فهرست مطالب جلیل مرشدیان

Membranes are thin layers that act as selective barriers to separate the components of materials and control the mass transfer between different phases. Therefore, their two main functions include: component selectivity and the permeability characteristics. Membranes according to their material sources are classified into four categories referred as polymeric, ceramic, metal and liquid types. Among these, polymeric membranes are the most favorable materials because of their availability in various chemical structures, their optimum physical properties and lower prices. Polymeric membranes are produced by four main methods known as solution casting, stretching, template leaching and track etching. Among them, stretching technique is inexpensive and because no solvent is used in this process, stretching method has lower environmental impacts. Among different polymers, polyolefines such as polyethylene (PE) and polypropylene (PP), due to their lower price, semi-crystallinity, good mechanical properties, chemical stability and easy process ability, are more appropriate for manufacturing of polymeric membranes by stretching method. Porous membranes are used in applications such as battery separators and drug delivery devices for controlling the permeation rate of chemical components. In this paper, we present some useful information on the above subject by reviewing the related published works in this area.

Hypothesis: Polymer nanocomposites have found enormous applications owing to superior physical and mechanical properties such as modulus, strength and barrier behaviour, etc. Contrary to polymer microcomposites, polymer nanocomposites benefit from lower density and being less problematic in processing. In this study, nanocomposites of polyolefin elastomer (POE)/nanosilicon carbide (SiC) and polyolefin elastomer/nanoclay with different percentages of nanoparticles were prepared using melt mixing method in the presence of vinyltriethoxy silane as interfacial modifier.
Nanocomposite samples were prepared in a Brabender internal mixer using a roller mixing equipment. The fill factor was selected as 0.75. The mixing was carried out at a speed of 60 rpm at 120°C. The resulting nanocomposites were then subjected to various tests to investigate their physical, mechanical and rheological properties.
Findings: Sheet-like nanoclay particles have higher aspect ratio compared to spherical nanoSiC particles. Nevertheless, the results indicated that POE/SiC nanocomposites had higher tensile strength and elongation-at-break compared to nanoclay-reinforced composites. This was attributed to higher interactive efficiency between SiC nanoparticles and POE matrix. The moduli of nanocomposites at similar content of nanoparticles showed the same values regardless of the type of nanoparticles. Higher rheological properties were observed for nanoclay nanocomposites, though; the amount of increase was lower than those reported in literature. Morphology investigations of SiC and clay nanocomposites exhibited a comparable degree of dispersion of nanoparticles for both types of nanocomposites at similar compositions. Thermal properties of nanocomposites were studied by thermogravimetric analysis and differential scanning calorimetry. The results showed that the melting temperature and degree of crystallinity of both types of nanocomposites decreased with increasing nanoparticles content; however, the observed decrement was higher for POE/SiC nanocomposites. Thermal stability of POE/clay nanocomposites was higher, which could be attributed to the nanoparticle geometry.

In order to increasing of hydroxy functionality of HTPB, an in-situ nitroxide mediated polymerization (NMP) of 1,3-butadiene was carried out in presence of TEPA as a polyfunctional nitroxide precursor. The effects of this new hydroxyl-terminated polybutadiene on thermal and dynamic-mechanical properties of its corresponding polyurethane elastomer were studied by DSC and DMTA tests. A significant enhancement in crosslink density of the elastomeric product with small increase in glass transition temperature was achieved using PFHTPB. Also the absence of any endothermic peak in DSC thermogram was an indication of no crystalline domain existing in these samples.

In this research the influence of using waste Poly Ethylene Terephthalate on the mechanical and rheological properties of wood flour filled PP composites has been studied. PET contents varied from 10-33 wt%. Mechanical properties were characterized by tensile testing، while their fracture resistance was determined by impact measurements. The melt rheological behavior of the composites was also studied by a rheometer in the oscillatory mode and dynamic rheological properties such as complex viscosity، storage modulus، loss modulus and damping factor were evaluated at190°C. The results showed that stiffness increases by adding waste Poly Ethylene Terephthalate. PET when added in low concentrations، caused tensile strength to be lower than that of PP composites filled with pure wood flour. Increasing the concentration of waste PET، led to composites with higher amount of tensile strength. The samples containing waste PET had higher complex viscosity and storage modulus than composite without PET. Likewise، it was observed that the damping factor in the PP/Wood composite decreased by incorporating waste PET to the compositions.

In order to increasing of hydroxy functionality of HTPB an in-situ nitroxide mediated polymerization (NMP) of 1،3-butadiene was carried out in presence of TEPA as a polyfunctional nitroxide precursor. The multi-modal molar mass distribution of the product was elucidated by reductive hydrolyzation of the oligomeric product. The new polyfunctional hydroxyl-terminated polybutadiene (PFHTPB) was characterized and used in preparation of an HTPB-based polyurethane. The effects of this new hydroxyl-terminated polybutadiene on mechanical properties and thermal stability of its corresponding polyurethane elastomer were studied. The mechanical and thermal stability characterization of the elastomer were evaluated by tensile and TGA tests. Due to an efficient increase in crosslink density of the PFHTPB-based polyurethane elastomer، a significant enhancement in mechanical properties (more than 2. 5 fold in tensile strength with small increase in elongation at break) was achieved. Furthermore the thermal stability of PFHTPB-based PU was comparable with its corresponding HTPB-based polyurethane elastomer.