Temperature-modulated Differential Scanning Calorimetry Research Articles

Dynamics of Di(propylene glycol) Dibenzoate-d10 in Poly(vinyl acetate) by Solid-State Deuterium NMR

Deuterium solid-state NMR and temperature-modulated differential scanning calorimetry were used to probe the dynamics of the plasticizer di(propylene glycol) dibenzoate (DPGDB-d10) in mixtures with...

Comparative evaluation of new carriers for controlled drug delivery based on Eudragit EPO/L100 interpolyelectrolyte complexes

New interpolyelectrolyte complexes (IPECs) between oppositely charged Eudragit® EPO and Eudragit® L100 were investigated with a view to the development of oral controlled drug delivery systems (DDS). Structural features of the samples were evaluated by modulated-temperature differential scanning calorimetry (MTDSC). The results confirmed that all IPECs were chemically homogeneous and were characterized by only one glass-transition temperature. Evaluation of the diffusion-transport properties of the investigated IPECs revealed the basic mechanisms responsible for the controlled delivery of drugs with different physicochemical properties. The results showed that the synthesized IPECs have great potential to be used as pH-sensitive oral controlled DDS.

A novel method for improving the physicochemical properties of diesel and jet fuel using polyaspartate polymer additives

Thermal Polyaspartate Anion, a derivative biopolymer of aspartic acid, was used to remove water residues of both diesel and jet liquid hydrocarbons fuels. In this work a novel and simple method for improving the properties of fuel is reported. Different masses of TPA polymer have been mixed with a constant volume of fuel and the humidity concentration, the heat of combustion, the flash point as well the cetane index were measured according to the ASTM standard protocols. For the evaluation of the effect of the polymer additive in the physicochemical properties of the fuel, a number of ASTM standard measurements were followed. In addition, Fourier transform infrared spectroscopy (FTIR), temperature-modulated differential scanning calorimetry (TM-DSC) and thermogravimetric analysis (TGA) were used in order to evaluate the interactions between water and polymer. The removal of the humidity/water is requisite in fuel technology because of the numerous problems related to the presence of water, such as: corrosion of engine parts, pipelines and storage reservoirs, ice formation at very low temperatures and turbidity growth due to impurities. Water removal improved the physicochemical properties of both studied fuels, diesel and jet, up to 463j/g and 1040j/g for the heat of combustion, 28.2% and 71.4% for the total acid number and up to 39.4% and 25.7% for humidity, for diesel fuel and jet fuel respectively. Overall, the proposed method can be used in a simple fuel cleaning process using a metal mesh vessel of Thermal Polyaspartate Anion (TPA) polymer. The polymer can be replaced and re-generated as often needed.

Synthesis of poly(acrylate-styrene)/poly(acrylate-styrene) core/shell latex and TOPEM-DSC characterization

Poly(acrylate-styrene)/poly(acrylate-styrene) core/shell latex particles were synthesized via seeded semi-continuous emulsion polymerization. Both core polymer (CP) and shell polymer (SP) were copolymerized by using three identical monomers of methyl methacrylate (MMA), butyl acrylate (BA) and styrene (St) with different composition ratios. The synthesized core/shell latex particle presents a phase separated state with the interfacial layer between CP and SP. In this study, the weight fractions and the corresponding thickness of this interfacial layer, CP and SP phase in the core/shell latex particle has be successfully calculated by using multi-frequency temperature-modulated differential scanning calorimetry (TOPEM-DSC). The results indicate that the interfacial layer thickness of the core/shell latex particle is determined by the core/shell structure, such as hard core/soft shell (defined as HC/SS) and soft core/hard shell (defined as SC/HS), the glass transition temperature (Tg) of the “hard” phase (correspondingly core or shell for HC/SS or SC/HS structure, respectively), and the existence of hydrophilic monomer during the copolymerization process such as acrylic acid. Meanwhile, the influence of film-formation-temperature on the microstructure of the latex films was systematically explored in this work.

