Microwave Heating Time Research Articles

Experimental Study on Fe3O4 Nanoparticle-Assisted Microwave Enhancing Heavy Oil

Nanoparticle-assisted microwave heating of heavy oil has the advantages of fast temperature rise and high thermal efficiency. Compared with traditional heating methods, it can reduce viscosity in a shorter time. In addition, the heavy components in the heavy oil are cracked into light components at high temperatures (this high temperature cannot be reached by conventional heating methods). This process is irreversible and avoids the problem of viscosity recovery of heavy oil after the temperature is reduced. Through absorbing microwave heating experiments, study the effect of nanoparticles on the improvement of the ability of heavy oil to absorb waves and raise temperature; through the heavy oil upgrading experiment and the four-component analysis experiment, the effect of adding hydrogen donor to assist microwave on the viscosity reduction of heavy oil upgrading by nanoparticles was studied, and the problem of viscosity recovery was determined; Through the gravity drainage experiment, the mechanism of nanoparticle-assisted microwave to improve the recovery of heavy oil is studied, and the influence of water content, nanocatalyst, and microwave power on the production of drainage is analyzed. The results show that nanoparticles can improve the wave absorption and heating capacity of heavy oil, and adding 0.6 wt% of nanomagnetic iron oxide catalyst can increase the heating rate of heavy oil in microwave by 60.6%; nanoparticle-assisted microwave heating method can effectively upgrade heavy oil and reduce viscosity. The experimental conditions are 2 wt% tetralin mass concentration, 0.5 wt% nano-Fe3O4 particle mass concentration, microwave heating time 50-60 min, and microwave power 539 W. Under this experimental condition, the viscosity is reduced by 40%. This method has viscosity recovery problems, but final viscosity reduction effect is still very significant. Obtaining the mechanism of nanoparticle-assisted microwave to enhance oil recovery, one of which is that nanoparticles improve the wave absorption and heating capacity of heavy oil and increase the heating speed of heavy oil; the second is that the nanoparticles form local high temperature under the action of microwave, which catalyzes the hydrocracking reaction between the heavy components in the heavy oil and the hydrogen donor, upgrading and reducing the viscosity of the heavy oil, and accelerating the production of heavy oil.

Hybrid composite materials generated via growth of carbon nanotubes in expanded graphite pores using a microwave technique

Herein we demonstrate a facile in-situ synthesis method by selection of expanded graphite as a matrix growth microreactor, nickel nitrate (Ni(NO3)2) as a growth catalyst and naphthalene as a carbon source, assisted by a conventional household microwave oven. Affection parameters related to control of the growth process, such as the microwave heating time, catalyst concentration and carbon source concentration. The optimized experimental conditions that exhibit excellent microstructure were: a carbon source concentration of 20.0 mg/ml, a catalyst concentration of 10.0 mg/ml and a microwave reaction time of 30 s. The microstructure of the synthesized composites was investigated and a solid-gas growth mechanism with this carbon source precursor is proposed. The micro morphology, formed CNT structure and resistivity of the composites are fully characterized and analyzed by thermal field emission high-resolution scanning electron microscopy (FESEM), confocal laser Raman spectrometer (Raman) and a four-point probe resistivity meter. All characterization data show a uniform CNT diameter distribution of approximately 30.0 nm with a low resistivity of the composites (1.12 × 10−5 Ω·m), indicating uniform hybrid composite material formation with novel physical properties.

