Search

Pure saturated triacylglycerols (TAGs) in canola oil were used as model systems to analyse oil loss in structured oil both from thermodynamic and kinetic perspectives. Two important parameters which effectively and predictively measure the relative propensity of a solid network to lose/hold oil were defined: (1) the rate of oil loss, K, which is a quantified representation of the kinetics of oil loss and (2) the initial amount of oil susceptible to be lost, i.e., the propensity for oil loss (POL), which is a representation of the thermodynamics of oil binding. It was found that the POL and K values do not always trend in the same fashion, suggesting that the mechanism of oil binding is complex, depending on the structurant's crystalline form locked within the oil network. The two parameters were, however, correlated to the melting and thermal behavior of the structurants, to the polymorphic structures that are obtained during the cooling process and to the habit (shape, size and morphology) of the crystalline phase in the oil. Both POL and K had a strong correlation to the oil loss.

The kinetic phase behavior and phase transformation paths of purified tristearoylglycerol (SSS), 3-palmitoyl-1,2-distearoyl-sn-glycerol (PSS) and 1,2-dipalmitoyl-3-stearoyl-sn-glycerol (PPS) were investigated in terms of polymorphism, crystallization and melting. The details of the phase transformation paths were obtained using the heating cycles of two sets of experiments: (a) cooling rate was varied and heating rate fixed and (b) cooling rate was fixed and heating rate varied. Kinetic effects were manifest in all measured properties, underscoring the complexity of the phase transformation paths for each TAG, and the intricate thermodynamics-molecular relationships. For the first time, XRD data obtained for SSS, PSS and PPS TAGs, cooled at rates higher than 0.5°C/min, suggested the formation of a transient structure similar to the so-called α(2)-phase which has been observed in mixed saturated-unsaturated TAGs quenched from the melt. The more stable phases (β' in PSS and PPS, and β in SSS) were only observed for cooling rates lower than 1.0°C/min. The kinetic and thermodynamic differences observed in the crystallization, structure and melting of SSS, PSS and PPS are proposed to be mainly due to the disturbances introduced at the "terrace" level via methyl-end group interactions, i.e., the missing of two or four CH(2) groups compared to SSS. The symmetrical SSS with a relatively flat "terrace" crystallizes preferably in the most stable β-form. Two missing CH(2) groups at the sn-1 position (PSS) introduces enough structural disturbances to promote the relative prevalence and persistence of the β'-phase, and four missing CH(2) groups at the sn-1 and sn-2 positions (PPS) is relatively too large of a disturbance and therefore favors the α-form., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

The phase behavior of 1-palmitoyl-2,3-distearoyl-sn-glycerol (PSS)/tristearoylglycerol (SSS) binary system was investigated in terms of polymorphism, crystallization and melting behavior, microstructure and solid fat content (SFC) using widely different constant cooling rates. Kinetic phase diagrams were experimentally determined from the DSC heating thermograms and analyzed using a thermodynamic model to account for non-ideality of mixing. The kinetic phase diagram presented a typical eutectic behavior with a eutectic point at the 0.5(PSS) mixture with a probable precipitation line from 0.5(PSS) to 1.0(PSS), regardless of the rate at which the sample was cooled. The eutectic temperature decreased only slightly with increasing cooling rate. PSS has a strong effect on the physical properties of the PSS-SSS mixtures. In fact, the overall phase behavior of the PSS-SSS binary system was determined, for a very large part, by the asymmetrical TAG. Moreover, PSS is a key driver of the high stability observed in crystal growth, polymorphism and phase development. Levels as low as 10% PSS, when cooled slowly, and 30% when cooled rapidly, were found to be sufficient to suppress the effect of thermal processing., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