Phase behaviour and in vitro hydrolysis of wheat starch in mixture with whey protein

Network formation of whey protein isolate (WPI) with increasing concentrations of native wheat starch (WS) has been examined. Small deformation dynamic oscillation in shear and modulated temperature differential scanning calorimetry enabled analysis of binary mixtures at the macro- and micromolecular level. Following heat induced gelation, textural hardness was measured by undertaking compression tests. Environmental scanning electron microscopy provided tangible information on network morphology of polymeric constituents. Experiments involving in vitro starch digestion also allowed for indirect assessment of phase topology in the binary mixture. The biochemical component of this work constitutes an attempt to utilise whey protein as a retardant to the enzymatic hydrolysis of starch in a model system with α-amylase enzyme. During heating, rheological profiles of binary mixtures exhibited dramatic increases in G′ at temperatures more closely related to those observed for single whey protein rather than pure starch. Results from this multidisciplinary approach of analysis, utilising rheology, calorimetry and microscopy, argue for the occurrence of phase separation phenomena in the gelled systems. There is also evidence of whey protein forming the continuous phase with wheat starch being the discontinuous filler, an outcome that is explored in the in vitro study of the enzymatic hydrolysis of starch.

Heat capacities and thermodynamic properties of Co(3,5-PDC)(H2O)

A novel metal-organic frameworks Co(3,5-PDC)(H2O) (CoMOF, 3,5-PDC = pyridine-3,5-dicarboxylic acid) has been synthesized hydrothermally and characterized by single-crystal XRD and FT-IR spectra. The thermal stability and the decomposition mechanism of CoMOF were investigated by thermogravimetry-mass spectrometry, and a two-stage shape curve of mass loss was observed. Moreover, the low-temperature molar heat capacities were measured by temperature-modulated differential scanning calorimetry for the first time. The thermodynamic parameters such as entropy and enthalpy relative to reference temperature 298.15 K were derived based on the molar heat capacity data.

Heat capacities and thermodynamic properties of a 3D Cu(II) supramolecular complex

A 3D supramolecule (H3O)2[Cu(2,6-pdc)2]·H2O (pdc = pyridinedicarboxylate) has been solvothermally synthesized and characterized by X-ray powder diffraction and FT-IR spectrum. The thermal decomposition characteristics of the complex were investigated by thermogravimetric analysis, which revealed a three-step mass loss process. The low-temperature molar heat capacities of crystalline (H3O)2[Cu(2,6-pdc)2]·H2O were measured by temperature-modulated differential scanning calorimetry for the first time. A phenomenon of glass transition was observed. The thermodynamic parameters such as entropy and enthalpy relative to 298.15 K were calculated based on the above molar heat capacity data.

Thermal Stability and Crystallization Behavior of TER Blends of Isotactic Polypropylene (iPP)/Ethylene-Propylene Diene Rubber (EPDM)/Nitrile Rubber (NBR)

The blends of isotatic polypropylene (iPP), ethylene-propylene diene rubber (EPDM), and nitrite rubber (NBR) were prepared using dimethylol phenolic resin as a crosslinking system. The dynamically crosslinked blends of iPP/EPDM/NBR showed superior thermal stability to that of virgin isotactic polypropylene (iPP). Dynamic crosslinking rendered the vulcanizate thermally more stable as compared to uncrosslinked blends, which can be attributed due to the variations in degree of crosslinking and degree of crystallinity. Crystallization of iPP in the blends of iPP/EPDM/NBR was also studied through Temperature Modulated Differential Scanning Calorimetry (TMDSC). Other detailed analysis of endotherm peaks obtained after first and second melts in terms of heat of enthalpy, degree of undercooling, and degree of crystallinity were also evaluated. Various kinetic parameters were also determined. Degree of crosslinking increases the interfacial adhesion between the iPP and EPDM/NBR phases. Dimethylol phenolic resin used as a compatibilizer also enhanced the thermal stability of the iPP/EPDM/NBR blends.

Unique evolution of spatial and dynamic heterogeneities on the glass transition behavior of PVPh/PEO blends

Glass transition behavior of hydrogen bonded polymer blends of poly(vinyl phenol) (PVPh) and poly(ethylene oxide) (PEO) is systematically investigated using normal differential scanning calorimetry (DSC) and recently developed multifrequency temperature-modulated DSC (TOPEM), in combination with Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) techniques, focusing on the effect of the PEO molecular weight on the spatial and dynamic heterogeneity. It is found, for the first time, that both the glass transition temperature (T g) and activity energy (E a) of the blends strongly depend on PEO molecular weight, and a common turning point, which separates the rapid and slow increasing regions, can be found. The interchain hydrogen bonding interactions, both determined by FTIR measurements and obtained from the Kwei equation, decrease with increasing PEO molecular weight, indicating a decrease of the componential miscibility. A series of parameters related to the microscopic spatial and dynamic heterogeneity, such as the activity energy, fragility, nonexponential factor and the size of cooperatively rearranging regions, are calculated from frequency dependency complex heat capacity measured using TOPEM. It is found that each of these parameters monotonically changes with increasing the PEO molecular weight during the glass transition process, demonstrating that hydrogen bonding interaction is the key factor in controlling the spatial and dynamic heterogeneity, thus the glass transition. NMR relaxation results reveal the existence of obvious phase separation large than 5 nm, implying that the cooperatively rearranging regions should be closely related to the interphase region between the two components. The above obtained origin and evolution of spatial and dynamic heterogeneity provide a new insight into the glass transition behavior of polymer blends.

