Preparação de membranas poliméricas porosas a partir de técnicas de espumação com agentes físicos de expansão
Resumo
The objective of this master’s thesis was to develop a process of
manufacturing porous polymer membranes for microfiltration by a one-step
foaming technique, using carbon dioxide (CO2) as physical blowing agent and
ethanol (etOH) as co-solvent. Initially this work was conducted with PC/PMMA
polymer blend samples in hollow fiber geometry, varying the blend composition,
foaming temperature and the co-solvent content. It was determined that the
blend composition PC/PMMA 60/40, sorbed with CO2 at 40°C with an ethanol
content of 10%mol (CO2 molar basis) provided an opened porous morphology
with potential for filtering applications. However, the pronounced fiber wall
expansion ratio after the foaming process resulted in a considerable reduction
of the fibers inner diameter, hindering its application as a hollow fiber
membrane. Thus, it was necessary to change the hollow fiber geometry for flat
films. DSC analysis showed that the PC/PMMA is a partially miscible blend.
Gravimetric sorption tests revealed a higher sorption of diluents in polymers
after adding ethanol as co-solvent with CO2, resulted from a stronger affinity
between the polymers and the CO2/etOH mixture. Gas permeation tests
showed a maximum pore size smaller than 10 micrometers, which is considered
as an upper limit in the definition of microfiltration membranes. However, when
compared to commercial membranes, the samples showed a considerably
lower water permeation. With respect to the samples morphology, SEM images
of the flat film samples revealed a cross section formed by a porous central
region with micrometric interconnected pores, while the skin layers were
composed of dense and foamed regions.