The binary phase behavior of purified 1,3-dilauroyl-2-stearoyl-sn-glycerol (LSL) and 1,2-dilauroyl-3-stearoyl-sn-glycerol (LLS) was investigated at a slow (0.1 degrees C/min) and a relatively fast (3.0 degrees C/min) cooling rate in terms of melting and crystallization, polymorphism, solid fat content (SFC), hardness and microstructure. Much of the behavior of the system is explained by its polymorphism and the influence of thermal processing. The alpha-form and the beta'-form of a double chain length structure were detected in the mixtures cooled at 3.0 degrees C/min, whereas only the beta'-form was detected in those cooled at 0.1 degrees C/min. X-ray diffraction data as well as thermodynamic data propose that the most stable phases are promoted by the symmetrical LSL. The measured trends in structural characteristics, thermal properties, SFC, relative hardness and microstructure delimit three groups of mixtures which imply a competition between the stabilizing effect of LSL and disordering introduced by kinetic effects: (a) LLS-rich mixtures with LSL molar fractions (X(LSL)) less than 0.3, (b) mixtures with X(LSL) clustered around 0.5 and (c) LSL-rich mixtures with X(LSL)>or=0.7. The balance between ordering and kinetic effects determines the polymorphism of the mixtures, which in turn determines the behavior of the LSL/LLS system. The kinetic phase diagram of the LSL/LLS binary system constructed using heating differential scanning calorimetry thermograms displayed a singularity at the 0.5(LSL) molar fraction which delimits two distinct behaviors: eutectic behavior in one region and monotectic behavior in the other. The molecular interactions, as depicted by a non-ideality parameter of mixing obtained from a thermodynamic model based on the Hildebrand equation, suggests an almost ideal mixing behavior and a moderate tendency to the formation of unlike-pairs in the liquid state., (Copyright 2010 Elsevier Ireland Ltd. All rights reserved.)

The isoconversional method, a model-free analysis of the kinetics of liquid-solid transformations, was used to determine the effective activation energy of the nonisothermal crystallization of melts of pure and complex systems of triacylglycerols (TAGs). The method was applied to data from differential scanning calorimetry (DSC) measurements of the heat of crystallization of purified 1,3-dilauroyl-2-stearoyl-sn-glycerol (LSL) and commercially available cocoa butter melts. The method conclusively demonstrated the existence of specific growth modes and critical rates of cooling at specific degrees of conversion. The existence of critical rates suggests that the crystallization mechanism is composed of growth modes that can be effectively treated as mutually exclusive, each being predominant for one range of cooling rates and extent of conversion. Importantly, the data suggests that knowledge of the critical cooling rates at specific rates of conversion can be exploited to select preferred growth modes for lipid networks, with concomitant benefits of structural organization and resultant physical functionality. Differences in transport phenomena induced by different cooling rates suggest the existence of thresholds for particular growth mechanisms and help to explain the overall complexity of lipid crystallization. The results of this model-free analysis may be attributed to the relative importance of nucleation and growth at different stages of crystallization. A mechanistic explanation based on the competing effects of the thermodynamic driving force and limiting heat and transport phenomena is provided to explain the observed behavior. This work, furthermore, offers satisfactory explanations for the noted effect of cooling-rate-induced changes in the physical functionality of lipid networks.

The phase behavior of a binary system constituted of purified 1,3-dicaproyl-2-stearoyl-sn-glycerol (CSC) and 1,2-dicaproyl-3-stearoyl-sn-glycerol (CCS) was investigated at a very slow (0.1 degrees C/min) and a relatively fast (3.0 degrees C/min) cooling rate using differential scanning calorimetry (DSC), low resolution NMR, X-ray diffraction (XRD), and polarized light microscopy (PLM). Related forms of the beta' polymorph were detected for all mixtures as well as a beta form for CSC-rich mixtures. A double chain length (DCL) stacking of the non-mixed CCS-CCS and CSC-CSC phases and a triple chain length (TCL) stacking of mixed CCS-CSC structure were detected for the different beta' forms. The kinetic phase diagram demonstrated an apparent eutectic at the 0.5(CSC) composition when cooled at 0.1 degrees C/min and at the 0.25(CSC) composition when cooled at 3.0 degrees C/min. The application of a thermodynamic model based on the Hildebrand equation suggests that compounds CSC and CCS are not fully miscible. In addition, the miscibility changes according to the structure of the growing solid phase which is dependent on CSC molar ratio as well as on the kinetics. It was also shown that the miscibility is concentration dependent and that the solid phase, which is growing at conditions well away from equilibrium, is determined kinetically. The molecular interactions were found to be strong and to favor the formation of CSC-CCS pairs in the liquid state. CSC and CCS were also shown to be immiscible in the solid state. Depressions in solid fat content (SFC) were observed for both rates. Relatively complex networks made of needle-like, spherulitic and granular crystals were observed in the CSC/CCS system. A pure CSC phase was found to be instrumental in promoting a higher SFC, and more stable polymorphic forms. The microstructure was shown to be strongly dependent on the cooling rate and was linked to the different polymorphic forms observed by DSC and XRD. Correlations between SFC and the eutectic behavior have been observed for the 3.0 degrees C/min cooling rate, but not directly in the case of the 0.1 degrees C/min cooling rate, where slower kinetics which favors the metastable to stable phase conversion processes prevented the same shifts in behavior.

