A Comprehensive Evaluation of the Density of Neat Fatty Acids and Esters

Density is one of the most important physical properties of a chemical compound, affecting numerous applications. An application in the case of fatty acid esters (biodiesel) is that density is specified in some biodiesel standards. In the present work, the density of fatty acid methyl, ethyl, propyl, and butyl esters as well as triacylglycerols in the C₈–C₂₄ range was determined in the range of 15–40 °C with a densitometer utilizing the oscillating U-tube technique. Literature data on density are compiled and compared, showing that data for these compounds are incomplete with discrepancies existing in some cases. Besides known effects such as density decreasing with increasing chain length and increasing saturation, it is shown that trans fatty compounds exhibit lower density than cis fatty compounds. Density data for several saturated odd-numbered, C₁₈, as well as C₂₀ and C₂₂ polyunsaturated fatty esters are reported for the first time. The density contribution of compounds with high melting points is predicted. An equation is given for the calculation of the density of mixtures.     

Heat Treatment and Chemical Composition of Fatty Acids and Rosin Acids Mixtures: Effects on Their Thermal Properties and Morphology

Mixtures of fatty acids and rosin acids are industrially important products utilized as a raw material for several purposes. Their thermal properties, especially cold stability and crystallization behavior is also important. Several fatty acid and rosin acid mixtures both from industrial products and from commercially available fatty and rosin acids were prepared and treated for 30 min at 80 °C under an inert atmosphere. Thereafter, the mixture was cooled to the desired temperature. Determination of the cloud point, chemical analysis of liquid and solid phase, thermal analysis by differential scanning calorimetry as well as morphology analysis by scanning electron microscopy were performed. The results revealed that crystallization was more rapid when it occurred at 10 °C compared to 25 °C. The crystal sizes increased with decreasing the crystallization temperature. Furthermore, crystals were of irregular shape and agglomerated when rapid cooling of the mixture occurred. Chemical analysis revealed that liquid phase was enriched with stearic acid, whereas crystals contained large amounts of abietic, dehydroabietic and linoleic acids. The cloud point of the mixtures increased with increasing amount of stearic and rosin acids. Dehydroabietic acid addition improved the cold stability of the synthetic fatty acid–rosin acids mixture.     

Melting Points and Viscosities of Fatty Acid Esters that are Potential Targets for Engineered Oilseed

Our previous isolation of branched-chain fatty acid (BCFA) methyl esters from lanolin was improved and scaled up. Also, oleate esters of isopropanol, oleyl alcohol and normal alcohols of 1–12 carbons chain lengths were prepared. Esters were made by interesterification with sodium alcoholates and by esterification with Candida antarctica lipase. It proved easier to obtain pure esters by the enzymatic synthesis. Melting points and viscosities over the range of 0–70 °C were determined in order to better identify potential lubricant targets that might be produced by genetically modified oilseed crops. Isopropyl and butyl oleate have melting points of −33 and −32 °C, respectively and viscosities that range from ~17 cp (0 °C) to ~2.5 cp (70 °C). They should have suitable stability for lubricants. BCFA esters had viscosities similar to their straight chain analogs. Viscosities increased with alcohol chain length and decreased with temperature. The dependence of viscosity on temperature was fit with an equation based on Erying’s rate equation. Some esters with branched acid or branched alcohol moieties, and some oleate esters might be utilized as biolubricants or biofuels on the basis of their melting points and viscosities.     

Solid Fat Content Estimation by Differential Scanning Calorimetry: Prior Treatment and Proposed Correction

The objective of this work was to develop a corrected method for solid fat content estimation by differential scanning calorimetry (DSC), as important differences are usually observed between the results given by DSC and pulsed nuclear magnetic resonance (NMR). Cold storage after full melting of fats was necessary to avoid the appearance of exothermic peaks in the modulated temperature DSC thermograms, in order to make an appropriate estimation of melting energy. Different fats were analyzed by NMR and DSC, obtaining considerably higher solid fat content values with the latter, uncorrected method. These differences were attributed to the fact that consumed energy per unit of melted mass tends to increase with the increase of the melting temperature of each fraction of the fats. A linear correlation between melting enthalpy and melting point of different triglycerides was used to estimate the energy per unit of mass consumed at each temperature. From these data, an estimated transformation of melting energy into melted mass was performed and new solid fat content values were calculated. The results obtained from this correction were much closer to the measurements made by NMR, in comparison to the uncorrected DSC method.     

