Activation Energy Profile Research Articles

On the path to kinetic solid-state chemistry: Activation energy-controlled stepwise synthesis and crystal structure of LiSc(NCN)2

Rationally designing new materials is a crucial objective in modern solid-state chemistry, employing different synthetic strategies to vary a reaction's energetic aspects and, hence, effectively control its direction. In that context, and aided by density-functional-based enthalpy diagrams, we have developed a solid-state cyanamide metathetic method allowing to synthetically scan its activation energy profile, thus yielding milder reaction conditions and preventing potential product decomposition. This approach has led to the preparation of the ternary cyanamide LiSc(NCN)2 via solid-state metathesis between Na2NCN, ScCl3 and LiCl, essentially by the existence of an intermediate, LixNa1–xSc(NCN)2, and the subsequent stepwise exchange of Na+ with Li+ ions. Both LiSc(NCN)2 and the solid solution crystallize in an orthorhombic crystal structure with Pbcn symmetry, similar to the rest of the LiM(NCN)2 cyanamide family with M = Al, In, Yb and Y. Structural analysis of the coordination environment around the NCN2− group reveals a relaxation in the distortion of this unit and also an inversion of the cyanamide orientation as Na+ ions are progressively replaced with Li+, thus making the formation of the targeted compound highly favorable.

Multistep kinetic analysis of additive-enhanced plastic degradation

In the realm of non-isothermal degradation kinetics, the utilization of multi-heating rate data has unveiled a fascinating distributed apparent activation energy (Eα) profile when employing isoconversional methods. The advanced isoconversional method (AIC) emerges as a reliable tool, offering Eα values that evolve as chemical reactions progresses. This phenomenon finds its roots in the complex solid-state degradation of plastics, where long-chain hydrocarbons undergo intricate transformations into smaller components through a web of parallel and sequential reactions under the influence of heat. To comprehensively characterize this multifaceted kinetic process, variable pre-exponential factor (A) values were calculated, considering all available heating rate data, in conjunction with the isoconversional principle. These factors complement the changing Eα values, providing crucial insights into the evolving material transformations throughout the reaction. Remarkably, our investigation revealed that in the initial degradation stage, centered around the breakdown of Brominated Flame Retardant (BFR), the reaction follows a contracting spherical model (R3). Transitioning to the subsequent stage, the polymer material undergoes degradation following the diffusion model D4. The incorporation of the isoconversional principle and Criados' masterplot technique effectively facilitates the precise determination of all three kinetic parameters. The process layout we present holds considerable promise for advancing the understanding and control of complex kinetic phenomena.

Proton-polaron and thermionic identity of BaCeO3 polymorph for intermediate temperature fuel cell technology: A first principles and molecular dynamics approach

This study employs first principles and classical molecular dynamics approach to investigate distinct proton landscape and scattering events among aristotype and hettotype BaCeO3 polymorph. We systematically sampled different migration pathways to examine the thermionic behaviour and lattice disorder against the activation energy profile as a function of operating temperatures. According to DFT outcomes, the asymmetric landscape among hettotype structures entails a feeble vacancy formation energy (Evac = 0.326 eV and 0.485 eV) with noticeable lattice strain (ε = 0.258 % and 0.167 %) and desirable proton transfer pathway relative to aristotype counterpart. The transport characteristics from molecular dynamics on the other hand reveals an accelerated proton transfer at intermediate temperatures (300–550 °C) due to symmetric hydrogen bonding around the proton neighbourhood with a curtailed translational barrier from the low frequency lattice phonons. However, repellent response at elevated temperatures (>550 °C) illustrates the advent of ambipolar characteristics (H+/O2−), structural phase transitions, defect scattering events and the rise of artificial barrier as localized proton traps via proton polaron and defect (VO..) interactions. The study as a result accentuates the demand of structural and dynamical coherence to extend the commercial utility of BaCeO3 polymorph for the fuel cell technology.

