Crystallization of sunflower oil waxes

Activation free energies of nucleation (ΔG _c ) were calculated using induction times of crystallization measurements. Results showed that ΔG _c decreased exponentially as wax concentration increased at a constant crystallization temperature (T _c ). In contrast, for a constant supersaturation, ΔG _c increased from 12 to 22°C but decreased between 22 and 35°C. Melting behavior of purified waxes and solutions of purified waxes in sunflower oil were studied by DSC after crystallization at fast and slow cooling rates (20 and 1°C/min, respectively). Low supercooling temperatures (T _c >65°C) showed an increase in the onset temperature (T ₀ ) as T _c increased for both fast and slow cooling rates. Broader peaks were obtained for samples crystallized at a slow cooling rate at the same T _c . Regarding the solutions of waxes in sunflower oil, the wax concentration (supersaturation of the system) controlled crystallization as well as T _c . As T _c increased, the enthalpy (ΔH) decreased at a constant wax concentration. When wax concentration decreased, ΔH decreased at a constant T _c . For a low driving force, a small shoulder was obtained in the DSC diagrams owing to some type of fractionation. These results showed that wax crystallization is affected by different experimental parameters, such as T _c and cooling rate, depending on the wax concentration of the sample.     

Storage of sunflower‐seeds: variation on the wax content of the oil

Storage conditions of oil seeds before industrial extraction might influence the quality of the crude oil. The objective of this work was to study the influence of sunflower seed storage conditions (temperature and time) on the quality of the resulting oil in terms of its wax content and composition. Sunflower seeds were stored under different conditions, 10, 21 and 37 °C, in sealed recipients. Extractions of the seeds with hexane were made to obtain the oil at different storage times. The amount of oil extracted (25–40%) showed no significant differences with storage conditions. Wax content of the samples was determined with two different methods (laser polarized turbidimetry and microscopy), and results showed that wax concentration increased with storage conditions (time and temperature). Composition of wax components, determined using capillary gas chromatography, during storage was approximately constant for C₃₅–C₃₉ and showed significant differences for C₄₀–C₄₈ components. Waxes with high carbon number cause more turbidity than waxes with low carbon number, due to their higher melting point, resulting in a low‐quality crude oil and therefore in variations in processing conditions during the oil refining. According to the data showed in this study, seed storage at low temperatures during short periods of time may be the more adequate conditions to obtain high‐quality oil.     

Ion-Induced Nucleation in Nanoparticle Synthesis by Ionization Chemical Vapor Deposition

Particle formation mechanisms in nanoparticle synthesis by ionization chemical vapor deposition (CVD), in which source gases are ionized before being fed into the reactor, were investigated experimentally. First, nonagglomerated nanoparticles were formed from a tetraethylorthosilicate (TEOS)/O ₂ mixture ionized with a sonic-jet ionizer at various furnace temperatures, T _f, and TEOS concentrations, N _TEOS. Then, the electrical mobility of the nanoparticles and ions were measured using a differential mobility analyzer combined with a Faraday cup electrometer, and the particle number concentration by a condensation nucleus counter. Measurements at 293 ≤ T _f ≤ 1173 K and 0 ≤ N _TEOS ≤ 1.38 × 10 ^?5 mol/l showed that (a) negative TEOS and TEOS cluster ions were formed at T _f = 293 K, (b) gas-phase intermediates forming nanoparticles were formed at T _f ≥ 673 K, (c) for T _f = 873 K condensation of the intermediates onto ions (i.e., ion-induced nucleation) started at N _TEOS ≥ 4.48 × 10 ^?7 mol/l, and (d) the growth from ions to nanoparticles was discontinuous for this change in N _TEOS.     

