Cold Press Methods Research Articles

Preparation and characterization of silica/carbon nanocomposites for a thermoelectric application

In this work, the silica/carbon nanocomposites are firstly fabricated by combining the cold-pressing methods and the sintering treatment, and then the thermal conductivity, the Seebeck coefficient and the electrical conductivity are experimentally studied. Results turn out that the thermal conductivity firstly decreases then rise with the increase of the sintering temperature, and there is an optimal sintering temperature for getting a low thermal conductivity. The decrease of the thermal conductivity is due to the enlarged porosity caused by a higher sintering temperature, while the rise arrives from the improved crystal degree of silica nanoparticles. Results also turn out that the Seebeck coefficient and the electrical conductivity of the silica/carbon nanocomposite are almost same to that of a common carbon material. This work is expected to supply some information for developing new thermoelectric nanocomposites.

Cucurbita maxima Pumpkin Seed Oil: from the Chemical Properties to the Different Extracting Techniques

Pumpkin seed oils are rich in bioactive compounds such as tocopherols, sterols, β-carotene, and lutein that have, along with some fatty acids, high nutritional value factors. In addition, it has so far been proven that these compounds have a positive effect on human health. The present study mainly aimed at evaluating the chemical composition and the bioactive compounds of pumpkin (Cucurbita maxima) seed oil of the ‘Béjaoui’ Tunisian cultivar using both cold pressing and solvent extraction methods. The seed oils contained substantial amounts of unsaturated fatty acids, particularly oleic and linoleic acids, with values ranging respectively from 28.19% for cold pressed pumpkin seed oil to 30.56% for pumpkin seed oil extracted by pentane and from 43.86% for pumpkin seed oil extracted by pentane to 46.67% for cold pressed pumpkin seed oil of the total amount of fatty acids. Investigations of different seed oils revealed that extraction techniques had significant effects on the antioxidant activity and the γ-tocopherol. Cold pressed pumpkin seed oil revealed the highest γ-tocopherol content (599.33 mg kg-1) and the highest oxidative stability (3.84 h). However, the chloroform/methanol extracted pumpkin seed oil, which is rich in total phenolics (54.41 mg Gallic Acid Equivalent kg-1), was a more effective scavenger of DPPH radicals (250 µmoles Trolox kg-1) than the poor phenolic pumpkin seed oils extracted by hexane and pentane (110 µmoles Trolox kg-1 vs 100 µmoles Trolox kg-1). Based on its unique seed oil features, cold press extracted pumpkin seed may add great value to product innovation in the industrial, nutritional, cosmetic, and pharmaceutical fields.

Effects of pomegranate seed oil and fermented juice polyphenols fraction in different solvents on copper-induced LDL oxidation

ABSTRACTEffects of pomegranate seed oils extracted with supercritical fluid or cold press methods (SFE-PSO and CP-PSO), unsaponifiable (N), and fermented juice polyphenols (W) fractions of pomegranate as well as olive oil and alpha-tocopherol, as pure or in different solvents were evaluated on preventing copper-induced LDL oxidation. The results showed addition of pure SFE-PSO, CP-PSO, N fractions, and olive oil had no significant effect on LDL oxidation. Also using various solvents did not help in the term of extending the oxidation lag phase. However, adding 0.5, 1, 1.5, and 3 µL of the W solution in EtOH could delay the lag phase 103.5, 145.9, 200, and 199.1 min, respectively. There was no synergistic effect between W and N on inhibiting the oxidation. It can be concluded that polyphenolic fraction of pomegranate juice can act as antiatherogenic supplementation and natural preservative for meat and fatty foods through direct inhibition of LDL oxidation.