Thermal, Morphological, and mineralogical characterization of ancient potsherds: Insights from activation energy and degradation profiles

The six representative potsherds sourced from the excavated Buddhist site of Udayagiri, Odisha, in eastern India, were studied using analytical characterization techniques of X-ray diffractometry (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), thermogravimetry (TG-DTG), and a porosity study. The analysis has unveiled the clay composition, firing temperatures, and environment along with internal morphology of these potsherds after firing process. The thermal behavior of the pottery samples was meticulously examined and degradation profiles depicted through TG-DTG curve. The activation energy of potsherds was calculated using the Horowitz and Metzger equation, shedding light on the various stages of degradation. Notably, the calculated activation energies for the first stage of degradation ranged from 5.78 to 16.64 kJ/Mole, while for the 2nd/3rd stage degradation, the range was between 2.59 KJ/Mole to 8.38 KJ/Mole, underlining the intricate firing processes involved. This research has successfully estimated firing temperatures across different environmental conditions, spanning from 450 to 900 °C. The pottery fragments were categorized into two distinct varieties following a comprehensive analysis of firing temperature, inclusions, morphological characteristics, firing conditions, and degradation profiles. The multifaceted approach employed in this study has contributed significantly to our understanding of these potsherds' composition and their firing profile.

Physicochemical Characterization of Woody Lignocellulosic Biomass and Charcoal for Bio-energy Heat Generation

Biomass and its interactions for heat generation have received little attention. In this study, the woody biomass materials were Prosopis africana (PA), Harungana madascariences (HM), Vitrllaria paradoxa (VP), and Afzelia africana (AA). The composition (extractives, carbohydrate, and lignin) of the biomass was determined. The biomass was converted to charcoal in a traditional kiln. A thermo-kinetic examination of the charcoal samples was carried out. The kinetic parameters and potential reaction mechanisms involved in the decomposition process were both obtained using the integral (Flynn–Wall Ozawa) isoconversional methods in conjunction with the Coats-Redfern approach. The activation energy profiles for the charcoal samples in oxidizing atmospheres were 548 kJ/mol for AA, 274 kJ/mol for VP, 548 kJ/mol for PA, and 274 kJ/mol for HM. All charcoal samples underwent comprehensive, multi-step, complex reaction pathways for thermal degradation. The charcoal samples exhibit not only great potential for biochemical extraction but also for bioenergy applications. The significant amount of combustion characteristics in the raw biomass and charcoal samples indicates that each type of wood charcoal produced has more fixed carbon, less ash, and less volatile matter, all of which are desirable for the thermo-chemical conversion of biomass for the production of heat.

Kinetics study of low-grade ilmenite fusion process using sodium hydroxide: Non-isothermal condition with model-free methods

The caustic fusion process is one of the alternative processes in titanium dioxide production from low-grade ilmenite ore. The kinetics of low-grade ilmenite ore caustic fusion using sodium hydroxide (NaOH: Ti ratio = 2:1 (w/w)) under inert atmospheric conditions were studied utilizing thermogravimetric analysis (TGA) at heating ratesof 5, 10, and 15 °C/minute. In a nitrogen atmosphere, the caustic fusion kinetic parameters were calculated using the model-free isoconversion methods of Friedman, FWO, and KAS. It was observed that as conversion (α) increases, Ea and log A decrease. Because of the pre-exponential factor's high value, the order of the reactions has no effect on the process. These methods calculated activation energy profiles of conversion values with results ranging from 8.7 to 149.11 kJ/mol. They varied in a sophisticated way based on the heating rate over a wide range. The fusion product's XRD analysis revealed that the minimum temperature for the formation of a large amount of sodium iron titanate is 850 °C.

Effects of Automotive Test Parameters on Dry Friction Fiber-Reinforced Clutch Facing Surface Microgeometry and Wear-Part 2.

Coefficient of friction values, wear and surface roughness differences are revealed using pin-on-disc test apparatus examinations under three pv loads, where samples are cut from a reference, unused, and several differently aged and dimensioned, used, dry friction fiber-reinforced hybrid composite clutch facings. Tests are characterized by surface activation energy and separated into Trend 1, ‘clutch killer’, and 2, ‘moderate’, groups from our previous study. The results reveal that acceptable, 0.41–0.58, coefficient of friction values among Trend 1 specimens cannot be reached during high pv tests, though the −0.19–−0.11 difference of minimum and maximum pv results disappears when activation energy reaches 179 MJ. The maximum pv friction coefficient can decrease by up to 30% at working diameter due to clutch killer test circumstances, as 179 MJ surface activation energy is applied, while by moderate tests such losses can only be detected close to 2000 MJ energy values among small-sized facings. Besides that, Trend 2 specific wear values are the third of trend 1 results at inner diameter specimens. Compared to reference facing values, specific wear results at working diameter under maximum pv decrease by 47–100%, while increasing specific wear during lifetime can only be detected at the inner diameter of facings enduring clutch killer tests or that are small-sized facings. Among Trend 1 radial and tangential Ra delta results, inner diameter samples provide more decreasing surface roughness data, while by Trend 2 values, the opposite relation is detected. Apart from the effects of activation energy, mileage and driver profile, facing size and friction diameter influence is also revealed.

