Differential Scanning Calorimetry Crystallization Research Articles

The effect of dibenzylidene sorbitol on the crystallization behaviour of polyethylene

The influence of dibenzylidene sorbitol (DBS) on the optical clarity, crystallization behaviour and morphology of polyethylene has been studied by UV/visible spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). By combining crystal growth rates with Avrami parameters derived from DSC crystallization exotherms, nucleation densities were determined as a function of crystallization temperature. In the blend without DBS, the nucleation density decreased progressively with increasing crystallization temperature whereas, in the system containing DBS, the nucleating efficiency was found to remain constant and then decrease dramatically above 120 °C. Throughout the crystallization range studied, the DBS increased the nucleation density substantially, often to a value comparable with that seen in a commercial sorbitol-clarified propylene/ethylene copolymer system. SEM revealed a change from a continuous lamellar texture at low temperatures to one based upon isolated sheaf-like objects at 124 °C. At high crystallization temperatures, both the DSC and the SEM also provided evidence of a significant rejected linear fraction, which appeared to decorate the sorbitol network on quenching. Possible explanations for these effects are discussed.

パーム油の結晶化温度のその結晶化への効果 ＩＶ １，３‐ジパルミトイル‐２‐オレオイル‐グリセロール（ＰＯＰ）と１，２‐ジオレオイル‐３‐パルミトイルグリセロール（ＰＯＯ）の結晶化へのトリパルミトイルグリセロールの影響

Triacylglycerin in Palm Oil contains POP (1,3-dipalmitoyl-2-oleoyl-glycerol) at 30%, POO (1,2-dioleoyl-3-palmitoyl-glycerol) at 20% and PPP (tripalmitoylglycerol) at 5%. The crystallization temperature of PPP is high and the rates of crystal nuclear formation and growth are fast. It is thus considered that PPP may have some effect on the manner or mode of Palm Oil. Examination was thus made to clarify how PPP may affect the crystallization of POP and POO by differential scanning calorimetry (DSC) and X ray diffractometry (XRD) conducted on PPP/POP and PPP/POO mixtures. High and low temperature peaks were noted to appear on the DSC crystallization curve for either of these mixtures. The high temperature peak was considered possibly due to PPP, and the low temperature peak, to POP or POO. DSC isothermal analysis indicated the rate of crystal growth of either mixture to exceed that of pure of POP or POO. Crystal mixture structure was also seen to be complicated than either compound in pure form. The present findings thus clearly indicate that clarification should be made of the effects of high melting point triacylglycerin, such as PPP, on the crystallization of Palm Oil.

Limitation of the Johnson–Mehl–Avrami (JMA) formula for kinetic analysis of the crystallization of a chalcogenide glass

The crystallization kinetics of Sb 9.1Te 20.1Se 70.8 chalcogenide glass have been studied by differential scanning calorimetry (DSC). The effective activation energy of crystallization has been evaluated on the basis of the Kissinger equation and the method of Matusita et al. The Sestak–Berggren model has been used for the description of DSC crystallization data as it provides the best fit to the experimental results. It has been found that the Johnson–Mehl–Avrami model could be applied at very high rates of heating.

Kinetic Analysis of Nonisothermal Differential Scanning Calorimetry of 1,3-Dipalmitoyl-2-oleoylglycerol

The crystallization of fats has been extensively studied because of its importance in the processing of food and food ingredients. Differential scanning calorimetry (DSC) is widely used in such studies. The aim of this study was to examine the determination of kinetic parameters from nonisothermal DSC crystallization of a model fat, 1,3-dipalmitoyl-2-oleoylglycerol. We applied peak and isoconversional methods to determine activation energies and compared these techniques with a nonparametric method, which separates the temperature dependence and degree of crystallization dependence of the crystallization rate. The Johnson-Mehl-Avrami-Erofeyev-Kolmogorov (JMAEK) model provided the best fit to the data, while the temperature dependence of the rate constant was best explained by a Vogel-Fulcher relationship, where the reference temperature was the melting point of the crystallizing species.