EFFECTS OF MICROWAVE ROASTING TIME ON PHYSICO-CHEMICAL PROPERTIES AND SENSORY EVALUATION OF GERMINATED RED BROWN RICE MILK

The study was aimed to investigate the effects of different microwave heating times (1, 2, and 3 min at output microwave of 800 W) in comparison with the traditional heating (3 min, 110oC) on some physico-chemical properties and sensory evaluation. The consumer survey for the final product use was also conducted to determine whether there is a significant difference in general liking of the product with gender. The results indicated that the product with the shorter microwave heating time contained higher protein and reducing sugar compared to traditional heating. The microwave heating time significantly affected the viscosity of milk, whereas insignificantly influenced color, pH, and TSS values of milk. Among samples, microwave roasted at 3 min provided the comparable total acceptance score in sensory evaluation of the traditional heating. The milk contains protein (0.18g/100ml), total lipid (0.87g/100ml), and carbohydrate (7.56g/100ml). No significant association between gender and opinion was found expressing the liking of the product in which there were 61.35% females and 45.58% males liking the product. This study revealed that microwave heating could be used for roasting step to replace the traditional roasting in terms of product quality and nutrient retention. The study also provided a basic formula of the main components of the rice milk and demonstrated that the using the germinated red-brown rice to produce the rice milk could provide the product, ensuring all main compositions of rice such as protein, lipid, and carbohydrate.

Thermal stresses and temperature distribution of granite under microwave treatment

Efficient breakage of high strength rocks is a challenging task where conventional drilling and blasting methods are not preferred or allowed, for example, rock excavation in long tunnels at a great depth and urban environment sensitive to noise and vibration. Microwave treatment is an efficient and environmentally friendly method, which is considered to be one of the most promising ways to increase the performance of mechanical excavators, such as roadheaders and impact hammers. However, the mechanisms of microwave fracturing of granitic rocks have not been well investigated. In this study, Chinese granite was used as the research material. Its mineral composition and grain size were first characterized using petrographic thin section observation. Cubic granite samples were then heated in a single-mode industrial microwave. The temperature was captured using a high resolution infrared thermal camera. Then a realistic 3-D rock model with the same mineralogical properties was established using Voronoi tessellation. The multi-physics numerical model was calibrated using data from microwave heating tests. The effect of microwave power intensity, heating time, and mineral grain size on the temporal and spatial temperature distribution, and thermal stresses in the granite matrix was investigated in a comprehensive manner. The temperature gradients and thermal stresses were calculated. The maximum temperature gradient and the maximum tensile stress appeared at the interface between quartz and biotite. As either power level or heating time increased, the thermal gradient and the maximum tensile stress increased, and with same microwave energy output, greater temperature gradient and thermal stress could be generated during microwave heating at higher power levels for shorter durations. Moreover, the greater the grain size, the bigger the maximum tensile stress. The finding of the paper contributes the understanding of the mechanisms of microwave fracturing of rocks.

Effect and Mechanism of Microwave Heating on the Functional Properties of Whey Protein Isolate

In this study, maillard reaction was used to modify whey protein isolate (WPI) with microwave assistance. The effects of microwave power, microwave heating time, pH, and mass ratio of lactose to whey powder on the functional properties of whey protein maillard reaction products (WPI-MRPs) were systematically investigated by using emulsification and antioxidant activity as the main indexes. The process was optimized, the secondary structure and amino acid composition during microwave treatment were also analyzed in details. The optimized microwave heating conditions are as follows: pH8.5, whey protein-lactose mass ratio 5:5, microwave heating time 7 min. The emulsification activity index, emulsifying stability index and DPPH free radical scavenging rate of the obtained MRPs was 0.35 m2/g, 88.39 min and 6.60%, respectively. The infrared spectroscopy data indicated that microwave heating could promote the maillard reaction process, during the process increases in the contents of hydroxyl and carbonyl groups were observed, and complex maillard intermediates and aldehydes and ketones were produced. Meanwhile, transformation of the protein secondary structure from a compact to a loose “swelling” structure could be also promoted. During the transformation, most of the tightly ordered structure firstly transforms into a loosely ordered structure, and then into a loosely disordered state, accompanied by a small part of the tight ordered structure changed to each other after a long time heating. In addition, amino acid analysis further confirmed that the reaction would result in a decrease in total amino acids content due to participation of free amino acids in WPI during maillard reaction.