Correlating the Local and Global Dynamics of an Enzyme in the Crowded Milieu.

Enzymes are dynamic biological macromolecules, with their catalytic function(s) being largely influenced by the changes in local fluctuations of amino acid side chains as well as global structural modulations that the enzyme undergoes. Such local and global motions can be highly affected inside the crowded physiological interior of the cell. Here, we have addressed the role of dynamic structural flexibility in affecting the activation energy barrier of a flexible multidomain enzyme adenylate kinase (AK3L1, UniProtKB: Q9UIJ7). Activation energy profiles of both local (at three different sites along the polypeptide backbone) and global dynamics of the enzyme have been monitored using solvation studies on the subnanosecond time scale and tryptophan quenching studies over the temperature range of 278-323 K, respectively, under crowded conditions (Ficoll 70, Dextran 40, Dextran 70, and PEG 8). This study not only provides the site-specific mapping of dynamics but reveals that the activation energies associated with these local motions undergo a significant decrease in the presence of macromolecular crowders, providing new insights into how crowding affects internal protein dynamics. The crowded scenario also aids in enhancing the coupling between the local and global motions of the enzyme. Moreover, select portions/regions of the enzyme when taken together can well mirror the overall dynamics of the biomolecule, showing possible energy hotspots along the polypeptide backbone.

Experimental Analysis of Intrinsic Kinetics and Rate Profiles for Coal Char Conversion under Different Atmospheres

ABSTRACT This study focuses on determining intrinsic kinetic parameters and interpreting and simulating the rate profile. First, reactivity of coal char prepared at different temperatures was analyzed. Results showed that when coal pyrolysis temperature increases, coal char reactivity decreases; however, activation energy for coal char conversion does not always increase. Next, the weight loss process in non-isothermal conversion was discussed, and results illustrated that the weight loss mechanisms differ in each stage. The weight loss at the second stage was slightly influenced by residual volatile matter and gas diffusion, and the activation energy at this stage was close to an intrinsic value. Meanwhile, discussions on the effects of kinetic analysis methods in determining activation energy showed that Friedman and advanced isoconversional methods can obtain a true activation energy profile, whereas the Kissinger–Akahira–Sunose method was unsuitable. The rate profiles of isothermal conversion were then studied. The results demonstrated that occurrence of a maximum was an inherent feature but the “gas change” operation could shift or even cover up the true position of the maximum. Moreover, an increase in particle temperature could intensify the maximum value but slightly shift its position. Finally, an intrinsic reaction model that combines random pore model and the derived intrinsic kinetic parameters properly reproduced the rate profile of isothermal conversion (e.g., maximal conversion deviation was less than 5%).

Kinetics modeling, thermodynamics and thermal performance assessments of pyrolytic decomposition of Moringa oleifera husk and Delonix regia pod

A non-isothermal decomposition of Moringa oleifera husk and Delonix regia seed pod was carried out in an N2 pyrolytic condition with the primary objective of undertaking the kinetics modeling, thermodynamics and thermal performance analyses of the identified samples. Three different isoconversional models, namely, differential Friedman, Flynn–Wall–Ozawa, and Starink techniques were utilized for the deduction of the kinetics data. The thermodynamic parameters were deduced from the kinetic data based on a first-order chemical reaction model. In the kinetics study, a strong correlation (R2 > 0.9) was observed throughout the conversion range for all the kinetic models. The activation energy profiles showed two distinctive regions. In the first region, the average activation energy values were relatively higher—a typical example is in the Flynn–Wall–Ozawa technique—MH (199 kJ/mol) and RP (194 kJ/mol), while in the second region, MH (292 kJ/mol) and RP (234 kJ/mol). It was also demonstrated that the thermal process for the samples experienced endothermic reactions thought the conversion range. In summary, both the kinetic and thermodynamic parameters vary significantly with conversion—underscoring the complexity associated with the thermal conversion of lignocellulosic biomass samples.

