Polyurethanes Based on Dicyclohexylmethane 4,4′-Diisocyanate and N-tert-Butyldiethanolamine for Enhancing the Dyeability of Fiber toward Acid Dye

Conventional polyurethane fiber (CPUF) has been widely used in clothes, but it is difficult to color CPUF into a deep hue with acid dyes. In this work, it is proposed that polyurethane is synthesized using dicyclohexylmethane-4,4′-diisocyanate (HMDI) and N-tert-butyldiethanolamine (TBDEA), named poly(HMDI-TBDEA), and is added to a CPUF spinning solution to prepare a modified polyurethane fiber (MPUF) which has an enhanced dyeability toward acid dyes. It is assumed that poly(HMDI-TBDEA) brings tertiary amine groups and tert-butyl groups to MPUF, of which the tertiary amine groups can be protonated under acidic conditions and electrostatically adsorbs anionic ions of acid dyes, and the tert-butyl groups disrupt the ordered arrangement of hard segments in polyurethane to increase the accessible area for acid dyes. The synthesis of poly(HMDI-TBDEA) was validated by proton and carbon nuclear magnetic resonance spectroscopy (1H and 13C NMR) and gel permeation chromatography. MPUF was characterized by differential scanning calorimetry, thermogravimetry, X-ray diffraction, and the tensile test. The study revealed that the addition of poly(HMDI-TBDEA) disrupted the ordered arrangement of the hard segments and strengthened the soft segments but had no obvious influence on the thermal stability. In comparison with CPUF, MPUF exhibited approximately the same elastic recovery, despite a drop in the elongation at break and the break strength. The zeta potential test demonstrated that MPUF might be protonated for enhanced electropositivity under acidic conditions. MPUF displayed superior dyeability than CPUF when dyed with C.I. Acid Orange 7 at pH 3.