56
D. Nedeljkovic
or explosive mixtures. Helium as a small, ideally round, non-polar, non-flammable
gas was measured in order to detect potential presence of the pinholes on membranes.
Selectivity of each gas was recalculated versus carbon dioxide.
Results and Discussion
The properties of the synthesized membranes (composition and the appearance) are
presented in Table 2. All presented percentages are mass percentages versus the
overall mass of the membrane.
In the ideal case, the membrane should appear transparent or slightly opaque, and
to be smooth on the touch. Transparent membrane indicates that the zeolite particles
are in good contact with polymer matrix, which indicates that practically all particles
are in contact with additive. Absence of white spots or zones also indicates that the
zeolite particles are evenly distributed through the volume of the membrane. The
presence of the white spots on the membranes indicates that zeolite particles aggregated at the particular position within the membrane, and therefore the distribution
of the zeolite particles is not uniform. As a consequence, the permeation properties are significantly lower in comparison with smooth membranes with uniformous
distribution. Secondary consequence of the agglomeration is reasonable assumption
that zeolite powder particles are not properly surface treated. In other words, most
of the particles remained uncovered by the additive, so the attraction electrostatic
forces prevailed, and agglomeration zones of particles were formed. White color of
the membrane indicates that the contact between the zeolite particles and polymer
chains is bad. If there are voids formed between zeolite particles and polymer chains,
the light refraction will occur, so the membrane is not translucent or opaque. Opacity
of membranes might indicate, at least partially bad contact. However, as they were
not completely non-transparent, it can be assumed that most of the zeolite particles
were covered with appropriate additive, and that the contact between the matrix and
dispersed phase is mainly obtained and only limited amount of the particles were
surrounded by the air gaps. White membranes were not used for the permeability
measurements, but opaque membranes were measured. For each polymer, one sample
was made with pure polymer and one with the polymer and additive (without zeolite
powder) as a control and testing sample. As the gained results for thickness and
appearance were good, membranes with zeolite additives were synthesized.
Analyzing the data from Table 2, it is obvious that application of the n-C14TMABr as an additive significantly improved the appearance of the membrane. There
was no system with better appearance without the additive in comparison with the
system with additive. This improvement was observed for both PEBAX and Polyactive based membranes. In the case of DMAP, it did not show the acceptable results.
Agglomeration was still present in most of the cases, and in some cases membrane
even could not be synthesized. Transparent and opaque membranes were used for
the permeability measurements, and the obtained results are presented in Table 3.
D. Nedeljkovic
or explosive mixtures. Helium as a small, ideally round, non-polar, non-flammable
gas was measured in order to detect potential presence of the pinholes on membranes.
Selectivity of each gas was recalculated versus carbon dioxide.
Results and Discussion
The properties of the synthesized membranes (composition and the appearance) are
presented in Table 2. All presented percentages are mass percentages versus the
overall mass of the membrane.
In the ideal case, the membrane should appear transparent or slightly opaque, and
to be smooth on the touch. Transparent membrane indicates that the zeolite particles
are in good contact with polymer matrix, which indicates that practically all particles
are in contact with additive. Absence of white spots or zones also indicates that the
zeolite particles are evenly distributed through the volume of the membrane. The
presence of the white spots on the membranes indicates that zeolite particles aggregated at the particular position within the membrane, and therefore the distribution
of the zeolite particles is not uniform. As a consequence, the permeation properties are significantly lower in comparison with smooth membranes with uniformous
distribution. Secondary consequence of the agglomeration is reasonable assumption
that zeolite powder particles are not properly surface treated. In other words, most
of the particles remained uncovered by the additive, so the attraction electrostatic
forces prevailed, and agglomeration zones of particles were formed. White color of
the membrane indicates that the contact between the zeolite particles and polymer
chains is bad. If there are voids formed between zeolite particles and polymer chains,
the light refraction will occur, so the membrane is not translucent or opaque. Opacity
of membranes might indicate, at least partially bad contact. However, as they were
not completely non-transparent, it can be assumed that most of the zeolite particles
were covered with appropriate additive, and that the contact between the matrix and
dispersed phase is mainly obtained and only limited amount of the particles were
surrounded by the air gaps. White membranes were not used for the permeability
measurements, but opaque membranes were measured. For each polymer, one sample
was made with pure polymer and one with the polymer and additive (without zeolite
powder) as a control and testing sample. As the gained results for thickness and
appearance were good, membranes with zeolite additives were synthesized.
Analyzing the data from Table 2, it is obvious that application of the n-C14TMABr as an additive significantly improved the appearance of the membrane. There
was no system with better appearance without the additive in comparison with the
system with additive. This improvement was observed for both PEBAX and Polyactive based membranes. In the case of DMAP, it did not show the acceptable results.
Agglomeration was still present in most of the cases, and in some cases membrane
even could not be synthesized. Transparent and opaque membranes were used for
the permeability measurements, and the obtained results are presented in Table 3.