Effect of pH and temperature on swelling Behaviour of tamarind gum

Natural gum tamarind is a plant polysaccharide extracted from seeds endosperm of the plant, Tamarindus indica Linn. Thin film of the gum was prepared by direct compression method. The prepared film was investigated for the effect of pH and temperature on solvent uptake property of film by gravimetric method. Different swelling parameters such as mass swelling ratio (MSR), equilibrium swelling ratio (ESR), equilibrium swelling ratio (ESw) and the equilibrium water content (EWC) were studied. It was found that swelling parameters were influenced by different pH and temperature conditions. The results suggested that the water content in equilibrium state was similar to body fluid. The gum converted to a high viscous gel of pseudo plastic characteristics in different pH conditions and the mechanism of continuous diffusion of solvent molecules into tablet during swelling was a non fickian and followed a second order kinetics.

Understanding the Molecular Dynamics of Dual Crosslinked Networks by Dielectric Spectroscopy

The combination of vulcanizing agents is an adequate strategy to develop multiple networks that consolidate the best of different systems. In this research, sulfur (S), and zinc oxide ( ZnO) were combined as vulcanizing agents in a matrix of carboxylated nitrile rubber (XNBR). The resulting dual network improved the abrasion resistance of up to ~15% compared to a pure ionically crosslinked network, and up to ~115% compared to a pure sulfur-based covalent network. Additionally, the already good chemical resistance of XNBR in non-polar fluids, such as toluene and gasoline, was further improved with a reduction of up to ~26% of the solvent uptake. A comprehensive study of the molecular dynamics was performed by means of broadband dielectric spectroscopy (BDS) to complete the existing knowledge on dual networks in XNBR. Such analysis showed that the synergistic behavior that prevails over purely ionic vulcanization networks is related to the restricted motions of rubber chain segments, as well as of the trapped chains within the ionic clusters that converts the vulcanizate into a stiffer and less solvent-penetrable material, improving abrasion resistance and chemical resistance, respectively. This combined network strategy will enable the production of elastomeric materials with improved performance and properties on demand.

Li-Nafion Membrane Plasticised with Ethylene Carbonate/Sulfolane: Influence of Mixing Temperature on the Physicochemical Properties

The use of dipolar aprotic solvents to swell lithiated Nafion ionomer membranes simultaneously serving as electrolyte and separator is of great interest for lithium battery applications. This work attempts to gain an insight into the physicochemical nature of a Li-Nafion ionomer material whose phase-separated nanostructure has been enhanced with a binary plasticiser comprising non-volatile high-boiling ethylene carbonate (EC) and sulfolane (SL). Gravimetric studies evaluating the influence both of mixing temperature (25 to 80 °C) and plasticiser composition (EC/SL ratio) on the solvent uptake of Li-Nafion revealed a hysteresis between heating and cooling modes. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) revealed that the saturation of a Nafion membrane with such a plasticiser led to a re-organisation of its amorphous structure, with crystalline regions remaining practically unchanged. Regardless of mixing temperature, the preservation of crystallites upon swelling is critical due to ionomer crosslinking provided by crystalline regions, which ensures membrane integrity even at very high solvent uptake (≈200% at a mixing temperature of 80 °C). The physicochemical properties of a swollen membrane have much in common with those of a chemically crosslinked polymer gel. The conductivity of ≈10−4 S cm−1 demonstrated by Li-Nafion membranes saturated with EC/SL at room temperature is promising for various practical applications.

Multivariate Analytical Approaches to Identify Key Molecular Properties of Vehicles, Permeants and Membranes That Affect Permeation through Membranes

There has been considerable recent interest in employing computer models to investigate the relationship between the structure of a molecule and its dermal penetration. Molecular permeation across the epidermis has previously been demonstrated to be determined by a number of physicochemical properties, for example, the lipophilicity, molecular weight and hydrogen bonding ability of the permeant. However little attention has been paid to modeling the combined effects of permeant properties in tandem with the properties of vehicles used to deliver those permeants or to whether data obtained using synthetic membranes can be correlated with those obtained using human epidermis. This work uses Principal Components Analysis (PCA) to demonstrate that, for studies of the diffusion of three model permeants (caffeine, methyl paraben and butyl paraben) through synthetic membranes, it is the properties of the oily vehicle in which they are applied that dominated the rates of permeation and flux. Simple robust and predictive descriptor-based quantitative structure–permeability relationship (QSPR) models have been developed to support these findings by utilizing physicochemical descriptors of the oily vehicles to quantify the differences in flux and permeation of the model compounds. Interestingly, PCA showed that, for the flux of co-applied model permeants through human epidermis, the permeation of the model permeants was better described by a balance between the physicochemical properties of the vehicle and the permeant rather than being dominated solely by the vehicle properties as in the case of synthetic model membranes. The important influence of permeant solubility in the vehicle along with the solvent uptake on overall permeant diffusion into the membrane was substantiated. These results confirm that care must be taken in interpreting permeation data when synthetic membranes are employed as surrogates for human epidermis; they also demonstrate the importance of considering not only the permeant properties but also those of both vehicle and membrane when arriving at any conclusions relating to permeation data.

