Effect of triglycerides containing 9,10-dihydroxystearic acid on polymorphism of sal (Shorea robusta) fat

The effect of the triglycerides containing 9,10-dihydroxystearic acid (DHS-TG) on the phase transition of polymorphic forms of normal triglycerides (TG) of sal fat was investigated by differential scanning calorimetry (DSC) under different cooling and heating modes. Four levels of DHS-TG, 2, 5, 8 and 10%, were used. DHS-TG accelerated the phase transition of lower melting crystal forms I → II → III of TG obtained under rapid (20°C/min) or slow (2°C/min) rates of cooling. They delayed the phase transition of crystal form III to IV of TG at 0°C. Also, DHS-TG reduced the heat of fusion (ΔH) of the stable form (V) of TG obtained after tempering at 0°C and at 26°C.     

Characterization ofβ-carotene thermal degradation products in a model food system

A model system developed in our laboratory for the study of thermal degradation products (TDP) of carotenoids was employed.β-Carotene (10 g) in glycerol was heated at 210 C for 4 hr, 1 hr, 15 min and 5 min. The time and temperature chosen were similar to edible oil deodorization and deep fat frying. In this study, the TDP ofβ-carotene were quantified as influenced by time and temperature of heating. Results indicate that at 210 C, degradation is almost complete after 4 hr and most of the nonvolatile products are viscous, yellow-brownish material. Shorter times (1 hr, 15 min and 5 min) cause less degradation. TDP include nonpolar as well as oxidized derivatives ofβ-carotene. The results of this study provide information on the type, amount and mechanism of formation of compounds resulting from heating carotenoids. Presented at the AOCS meeting in Dallas, Texas, in 1984.     

Thermal analysis of palm stearine by DSC

The chemical composition and thermal properties of palm stearine have been investigated. The sample consists of triglycerides containing mainly the fatty acid residues: palmitic (P) 51.4%; oleic (O) 32.7%; linoleic (L) 8.3% and stearic (S) 5.0%. The sample melts as almost two independent components in separate temperature ranges. DSC analysis and analogy with the work of Persmarket al. (1) indicate that the high melting component, consisting mainly of the triglycerides POP (33%), PPP (≈15%), POS (4%) and PPS (2%), crystallizes initially in an α crystal form which rearranges on tempering successively to β′ and β crystal forms. The constitution of the lower melting component is much more dependent on thermal history but is mainly POO (14% overall), PLP (13% overall) and SOO (1% overall). It crystallizes initially in a sub α form which rearranges to β′ when tempered at 0°C and to the β crystal form when tempered at 10°C. The liquid phase contains mainly PLO (8% overall), OOO (6% overall), PLL (4% overall) and LOO (1% overall).     

Pan-frying stability of NuSun oil,a mid-oleic sunflower oil

Pan-frying is a popular frying method at home and in many restaurants. Pan-frying stabilities of two frying oils with similar iodine values (IV)—mid-oleic sunflower oil (NuSun oil; IV=103.9) and a commercial canola oil (IV=103.4)—were compared. Each oil sample was heated as a thin film on a Teflon-coated frying pan at ∼180°C to a target end point of ≥20% polymer. High-performance size-exclusion chromatography analysis of the mid-oleic sunflower and canola oil samples indicated that the heated samples contained 20% polymer after approximately 18 and 22 min of heating, respectively. The food oil sensor values increased from zero to 19.9 for the canola sample and from zero to 19.8 for the mid-oleic sunflower sample after 24 min of heating. The apparent first-order degradation rate for the mid-oleic sunflower sample was 0.102±0.008 min⁻¹, whereas the rate for the canola sample was 0.092±0.010 min⁻¹. The acid value increased from approximately zero prior to heating to 1.3 for the canola sample and from zero to 1.0 for the mid-oleic sunflower sample after 24 min of heating. In addition, sensory and volatile analyses of the fried hash browns obtained from both oils indicated there were no significant differences between the two fried potato samples.     