The product of the self-metathesis of soybean oil (MSBO) containing ∼80% of triacylglycerol (TAG) oligomers was easily transformed into polyols by a conventional one-pot epoxidation and hydroxylation reaction. The MSBO polyol inherited the oligomeric structure of its parent oil without significantly altering its functionality. The OH-value of the polyol from MSBO was easily customized by controlling the reaction conditions. Polyols having OH-values between 83 and 263 mg KOH/g were achieved and used to make polyurethane foams with controlled combinations of strength (stress at 10% deformation of 0.07–0.75 MPa) and flexibility (recovery from deep compression of 75–95%) suitable for versatile applications, particularly those requiring strength and resiliency. The large resistance to load and significant spring for recovery achieved by the polyurethane foams are attributable to the association of the high OH value and oligomeric structure of the MSBO polyols. More importantly, the self-metathesis is demonstrated to extend the range of the products derived from vegetable oils, particularly polyols and polyurethane foams. [ABSTRACT FROM AUTHOR]

Three pure triacylglycerols (TAG) containing decenoic acid (D), and stearic acid (S), were hydroxylated into chlorinated and non-chlorinated polyols and studied in detail. D is a fatty moiety that can result from the cross metathesis of small olefins with common vegetable oils such as soybean oil. A fundamental understanding relating chemical composition and derived structure, particularly the number and position of the hydroxyl groups, to physical properties was established allowing us to add some perspective to the growing body of knowledge on industrially relevant polyol and polyurethane systems produced with metathesis-modified TAG (MTAG). The hydroxyl value, crystallization and melting behaviors, thermal degradation behavior of the polyols were directly related to their peculiar shortened and primary functionality inherited from the parent MTAG. The effect of regiochemistry on the physical properties of the polyols was investigated with the chromatography fractions of the trichlorinated polyol of propane-1,2,3-triyl tris(dec-9-enoate), giving an unhindered insight into the role of short and terminal functionality of MTAG polyols that will help select the optimal isomer composition for designer polyurethane materials. [ABSTRACT FROM AUTHOR]

The derivatives of vegetable oils with specific chemical structures, such as TAG (triacylglycerols) having mixed straight and kinked moieties, have proven very effective in lowering the crystallization of biodiesel. SOO (1, 2-dioleoyl-3-stearoyl sn -glycerol)/MeS (methyl stearate) is part of a series of studies of TAG/FAME (fatty acid methyl ester) binary model systems conducted to establish structure–function relationships of lipid-based cold flow improvers in biodiesel with a particular attention to the effect of molecular symmetry in contrast with a previously published study of the OSO (1, 3-dioleoyl-2-stearoyl sn -glycerol)/MeS binary system. The phase behavior of several SOO/MeS mixtures were investigated at different length scales with XRD (X-ray diffraction), DSC (differential scanning calorimetry) and PLM (polarized light microscope). A complete phase diagram including the transformation lines, crystal structure and microstructure was constructed. The solubility behavior was discussed using a simple thermodynamic model based on the Hildebrand equation and pair interactions. The asymmetric position of the oleic moieties of SOO was shown to be crucial in modifying the thermal transformation behavior of MeS. The findings may be used to design effective crystallization modifiers of biodiesel based on particular structural determinants, and underscores the importance of symmetry in such designs. [ABSTRACT FROM AUTHOR]

