دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و سوم شماره 1 (پیاپی 105، فروردین و اردیبهشت 1389)

Sandwich panels as composite materials have two external walls of either metallic or polymer type. The space between these walls is filled by hard foam or other materials and the thickness of different layers is based on the final application of the panel. In the present work, the extent of variation in core density of polyether urethane foam and subsequent flexural and compressive changes in sandwich panels with glass or epoxy face sheets are tested and investigated. A number of hard polyether urethane foams with different middle panel layers density 80-295 kg/m3 are designed to study the effect of foam density on mechanical properties including flexural and compressive properties. Flexural and compressive test results show that increased core density leads to improved mechanical properties. The slope of the curve decreases beyond density of 235 kg/m3. The reason may be explained on the limitation of shear intensity in increasing the mechanical properties. In this respect an optimum density of 235 kg/m3 is obtained for the system under examinations and for reaching higher strength panels, foams of different core materials should be selected.

CO2/CH4 gas separation is a very important applicatable process in upgrading the natural gas and landfil gas recovery. In this work, to investigate the membrane separation process performance, the gas permeation results and CO2/CH4 separation characteristics of different prepared membranes (via blending different molecular weights of polyethylene glycol (PEG) as a modifier with acrylonitrile-butadiene-styrene (ABS) as a backbone structure) have been studied. Furthermore, SEM analysis was carried out for morphological investigations. The effect of PEG content on gas transport properties on the selected sample was also studied. The effect of pressure on CO2 permeation was examined and showed that at the pressure beyond 4 bar, permeability is not affected by pressure. The results showed that more or less in all cases, incorporation of PEG molecules without any significant increase in CH4 permeability increases the CO2/CH4 selectivity. From the view point of gas separation applications the resultant data are within commercial attractive range.

The acrylated epoxidized soy oil (AESO) was synthesized from epoxidized soy oil and its properties were investigated. Wheat straw particle boards were produced by the synthesized resin with 8% and 13% contents based on straws weight at three pressing times: 8,10 and 12 min. Boards’ modulus of rapture, modulus of elasticity, internal bonding, minimum degree of thickness change and water absorption were investigated. The swelling and water absorption results showed that the highest amounts of boards’ modulus of rapture, modulus of elasticity and internal bonding with board samples of lowest thickness belong to boards made from 13% resin content with 12 minute pressing time; and these amounts were in range of EN particleboard standard and the produced particleboard which totally compete with wood particleboard. The AESO-wheat straw particleboard due to its non-formaldehyde emission and bio-based structure can substitute wood particleboard effectively.

An ultra-glide twin screw extruder is employed to allow the quick and easy removal of the screws from the fixed processing section within few seconds, probing the current degree of the melting state, the dispersive and distributive processing steps and finally the level of morphology development along extruder screws. For morphological studies the molten samples, collected from different points along the screw length, were quickly frozen in liquid nitrogen and observed under a scanning electron microscope. The morphology development along screws was studied for the compatibilized PA6/ABS blends with different ABS contents. It was observed that the co-continuous morphology was formed in an initial stage of mixing, which then transformed into a refined co-continuous structure and developed along the extruder. The level of co-continuity decreased at higher ABS content. In addition the effect of processing condition on morphology development was studied. In view of the mechanical properties, the effect of morphology on the impact strength could be elucidated. It was found that not only the co-continuous morphology but also the level of co-continuity plays an important role in determination of ultimate impact properties. The impact strength was lowered to 35 kJ/m2 from initial value of 47 kJ/m2 by increasing the ABS content from 60 to 70 wt%.

Polyacrylontrile synthesis, via atom transfer radical polymerization, is studied in various initiator concentrations, transitional metal catalyst and different concentrations of CuBr2. The variations of monomer conversion and the lin- earity of semi-logarithmic kinetic profile which is the evidence of living polymerization and constant radical concentration in the reaction medium, were revealed by gas chromatography technique (GC). Gel permeation chromatography (GPC) studies revealed that, the number average molecular weight increases linearly against monomer conversion, an indicative of living nature of the polymerization process. Additionally, the conversion, apparent rate constant and number average molecular weight increased with increased initiator concentration as well as the transitional metal complex concentration. However, addition of CuBr2 lowered conversion, kapp, and the number average molecular weight of polyacrylonitrile. Molecular weight distribution of synthesized polymers broadened with increased initiator concentration and also transitional metal complex concentration. However, addition of CuBr2 has resulted in narrower molecular weight distribution polyacrylonitrile. Moreover, all the samples experienced a drop in PDI value from nearly 2 to almost 1.1 as the reaction progressed.

Nanocomposite vulcunizates based on styrene-butadiene rubber (SBR), organoclay and a conventional sulfur curing system were prepared by melt blending process in an internal mixer. In order to study the effects of the type of interfacial compatibilizer on the properties of SBR and clay nanoparticles,three types of compatibilizers, maleic anhydride grafted ethylene-propylene diene rubber (EPDM-g-MAH), acrylonitrile-butadiene rubber (NBR) and epoxidized natural rubber (ENR50) have been used. The nanocomposites have been compared together from view point of their curing behavior, rheological and mechanical properties. The developed microstructure and dynamics of the macromolecular chains in proximity of the clay nanolayers have been characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and melt rheo-mechanical spectroscopy (RMS). Curing behavior of the prepared nanocomposites has been evaluated using a rubber curing rheometer. EPDM-g-MAH and ENR50 showed to enhance the interactions between SBR chains into clay tactoids much stronger than NBR as a compatibilizer. These were consistent with the dynamic mechanical thermal analysis (DMTA) data as well as macroscale mechanical properties tested on the samples.

Crosslinked poly(acrylic acid)s were prepared using two types of crosslinker by precipitation polymerization method in a binary organic solvent. N,N’-methylenebisacrylamide (MBA) and polyethylene glycol dimethacrylate (PEGDMA-330) were used as low-molecular weight and long-chain crosslinkers, respectively. The effect of various types of crosslinkers on polymer characteristics (i.e., gel content, equilibrium swelling, glass transition temperature, and rheological properties) was investigated. Maximum amount of viscosity was obtained by using long-chain crosslinker. The Flory-Rehner equation and rubber elasticity theory were used to discuss the network structure of polymer. It was observed that, the glass transition temperature (Tg) of the synthesized polymer containing PEGDMA-330 is higher than that of polymer containing MBA. Apparent and rotational viscosity were used to determine the optimal crosslinker type. In addition, the consistency coefficient (m) and flow behavior index (n) parameter of Ostwald equation were investigated as well.

The neat bitumen, an oil refining by-product, has its own inherent weakness under long-time loading at low and high temperatures. These performance limitations of neat bitumen have led researchers to modify its physical andmechanical properties. According to several studies, polymers can be used to modify the properties of bitumen. Due to much lower production costs and aiming to reduce environmental impacts, recycled waste polymers are preferred as compared with virgin polymers. In this study, the effect of recycled waste polymers including crumb rubber modifier (CRM), polyethylene and latex and non-polymeric materials such as natural bitumen (NB) and heavy vacuum slops (HVS) cut on physical and mechanical properties of vacuum bottom residue (VB) of crude oil distillation was investigat-ed. Based on the results, recycled waste polyethylene and NB can improve the performance grade of VB at high temperatures and CRM, latex and HVS can improve the performance grade of VB at low temperatures. Thus, by designing various blends of these additives with VB, different modified bitumens can be directly obtained from VB without any need to air-blowing process.