Synthesis and properties of polyurethane elastomers based on renewable castor oil polyols

In this contribution, castor oil polyols with functionality of f = 2.7 and f = 2 are used as soft segments (SS) for synthesizing polyurethane elastomers (PUEs) without addition of petroleum-based polyol. The effect of molar ratio of castor oil polyols on structure and properties of PUEs has been investigated by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, X-ray diffraction, tensile, swelling, and water absorption tests. The results reveal that hydrogen bonding mainly exists in hard segments (HSs) and weakens with decreasing the molar percentage of castor oil polyol (f = 2.7) in SS. T _g of SS decreases while T _g of HS remains constant as molar percentage of castor oil polyol (f = 2.7) decreased. The initial degradation temperatures (T_5%) are above 300 °C and independent of the molar ratio of castor oil polyols. However, the temperature at 50% weight loss (T_50%) decreases significantly as molar percentage of castor oil polyol (f = 2.7) decreased. Moreover, PUEs exhibit very low water absorption rate, <1%, after immersing in water for 140 h at room temperature. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47309.     

Studies on the crystal growth of rice bran wax in a hexane medium

Rice bran oil (RBO) is well known for its high wax content (2–4%). A good separation of waxes must be ensured through the formation of crystals that can be removed with a minimal retention of oil to maintain high yields of refined oil. In the present study, the form and size distribution of RBO wax crystals were investigated using a laser diffraction technique. An attempt was made to study the effect of cooling on growth and size distribution of RBO wax crystals in hexane medium, and it showed that high cooling rate and low temperature induces the formation of a great number of small nuclei. In addition, experiments were performed to evaluate the effect on the growth of wax crystals of successive additions of gum and pure TG to the medium. The entire experiment was designed to optimize the temperature and incubation time of wax crystallization to facilitate the efficient separation of wax from crude RBO-hexane miscella using membrane technology.     

Nucleation and Self‐Nucleation of Bio‐Based Poly(ethylene 2,5‐furandicarboxylate) Probed by Fast Scanning Calorimetry

The present work focuses on the influence of nucleation processes on the crystallization of bio‐based poly(ethylene 2,5‐furandicarboxylate) (PEF). Nuclei formation has been studied by means of fast scanning calorimetry (FSC) both when cooling from the melt (nonisothermal conditions) and when annealing at either low‐ or high‐temperatures (isothermal conditions). FSC results show that nucleation on cooling can be prevented by using fast rates allowing to keep the polymer in its amorphous state; whereas cooling at moderate rates results in sample nucleation with a subsequent increase of the crystallization rate. Isothermal pretreatment just above the PEF glass transition temperature (T_g) results in nuclei formation whose rate decreases when the nucleation temperature approaches PEF T_g. On the other hand, annealing below the PEF melting point allows determination of the sample self‐nucleation behavior which occurs in a very narrow temperature range, i.e., between 195 and 198 °C.

     

Fischer–Tropsch Synthesis: Effect of K Loading on the Water–Gas Shift Reaction and Liquid Hydrocarbon Formation Rate over Precipitated Iron Catalysts

The effect of K loading on the water–gas shift (WGS) reaction and hydrocarbon formation rate during Fischer–Tropsch synthesis (FTS) was studied over 100 Fe/5.1 Si/2 Cu/x K (x = 1.25 or 3) precipitated catalysts using a 1-L continuously stirred tank reactor. The catalysts were tested over a wide range of experimental conditions: 260–270 °C, 1.3 MPa, H₂/CO = 0.67 and 20–90 % CO conversions. On the low K loading (1.25 % K) Fe catalyst, the H₂ deficiency required for the FTS reaction was made up by the WGS reaction only at high CO conversion level, i.e. >70 %; however, increasing potassium loading to 3 % dramatically improved the WGS reaction rate which provided enough hydrogen for the FTS reaction even at low CO conversion level, i.e. 30 %. Kinetic analysis suggests that increasing K loading resulted in significant increases in the WGS rate constant relative to that of FTS, which is a major cause of the high WGS activity on the high K loading catalyst. Both the low and high potassium containing iron catalysts have high liquid oil and solid wax formation rates, i.e. 0.78–0.93 g/g-cat/h at 260 °C, 1.3 MPa, H₂/CO = 0.67 and 50 % CO conversion, but increasing potassium loading from 1.25 to 3 % shifted the primary product to wax (70 %) from oil (73.5 %). The wax fraction increased with increasing CO conversion for both iron catalysts. The effect of K loading on initial FTS activity and hydrocarbon distribution/selectivity of the Fe catalysts was also studied. High K loading, i.e. 3 % K, increased the iron carburization rate and significantly shortened the induction period of the FTS reaction. Secondary reactions of olefins were remarkably suppressed and the olefin content was greatly enhanced with increasing K loading from 1.25 to 3 %, consistent with a number of studies in the open literature.     

