Application of Kissinger analysis to glass transition and study of thermal degradation kinetics of phenolic–acrylic IPNs

Degradation kinetics of sequential IPNs, based on novolac resin and poly (2-ethyl hexyl acrylate), are studied at linear heating rates of 2°C/min, 5°C/min, 10°C/min and 20°C/min by thermogravimetric analyser (TGA). Activation energy (E _a and order (n) of thermal decomposition reaction for IPNs and pure phenolic resin are evaluated from TGA curves using differential method of Freeman and Carroll. Decrease in T _g with an increase of acrylate content in IPNs are seen. Lower activation energy (E _a′), as calculated by applying Kissinger equation, for the concerned transition of IPNs, compared to that of pure phenolic resin is quite evident from DSC study.     

EXTENDED STORAGE LIFE OF LITCHI FRUIT USING CONTROLLED ATMOSPHERE AND LOW TEMPERATURE

The postharvest quality of litchi (Litchi chinensis Sonn.) cv. Bombay stored under controlled atmosphere (CA) at 3.5% O₂and 3.5% CO₂, 2C temperature and 92–95% relative humidity was studied. Fruits were also held in regular atmosphere (RA) maintained at 2C temperature and 92–95% relative humidity. Fruits kept at normal ambient conditions were used as controls. Various quality attributes measured revealed that fruits stored in CA exhibited Hunter “a” values of 11.2 after 56 days of storage, indicating the beneficial effect of CA on retaining the red color of litchi fruits. Fruits held in RA exhibited Hunter “a” values (7.9) lower than that of CA‐stored litchi, showing that browning of litchi was noticeable in RA. Loss of weight was lowest (4.9%) for the fruits stored in CA compared to those stored in RA (11.0%) and control (33.1%). Loss of acidity and ascorbic acid content of fruits stored in CA were less than that of RA. The smallest increase of litchi firmness and pericarp puncture strength of 2.2 and 3.9 times of initial level, respectively, were observed even after 56 days of storage in CA. Total soluble solid of litchi increased from 19.3° Brix at harvest to 23.0° Brix until 48 days of storage in CA after which it declined to 22.8 °Brix. The sensory evaluation of aril color and taste showed that the fruits held in CA were rated good throughout 56 days of storage.     

Characterization and in vitro and in vivo evaluation of cross-linked chitosan films as implant for controlled release of citalopram

The aim of the present study is to develop cross-linked chitosan (CH) films that can release drug over an extended period of time and that too in a controlled manner. A solution of different percentages of CH, is prepared in 1% lactic acid, followed by addition of citalopram (CTP) and then reacted with increasing amounts of glutaraldehyde (GL) to obtain films with different cross-linking densities. Prepared films are characterized for their physical and mechanical properties. The films are then subjected to in vitro drug release studies using pH 7·4 phosphate buffer saline (PBS) as dissolution medium and cumulative amount of drug released is calculated. Kinetic analysis of drug release is performed using Power law model and Higuchi’s model. With increase in concentration of CH, water absorption capacity and mechanical strength are increased; whereas, water vapour permeability and elasticity of the films are decreased. The effect of cross-linking agent, GL, is such that with an increase in the amount of GL, water vapour permeability, water absorption capacity and elasticity of the films are decreased; whereas, mechanical strength increased to some extent and then decreased. In vitro release studies indicate that films containing 3% CH, cross-linked with 2–3% GL and films containing 4% CH, cross-linked 1% GL are able to sustain the drug release for a prolonged time along with releasing almost complete drug in a desired period. Out of these batches, films containing 3% CH, cross-linked with 2–3% GL are having sufficient strength, water vapour permeation, water absorption capacity and elongation at break for implantation purpose. The in vitro degradation studies and histopathological studies were carried out with a sample film (batch C3 as in table 1) in rabbit model. In vitro degradation study indicates that the films maintained their integrity for desired implantation. The histopathological studies under optical microscope indicates that on implanting, there is no evidence of any inflammation, any foreign body granuloma or any necrosis or hemorrhage. Tissue configuration remains unaltered after 30 days of implantation. So, it can be suggested that cross-linked CH films of above said composition can be used as implant for long term application in depression and related disorders.     

