Iranian polymer journal
Volume:15 Issue: 2, 2006

An investigation was conducted based on: (1) The study of cure mechanisms and kinetics of diglycidyl ether of bisphenol A (DGEBA) using imidazole (H-MI) and 1-methyl imidazol (1-MI) as the curing agents and, (2) the study of some of the properties of the cured epoxy resins. The cure kinetics of DGEBA was studied using dynamic differential scanning calorimetry (DSC) in various low concentrations (>0.5 mol%) of the curing agents. Kinetic analysis using integral procedure on dynamic DSC data indicates that both H-MI and 1-MI are effective curing agents. The curing reaction of DGEBA with H-MI took place almost 10oC lower than the temperature of its curing reaction with 1-MI. Small low temperature shoulder peaks were observed for both curing systems and for all studied concentrations which are related to the formation of adduct. The formed adduct will initiate the etherification reaction which appears as a large high temperature exothermic peak in dynamic DSC thermogram. Water absorption, chemical resistance to acetone and sodium hydroxide solution, and thermal oxidation of the cured systems are also studied. The DGEBA/H-MI and DGEBA/1-MI cured systems indicated similar properties.

Emulsion copolymerization of vinyl chloride with vinyl acetate comonomer was performed. Different conditions of initiators, emulsifier, and comonomer concentration were chosen in order to investigate the copolymerization reaction. Potassium persulphate, a mixture of stearyl alcohol and sodium lauryl sulphate (SLS) were used and reactions were performed at 55oC in a pressurized reactor. Two region of pressure change were distinguished in the pressure-time curves in which by increasing the initiator concentration the flat region was shortened and the descending region showed a higher slope indicating higher reaction rate. Higher initial pressure was found in higher emulsifier concentration while higher pressure drop was achieved in the second region of pressure-time curves. Effect of comonomer content on heat release during copolymerization was studied. Conversion and intrinsic viscosity of the copolymers and their correlation with reaction parameters were also investigated.

The effect of annealing and pressure were studied on the crystalline structure and melting of a random copolymer of propylene with low content of ethylene. The copolymer samples were compression molded at different pressures and while thesample remained under the press, slowly cooled to room temperature. The result was acrystalline structure of both α- and γ-form with no substantial increase in proportion of theγ-phase with the amount of pressure. Annealing of the samples at temperatures higherthan 408 K, showed two melting endotherms which were attributed to the melting ofspecies produced by molecular segregation during annealing and rapid cooling. Observation of the sharp melting endotherm at higher temperature after annealing couldbe related to the transformation of less ordered α1- structure to a more ordered α2- form.

The dynamic rheological properties of injection moulding of feedstock powder-binder blends (suspension) based on iron powder and HDPE (High Density Polyethylene)were investigated by using a parallel plate rheometer. The solid content ranging from 30 to 60 vol% of the total volume of loaded metal powder, compatibilizer, stearic acid, and stearamide. The dynamic rheological response of the materials was used to analysis the effect of the mentioned factors on the material functions of the mixtures (dynamic viscosity η*, storage modulus G’, and loss modulus G”) at frequency range 0.1- 100 s-1. These parameters showed large differences in the response of the suspensions with changes in loading and addition of compatibilizer. All dynamic parameters increase by increasing the volume fraction of solid loading. As compatibilizer, stearamide shows asignificant effect on rheological behaviour of suspensions. Falkner-Schmit models wereused to fit the experimental rheological data. It was found that our experimental data andmodified composition fit the modified forms of these models.

Shape memory polymers are defined by their ability to store and recover strains when subjected to a particular thermo-mechanical cycle. The thermomechanical behaviour of shape memory polymers can be tailored by modifying the molecular structure of the polymer or by using the polymer as a matrix of multiphase composites. In the present paper, we have presented the shape memory behaviour of functionalized multi-wall carbon nano tube (MWNT) reinforced segmented polyurethane (SPU) copolymer.The experimental results showed that the shape memory effect of developed MWNTreinforced SPU composites were influenced by MWNT weight fraction in the polymermatrix. MWNT At low concentration in the SPU does not have much influence on shapememory behaviour. However, the shape recovery properties were improved for the SPUhaving 2.5 wt% of MWNT. All the SPU/MWNT-SPU samples showed excellent shape fixity.

