Linear isothermal crystal growth rate of i-polypropylene by differential scanning calorimetry

In the present work equations are derived that enable us to calculate the linear crystal growth rate using DSC-isothermal peaks. The primary nuclei density is taken into account by measuring the average spherulite radius of already crystallized samples by means of polarization microscopy. The results, thus obtained, show that the isothermal crystallization process of i-polypropylene proceeds in two stages, the second one being of higher rate.     

Differential scanning calorimetry of confectionery fats. Pure triglycerides: Effects of cooling and heating rate variation

Differential scanning calorimetry (DSC) measurements of the crystallization and melting phenomena of pure forms of the three principal triglycerides present in cocoa butter and related confectionery fats are presented. The results are used to exhibit the usefulness of the DSC technique for potential application in quality control of these types of material, but also as a warning of the difficulties in interpretation of data. The results also serve as a reference for future use in DSC studies of similar materials. On behalf of Loders-Croklaan.     

Studies of polymerization of acrylic monomers using luminescence probes and differential scanning calorimetry

A fiber optic system has been designed to couple calorimeter and fluorimeter equipment for in situ monitoring of polymerization reactions by both techniques simultaneously. Two acrylic monomers (cyclohexyl methacrylate, CHM, and 2-ethylhexyl acrylate, EHA) were studied at different temperatures. Pyrene (Py) was employed at a low concentration (≤10^?4 mol/L) as a fluorescence probe. The emission spectrum of pyrene shows a broad band peaking at 390 nm, whose intensity grows with polymerization progress. A correlation with conversion degree could be established by collecting fluorescence intensity through the optical fiber at different polymerization times. For the more flexible polymer formed, poly(ethylhexyl acrylate) (PEHA), Py emission sharply increases only when high conversions are reached and continues increasing for a long time after the limiting conversion is attained. For CHM polymerizations, S-shaped curves are found. Isochronal plots of intensity vs. scaled conversion allow elaboration of master curves for the peak emission. Data at 50°C for CHM cannot be fitted to the master curve, and this is explained in terms of vitrification.     

Polymerization of methyl α-cyanoacrylate: 3. Study of radical polymerization by differential scanning calorimetry

A calorimetric method has been used to follow the free radical polymerization of methyl α-cyanoacrylate in bulk at 50°, 60° and 70°C and with nitromethane, benzene and dioxane as diluents at 60°C. In the initial stages, kinetic orders with respect to initiator were close to 0.5 even in systems where polymer separated as it was formed. For bulk monomer, polymerization ceased at about 90% conversion but resumed on raising the temperature. The heat of polymerization was ～42 kJ/mol.     

Characterisation of waxes by differential scanning calorimetry

The characterisation of hydrocarbon and natural waxes by differential scanning calorimetry is described. It is shown that the determination of the melting, cooling and remelting curves of a wax, and comparison with the corresponding curves of authenticated waxes, affords a rapid and valuable method for the identification of many waxes. Heats of transition of many waxes are also given.     

Influence of hot-melt extrusion and compression molding on polymer structure organization,investigated by differential scanning calorimetry

A blend of a pullulan polymer and 1,2,6-hexanetriol as a plasticizer were used to study the effect of melt processing techniques on the physical properties of the resulting materials. The main advantage of pullulan is its linear polysaccharide chain model structure. Hot-melt extrusion and compression molding were performed under the same temperature and pressure conditions. The materials obtained were analysed by differential scanning calorimetry. For the first time, the comparative effect of the two processing techniques, i.e., extrusion and compression molding, on the polymer arrangement is reported. Endothermic events resulted from the melt extrusion process were shown to be related to different structures of oriented populations of macromolecules and to microphase separation. Orientation was enhanced by cooling the extrudate at the die exit, with a corresponding increased enthalpy from 34.7 to 51.4 J/g. In contrast, when using compression molding, the endotherm was less marked (11.9 J/g), suggesting less orientation, but the shape of the thermogram was quite similar to that of the extrudate. In both cases, we observed a loss of orientation when the molded materials were milled. A semiquantitative kinetic study of the disorientation process of the extrudate upon isothermic tempering suggests that a disorientation phenomenon occurs at the same time as a swelling process due to the presence of microphase separation. The extrudate was shown to be stable at 25°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3124–3132, 2001     