FTIR Characterization of Polymorphic Transformation of Ammonium Nitrate

Solid ammonium nitrate (NH ₄ NO ₃ ) exists in five stable polymorphic forms (designated as phases I, II, III, IV, and V) below its melting point at around 170°C. Phase IV is stable in a temperature range of ?17°C ～ 32°C and is the only phase that has been considered by the atmospheric research community until recently. In this study, we examine the IV ? III phase transition of NH ₄ NO ₃ and how relative humidity (RH) affects the transition path and the transition temperatures using in-situ microscopic Fourier Transform InfraRed spectroscopy. Two kinds of NH ₄ NO ₃ samples, powder produced from grinding commercially produced chemicals and single particles obtained by efflorescence of droplets on PTFE filters, were studied. The powder samples exhibit the IV?III phase transition and the transition temperature depends on the RH while the single particle samples exhibit only the IV?II transition at about 52°C (forward) and 48°C (reverse), bypassing phase III, with transition temperatures independent of the RH. However, grinding of the particles produced through efflorescence results in the IV?III transitions. Differences in crystal structure and moisture content may explain the distinct phase transition behaviors of the two types of samples. These results suggest that solid and pure NH ₄ NO ₃ aerosol particles are stable in phase IV under ambient conditions.     

Formation of Ceramics from Metakaolin-Based Geopolymers. Part II: K-Based Geopolymer

The structural evolution and crystallization of potassium-based geopolymer (K₂O·Al₂O₃·4SiO₂·11H₂O) on heating was studied by a variety of techniques. On heating from 850–1100°C, potassium-geopolymer underwent significant shrinkage and surface area reduction due to viscous sintering. Small, 15–20 nm sized precipitates present in the unheated geopolymer coarsened substantially in samples heated between 900° and 1000°C. However, the microstructural surface texture was dependent on the calcination conditions. Leucite crystallized as the major phase after being heated to >1000°C, although a minor amount of kalsilite was also formed. Prolonged heating for 24 h at 1000°C led to the formation of ∼80 wt% of leucite, along with 20 wt% of remnant glassy phase. The surface of geopolymers heated to 1000°C attained a smooth, glassy texture, although closed porosity persisted until 1100°C. Thermal shrinkage was completed by 1100°C, and the material reached 99.7% of the theoretical density of tetragonal leucite.     

Capabilities of different cooking oils in prevention of cholesterol oxidation during heating

The potential of various cooking oils to prevent cholesterol degradation and/or oxidation, as measured by the production of 7-ketocholesterol during heating at different temperatures, was studied using a cholesterol model system. In the control group (without cooking oil), cholesterol was relatively stable, and 73% of its initial concentration was present after 30 min of heating at 125°C. Less than 30 and 10% of cholesterol remained at 150 and 175°C after 30 min, respectively, and 10% at 200°C after 10 min. In the treatment group, cholesterol mixed with corn, canola, soybean, or olive oil had significantly improved thermal stability. More than 60 and 40% of cholesterol remained at 150 and 175°C after 30 min, respectively. In the control group, 7-ketocholesterol was produced when samples were heated above 150°C, and levels increased consistently during 30 min of heating. At 175 or 200°C, the level of 7-ketocholesterol did not increase further after reaching the highest level after 10 min of heating. 7-Ketocholesterol is not stable above 175°C, and its degradation rate could be much faster than its production at 200°C. 7-Ketocholesterol was not found in samples of cholesterol mixed with corn oil or laboratory-prepared soybean and rice bran oils until the heating temperature was raised to 175°C for 20 min. The levels of 7-ketocholesterol in those treatment groups were greater than that in the control group at 175°C for 30 min. These oils may increase the thermal stability of 7-ketocholesterol and retard its degradation rate.     

Heat treatment of vegetable oils III. GC-MS characterization of cyclic fatty acid monomers in heated sunflower and linseed oils after total hydrogenation