ESTIMATION OF MOISTURE LOSS FROM THE COOLING DATA OF POTATOES

A procedure was developed to predict moisture loss from cooling data of potato packed in gunny bags and stacked on wooden platforms in commercial cold stores. To predict the moisture loss, mass transfer coefficients k_cand k_mwere estimated during the storage period, which were found to decrease with time. The calculated time average k_cand k_mvalues were 1.83 × 10^?4 m/s and 2.31 × 10^?10 kg/s·m²·Pa during the transient cooling period and 1.59 × 10^?4 m/s and 2.27 × 10^?10 kg/s·m²·Pa for the rest of the storage period, respectively. The estimated moisture losses were 4.8, 4.74 and 4.78%, at the center of three different stacks, for a storage period of 8 months. The corresponding experimentally measured weight losses at the center of the same stacks were 5.2, 5.1 and 5.26% with a variation of 11, 7.5 and 10.2%, respectively. Therefore, the procedure adopted in this study may be used to assess the moisture loss from potatoes under the different storage conditions. The effect of relative humidity (RH) and potato temperature on moisture loss was also predicted using the developed procedure. Decrease in RH of the storage air increased the moisture loss. The potatoes stored below 85% RH incurred more than 7% water loss. Therefore, 88–90% RH in the cold store may be used to limit the maximum moisture loss within the permissible limit of 5% even after 8 months of storage. It was also found that increasing the potato temperature exponentially increased the rate of moisture loss.     

TIME-TEMPERATURE RELATIONSHIPS FOR IQF SHRIMP WITH LIQUID NITROGEN AND ITS QUALITY ASSESSMENT

Experiments were conducted to study the time temperature relationship during freezing of individual raw shrimp by dipping in Liquid Nitrogen. Four sets of experiments were conducted. The first set involved the assessment of the temperature profile of the gaseous nitrogen environment in a thermocole container with varying quantity of liquid nitrogen. The next two sets of experiments involved direct dipping of the raw shrimp in a liquid nitrogen bath in a thermocole container using perforated stainless steel tray suspended by means of a wire loop, one in a single tier and the other in a double tier. The fourth set was conducted in a laboratory model tunnel provided with immersion freezing facility. In each case, the dipping time was progressively increased from 5 s to 30 s at 5 s increments. The time‐temperature relationships obtained were compared with those from available literature and were found to exhibit similar trend. The quality of the frozen shrimp was also studied in terms of pH, TVB, TMA and Indole content. It was observed that dipping shrimp in liquid nitrogen for the specified period retained the quality well within the acceptable commercial limit.     

Effect of Two-Dimensional Pressure on the Permittivity of Fine- and Coarse-Grained Barium Titanate

The effect of two-dimensional pressure on the permittivity of fine-and coarse-grained ceramic BaTiO₃ was investigated. It was shown that, unlike coarse-grained (10μ or above) barium titanate, the permittivity of the fine-grained (1μ mean) material increased with the increase in two-dimensional compression perpendicular to the electrode, whereas for an intermediate grain size, the permittivity was almost independent of pressure. The apparent anomalous effect of the fine grain size on the pressure coefficient of permittivity was explained satisfactorily on the basis of an internal stress model using a modified Devonshire thermodynamic treatment.     

Phenomenological Theory of High Permittivity in Fine-Grained Barium Titanate

The anomalously high permittivity in fine-grained ceramic barium titanate is explained by the absence of 90° twinning within the grains, giving rise to internal stresses as the ceramic cools below the Curie temperature. Using the Devonshire phenomenological thermodynamic method and a simplified model, the stresses involved are calculated. At these stress levels, the reduced strain calculated on this model agrees well with X-ray data for the fine-grained material. The limitations and possible developments of the proposed model are discussed.     

Dielectric Properties of Explosively Compacted BaTiO3

Polycrystalline BaTiO₃ was explosively compacted to nearly theoretical density, and its dielectric and piezoelectric properties were investigated. The compacted bodies did not exhibit dielectric hysteresis, a Curie point, or piezoelectric properties; their dielectric constant and dissipation factor increased linearly with temperature. The dielectric constant was much lower than those of similar dense bodies obtained by conventional sintering. These results may be interpreted in terms of weak intergranular bonding and increased numbers of defects generated in the shocked material. When explosively compacted bodies were sintered, normal ferroelectric and piezoelectric properties and improved microstructures were obtained.