Abstract
In the present work, N,N-dimethylformamide was chosen as a cosolvent of cellulose acetate (CA) and polyacrylonitrile (PAN). The blend solution showed appropriate viscosity, good membrane-forming property and relative stability. The structure and compatibility of the blend membrane was investigated by means of phase contrast microscopy (PCM), infrared spectrophotometry (IR), scanning electron microscopy and differential scanning calorimetry (DSC). PCM analysis showed that both pure PAN and CA membranes possess homophase structures, and the size of phase domain gradually increases with increasing content of either of the two components. From IR spectrograms, the peaks characterizing the crystal lattice of CA (3490, 902 and 604 cm1) appeared at the same positions and their magnitudes increased as the increase of CA content when the percentage of CA in the polyblend was not less than 60% by weight. The characteristic peak of PAN (2242 cm1) appeared at the same position to all membranes except for pure CA membrane and its magnitude decreased with the decrease of PAN content in the polyblend. It was found that the crystal regions of CA and PAN in the blend membrane were incompatible. According to scanning electron micrographs, the cross-section of the blend membrane could be divided into dense layer, transition layer and support layer. Pure CA membrane showed a spongelike structure and PAN a fingerlike one. The structure of the blend membrane with a lower CA percentage (10–20% by weight) was similar to that of pure PAN membrane and the degree of phase separation was lower. The blend membrane with a moderate CA percentage (30–60% by weight) showed a distinctive structure with evident phase separation. The blend membrane with a higher CA percentage (70–90% by weight) presented severe phase separation. By DSC analysis, the glass transition temperature of the polyblend became a little higher as the CA content in the polyblend increased. It indicated that there was partial mixing at molecular level in the amorphous region of the polyblend. © 1997 John Wiley & Sons, Ltd.
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