Development of fully amorphous dispersions of a low Tg drug via co-spray drying with hydrophilic polymers

The aim of the study was to prepare molecular dispersions of a physically highly unstable amorphous drug, paracetamol (acetaminophen with a Tg of ca. 25°C) via co-spray drying with a variety of polymers. Solid dispersions at a range of drug loadings (10–90%w/w) using hydroxypropyl methylcellulose/acetate succinate (HPMC/HPMC AS), polyvinylpyrrolidone (PVP) and copovidone were produced and characterised by modulated temperature differential scanning calorimetry (MTDSC), thermogravimetric analysis (TGA), X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). PVP-based polymers showed a greater tendency than the HPMC-based group to generate temperature-stable dispersions. In particular, copovidone (Plasdone® S-630) was found to be the most effective of the polymers studied and could formulate molecular dispersions at drug loadings up to and including 40%w/w. However, no evidence for direct drug–polymer interactions was found for such systems as a possible stabilising mechanism. The expected relationship of a higher Tg of the polymer leading to greater stabilisation was not observed, while there was an inverse relationship between viscosity grade and amorphous phase generation. The study has therefore shown that temperature-stable amorphous dispersions of a low Tg drug may be prepared by co-spray drying, particularly using PVP-based polymers.

Thermal degradation kinetics of poly(trimethylol propane triacrylate)/poly(hexane diol diacrylate) interpenetrating polymer network

Interpenetrating polymer networks (IPNs) of trimethylol propane triacrylate (TMPTA) and 1,6-hexane diol diacrylate (HDDA) at different weight ratios were synthesized. Temperature modulated differential scanning calorimetry (TMDSC) was used to determine whether the formation resulted in a copolymer or interpenetrating polymer network (IPN). These polymers are used as binders for microstereolithography (MSL) based ceramic microfabrication. The kinetics of thermal degradation of these polymers are important to optimize the debinding process for fabricating 3D shaped ceramic objects by MSL based rapid prototyping technique. Therefore, thermal and thermo-oxidative degradation of these IPNs have been studied by dynamic and isothermal thermogravimetry (TGA). Non-isothermal model-free kinetic methods have been adopted (isoconversional differential and KAS) to calculate the apparent activation energy (Ea) as a function of conversion (α) in N2 and air. The degradation of these polymers in N2 atmosphere occurs via two mechanisms. Chain end scission plays a dominant role at lower temperature while the kinetics is governed by random chain scission at higher temperature. Oxidative degradation shows multiple degradation steps having higher activation energy than in N2. Isothermal degradation was also carried out to predict the reaction model which is found to be decelerating. It was shown that the degradation of PTMPTA follows a contracting sphere reaction model in N2. However, as the HDDA content increases in the IPNs, the degradation reaction follows Avrami–Erofeev model and diffusion governed mechanisms. The intermediate IPN compositions show both type of mechanism. Based on the above study, debinding strategy for MSL based microfabricated ceramic structure has been proposed.

Mechanical spectra and calorimetric evaluation of gelatin–xanthan gum systems with high levels of co-solutes in the glassy state

Mechanical properties of gelatin–xanthan gum (XG) mixtures with high levels of co-solutes were examined by dynamic mechanical analysis (DMA). The mechanical spectra of the samples were modeled according to the Williams–Landel–Ferry (WLF) equation/free-volume theory, which requires an entropic lightly cross-linked network. For the α dispersion, E′ and E′′ superposed with the horizontal shift factor aT, which was temperature-dependent according to the WLF equation; no other secondary dispersion mechanism was detected. The addition of XG to gelatin networks with high levels of co-solutes changed the glass transition temperature (Tg) and kinetics of glass transition and glassy states. In the glassy state, the WLF equation was unable to follow progress in the mechanical properties, which were better described by the Andrade equation. The calorimetric measurements of the gelatin–XG systems were made using a modulated temperature differential scanning calorimetry (MTDSC) to improve the determination of Tg. The samples were exposed to two cooling and heating cycles to provide a controlled recent thermal history in the temperature range of 40 °C to −70 °C. The Tg values of the samples were determined from the second heating cycle in the reversing heat signal. The calorimetric Tg values increased with increasing glucose syrup:sucrose ratio due to increased crosslinking, whereas mechanical Tg decreased with increased XG content due to network formation.

