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The visible absorption spectra of the cross-sections of the dyed various synthetic-polymer fibres were measured by means of a microspectrophotometer. We found that the spectra of Acridine Orange hydrochloride in the crosssections of fibres showed a maximum of α-band and β band, and the spectra of Acridine Orange (free base), indicated a maximum of α-band, β-band and the crystal peak of the dye. These results suggest that the monomeric state, the aggregate as well as the crystal of the dye exist in these dyed synthetic-polymer fibres.

The visible absorption spectra of the cross-section of dyed PVA fibre with AO were measured by means of a microspectrophotometer. The spectra showed a high maximum at 475 nm, which would be referred to as β-band (a monomer peak at 498 nm). Many void places were recognized in core layer by electron or scanning electron microscopy. It was explained that the dimer band mainly arose from dye aggregates or crystals at the void places of fibre.

The visible absorption spectra of dye crystals and the cross-section of the polyvinyl alcohol fibre dyed with Acridine Orange as free base were measured by means of a microspectrophotometer. The spectra of crystals show a sharp and high maximum at 450 nm which will be referred to as the peak from dye crystals. The spectra of the cross-section of dyed fibre show three peaks of 443 nm (crystals-band), 470 nm (β-band) and 499 nm (α-band). These results suggest that crystals, aggregates and monomer of the dye exist within the dyed polyvinyl alcohol fibre.