Rehydration of Rosa rubiginosa Fruits Dried with Hot Air

The effect of perforation, drying temperature, and rehydration temperature on the rehydration kinetics of Rosa rubiginosa fruits was investigated. Before drying, half of the fruit sample was perforated three times at equidistant points along the equatorial plane of the fruit, in order to speed up the drying process. Samples were dried at various air temperatures (60, 70, and 80°C), with an air velocity of 5 m/s and 5% relative humidity. Then, dried samples were rehydrated at different temperatures (20, 40, 60, and 80°C). The rehydration kinetics was fitted by two empirical models, Peleg and Weibull, and both represented the phenomenon well, in perforated and nonperforated fruits. Regardless of the drying temperature, the higher the rehydration temperature of rose hip fruits, perforated or not, the higher the water absorption capacity. Temperature dependence of the kinetic parameters was E_a = 47.5 kJ/mol (Peleg) and 55.9 kJ/mol (Weibull) for nonperforated fruits and E_a = 40.1 kJ/mol (Peleg) and 45.5 kJ/mol (Weibull) for perforated fruits; thus, perforated fruits were influenced more by rehydration temperature than nonperforated fruits. Perforated fruits rehydrated 30% faster than nonperforated fruits.     

Mathematical modelling of mass transfer during rehydration process of Aloe vera (Aloe barbadensis Miller)

Aloe vera (Aloe barbadensis Miller) slabs dried at 60 °C were rehydrated at three temperatures (20, 40 and 60 °C) in order to study the influence of temperature on the kinetics of mass transfer during rehydration phenomenon. Fick, Peleg and Weibull models were applied for rehydration modelling, as well as one new proposed model. All kinetic parameters of the models showed positive dependence on temperature, according to the Arrhenius-type equation. Weibull model and the new proposed model provided the best fit quality for each rehydration curve based on the statistical tests RMS, SSE and Chi-square. In accordance with the results, both models may be used to estimate the rehydration time of A. vera. Furthermore, two rehydration indices (RR and WHC) were analysed, which decreased as temperature increased. These indices confirm that drying process modifies the cell structure of A. vera, reducing the rehydration ability due to cellular and structural disruption that takes place during dehydration.     

Rehydration Behavior of Vacuum-Microwave-Dried Potato Cubes

Rehydration properties and microstructure of vacuum-microwave and hot air–dried potato cubes were examined. Two kinds of models were considered to describe the hydration kinetics: a diffusion model for a cube and two empirical equations, Peleg and Weibull. The values of the effective moisture diffusivity of soaked potatoes were in the range 1.17 × 10^?9 to 4.73 × 10^?9 m²/s. The vacuum-microwave drying technique resulted in puffed potato particles characterized by porous microstructure with a network of open cavities and the hot air drying gave the potato particles containing compacted cells with the low amount of open micro-caves. Higher rehydration ability was observed for the samples dried with microwaves under low pressure. Vacuum-microwave drying at 6 kPa seems to be the optimal drying condition for potato cubes, ensuring porous microstructure of dried material and low shrinkage of dried potato particles as well as their high recovery properties and rehydration.     

Pulsed vacuum drying (PVD) of wolfberry: Drying kinetics and quality attributes

The effects of drying temperature (50, 53, 56, 59, 62, and 65°C) and pulsed vacuum ratio defined as the vacuum pressure duration versus atmosphere pressure duration (3:3, 6:6, 9:2, 12:5, 15:1, 18:4?min/min) on pulsed vacuum drying (PVD) characteristics and quality attributes of wolfberry in terms of polysaccharide content, color parameters (L^*, a^*, b^*, ΔE, and C), rehydration ratio and microstructure were investigated. Results revealed that appropriate PVD can reduce drying time by 73.2% compared to hot air drying at the same drying temperature. The moisture effective diffusivity (D_eff) ranged from 5.23?×?10^?10 to 9.73?×?10^?10?m²/s, calculated using the Weibull distribution model. The polysaccharide content, L^* (lightness), a^* (redness/greenness) of the PVD products were higher than those of the hot air-dried samples at the same drying temperature. The total color difference (ΔE) and color intensity (C) of PVD samples were close to those of the fresh ones. The retention rate of total polysaccharide content of PVD samples was about 49–77%, which was significantly higher than 30% of the hot air-dried samples. The surface of PVD wolfberry was highly porous, which may enhance moisture transfer during drying as well as rehydration processes. The results of current work indicate that PVD is a promising technology for wolfberry process, for the reason that PVD can reduce drying time significantly as well as enhance the quality attributes in terms of the total polysaccharide content, color parameters and rehydration ratio.     

