EFFECT OF HYDRATION ON THE MECHANICAL PROPERTIES OF A PVA DUAL-CROSSLINKED HYDROGEL

91 pagesThe effect of drying on the constitutive behavior of a dual cross-linked poly(vinyl alcohol) (PVA) hydrogel is studied. This gel contains about 90% water when fully hydrated. The mass-volume relationship of the gel is measured using a microbalance with a density kit. Our results show that as the gel dries the volume is linearly proportional to the mass. The impact of drying on the gel’s mechanical properties is measured in uniaxial tension tests, which include loading-unloading tests at three different constant stretch rates, a complex loading history test and a stress-relaxation test. Data from specimens with different hydration levels can be described by a constitutive model of the gel. The results show that the model parameters are strongly dependent on hydration level and that as the gels dry, the gels become much stiffer than in the fully hydrated state. Fracture tests, including constant rate loading test and creep test, are also done for this hydrogel at different hydration levels. The results show that the breaking stress is much larger as the gels dry. Furthermore, experimental and numerical studies are done on the effect of compression in torsion-rheometry tests. The results show the compression will make us overestimate the dynamic modulus and give a shift factor for different compression