Degradation of aflatoxin B1 by water-assisted microwave irradiation: Kinetics, products, and pathways

The effect of aflatoxin B1 (AFB1) degradation by water-assisted microwave irradiation (WMI) and the identification of the degradation products of AFB1 are key issues in the feasibility study of WMI detoxification. In this study, WMI was applied to degrade pure AFB1 in aqueous medium, and the kinetics, products, and pathways of the degradation of AFB1 were studied. The results showed that AFB1 could be effectively degraded by WMI, and the degradation process followed pseudo-first-order reaction kinetics. In addition, six new main degradation products were identified by ultra-high-performance liquid chromatography Q-Orbitrap mass spectrometry, and a possible degradation pathway was proposed. Furthermore, the variety and quantity of AFB1 degradation products and the degradation pathway of AFB1 were affected by microwave heating temperature, time, and power. After WMI treatment, the double bond in the terminal furan ring or the lactone bond of AFB1 was destroyed, which implied that the toxicity of the degradation product was significantly reduced. Therefore, WMI is deemed to be an effective method to degrade AFB1.

Selective Leaching Trace Elements from Bauxite Residue (Red Mud) without and with Adding Solid NH4Cl Using Microwave Heating

Bauxite residue (red mud), which is an industrial byproduct, contains valuable trace elements. Solid NH4Cl was used as a chlorinating agent during the microwave heating of red mud to convert trace elements into soluble metal chloride. Red mud was heated using microwave ovens under various conditions (i.e., with the addition of solid NH4Cl and with a range of microwave output powers and microwave heating times). Leaching tests were then conducted using deionized (DI) water on the microwave-heated red mud to leach trace elements from red mud. V, Cr, and As were selectively leached from the microwave heated red mud slurry (30% water content), whereas Mn, Cu, Co, Ni, Zn, and Pb were selectively leached from the microwave-heated red mud with the addition of solid NH4Cl. The oxides of V, Cr, and As in red mud could be transformed into metal chlorides by chlorination, which are insoluble in water, or could be easily volatilized when red mud was microwave-heated in the presence of solid NH4Cl. On the other hand, the oxides of Mn, Cu, Co, Zn, Ni, and Pb in red mud could be heated rapidly by microwave irradiating, resulting in metal chlorides in the presence of solid NH4Cl. Those metal chlorides are relatively soluble in water, leading to higher leaching efficiency for microwave-heated red mud with the addition of solid NH4Cl. Experimental results suggest that trace elements from red mud can be selectively leached by microwave heating of red mud without or with the addition of solid NH4Cl.

Kinetic study of the microwave‐induced thermal degradation of cv. Arbequina olive oils flavored with lemon verbena essential oil

AbstractThe effect of typical domestic microwave heating (0–15 min, at 800 W) on the thermal degradation of unflavored and flavored olive oils' minor bioactive compounds and related antioxidant activity was studied. Olive oils from cv. Arbequina were flavored with lemon verbena essential oil (0%, 0.2% and 0.4%, w/w) leading to a linear increase of total phenols (112–160 mg gallic acid kg−1 oil, R‐Pearson = +0.9870), total carotenoids (2.19–2.56 mg lutein kg−1 oil, R‐Pearson = +0.9611), and, to a less extent, of chlorophyll (2.32–3.19 mg pheophytin kg−1 oil, R‐Pearson = +0.8238). However, no such linear trend was observed for the oxidative stability (6.5–7.8 h) or the radical scavenging activity (inhibition rates: 40%–43%). The contents of total phenols, total carotenoids, and chlorophyll decreased with the rise of the microwave heating time, following their thermal degradation, a second‐order kinetic model (0.8784 ≤ R‐Pearson ≤ 0.9926). The essential oil addition did not influence the estimated second‐order rate reaction constants of total phenols (0.00070–0.00072 kg oil min−1 mg−1 gallic acid)and total carotenoids (0.14–0.17 kg oil min−1 mg−1 lutein), with a broader variation observed for chlorophyll (0.014–0.022 kg oil min−1 mg−1 pheophytin). Globally, total carotenoids degraded faster than total phenols and chlorophyll (half‐life of 2.3–3.4, 8.8–12.8, and 14.5–30.8 min, respectively). Moreover, except for chlorophyll, the half‐life of total phenols and carotenoids linearly decreased with the essential oil addition (R‐Pearson: −0.9999 and −0.9421, respectively), showing that flavoring did not have a protective effect against degradation when subjected to a microwave heating.