Fractionation of menhaden oil and partially hydrogenated menhaden oil: Characterization of triacylglycerol fractions

AbstractMenhaden oil (MO) and partially hydrogenated menhaden oil (PHMO) were dry‐fractionated and solvent‐fractionated from acetone. After conversion to fatty acid methyl esters, the compositional distribution of saturated, monounsaturated, trans, and n−3 polyunsaturated fatty acids (PUFA) in the isolated fractions was determined by gas chromatography. Acetone fractionation of MO at −38°C significantly increased the n−3 PUFA content in the liquid fractions over that of starting MO (P<0.05). For PHMO, liquid fractions obtained by low‐temperature crystallization (−38, −18, and 0°C) from acetone showed significant increases (P<0.05) in monounsaturated fatty acid (MUFA) content over that of the starting PHMO. For selected MUFA‐enriched fractions, reversed‐phase high‐performance liquid chromatography (HPLC) was used to separate, isolate, and characterize the major triacylglycerol (TAG) molecular species present. Thermal crystallization patterns for these fractions also were determined by differential scanning calorimetry (DSC). The results demonstrated that under the appropriate conditions it is possible to dry‐fractionate or solvent‐fractionate MO and PHMO into various solid and liquid fractions that are enriched in either saturated, monounsaturated, polyunsaturated, or the n−3 classes of fatty acids. Moreover, characterization of these TAG fractions by reversed‐phase HPLC gives insight into the compositional nature of the TAG that are concentrated into the various fractions produced by these fractionation processes. Finally, the DSC crystallization patterns for the fractions in conjunction with their fatty acid compositional data allow for the optimization of the fractionation schemes developed in this study. This information allows for the production of specific TAG fractions from MO and PHMO that are potentially useful as functional lipid products.

Crystallization mechanism and properties of a blast furnace slag glass

The complex crystallization process of a Brazilian blast-furnace slag glass was investigated using differential scanning calorimetry (DSC), X-ray diffraction, optical microscopy, transmission electron microscopy (TEM), selected area diffraction (SAD), energy dispersive spectroscopy (EDS) and micro-Raman spectroscopy. Three crystalline phases (merwinite, melilite and larnite) were identified after heat treatment between T g (742°C) and the DSC crystallization peak ( T=1000°C). Merwinite was identified as a metastable phase. A small amount (0.004 wt%) of metallic platinum was found in the glass composition. Particles of Pt 3Fe, detected by EDS and SAD–TEM, were the starting points of crystallization acting, therefore, as heterogeneous nucleating sites. Only melilite and larnite precipitated in a glass sample heat-treated at 1000°C for 1 h. The flexural strength of this crystallized sample was less than that of the glass, probably due the allotropic phase transformation of larnite.

Differential scanning calorimetric analysis of edible oils: Comparison of thermal properties and chemical composition

AbstractThe thermal profiles of 17 edible oil samples from different plant origins were examined by differential scanning calorimetry (DSC). Two other confirmatory analytical techniques, namely gas‐liquid chromatography (GLC) and high‐performance liquid chromatography (HPLC), were used to determine fatty acid (FA) and triacylglycerol (TAG) compositions. The FA and TAG compositions were used to complement the DSC data. Iodine value (IV) analysis was carried out to measure the degree of unsaturation in these oil samples. The DSC melting and crystallization curves of the oil samples are reported. The contrasting DSC thermal curves provide a way of distinguishing among these oil samples. Generally, the oil samples with a high degree of saturation (IV<65) showed DSC melting and crystallization profiles at higher temperature regions than the oil samples with high degree of unsaturation (IV>65). Each thermal curve was used to determine three DSC parameters, namely, onset temperature (To), offset temperature (Tf) and temperature range (difference between To and Tf). Reproducibility of DSC curves was evaluated based on these parameters. Satisfactory reproducibility was achieved for quantitation of these DSC parameters. The results show that To of the crystallization curve and Tf of the melting curve differed significantly (P<0.01) in all oil samples. Our observations strengthen the premise that DSC is an efficient and accurate method for characterizing edible oils.

