P01

NOVEL HYDROPHILIC/HYDROPHOBIC POLYMER BLENDS AS MEMBRANE MATERIALS

Jun Qiu, K.-V. Peinemann

GKSS Forschungszentrum GmbH, 21502 Geesthacht, Germany

Two phase interpenetrating polymeric structures may show unexpected transport properties, which cannot be predicted easily by the pure phases. A famous example of a two phase interpenetrating membrane material is DuPont's Nafion, which consists of a perfluorcarbon matrix containing a second continuous phase comprised of sulfonated perfluorocarbon. The hydrophobic perfluorocarbon phase prevents excessive swelling of the hydrophilic sulfonic acid phase. This leads to unusual high cation permselectivity. In this lecture preparation methods and transport properties of new blends of hydrophilic and hydrophobic polymers are presented. These blends can usually not been prepared by solution casting, because in most cases no common solvents exist for the two polymers. We solved this problem by a " Trojan Horse" approach. The hydrophilic polymer was transferred by a simple chemical modification into a hydrophobic polymer, which subsequently could be mixed with a second hydrophobic polymer. After obtaining the solvent-free blend the chemically modified hydrophobic polymer (the Trojan Horse) was changed back into the original hydrophilic polymer. By this method unique blends could be prepared.

Transport properties for gaseous and liquid mixtures will be discussed.

P02

IONOMER CHARACTERIZATION FOR USE IN FUEL CELLS

F. J. Fernández-Carretero,^a* V. Compañ,^a, E. Riande,^b R. Díaz-Calleja,^a A. Quijano,^c

^a Departamento de Termodinámica Aplicada. ETSII. Universidad Politécnica de Valencia. 46020, Valencia. Spain

^b Instituto de Ciencia y Tecnología de Polímeros (CSIC), 28006, Madrid. Spain

^c Instituto de Tecnología Eléctrica, 46980, Valencia. Spain

*fraferc4@etsii.upv.es

INTRODUCTION

Ionic conductive solid materials are good electrolyte candidates for fuel cells, electrodialyzers, batteries, sensors, etc. The growing interest in the development of fuel cells and batteries has prompted a flourishing research in the preparation of ionic organic solid conductors based on polymers due to the excellent mechanical properties and easy processing of these materials. From a practical point of view, ion-exchange membranes displaying good performance for a variety of applications should exhibit high ionic selectivity, good ionic conductance, low permeability to free diffusion of electrolytes and low electroosmosis, as well as chemical stability, high mechanical resistance, high flexibility and good dimensional stability at the working conditions. Moreover, fuel diffusion across membranes should be severely hindered. Some of these properties are incompatible and therefore it is necessary to reach a balance among them in order to design membranes with optimum performance^, .

The deleterious permeation effect of perfluorocarbon commercial membranes together with their still high cost and negative environmental effects have promoted the search for alternatives to these materials.

MEMBRANE PREPARATION

Semicrystalline polypropylene (Repsol) and EPDM Vistalon 9500 (Exxon Chemical, France), a polyolefinic terpolymer containing 60 wt % of ethylene, 29 wt % of propylene, and 11 wt % of 5-ethylidine-2-norbornene, were used. The 5-ethylidine-2-norbornene units were sulfonated using the procedure developed by Makowski et. al. In brief, acetic anhydride and concentrated sulphuric acid were slowly added to a solution of EPDM in n-hexane under vigorous stirring. The temperature of the solution was not allowed to exceed 0 ºC and the reaction was stopped after 30 min by adding alcohol to the reaction medium. The acidic form of the sulfonated polymer was further separated by adding deionized water to the reaction medium and flashing off the hydrocarbon solvents. The polymer was washed several times with water until neutral pH was obtained and dried at 100 ºC.

Two blends of sulfonated EPDM and polypropylene (PP) containing 0.10 (wt/wt) (ICTP1) and 0.20 (wt/wt) (ICTP2) of the latter component respectively, were prepared in a Brabender torque rheometer using a thermoplastic mixing chamber (type W60) of 75 cm³ of capacity, keeping the temperature in the preheating step at 453 K. The rotor speed was set at 55 rev min^-1 and once the torque was constant the materials was sheared in the chamber for about 10 min more to ensure good blending homogenization. A small amount of butyl phthalate was used as plasticizer in the blending process.