Physico-chemical characterization, thermal decomposition and kinetic modeling of Digitaria sanguinalis under nitrogen and air environments

The study undertook the thermal degradation of a tropical grass species, Digitaria sanguinalis, in nitrogen (pyrolysis) and air (combustion) atmospheres through thermogravimetric analysis as well as comparative kinetic investigation. The differential (Friedman) and integral (Flynn-Wall-Ozawa and Straink) isoconversional methods in conjunction with the Coats-Redfern method were utilized. This was to obtain the kinetic parameters and also predict the probable reaction mechanisms involved in the decomposition process. Before the thermal and kinetic investigations, the grass was analyzed for its physical, chemical, and structural properties utilizing diverse wet-chemistry and spectroscopic techniques. This research attempt is part of a larger project designed to investigate a couple of local grass species, which are invasive by nature, as potential energy crops for pyrolytic and combustion applications. The grass had a fixed carbon content of 17.85% and a calorific value of 13.7 MJ kg−1. The fatty acids detected were from C12 (lauric acid) to C24 (lignoceric acid), with the three most abundant being palmitic (94 mg/g extract), linoleic (27 mg/g extract), and oleic (19 mg/g extract) acids. The average residual weight in air (25.3%) was relatively less than in nitrogen (38.7%), affirming the higher rate of reaction in an oxidative process (combustion). The activation energy profiles in both atmospheres were markedly different, as shown by the Flynn-Wall-Ozawa technique for a conversion ratio of 0.1–0.2 (nitrogen, 149 kJ/mol; air, 177 kJ/mol) and 0.65–0.8 (nitrogen, 366 kJ/mol; air, 170 kJ/mol). Of all the models tested, the model-fitting technique indicates that the chemical reaction and diffusional models play predominant roles in the thermal decomposition of the grass under investigation. The thermal degradation of Digitaria sanguinalis proceeded mainly as complex multi-step reaction mechanisms. Aside from the potential suitability of the grass species for bioenergy applications and biofuels production, it also demonstrated huge capability for biochemical extraction. Future work will incorporate the kinetic data for the associated thermochemical processes development, and the design and optimization of reactors/combustors.

Investigation of slow pyrolysis mechanism and kinetic modeling of Scenedesmus quadricauda biomass

Bioenergy potential of microalage Scednedesmus quadricuda through pyrolysis was investigated using kinetic and thermodynamic analyses. From model-free isoconversional methods, the estimated average activation energies were 152.37 (±20.93), 174.98 (±22.38), and 153.00 (±21.23) kJ/mol, using Friedman, OFW and advance Vyazovkin methods, respectively. Avrami-Erofeev’s A1/4 reaction model was the most probable single-step reaction mechanism determined from the combined kinetic analysis. The activation energy profile, however, indicated a complex degradation process in the active pyrolysis zone. Two independent parallel reactions were considered in the active pyrolysis zone. Average activation energy for low temperature conversion was 77.95 (±3.12) kJ/mol, pre-exponential coefficient 4.86E4 (±2.24E4) s−1, and n = 1.51 (±0.10), whereas for high temperature conversion, the activation energy was 73.26 (±17.93) kJ/mol, pre-exponential coefficient 1.32E3 (±2.61E3) s−1, and n = 1.21 (±0.16). Thermodynamic analysis of pyrolysis in terms of enthalpy, Gibbs free energy, and entropy indicated the feasibility of conversion.

