M.N. de Pinho

Structural characteristics and gas permeation properties of polynorbornenes with retained bicyclic structure

Abstract Polynorbornenes of different molecular weights were synthesised by addition polymerisation, using a nickel based catalyst. This polymerisation route leads to amorphous polymers that were shown to display unique properties: high glass transition temperature, rigid random coil conformation, and dense packing in the amorphous state. Gas permeation membranes were prepared from these addition type non-substituted polynorbornenes. A study of their gas transport properties was performed and compared with both substituted addition polynorbornenes and ring opening metathesis polymerised polynorbornenes. The observed behaviour, in terms of permeability and selectivity, is in accordance with the low free volume and the dense packing confirmed by positron annihilation spectroscopy and WAXD in these polymer structures.

Membrane surface characterisation by contact angle measurements using the immersed method

Abstract A new concept of contact angle measurements by the immersed method is applied to membrane surface characterisation. The general system of two immiscible liquids is used wherein a droplet of CCl4 is deposited on the membrane surface immersed in an aqueous solution. When the solution is pure water, membrane hydrophilicity is evaluated. With aqueous solutions of a cationic surfactant (below its critical micelle concentration) at different pH values, membrane titration curves are obtained. From these curves we obtain the acid-base behaviour of each membrane and the pH value at which half of the membrane surface groups are ionised, p K 1 2 . This method is tested with five nanofiltration membranes, a series of three cellulose acetate membranes, CA-316, with increasing hydraulic permeabilities and two commercial thin film composite membranes, CD-NF-50 of poly(trans-2,5-dimethyl)piperazin thiofurazanamide/polyethersulfone and HR-98-PP of polyamide/polysulfone. The results show that the method (i) is easy to perform and avoids dynamic measurements (requires 5 min of drop deposition); (ii) is reproducible (maximal deviations of 7°); (iii) simulates multiple membrane technical environments (e.g. pure water, aqueous solutions); (iv) is not affected by the presence of pores in the nanofiltration range of operation; and (v) is sensitive to membrane hydrophilicity and membrane acidity/basicity (titration curves and p K 1 2 values). Furthermore, the results show the direct effect of the annealing treatment on the acidity of the CA-316 membranes and they evidence the importance of the membrane chemical properties (hydrophilicity, acidity/basicity) on the membrane permeation performance.

Mass transfer in radiation-grafted pervaporation membranes

Abstract Based on the solution-diffusion-desorption mechanism, a model is derived to describe mass transfer in pervaporation. A set of assumptions based on transport characteristics of the studied system leads to a simple model involving a small number of fitted parameters that lump together constants pertaining to the concentration-dependent diffusivities and to the sorption coefficients. The membranes investigated are 4-vinylpyridine grafted with poly (vinylidene fluoride) as trunk polymer and N -vinylimidazole grafted with poly (vinyl fluoride) as trunk polymer. Pervaporation experiments were performed for the following binary mixtures: water-isopropanol, water-ethylene glycol monomethyl ether and water-ethylene glycol monoethyl ether. The entire concentration range was covered.

Free-volume studies in polyurethane membranes by positron annihilation spectroscopy

Abstract The free-volume parameters in various urethane/urea membranes obtained by varying the ratio of the structural constituents, polypropylene oxide and polybutadiene, were studied by positron lifetime and Doppler broadening measurements. On bi-soft segment membranes, a correlation was found between the composition of membranes, the normalized free volume, the radii of the holes and gas permeability. However, the correlation is not clear when PU data are also considered, indicating that other features must also play an important role in the permeation mechanism.

Shear-induced order effects in bi-soft segment urethane/urea elastomers

Abstract In this work we study shear-induced order effects, observed on thin films (∼20–60 μm) of urethane/urea elastomers prepared from a polypropylene oxide based isocyanate terminated triol prepolymer (PU) and polybutadiene diol (PBDO) in the amount of 25% (PU/25PBDO), 50% (PU/50PBDO), 60% (PU/60PBDO) and 75% (PU/75PBDO) by weight of polybutadiene. Optical microscopy and light scattering as a function of temperature were used in this study. The initial isotropic elastomers, PU/60PBDO and PU/75PBDO, after cessation of a uniaxial mechanical deformation relax to a band texture, consisting of equidistant bright and black lines perpendicular to the shear direction. If the uniaxial mechanical stress is applied again perpendicular to the band structure in PU/60PBDO, a new periodicity with wave vector perpendicular to the axis of the field develops, while for PU/75PBDO two new periodicities can be observed, one with wave vector perpendicular to the axis of the field and the other transverse. The process of band formation is completely reversible in cycles of increasing and decreasing strain ratios. In samples PU/25PBDO and PU/50PBDO this kind of effect is not observed. The bands periodicity is temperature independent. The temperature dependence of the scattered intensity produced by the bands is different for bands perpendicular and transverse to the axis of the stress field. We show evidence that the urethane linkage is responsible for the relaxation instabilities observed, in this kind of material.