Membranes were prepared from the sulfonated blends by compression at 200 bars in a Collins Hydraulic press for about 20 min. During compression the samples were kept at 200 ºC for 10 min and then cooled down to room temperature without removing the pressure

A commercial Nafion 117 membrane manufactured by DuPont was used as a referent to check the electrochemical performance of the membranes prepared from sulfonated EPDM-polypropylene blends.

CHARACTERIZATION

Water uptake

Dry sulfonated membranes in the acidic (R-SO₃H) form were weighed and further immersed in distilled water. From time to time the membranes were removed from water, superficially dried by gently pressing between filter paper and weighed. This operation was repeated until a constant weight was reached. From the weights of the dried and wet membranes the water uptake was obtained, and the pertinent results are shown in Table 1.

Ion-exchange capacity

The membranes were equilibrated in a 2 M HCl solution overnight. The acidic membranes were further washed several times with distilled water and then equilibrated with a 2 M sodium chloride solution. The protons delivered after the ion-exchange reaction R-SO₃H + Na⁺ →R-SO₃Na + H⁺ took place were titrated with a 0.01 M sodium hydroxide solution. The values of the ion-exchange capacity of the membranes used in this study are collected in Table 1.

Table 1 Water uptake and ionic exchange capacity

It can be seen that water uptake decreases in ICTP2 due to the percent of EPDM is lower than in ICTP1 so there are less hydrophilic groups (5-ethylidine-2-norbornene units). In this way, ionic exchange capacity of ICTP2 is also low than ICTP1. Both membranes have suitable values of the IEC for its use as ionic exchange membranes.

Transport Number

Transport numbers were determined according to the irreversible processes thermodynamics to characterize the transport properties of the membranes^{, , , ,} .

Experimental electrochemical potentials were measured in a cell with the following configuration:

Ag | AgCl | HCl solution (c_L)| membrane | HCl solution (c_R) | AgCl | Ag.

c_L is fixed, 0,01M, while c_R varies from 0,001 to 1.

The cell employed is made of Pyrex glass and the membrane was tightly campled between two compartments of 150 cm³ capacity. The electrodes were dipped into the cell and connected to a multimeter HP 3441. The electromotive force was recorded with a PC that took measures every 5 s. During the measurements, the cell solutions were stirred to minimize polarization effects.

Experiments have been repeated changing HCl solutions for NaCl to study the membrane behaviour when the size of the ion raises (H⁺ vs. Na⁺).

Results are shown in table 2, where one can see that near 1 transport numbers are obtained when working with H⁺ as a result of good ionic exchange properties. When using Na⁺ the increase in ion size results in a decrease of the transport numbers.

Table 2 Membranes transport number

Electrical analysis

Proton conductivity was measured using impedance spectroscopy using a dielectric spectrometer Novocontrol with Alpha analyzer and Quatro temperature control. Samples were measured sandwiched in the liquid sample cell BDS 1308 in distilled water to simulate 100% RH. Frequency range was from 10^-2 to 10⁶ Hz in isothermal conditions with amplitude of 1V.Conductivity has been obtained from intersection with the real impedance axis in the high frequency side of Nyquist and, using a second method, from the Bode plots, obtaining conductivity when phase angle trends to 0 in the high frequency area.

Fig. 1 ICTP1 Bode plot

Fig. 2 ICTP2 Nyquist Plot

Conductivities are shown in table 3,

Table 3 Conductivities of the membranes

Conductivity is better in ICTP1; this was expected because ICTP1 has the highest ionic exchange capacity. And there's an increase in the conductivity when the temperature raises form 75 to 90ºC in the EPDM membranes, while there's no raise in Nafion one's.

CONCLUSIONS

The comparison of the electrochemical properties of the ICTP1 and ICTP2 membranes expressed in terms of the conductivity and proton transport number with those of Nafion, suggests that the ICTP1 membrane exhibits similar performance as the Nafion membrane.

However, to conclude whether the ICTP membranes could be used in fuel cells would require to investigate their chemical and mechanical stability at high temperatures.

ACKNOWLEDGEMENTS

This work was supported by the AVCT ( Generalitat Valenciana), CAM (Comunidad Autónoma de Madrid) and the DGCYT through Grants Grupos03/030, IMCITA2005/31, GR/MAT/0723/2004, and MAT2002-04042-C0-1, respectively.

