Taking, as the samples for investigation, filaments of viscose rayon (60% crystallinity) and acetate rayon (54% acetyl) both crosslinked to various extents by tetramethylenebisethylene urea and tetramethylenediisocyanate urea as the crosslinking agents, the dynamic and transient moduli, E′, G1, G2, the internal friction, Q−1, and the apparent activation energy for relaxation of segment, ΔU, were measured and the results were considered in their relation to the degree of crosslinking. From the results, the following conclusions were made: (1) When crosslinking is caused by long molecular chains of the crosslinking agents between the nearest neighboring molecules, the intermolecular spaces are widened to some extent and the restraint of segmental motion due to the dipole interaction of the strong polar hydroxyl groups is partly relieved so that the decreases in ΔU, E′, G1, and G2 are rather caused by a small amount of the crosslinking agents; for example, while the values of ΔU and E′, for the original viscose rayon not crosslinked are 230 kcal./mole and 2.0 × 1011 dynes/cm.2, respectively, they both decrease with an increase in degree of crosslinking and each shows a minimum (ΔU = 95 kcal./mole, E′ = 0.9 × 1011 dynes/cm.2) at the amount of bound nitrogen N = 0.73%. When the crosslinking proceeds further, the primary crosslinking effect makes its appearance so that ΔU, E′, G1, and G2 begin to rise with an increase in degree of crosslinking. (2) Due to the strong solvating or plasticizing effects, the water molecules absorbed bring about a strong decrease in the apparent activation energy; ΔU = 90 kcal./mole at 80% RH, 200 kcal./mole at 66% RH, and 210 kcal./mole at 55% RH for viscose rayon.
