Abstract
In this work composite hollow-fibers were prepared by dip-coating of commercial polypropylene (PP) with a thin layer of ethylene–chlorotrifluoroethylene copolymer (ECTFE). The employment of N-methyl pyrrolidone (NMP) as solvent improved the polymer processability favoring dip-coating at lower temperature (135 °C). Scanning electron microscopy (SEM) analyses showed that after dip-coating the PP support maintained its microstructure, whereas a thin coated layer of ECTFE on the external surface of the PP hollow-fiber was clearly distinguishable. Membrane characterization evidenced the effects of the concentration of ECTFE in the dope-solution and the time of dip-coating on the thickness of ECTFE layer and membrane properties (i.e., contact angle and pore size). ECTFE coating decreased the surface roughness reducing, as a consequence, the hydrophobicity of the membrane. Moreover, increasing the ECTFE concentration and dip-coating time enabled the preparation of a thicker layer of ECTFE with low and narrow pore size that negatively affected the water transport. On the basis of the superior chemical resistance of ECTFE, ECTFE/PP composite hollow fibers could be considered as very promising candidates to be employed in membrane processes involving harsh conditions.
Highlights
Membrane technology has received important attention thanks to socio-economical impulses such as increased environmental concern and the search for cleaner and more energy-efficient technologies [1]
A systematic study was devoted to the evaluation of the effects of the operating conditions of the dip-coating, such as time of dipping and ECTFE concentration, on the properties and the performance in terms of water transport of the selective layer made of ECTFE
According to Equation (1) and using as ideal contact angle for a perfectly smooth surface made of ECTFE the value of 92◦ [19], the roughness (r) of ECTFE coating dramatically decreased by increasing the time of dip-coating and ECTFE concentration
Summary
Membrane technology has received important attention thanks to socio-economical impulses such as increased environmental concern and the search for cleaner and more energy-efficient technologies [1]. Advances in the area of chemical resistant membranes over a large pH range preserving hydrolytic and mechanical stability should lead to many novel applications in the food and pharmaceutical industries for selective recovery of organics and recycling of solvent streams [6], in chemical and petrochemical industries for the separation of mixtures [7] as well as in the recovery of hazardous materials and contaminants from aqueous solutions [8,9]. The current investigation refers to the development of novel composite hollow fiber membranes made by a porous support of PP coated with a thin resistant active layer of ECTFE in order to improve the chemical resistance of the membranes. A systematic study was devoted to the evaluation of the effects of the operating conditions of the dip-coating, such as time of dipping and ECTFE concentration, on the properties and the performance in terms of water transport of the selective layer made of ECTFE
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