Hot-Air Drying and Rehydration Characteristics of Red Kidney Bean Seeds

The effects of pretreatments such as citric acid and hot water blanching and air temperature on drying and rehydration characteristics of red kidney bean seeds were investigated. Drying experiments were carried out at four different drying air temperatures of 50°C, 60°C, 70°C, and 80°C. It was observed that drying and rehydration characteristics of bean seeds were greatly influenced by air temperatures and pretreatments. Four commonly used mathematical models were evaluated to predict the drying kinetics of bean seeds. The Weibull model described the drying behaviour of bean seeds at all temperatures better than the other models. The effective moisture diffusivities (D_eff) of bean seeds were determined using Fick's law of diffusion. The values of D_eff were between 1.25 × 10^?9 and 3.58 × 10^?9 m²/s. Activation energy was estimated by an Arrhenius-type equation and was determined as 24.62, 21.06, and 20.36 kJ/mol for citric acid, blanch, and control samples, respectively.     

The Moisture Migration Behavior of Plasticized Starch Biopolymer

Using plasticized starch pellets as a precursor for making thermoformed products is a commercially viable and profitable idea. However, drying of plasticized starch is quite complex in nature, partly due to the synergistic interactions between starch and plasticizers in the presence of water. The migration of water from starch pellets plasticized by two components, glycerol and xylitol, at three different temperatures was investigated in the present work. Evidence for synergistic interaction between plasticizers and water within starch is shown by the reduced effective moisture diffusivities and moisture migration fluxes at different overall plasticizer concentrations. In addition, the effective moisture diffusivities showed stronger dependence on moisture concentration and the plasticizer molecular weight even though the moisture flux was comparable. The drying process was characterized by two effective diffusion coefficients (D ₁, D ₂) and, interestingly, the coefficients were an order of significance apart. The Peleg model was investigated for predicting the drying behavior and it is shown that the Peleg constants k ₁ and k ₂ increase with temperature. k ₂, Which is related to material structure and morphology, showed comparable modification by addition of plasticizers, indicating that plasticizers were able to modify the fundamental structure, and xylitol showed greater average k ₂ values than glycerol. Further, because k ₁ is related with moisture diffusivity, the effect of temperature on diffusivity was interpreted using the Arrhenius relationship. The activation energy values confirm that plasticizers can lock in water within the new structure. Overall, the larger structure of xylitol showed better stability in controlling moisture diffusivities and migration fluxes. These findings can provide better insights in designing and controlling the vapor barrier properties of starch-based packaging materials.     

Kinetics and crystal structure of isothermal crystallization of poly(lactic acid) plasticized with triphenyl phosphate

In this article, the spherulitic growth rate of neat and plasticized poly(lactic acid) (PLA) with triphenyl phosphate (TPP) was measured and analyzed in the temperature range of 104–142°C by polarizing optical microscopy. Neat PLA had the maximum value of 0.28 μm/s at 132°C, whereas plasticized PLA had higher value than that of neat PLA, but the temperature corresponding to the maximum value was shifted toward lower one with increasing TPP content. The isothermal crystallization kinetics of neat and plasticized PLA was also analyzed by differential scanning calorimetry and described by the Avrami equation. The results showed for neat PLA and its blends with various TPP contents, the average value of Avrami exponents n were close to around 2.5 at two crystallization temperatures of 113 and 128°C, the crystallization rate constant k was decreased, and the half‐life crystallization time t_1/2 was increased with TPP content. For neat PLA and its blend with 15 wt % TPP content, the average value of n was 2.0 and 2.3, respectively, the value of k was decreased, and the value of t_1/2 was increased with crystallization temperature (T_c). Further investigation into crystallization activation energy ΔE_a of neat PLA and its blend with 15 wt % TPP showed that ΔE_a of plasticized PLA was increased compared to neat PLA. It was verified by wide‐angle X‐ray diffraction that neat PLA and its blends containing various TPP contents crystallized isothermally in the temperature range of 113–128°C all form the α‐form crystal. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Curing kinetics and thermal property characterization of a bisphenol‐S epoxy resin and DDS system

