Effect of cross-linking methods on stress relaxation of PVA/PAM-co-PAA-based hydrogels

Abstract

Both physical and chemical cross-linking methods can improve the mechanical properties of hydrogel by increasing the cross-link density. In this study, a series of polyvinyl alcohol/polyacrylamide-co-polyacrylic acid (PVA/PAM-co-PAA)-based hydrogels were prepared by using Fe³⁺ as physical cross-linking agent and N,N’-methylenebisacrylamide (MBA) as chemical cross-linking agent. The stress relaxation experiments of PVA/PAM-co-PAA-based hydrogels and nonlinear fitting analysis were performed to study the effects of cross-linking methods on stress relaxation behavior of hydrogels. Furthermore, the four-element generalized Maxwell model succeeded in simulating stress relaxation behavior of hydrogels. When Fe³⁺ was used as the cross-linking agent of Fe³⁺/PVA/PAM-co-PAA hydrogel, it took a long time of 199.9 s when the structural units began to move. However, when MBA was used as the cross-linking agent of PVA/PAM-MBA-PAA hydrogel, the time was shortened significantly. Compared with PVA/PAM-co-PAA hydrogel, the initial and equilibrium stress of Fe³⁺/PVA/PAM-co-PAA and PVA/PAM-MBA-PAA hydrogel significantly increased. When Fe³⁺ and MBA were used as the cross-linking agent of Fe³⁺/PVA/PAM-MBA-PAA hydrogel together, the network structure became looser. The initial and equilibrium stress were 0.04 and 0.015 MPa, respectively.

Keywords:

• Hydrogel
• stress relaxation
• generalized Maxwell model
• nonlinear fitting
• cross-linking network

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

This work has been supported by the Natural Science Foundation of China [11802197] and Key R&D Program of Shanxi Province [International Cooperation, 201903D421064].