Differential Scanning Calorimetry Analysis of Goat Fats: Comparison of Chemical Composition and Thermal Properties

The physical–chemical properties, fatty acid composition and thermal properties of goat subcutaneous (SF), tallow (TF) and intestinal (IF) fats were determined. SF differed from other fat types with respect to its lower melting (41.6 °C), lower saponification (190.3 mg KOH/g) and higher iodine (40.4) values as compared to those of other fats. Goat fat types contained palmitic acid (C_16:0), stearic acid (C_18:0), oleic acid (C_18:1ω9) and linoleic acid (C_18:2ω6) as the major components of the fatty acid composition (23.06–23.52, 22.95–39.03, 21.94–36.16 and 1.96–2.22%, respectively). A differential scanning calorimetry (DSC) study revealed that two characteristic peaks were detected in both crystallization and melting curves. Major peaks (T _peak) of TF and IF were similar and determined as 34.02–35.24 and 9.95–10.72 °C, respectively for the crystallization peaks and 15.11–18.26 and 50.70–52.76 °C, respectively for the melting peaks in the DSC curves; but those of SF (27.14 and 4.36 °C for crystallization peaks and 8.39 and 44.93 °C for melting peaks) differed remarkably from those of other fat types.     

Differential Scanning Calorimetry Study of Blends of Poly(ethylene glycol) with Selected Fatty Acids

A series of blends of poly(ethylene glycol) (PEG) with different molecular weights with: (i) capric, (ii) lauric, (iii) myristic, (iv) palmitic or (v) stearic acid, as a thermal energy storage material, has been investigated by differential scanning calorimetry (DSC). Transition temperatures and latent heat of transition of PEG, fatty acids and their binary blends were determined since these properties are of primary importance in the design of phase change energy storage materials. The experimental results showed that it is possible to obtain homogeneous (as indicated by DSC data) polymer/fatty acid blends by mixing in the melt and subsequent solidification. The melting ranges of PEG/fatty acid systems were observed to be from 30 to 72 °C while their heat of transition lies in the range of 168–208 J · g^?1. Synergistic action of the components was found for PEG 10 000/stearic acid blend – heat of transition was ca. 15 and 35% higher than for pure stearic acid and PEG, respectively. This phenomena may be explained in terms of strengthened specific interactions via hydrogen bonding leading to formation of more perfect crystalline lattice.

DSC melting and freezing curves of blends PEG/lauric acid. 1 ‐ PEG 3 400/lauric acid, 2 ‐ PEG 10 000/lauric acid, 3 ‐ PEG 20 000/lauric acid, 4 ‐ PEG 35 000/lauric acid (cooling ‐ 10 K · min^?1), 5 ‐ PEG 3 400/lauric acid, 6 ‐ PEG 10 000/lauric acid, 7 ‐ PEG 20 000/lauric acid, 8 ‐ PEG 35 000/lauric acid (heating ‐ 10 K · min^?1).     

喷气燃料冰点的差示扫描量热法测定

介绍差示扫描量热法(DSC)测定喷气燃料冰点的原理和实验过程。用DSC法测定了不同型号的8种喷气燃料的冰点,测定结果与国标法GB/T 2430-1981测定的一致。     

Isothermal Curing Kinetics of Epoxidized Fatty Acid Methyl Esters and Triacylglycerols

Plant oil triacylglycerols are attractive renewable resources for biobased epoxy resins. We investigated the curing kinetics of three model epoxidized fatty acid methyl esters and representative epoxidized triacylglycerols with varied epoxide functionalities and distributions in the presence of a latent cationic initiator. Isothermal differential scanning calorimetry (DSC) was used to analyze the curing kinetics of the epoxy systems, and kinetic parameters (i.e., rate constants, reaction orders) were determined. Both epoxidized fatty esters and triacylglycerols followed the autocatalytic curing mechanism, and the DSC data were analyzed according to the Kamal autocatalytic model. Epoxidized methyl linoleate (EMLO) had the highest maximum curing rate, followed by epoxidized methyl linolenate (EMLON), and epoxidized methyl oleate (EMO) had the lowest maximum curing rate. We conclude that EMLO with two epoxide groups has the highest reactivity in this curing system, while the EMO with one epoxide group has the lowest reactivity. For epoxidized triacylglycerols, epoxidized camelina oil had the highest curing reactivity at higher temperatures, followed by epoxidized linseed oil and soybean oil.     

