to a solid film. After casting of the polymer solution, the
phase inversion can be done in different ways. A first way is
by evaporation of solvent, called evaporation induced phase
separation (EIPS), a second one is by decreasing the temperature, called temperature-induced phase separation
(TIPS), and a third one is by adding a non-solvent to the
solution, called non-solvent induced phase separation
(NIPS). For the last one, two options are possible, by adding
liquid non-solvent, called wet-NIPS or just NIPS, or by
adding vaporized non-solvent, called dry-NIPS or
vapor-induced phase separation (VIPS). The type of structure, dense or porous, symmetric or asymmetric, obtained by
these methods, is highly dependent of the process, its
parameters and the chemicals involved (Bouyer et al. 2011).
For the case of PHAs, Table 6 summarizes some studies that
reported the use of phase inversion to make tailored
structures.
Regarding Table 6, PHAs were processed with the
three phase inversion techniques (EIPS, NIPS, and TIPS).
Moreover, the obtained structures vary from dense symmetric to porous asymmetric. It highlights the potential of
PHAs for membrane fabrication. Since the structure formation depends on numerous parameters, from the chemicals
interactions to the phase inversion conditions, it is difficult to
predict the structure as a function of the process parameters,
but some recurrences may be cited.
The EIPS technique tends to form dense structures.
However, porous structures could be obtained when salts or
other additives, such as PEG, were added. The TIPS technique usually makes porous structures. The NIPS technique
mostly leads to porous asymmetric structures. These general
observations are similar to what has been reported in the
literature for more common membranes made out of
petro-based polymers (Lalia et al. 2013; Tae et al. 2016;
Broens et al. 1980).
In the case of the NIPS technique with the P(3HB4HB)
(13 mol% 4HB)/NMP/water system, the effect of different
parameters has been discussed (Marcano et al. 2015, 2017).
The discussions mainly refer to the demixing rate. Indeed, a
higher demixing rate results in a more porous structure. In
that sense, increasing the PHA concentration increases the
solution viscosity and so decreases the demixing rate, leading to a denser membrane. Increasing the casting thickness
leads to denser membranes. About the influence of the
coagulation bath temperature, with an increase of the temperature the viscosity would decrease and the non-solvent
and solvent diffusivity would increase, leading to a more
porous structure. Nevertheless, for this system, no major
changes were observed when the coagulation bath temperature was varied. The influence of the polyvinylpyrrolidone
(PVP) addition in the dope solution, its molecular weight
and its concentration were studied (Marcano et al. 2017).
The authors were able to increase the pore density and
surface porosity by increasing the PVP concentration. It was
explained by a decrease of the solution viscosity by adding
PVP. However, an additive concentration above 30% had a
reversible effect and decreased the surface porosity.
Solvent casting particulate leaching method was used to
make highly porous scaffolds. Sodium salt crystals or sugar
were used as porogens. The evaporation followed by the
porogens leaching leads to highly porous structures with
pore sizes around 100 µm. Tan et al. worked on this
leaching technique on P(3HB) films and recognized the
potential of this material for separation membrane applications (Tan et al. 2016).
At the end, PHAs can be easily processed via phase
inversion to form tailored structures. Then, it is of interest to
test these structures as potential filtration membranes.
3.2 Separation Purpose
A few examples of concrete separation applications of
PHAs-based membranes have been reported in the literature
(Mas et al. 1996; Villegas et al. 2011, 2015, 2016; Nicosia
et al. 2015; Keawsupsak et al. 2014; Guo et al. 2016).
3.2.1 Pervaporation
Pervaporation is a separation process that finds applications
for dehydration of organic solvents, removal of dilute
organic molecules or organic–organic mixture separation. In
such processes, the solution–diffusion is the most accepted
model to describe the mass transport, so that during the
separation, the selectivity occurs following unequal affinities
between the solutes and the membrane (Jyothi et al. 2019).
Mas et al. were the firsts to consider PHAs-based membranes as candidates for pervaporation applications (Mas
et al. 1996). They made dense membranes by EIPS with
different P(3HB3HV) having different values of HV content.
The membrane performances were analyzed by separation of
an ethanol/water mixture. The flux varied from 0.008 to
0.027 kg m
−2 h
−1 and the separation factor from 5.0 to 12.6
in favor to water permeation. No major correlation was
observed between the HV ratio content and the membrane
performances. However, with the increase of the filtration
time, the flux tends to increase and the separation factor
tends to decrease. It is argued by a progressive deformation
of the macromolecular structure accentuated by the plasticizing effect of ethanol molecules.