The rate of crystallization of poly(ethylene terephthalate) by differential scanning calorimetry

The value of t_max in differential scanning calorimetry is correlated with the crystallization kinetics of poly(ethylene terephthalate) (PET). The Avrami exponent, n, obtained varies as a result of a change in slope of the curve at the point t_n, a secondary crystallization transition. The plot of t_n vs. t_max shows a linear relationship. The rate of crystallization depends upon both molecular weight and crystallization temperature. Under a nucleation controlling step, the plot of log t_max vs. \documentclass{article}\pagestyle{empty}\begin{document}$ t_{\max } vs.\frac{1}{{T^2 \Delta T}} $\end{document}gives a linear relationship. Theoretical concepts of the treatment are discussed.     

Study of polyethylene blends by differential scanning calorimetry

The melting behaviors of linear and branched polyethylene blends were studied using a Perkin-Elmer DSC-1B differential scanning calorimeter. Three endothermic peaks were occasionally observed in the DSC thermogram on polyethylene blends which had not been subjected to any isothermal annealing. The nature of the third intermediate temperature peak is discussed in relation to the prior cooling rate, the blend composition and the molecular structures of both components. The results appear to indicate that the intermediate peak is associated with the fusion of the hybrid crystallites of linear and branched polyethylenes. These hybrid crystallites seem to be formed on the rapid cooling of lean linear polyethylene blends. Blends containing low molecular weight branched polyethylene seem inclined to form the hybrid crystallites.     

Determination of cellulose accessibility by differential scanning calorimetry

The thermal behavior of various cellulose samples with different degrees of crystallinity as measured by X-ray diffraction techniques was studied with a differential scanning calorimeter (DSC). The broad endothermic peak which appears between 110 and 160°C is due to loss of absorbed (bound) water. Since a direct relationship was observed between the area of this peak and the crystallinity of the sample, a new procedure for estimating cellulose accessibility (which is related to crystallinity) was proposed and developed. DSC curves obtained on cellulose samples preconditioned at certain constant relative humidities were used to determine sample accessibilities by the proposed method. The accessibility values obtained by DSC showed excellent agreement with crystallinity values determined by more traditional techniques. Completely amorphous cellulose was obtained by anhydrous deacetylation of cellulose triacetate and was used as the standard amorphous cellulose material.     

Characterization of epoxy thermosetting systems by differential scanning calorimetry

Differential Scanning Calorimetry (DSC) is used to study the curing behavior of epoxy systems. For non-catalyzed diamine-epoxy systems, the reaction enthalpy ΔH and the glass transition temperature T_g are evaluated and related to the structure of the hardener. A method is developed to determine the activation energy. The effect of variations in the amine-to-epoxy ratio r on T_g is also examined. A maximum value is observed for r = 1. Then, the influence of benzyldimethylamine as catalyst in an anhydride/DGEBA system and in three diamine/DGEBA systems is reported. In the cases of DDS and DDA curing agent the maximum value of T_g is shifted, to r = 0, 6. The results are explained by different reaction mechanisms.     

The measurement of fatty solids by differential scanning calorimetry

A method has been developed for the measurement of the solids content of vegetable and animal fats by differential scanning calorimetry. Although precision is about half that of existing dilatometric methods, this is a rapid procedure, designed for hydrogenation control. Elapsed analysis time for the determination of solids at two temperatures is about 40 min, compared with 3 to 4 hr by dilatometry. Procedures are outlined employing either of two commercially available instruments.     

Characterization of multicomponent polyethylene blends by differential scanning calorimetry

The melting behavior of physical blends prepared from low, medium, and high density polyethylene was examined by differential scanning calorimetry. Binary low/high and ternary low/medium/high density polyethylene blends showed two endothermic peaks which were attributed to the melting of the lower and higher density components. The percent crystallinity of the blends was calculated according to an additivity relationship using the crystallinity of the pure components. These results compared favorably with an experimental crystallinity measured from the area under the melting curves.     