REFERENCES

P 03

THERMAL BEHAVIOR AND MORPHOLOGY OF BIODEGRADABLE P(3HB)-BASED MEMBRANES

K. Wessler^a, A.P.T. Pezzin^b, S.H. Pezzin^b

^aCenter for Technological Sciences, Santa Catarina State University - UDESC, Campus Universitário s/n, CP 631, 89223-100 Joinville-SC, Brazil (pezzin@joinville.udesc.br)

^bUNIVILLE, CP 246, 89201-972 Joinville-SC, Brazil

Summary. The miscibility behavior and the morphology of blends of poly(3-hydroxybutyrate), P(3HB), and polycaprolactone triol, PCL-T, obtained by casting, were studied by differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction, infrared spectroscopy and scanning electron microscopy. It was observed that higher PCL-T ratios results in transparent, porous and flexible films.

Polyhydroxyalkanoates (PHAs) are thermoplastic polyesters made from bacterial fermentation using renewable resources. The polymers are produced as an intracellular storage polymer of carbon and energy under various nutritional and environmental conditions (1). In the past two decades, PHAs have been the focus of extensive research considering their potential application as biocompatible and biodegradable thermoplastics, due to their hydrolyzability in the human body as well as in natural circumstances (2). The polymers of PHAs family more extensively studied are poly(3-hydroxybutyrate), P(3HB) and the copolymer poly(3-hydroxybutyrate)-co-(3-hydroxyvalerate) (P(3HB-co-3HV)). P(3HB) can in principle be used in many applications, however, since P(3HB) is highly crystalline and forms large spherulites and also has a relatively high glass transition temperature in comparison with polypropylene, polyethylene, etc., the material itself is regarded as unacceptable brittle. Furthermore, P(3HB) suffers from an economic disadvantage and limited processing temperatures. These drawbacks have restricted the widespread application of P(3HB) (3). On the other hand, poly(caprolactone - triol) (PCL-T) is a semi-crystalline polymer with melting point around 30şC and glass transition temperature around -68şC, being potentially interesting to be used in biomaterials (4). Thus, it seems that PCL-T can be a good choice to plasticize P(3HB-co-3HV), maintaining its biodegradability and bioreabsorption properties.

Aiming the development of new ductile and porous biodegradable materials, blends of P(3HB) and P(3HB-co-3HV) with polycaprolactone triol (PCL-T) in compositions varying from 100/0 to 70/30 P(3HB)/PCL-T (w/w), were obtained by casting. P(3HB) and P(3HB-co-3HV) used in this research were kindly supplied by PHB Industrial S.A. and purified prior to use by dissolution in chloroform and precipitation in n-hexane. The number average molecular weight of P(3HB) and P(3HB-co-3HV), obtained by GPC, was around 3.0 x 10⁵ g mol^-1. PCL-T with 900 g mol^-1 was purchased from Aldrich. Membranes were obtained by casting from 1% chloroform solutions. The solution was poured in a glass mold and placed in an evaporator system for 48 hours. The films were completely dried in a vacuum oven at 60°C for 24 hours and stored in a desiccator. The blends were further analyzed by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM).

The DSC data for P(3HB) blends are summarized in Table 1. It was observed that the PCL-T melting temperatures did not change in all compositions, while the P(3HB) melting temperatures decreases a little when the PCL-T content is increased. It was also noted that the Tg of PHB did not vary in function of the PCL-T content. The T_g of the samples with low plasticizer content are badly defined, however those from samples with higher PCL-T contents are best defined, suggesting that the PCL-T addition diminishes the crystallinity of the sample. These results suggest that the P(3HB)/PCL-T system is immiscible. Indeed, FTIR analyses did not show evidences of hydrogen bonds between the polymers. XRD analysis confirmed that the addition of PCL-T to P(3HB) causes a decrease of ca. 30% on the crystallinity, independently of the PCL-T content.

Table 1: DSC data (T_m) for PHB/PCL-T blends

For P(3HB-co-3HV) blends, it was observed (Table 2) that the glass transition temperatures decreased from 1,66şC to ca. -10şC with the addition of 15 wt% of PCL-T. Further addition of PCL-T does not modifies the Tg of P(3HB-co-3HV). It is also noticed that the melting temperatures of P(3HB-co-3HV) and PCL-T decreases gradually as the PCL-T content is increased. The Tg of the samples are best defined with higher PCL-T contents, suggesting that the PCL-T addition decreases the crystallinity of the sample. These results evidence a partial miscibility between PCL-T in P(3HB-co-3HV).

