Stress intensification – an abnormal phenomenon observed during stress relaxation of dynamic coordination polymer

Abstract

Abstract. The authors report that during tensile stress relaxation test of a polyurethane crosslinked by catechol-iron coordination bonds, the stress gradually increases with time after the initial drop, which differs from the documented behaviors of other materials. Based on model experiment and structural characterization, water triggered rapid increase of dynamic crosslinkages accompanied by Poisson's contraction is found to be responsible for the stress intensification effect. In addition, the influential factors are carefully discussed. The findings might help to develop novel polymeric materials with improved application performance under loading conditions.

Self-Healing of Polymer in Acidic Water toward Strength Restoration through the Synergistic Effect of Hydrophilic and Hydrophobic Interactions

“…Aside from the fast decrease of stress at the initial stage due to adjustment of conformation, the stress of HBPU-MSA-ABS saturated by water gradually decreases with time and approaches zero when pH = 4. In contrast, stress of the same polymer is stabilized at a higher level in the cases of pH = 7 and 9, which resembles a conventional cross-linked polymer . For the dried specimens (Figure b), the time dependencies of stress are almost identical no matter whether pH = 4 or 7 or 9, and the equilibrium stresses are much higher than zero.…”

“…In contrast, stress of the same polymer is stabilized at a higher level in the cases of pH = 7 and 9, which resembles a conventional cross-linked polymer. 54 For the dried specimens (Figure 3b), the time dependencies of stress are almost identical no matter whether pH = 4 or 7 or 9, and the equilibrium stresses are much higher than zero. The distinct manner of water-saturated HBPU-MSA-ABS at pH = 4 indicates that the hydrogen bonds formed by the protonated hydrophilic groups must become dynamically reversible in the acidic aqueous environment, 55 coinciding with the analysis of water contact angle measurement in the last paragraph.…”

Behaviour of Long-Lasting Stress Relaxation of Various Types of Yarns

“…Stresses decrease in a time under constant strain, and understanding of behaviour of the stress relaxation process is very important when desirable properties are required in a textile for a long period of time [4,5]. In textiles as well as in other polymeric materials, the macromolecular conformation has to be at a non-equilibrium state upon being stressed and the movement of chain segments would take place to reduce or relieve the internal stress in time [6].…”