Production of nutty-like flavour from soybean protein isolate hydrolysate pretreated or assisted by microwave irradiation: impact of encapsulation on nutty flavour quality.

The aim of this study was to prepare a nutty-like flavour from enzymatic hydrolysates of soybean protein isolate pretreated or assisted by microwave heating. In both cases the time of microwave heating was optimized and degree of hydrolysis (DH) and content of free amino acids in each hydrolysate were determined and compared with those of hydrolysate prepared by conventional method (E-HSC). The hydrolysates showed the best results were used as main precursors of nutty flavour. The generated volatiles were subjected to GC-MS analysis and odour evaluation. The effect of encapsulation and storage on the nutty flavour was evaluated. The results revealed that the hydrolysates pretreated (E-HSMP7) or assisted (E-HSMA6) by microwave at 7 and 6min, respectively showed a significant increase in DH. The nutty flavour generated from these hydrolysates (NFMP7 and NFMA6) were dominated with pyrazines whereas, the volatiles from E-HSC (NFC) dominated with furans. NFMA6 showed the highest intensity of nutty and overall acceptability notes, compared with NFMP7 and NFC. Encapsulation resulted in a significant decrease in pyrazines, which are responsible for the nutty note. The significant increase in nutty aroma intensity of the stored encapsulated sample was correlated to the increase in pyrazines.

Impregnation of Microwave treated exfoliated MoS2 nanosheets into PMMA matrix by solution casting for reinforcing applications

In the present work, poly methyl methacrylate (PMMA)-MoS2 nanocomposite films were prepared by impregnation of exfoliated MoS2 nanosheets into PMMA matrix by solution casting method. Synthesis of exfoliated MoS2 nanosheets through microwave irradiation techniques was found to be simple, less time consuming, eco-friendly and cost effective. We have identified the optimization conditions by varying the parameters like microwave heating time, power and concentration of bulk MoS2. The structural and optical properties of the exfoliated MoS2 nanosheets were investigated. These optimized exfoliated MoS2 nanosheets were introduced into the polymer matrix which was then subjected to different characterization techniques. The effect of exfoliated MoS2 nanosheets on the mechanical properties of the polymer-MoS2 composite was evaluated in detail.

Preparation of Graphene Oxide from Expanded Graphite at Different Microwave Heating Times

Exfoliated graphite (EG) was prepared by mixing graphite with HNO3 and KMnO4 at weight ratio 1:2:1 using microwave heating at times 20, 60, 80 and 120 sec. Graphene oxide (GO) was then prepared using EG as precursor by the modified Hummer’s method. Atomic force microscopy (AFM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy analyses showed successful conversion of EG into GO. The XRD results of the GO showed that the maximum interplanar distance (d-spacing) increased from 0.344 to 0.831 nm. The AFM showed a minimum thickness of 0.519 nm for a single layer of GO prepared from EG 80 sec. The XRD examination also showed an increase in the d-spacing between the GO layers after sonication compared to before sonication.