Kinetics of Melt Crystallization of a Sunflower Oil‐Based Polyunsaturated Fatty Acid Mixture

Important parameters like supercooling and cooling rates affecting the melt crystallization of a polyunsaturated fatty acid (PUFA) mixture obtained from sunflower oil were investigated and compared via high‐resolution polarized‐light microscopy. PUFA was thermally characterized in a differential scanning calorimeter and the significant liquid‐solid‐phase transition temperatures determined were then implemented in the development of specific temperature profiles. Analyzed between two glass slides, induction times were found to decrease with low crystallization temperatures and the number of nuclei per unit area increased with higher supercooling and cooling rates. A comparison between the linear crystal growth rates of pure standards of each of the main fatty acids present in the PUFA mixture and the PUFA mixture itself indicated that the latter is much slower than that of each of its pure components.     

高密度烃燃料冰点的DSC法测定

介绍了用差示扫描量热法(DSC)测定高密度烃燃料冰点的原理和方法,并对测试中的主要影响因素进行讨论。结果表明,当高密度烃燃料冰点在-80℃以下时,该方法具有较好的重复性和再现性,可作为高密度烃等低冰点燃料的常规检测方法。     

Green Process of Propylene Oxide Reaction for Thermal Hazard Assessment by Differential Scanning Calorimetry and Simulation

In addition to polypropylene, acrylonitrile, and carbonyl alcohol, propylene oxide is the fourth major derivative among propylene derivatives and one of the important basic organic chemicals. A thermal stability test of catalyst, methanol, and hydrogen peroxide (H₂O₂) was conducted via differential scanning calorimetry (DSC). Propylene epoxidation with H₂O₂ over catalyst, methanol, and propylene evenly mixed by specific pressure was carried out, and then the runaway reaction under adiabatic conditions was further simulated by the vent sizing package 2 (VSP2) to measure temperature and pressure data with respect to time of the runaway excursion. Finally, the apparent activation energy of H₂O₂ and propylene oxide reaction was obtained via temperature variation equation to evaluate the degree of potential hazard in industry.     

Crystallization Behavior of Fatty Acid Methyl Esters

Biodiesel from most agricultural feedstocks has flow properties that are prone to startup and operability problems during cold weather. Biodiesel from soybean oil is generally a mixture of long-chain fatty acid alkyl esters composed of 0.15–0.20 mass fraction saturated esters (melting point [MP] ≫ 0 °C) mixed with unsaturated esters (MP < 0 °C). This work investigates the crystallization properties of two saturated fatty acid methyl esters (FAME) commonly found in biodiesel from soybean oil. Differential scanning calorimetry (DSC) heating and cooling scans of methyl palmitate (MeC16), methyl stearate (MeC18) and methyl oleate (MeC18:1) in pure form were analyzed. Crystallization behavior in ternary FAME mixtures was inferred by the application of thermodynamic models based on ideal solution and freezing-point depression theories. Activity coefficients for MeC16 and MeC18 in MeC18:1 solvent were determined by analyzing DSC cooling curves for binary FAME mixtures. Eutectic points were predicted by both models. Crystallization onset temperatures inferred from freezing point depression theory were more accurate than those for ideal solutions with respect to a direct DSC cooling curve analysis of corresponding ternary mixtures. This work shows that the crystallization onset temperature (cloud point) of biodiesel may be predicted by freezing-point depression theory if the activity coefficients of the component FAME are known. The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by USDA or ARS of any product or service to the exclusion of others that may be suitable.     

Comparative Oxidative Stability of Fatty Acid Alkyl Esters by Accelerated Methods

Several fatty acid alkyl esters were subjected to accelerated methods of oxidation, including EN 14112 (Rancimat method) and pressurized differential scanning calorimetry (PDSC). Structural trends elucidated from both methods that improved oxidative stability included decreasing the number of double bonds, introduction of trans as opposed to cis unsaturation, location of unsaturation closer to the ester head group, and elimination of hydroxyl groups. Also noticed with EN 14112 was an improvement in oxidative stability when a larger ester head group was utilized. Methyl esters that contained ten or less carbons in the fatty acid backbone were unacceptable for analysis at 110 °C (EN 14112) due to excessive sample evaporation. With respect to PDSC, a correlation was noticed in which the oxidation onset temperature (OT) of saturated fatty esters increased with decreasing molecular weight (R ² 0.7328). In the case of the monounsaturates, a very strong inverse correlation was detected between molecular weight and OT (R ² 0.9988), which was in agreement with EN 14112. Lastly, a strong direct correlation (R ² 0.8759) was elucidated between OT and oil stability index (OSI, EN 14112, 80 °C). The correlation was not as strong (R ² 0.5852) between OSI obtained at 110 °C and OT. Disclaimer: Product names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.     

