Preparation And Characterazation Of Bacterial Cellulose-Polyvinyl Alcohol Nanocomposite Hydrogels

In this paper, the bacterial cellulose (BC)-polyvinyl alcohol (PVA) nanocomposite hydrogels using BC as the reinforcement and PVA as the matrix materials were formed in coagulating bath and cross-linked with crosslinking agents. The effect of hydrogels properties by different PVA, BC content and reaction conditions were discussed and the results showed that:the mechanical properties were enhanced as the PVA and BC content increased, while high levels of BC affected its dispersion in the casting solution, so chose the concentration of PVA and BC in the casting solution was 10% and 0.5% respectively, that's to say, BC's mass fraction in the solid content was 4.76%. Technology conditions of crosslinking by formaldehyde were also discussed and found that when crosslinking temperature was 85℃, pH=2-3, the hydrogels showed the best mechanical properties, besides when the crosslinking time reached 30min, the crosslinking reaction was basically completed. Forthemore, the hydrogels were characterized by IR, crosslinking degree, equilibrium swelling ratio, mechanical properties tests, thermo-gravimetric (TG) analysis and XRD. The results show that:by formaldehyde crosslinking treatment, there were C-O-C ether bond absorption peaks at 1167cm-1 and 1019cm-1 in the IR spectra, indicating that the chemical crosslinking happened during the reaction, which led to the equilibrium swelling ratio of nanocomposite hydrogels was significantly reduced, while the mechanical strength was increased, including elongation at break reduced and tensile modulus increased significantly. Moreover, the thermal stability was inproved by formaldehyde crosslinking.At the same crosslinking conditions describled as before. Using aldehyde, glyoxal and glutaradehyde as crosslinking agents, the hydrogels were characterized by IR, crosslinking degree, equilibrium swelling ratio, mechanical properties tests, thermo-gravimetric (TG) analysis and XRD, while the non-crosslinked and formaldehyde crosslinked as contrast. The results showed that:the same mole of bifunctional aldehydes (glyoxal, glutaraldehyde) produced the lager crosslinking degree than the mono-functional aldehydes (formaldehyde, acetaldehyde). The tensile strength, Young's modulus of the resulting hydrogels crosslinked by glyoxal, glutaraldehyde were relatively larger than the other two, which indicating that the greater the degree of crosslinking, the greater the tensile strength and Young's modulus. In addition, by chemimal crosslinking treatment, BC/PVA nanocomposite hydrogels'thermal stability were improved than non-crosslinked hydrogels, while thermal degradation temperature of different cross- linking agents was not obvious. From the XRD patterns before and after crosslinking after crosslinking did not change significantly, because the characteristic diffraction peaks of BC or PVA were not changed, and also there was no significant change in crystallinity. Therefore, it could be inferred that crosslinking treatment did not change its crystallinity, in other words, crosslinking degree had little effect on its crystallinity.