Isothermal crystallization of tripalmitin in sesame oil

Crystallization of tripalmitin (TP) in sesame oil was investigated under isothermal conditions at a cooling rate similar to the one achieved in industrial crystallizers (1 K/min). The results obtained indicated that, at TP concentrations <0.98%, triacylglycerides of sesame oil developed mixed crystals with TP. However, at concentrations within the interval of 0.98 to 3.44%, tripalmitin crystallized independently from sesame oil. Within this concentration interval, discontinuities were observed in the behavior of the induction time of TP crystallization (T _i) in sesame oil as evidenced by differential scanning calorimetry, polarized microscopy studies, and determination of the Avrami index (n). In general, the discontinuities in T _i were associated with different polymorph states developed by TP in sesame oil as a function of its concentration and crystallization temperature. Thus, TP crystals obtained at temperatures above 296 K with 1.80 and 2.62% TP solutions had n values close to 3 and developed lamellar-shaped crystals that are characteristic of β tripalmitin. In contrast, the crystals obtained at temperatures of 296 K and below with 1.80% and 2.62% TP solutions provided n values close to 3. Axialite-shaped β′ TP crystals were obtained under these conditions. For the 0.98% TP solution, simultaneous production of α and β′ crystals occurred below 291 K. However, at temperatures above 291 K, a crystallization process with n=3 was obtained, and it developed a different polymorph state, i.e., β, with lamellar-shaped TP crystals.     

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

The 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 (T _o ), offset temperature (T _f ) and temperature range (difference between T _o and T _f ). Reproducibility of DSC curves was evaluated based on these parameters. Satisfactory reproducibility was achieved for quantitation of these DSC parameters. The results show that T _o of the crystallization curve and T _f 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.     

Quiescent and shear-induced non-isothermal crystallization of isotactic polypropylene-based nanocomposites

The paper reports a study of the effect of the addition of clay nanoparticles on melt rheology, phase structure, and non-isothermal crystallization process of isotactic polypropylene/hydrogenated oligocyclopentadiene (iPP/HOCP) system in quiescent conditions by DSC and under shear applied at different temperatures by SAXS. For both crystallization conditions, the addition of clay and/or HOCP shifts always the crystallization onset to lower values with respect to iPP. These results can be attributed to the diluent effect of HOCP that causes a decrease in the rate of nucleation and grow of the crystals, to the presence of segregated non-crystallizable phases/particles which hinder the transport of macromolecules chains toward the growing nuclei, and to the formation of beta iPP crystals and in the case of shear-induced crystallization to the presence of HPS which seems to reduce, mainly at low T _s, the amount of oriented polymer crystals, which are nuclei for the crystallization. At a given composition, the crystallization temperatures related at the crystallization under shear are always higher that those obtained by quiescent crystallization supporting the idea that the presence of extended chains in these samples act as nucleating agents favoring the crystallization process of iPP.     

Radiation hardening of silica glass through fictive temperature reduction

The aim of this article was to report the effects of γ-radiation on type-I Infrasil silica glass with different fictive temperatures, T_f, for harsh environment applications. Radiation-induced attenuation in the visible range is found to be much lower in low fictive temperature samples. Photoluminescence experiments show that glasses with higher fictive temperatures have a higher nonbridging oxygen hole centers defect concentration generated by irradiation. In addition, electron paramagnetic resonance studies reveal higher E’ point defects, AlOHC, and hydrogen(II) defects in high T_f samples. In general, we find that the γ-radiation “hardness” of Infrasil301 silica glass becomes significantly higher with decreasing fictive temperature.     

