By using dynamic method, more accurate results compared with that by isothermal one were obtained. In addition to this, smaller amount of sample was needed for the former method to evaluate the degradation. Furthermore, the dynamic method was more sensitive than other conventional methods used for degradation studies, such as tensile strength test and FT-IR analysis.

Cure kinetics, dynamic mechanical and morphological properties of epoxy resin–Im6NiBr2 system

The aim of this study was to examine effects of a catalyst of Nickel–imidazole, i.e. Im6NiBr2 on the cure reaction and network properties of diglycidyl ether of bisphenol A. DSC and FT-IR measurements are carried out on the epoxy resin loaded with 5, 15, and 30 phr of nickel salt to get some insights into the storage stability. It has been concluded that the storage stability has mainly depended on the epoxy composition and was the lowest for the highest level of curing agent. Kinetics of the cure has been described by applying iso-conversional method of Ozawa to scanning DSC data demonstrating that the studied cure reaction is autocatalytic in nature. The Kamal phenomenological approach has been utilized to fit the experimental isothermal DSC data. The model showed a satisfactory fitting of the experimental results at either early stages or at the final steps of the studied cure reaction. Further, the model did not provide a reasonable fitting in the propagation step of polymerization, 0.3<α<0.5, possibly due to existence of the additional reaction/s which did not consider in the used model. DMTA is used to find the optimum cure schedule. It has been shown that the sample with a postcure treatment offers the highest value of glass transition temperature (Tg) in the tanδ peak. SEM and X-ray analyses are employed to investigate the fracture surface morphology and to understand the distribution of nickel in the cured samples exhibiting that the nickel is scattered in the continuous phase homogenously. Flexural properties of the sample cured at optimum conditions are also determined.

Triton X-100 Partitioning into Sphingomyelin Bilayers at Subsolubilizing Detergent Concentrations: Effect of Lipid Phase and a Comparison with Dipalmitoylphosphatidylcholine

We examined the partitioning of the nonionic detergent Triton X-100 at subsolubilizing concentrations into bilayers of either egg sphingomyelin (SM), palmitoyl SM, or dipalmitoylphosphatidylcholine. SM is known to require less detergent than phosphatidylcholine to achieve the same extent of solubilization, and for all three phospholipids solubilization is temperature dependent. In addition, the three lipids exhibit a gel-fluid phase transition in the 38–41°C temperature range. Experiments have been performed at Triton X-100 concentrations well below the critical micellar concentration, so that only detergent monomers have to be considered. Lipid/detergent mol ratios were never <10:1, thus ensuring that the solubilization stage was never reached. Isothermal titration calorimetry, DSC, and infrared, fluorescence, and 31P-NMR spectroscopies were applied in the 5–55°C temperature range. The results show that, irrespective of the chemical nature of the lipid, Δ G° of partitioning remained in the range of −27 kJ/mol lipid in the gel phase and of −30 kJ/mol lipid in the fluid phase. This small difference cannot account for the observed phase-dependent differences in solubilization. Such virtually constant Δ G° occurred as a result of the compensation of enthalpic and entropic components, which varied with both temperature and lipid composition. Consequently, the observed different susceptibilities to solubilization cannot be attributed to differential binding but to further events in the solubilization process, e.g., bilayer saturability by detergent or propensity to form lipid-detergent mixed micelles. The data here shed light on the relatively unexplored early stages of membrane solubilization and open new ways to understand the phenomenon of membrane resistance toward detergent solubilization.

Curing behavior study of polydimethylsiloxane‐modified allylated novolac/4,4′‐bismaleimidodiphenylmethane resin

AbstractThe curing behavior of polydimethylsiloxane‐modified allylated novolac/4,4′‐bismaleimidodiphenylmethane resin (PDMS‐modified AN/BDM) was investigated by using Fourier transform infrared spectrometry (FTIR) and differential scanning calorimetry. The results of FTIR confirmed that the curing reactions of the PDMS‐modified AN/BDM resins, including “Ene” reaction and Diels–Alder reaction between allyl groups and maleimide groups, should be similar to those of the parent allylated novolac/4,4′‐bismaleimidodiphenylmethane (AN/BDM) resin. The results of dynamic DSC showed that the total curing enthalpy of the PDMS‐modified AN/BDM resins was lower than that of the parent resin. Incorporation of polydimethylsiloxane (PDMS) into the backbone of the allylated novolac (AN) resin favored the Claisen rearrangement reaction of allyl groups. The isothermal DSC method was used to study the kinetics of the curing process. The experimental data for the parent AN/BDM resin and the PDMS‐modified AN/BDM resins exhibited an nth‐order behavior. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Thermal studies of pre-formulates of metronidazole obtained by spray drying technique

Compatibility studies between active drugs and excipients are substantial in the pharmaceutical technology. The objective of the present work was to develop pre-formulated mixtures of metronidazole (MT) obtained by spray drying (SPDR) and their thermoanalytical characterization. Dynamic and isothermal TG, conventional DSC and DSC coupled to a photovisual system were used. DSC experiments with both techniques confirmed the homogeneity of the conventional and pre-formulated mixtures. The TG data made possible the comparison the thermal stability of the different mixtures. Similar thermal stabilities were found of the conventional and pre-formulated mixtures, with slower particles sizes of MT.

Curing behavior of a novel polytriazole resin

AbstractThe curing behavior of a novel low temperature curing polytriazole resin, prepared from p‐xylylene diazide and N,N,N′,N′‐tetrapropargyl‐p,p′‐diaminodiphenylmethane, was investigated by DSC and rheological analyses. The kinetics of the curing of the resin was studied by nonisothermal and isothermal DSC measurements and the kinetics parameters were obtained. The values of apparent activation energy Ea of the curing reaction obtained by nonisothermal and isothermal DSC are 80.7 and 75.3 kJ/mol, respectively. The curing of the resin was traced by the isothermal rheological analysis. The gelation times of the resin at 70, 75, 80, and 85°C are about 200, 150, 110, and 75 min, respectively. The viscosity equation for the resin was found as follows: $ \ln \eta= -107 + {{33.5 \times 10^3} \over T} + t \exp \left(26.3 + {{9.87 \times 10^3} \over T}\right). $ © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007