Thermostability of Lyocell Dopes Modified with Surface-Active Additives

Cellulose/N‐methylmorpholine‐N‐oxide monohydrate (NMMO) spinning solutions were modified with surface‐active additives to yield Lyocell fibers with functional properties. Based on cellulose fibers, a new class of materials with tailored adsorption characteristics are produced. Activated charcoal and carbon black used as additives significantly affect the thermostability of the spinning solutions. Considering the degree of filling three general tendencies become evident. It is most obvious that the onset temperature of dope decomposition is shifted towards lower values accompanied by viscosity reduction after annealing at elevated temperatures and an enhanced formation of degradations products. Morpholine, N‐methylmorpholine and formaldehyde as the main degradation products were detected in aqueous distillates by means of HPLC. To study the rate of by‐product formation during preparation of the solution kinetic measurements were carried out. Thermal instabilities are not only initiated by heavy metal ions, especially Fe(II), but also by the particle size and porosity of the charcoal. The nano‐scaled carbon black used causes autocatalytic reactions as revealed by calorimetric measurements. Relationships between amount of Acc versus onset temperature (Ton) and concentration of N‐methylmorpholine.