Effects of temperature on elastic behavior of short compact polymers

In this paper, we study further to explore the effects of temperature on the elastic behavior of short compact polymers. Average conformations and thermodynamics statistical properties at various temperatures T are calculated here. Different chain lengths N and elongation ratio λ are also considered simultaneously. From the plots of f and f_U vs. elongation ratio at low temperature, we can know that compact polymers are more close to the native states. With temperature decreasing deeply, polymer chains have the tendency to form globular structures. The results are concluded from: the ratio of 〈L₁²〉/〈L₂²〉 increase abruptly with temperature decreasing at low temperature, and both characteristic ratio 〈R²〉/Nb² and average energy per bond 〈U〉 decreases abruptly with temperature decreasing at low temperature, here L₁², and L₂² are the eigenvalues of the radius of gyration tensor S (L₁²≤L₂²). We also analyze the relationship between the heat capacity C_V and temperature T for different chain lengths in the process of tensile elongation. The coil-to-globule transition temperature T_c can be estimated from the location of the peak on the heat capacity plot as a function of temperature. The plots of 〈R²〉 as a function of chain length N at different temperatures are also shown, and the correlation 〈R²〉∼N^α is obtained at T>T_c or T<T_c, while at T=T_c, the plots are irregular, here α depends on temperature and elongation ratio simultaneously. Elastic force (f), energy contribution to elastic force (f_U), and the ratio f_U/f are also discussed at various temperatures. These investigations may provide some insights into elastic behaviors of compact polymers at different temperatures, especially at low temperature.     

Study of crystallization behavior of neat poly(vinylidene fluoride) and transcrystallization in carbon fiber/poly(vinylidene fluoride) composite under a temperature gradient

The crystallization behavior of poly(vinylidene fluoride) (PVDF) and transcrystallization in carbon fiber (CF)/PVDF composite were investigated under a temperature gradient. The crystallization temperature (T_c) was controlled in the range of 110–180 °C. For neat PVDF, the results showed that exclusive γ phase formed at T_c above 164 °C, but coexisted with α phase at T_c ranging from 137 to 160 °C. The promotion of γ phase to nucleation of α phase at low T_c was observed for the first time. For CF/PVDF composite, a cylindrical transcrystalline (TC) layer formed on the surface of CF when T_c was between 137 and 172 °C. The TC layer was exclusively composed of γ phase at T_c above 164 °C. The hybrid nucleation was dominated by γ phase though some α phase nuclei emerged on the surface of CF when T_c was in the range of 144–160 °C. As T_c decreased, competition between the hybrid nucleation of α and γ phase became more intense. The γ phase nuclei was soon circumscribed by the rapidly developed α phase when T_c was below 144 °C. Furthermore, some α phase nuclei were induced at the surface of the γ phase TC layer, and developed into α phase TC layer when T_c was in the range of 146–156 °C, which resulted in a doubled TC layer of α and γ phase at the interface of the composite. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43605.     

Effect of glass transition temperature and saturation temperature on the solid‐state microcellular foaming of cyclic olefin copolymer

Effect of glass transition temperature and saturation temperature on the solid‐state microcellular foaming of cyclic olefin copolymer (COC)—including CO₂ solubility, diffusivity, cell nucleation, and foam morphology—were investigated in this article. COCs of low T_g (78°C) and high T_g (158°C) were studied. Solubilities are 20–50% higher in high T_g COC than in the low T_g COC across the saturation temperature range. Diffusivities are about 15% higher on average in high T_g COC for temperatures up to 50°C. A much faster increase of diffusivity beyond 50°C is observed in low T_g COC due to it being in the rubbery state. Under similar gas concentration, high T_g COC starts foaming at a higher temperature. And the foam density decreases faster in low T_g COC with foaming temperature. Also, high T_g COC foams show about two orders of magnitude higher cell nucleation density than the low T_g COC foams. The effect of saturation temperature on microcellular foaming can be viewed as the effect of CO₂ concentration. Nucleation density increases and cell size decreases exponentially with increasing CO₂ concentration. Uniform ultramicrocellular structure with an average cell size of 380 nm was created in high‐T_g COC. A novel hierarchical structure composed of microcells (2.5 μm) and nanocells (cell size 80 nm) on the cell wall was discovered in the very low‐density high‐T_g COC foams. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42226.     

