فهرست مطالب zahra shoeyb

Polymeric hollow fiber membranes with high area per unit volume are proper configurations in membrane technology. Linear low density polyethylene (LLDPE) with specific properties is a suitable polymer for fabrication of hollow fiber membrane through thermally-induced phase separation method. The aim of this study was to evaluate the effect of different extractants, take-up speed and bore fluid flow rate on the structure and performance of LLDPE hollow fiber membranes. The LLDPE and mineral oil were heated in order to obtain a homogeneous solution and fed to spinneret. The hollow fiber extruded from the spinneret entered into a coagulation bath and then extracted by different extractants. The effects of ethanol, hexane and acetone with different solubility parameters were studied on the structure of membranes. In the following, the effect of take-up speed and bore fluid flow rate was studied with respect to the structure as well as performance of membranes extracted with acetone. Membranes extracted with ethanol showed low porosity and water permeability which implied that ethanol cannot extract diluent. Due to similar solubility parameter of hexane and LLDPE, hexane swells the amorphous region of the polymer and it blocks the pores. Acetone extracted the diluent successfully and the SEM images confirmed porous structure of the membranes. The other results showed that pure water permeability, surface roughness and tensile strength of the hollow fiber membranes increased when the take-up speed was increased. In addition, raising the bore fluid flow rate improved the strength of the membrane while it reduced the water permeability. Finally, it was revealed that the rejection of membranes in the separation of collagen protein solution was increased by increasing bore fluid flow rate and also decreased slowly by increasing the take-up speed.

The adjustment of material composition in fabrication of modified polymeric membrane has been considered the most efficient and easiest method. For this purpose blended membranes of high density polyethylene (HDPE) –ethylene vinyl acetate (EVA) were prepared by thermally induced phase separation method. The impact of EVA in the presence of diluent on the crystalization temperature was assessed using differential scanning calorimetry (DSC). The obtained results showed that EVA has no significant effect on the crystalization temperature of HDPE. The absorption frequencies at 1248 and 1749 cm-1، respectively، due to C-O and C=O streching vibrations of EVA functional groups، confirmed the existence of EVA in HDPE membrane. The pure water permeability of HDPE/EVA blend was measured and compared with that of neat HDPE membrane. The results showed that an EVA content up to 2. 5 wt% raised water permeability considerably and the leafy structure of the membranes contracted and the pure water permeation dropped with higher EVA content. The results of porosity measurement and scanning electronic microscopic (SEM) analysis also confirmed these findings. Contact angel measurements and atomic force microscopy (AFM) examinations and static absorption of collagen protein on the membrane surfaces revealed that EVA content up to 5 wt% lowered the hydrophobicity of the membrane. By EVA content above 10 wt%، due to the structural alteration on the membrane surface، the contact angel and the collagen absorption on the surface of membrane increased. The measurement of tensile strength showed that with increasing EVA content the mechanical properties of the membranes improved due to interactions of polar groups in EVA.