Infiltration sintering of WCu alloys from copper-coated tungsten composite powders for superior mechanical properties and arc-ablation resistance

W70Cu30(W-30 wt.% Cu) alloys were fabricated using cold pressing and infiltration sintering methods from two types of powders, i.e., mixed copper-tungsten (M-Cu-W) powders and our newly developed copper-coated tungsten composite (Cu@W) powders. Microstructure, mechanical and arc-ablation properties of the W70Cu30 alloys were investigated, and the mechanism of enhanced physical/mechanical properties and arc-erosion resistance of the W70Cu30 alloys was discussed. For the W70Cu30 alloys prepared using the Cu@W powders, their physical properties, including hardness, electrical conductivity and relative density were much better than those prepared from the M-Cu-W powders. The W70Cu30 alloys fabricated from the Cu@W powders were free of cracks, and showed homogenous distributions of W and Cu network structures. Whereas for the alloys prepared from the M-Cu-W powders, segregation of Cu was observed and the segregation size was about 40–100 μm. Characterization of arc-erosion morphologies of the W70Cu30 alloys prepared with the Cu@W powders revealed the occurrence of evaporation of Cu phase; whereas that of W70Cu30 alloys prepared with the M-Cu-W powders revealed the occurrence of the sputtering of Cu. After arc breakdown for 200 times, mass loss of alloys made using the mixed powders was twice as much as those made using the coated composite powders. Based on the experimental results and theoretical analysis, an arc breakdown mechanism of the WCu-C alloys using the composite powders was proposed which is attributed to the formation of a homogeneous Cu-Cu network structure to uniformly disperse arc energy and dissipate the generated heat, thus prolonging the service life of the WCu alloy contacts.

Major role of process conditions in tuning the percolation behavior of polyvinylidene fluoride based polymer/metal composites

The percolation behaviour of a polymer/metal composite (PMC), comprising polyvinylidene fluoride (PVDF)/nanocrystalline nickel (n-Ni) prepared by cold press and hot press methods, has been compared. Higher effective dielectric constants (εeff) with lower loss tangent (Tan δ) were observed for the cold pressed samples as compared to the hot pressed samples, which is attributed to better homogeneity and uniform distribution of n-Ni in the PVDF matrix. The percolation parameters [percolation threshold (fc) and critical exponents (s and s′)] are largely tuned due to the difference in process conditions. The non-universal fc, s, and s′ have been explained with the help of the percolation theory. PMC prepared though cold pressing would be a better candidate for static and low frequency dielectric applications.

Effect of Extraction Method on the Oxidative Stability of Camelina Seed Oil Studied by Differential Scanning Calorimetry.

Camelina seed is a new alternative omega-3 source attracting growing interest. However, it is susceptible to oxidation due to its high omega-3 content. The objective of this study was to improve the oxidative stability of the camelina seed oil at the extraction stage in order to eliminate or minimize the use of additive antioxidants. Camelina seed oil extracts were enriched in terms of natural antioxidants using ethanol-modified supercritical carbon dioxide (SC-CO2 ) extraction. Oxidative stability of the camelina seed oils extracted by ethanol modified SC-CO2 was studied by differential scanning calorimeter (DSC), and compared with cold press, hexane, and SC-CO2 methods. Nonisothermal oxidation kinetics of the oils obtained by different extraction methods were studied by DSC at varying heating rates (2.5, 5, 10, and 15 °C/min). Increasing ethanol level in the ethanol-modified SC-CO2 increased the oxidative stability. Based on oxidation onset temperatures (Ton ), SC-CO2 containing 10% ethanol yielded the most stable oil. Oxidative stability depended on the type and content of the polar fractions, namely, phenolic compounds and phospholipids. Phenolic compounds acted as natural antioxidants, whereas increased phospholipid contents decreased the stability. Study has shown that the oxidative stability of the oils can be improved at the extraction stage and this may eliminate the need for additive antioxidants.

Impact of Extraction Methods on Antioxidant and Antimicrobial Activities of Citrus Essential Oils

In this study, impact of extraction methods, cold-pressing and vacuum-distillation methods, on yield, chemical composition, antioxidant and antimicrobial activities of citrus essential oils were investigated. The antioxidant activities of citrus essential oils were determined by DPPH scavenging and Ferric thiocyanate assays, while the antimicrobial activities were determined by growth inhibition zone diameter and broth dilution assays against several important foodborne pathogens. The yields of essential oils of Dao lime, PhuTho orange and DoanHung pomelo, extracted by the vacuum-distillation method, were 0.16 %, 0.59 % and 0.04 %, respectively, significantly higher than those extracted by the cold-pressing methods (0.03 %, 0.25 % and 0.03 %, respectively). Total relative concentrations of nine major components of the essential oils extracted by the cold-pressing and vacuum-distillation methods were not significantly different. However, concentration of individual component in the essential oils was changed when using the vacuum-distillation method. Although the essential oils extracted by both cold-pressing and vacuum-distillation methods showed strong antioxidant and inhibition capacities, the antioxidant and antimicrobial activities of citrus essential oils extracted by the vacuum-distillation method were lower than those extracted by the cold-pressing method. As a result, the vacuum-distillation is considered to be the promising innovation theme for producing natural fragrance and essential oil with high production efficiency.