A model binary system made of methyl palmitate (MeP) and (E)-1-(1-(oleoyloxy)-3-(stearoyloxy)propan-2-yl) 18-(1-(oleoyloxy)-3-(stearoyloxy) propan-2-yl) octadec-9-enedioate (dimer, D), a structured triacylglycerol dimer, one of a series of fatty molecules that have been found to significantly reduce the crystallization temperature of biodiesel, was investigated with DSC (differential scanning calorimetry), XRD and PLM (polarized light microscopy). A complex and unusual phase behavior was uncovered for this system. The exclusive orthorhombic crystal packing that was detected by XRD was shown to be guided by the bulky D molecules. The findings are explained by the formation of dimer/methyl palmitate composite units in which the dimer associates with the MeP molecules at its fatty acid branches as well as bridges. This association was initiated in the liquid state where the mobility of MeP and free rotation of the fatty branches of D are favorable. The disruptive effect of D on the packing of the saturated FAME was effective only at low concentrations (<0.10) with the system presenting a eutectic at 5% of D, followed by three stepped transformation lines indicating three concentration regions of defined phases of increasing stability. The findings indicate that the dimer may be an effective cold flow improver of biodiesel but only at concentrations lower than 5%. [ABSTRACT FROM AUTHOR]

The flow behavior and viscosity of TAGs containing oleic and stearic acids were examined in the liquid phase as well as at temperatures close to the onset of crystallization by means of a temperature-controlled rheometer. Gelling and crystallization transitions were unambiguously identified by singularities in the viscosity versus temperature curves of the TAGs. An additional transition between the gelling and onset of crystallization temperatures, attributed to the reorganization of the gel, was observed in the symmetrical TAGs only. The effect of the cooling rate, ranging between 0.1 and 5 °C/min, was investigated. The flow behavior of the studied TAGs was shown to be strongly determined by structural parameters (symmetry, degree of unsaturation). The flow behavior was also affected significantly by the cooling rate, suggesting that to certain extents the flow behavior determined by structural parameters could be changed by manipulating the cooling rate. The study confirmed that TAG crystallization is initiated by and depends, at least in part, on complex molecular short range order transformations occurring in the melt. The findings of the study may be valuable for evaluating systems and equipment that are involved in the storage, handling and processing of materials incorporating these TAGs. [ABSTRACT FROM AUTHOR]

Positional isomerism in triacylglycerols (TAG), present in a molecular ensemble arising from genetic, environmental or processing-induced changes, can result in significant differences in the macroscopic physico-chemical functionality of crystallized networks of the ensemble. The differences in phase behavior induced by positional isomerism and levels of unsaturation of pure oleoyl-distearoyl TAG (SOS, SSO) were detailed at different length scales. The effect of cooling rate on the polymorphism, thermal properties and microstructure were systematically investigated between 0.1 and 5 °C/min. The symmetrical SOS presented a complex polymorphism and microstructure, which varied predictively with cooling rate. The crystal phases and transitions observed for this TAG are similar to those of cocoa butter. In contrast, the cooling rate had limited effect on the phase behavior of the asymmetrical SSO. The differences between the crystallization of SSO and SOS induced by kinetics are related to the kinked oleic acid at the outer position in the SSO molecule and favorable end group structure for SOS. The fundamental understanding gained from such model systems can be used in many industrial formulations, particularly foods. [ABSTRACT FROM AUTHOR]