Villegas et al. evaluated the performances of a
PHA-based membrane for pervaporation application on
methanol/methyl tertiary butyl ether (MTBE) mixtures
(Villegas et al. 2011). They made P(3HB) dense membranes
by EIPS. Performances were measured as a function of the
feed temperature and feed composition. In the case of
40 mol% methanol/MTBE mixture, the best performances
Polyhydroxyalkanoates (PHAs) for the Fabrication …
185
phase inversion can be done in different ways. A first way is
by evaporation of solvent, called evaporation induced phase
separation (EIPS), a second one is by decreasing the temperature, called temperature-induced phase separation
(TIPS), and a third one is by adding a non-solvent to the
solution, called non-solvent induced phase separation
(NIPS). For the last one, two options are possible, by adding
liquid non-solvent, called wet-NIPS or just NIPS, or by
adding vaporized non-solvent, called dry-NIPS or
vapor-induced phase separation (VIPS). The type of structure, dense or porous, symmetric or asymmetric, obtained by
these methods, is highly dependent of the process, its
parameters and the chemicals involved (Bouyer et al. 2011).
For the case of PHAs, Table 6 summarizes some studies that
reported the use of phase inversion to make tailored
structures.
Regarding Table 6, PHAs were processed with the
three phase inversion techniques (EIPS, NIPS, and TIPS).
Moreover, the obtained structures vary from dense symmetric to porous asymmetric. It highlights the potential of
PHAs for membrane fabrication. Since the structure formation depends on numerous parameters, from the chemicals
interactions to the phase inversion conditions, it is difficult to
predict the structure as a function of the process parameters,
but some recurrences may be cited.
The EIPS technique tends to form dense structures.
However, porous structures could be obtained when salts or
other additives, such as PEG, were added. The TIPS technique usually makes porous structures. The NIPS technique
mostly leads to porous asymmetric structures. These general
observations are similar to what has been reported in the
literature for more common membranes made out of
petro-based polymers (Lalia et al. 2013; Tae et al. 2016;
Broens et al. 1980).
In the case of the NIPS technique with the P(3HB4HB)
(13 mol% 4HB)/NMP/water system, the effect of different
parameters has been discussed (Marcano et al. 2015, 2017).
The discussions mainly refer to the demixing rate. Indeed, a
higher demixing rate results in a more porous structure. In
that sense, increasing the PHA concentration increases the
solution viscosity and so decreases the demixing rate, leading to a denser membrane. Increasing the casting thickness
leads to denser membranes. About the influence of the
coagulation bath temperature, with an increase of the temperature the viscosity would decrease and the non-solvent
and solvent diffusivity would increase, leading to a more
porous structure. Nevertheless, for this system, no major
changes were observed when the coagulation bath temperature was varied. The influence of the polyvinylpyrrolidone
(PVP) addition in the dope solution, its molecular weight
and its concentration were studied (Marcano et al. 2017).
The authors were able to increase the pore density and
surface porosity by increasing the PVP concentration. It was
explained by a decrease of the solution viscosity by adding
PVP. However, an additive concentration above 30% had a
reversible effect and decreased the surface porosity.
Solvent casting particulate leaching method was used to
make highly porous scaffolds. Sodium salt crystals or sugar
were used as porogens. The evaporation followed by the
porogens leaching leads to highly porous structures with
pore sizes around 100 µm. Tan et al. worked on this
leaching technique on P(3HB) films and recognized the
potential of this material for separation membrane applications (Tan et al. 2016).
At the end, PHAs can be easily processed via phase
inversion to form tailored structures. Then, it is of interest to
test these structures as potential filtration membranes.
3.2 Separation Purpose
A few examples of concrete separation applications of
PHAs-based membranes have been reported in the literature
(Mas et al. 1996; Villegas et al. 2011, 2015, 2016; Nicosia
et al. 2015; Keawsupsak et al. 2014; Guo et al. 2016).
3.2.1 Pervaporation
Pervaporation is a separation process that finds applications
for dehydration of organic solvents, removal of dilute
organic molecules or organic–organic mixture separation. In
such processes, the solution–diffusion is the most accepted
model to describe the mass transport, so that during the
separation, the selectivity occurs following unequal affinities
between the solutes and the membrane (Jyothi et al. 2019).
Mas et al. were the firsts to consider PHAs-based membranes as candidates for pervaporation applications (Mas
et al. 1996). They made dense membranes by EIPS with
different P(3HB3HV) having different values of HV content.
The membrane performances were analyzed by separation of
an ethanol/water mixture. The flux varied from 0.008 to
0.027 kg m
−2 h
−1 and the separation factor from 5.0 to 12.6
in favor to water permeation. No major correlation was
observed between the HV ratio content and the membrane
performances. However, with the increase of the filtration
time, the flux tends to increase and the separation factor
tends to decrease. It is argued by a progressive deformation
of the macromolecular structure accentuated by the plasticizing effect of ethanol molecules.
Villegas et al. evaluated the performances of a
PHA-based membrane for pervaporation application on
methanol/methyl tertiary butyl ether (MTBE) mixtures
(Villegas et al. 2011). They made P(3HB) dense membranes
by EIPS. Performances were measured as a function of the
feed temperature and feed composition. In the case of
40 mol% methanol/MTBE mixture, the best performances
Polyhydroxyalkanoates (PHAs) for the Fabrication …
185