Application of the molecular dynamics method and the excited state model to the investigation of the glass transition in argon

The glass transition in argon at a high cooling rate is simulated. At a temperature of 50 K (considerably below the melting temperature T _f = 83.8 K), the fluctuation volume fraction reaches the constant value f _g ? 0.03–0.05, which is close in the order of magnitude to the criterion for the glass transition in liquids f _g = const 0.02–0.03 within the excited state model. At this temperature, the second maximum of the radial distribution function is split as a result of the glass transition at the temperature T _g = 50 K. The approximate empirical “two-thirds” rule T _g = (2/3)T _f is reasonably satisfied for argon. The data obtained are interpreted in the framework of the excited state model.     

High resolution solid-state NMR and DSC study of poly(ethylene glycol)-silicate hybrid materials via sol-gel process

Hybrid materials incorporating poly(ethylene glycol) (PEG) with tetraethoxysilane (TEOS) via a sol-gel process were studied for a wide range of compositions of PEG by DSC and high resolution solid-state ¹³C- and ²⁹Si-NMR spectroscopy. The results indicate that the microstructure of the hybrid materials and the crystallization behavior of PEG in hybrids strongly depend on the relative content of PEG. With an increasing content of PEG, the microstructure of hybrid materials changes a lot, from intimate mixing to macrophase separation. It is found that the glass transition temperatures (T_g) (around 373 K) of PEG homogeneously embedded in a silica network are much higher than that (about 223 K) of pure PEG and also much higher in melting temperatures T_m (around 323 K) than PEG crystallites in heterogeneous hybrids. Meanwhile, the lower the PEG content, the more perfect the silica network, and the higher the T_g of PEG embedded in hybrids. An extended-chain structure of PEG was supposed to be responsible for the unusually high T_g of PEG. Homogeneous PEG-TEOS hybrids on a molecular level can be obtained provided that the PEG content in the hybrids is less than 30% by weight. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 139–147, 1998     

New soybean oil–styrene–divinylbenzene thermosetting copolymers. I. Synthesis and characterization

The cationic copolymerization of regular soybean oil, low‐saturation soybean oil (LoSatSoy oil), or conjugated LoSatSoy oil with styrene and divinylbenzene initiated by boron trifluoride diethyl etherate (BF₃·OEt₂) or related modified initiators provides viable polymers ranging from soft rubbers to hard, tough, or brittle plastics. The gelation time of the reaction varies from 1 × 10² to 2 × 10⁵ s at room temperature. The yields of bulk polymers are essentially quantitative. The amount of crosslinked polymer remaining after Soxhlet extraction ranges from 80 to 92%, depending on the stoichiometry and the type of oil used. Proton nuclear magnetic resonance spectroscopy and Soxhlet extraction data indicate that the structure of the resulting bulk polymer is a crosslinked polymer network interpenetrated with some linear or less‐crosslinked triglyceride oil–styrene–divinylbenzene copolymers, a small amount of low molecular weight free oil, and minor amounts of initiator fragments. The bulk polymers possess glass‐transition temperatures ranging from approximately 0 to 105°C, which are comparable to those of commercially available rubbery materials and conventional plastics. Thermogravimetric analysis (TGA) indicates that these copolymers are thermally stable under 200°C, with temperatures at 10% weight loss in air (T₁₀) ranging from 312 to 434°C, and temperatures at 50% weight loss in air (T₅₀) ranging from 445 to 480°C. Of the various polymeric materials, the conjugated LoSatSoy oil polymers have the highest glass‐transition temperatures (T_g) and thermal stabilities (T₁₀). The preceding properties that suggest that these soybean oil polymers may prove useful where petroleum‐based polymeric materials have found widespread utility. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 658–670, 2001     