Microwave stabilization and process optimization of rice bran cultivar Jhelum

This study was optimizing microwave stabilization process of rice bran obtained from freshly milled paddy (Jhelum variety) using response surface methodology. This study was conducted at different moisture contents (12%–30%), sample weight (5–250 g), and heating time (1–5 min) which were examined to determine their influence on dependent variables––free fatty acids (FFAs) and color coordinates. Regression analysis showed effective influence of microwave heating on all response variables studied. Stabilization treatments resulted in reduction of FFAs, prime indicator of lipase activity, indicating that hydrolytic rancidity could be prevented thereby making it fit for human consumption and food applications. The optimum conditions obtained for microwave stabilization were found to be 16% sample moisture, 100 g sample weight, and 4 min microwave heating time. Proximate analysis showed that crude fat and crude fiber contents reduced while crude protein and ash contents increased after microwave heat treatment in rice bran. Practical applications Rice bran has the ability to be used as a food ingredient and oil source to satisfy the growing oil demands. However, the individual cells are disturbed and the inherent lipase enzyme comes into contact with fat during milling process while extracting bran layer from endosperm. This causes hydrolysis of fats to free fatty acids (FFAs) and glycerol leading to the development of hydrolytic rancidity which is responsible for off-flavor development during storage. The rate of oil degradation and FFA formation can be very high (about 5%–7% per day and 70% in a month) under favorable conditions. Bran oil with an excess of 10% FFA is unfit for human consumption. Now-a-days efforts are being made to stabilize the rice bran using stabilization techniques in order to improve its utilization in food. The microwave stabilization technique seems to be a wiser approach to widen the utilization of rice bran in food industry.

Effect of microwave radiation on the magnetic properties of ludwigite and iron-boron separation

To effectively separate and recover the valuable elements iron and boron from ludwigite, this study investigated the magnetic properties and the magnetic separation efficiency. And the reactivity of boron component in the B-bearing tailing was studied. The results indicated that the saturation magnetization of ore samples was increased with the increase of microwave power and heating time. Under condition of 40 s with 4 kW, the saturation magnetization of ore samples increased from 12.73 emu/g for the raw ore to 24.70 emu/g for the treated ore, an increased of 94.03%. After magnetic separation, the grade and recovery rate of iron in the iron concentrate and the boron grade in the tailing for the treated sample with 4 kW for 40 s were increased by 19.74%, 31.46% and 86.46% in comparison with those of the untreated ore. The sample was heated to 600 °C at 4 kW and held for 20 min, the reactivity of boron component in the B-bearing tailing reached 86.68 wt%, which increased by 34.01% compared with that of the raw ore and 4.43% compared with that of the optimal traditional roasting value at 700 °C for 2 h, indicating that the roasting temperature and time were obviously decreased and the reactivity was significantly improved by the microwave radiation.

Efficient production of lignin-based slow-release nitrogen fertilizer via microwave heating

Microwave heating was first introduced into the Mannich reaction to prepare lignin-based organic slow-release nitrogen fertilizers. The response surface method was applied to acquire optimal conditions (amount of ethylenediamine, microwave heating temperature and time) for lignin with high organic nitrogen content. FT-IR spectra result revealed that the organic nitrogen was successfully grafted into the macromolecular structure of lignin. Elemental analysis showed that the organic nitrogen content increased (4.11–7.26 %) in lignin with the ethylenediamine content (4.0–8.0 g) or temperature (60–80 °C) or time (10–40 min) of microwave heating increased. By response surface analysis, the highest organic nitrogen content (7.84 %) was obtained under the condition (8.0 g ethylenediamine, 80 °C, 40 min). Contact angle, scanning electron microscopy, particle size, zeta potential, and thermal analysis results showed that lignin-based nitrogen fertilizers exhibited good slow-release properties of nitrogen. In short, lignin could be efficiently converted into organic slow-release nitrogen fertilizers by microwave heating. The approach with short processing time and simple operation was a potential method for preparing lignin-based fertilizer. The experiment will help to promote the value-added application of TL in the agricultural field.

Graphene Nanosphere as Advanced Electrode Material to Promote High Performance Symmetrical Supercapacitor.

