0000000000480562
AUTHOR
Maria Do Carmo Gonçalves
showing 4 related works from this author
Formation of micro- and nano-spheric particles (filter dust) during the preparation of cellulose acetate membranes
2003
Abstract Membranes were prepared from six samples of cellulose acetate (CA) differing in their average molecular weight (75–260 kg/mole) and molecular weight distribution using methyl acetate as solvent and 2-propanole as precipitant. The routes through the phase diagram and the evaporation times were varied in these experiments. Electron microscopy demonstrates that the amount of filter dust (CA particles deposited on the membrane surface) decreases as the fraction of low molecular weight material in the starting polymer becomes less. For low average molar mass of CA and moderate polymer concentrations in the casting solution the dust consists of individual spheres of relatively uniform si…
Thermodynamics of pseudo-ternary systems as a tool to predict the morphologies of cellulose acetate/polystyrene blends cast from tetrahydrofuran solu…
2003
Abstract The demixing behavior of the ternary system THF/CA/PS (tetrahydrofuran/cellulose acetate/polystyrene) was investigated at 25 °C. Cloud point measurements show that the system exhibits a large miscibility gap caused by the incompatibility of CA and PS. Both ends of the experimentally determined tie lines are located inside the two-phase area of the phase diagram. By means of the measured critical composition of the ternary system and the Flory–Huggins interaction parameters published for two of the binary subsystems ( χ CA/THF =0.442 and χ PS/THF =0.475) the polymer/polymer interaction parameter was adjusted (directly minimizing the Gibbs energy) to χ CA/PS =0.057. These thermodynam…
Polydispersity effects on the phase diagram of the system chloroform/poly-l-(lactic acid)/poly(methyl methacrylate) and morphology of PLA/PMMA films
2000
Abstract Cloud point curve, critical composition and several critical coexistence curves were measured at 25°C for the ternary system poly- l -(lactic acid) (PLA), poly(methyl methacrylate) (PMMA) — where both polymers exhibit broad molecular weight distributions — and the common solvent chloroform. In contrast to the situation encountered in the absence of the second polymer both branches of the critical coexistence curves are located without any doubt inside the miscibility gap as defined by the cloud point curve. This unexpected experimental finding is corroborated by model calculations on the basis of continuous thermodynamics. The removal of solvent from the ternary mixtures yields fil…
Asymmetric polysulfone and polyethersulfone membranes: effects of thermodynamic conditions during formation on their performance
2000
Abstract Membranes of polysulfone (PSU) and polyethersulfone (PES) were prepared from ternary and quaternary mixtures containing N , N -dimethylformamide (DMF) as solvent, water as non-solvent, and acetone (AC) as additive. The conditions for phase inversion and the desired phase separation mechanisms were selected on the basis of the phase behavior determined for the solvent/non-solvent/polymer systems. The influences of the composition of the casting solution, of the support, and of film thickness on structure and permeation properties of the membranes were analyzed by scanning electron microscopy (SEM) plus flux and separation experiments. The mechanisms of phase inversion that should pr…