Effects of Al doping upon ac susceptibility of Pr0.5Ca0.5MnO3

Pr_0.5Ca_0.5Mn_1?xAl_xO₃ (0≤x≤0.07) compounds were prepared by standard solid-state reaction. The ac susceptibility of the samples at low temperatures was investigated. The real component χ′ peak at the freezing temperature T_f is suppressed with increasing the frequency. χ′ shows a linear relation between T_f and the logarithm of the frequency. The normalized slope P=ΔT_f/T_fΔ log₁₀ω is much lower than for canonical insulating spin glass systems (0.06≤P≤0.08). The intensity of imaginary component χ″ at T_f for the x=0, 0.01, 0.02 samples increases with increasing frequency. The results of χ′ and χ″ suggest that the x=0, 0.01, 0.02 samples have a cluster glass ground state. The intensity of χ″ at T_f for the x=0.05, 0.07 samples decreases with increasing frequency, suggesting a phase separation ground state. The intensity of χ″ at T_f for the x=0.03, 0.04 samples decreases with increasing frequency for ω≤701 Hz and increases with further increase of frequency. This complex behavior is ascribed to the competition between the effects of large and small ferromagnetic clusters in the sample. The ground state of the x=0.03, 0.04 samples is the transition state from cluster glass (for the x=0.02 sample) to phase separation (for the x=0.05 sample). AFM cluster blocking and the spin blocking were observed in the same sample.     

The avrami index and the fractal dimension in vegetable oil crystallization

The behavior of the Avrami plot during TAG crystallization was studied by DSC and rheological measurements in oil blends of palm stearin (26 and 80%) in sesame oil, using different crystallization temperatures (T _Cr ^o) attained under several cooling rate conditions (1, 10, and 30°C/min). In the same way, the relationship between the growth mechanisms of TAG, measured by the Avrami index (n), and the mass fractal dimension (D) of the crystal network was investigated. This last parameter was measured as TAG crystallized in the oil blend under isothermal conditions. Results showed that TAG crystallization in a vegetable oil involves the process of TAG lamellar development, nucleation, and crystal growth. Each event occurred at a different rate and extent as affected by cooling rate and T _Cr ^o, and as a function of crystallization time under isothemal conditions at a given cooling rate. Within this framework, we proposed that n calculated from the second region of the Avrami plot is a parameter mainly associated with crystal growth, whereas n from the first region is associated more with nucleation. On the other hand, changes in D values followed the different polymorphic states developed by TAG as a function of T _Cr ^o. Additionally, it was shown that, independent of the concentration of palm stearin in the oil blend, at cooling rates of 1 and 10°C/min the increase in n from ∼3 to ∼4 produced a curvilinear increase in D from ∼1.75 to ∼3.0. The growth mechanism of the TAG crystals (i.e., n), also affected the magnitude of D. However different behavior was observed in the n-D relationship when n<2.7 and at 30°C/min.     

Castor-oil-modified epoxy resins as model systems of rubber-modified thermosets. 2: Influence of cure conditions on morphologies generated

Phase separation during polymerization was studied in a model system consisting of a diepoxide based on the diglycidyl ether of bisphenol A (DGEBA), ethylenediamine (EDA) and variable amounts of castor oil (CO). Different events taking place during cure, i.e. phase separation, gelation and vitrification, are described in temperature versus time transformation diagrams (TTT), and conversion versus temperature phase diagrams. Thevconcentration (P) and average size (D?) of dispersed-phase particles followed opposite trends, i.e. one increased while the other decreased, when varying the castor oil concentration and the cure temperature. This is explained by assuming that the competition between nucleation and growth is determined by the viscosity at the cloud point, η_cp. Low values of η_cp favour growth over nucleation while the opposite is observed for conditions leading to high values of η_cp. The greater the conversion range between the cloud point and gelation, the broader the particle-size distribution.