To get carbon electrode with both excellent gravimetric and volumetric capacitances at high mass loadings is critical to supercapacitors. Herein, cracked defective graphene nanospheres (GNS) well meet above requirements. The morphology and structure of the GNS are controlled by polystyrene sphere template/glucose ratio, microwave heating time, and Fe content. The typical GNS with specific surface area of 2794 m2 g-1 , pore volume of 1.48 cm3 g-1 , and packing density of 0.74g cm-3 performs high gravimetric and volumetric capacitances of 529 F g-1 and 392 F cm-3 at 1A g-1 with a capacitance retention of 62.5% at 100 A g-1 in a three-electrode system in 6mol L-1 KOH aqueous electrolyte. In a two-electrode system, the GNS possesses energy density of 18.6Wh kg-1 (13.8Wh L-1 ) at the power density of 504 W kg-1 , which is higher than all reported pure carbon materials in gravimetric energy density and higher than all reported heteroatom-doped carbon materials in volumetric energy density, in aqueous solution, as far as it is known. A structural feature of carbon materials that possess both high energy density and high power density is pointed out here.

The Prospect of Microwave Heating: Towards a Faster and Deeper Crack Healing in Asphalt Pavement

Microwave heating has been shown to be an effective method of heating asphalt concrete and in turn healing the damage. As such, microwave heating holds great potential in rapid (1–3 min) and effective damage healing, resulting in improvement in the service life, safety, and sustainability of asphalt pavement. This study focused on the microwave healing effect on porous asphalt concrete. Steel wool fibres were incorporated into porous asphalt to improve the microwave heating efficiency, and the optimum microwave heating time was determined. Afterwards, the microwave healing efficiency was evaluated using a semi–circular bending and healing programme. The results show that the microwave healing effect is largely determined by the steel fibre content and the mix design of the porous asphalt concrete.. Besides, the uneven heating effect of microwave contributes to an unstable damage recovery in the asphalt mixture, which makes it less efficient than induction heating. However, microwaves exhibited the ability to penetrate further into the depth of the test specimen and heat beneath the surface, indicating deeper damage recovery prospects.

POLYETHYLENE TEREPHTHALATE BASED ACTIVATED CARBON PRODUCTION: PRELIMINARY STUDY ON KOH ACTIVATION WITH MICROWAVE ASSIST

Since the beginning of the plastic age, drinking-bottle waste has been increasing worldwide. Petroleum plastic waste is composed mainly of Polyethyleneterephthalate (PET), which is remained in the environment for a long period, thereby causing significant harm to humans, flora, and fauna. Waste recycling is one of the promising mitigation strategies, being used to reduce the amount of final disposal. This research, a preliminary investigation of activated carbon production conditions from PET bottle waste, was carried out using Fractional Factorial Design (FFD) with 95% confidence level. Starter material PET waste was obtained from a local recycling factory. Crusted and sieved PET was carbonized at 700oC for 1 hr. (called PET-char), then impregnated with potassium hydroxide (KOH) at a designed ratio and heated in a microwave. The production factors included PET-char:KOH ratio (1 and 3 by weight), microwave power (540 and 900 watts), and microwave heating time (10 and 30 mins). It was found that all production factors were significant contributors to the characteristics of PET-based activated carbon (PET-AC). The highest iodine adsorption capacity was found at the condition of 3 by weight, 900 Watts, and 30 mins for ratio, microwave power, and heating time, respectively. PET-AC shown highest iodine adsorption capacity with 1,125.34 mg/g andBrunauer Emmett Teller (BET) surface area with 1,345 m2/g. It was confirmed that PET bottle-based waste can be converted to a highly valuable nanoporous adsorbent.

