Synthesis And Properties Of Organic-Inorganic Silica Hybrid Hydrogels

Hydrogels are a new type of functional polymer materials. Because of its unique water-absorbent, water-retention properties, hydrogels have been widely used in the health, agriculture, forestry, horticulture and bio-medicine and other fields, but the traditional superabsorbents have poor salt resistance and poor mechanical strength which limits the application of hydrogels.Sol-gel technique was chosen on the preparation of organic-inorganic silica hybrid hydrogels. Sodium silicate (SS) was firstly chosen, in this work, as a water-soluble inorganic silica precursor due to its low cost and good degradability. A Si-O-Si inorganic network was built by hydrolysis and condensation process of SS, and then interacted with organic monomers(AA)through non-bonding. Meanwhile, a organic network was produced by polymerization of AA under the existence of cross-linker and initiator. Some factors, including proportion of SS/AA and neutralization degree of AA, were discussed with respect to the swelling ability and mechanical strength. The characteristics of the hydrogels were determined by FTIR. The distribution of SiO2 was observed by TEM after HF treatment. The formation process was proposed. The result showed a core-shell structure was formed with SiO2 inner core and acrylic acid (AA) outer shell. When the mass ratio of SS/AA was 0.23, the compressive strength of the hydrogel reached 45.6 KPa at 99.1% water content while the swelling ratio was 1017.2 g/g in deionized water and the hydrogel showed good salt tolerance. In addition, chitosan(CS)as a kind of polycation was introduced to synthesize PAA/SS/CS silica hybrid hydrogel. The hydrogel formation process was proposed after the investigation of reaction conditions. The introduction of polycation was beneficial to improve the mechanical strength of hydrogels. The hydrogels showed a improved mechanical strength up to 57.9 KPa and better pH sensitivity when the PAA/SS/CS hydrogels have the same mass ratio of SS/AA and water content as PAA/SS hydrogels and the mass ratio of CS/AA was 0.09.In order to investigate the structure and properties of hydrogels, PAA/APTEOS/CS silica hybrid hydrogels were synthesized usingγ-aminopropyl triethoxysilane (APTEOS) as precursor. The chemical composition and structure are observed by FTIR, TEM and the formation process was proposed. The pore structure of hydrogels was investigated by SEM after swelling in stimulated gastric fluids (SGF) and stimulated intestial fluids (SIF). This series of products showed good pH-sensitivity and good swelling ability. Besides, a high compressive stress of 775 KPa was achieved under 80% strain with water content of 85.1% when AA was not neutralized.