Fractions of cyclic fatty acid monomers (CFAM) were isolated from linseed oil heated at 275°C for 12 hr under nitrogen, at 240°C for 10 hr under nitrogen and at 240°C for 10 hr under air. Cyclic fatty acid monomers fractions were also isolated from a sunflower oil heated at 275°C for 12 hr under nitrogen and at 200°C for 48 hr in a commercial fryer. The CFAM fractions were hydrogenated and their composition studied by gas liquid chromatography coupled with mass spectrometry (GC-MS). The CFAM in the fraction isolated from heated linseed oil samples were a mixture (1:1) ofcis andtrans cyclopentyl and cyclohexyl isomers, while the CFAM in the fractions isolated from heated sunflower oils were mostly cyclopentyl isomers. The major cyclopentyl isomers weretrans andcis methyl 7-(2′-hexylcyclopentyl) -heptanoate, methyl 9-(2′-butyl-cyclopentyl)-nonanoate and methyl 10-(2′-propylcyclo-pentyl)-decanoate. The major cyclohexyl isomers were thetrans andcis methyl 9-(2′-propylcyclohexyl)-nonanoate which represented about 50% of the CFAM isomers isolated from heated linseed oil samples. For part II in this series see Ref. 1.     

Structural changes of injection molded starch during heat treatment in water atmosphere: Simultaneous wide and small‐angle X‐ray scattering study

Native starches with wide varying amylose content were processed by injection molding. The injection‐molded materials were conditioned in water for 20 days and sealed in glass capillaries. Simultaneous wide‐ and small‐angle X‐ray scattering (WAXS and SAXS, respectively) were recorded during thermal heating using a synchrotron source. Crystallinity, SAXS invariant, Q, and long period, L, were measured as a function of heating temperature. The injection‐molding process provokes a destruction of the crystal forms A (cereal starch) and B (tubercle starch) but favors a development of the crystal form V_h. After wet conditioning, WAXS of the injection‐molded samples shows again the appearance of the crystal forms A or B, and crystallinity reaches values similar or larger than those of native starch. A constant heating rate (5°C/min) was particularly used for a comparison of potato and corn starch with a similar amylose content. While the crystallinity associated to forms A and B slowly decreases below 55°C and then rapidly decreases until its disappearance at 85–90°C, the invariant shows a maximum around 40°C and rapidly decreases thereafter. The total nanostructure disappearance occurs at temperatures about 10°C higher for the case of potato starch. In addition, a recovery of the WAXS and SAXS maxima during the subsequent cooling process before reaching room temperature was observed only for potato starch. Analysis of WAXS and SAXS for the rest of the starch materials reveals clear differences in the structural parameters of the samples that cannot be easily explained solely on the basis of the amylose content. Thus, for Cerestar and Roquette, it is noteworthy that there was a continuous decrease of L until its total disappearance as well as the persistence of crystallinity (form B), presumably stabilized by the presence of the V_h structure (12–15%). Real‐time crystallization experiments on two amorphous injection molded samples, waxy maize (free amylose starch) and potato starch, are also discussed. It is shown that the absence of amylose delays the recrystallization of amylopectine during the experiment. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 301–309, 2004     

Synthesis and evaluation of mechanical and thermal properties of segmented condensation polyurethanes

Abstract

Condensation polyurethanes with different hard segment (HS) content were prepared by condensation reaction of urea, phenol sulphonic acid and formaldehyde and tested for their mechanical, physical and thermal properties. Obtained polyurethane (PUR) films were first heated at 50°C for 120 min and then treated at 135°C for 15 min or 160°C for 10 min. The tensile strength of samples thermally treated at 50°C then at 135°C was 120% higher than for samples treated only at 50°C. The obtained polyurethanes exhibited segmented structures with phase separation between HSs and soft segments (SSs). Films containing 19 and 21%HSs heated at 50°C then 135°C exhibited acceptable mechanical properties and water resistance. The lower and higher end use temperatures of PUR films were affected mainly by the polymer composition. Moreover, the polyurethane samples containing 19 and 21%HSs have shown the highest decomposition temperature (i.e. >165°C), compared to 80°C for polymers with 32%HSs.     

The autoxidation of linoleates at elevated temperatures

To investigate the effects of heating conditions on the decomposi-tion of linoleates, samples of linoleic acid and its esters were heated at 70 C, 180 C and 250 C for different periods of time and their decomposition products analyzed by gas chromatography and mass spectrometry. Qualitatively, the polar decomposition products were basically the same. However at the higher temperature and longer heating time the nonpolar decomposition products contained a large number of cyclic hydrocarbons which could not be detected with the milder heat treatments. A series of alkyl ethers, not previously reported, was identified in samples heated at 250 C for 5 hr. Quanti-tatively, hexanal and aldehyde esters were found in significantly greater amounts in the samples heated at a lower temperature, whereas the reverse was true fort, t-2,4-decadienal.     