Extraction of omega-3-rich oil from Camelina sativa seed using supercritical carbon dioxide

Camelina sativa seed is an underutilized oil source; however, it is a potential source of omega-3-rich oil. Supercritical carbon dioxide (SC-CO2) is a desired green solvent for the extraction of omega-3 oils; however, there is no reported study on the SC-CO2 extraction of Camelina seed oil. Therefore, the objective of this study was to evaluate the use of SC-CO2 for the extraction of Camelina seed oil and to compare with traditional extraction methods. Response surface methodology (RSM) based on central composite rotatable design was employed to investigate the extraction conditions: pressure (35–45MPa), temperature (50–70°C), and time (90–250min). A second order polynomial model was developed to predict the oil yield. Increasing pressure and time increased the oil yield, whereas increasing temperature did not have a significant effect. RSM-optimized conditions (45MPa, 70°C and 224.5min) obtained by RSM for the range of variables predicted a yield of 27.0% oil, whereas the actual yield was 25.1±2.0%. Oil yield was further increased to 31.6% at the RSM-optimized conditions by increasing the SC-CO2 extraction time to 510min. Soxhlet (hexane) and cold press methods yielded 35.9% and 29.9% oil, respectively. Extraction method did not have a significant effect on the fatty acid composition and tocopherol content (P>0.05); however, phytosterol content of the cold pressed oil was significantly lower than that of SC-CO2 and Soxhlet (hexane) (P<0.05). Results indicated that SC-CO2 is a promising green solvent for the extraction of Camelina seed oil.

Comparison of lemon oil composition after using different extraction methods

Kıbrıs lemon (Citrus limon (L.) Burm. f.) peel was extracted by supercritical CO2 extraction (SFE), cold pressing (CP) and hydrodistillation (HD) methods. SFE, CP and HD methods have been compared and evaluated for their effectiveness in the separation of extract from fresh lemon peels. The chemical compositions of the three different extract samples were analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). Forty-four components were fully characterized by mass spectra and linear retention indices. The lemon extracts showed a high content of limonene (71.81%, 70.36% and 72.48%) with γ-terpinene (8.72%, 8.91% and 8.88%), β-pinene (6.61%, 6.72% and 6.60%), myrcene (1.55%, 1.59% and 1.73%), sabinene (1.21%, 1.48% and 1.09%), α-pinene (0.98%, 1.27% and 0.98%) and p-cimene (0.87%, 1.23% and 0.87%) being the major monoterpene hydrocarbons in the SFE, CP and HD methods, respectively. The principal sesquiterpene hydrocarbon was β-bisabolene (1.42%, 1.41% and 1.22%) in the SFE, CP and HD extracts, respectively. Neryl acetate and geranial were the main oxygenated compounds (1.25%, 1.28% and 1.21%) and (1.13%, 0.97% and 0.99%), in the SFE, CP and HD extracts, respectively. The composition of lemon extract has been split into six classes (monoterpene hydrocarbons, sesquiterpene hydrocarbons, carbonyl compounds, alcohols, esters and oxides). It was noted that there were significant differences in the carbonyl compounds, alcohol and ester classes in the SFE, CP and HD extracts.