Sorption and Diffusion Properties of Wood/Plastic Composites

The area of sorption and diffusion behaviour of wood/plastic composites has gained considerable attention during the last decade owing to the variety of applications it offers. When it comes to polymers filled with wood particles there are essentially two major limiting factors that controls the final products end user applications; 1) diffusion and 2) sorption/solvent uptake of (especially moisture) the product, since these two processes lead to property degradation in the composite materials. The properties and end use application of a given product can be predicted thorough the knowledge of the parameters like diffusion, sorption and permeation coefficients. Transport (sorption, diffusion & permeation) properties of wood plastic composites (WPC’s) are now a day’s one of the most intensively researched areas owing to its significance in materials science. Liquid transport through plastics is one of the most extensively researched fields in materials science. Present chapter provides a brief insight into the transport (mainly moisture/water) properties of wood/plastic composites. Keywords: Wood particles, wood plastic composites, diffusion coefficient

NATURAL RUBBER/MICROCRYSTALLINE CELLULOSE COMPOSITES WITH EPOXIDIZED NATURAL RUBBER AS COMPATIBILIZER

ABSTRACT An exploration of the effect of epoxidized NR with 50 mole% epoxide groups (ENR-50) as compatibilizer on the rubber–filler interaction of microcrystalline cellulose (MCC)-filled NR composites was conducted. The compatibilizing efficiency of ENR-50 was systematically examined in terms of cure and mechanical and thermal properties of NR/MCC composites. ENR-50 compatibilized NR/MCC composites showed moderate enhancement in the maximum rheometric torque and tensile properties compared to either uncompatibilized NR/MCC composite or unfilled NR system. The solvent uptake measurements indicated improved interfacial interaction between NR matrix and MCC in presence of ENR-50 as compatibilizer. A thermogravimetric analysis confirmed excellent improvement in the thermal stability of NR/MCC composite in the presence of ENR-50 as compatibilizer. Fourier transform infrared spectroscopy was used to explain the probable mechanism of interaction between NR matrix and MCC in the presence of ENR-50.

Graphene Nanoplates Filled Nylon 6,6 Nanocomposites, Morphological, Thermal, Mechanical and Solvent Uptake Study

Effect of graphene nanoplates (GNPs) on the properties of Nylon 6,6 (Nyl 6,6) is investigated in present study. The morphological studies presented that the GNPs were dispersed inside the Nyl 6,6 matrix. The thermo gravimetric analysis (TGA) illustrated that the thermal degradation of nanocomposites samples were started at the range of 350-393 oC, which was appreciably higher than neat Nyl 6,6 (360 oC). The differential scanning calorimetry (DSC) analyses revealed that the crystallization temperature (Tc) of GNPs/Nyl 6,6 increased as increased the addition of GNPs, which might be due to the nucleation effect of GNPs. The mechanical properties of Nyl 6,6 was enhanced by incorporation of GNPs upto the addition of an optimal quantity of filler (5%wt GNPs) into the polymer matrix. The stress yield and Young’s modulus of 5%wt GNPs/Nyl 6,6 was 96.79 and 1.54, N/nm2, respectively. Both Nyl 6,6 and nanocomposites samples were also used for the adsorption of Neutral red chloride (NRC) dye, which significantly remove the dye from the aqueous solution. The neat nylon 6,6 and GNPs (5 and 10 wt%)/Nyl 6,6 adsorbed about 88.49, 93.15, and 93.60% within 2 h, respectively.

Effect of reinforcement filler on vulcanization, diffusion, mechanical, and electrical properties of natural rubber

The present work investigates the properties of natural rubber (NR) filled with different contents of reinforcing carbon black (CB) and other compounding ingredients. The curing characteristics were tested at 157°C. It was found that the equilibrium solvent uptake ( Qmax) decreases with the increase of the CB concentration due to reduction of the free volume. Mechanical properties such as tensile strength and hardness of CB filled rubber composites were remarkably improved, indicating the inherent reinforcing potential of CB. The percentage of elongation at break of filled CB rubber was found to be lower than that of pure NR. The dielectric constants ( ε′), dielectric loss ( ε″), and alternating current (AC) electrical conductivity ( σAC) were investigated for all samples as a function of frequency and temperature. It is concluded that the high CB content causes the formation of channels, increasing the AC conductivity of the composites.