Phenol-formaldehyde impregnant characterization by infrared spectroscopy and differential scanning calorimetry

A series of resol-type phenol-formaldehyde resins was investigated by infrared spectroscopy and differential scanning calorimetry. The molar ratio of phenol to formaldehyde was determined from the absorbance ratio D₁₀₁₀/D₁₆₁₀. Differences between the reactivities of resins were confirmed by the molar phenol to formaldehyde ratio, heat of reaction and gelation time.     

Effects of various parameters in differential scanning calorimetry of hydrogen-peroxide-treated lignocellulose

Differential scanning calorimetric (DSC) analyses of mixtures of hydrogen peroxide and lignocellulosic materials have been performed. The influence of chamber atmosphere composition, heating rate, pinhole size, lignocellulose particle size, and hydrogen peroxide-to-lignocellulose ratio were examined. With the exception of particle size, the variables produced significant effects on the DSC curves. These effects were mainly connected with changes in the atmosphere surrounding the sample, sample density, heat capacity, and heat conductance.     

Poly (acrylic acid) and poly (sodium styrenesulfonate) compatibility by Fourier transform infrared and differential scanning calorimetry

Blends of poly(acrylic acid) (PAA) and poly(sodium styrene sulfonate) (PSSNa) were prepared from polymer solutions by solvent evaporation. The observed decrease in PAA-solution pH upon addition of PSSNa suggests an inter-penetration of the two polymer chains, thus the polymer compatibility, in solution. The blend compatibility was studied with the attenuated total reflection-Fourier transform infrared (atr-FTIR) and the differential scanning calorimetry (DSC) techniques. The unique and composition-dependent glass transition temperature indicates that the two polymers are compatible, but the ΔT_g broadening suggests a certain degree of nano-heterogeneity. The T_g of pure PSSNa which was non-detectable in DSC, was calculated from the Fox equation. From FTIR data, the polymer compatibility could be attributed to the establishment of hydrogen bonds, and dipole-ion interactions between carboxylic groups, sulfonate groups, and sodium ion on the polymer segments.     

Investigation of thermal degradation of polystyrene by differential scanning calorimetry

Thermal degradation of polystyrene was performed in a differential scanning calorimeter under nitrogen atmosphere, and the glass transition temperature was measured continuously. From random chain scission kinetics and T_g-molecular weight relationships, the rate constant for random scission was obtained. The rate constant was found to undergo a drastic change at a critical molecular weight (∽45,000), which corresponds to a similar observation in relaxation studies. A viscosity-dependent mechanism for radical chain end termination is thus suggested.     

Cure kinetics of epoxy resins by differential scanning calorimetry technique

The curing reactions of epoxy resins with aliphatic amine are investigated using the differential scanning calorimetry technique with a single dynamic scan. The rate of the reaction was followed over the temperature range 30–250°C, and the activation energy and the order of the reaction are determined using four different computational methods. The activation energy for the various epoxy systems is observed in the range 40–76 kJ mol^?1 and the order of the reaction is observed to be ? 1·0.     

Low temperature annealing of isotactic polypropylene by differential scanning calorimetry

Differential scanning calorimetry has shown that secondary crystallization occurs in both smectic and monoclinic polypropylene during annealing processes at temperatures as low as 25°C. This effect has been studied in the range 25–130°C. The extent of secondary crystallization increases with both time and temperature of anneal. The rate is increased by prior annealing at either higher or lower temperature; is slightly reduced in samples cooled more slowly from the melt and is significantly reduced in γ-irradiated samples. Rate curves suggest that secondary crystallization consists of a fast process with a half life of a few hours and a slow process which continues for years. The observations are consistent with the currently accepted structural reorganisation theory for annealing at temperatures closer to the melting point. The occurrence of significant secondary crystallization at room temperature has implications with the ageing effect previously observed for some semi-crystalline polymers.