The kinetics of the cure reaction for a system of bisphenol‐S epoxy resin (BPSER), with 4,4′‐diaminodiphenyl sulfone (DDS) as a curing agent was investigated with a differential scanning calorimeter (DSC). Autocatalytic behaviour was observed in the first stages of the cure which can well be described by the model proposed by Kamal, using two rate constants, k₁ and k₂, and two reaction orders, m and n. The overall reaction order, m + n, is in the range 2∼2.5, and the activation energy for k₁ and k₂ was 86.26 and 65.13 kJ mol⁻¹, respectively. In the later stages, a crosslinked network was formed and diffusion control was incorporated to describe the cure. The glass transition temperature (T_g) of the BPSER/DDS samples partially cured isothermally was determined by means of torsional braid analysis (TBA) and the results showed that the reaction rate increased with increasing T_g, in terms of rate constant, but decreased with increasing conversion. It was also found that the  SO₂ group both in the epoxy resin and in the hardener increases the T_g values of the cured materials compared with that of BPAER. The thermal degradation kinetics of this system was investigated by thermogravimetric analysis (TGA). It illustrated that the thermal degradation of BPSER/DDS has nth order reaction kinetics. © 2000 Society of Chemical Industry     

Modeling of Sorption Isotherms of Various Kinds of Wood at Different Temperature Conditions

Adsorption and desorption isotherms of pine, spruce, birch, and willow Salix viminalis v. Orm (2-year stem) under three temperature conditions (20, 50, 75°C) in the range of water activity 0.0–0.9 were studied. In order to describe our experimental data, five models were implemented (GAB, Peleg, Chung-Pfost, Oswin, Halsey) and compared. It was found that GAB and Peleg models provide the best fit to the experimental data. On the basis of GAB modeling, the monolayer moisture content for each kind of wood was calculated. Moreover, the hysteresis phenomenon was investigated. The influence of temperature and wood variety on sorption isotherms was also tested.     

Adsorption Kinetics for the Chemical Filters Used in the Make-Up Air Unit (MAU) of a Cleanroom

The adsorption of toluene onto commercially available coconut-based granular activated carbon (GAC) loaded within a piece of nonwoven fabric was investigated in a filter media at face velocities 0.076 through 0.152 m/s. The results showed that the adsorption capacity increases with increasing toluene concentration but decreases as the face velocity was increased. In order to investigate the adsorption mechanisms, three simplified kinetic models, i.e., the pseudo-first-order, second-order kinetic models, and intraparticle diffusion model were used to describe the kinetic data and the rate constants were calculated. The rate parameter, k _i, of intraparticle diffusion, the rate parameter, k ₂, of the pseudo-second-order and k ₁, the rate parameter for the pseudo-first-order mechanism were compared. It was found that the pseudo-first-order adsorption mechanism is predominant and the overall rate of the GAC adsorption process appears to be controlled by more than one step, namely both the external mass transfer and intraparticle diffusion mechanisms.     

Solid‐state polymerization of poly(trimethylene terephthalate)

The solid‐state polymerization (SSP) of poly(trimethylene terephthalate) (PTT) has been studied and compared with that of poly(ethylene terephthalate) (PET). Because PTT and PET share the same SSP mechanism, the modified second‐order kinetic model, which has successfully been used to describe the SSP behaviors of PET, also fits the SSP data of PTT prepolymers with intrinsic viscosities (IVs) ranging from 0.445 to 0.660 dL/g. According to this model, the overall SSP rate is ?dC/dt = 2k_a(C ? C_ai)², where C is the total end group concentration, t is the SSP time, k_a is the apparent reaction rate constant, and C_ai is the apparent inactive end group concentration. With this equation, the effects of all factors that influence the SSP rate are implicitly and conveniently incorporated into two parameters, k_a and C_ai. k_a increases, whereas C_ai decreases, with increasing SSP temperature, increasing prepolymer IV, and decreasing pellet size, just as for the SSP of PET. Therefore, the SSP rate increases with increasing prepolymer IV and increasing SSP temperature. The apparent activation energy is about 26 kcal/mol, and the average SSP rate about doubles with each 10°C increase in temperature within the temperature range of 200–225°C. The SSP rate increases by about 30% when the pellet size is decreased from 0.025 to 0.015 g/pellet. Compared with PET, PTT has a much lower sticking tendency and a much higher SSP rate (more than twice as high). Therefore, the SSP process for PTT can be made much simpler and more efficient than that for PET. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3188–3200, 2003     

Fluorescence study on drying of ι-carrageenan gels at different temperatures prepared with various CaCl<Subscript>2</Subscript> content

The influence of temperature and salt content on drying was investigated by using steady-state fluorescence (SSF) technique. Supporting gravimetric and volumetric measurements were also carried out during drying of gels at various temperatures. ι-Carrageenan gels were prepared with various CaCl₂ content. Pyranine was introduced as a fluorescence probe during gel preparation. Apparent fluorescence intensity, I, was measured during in situ drying process at each temperature and it was observed that fluorescence intensity values decreased for all gel samples. A simple model consisting of Case II diffusion was used to produce the packing constants, k ₀, for helixes. It was observed that k ₀ increased as the drying temperature was increased. On the other hand at each temperature, it was seen that k ₀ decreased as CaCl₂ content was increased. Packing energies for drying processes were obtained from fluorescence, volumetric, and gravimetric measurements separately.     

