Preparation Of Highly Stretchable And Tough Hydrogels

Hydrogels are cross-linked, three-dimensional, hydrophilic polymer networks, which swell in water but do not melt or dissolve. Hydrogels have good biocompatibility and other excellent properties, such as: environmental responsiveness, antimicrobial, self-healing and super absorbent et al. Because of the superior properties, the hydrogels have an extensive application in medicine & biomedical sciences, intelligent sensors, shape-memory, separation and water retention. However, the traditional, chemical cross-linked hydrogels are so weak that severely limited their applications. For a long time, to enhance the mechanical properties of hydrogels, a series of research and a variety of hydrogels with novel structures had been developed. Recently, the tough composite hydrogels and Interpenetrating network hydrogels has attracted great attention in the field of hydrogels science because of their simple method of preparation and excellent mechanical properties. Cellulose nanocrystals(CNs) is a kind of excellent biological reinforced materials. As a result, nanocomposite hydrogels(NC gel) with high mechanical properties reinforced by CNs were prepared. On the other hand, as a kind of excellent emulsifier, CNs also can be used to stable Pickering emulsions. Further, we can prepare emulsions composite hydrogels(ECG gel) and IPN hydrogels. In this study, to improve the mechanical properties of the hydrogels, we prepared highly stretch and tough CNs/PAM nanocomposite hydrogels, ECG hydrogels and IPN hydrogels based on CNs.The main task and results are list as follow:1. CNs modified with Ammonium persulfate(APS) were obtained from pulp fibers using H2SO4 hydrolysis with minor modifications. CNs/PAM hydrogels with tough and ultrahigh tensibility were synthesized through thermally induced polymerization of Acrylamide(AM) and the CNs. The properties of the hydrogels with different concentration of CNs, AM and APS were monitored and investigated. The mechanism of CNs/PAM hydrogels was analyzed by the reaction mechanism, mechanical properties, swelling properties and SEM morphology of hydrogels. The results showed that the CNs/PAM hydrogels had typical honeycomb-like structure. The section of the hydrogels had many whiskers of CNs covered by PAM because of multive of H-bonding on the surface of CNs. As long as a tiny amount of CNs was added, the mechanical properties of hydrogels were improved significantly. As the concentration of CNs was about 0.5 mg/ml, hydrogels had the best mechanical properties. The elongation at break of hydrogels reached 3183%, fracture strength also has 81.4 KPa. In addition, the concentration of monomer AM was the key to form integrated polymer networks. APS also has an essential effect on the crosslinking degree and kinetic chain length of the hydrogels, which acted as modifier and initiator.2. The CNs was used to prepare ECG hydrogels with different volume of internal phase and different crosslinking degree in this study. The volume of internal phase and crosslinking degree that had an influence on mechanical properties was discussed. The emulsions and the morphology, swelling and mechanical property of ECG hydrogels were monitored. We concluded that as the increase of volume of internal phase, polymer networks and crosslinking density of hydrogels decreased, the stress concentration and defects increased. From what has been discussed above, we can draw the conclusions that mechanical property of ECG gels cannot be significantly improved. In this dissertation we prepared high strength IPN gels based on template method of ECG hydrogels, which can further enhance the mechanical properties of hydrogels. The network structures of IPN hydrogels had discussed carefully. And highly strength IPN hydrogel based on the use of ECG hydrogels templates has a sufficient feasibility and broad universality.