Microwave intermittent drying characteristics of camellia oleifera seeds

AbstractThis paper reports on an experimental investigation of the drying characteristics and kinetics of camellia oleifera seeds under microwave intermittent drying conditions. The effects of key parameters such as microwave power, heating time, and the length of the intermittent time are discussed in detail. The energy consumption in the drying process along with the main quality parameters of camellia oil, namely the peroxide and acid values, have also been determined and compared with hot‐air drying. Results show that the microwave drying curve consists of an acceleration rate period, a constant rate period and a falling rate period. As the microwave power and heating time increase, the drying time decreases. While as the length of the intermittent time increases, the drying time increases. The hot‐air drying time was found to be much longer than microwave drying time, and the energy consumed during hot‐air drying was also several hundred times higher than that used during microwave intermittent drying. The acid and peroxide values of camellia oil after hot‐air and microwave drying were both within the allowable range in the National Standard of China. The Midilli and Kucuk model was the best model to describe the kinetics of the drying process.Practical applicationsDrying is the first step in the processing of camellia oleifera seeds, which not only affects the storage of camellia oleifera seeds, but also affects the quality of camellia oil, and has thus become a research hotspot in recent years. However, several disadvantages of hot‐air drying have been identified like the slowness of the drying process and the relatively large energy consumption. Therefore, finding a drying method that is more suitable is necessary. Microwave intermittent drying is a type of discontinuous drying. The moisture and temperature inside the material can be evenly redistributed during the intermittent time, so that the material is not overheated. This feature of preserving the quality of the products to be dried has made microwave intermittent drying attractive and has been successfully applied to agricultural, forestry, and food products.

Study on preparation and thermophysical characteristics of molten salt nanocomposite by microwave method

Molten salts are widely applied as heat transfer and thermal storage medium for solar thermal power. In order to research the effect of preparation conditions and the types of nanoparticles on the thermophysical properties of molten salt nanocomposite, different molten salt nanocomposites were developed by mixing the nitrates (Ca (NO3)2·4H2O–KNO3–NaNO3–NaNO2) with 1.0 wt% of SiO2, MgO, TiO2 and CuO nanoparticles using a microwave method, which was a new preparation process of molten salt nanocomposite based on high temperature mixing without water. The effect of different microwave heating temperature (250, 350 and 450 °C) and heating time (30, 60, 90 and 120 min) were experimentally studied. The melting point, latent heat and specific heat of the samples were analyzed by differential scanning calorimeter (DSC). The morphology was observed by scanning electron microscope (SEM). The results showed that the nanoparticles induced a decrease of the melting point of 0.1–2.4% while the latent heat decreased by 3.3–7.9%. Compared with other molten salt nanocomposites, the molten salt with the addition of SiO2 nanoparticles had the biggest increase in specific heat, which increased by 7.7% in solid state and 21.0% in liquid state after heating for 90 min at 250 °C. The total heat storage density could reach to 783.0 J/g between 30 and 500 °C, which was 13.3% higher than the base salt. In addition, according to the morphology of the samples, network nanostructures were observed in the molten salt nanocomposite doped with SiO2.

The microwave assisted extraction sway on the features of antioxidant compounds and gelling biopolymers from Mastocarpus stellatus

Microwave assisted water extraction of hybrid carrageenan and antioxidant compounds from Mastocarpus stellatus red alga was first proposed to recover biopolymers with specific rheological properties, saving time, avoiding chemicals and enhancing extraction yields when compared with conventional treatments. The hybrid carrageenans, precipitated from the liquid fractions recovered after microwave assisted water extraction were analyzed by Fourier transform infrared attenuated total reflectance, high-performance size-exclusion chromatography and rheology. The corresponding soluble extracts were also characterized by total phenolic content, antioxidant capacity, proteins, sulfate and carbohydrate content. The highest phenolic, antioxidant capacity and sulfate content were observed at 190 °C, without notable effect of heating time between 3 and 6 min. In contrast, a clear impact of both microwave heating temperature and time on the molecular weight distribution of hybrid carrageenans as well as on the viscoelastic behavior of formulated hydrogels was identified, being the strongest hydrogels achieved at 170 °C for 6 min. It should be highlighted that all proposed hydrogels exhibited stable mechanical properties in the absence of syneresis for a month of cold storage, except those made with biopolymers obtained with the mildest extraction conditions (3 min at 70 °C).