Solar pyrolysis of waste biomass: A comparative study of products distribution, in situ heating behavior, and application of model-free kinetic predictions

A fixed-bed based solar pyrolysis of three waste biomass types: waste wood (WW), waste straw (WS), and sewage sludge (SS) was performed with emphasis on heating behaviour description, products yields, and quality. Laboratory solar pyrolysis reactor setup consists of a copper block indirectly heated by research-grade 1.6 kW xenon lamp radiation. Actual heating rates observed for 90, 95 and 100% xenon lamp power are 4.51, 5.32, and 5.49 K/min for WS; 5.10, 5.19, and 5.37 K/min for WW; and 3.95, 4.48, and 5.25 K/min for SS, respectively. Solar pyrolysis product yields (bio-oil, gas, char) were 51.68, 9.53, and 38.79 wt% for SS, 69.23, 9.18, and 21.59 wt% for WW, 62.30, 10.64, and 27.06 wt% for WS, denoted for the specific heating rates in ascending order. The highest quality bio-oil was obtained from WW pyrolysis with the lowest oxygen to carbon fraction and higher heating value (HHV) of 21.99 MJ/kg. Obtained chars, especially after solar pyrolysis of lignocellulosic biomass, presented HHV of 27.09 MJ/kg and 22.02 MJ/kg for WW and WS respectively, showed significant potential for renewable solid fuel. The increase of the lamp power, and long process time, caused degradation of porous structures within the biomass, where among the samples the highest specific surface area (BET) was denoted for WW samples at 5.2 K/min with 145.09 m2/g. Correlation between model-free kinetic predictions and gaseous species evolution was found, proving the value of apparent isoconversional activation energy profiles in describing actual solar pyrolysis gas compound formation at the laboratory scale.

Analytical investigation of activation energy for Mg-doped p-AlGaN

An analytical model has been developed to investigate the activation energy profile in Mg-doped p-AlxGa1−xN alloy for the entire range of Al composition. For any Al content, the calculated activation energy quantitatively shows a good agreement with experimental result which has also been confirmed by both Hydrogen atom model and effective Bohr radius model. Through this empirical analysis, a breakthrough is apparent for the hole concentration and sheet resistivity with particular Al concentration. It is found that the hole concentration is 30% in p-AlxGa1-xN. Moreover, the sheet resistivity is found to be < 1 Ω-cm up to the Al content of 30%. Finally, the temperature-induced changing behavior of hole concentration and sheet resistivity have been explored here. These results could be a good insight for fabricating the AlGaN-based real-world devices for future optoelectronics.

Super‐crosslinked ionic liquid‐intercalated montmorillonite/epoxy nanocomposites: Cure kinetics, viscoelastic behavior and thermal degradation mechanism

AbstractSuper‐crosslinked epoxy nanocomposites containing N‐octadecyl‐N′‐octadecyl imidazolium iodide (IM)‐functionalized montmorillonite (MMT‐IM) nanoplatelets were developed and examined for cure kinetics, viscoelastic behavior and thermal degradation kinetics. The structure and morphology of MMT‐IM were characterized by FTIR, XRD, TEM, and TGA. Synthesized MMT‐IM revealed synergistic effects on the network formation, the glass transition temperature (Tg) and thermal stability of epoxy. Cure and viscoelastic behaviors of epoxy nanocomposites containing 0.1 wt% MMT and MMT‐IM were compared based on DSC and DMA, respectively. Activation energy profile as a function of the extent of cure was obtained. DMA results indicated a strong interface between imidazole groups of MMT‐IM and epoxy, which caused a significant improvement in storage modulus and the Tg of epoxy. Network degradation kinetics of epoxy containing 0.5, 2.0, and 5.0 wt% MMT and MMT‐IM were compared by using Friedman, Kissinger‐Akahira‐Sunose (KAS), Flynn‐Wall‐Ozawa (FWO) and the modified Coats‐Redfern methods. Although addition of MMT to epoxy was detrimental to the Tg value, as featured by a fall from 94.1°C to 89.7°C detected by DMA method, and from 103.3°C to 97.9°C by DSC method, respectively. By contrast, meaningful increase in such values were observed in the same order from 94.1°C to 94.7°C and from 103.3°C to 104.7°C for super‐crosslinked epoxy/MMT‐IM systems.

