Determine the influence in microcapsules wall morphology of two factors: the solvent used, and the amount of that solvent that is added to the coagulation bath.

POLYSULFONE MICROCAPSULES PRODUCTION AND WALL MORPHOLOGY MODIFICATIONS BY

CHANGES IN THE PREPARATION CONDITIONS.

Cinta Panisello, Supervisor: Ricard Garcia-VallsDepartament d’Enginyeria Química, Escola Tècnica Superior d’Enginyeria Química, Universitat Rovira i Virgili,

Av. Països Catalans, 26, 43007 Tarragona, Spain. Telf: +34977558506; E-mail: cinta.panisello@urv.cat

INTRODUCTIONA novel method is proposed for the production of Polysulfone microcapsules, based on Loeb-Sourirajan Phase inversion process, that is a method widely used for the

preparation of polymeric flat membranes.This method is based in the interaction among at least three compounds, the polymer, the solvent and the non solvent.

It consists in preparing a polymeric solution by solving the polymer in a compatible solvent, then preparing a thin film of the solution on a support and finally immersing the film together with the support in a coagulation bath containing the non solvent.

The polymer precipitates because the solution reaches a two immiscible phases region and it becomes thermodynamically unstable, which causes a liquid – liquiddemixing, splitting the solution in two different phases, a polymer rich phase and a polymer poor one.

The membrane morphology obtained depends on the interaction among the cited compounds, and some other variables such as the temperature of the bath and the polymer concentration in the solution [1].

Polymeric microcapsules, which preparation method is an adaptation of the one described before for flat membranes preparation, are the focus of this study.In these microcapsules preparation the polymeric solution is dispersed in order to form microdroplets by means of an atomization process using an airbrush. The

polymeric solution is atomized into a coagulation bath containing the non solvent, and the polymer precipitates in the spherical shape of the microdroplet.The hypothesis of the present work is that, as in flat membranes, the morphology of the capsules wall can be modified by changing the solvent and/or the coagulant

bath used.

REFERENCES[1] C.Torras, F.Ferrando, J.Paltakari, R.Garcia-Valls, Performance, morphology and tensile characterization

of activated carbon composite membranes for the synthesis of enzyme membrane reactors. Journal of membrane science, 2006; 282:149-161

[2]C. Torras, et al., Two methods for morphological characterization of internal microcapsule structures, Journal of membrane science, 2007; 305 (1-2): 1-4

[3] M. Mulder, Basic Principles of membrane technology, 2nd edition, Kluwer academic publishers, Dordrecht, The Netherlands. 2003 (© 1996).

[4] JY.Kim, HK. Lee, KJ.Baik, SC.Kim. Liquid–Liquid Phase Separation in Polysulfone/Solvent/Water Systems. Journal of applied polymer science, 1997; 65 (13): 2643-2653

[5] C. Torras. Obtenció de membranes polimèriques selectives, 2005.

ACKNOWLEDGEMENTS

•Generalitat de Catalunya for funding (FI-AGAUR scholarship).

•Universitat Rovira i Virgili for research facilities.

•SYSTEMIC group members for help and support.

METHOD

•A new method for preparation of polysulfone microcapsules has been developed. Therefore, the developed method allows to the preparation of

microcapsules “on demand” where wall morphology can be designed in order to fit possible applications.

•The morphology of the microcapsules wall doesn’t change by changing the solvent used in the polymer solution, because the three solvents studied

present similar affinity with the non solvent and similar interaction parameters with the polymer.

•The affinity of the solvents with the non solvent is high, so if the coagulation bath contains only water macrovoids appear in the wall structure.

•The addition of solvent to the coagulation bath has been proved to be successful in order to remove macrovoids from the microcapsules wall.

CONCLUSIONS

OBJECTIVES

Material:• Polysulfone (PSf) (Sigma–Aldrich, Spain, transparent pellets of Mw = 16,000) was used

as polymer. • The solvents used were dimethylformamide (DMF, Scharlab, reagent grade ACS-ISO),

dimethylacetamide (DMAc, Scharlab, synthesis grade) and 1-methyl-2-pyrrolidinone (NMP, Scharlab, 99 +% A.C.S. reagent).

• The non-solvent was distillated water.

Steps:• Polymeric solution preparation.• Atomization (5 ml of polymeric solution over 100 ml coagulation bath).• Phase inversion by immersion precipitation.• Filtration: Void filtration equipment using 0.8 µm nylon filters.• Characterization: The diameter and surface features of the microcapsules were

investigated by scanning electron microscopy (SEM).To visualize the wall morphology microcapsules were cut by cryogenic breaking. The followed procedure was the one described by C.Torras, et al. [2]

RESULTS

0 %

15 %

45 %

60 %

DMF DMAcNMP

% w

solv

ent in

coagula

tion b

ath

Solvent

Differences among the structures due to the solvent used are not appreciable, due to that all solvents show high affinity with water and similar interaction parameters with the polymer. χ23 = 0.24 for NMP [4] and 0.2 for DMF [5].

100 % water

15% DMAc in 85 % water

45 % DMAc in 55 % water

60 % DMAc in 40 % water

15 % w PSU in DMAc

100 % water

15% DMF in 85 % water

45 % DMF in 55 % water

60 % DMF in 40 % water

15 % w PSU in DMF

100 % water

15% NMP in 85 % water

45 % NMP in 55 % water

60 % NMP in 40 % water

15 % w PSU in NMP

Coagulation bath (% w)Polymeric Solution

Table 1 Summary of the experiments performed.

Figure 1 Schematic diagram of atomization set up.

Airbrush with a nozzle size of 80 µm

installed over a beaker containing the

coagulation bath. This device atomizes

the polymeric solution by a simple shearing action provided by a

high velocity air stream (about 200 m/s) impacting on

the liquid.

Cross section photomicrographs show

Sponge like wall structureMacrovoid wall structure

Big Flory Huggins interaction parameters between polymer and non

solvent (Big for the pair polysulfone water)

Instantaneous liquid-liquid demixing Delayed liquid-liquid demixing

High affinity between solvent and non solvent(DMF, NMP, DMAc showhigh affinity with water)

Addition of solvent to the coagulation bath causes delay on demixing rate due to the reduction of the chemical

potentials.

% Solvent in

Coagulation Bath

Macrovoids

[3]

Sponge –

like s

tructu

re

Macrovoid

str

uctu

re

Figure 2 Cross section photomicrographs of the microcapsules prepared.