The effects of four low-profile additives (LPAs) namely poly (vinyl acetate) (PVAc), poly (methyl methacrylate) (PMMA), general purpose polystyrene (PS), and a high density polyethylene (HDPE) on the volume shrinkage of two series of unsaturated polyester (UP) resins with different chemical composition or structure have been investigated by volume shrinkage method. Different low cure temperatures from 25 to 70oC have been used to cure the specimens. Within limits of this study, it was found that shrinkageincreases as the curing temperature increases. In addition, our studies show thatthere are two phase transitions for UP resins containing PVAc and PMMA cured at lowtemperatures. Adding LPAs to the neat UP resins can decrease the volume shrinkage todifferent extents, depending on the types of LPAs added and the kind of UP resin used.Results show that the nature of UP resin has a significant effect on the amount of volumeshrinkage but, the trend is similar for each kind of LPAs. In both unsaturated polyesterresins the best, second best, and worst shrinkage control obtained by adding PVAc,PMMA, and PS, respectively. But, surprisingly HDPE has a good shrinkage control effectat 70oC.

Film blowing is the most important method in producing polyethylene films. For years, low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) blends have been used in blown film manufacture. In this paper basic mathematical models and response surface graphs have been used to illustrate the relationship between blown film fabrication variables and mechanical and optical properties of 50μm films made from LLDPE and LDPE blends. These films are currently used in various non-barrier packaging applications. Using a Box-Behnken statistical design experiment methodology, the effects of LLDPE/LDPE ratios (25-75%), blow up ratio (1.5-2.5), melt temperature (215-235oC) and frost line height (1-3D) were evaluated on the mechanical properties, e.g., tensile and tear properties in both machine direction (MD) and transverse direction (TD) and impact strength as well as optical property such as haze. The R2 values of all the responses of mathematical models are obtained to be more than 0.85 which is an indication of very good fiting of the model with the experimental data of response surface method used. Although this study is confined to the equipment and resin types used, it can offer some curves and equations for predicting the properties of produced films. The processors can use these data to find the first approximation of the most important blown film parameters to achieve their favorite product properties.

Cyclopentene is known to undergo equilibrium polymerization through a metathesisreaction which its bulk and solution polymerizations have been thoroughly investigated.However, we have found that under specific experimental conditions, this monomer polymerizes in the gas phase. The gas phase polymerization is defined here as the conversion of pure gaseous monomer into polymer in the condensed phase. Pure gaseous cyclopentene is found to polymerize on a glass surface in the upper part of theampoule above the liquid phase when the polymerization is initiated with only tungstenhexachloride. Polymerizations are carried out under high vacuum and in the 10-60oCtemperature range. In presence of methanol, the colourless formed polymer shrinksslightly, then it can be removed easily from the glass surface and simply dried under vacuum without any other purification process. From kinetic measurements, an overall activation energy of 63.47 kJ/mol is obtained for the conversion of one mole of gaseousmonomer to one unit of condensed polymer. GPC Chromatograms of polymer samplesare compared with chromatograms of polystyrene standards obtained in the same conditions in chloroform. All polymer chromatograms show a narrow molar mass distribution. Elution peaks of the polymer correspond to peaks obtained for the standards with high molar mass ranging from 2×104 to above 2×106 g/mol. 1H NMR Spectra at 200 MHz show no loss of double bonds in the polymer, nor any presence of tertiary proton. This results indicate that the polymer is linear and branching or cross-linking, if present, cannot be detected. Spectra obtained through 13C NMR spectrometry at 22.63MHz allow the determination of the proportion of cis and trans configurations.