Effects of thermal oxidation on the constitution of butterfat,butterfat fractions and certain vegetable oils

To evaluate the thermal oxidative behavior of butterfat in comparison to selected vegetable oils, samples of winter and summer butterfat, liquid and solid butterfat fractions, and selected vegetable oils were heated at 185 C in the presence of air (30 ml/min) for 8 and 16 hr. The resultant heated fats and oils, as well as the methyl esters of their fatty acids, were examined by gel permeation chromatography. The results indicated that butterfat is much more stable to thermal oxidation than canola, sunflower and soybean oils. This was evidenced by a substantially higher content of both dimeric and higher oligomeric triglycerides in the vegetable oils than in any of the butterfat samples after both 8 and 16 hr of heating. The corn oil also exhibited a high degree of stability to thermal oxidation after 8 hr of heating. The 16 hr corn oil data, however, was less certain due to the presence of a very viscous and dark colored material which could not be removed from the oxidation flask; this was believed to contain highly polymerized oil and was not observed with any of the other samples. There were some differences in the inter- and intramolecular polymerization of the butterfat fractions compared with each other and with whole butterfat. With the winter butterfat samples, after 8 hr of thermal oxidation, both the solid and liquid butterfat fractions exhibited more stability toward intermolecular polymerization than did the whole butterfat. After 16 hr of heating the ratio of trimeric and higher oligomeric triglycerides to dimeric triglycerides increased with increasing degree of unsaturation of the butterfat and with increased time of heating. Similar trends were observed with regard to the degree of intramolecular polymerization. Presented at the AOCS meeting in Philadelphia in May 1985.     

Characterisation of cellulose treated by the steam explosion method. Part 3: Effect of crystal forms (cellulose I,II and III) of original cellulose on changes in morphology,degree of polymerisaion,solubility and supermolecular structure by steam explosion

An attempt was made to clarify the effect of the crystal form of untreated cellulose on the morphological and structural changes of cellulose during steam explosion treatment (steam pressure P = 2.9MPa (T = 508K), treatment time t = 15-300 s). For this purpose, the crystal form of soft wood pulp (cellulose I) was converted by solid-to-solid transition, with minimal unavoidable change in other structural characteristics including morphology and average degree of polymerisation, into cellulose II or cellulose III. It was proved by both X-ray and solid-state cross-polarisation/magic-angle sample-spinning (CP/MAS) ¹³C NMR analyses that even a simple addition of water at room temperature brought about a significant structural change in the steam-untreated cellulose samples. The solubility towards 9.1 wt% aqueous sodium hydroxide, S_a, of the cellulose samples of crystal forms I and III could be improved from 31-33% up to almost 100% by selecting appropriate steam explosion conditions (for example, P = 2.9MPa, t = 30 s). Such a magnificent increase in S_a by the steam explosion treatment was not observed for the cellulose II sample, even under the rather severe conditions of the steam explosion treatment at which the cellulose III crystal was converted to a large extent to cellulose I, as confirmed by X-ray diffraction. X-ray diffraction analysis showed that crystallisation of samples with cellulose I or II crystal occurred to some extent during the steam explosion treatment. Contrary to this, the degree of breakdown of the intramolecular hydrogen bond O₃…O'₅, as estimated by CP/MAS ¹³C NMR analysis, significantly increased for cellulose I and I11 during the treatment. The decrease in the viscosity-average degree of polymerisation, P, observed for all treated samples can be roughly categorised into two or three steps of the first-order decomposition reaction with different reaction rates.     

Liquefaction of Turkish coals in tetralin with microwaves

The effect of the ratio of solvent to coal (S/C) and the period of heating by microwave on the solubilization of Turkish Coals (Beypazarı, Bolu-Göynük, Muğla-Yatağan, Soma-Merkez, Tunçbilek lignites and Zonguldak coal) in tetralin have been investigated. For the investigation of the effect of the S/C ratios with values of 4/1, 5/1, 6/1, 7/1 and 8/1, the coal samples were heated by microwave for 10 min. The results indicated that the optimum S/C ratio depends on the coal type to obtain the highest yields of THF solubles. The effect of microwave heating period was investigated at the values of 4/1 and 8/1 of S/C ratios and the heating period was changed from 2 to 10 min at 2-min intervals. The yield of THF solubles decreased with increasing heating period at the value of S/C ratio of 4/1, they increased with increasing heating period when the value of S/C ratio was 8/1. The yield of THF soluble coal products after 10 min of microwave heating period changed from 13% to 23%, depending on the coal type.     