Application of HS-SPME, SDME and Cold-Press Coupled to GC/MS to Analysis the Essential Oils of Citrus sinensis CV. Thomson Navel and QSRR Study for Prediction of Retention Indices by Stepwise and Genetic Algorithm-Multiple Linear Regression Approaches

Volatile fractions in the essential oils (EOs) obtained from the peels of Citrus sinensis CV. Thomson Navel by head-space solid phase micro-extraction (HS-SPME), single drop micro-extraction (SDME) and cold-press (CP) techniques were analyzed by means of gas chromatography-mass spectrometry (GC-MS). Fifteen, nine and fourteen compounds were identified by HS-SPME, SDME and CP methods, respectively representing 99.75 %, 99.45 % and 98.5 % of the chemical profiles in the peels of C. sinensis. The main components were found to be limonene (72.69 %, 71.96 %, 90.40 %), myrcene (9.65 %, 9.80 %, 1.10 %), sabinene (2.63 %, 9.35 %, 0.90 %) and α-pinene (2.00 %, 7.05 %, 1.60 %) by HS-SPME, SDME and CP, respectively. In addition, a quantitative structure-retention relationship (QSRR) study has been developed for prediction of retention indices (RIs) of the occurred natural compounds. The suitable set of molecular descriptors was calculated and the important descriptors were selected by stepwise (SW) and genetic algorithm (GA) variable selection features combined with multiple linear regression (MLR). A comparison between the attained results indicated the superiority of the genetic algorithm over the stepwise in the feature-selection step. The predictive quality of the QSRR models was tested for an external set of five compounds, randomly chosen out of 27 compounds. The genetic algorithm-multiple linear regression model (GA-MLR) with two selected descriptors gave rise in the best predicted results. The accuracy of the proposed GA-MLR model is illustrated using cross-validation, validation through an external test set and Y-randomization evaluation techniques.

Residual Tensile Stress of Kenaf Polyester and Kenaf Hybrid under Post Impact and Open Hole Tensile

Abstract Natural fibres have emerged as the potential reinforcement material for composites and have thus gained an attraction by many researchers. This is mainly due to their applicable benefits as they are light weight and offer low cost compared to synthetic fibre composites. Kenaf fibres recently have been a substitute material in many weight-critical applications in areas such as aerospace, automotive and other high demanding industrial sectors. In this study, natural fibre kenaf composites and kenaf/fibreglass hybrid composites were fabricated by a combination of hand lay-up and cold-press methods. The post impact tensile and open hole tensile of long kenaf fibre composites with and without the addition of fibreglass were further studied. The fracture behaviour verified qualitatively via scanning electron microscopy. A significant improvement in tensile strength and modulus were indicated by the introduction of long kenaf/woven fibreglass hybrid composite. Investigation on the tensile and low velocity impact of kenaf composites and kenaf/fibreglass reinforced polyester resin composites revealed that the composites were seriously impaired when a low energy impact was applied. The tensile strength of open hole long kenaf composites was more notch sensitive than long kenaf/woven glass hybrid composite. Although the hybrid composite was stronger than pure kenaf composites, the damage progression mechanisms in the two materials were very similar. In the above case the polymer matrix failed initially. It is followed by fibre matrix debonding and finally ending in fibre ruptures or pull-outs.

Numerical Simulation of NbTi Superconducting Joint With Cold-Pressing Welding Technology

The cold-pressing welding methods are employed to fabricate joints between NbTi multifilamentary conductors, and a series of joints are made at different press amounts for nuclear magnetic resonance magnet applications. The Abaqus-Explicit method was used to do a quasi-static analysis of the cold-pressing welding process. In the simulation, we consider the contact area and equivalent plastic strain to determine the resistance of the superconducting joints qualitatively. The simulation shows that a press amount of 61%-65.5% should be the optimum range, in which the lowest joint resistance can be obtained. Resistances of these joints are also tested using the current decay method to verify the simulation.

Comparison of Essential Oils Compositions of Citrus maxima Merr. Peel Obtained by Cold Press and Vacuum Stream Distillation Methods and of Its Peel and Flower Extract Obtained by Supercritical Carbon Dioxide Extraction Method and Their Antimicrobial Activity

The oils and extracts of the fruit peels of pomelo (Citrus maxima Merr. cultivar ‘khao-yai’) were obtained by cold-pressing (CP), vacuum steam distillation (VSD) and supercritical carbon dioxide extraction (SC-CO2) and the extract of the flowers was obtained by SC-CO2. The composition of the oils and extracts of the peel and flower were determined by GC and GC/MS. Fifty, 53 and 60 components of the oils and extract from peels by CP, VD and SC-CO2 were identified, respectively. Their main components were limonene (93.4–95.4%). Fifty-one components of the flower extract were identified and the main component was also limonene (86.2–86.8%). The oils and extract of pomelo showed fairly good activity against Staphylococcus aureus and Candida albicans.

