Structure of polyacrylonitrile fibres modified with polyethylenimine

Abstract

After the treatment of carboxylated PAN with polyethylenimine the fibre center retains the absorption band at 1720 cm-i produced by the free-CO groups and contains new bands at 1410 and 1590 cm-1 (ionized COO-groups), a fact which shows that the sorption of PEI by carboxyl-contain ing PAN fibre proceeds in accordance with an ionic mechanism. Since sorbents of this type contain amino groups as well as carboxyl groups they must be classed as amphoteric ion exchangers, a finding which was corroborated by potentiometric titration. The structural analysis was conducted on a DRON-2.0 x-ray diffraetometer. The original and modified specimens were analyzed in identical conditions. The x-ray diagram of the original PAN fibre (Fig. 2a) contains distinct reflections with interplanar spacings of 5.5 and 5.2 ~, a fact which agrees with earlier findings [4]. The structure of partly carboxlated PAN fibre (Fig. 2b) has undergone a slight rearrangement compared with that of the original fibre. The sharp decrease in the strength of the reflections indicates that the macromolecule chains in the crystalline part of the polymer have become randomized. The degree of order of the structure is lower. After modification with PEI the partly carboxylated PAN fibre (fibre PAN-PEI) is almost wholly amorphous (Fig. 2c). The x-ray diagram contains two very faint reflections with 5.5 and 5.2 ~ against a background of an amorphous halo. The heating of PAN- PEI fibre for 30 rain at 150°C produced no effect on the order of its structure, i.e., the x-ray diagram in Fig. 2d differs sacrcely at all from that in Fig. 2c. TABLE i. Physicomechanica l Properties of PAN Fibres