Synthesis of nano-phase ZrC by carbothermal reduction using a ZrO2–carbon nano-composite

Carbothermal reduction of Zr-sucrose gels powders into nano-phase ZrC, or ZrC-Zr(C,O) core-shell powders, via a composite of 2–4 nm sized ZrO₂ and amorphous carbon, is described. Samples with 1.7–20 sucrose-carbon:Zr ratio gels heated to 1495 °C at 10 °Cmin^?1, with 3 and 30 min hold time were studied in detail using; TG, XRD, SEM, TEM, STEM-EDX, and XPS with Ar⁺-ion etching. After 1495 °C, 3 min, the samples with 12-20C:Zr ratios yielded weakly agglomerated 30 to 40 nm sized ZrC particles, surrounded by a dense 5 nm thick shell of Zr(C,O). With 5C:Zr significant amounts of ZrO₂ was present after heating at 1495 °C for 3 min, while after 30 min annealing, ZrC particles without residual amorphous carbon was obtained. Minor amounts of zirconia was found in most samples, which in similarity with the 5 nm Zr(C,O) shell, is believed to stem from post synthesis oxidation.     

Geometrical isomerization of linolenic acid during heat treatment of vegetable oils

Heat treatment of rapeseed (primor) and soybean oils resulted in the geometrical isomerization of linolenic acid. The geometrical isomers were isolated from a rapeseed oil heated at 240 C for 10 hr by a combination of thin layer chromatography (TLC) of the methoxy bromomercuric adducts of the total methyl esters and AgNO₃-TLC. Three major isomers were identified after hydrazine reduction followed by ozonolysis in BF₃-MeOH as 18:3Δ9c, 12c, 15t, 18:3Δ9t, 12c, 15c and 18:3Δ9t, 12c, 15t. These were accompanied by minor amounts of 18:3Δ9c, 12t, 15c, 18:3Δ9c, 12t, 15t and 18:3Δ9t, 12t, 15c. The 18:3 isomers were detected in both soybean and rapeseed oil heated at 240 C for 10 hr. At this temperature, the increase in time of the heat treatment from 10 to 40 hr resulted in a relative increase of the di-trans and in a decrease of the mono-trans isomers. Only minor quantities of these isomers were detected in the oils heated at 200 C for 10 hr. At this temperature, the increase in time of the heat treatment resulted in an increase of both the mono- and di-trans isomers. Presented in part at the I.S.F. Congress, October 1983, Budapest, Hungary.     

Study on the crystal morphology and melting behavior of isothermally crystallized composites of short carbon fiber and poly(trimethylene terephthalate)

The spherulites of the short carbon fiber(SCF)/poly (trimethylene terephthalate) (PTT) composites formed in limited space at designed temperatures, and their melting behaviors were studied by the polarized optical microscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM), respectively. The results suggest that SCF content, isothermal crystallization temperatures, and the film thicknesses influence the crystal morphology of the composites. The dimension of the spherulites is decreased with increasing SCF content, but whether banded or nonbanded spherulites will form in the composites is not dependent on SCF content. However, the crystal morphology of the composites depends strongly on the temperature. When the isothermal crystallization temperatures increase from 180°C to 230°C, the crystal morphology of SCF/PTT composites continuously changes in the following order: nonbanded → banded → nonbanded spherulites. Discontinuous circle lines form in the film when the film thickness increases from 30 to 60 μm. Basing on the SEM observation, it is found that these circle lines are cracks formed due to the constriction difference of the different parts of the spherulites. These cracks are formed when the film is cooled from the isothermal crystallization temperature to the room temperature at a slow cooling rate; while they will disappear gradually at different temperatures in the heating process. The crack will appear/disappear first around the center of the spherulite when the film was cooled/heated. The nontwisted or slightly twisted lamellas will reorganize to form highly twisted lamellas inducing apparent banded texture of the spherulites.     