Seven model oligomers (from dimer to octamer) of thetriacylglycerol(TAG) triolein were synthesized from oleic acid and fully characterizedby 1H NMR, 13C NMR, mass spectroscopy, and gelpermeation chromatography (GPC). The thermal stability of the oligomersas determined by TGA was excellent, with degradation beginning at342 °C for the most thermally labile samples. The samples allpresented glass transitions at low temperatures, with Tgcontinuously shifting to higher temperatures with increasingnumbers of monomers. The crystallization and melting behavior scaledwith molecular size and relative number of double bonds in the trans-configuration. Flow behavior was investigated over a large range oftemperatures (−10 to 110 °C), and application of the Herschel–Bulkeymodel to shear stress versus shear rate data evidenced a flow behaviordependent on molecular size and temperature. The oligomers presenteda thinning to Newtonian flow transition temperature proportional tomolecular size. The viscosity versus temperature data, fitted witha generalized van Velzen equation, suggested that it is the competitionbetween the trans- character and size of the molecules which determinesthe rheology of these molecules. Overall, all the investigated propertiesplateaued at the hexamer, suggesting that no further marginal utilitycan be obtained with larger oligomers. [ABSTRACT FROM AUTHOR]

The cross-metathesis of vegetable oils containing a finite amount of unsaturation with small olefins such as ethylene or 1-butene results in the production of important platform chemicals. However, a largely unused portion of the original triacylglyceride molecule is left unused: a metathesis modified triacylglyceride or MTAG. The byproduct MTAGs are very interesting precursors for many materials; particularly for the synthesis of polyols and polyurethanes because of their shortened acyl chain and terminal double bond structure. The liquid-solid phase behavior of five metathesis modified triacylglycerols (MTAGS) produced when, for instance, canola, soy and palm oils are cross metathesized with ethylene or 1-butene; namely propane-1,2,3-triyl tris dec-9-enoate (DDD), 3-(stearoyloxy) propane-1, 2-diyl bis dec-9-enoate (DDS), 2-(stearoyloxy) propane-1, 3-diyl bis dec-9-enoate (DSD), 1,2-(stearoyloxy) propane-3-diyl bis dec-9-enoate (SSD) and 1,3-(stearoyloxy) propane-2-diyl bis dec-9-enoate (SDS), was comprehensively examined with DSC and XRD. The differences observed in the thermal transition behavior, melting temperatures and polymorphism between these MTAGs and their unmodified natural stearic-oleic TAG counterparts were well correlated with the number of terminal double bonds, number of shortened fatty acid chains, and number and positions of saturated fatty acid chains. The competition between the effects of unsaturation and position of the short moieties explained the distinctive phase trajectories of the MTAGs. The role of the large chain length mismatch (CLM) between the stearic and decenoic moieties was particularly highlighted in the chain length packing. The structure-function relationships established for MTAGs have never been reported before, and are important to the utilization of this feedstock which is growing in volume due to the commercial utilization of olefin cross metathesis of vegetable oils in the manufacture of oleochemicals. [ABSTRACT FROM AUTHOR]

Palm oil metathesized triacylglycerol (PMTAG), the product of 1-butene cross-metathesis of palm oil stripped from it olefins, was fractionated using dry and solvent mediated crystallization. The fractionation yielded solid and liquid fractions (LF-PMTAG and SF-PMTAG, respectively) reminiscent of the stearin and olein portions of the natural palm oil. The polyol which was synthesized from LF-PMTAG (LF-Polyol) comprised ∼30% more hydroxyl groups (diols, tetrols and hexols) and more short chain moieties than the polyol from SF-PMTAG (SF-Polyol). As a result, LF-Polyol presented a much higher OH value (184 mg KOH/g) than SF-Polyol (136 mg KOH/g) and more advantageous thermal and viscosity properties than SF-Polyol. The LF-Polyol was demonstrated to make improved rigid and flexible foams compared the polyol from PMTAG (PMTAG-Polyol) or from the natural palm oil. The rigid foam (RF) obtained with LF-Polyol presented compressive strength which was 1.5 times higher than the RF prepared with PMTAG-Polyol, indicating that the removal of stearin-like components can significantly increase the rigidity. The study demonstrate that controlled fractionation of PMTAG can produce customized functional feedstocks for enhanced polyurethane foams. [ABSTRACT FROM AUTHOR]