Stress Relaxation under Large Step Strain for Ionomers Based on Ethylene-co-Methacrylic Acid Copolymer in the Melt State.

Abstract

Stress relaxation behavior under large step shear strain γ for ethylene-co-methacrylic acid copolymer (EMAA) and its ionomers (EMAA-Zn and EMAA-Na) was studied in the melt state. EMAA ionomers show higher relaxation modulus G (t,γ ) and slower relaxation rate than EMAA. At 140°C the strain dependence of G (t,γ ) for EMAA ionomers is very strong. The corresponding damping function h (γ ) decreases with γ in two steps around γ =0.6 and γ =4. This suggests that the ion aggregates become small in two steps. However, at 200°C h (γ ) monotonically decreases with γ , indicating that the ion aggregates are already small and become smaller monotonically with increasing γ . Compared with EMAA-Na, EMAA-Zn has higher stress relaxation modulus because of strong interactions due to cooperation between the carboxyl acid group and Zn 2+ .

Rheological study of quaternary ammonium‐containing star‐shaped polylactic acid

“…Zeng et al 65 stipulated that this behavior can be explained by the model proposed by Eisenberg 66 : according to Eisenberg, the ionic aggregates subsists within the polymer in two different forms which are clusters and multiplets; the clusters are of large size (sometimes induce microphase separation) and can be dissociated to give multiplets (association of a small number of ion-containing macromolecules).…”