Factors affecting moisture absorption in polymer composites. I - Influence of internal factors. II - Influence of external factors

Moisture absorption data obtained for jute and glass-epoxy composites under the influence of identical internal factors are presented. The observed dissimilarities in behavior are described in terms of different composite schematic models depicting the typical flow paths in both types of materials. The relative composite permeabilities are discussed in terms of typical fiber permeabilities and the diffusion paths preferred by the moisture in the composites. Then, the influence of external factors on the moisture absorption characteristics of permeable and impermeable jute-epoxy, glass, and graphite-epoxy composites is reported

Science of engineering materials : engineering properties

Volume 3.xiii, 232 p.; 21 cm

Atomic structure and the chemical bond : including molecular spectroscopy

xiii+506hlm.;22c

Science of engineering materials : structure of matter

Vol I.xi, 247 p.; 21 cm

Sorption of copper ions on templated poly (4- vinly pyridine) resins

The equilibrium and kinetics of sorption of Cu ions at low solution concentration on $Cu^{2+}$-templated poly(4-vinylpyridine) resin were studied. The Langmuir isotherm equation fits the equilibrium sorption data well, while the kinetic data agree with a modified shrinking core model for fluid-solid chemical reactions. Pore diffusion controls the exchange rates at low solution concentration. The diffusion coefficient which lies within the normal expected range for chelating resins increases with increasing solution concentration, besides temperature. This phenomenon is discussed in the light of similar observations reported for ion exchange resins in the literature

Monitoring the Curing of Furan Resins through the Exothermic Heat of Reaction

The curing reaction of furan resins was monitored through the exothermic heat of reaction by means of a simple technique. p-Toluene sulphonic acid dissolved in acetone was used to catalyse the curing reaction. A "cure rate index", defined as the maximum temperature rise per unit time per unit mass of the resin, was used as a measure of the rate of cure. The index value increases exponentially with the catalyst concentration. Interestingly, for the same catalyst concentration the index value also increases significantly with the period of ageing of the catalyst solution. A method is developed for deriving the activation energy for the curing reaction from the exothermic heat data for non-isothermal cure. The activation energy is found to increase with resin viscosity and to decrease exponentially with increasing catalyst concentration. Quantitative expressions are derived relating activation energy with catalyst concentration

Attaching chelating ligands to polybenzimidazole via epoxidation to obtain metal selective sorbents

Microporous polybenzimidazole of 250–500 μm spherical bead size from Celanese has been reacted with epichlorohydrin and sodium hydroxide and the resulting product with pendant epoxy groups has been reacted with various chelating ligands in order to augment the metal sorption capacity and selectivity of the resin. The chelating ligands used include ethylenediamine, diethylenetriamine, diethanolamine, dimethylglyoxime, L-cysteine, thiourea, dithiooxamide, glyoxal-bis-2-hydroxyanil, salicylaldehyde-ethylenediimine, and glyoxal-bis-2-mercaptoanil. The aminolysis of the pendant epoxy groups with the oligoamines has been performed in pyridine under reflux conditions, while the addition reactions with the other ligands which are alkali soluble have been carried out at room temperature in a mixture of dioxane and aqueous KOH using tetra-n-butylammonium iodide as the phase transfer catalyst. The products are found to possess high capacity and selectivity in metal sorption depending on the ligand attached

Use of maleic anhydride-grafted polyethylene as compatibilizer for HDPE-tapioca starch blends: Effects on mechanical properties

Tapioca starch in both glycerol-plasticized and in unplasticized states was blended with high-density polyethylene (HDPE) using HDPE-g-maleic anhydride as the compatibilizer. The impact and tensile properties of the blends were measured according to ASTM methods. The results reveal that blends containing plasticized starch have better mechanical properties than those containing unplasticized starch. High values of elongation at break at par with those of virgin HDPE could be obtained for blends, even with high loading of plasticized starch. Morphological studies by SEM microscopy of impact-fractured specimens of such blends revealed a ductile fracture, unlike blends with unplasticized starch at such high loadings, which showed brittle fracture, even with the addition of compatibilizer. In general, blends of HDPE and plasticized starch with added compatibilizer show better mechanical properties than similar blends containing unplasticized starch. (C) 2001 John Wiley & Sons, Inc

Kinetics of Anhydride Curing of lsophthalic Diglycidyl Ester Using Differential Scanning Calorimetry

The cure reaction of a model diglycidyl ester, bis- (2,3-epoxypropyl) -1,3-benzenedicarboxylate, with hexahydrophthalic anhydride as the curing agent and benzyldimethylamine as the catalyst, was studied by differential scanning calorimetry using an isothermal approach over the temperature range 100-135°C. The results indicate that the cure reaction is autocatalytic in nature and does not follow simple nth-order kinetics. A semiempirical equation for autocatalytic systems containing two rate constants and two reaction orders, viz., 0.5 and 1.5, provided a good phenomenological description of the cure kinetics up to the point of vitrification. With the inclusion of a diffusion factor into this model, it was, however, possible to predict with precision the cure kinetics over the whole range of conversion covering both pre- and postvitrification stages and over the entire temperature range of 100-135°C employed for isothermal curing