Study on the Crystallization Properties of Polypropylene/Montmorillonite Composites

The crystalline size of polypropylene (PP) filled with montmorillonite (MMT) was studied by X-ray diffraction (XRD). The isothermal crystallization behavior of polypropylene was studied by means of differential scanning calorimetry (DSC). The Avrami equation was used to describe the isothermal crystalline kinetics of PP/MMT composites. The result showed that the addition of MMT decreased the crystalline size L _hkl of the polymer. MMT was used as nucleating agent during isothermal crystallization process of polypropylene. The addition of montmorillonite decreased the crystallization time of the polypropylene and the melt point was raised. The value of Avrami exponent n was related with the crystallization temperature. The value of Avrami pre-index factor k of PP/MMT composite was decreased with increasing crystallization temperature. The value of half crystallization time t _1/2 of PP/MMT composite was less than that of PP at a given crystallization temperature, signifying that montmorillonite acted as nucleating agent, accelerated the overall crystallization process.     

Kinetics and crystal structure of poly(lactic acid) crystallized nonisothermally: Effect of plasticizer and nucleating agent

The kinetics of neat poly(lactic acid) (PLA) and its composites with triphenyl phosphate (TPP) and/or talc crystallized nonisothermally at different cooling rates of 1, 2.5, 5, 7.5, and 10°C/min was analyzed by differential scanning calorimetry and described by Avrami equation and combined Avrami‐Ozawa equation. The results showed that talc acted as PLA nucleating agent accelerated crystallization rate by decreasing the crystallization half‐time t_1/2 or rate parameter F(T), whereas TPP acted as PLA plasticizer decreased crystallization rate. For neat PLA and plasticized PLA, the average values of Avrami exponent n were almost close to each other, but added TPP decreased crystallization rate constant k. As for PLA composites with talc, the crystallization process was relatively complex, and was divided into three regimes. At a given cooling rate, the value of n₂ was almost larger than that that of n₁ or n₃, whereas the value of k₂ was less than that of k₁ or k₃. The effective activation energy ΔE_x calculated from Friedman formula increased with the increase of relative crystallinity and TPP content, whereas decreased with the presence of talc. Wide angle X‐ray diffraction verified that all samples crystallized nonisothermally in cooling rate range of 1–10°C/min form α‐form. POLYM. COMPOS., 31:2057–2068, 2010. © 2010 Society of Plastics Engineers     

Free radical polymerization in ionic liquids—Influence of the IL-concentration and temperature

The influence of the ionic liquid (IL) 1-ethyl-3-methylimidazoliumethylsulfate ([EMIM]EtSO₄) on the polymerization kinetics of methyl methacrylate was investigated. ILs are liquids with relatively high polarities and viscosities. These two characteristic properties are strongly correlated with the rate coefficients of propagation k_p and termination k_t of polymerizations carried out in ILs. The rate constant of termination k_t decreases when the concentration of ionic liquid, and thus the viscosity is increased, whereas the propagation rate coefficient k_p increases with increasing IL content. The viscosity of ILs can be varied by either working with mixtures of ILs with conventional organic solvents – here the IL [EMIM]EtSO₄ was mixed with dimethyl formamide (DMF) – or by variation of the temperature. The studies were carried out to determine the influence of the viscosity on the propagation and the termination reaction as well as the molecular weight distribution.     

Oxidation kinetics of linoleic acid in the presence of saturated acyl <Emphasis Type="SmallCaps">l</Emphasis>-ascorbate

The oxidation processes of linoleic acid (LA) in the presence of l-ascorbic acid or saturated acyl l-ascorbate additives were measured at various temperatures and molar ratios of the additive to LA. Higher oxidative stability of LA was observed at higher additive levels for all additives. The addition of the ascorbates lengthened the induction period for the oxidation of LA. An autocatalytic kinetic rate equation was used to model the oxidation processes of LA mixed with the ascorbates, and the dependence of the rate constant, k, on acyl-chain carbon number was determined. At any temperature, the use of ascorbate additives decreased the k value for LA, and there was a slight tendency for k values to decrease with increasing acyl-chain length. The apparent activation energy, E _a, and the frequency factor, k ₀, for the rate constant were determined from Arrhenius plots. The calculated E _a and k ₀ values also decreased with increasing ascorbate acyl-chain length.     