Physicochemical Properties of Garden Cress (Lepidium sativum L.) Seed Oil

AbstractGarden cress (Lepidium sativum L.) is an edible, underutilised herb, grown mainly for its seeds in India. Physicochemical properties, minor components (unsaponifiable matter, tocopherols, carotenoids), fatty acid composition and storage stability of garden cress seed oil (GCO) were studied. Cold press, solvent and supercritical CO2 extraction methods were employed to extract the oil. The total oil content of garden cress (GC) seeds was 21.54, 18.15 and 12.60% respectively by solvent, supercritical CO2 and cold press methods. The physical properties of GCO extracted by the above methods were similar in terms of refractive index, specific gravity and viscosity. However, cold pressed oil showed low PV and FFA compared to the oil extracted by other methods. α‐Linolenic acid (34%) was the major fatty acid in GCO followed by oleic (22%), linoleic (11.8%), eicosanoic (12%), palmitic (10.1%) erucic (4.4%), arachidic (3.4%) and stearic acids (2.9%). Oleic acid (39.9%) and α‐linolenic acid (42.1%) were the predominant fatty acids at the sn‐2 position. The total tocopherol and carotenoid content of GCO was 327.42 and 1.0 μmol/100 g oil, respectively. The oil was stable up to 4 months at 4 °C. Tocopherol and BHT offered the least protection, while ascorbyl palmitate (200 ppm) offered the maximum protection to the oil, when subjected to the accelerated oxidative stability test. Thus GCO can be considered as a fairly stable oil with a high content of α‐linolenic acid.

Comparison of Juice Extraction Methods from Fresh and Frozen Mayhaw (Crataegus opacaHook.) Fruit

ABSTRACT The highest juice yields were obtained from a combined interaction of temperature, maceration, application of pectolytic enzyme, and previously frozen fruit. Freezing mayhaw fruit prior to juice extraction increased juice yield regardless of the method used in extraction. The average juice yield obtained from previously frozen fruit was 157% higher than when using fresh fruit. Maceration of fruit plus the application of heat to the fruit pulp prior to juice expression had a significant influence in juice extraction efficacy for both fresh and frozen fruit. When heat was applied to fruit pulp prior to expression, juice yields increased from 31.4% for cold press extraction and 63.5% for hot press extraction. Application of a pectolytic enzyme to preheated fruit pulp increased total soluble solids (TSS) in extracted juice by 15% when utilizing frozen fruit compared to hot-press extraction without enzymes yield of 6.6%. There was no significant difference in TSS recovered by either fresh or frozen cold press methods without enzymes. All steam extraction methods utilizing fresh fruit had a lower percent recovery of total acid (TA) than when a pectolytic enzyme was added to fresh fruit before extraction. There were no significant differences in juice pH regardless of whether fresh or frozen fruit were used. Recovery of both TSS and fructose was significantly increased when pectolytic enzyme was added to fresh fruit. The lowest recovery of fructose was from steam extraction for both fresh and frozen.

Electrical properties and longitudinal modulus of superconductor/polymer NdBa2Cu3O7−δ/PVC composites

High temperature superconductor NdBa2Cu3O7−δ/poly(vinyl chloride) (Nd123/PVC) composites have been prepared by cold press and hot press methods. Addition of PVC resulted in increase of the electrical resistivity with percolation occurring between 0.3 and 0.5 Nd123 volume fraction for both preparation methods. Although the samples showed some form of magnetic levitation at liquid nitrogen temperature, they do not show any zero-resistance temperature indicating the lack of effective superconducting percolative path. The density deviates from the linear calculated value with increasing Nd123 content at 0.3 volume fraction for the cold press and at 0.6 for the hot pressed samples due to increasing porosity. X-ray powder diffraction patterns suggest that the Nd123 crystals tend to align when the composites are prepared by hot press method. A resistance anomaly is observed at 90 K in the hot press composites indicating improved electrical contact between the aligned Nd123 grains. The longitudinal modulus increases as Nd123 content is increased.