TMDSC phase angle for a better nanocomposite interphase identification

The present study suggests a new approach, based on the utilization of temperature modulated differential scanning calorimetry (TMDSC) technique, for identifying and characterizing the organic–inorganic interphase of two materials: an epoxy–fumed silica nanocomposite and a thermoplastic polyurethane (TPU)–multiwalled nanotube (MWNT) composite. The approach used here makes use of TMDSC data and basically consists of using the phase angle or the derivative of the reversing heat flow instead of the reversing heat flow curve itself. In the case of epoxy–fumed silica composites, two glass transition regions were identified. The glass transition temperature (Tg) of the composite was observed to vary as a consequence of the filler content. This study shows that the Tg variation is due to the formation of an organic–inorganic interphase, with its own glass transition temperature, which is different from the epoxy matrix Tg. In the case of TPU–MWNT composites, two relaxations and an additional first order transition were observed: the first relaxation corresponds to the hard segment, the second is related to an interaction between filler and matrix and the third process may be connected to the partial melting of the hard segment. The addition of 0.5 wt% MWNT causes a small reduction in Tg of the TPU. A major nanotube addition, 10 wt%, induces the appearance of a new relaxation that may be associated with the existence of an interface. In general, a better separation between the matrix and interphase glass transitions was obtained by the TMDSC phase angle signal.

Thermal behavior and phase identification of Valsartan by standard and temperature-modulated differential scanning calorimetry

Thermal behavior of angiotensin II type 1 (AT1) receptor antagonist, Valsartan (VAL), was examined employing thermogravimetric analysis (TGA), standard differential scanning calorimetry (DSC) and temperature-modulated differential scanning calorimetry (TMDSC). The stability of VAL was measured by TGA from 25 to 600°C. Decomposition of Valsartan starts around 160°C. The DSC curve shows two endotherms, occurring around 80°C and 100°C, related to evaporation of water and enthalpy relaxation, respectively. Valsartan was identified by DSC as an amorphous material and it was confirmed by X-ray powder diffraction. The glass transition of fresh Valsartan appears around 76°C (fictive temperature). TMDSC allows separation of the total heat flow rate into reversing and nonreversing parts. The nonreversing curve corresponds to the enthalpy relaxation and the reversing curve shows changes of heat capacity around 94°C. In the second run, TMDSC curve shows the glass transition process occurring at around 74°C. Results from standard DSC and TMDSC of Valsartan were compared over the whole range of temperature.

Apparent heat capacity measurements and thermodynamic functions of d(−)-fructose by standard and temperature-modulated calorimetry

The qualitative and quantitative thermal analyses of crystalline and amorphous d(−)-fructose were studied utilising methods of standard differential scanning calorimetry (DSC), quasi-isothermal temperature-modulated differential scanning calorimetry (quasi-isothermal TMDSC), and thermogravimetric analysis (TGA). Advanced thermal analysis of fructose was performed based on heat capacity. The apparent total and apparent reversing heat capacities, as well as phase transition parameters were examined on heating and cooling. The melting temperature, Tm, of crystalline d(−)-fructose shows a heating rate dependency, which increases with raising the heating rate and leads to superheating. The equilibrium melting temperatures: Tm∘(onset)=370K and Tm∘(peak)=372K, and the equilibrium enthalpy of fusion ΔfusH°=30.30kJ·mol−1, of crystalline d(−)-fructose were estimated on heating for the results at zero heating rate. Anomalies in the heat capacity in the liquid state of d(−)-fructose, assigned as possible tautomerisation equilibrium, were analysed by DSC and quasi-isothermal TMDSC, both on heating and cooling. Thermal stability of crystals in the region of the melting temperature was examined by TGA and quasi-isothermal TMDSC. Melting, mutarotation, and degradation processes occur simultaneously and there are differences in values of the liquid heat capacity of d(−)-fructose with varied thermal history, measured by quasi-isothermal TMDSC. Annealing of amorphous d(−)-fructose between the glass transition temperature, Tg, and the melting temperature, Tm, also leads to crystallization of the sample and shows changes in the total apparent heat capacity. The experimental, apparent heat capacity of fully crystalline and fully or partially amorphous d(−)-fructose was analysed with reference to the solid (vibrational) and liquid heat capacities based on the ATHAS scheme.

