Iranian Journal of Polymer Science and Technology
Year:2004 | Volume:16 | Issue:5 (ISSUE NO. 67)|Papers Count:9

Immobilized ligands, produced by grafting the ligands to an insoluble base are employed in metal extractions, and chromatography and the ligands the transition metal complexs are utilized as catalysts in various reactions. Silica, for its high thermal stability and its chemical has been employed as a matrice base. In this research insoluble amine ligands have been prepared with two different methods. First by immobilization of the compound (CH3O)3 Si(CH2)3NH2 on activated silica and second method by incorporation of this compound into a siloxane polymer by co-hydrolysis using Si (OC2H5)4. The latter gives robust materials with a higher content of available ligand groups than their immobilized counterparts, as measured by the uptake of protons and copper (II) ion.

Differential scanning calorimetry (DSC) technique was employed to study thermal behavior of polyester and epoxy/polyester powder lacquers cured under different curing schedules. The flow properties of the powders were determined using inclined plate flow test. Corrosion performance of the powder lacquers on the degreased mild steel substrate was also investigated. In addition, mechanical properties of samples, including adhesion strength and hardness, cured at various temperatures were evaluated. DSC curves reveal that heating schedules do not significantly affect the thermal behavior of the powders, as well as the corrosion performance and mechanical properties of the samples. Inclined plate flow tests revealed that the higher curing temperatures may improve leveling property of the molten powder and surface appearance of the cured samples.

Viscoelastic behavior of bitumen, recycled polyethylene (RPE) and RPE-modified bitumen were investigated in a wide frequency range. Based on microscopic observation, the RPE particles are suspended in the bitumen matrix. The radius distribution of particles in the bitumen is 5-25 µm and for washing particles in the range of 1 to 5µm. In addition, the RPE particles are completely expanded in the bitumen. This morphology is attributed to the physical interactions and it leads to formation of physical structures like clusters and physical networks. RPE in bitumen is appeared as two mixture phases. Viscoelastic behavior of RPE-modified bitumen was considered as a two-phase composites which the polymer particles were dispersed in bitumen matrix. It is observed that the rheological and viscoelastic properties change largely with addition of only 1%RPE. On the other hand, the rheological properties of RPE-modified bitumen change largely by aging of bitumen. This has been attributed to absorption of residual oil by polymer particles and the interactions between asphalt constituent and polymers. As a consequence, the changes in rheological properties of bitumen during mixing should be considered separately. For this reason, the rheological data is measured on polymer modified as well as the blank bitumen (called Shahed) with the same thermomechanical history as reference. Firstly, the shear modulus curves were obtained in the wide range of frequencies. Then the equations in the fourth order were fitted in the experimental results. These equations were used for calculation of the unmeasured points in the intervals of the experimental results. Christensen and Lo's model was used to predict the viscoelastic behavior of RPE modified bitumen. This model is based on a representative element volume (REV) accounting for a morphology analysis. Based on the use of the mechanical model and the experimental results, the viscoelastic behavior of RPE-modified bitumen depends not only on the relative amount and the polymer distribution with in the matrix, but also on the changes in the mechanical properties of bitumen in the mixing process.

In the last decades, extensive research works have been devoted to bitumen and asphalt modification by using polymeric thermoplastic-elastomers. In this research a physical thermoplastic elastomer was prepared by mixing polystyrene (PS) and polybutadiene (PB) for bitumen modification purposes. These blends were introduced into bitumen for making polymer-bitumen mixtures. Then, stabilization mechanism and mechanical properties of the mixture were studied by optical microscopy and conventional tests such as: Frass test, softening point, penetration, performance grade and penetration index. The PS/PB (75/25) blend forms larger PS droplets and shows minimum stability among the blends. The co-continuous composition of PS/PB blend (27/73) is stable and PS droplets are very well dispersed and its particle sizes are the lowest. In the next step, PS/PB/SBR compatibilized blend was mixed with bitumen and than further studies were carried out. The results show that mechanical properties and elastic recovery of these blends are highly improved as compared with the former non-compatibilized blend admixtures.

If the bodies, such as the head and nose of missile, nozzle or combustion chamber of the rocket, which are exposed to sever heat, are not protected against it, then they cannot perform for the purpose they are designed. One of the recommended methods to protect these systems against heat is the usage of the ablative insulators. In this work, the thermal behavior of ablative composites of silicon rubber matrix and glass reinforced fibers was studied and modelled. For this purpose, the mass and energy equation in ablation conditions were simultaneously solved numerically using finite difference method and the various related parameters of the insulator were determined as a function of temperature and time. This modelling will allow to predict the proper thickness of the ablative composite in the actual service conditions. This method can also be used in designing of the other ablative composites.

Phenolic foams are one of the most customer consuming polymeric foams which can be prepared from resoles or novolacs. It is possible to apply an external thermal reservoir to achieve curing and expansion simultaneously, or to use an acid as curing agent, without external heating, and utilizing heat of curing reaction for expansion of the foaming mixture. Because of economic point of view and ease of processing, the latter method is preferable. However, the existing problem is that the resole resin must be so active to react with acid curing agent and produce suitable heat for foaming. Also physical properties of resin, such as, viscosity plays great role in the efficiency of resin in foam processing. In this research, resole resins were prepared by polycondensation polymerization of phenol and paraformaldehyde in presence of different catalysts. Their properties were analyzed by analytical techniques such as FTIR, 1H NMR, DSC-TG and VPO in order to produce suitable and efficient resoles for preparation phenolic resin foams through acid curing process.

Ziegler-Natta catalyst system of VCl4/Al(iBu)3/CHCl3 for solution polymerization of ethylene, propylene and ethylidene norbornene (ENB) was used. ENB Was added batchwise, while ethylene and propylene gases were added continuously depending on the reactivity of the catalyst. The pressure inside the reactor was kept constant at 1±0.1 bar, but the relative pressure of propylene to ethylene was Pp/Pe=1.3:1. CHCl3 was used as a promoter. Polymer was precipitated from n-heptane using methanol as a non-solvent. Activity of the catalyst was decreased by polymerization time. The behavior also affected the composition of EPDM obtained. Ethylene and ENB content of the polymer almost increased linearly with smooth slope, while ENB content of polymer decreased sharply, somewhat exponentially decay behavior was observed.