Crystallization behavior of high‐density polyethylene/linear low‐density polyethylene blend

AbstractBinary blend of high‐density polyethylene (HDPE) and linear low‐density polyethylene (LLDPE), prepared by melt mixing in an extruder, in the entire range of blending ratio, is studied for crystallization behavior by differential scanning calorimetry (DSC) and X‐ray diffraction measurements. Cocrystallization was evident in the entire range of blend composition, from the single‐peak character in both DSC crystallization exotherms and meltingendotherms and the X‐ray diffraction peaks. A detailed analysis of DSC crystallization exotherms revealed a systematic effect of the addition of LLDPE on nucleation rate and the subsequently developed crystalline morphology, which could be distinguished in the three regions of blending ratio, viz, the “HDPE‐rich blend,” “LLDPE‐rich blend,” and the “middle range from 30–70% LLDPE content.” Variations in crystallinity, crystallite size, and d spacing are discussed in terms of differences in molecular structure of the components.

Crystallization characteristics of isotactic polypropylene with and without nucleating agents

AbstractNucleation effects of two sorbitol derivatives on the crystallization of isotactic polypropylene (iPP) were studied by means of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). A nonisothermal crystallization kinetic equation was employed to analyze the crystallization characteristics of iPP with or without the nucleating agents from DSC crystallization thermograms. The equilibrium melting temperature of iPP necessary for the kinetic study was obtained by the extrapolation method to be 209°C. The nonisothermal crystallization kinetic analysis for the unnucleated iPP at different cooling rates was possible by assuming the spherulite growth initiated simultaneously by heterogeneous and homogeneous nucleation. On the other hand, the crystallization kinetics of the nucleated iPP could be described by the heterogeneous nucleation and growth process alone. The addition of the nucleating agents up to their saturation concentrations in iPP increased the crystallization peak temperature by 17°C, and the number of effective nuclei by three orders of magnitude. A high concentration of the nucleating agents caused agglomeration of the agents to lower the number of effective nuclei.

Calorimetric measurements of paraffinic transformer oil containing pour point depressant.

In order to investigate how the addition of a pour point depressant affects the crystallization/melting characteristics of paraffin wax contained in a paraffinic transformer oil in a low temperature range, specimens were made by dissolving an oligomer consisting of ethylene-propylene copolymer into a paraffinic transformer oil. Heats of crystallization were calculated by measuring thermograms of the specimens between room temperature and -100°C, using Differential Scanning Calorimetry (DSC). Such physical properties as pour point, kinematic viscosity, etc., were also measured. Consequently, it has become clear that, when being subjected to cooling with the addition of a pour point depressant, the crystallization/deposition of its paraffin wax is disturbed within a temperature range of DSC crystallization peak temperature to -60°C, but its paraffin wax ends in crystallization/deposition regardless of its addition at about -80°C. In other words, its heat of crystallization within a temperature range of room temperature to about -80°C is constant, being independent of the addition of a pour point depressant. Finally, it is suggested that the approved theory that a pour point depressant does not disturb the deposition of paraffin wax crystals in a paraffinic mineral oil at low temperatures should be modified, based upon experimental results obtained by the author.

Calorimetric measurements of paraffin wax in paraffinic transformer oil.

In order to estimate the amount of paraffin wax expected to be precipitated from deep dewaxed paraffinic transformer oil in a temperature range from -50 to -60°C, the paraffin wax was separated by using an urea adducts method, and calorimetric measurements were made of the oil, the wax and the residual oil by use of Differential Scanning Calorimetry (DSC). Adding various amounts of the wax to the residual oil, calorimetric measurements were also made of them. The paraffin wax was also chemically analyzed. Consequently, it has become clear that the paraffin wax content can be estimated roughly by using its heat of fusion and that the pour point of the paraffinic oil specimen seems to be related to the DSC crystallization peak temperature and to the heat of fusion, respectively. Finally, it has been suggested that one may employ this DSC method as one of the excellent methods for estimating paraffin wax content in paraffinic transformer oil.