Solid-state Reaction Study on Physically and Tribochemically Prepared BaC2O4-SnC2O4 Mixtures

The synthesis of barium metastannate, BaSnO3, by heating mixtures of metal oxalates, either physically mixed or subjected to a phase of mechanical activation, up to temperatures in the range 750- 1200 °C has been studied. Simultaneous thermogravimetric-differential scanning calorimetric (TGDSC) analyses and powder X-ray diffractometry have been applied to check the advancement of the reactions. BaSnO3, though slightly contaminated by BaCO3, can be obtained by heating the activated mixture up to T ≥ 1000 °C while heating a sample of a physical mixture at temperature as high as 1200 °C resulted in a mixture of BaSnO3, SnO2 and Ba2SnO4. The heat capacities of BaSnO3 samples prepared at temperatures between 1000 and 1200 °C have been measured by modulated temperature differential scanning calorimetry (MTDSC) in the temperature range 50-400 °C.

The Extrapolation Method for Hyper Differential Scanning Calorimetry

In order to eliminate the temperature lag effect and obtain the accurate temperature results from hyper differential scanning calorimetry (Hyper-DSC) operated at high heating rate, an adjustable method, namely “Extrapolation Method”, had been introduced by us in former papers. And in this paper, we wanted to support the accuracy of this method by other instruments. Specifically, the extrapolated glass transition temperatures (Tg, 61.5 °C) of PLA film, which was obtained by Hyper-DSC, was close to the value detected directly by normal DSC (62.0 °C). And the extrapolated Tg of waxy starch film (59.7 °C for 8.7% moisture content, and 57.2 °C for 11.2% moisture content) was close to the values detected by modulated temperature DSC (MT-DSC) (63.6 °C and 56.8 °C correspondingly). Consequently, these experimental results support that the “Extrapolation Method” is a feasible way to eliminate temperature lag effect for Hyper-DSC.

Improvement of Water Barrier Properties of Poly(ethylene-co-vinyl alcohol) Films by Hydrophobic Plasma Surface Treatments

Poly(ethylene-co-vinyl alcohol) (EVOH) films with two different ethylene contents (29 and 44 mol %) have been treated by hydrophobic plasma (CF4, tetramethylsilane (TMS), CF4/H2, and CF4/C2H2). Conditions of the cold plasma treatment were optimized by the water contact angle measurements as a function of the different plasma parameters (plasma power, gas flow, and treatment time). Chemical changes of the film surface were characterized by X-ray photoelectron spectroscopy. The obtained results revealed the presence of fluorine containing functional groups such as CF, CF2, and CF3 in the case of CF4, CF4/H2, and CF4/C2H2 plasma treatment and the presence of SiOxCy compounds after TMS treatment. The morphology of the plasma treated EVOH films was examined by atomic force microscopy, which indicated an increase of the film roughness after treatment. Negligible changes of thermal properties of the modified EVOH films were observed by means of the temperature modulated differential scanning calorimetry. The barrier properties of films were characterized by water permeability measurements. It was found that the hydrophobicity was significantly improved after plasma treatment and for some treated films the water permeability was decreased up to 28%.

Influence of temperature and UV intensity on photo-polymerization reaction studied by photo-DSC

Photo-DSC was used to investigate the cure kinetics of a photo-initiated resin. The exothermal photo-polymerization reactions were performed in isothermal mode. The irradiation of photo-initiated resin was studied under different conditions of temperature, UV lamp intensity, and reaction atmosphere (nitrogen and air). The results obtained by photo-DSC allowed us to determine kinetic data of the photo-polymerized reactions: the global activation energy and reaction enthalpy, and the conversion as a function of time and temperature. Modulated temperature DSC measurements were carried out to verify whether vitrification occurs during polymerization. The conversion at the top and bottom of irradiated samples was obtained by FT-IR spectroscopy before and after photo-polymerization. A non-homogenous photo-polymerization into the material was observed, probably because of the light absorptions effects within the uppermost layers.

On the frequency correction in temperature-modulated differential scanning calorimetry of the glass transition

Temperature-modulated differential scanning calorimetry (TMDSC) is based on conventional DSC but with a sinusoidally modulated temperature path. Simulations of TMDSC signals were performed for Corning EAGLE XG glass over a wide range of modulation frequencies. Our results reveal that the frequency correction commonly used in the interpretation of TMDSC signals leads to a master nonreversing heat flow curve independent of modulation frequency, provided that sufficiently high frequencies are employed in the TMDSC measurement. A master reversing heat flow curve can also be generated through the frequency correction. The resulting glass transition temperature from the frequency corrected reversing heat flow is thereby shown to be independent of frequency.