Table 2. DSC data (T_m) and (T_g) for P(3HB-co-3HV)/PCL-T 900 blends.

Thermal degradation studies were carried out by thermogravimetric methods, showing that the addition of PCL-T slightly decreases the onset temperature of the P(3HB) degradation. SEM micrographs revealed that higher PCL-T ratios result in very porous membranes. It is also noted that the transparency of the membranes increases with the PCL-T content, as well as the flexibility. These results suggest that these materials have great potential to biomedical applications and packings.

References

[1] P. D'haene, E.E. Remsen, J. Asrar. Macromolecules 32, 5229-5235 (1999).

[2] H. Tsuji, K. Suzuyoshi. Polym. Degrad. Stab. 75, 347-355 (2002).

[3] W. Chen, D.J. David, W.J. MacKnight, F.E. Karasz. Polymer 42, 8407-8414 (2001).

[4] 3. H.R. Lin, C.J. Kuo, Y.J. Lin. J.Cell.Plast. 39, 101 (2003).

P04

GRAFTING OF POLY(STYRENE-CO-MALEIC ANHYDRIDE)  WITH POLY(ETHYLENE GLYCOL) FOR MEMBRANE PREPARATION

Diógenes Rojas, Peter F.W. Simón, Volker Abetz

GKSS Forschungzentrum Gesthaacht GmbH, Max Planck Str. 1, Gesthacht, D-21502 Germany

Diogenes.rojas/gkss.de

In the last year the use of copolymer membranes has emerged as a new alternative and it has interested too many researchers. The main focus of this area is to find the structure/property relation in polymers materials and correlation with gas separation membranes properties. In this way, the use of self-assembly polymer material which lead up to obtain well-ordered structures due to the ease of accessing complex structures with small features sizes (1-4).

The aims are to investigate the relation between the morphology and the overall composition of Poly(Ethylene Glycol) (PEG) / Poly(Styrene-co-Maleic Anhydride) (SMA) and their functionality, as well as, to study the effect of the morphology on the membrane properties (permeability, selectivity and diffusion). In our experiments we use poly(styrene-co-maleic anhydride) and poly(ethylene glycol). These copolymers are used to prepare the new copolymers by esterification reaction and then all these products are characterized by ¹H-NMR, DSC, TGA and GPC. The dense membrane method by casting is used to prepare films and then theses are analyzed for contact angle, AFM, SEM, and finally are measured their properties. Our first conclusion shows that due to the esterification reaction it is possible to link and to increase PEG contents in the matrix SMA which helps to reduce the glass transition temperature (Tg) in the films. The contact angle showed that the membranes have more hydrophilic behavior in comparison to the original matrix. And finally, the functionality play particular role in the behavior of the membrane properties.

References

• J.N Chan, G. D. Stucky, D. E. Morse, T.J. Deming, Nature 2000, 403, 289
• G.M. Whitesides. B. Grzybowski, Science 2002,295,2418
• Abetz, V.; Simon, P.W.F. Adv. Pol. Sci. 2005, 189,125
• S. H. Kim, M. J. Misner , T. P. Russell Adv. Mater. 2004, 16, 3 ,226

P05

6F6F AS GAS SEPARATION MEMBRANE. EFFECT OF THE FORMATION TEMPERATURE ON PERMSELECTIVITY

Roberto RecioVázquez¹, Laura Palacio¹, Pedro Prádanos¹, Antonio Hernández¹,

Ángel E. Lozano², Ángel Marcos, José G. de la Campa², Javier de Abajo²

¹ Dpto. Física Aplicada, Universidad de Valladolid, Facultad de Ciencias, Real de Burgos s/n, 47071 Valladolid. Spain

² Dpto. Química Macromolecular, Instituto de Polímeros, CSIC, Juan de la Cierva 3, 28006 Madrid. Spain

Over the last decades, polymeric membranes have proven to operate successfully in industrial gas separations. To obtain membranes that combine high permeability and high selectivity together with thermal stability, new polymers, high added value materials, so-called high-performance polymers, were developed like polyimide (PI). Several aromatic polyimides as 6F6F have shown promising properties when separating gas mixtures like O₂/N₂ and CO₂/CH₄. In addition, a inverse relationship between permeability and selectivity is observed, which fit a limit to the development of new polymer structure that show a landmark in this field.