The temperature dependence of the laminar burning velocity and superadiabatic flame temperature phenomenon for NH3/air flames

Combustion of ammonia (NH3) as a carbon-free alternative fuel has been recently widely studied, with vast majority of the burning velocity data obtained at room temperature. In the present study, the laminar burning velocity SL of NH3/air mixtures has been measured at unburnt gas temperature Tu from 298 K to 448 K, covering equivalence ratios from 0.85 to 1.25 and at 1 atm using the heat flux method. Kinetic simulations were made with five literature mechanisms developed for NH3 combustion, i.e., Nakamura et al., Otomo et al., San Diego, Okafor et al., and Mei et al. mechanisms, and the influence of radiation heat losses was considered. Using the obtained burning velocity data at different temperatures, the temperature dependence coefficients α in SLSL0=(TuTu0)α were derived, and compared with different models’ predictions. Further analyses of the temperature dependence of SL were carried out through examination of the overall activation energy, temperature and species profiles as well as the reaction paths, and a unique flame structure at the rich side of adiabatic NH3/air flames was found, which resembles ‘over-rich’ phenomena in hydrocarbon flames. At equivalence ratio larger than 1.1 ± 0.05, the NH3/air flames become so rich that (1) the NH2 radical overwhelms the H and OH radicals in maximum mole fraction; (2) after the flame front, H2O converts back to H2 with NO formed at the same time, causing the superadiabatic flame temperature phenomena, i.e. adiabatic flame temperature being lower than the maximum achieved in the flame. Moreover, local minimum NO concentration is found right after the over-rich NH3/air flame front, which may be helpful in reducing NO emissions from NH3 flames in practical applications.

Kinetic studies on the pyrolysis of plastic waste using a combination of model-fitting and model-free methods.

In this work, the pyrolysis behavior of plastic waste-TV plastic shell-was investigated, based on thermogravimetric analysis and using a combination of model-fitting and model-free methods. The possible reaction mechanism and kinetic compensation effects were also examined. Thermogravimetric analysis indicated that the decomposition of plastic waste in a helium atmosphere can be divided into three stages: the minor loss stage (20-300°C), the major loss stage (300-500°C) and the stable loss stage (500-1000°C). The corresponding weight loss at three different heating rates of 15, 25 and 35 K/min were determined to be 2.80-3.02%, 94.45-95.11% and 0.04-0.16%, respectively. The activation energy (Ea) and correlation coefficient (R2) profiles revealed that the kinetic parameters calculated using the Friedman and Kissinger-Akahira-Sunose method displayed a similar trend. The values from the Flynn-Wall-Ozawa and Starink methods were comparable, although the former gave higher R2 values. The Eα values gradually decreased from 269.75 kJ/mol to 184.18 kJ/mol as the degree of conversion (α) increased from 0.1 to 0.8. Beyond this range, the Eα slightly increased to 211.31 kJ/mol. The model-fitting method of Coats-Redfern was used to predict the possible reaction mechanism, for which the first-order model resulted in higher R2 values than and comparable Eα values to those obtained from the Flynn-Wall-Ozawa method. The pre-exponential factors (lnA) were calculated based on the F1 reaction model and the Flynn-Wall-Ozawa method, and fell in the range 59.34-48.05. The study of the kinetic compensation effect confirmed that a compensation effect existed between Ea and lnA during the plastic waste pyrolysis.

Thermal and kinetic analysis of diverse biomass fuels under different reaction environment: A way forward to renewable energy sources

This study investigates the thermal and kinetic analysis of six diverse biomass fuels, in order to provide valuable information for power and energy generation. Pyrolytic, combustion and kinetic analyses of barley straw, miscanthus, waste wood, wheat straw, short rotation coppicing (SRC) willow and wood pellet were examined by non-isothermal thermogravimetry analyser (TGA), differential thermogravimetric (DTG) and differential scanning calorimetry (DSC) techniques. Biomass fuels were thermally degraded under N2, air, CO2 and the selected oxy-fuel (30% O2/70% CO2) reaction environments. The thermal degradation under inert N2 and CO2 atmospheres showed an almost identical rate of weight loss (R), reactivity (RM × 103) and activation energy (Ea) profiles. Similar profiles for R, RM and Ea were observed for the environments under air (21% O2/79% N2) and the oxy-fuel combustion. Results indicated that the thermal decomposition rate for biomass fuels in an oxidising condition was faster than in an inert atmosphere, favourable effect on thermal degradation of biomass fuels was observed when oxygen content increased from 21 to 30%. Higher activation energies with lower reactivity were observed for the biomass fuels that have low cellulosic contents as compared to the other fuels. Regression analysis confirmed that the reaction order 0.5 modelled fitted well for all biomass samples. All these findings will provide valuable information and promote the advancement of future researches in this field.