Optical Polarizing Studies of Cellulose Acetate Membranes Prepared by Phase-Inversion

Abstract Anisotropic spherical cells dispersed in an isotropic medium were observed, using polarizing microscopy, in asymmetric cellulose acetate (CA) membranes. Membranes CA-400 and CA-316 were prepared from ternary casting solutions of CA-acetone-formamide and CA-acetone-magnesium perchlorate/water respectively. The content of nonsolvent, formamide, was varied to yield membranes CA-400-22, CA-400-27 and CA-400-32 that show a decreasing number of larger anisotropic cells with the increase of nonsolvent content. The membranes CA-316 were subjected to a heat treatment—annealing—at varying temperatures yielding membranes CA-316-50, CA-316-68 and CA-316-86. The crystallinity observed was dependent on the temperature of this heat post-treatment. The selective permeation properties are correlated with the ratio of isotropic to anisotropic phases at the membrane skin surface. This ratio is in turn dependent on the casting solution composition-type and concentration of nonsolvent and on the annealing treatment. ...

Treatment of Bleaching Effluents by Pressure - Driven Membrane Processes — A Review

One of the bleach stages in the treatment of wood for the manufacture of pulp is the extraction of lignin with sodium hydroxide. The resulting effluent is highly coloured at a pH of 7 to 10 and a conductivity of 4 to 7 mS/cm. The high-molecular-weight fraction of lignins results in the dark colour of the effluent, whereas the low-molecular-weight fraction of chlorinated lignins has recently been shown to be most toxic. Thus, without treatment, the potential for the extraction effluent reuse, in the bleaching section of the pulping process is limited. On the other hand, the kraft pulp and paper industry has been faced with the challenge of reducing the discharge of conventional and toxic pollutants to the environment. Alternative schemes should be developed on two areas: a) pollution prevention through the implementation of internal measures, b) development of innovative effluent treatment schemes for the removal of undesirable components from waste streams, in order to minimize water consumption and reduce the production of toxic contaminants. Among the separation processes under investigation for the removal of colour and chlorinated organic compounds, ultrafiltration (UF) and nanofiltration (NF) are attracting considerable attention in many industrialized countries. These membrane — based processes are of particular interest because they produce diluted and concentrated streams which can be recycled and disposed of in a cost — effective manner. In-plant changes have minimized the levels of chromophores and chlorinated organics present in the extraction stage. Therefore, now the emphasis of UF and NF use is on the integration of these processes in the milling process flow schemes, reusing the permeate as process water and using oxidation or thermal processes to treat the concentrate. A significant consideration in NF application for pulp mill effluent treatment relates to the fact that the rejection of a compound is not only dependent on its molecular weight but also on its physical/chemical characteristics. It appears that NF not only removes high-molecular-weight compounds but also low-molecular-weight compounds which are relatively lipophilic. This paper provides an overview of the potential uses of the UF and NF in the treatment of kraft mills bleaching effluents.

All-Cellulosic Based Composites

The use of cellulosic fibers as load bearing constituents in composite materials has increased over the last decade due to their relative cheapness compared to conventional materials such as glass and aramid fibers, their ability to recycle, and because they compete well in terms of strength per weight of material. All-cellulosic based composites prepared from cellulose derivatives based matrices and microcrystalline cellulosic fibers made by direct coupling between fibers and matrix present interesting mechanical and gas permeation properties, thus being potential candidates for packaging materials. Both the cellulosic matrix and the reinforcing fibers are biocompatible and widely used in the pharmaceutical industry, which is very important for the envisaged application. In addition to their biocompatibility, cellulosic systems have the ability to form both thermotropic and lyotropic chiral nematic phases, and the composites produced from the latter show improved mechanical properties due to fiber orientation induced by the anisotropic matrix. The preparation and characterization (morphological, topographical, mechanical, gas barrier properties) of all-cellulosic based composites are described in this chapter.