Nevertheless, membranes used for gas separation at the moment are of solution-diffusion type polymeric membranes. One of the immediate challenges facing membrane material design is achieving higher permselectivity with equal or greater productivity compared to existing materials. A high selectivity leads to a high purity of products and allows a reduction in the number of operation steps and thus a cutback in the needed membrane area. A high permeability involves a high process velocity or productivity.

In this work, transport properties like permeability and selectivity of gas separation membranes made from 6FDA-6FpDA with a N,N-dimethylacetamide (DMAc) as solvent have been measured in a time lag equipment. It has been shown that an increase in the temperature of formation of the membrane leads to better selectivity versus permeability compromise. This has been tested for O₂/N₂ and CO₂/CH₄ gas pairs.

An increase in the temperature of formation, to approach the boiling temperature of the solvent, increases both the glass transition temperature and the fractional free volume. These factors help to explain the structural changes that allow simultaneous improvements of permeability and selectivity.

P06

EFFECT OF FULLERENE ADDITIVES ON PERVAPORATION PROPERTIES OF POLY(PHENYLENE OXIDE) MEMBRANES

A.V. Penkova^a, A.M. Toikka^a, G.A. Polotskaya^b

^a Dep. Chem. Thermodynamics & Kinetics, St. Petersburg State University, University pr. 26, Petrodvoretz, St. Petersburg, 198504, Russia (stasya84@nm.ru)

^bInstitute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Bolshoy pr. 31, 199004, Russia

The allotropic form of carbon known as fullerene exhibits unique physico-chemical properties and can provide a possibility for modification of polymer membrane. It has been shown that fullerene C₆₀ improves polyphenylene oxide (PPO) transport properties in gas separation [1]. The combination of С₆₀ and PPO gives a donor-acceptor complex that leads to increasing membrane density and influence on gas transport properties. In the present work, fullerene-containing PPO membranes are considered in pervaporation processes. The effect of fullerene additives on PPO transport properties is studied in the pervaporation of the reacting mixture: ethanol - acetic acid - water - ethyl acetate in binary, ternary, and quaternary combination of components. The shifting of the esterification equilibrium:

C₂H₅OH + CH₃COOH = Н₂О + CH₃COOC₂H₅ is one of the ways for maximizing yield of ethyl acetate in hybrid process involving pervaporation.

Homogeneous C₆₀-PPO membranes containing up to 2 %wt C₆₀ (~60 mm thick) were prepared by mixing PPO and C₆₀ solutions in toluene, by casting the solution on a cellophane surface, and by drying at 40^оС. These membranes were studied in pervaporation of mixtures involving ethanol, acetic acid, ethyl acetate, and water in different combination. It was shown that permeate is enriched by ethyl acetate in pervaporation of four-component mixture in equilibrium composition. Acetic acid does not essentially permeate through all membranes under study. High selectivity with respect to ethyl acetate was established in pervaporation of two-component ethyl acetate/water mixtures. The use of fullerene-containing membranes made it possible to increase selectivity to 700 for 7% ethyl acetate in water (azeotrope). High selectivity with respect to ethyl acetate is caused by hydrophobic properties of our membranes.

Pervaporation properties of membrane depend on interactions between components of the feed solution and the polymer of the membrane. To estimate the interaction, equilibrium vapour sorption of ethanol, acetic acid, water, and ethyl acetate was studied. Fullerene-containing membranes show a better sorption capacity for ester, acid, and alcohol than that of PPO membranes. Ethyl acetate exhibits the highest sorption (the lowest value of χ), then acetic acid and ethanol come. Water is absolutely inert to polymers under study. These results are in good agreement with data on pervaporation.

Thus, it was established that fullerene as a component of the С₆₀-PPO composition profoundly affects membrane properties.

Acknowledgement. This work was supported by Russian Foundation for Basic Research (grant 06-03-32493).

Reference

1. G.Polotskaya, Yu.Biryulin, Z.Pientka, L.Brozova, M.Bleha, Transport properties of fullerene - polyphenylene oxide homogeneous membranes, Fullerenes, Nanotubes, and Carbon Nanostructures, 12(1) (2004) 387-391