Phase transitions in mesophase macromolecules: The transitions of poly(p-acryloyloxybenzoic acid)

Poly(p-acryloyloxybenzoic acid) has been obtained in twelve single and two-phase physical states, which include the amorphous glassy and liquid states, the mesomorphic glassy and the mesomorphic liquid states and in addition eight two-phase semicrystalline states (crystal forms I and II). Using mainly differential scanning calorimetry, the transition temperatures, energies and heat capacity changes at the glass transitions have been studied. The time dependency of the glass transition has also been determined. The strongly heating rate dependent amorphous glass transition occurs at 348K (20k min^?1 heating rate, ΔC_p = 39 JK^?1 mol^?1), the mesophase glass transition, at 408K (also at 20k min^?1, ΔC_p = 43 JK^?1 mol^?1). The latter is less heating rate dependent. The amorphous to mesophase transition occurs between 375 and 475K (ΔH = ?4.5 KJ mol^?1); the peaks of melting transitions, which are also strongly heating rate dependent, were observed at 573K and 553K (20 K min^?1 heating rate) for crystal forms I and II, respectively. The heat of fusion of crystal form I is estimated to be 22 KJ mol^?1. There seems to be no partially amorphous-partially mesomorphic state.     

Characterization of poly(lactic acid) multifilament yarns. I. The structure and thermal behavior

The structure and thermal behavior of poly(lactic acid) (PLA) multifilament yarns were studied by complementary techniques of differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and wide angle X‐ray diffraction (WAXD). As for PLA filaments, notable differences in the WAXD patterns, DSC curves, and FTIR spectra were observed. The combination of the WAXD and FTIR results showed that PLA samples with different crystallinity contain α‐form crystal structure. The FTIR spectra of the filaments were analyzed to study their crystallinity and crystal structure. The total crystallinity of the PLA filaments was obtained from the percent area loss of the skeletal amorphous band at 955 cm^?1. Crystalline fraction from FTIR and DSC were comparable with each other. The C?O stretching region, which is sensitive to crystallization and dipole–dipole interactions, was evaluated to provide information about chain conformers and crystallinity of the samples. Depending on the processing conditions, double melting peaks were observed in the DSC curves of the samples. This exhibited the structural reorganization of the crystal phase during heating affected by heating and cooling rate. In the DSC curves of the nearly amorphous multifilament yarn, the exothermic peak observed right above the glass transition temperature (T_g) indicated two relaxed and deformed amorphous regions. However, the multifilament yarn with higher crystallinity showed just endothermic melting peak after its glass transition. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A thermal investigation on coals from Assam (India)

A thermal characterization of two coal samples from Ledo and Tikak collieries of Makum coalfield, Assam, India using XRD, FT-IR, and TGA was reported in this paper. The coal samples were heated for 20, 40 and 60 min in a 1000-watt heater (temperature ∼ 250 °C) in presence of air and characterized by XRD and FT-IR spectroscopy. Both the coals contain amorphous and crystalline phases. The raw coals also contain very small peaks due to quartz, calcite, gypsum, pyrite, and chlorite. The XRD patterns were found to change upon heating. In the coals heated for 20 and 40 min, it was observed that both amorphous and crystalline parts are common in them; crystalline part being the major one in the 40 min heated samples. The XRD patterns of the samples heated for 60 min indicate the presence of major quantities of α-quartz, hematite, and chlorite in them. They also show some new peaks, which are assigned to be kaolinite, illite, magnetite and very small in comparison to the amorphous portion in raw coals. α-quartz was found to be most stable crystalline phase of silica in the coals. The crystallinity % (X-ray) of the coals heat-treated for different times was determined and found to be increasing with time of heating. The FT-IR spectra of raw and heat-treated coal samples at 250 °C were also recorded and compared. The spectra were observed to be almost similar and it was observed that few functional groups disappear on heating at 250 °C. The same coal samples were also characterized by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) techniques. On heat treatment in air atmosphere up to 800 °C, 20–27% weight loss occurs due to removal of various volatile materials. DTA results indicate the chemical reactivity of the coal sample initially at 80–110 °C due to loss of water, and two other major reactions at around 420 and 530 °C due to primary and secondary volatization.