Evaluation of different hydrocolloids and drying temperatures in the drying kinetics, modeling, color, and texture profile of murta (Ugni molinae Turcz) berry leather

AbstractThe aim of this study is to describe the drying kinetics of a murta (Ugni molinae Turcz) berry purée to obtain a fruit leather through mathematical model and determine the effect of different hydrocolloids on the mass diffusion coefficient, activation energy, surface color, and texture profile at different drying temperatures. Three hydrocolloids were used: 1% gelatin, 0.2% carrageenan, and 4% starch at three process temperatures: 50, 60, and 70°C and a formulation without hydrocolloid as control. The hydrocolloids and process temperature influenced the drying time. The mass diffusion coefficient varied depending on the process temperature and hydrocolloids with values between 1.2665 × 10−10 m2 s−1 and 4.5341 × 10−10 m2 s−1. The Midilli &amp; Kucuk model had a better fit to experimental values. A MANOVA indicated that hydrocolloids and process temperature had a significant effect on color and texture of fruit leather. The process temperature and concentration of hydrocolloids are important factors for drying process design.Practical ApplicationsFruit leather is a low humidity product and stable at room temperature. It can be made with surpluses, discards, or mixtures of fruits, being a new alternative of preservation and healthy consumption. The murta berry is a stationary fruit with antioxidant properties hardly been explored at an industrial level and fruit leathers can be a novel production alternative. Hydrocolloids have gelling and stabilizing characteristics. For this reason, they are used to improve the formation of fruit leathers, although it is necessary to know their effects on physical characteristics as color and texture of the final product. These features are important for consumers' purchasing decision. The convective drying process parameters for fruit leather production as: moisture content, diffusion coefficient, and activation energy can be determined by mathematical modeling. The knowledge of these parameters is important for drying process designs.

Thermal decomposition, kinetics and electrical measurements of Poly(3-Acetamidopropyl Methacrylate)/graphite composites

3-Acetamidopropyl methacrylate [AAPMA] (monomer) were synthesized. The homopolymer of AAPMA was prepared by free radical polymerization method. Novel composites based on poly(3-acetamidopropyl methacrylate) [PAAPMA] containing graphite nanoparticles were prepared using ultrasonic bath. The decomposition behavior of PAAPMA before and after adding graphite to PAAPMA was thermally investigated through thermogravimetric analysis measurements (TGA). Flynn-Wall-Ozawa method for thermal decomposition kinetics of poly(AAPMA) was applied to thermogravimetry curves. The activation energies for the first stage of poly(AAPMA), poly(AAPMA)/1.5% by wt graphite and poly(AAPMA)/6.0% by wt graphite are found to be 115 kJ/mol, 76.7 kJ/mol and 58.7 kJ/mol for conversion of 0.40, respectively. The activation energies in the second step are found to be 116 kJ/mol and 57 kJ/mol at the different conversion of 0.75, respectively. The thermal degradation of both poly(AAPMA) and poly(AAPMA)/graphite 6.0% by wt showed that monomer produced by main chain breaking. And also, in case of composite with graphite 6.0% by wt of poly(AAPMA) was observed that the more amount of monomer revealed at lower temperatures during degradation of composite. 1H, 13C-NMR, FT-IR and GC-MS analyses results showed that as major component of products formed during degradation of the pure polymer (to 365 °C) and poly(AAPMA)/graphite 6.0% by wt (to 265 °C) was AAPMA (monomer). Electrically conductivity of graphite-based poly(AAPMA) composites were investigated. So, dc and ac electrical conductivity and dielectric properties, i.e., real and imaginary parts of the permittivity of pure polymer and polymer composites were revealed. The ac dielectric measurements of poly(AAPMA) were investigated at room temperature between 100Hz and 2kHz depending on the alternating current conductivities. The dipolar functional groups (C-O, C = O and N-C = O) of the AAPMA segment showed that possess significantly effect on the dielectric constant. Also, the activation energy profile of different poly(AAPMA)/graphite composites was revealed by measuring dc conductivity of individual composite material.