The Stability Of The Pva Hydrogel

The current domestic and foreign research on the preparation, properties, characterization and application of polyvinyl alcohol hydrogels were reviewed in the beginning. The swollen properties, the degradation, the crystallinity, the water state and the structural organization of poly (vinyl alcohol) hydrogels obtained by freezing and thawing techniques were systematically and quantitatively investigated in this paper. All of the work can be divided into six parts:1. PVA/H2O gels and PVA/ dimethylsulfoxide (DMSO)/H2O gels were prepared by twin-screw extruder. The swollen properties and mechanical properties changes of the two kinds of PVA hydrogels with the time of dipping in different solvent at different temperatures were systematically studied.The results show that the swollen properties of the two kinds of PVA hydrogels were different.But both of their mechanical performances were excellent and close to each other at the same PVA concentration.But the mechanical strength are not very stable.It always varies in a small scope. Because it is influenced by the forming state of the gel. The increasement in the concentration of the polymer in the gel will get its mechanical properties enhanced. But both the mechanical properties of the two kinds of gel with high PVA concentrations decreased when they were dipped in the water and brine for a long time.2. The transfer of DMSO with a certain toxicity from PVA/DMSO/H2O gel when dipped in water for a long time may influence the stability and the structure of the gel. Hence the ultraviolet absorption standard curve of DMSO/H2O solution was established by the quantitative analyzation with ultraviolet spectrophotometry and the transferring speed of DMSO from PVA/DMSO/H2O gel when the gel was dipped in the distilled water was studied.The result indicates that the transferring speed of DMSO from PVA/DMSO/H2O gel is very high.80% of DMSO has transferred out in several days.3. The viscosity-average molecular weights of PVA were measured and the influences of different factors on the degradation of PVA were studid. 4. The changes of the crystallinity of the two kinds of PVA hydrogels when putting the gel as prepared immediately into water for a long time and the influence of the PVA concentration on the crystallinity was investigated by X-ray diffraction. The result shows that the rystallinity of the two kinds of PVA hydrogels enhanced as PVA concentration increased. But the changes of the crystallinity of the two kinds of PVA hydrogels are not the same.5. The water in PVA hydrogels were quantitatively investigated by differential scanning calorimetry (DSC) and thermo gravimetry (TG).The results indicate that the content of non-freezing water increased along with the content of free water declined as PVA concentration of the hydrogel increases; along with the increase of freezable water (free water and freezable bound water).DSC figures show that the weight ratioof non-freezable bound water to dry membrane is almost permanent (about 0.5).6. The microstructure of PVA hydrogels was observed by Scanning electron microscopy (SEM) after the hydrogels were dried by critical-point dry technique (CPD). It is observed that the two kinds of PVA hydrogels both have a complex hierarchical structure, extending over a wide range of length scales.