Ion Exchange Adsorption Studies of Miglitol in a Fixed Bed

The adsorption of miglitol on the D001 resin in a fixed bed was studied at different flow rates, temperatures, and height‐to‐diameter ratios (H/D). The exhaustion time decreased and the height of the mass transfer zone (H_MTZ) increased with increasing flow rate. The surface area of the adsorbent increased with decreasing solution flow rate. Breakthrough curves at different flows were described by the Thomas, Yoon–Nelson, and Adams‐Bohart models. The rate constants for the kinetic models increased with increasing flow rate. The theoretical and experimental times required for 50 % adsorbate breakthrough slightly differed at varying flow rates. The change trend in the values of the maximum volumetric adsorption capacity was the same as that of the values at the maximum adsorption capacity of the D001 resin. The temperature did not obviously affect the breakthrough curves. The slope of the breakthrough curve decreased and the H_MTZ increased with increasing H/D ratio. The adsorption capacities of the fixed bed for H/D = 7.6 and 0.7 were greater than that for H/D = 1.5.     

Drying of sardine muscles: Experimental and mathematical investigations

The aim of this work was to study the effect of air drying process on the dehydration kinetics of sardine muscles (Sardina pilchardus). Experimental drying kinetics were measured at five air temperatures (40, 50, 60, 70 and 80 °C), two relative humidity and at a constant air velocity of 1.5 m/s. The sardine drying kinetics were accelerated by increasing air temperature and were showed down when increasing air humidity. Moisture desorption isotherms of sardine muscles were determined at three temperatures (40, 50 and 70 °C) by using the static gravimetric method. The equilibrium moisture contents of sardine muscles were used to treat mathematically the experimental drying kinetics. Experimental drying kinetics and desorption isotherms of sardine muscles were described by using empiric models available in the literature. Eight models (GAB, BET, Henderson–Thompson, Modified Chung & Pfost, Modified Halsey, Oswin, Peleg and Adam & Shove models) were compared in order to describe the desorption isotherms. The Peleg model showed the best fitting of experimental data. For the drying kinetics, the Page model allowed a better fitting than the Newton and the Henderson and Pabis models. The Page model was thus used for simulating the drying kinetics of sardine muscles between 40 and 80 °C.     

Swelling behavior of crosslinked hydroxypropyl cellulose films retaining cholesteric liquid crystalline order. I. Effect of temperature

Temperature dependence of the swelling behavior in both water and propanol was determined for the crosslinked hydroxypropyl cellulose (HPC) films retaining cholesteric liquid crystalline order (CLCO) and for the crosslinked amorphous HPC films. The dependence of swelling behavior in water for the films retaining CLCO was different from that of the amorphous films. With increasing temperature, the equilibrium swelling ratio (B_e) for the films retaining CLCO decreased, whereas B_e for the amorphous films increased. In propanol, both films exhibited the same temperature dependence. B_e increased with increasing temperature. The increasing rate of the swelling in transient state showed similar temperature dependence on B_e. The increasing rate for the films retaining CLCO decreased with temperature, but that for the amorphous films increased in water; in propanol, the increasing rate for two types of films increased. The difference in the swelling behavior between the two types of films may be due to the difference in the number-average molecular weight between crosslinks. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1015–1022, 1999     

Cure kinetics and properties of epoxy/dicyanate blends

The cure behavior and properties of epoxy/dicyanate blends containing a stoichiometric amount of an amine curing agent for epoxilde groups were investigated as a function of blend composition. Differential scanning calorimetry (DSC) was used to investigate the dynamic and isothermal cure behavior of the blends. The cure rate of the blend increased with increasing dicyanate content. A second order autocatalytic reaction mechanism described the cure kinetics of the blends. The kinetic parameters were determined by fitting the dynamic DSC data to the model kinetic equation. The k₁₀ and E₁ values were mainly affected by the change of dicyanate content. The glass transition temperature of the blend decreased with increasing dicyanate content. The thermal decomposition characteristics of the blends were investigated by thermogravimetric analysis (TGA). Dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA) were used to investigate the mechanical properties of the blends. With increasing dicyanate content, the cure rate increased but the thermal and mechanical properties of the cured blends were not improved.