差示扫描量热熔点分析法的应用性分析

选择不同温度段熔融的5个代表性品种、国内外不同来源的13个法定熔点标准物质作为研究对象,进行差示扫描量热法和毛细管法两种熔点分析方法的关联性研究,并进一步开展差示扫描量热熔点分析法关键参数的应用性分析。研究表明,毛细管法的熔点分析结果一般延后1~2℃;差示扫描量热熔点分析法的准确性和精密度更好,并且推荐采用10℃/min的升温速率参数,而升温起点、气体流量等方法参数影响较小。质量分析还证实,我国药典熔点标准物质已经具备国际竞争力。     

用差示扫描量热法测量涂膜中的锌粉含量

作为测量锌粉含量最为快捷的一种方法——差示扫描量热法,现已在国际上得到广泛应用,叙述利用其方法测量涂膜中锌粉含量的原理及检测条件,探讨了产生误差的原因。     

差示扫描量热法对乙烯-醋酸乙烯酯热性能的研究

乙烯-醋酸乙烯醑（EVA）由于在分子链中引入了醋酸乙烯酯（VA）单体,降低了分子链的规整性．随着VA含量的增加,EVA树脂的结晶度降低。文章通过改变DSC测试条件对EVA树脂的热性能做进一步研究,分别讨论了常规方法与恒温结晶后的方法的玻璃化转变以及结晶的行为。从而估算出EVA的玻璃化转变温度。     

DSC法测试瓶级聚酯切片熔点的不确定度评估

对采用差示扫描量热法测试瓶级聚酯切片熔点过程中产生的不确定度来源进行了分析,结果表明仪器及标准校准物质的测量不确定度、样品的不均匀性带来的不确定度及气体波动引起的不确定度等,是瓶级聚酯切片熔点测试结果不确定度的主要来源。     

Kinetic of 8-quinolinyl Methacrylate Polymerization by Differential Scanning Calorimetry

Abstract

The kinetic of 8-quinolinyl methacrylate (8-QMA) polymerization was studied using 2,2′-azobisisobutyronitrile (AIBN) as a free radical initiator by differential scanning calorimetry (DSC) under two different experimental variables viz., heating rate and initiator concentration. Borchardt ‐ Daniel (B [tbnd]) kinetic method was applied to estimate the various kinetic parameters for the free radical polymerization of 8-QMA. The effect of initiator concentration and heating rate on the rate of polymerization was discussed. The importance of isothermal and isoconversion predictive curves in optimizing the polymerization process parameters has also been discussed.     

Correlation Between Enzyme Activity and Stability of a Protease, an Alpha-Amylase and a Lipase in a Simplified Liquid Laundry Detergent System, Determined by Differential Scanning Calorimetry

Enzymes used during washing in laundry detergents have become a universal tool to lower energy consumption and to generate a broad, consumer-relevant, cleaning effect. However, the stability of these enzymes remains a major obstacle, particularly in liquid products, due to increased interaction between the enzymes and the other components of the detergent. The process of formulation involves extensive shelf-life stability studies where residual enzyme activities are correlated with formulation variations. As a way to improve the formulation process, we evaluated the possible use of differential scanning calorimetry (DSC) as a tool to predict enzyme stability in liquid detergents. Thus, residual enzyme activity after incubation in a multitude of formulations was determined and compared to thermodynamic data obtained by DSC. The enzymes tested were a protease, an alpha-amylase and a lipase. We found a strong linear correlation between DSC-derived data, in particular T _max (temperature at peak maximum of the transition from the folded to unfolded state) and enzyme activity studies with R ²-values: 0.98 (protease), 0.99 (amylase) and 0.98 (lipase), respectively. Thus, a higher T _max for the same enzyme in a particular formulation is directly proportional to longer storage stability. These results suggest a new way of greatly accelerating this type of formulation study, allowing estimation of enzyme compatibility with a specific formulation on a daily, rather than the weekly or monthly basis used at present.