Iranian Journal of Polymer Science and Technology
Year:2004 | Volume:17 | Issue:3 (ISSUE NO. 71)|Papers Count:7

To determine the kinetics characteristics of thermoset resins, it is required to optimize curing conditions due to their dependency on time, temperature and curing conditions. In this work, curing kinetics of epoxy resin 5052, with amine-based hardener was investigated using DSC at nonisothermal conditions with various heating rates. Kinetic parameters were firstly deduced experimentally using isoconversional method, which was introduced by Malek. Then, by choosing Sestak-Berggren model, the experimental data obtained from DSC showed good agreement with this model. Considering this model, it is able to interpret the curing behavior of resin at various thermal and time dependent conditions.

Sugar cane bagasse was delignified to prepare a cellulose pulp. The pulp was modified by graft copolymerization with styrene monomer, using potassium persulfate (KPS) as initiator. Ethylene glycole dimethacrylate (EGDM) and divinylbenzene (DVB) were used as cross-linkers to prepare a three-dimensional grafted network with maximum toluene absorption capacity. The graft polymerization variables such as: KPS, EGDM, (or DVB), time and bath temperature of the reaction were optimized. Toluene uptake by the resin prepared under the optimized conditions such as: bagasse 4.7%, styrene 15.6%, KPS 1.09%, EGDM 0.78%, temperature 80°C, time 1 h, stirrer rpm 400 was measured to be 800%.

In this study, to increase the dye absorption capacity of polyester fibers, they were pre-treated in water and tetrachloroethylene using microwave and exhaustion method. The results revealed that pre-treatment in C2Cl4 and dyeing by microwave irradiation leads to a better dye absorption in comparison to untreated fibers. Finally, pre-treated fibers in water and the other pre-treated and untreated samples dyed by common exhaustion method.

Alpha cellulose pulps contain 90-98% alpha cellulose. Alpha cellulose is an important raw material for cellulose derivatives production. Wood and its residues are main sources of alpha cellulose. In order to prepare alpha cellulose from poplar sawdust, the following steps were carried out: three types of prehydrolysis including: water, 5% sulfuric acid and 20% potassium hydroxide for pentosan removal, then, three types of cooking liquor including: Kraft liquor,50% aqueous-ethanol with 4% NaOH and a liquor compound of acetic acid, hydrochloric acid and acetone for delignification (pulping), and finally three types of bleaching sequences including: CEH, HEHEP and CEHEP for residual lignin removal and enhancement of alpha cellulose purity. In prehydrolysis with water and cooking with liquor compounds of acetic acid, acetone and hydrochloric acid and bleaching sequence of HEHEP, the lowest percentage amount of alpha cellulose was gained. In prehydrolysis with potassium hydroxide and cooking with Kraft liquor and bleaching sequence of CEHEP the highest value of alpha cellulose was gained. Cellulose chains length (degree of polymerization) was in contrast to those of alpha cellulose values.

Superabsorbent polymers can help to improve soil conditions by collecting and storing rain water and irrigation water that would be otherwise lost due to gravity and/or run-off due to their water retention properties. This phenomenon enhances the irrigation efficiency particularly in arid and semi-arid regions of the world. The objective of this study was to evaluate the application of superabsorbent polymers on soil water capacity and soil moisture characteristic curve. Two computer models, RETC and Rosetta, were used for analysis. The RETC program used the parametric models of Brooks-Corey and van Genuchten to represent the soil water retention curve, and the Rosetta used the van Genuchten model based on neural networks. Two polymers, PR3005A and Super AB A100 in four levels, 2, 4,6 and 8 g/kg were mixed with three soil textures, sandy, loamy and clay. The result of the soil moisture characteristic models showed that for each texture, superabsorbent polymers caused increase of the residual water content (θr), saturated water content (θs) and soil moisture gradient curve. Air entry value, hb = 1/α,increased in sandy soil, but decreased in the other soils. The result of the statistical analyses showed that there was a significant difference between samples containing polymers and the control (without polymer), between level of polymer application and the type of polymers. The plant available water increased from 1.5 to 3.5 with superabsorbent polymers in two levels,6 and 8 g/kg. Also soil capillary porosity increased, particularly in the sandy soil.    

Emulsion polymerization in gas-liquid systems has complications caused by the existence of a gas monomer. Entrance of the gas monomer into the reaction sites is the main problem which depends on many variables. In reactor scale up, different parameters such as: height to diameter ratio, L/D, agitation rate, gas injection method and the amount of raw materials are important. By raising the reactor volume from 1.8 to 7.5 L, the amount of the raw material increases. On the other hand, the copolymer chain composition changes due to unscaled height to diameter ratio in reactor volume expansion, which decreases the ethylene mass transfer. Furthermore, the trend of vinyl acetate conversion is almost the same in both systems. In addition, the measured heat build up via differential and integral methods showed dependency on the rates of consumed ethylene and vinyl acetate.