Synthesis And Properties Of Double Network Nanocomposite Hydrogel

Hydrogels are a new kind of three-dimensional hydrophilic crosslinked polymers. The low fracture toughness of chemically crosslinked hydrogels restricts their application in biomedicine, organ engineering and other fields. Many efforts have been made to increase the mechanical strength of hydrogels by the introduction of inorganic nanoclay into organic polymer networks and double network.At first, polyacrylamide nanocomposite hydrogels with two crosslinkers, Laponite and MBAM, was prepared by free radical initiation. Different crosslinkers contents were investigated in terms of tensile and compressive strength. In addition, the PAAm hydrogels were hydrolyzed and the swelling capacity, mechanical strength and the swelling dynamics were studied. The results indicated that a compressive stress of 8.26 KPa was obtained with 10.7% Laponite and 0.02% MBAM. In addition, the swelling capacity was 459.8 g/g in distilled water and 66.7 g/g in 0.9% NaCl. The swelling of the hydrolyzed PAAm hydrogel was faster and the diffusion behaviors obeyed non-fickian type. To investigate the crosslinking effect of Laponite further and enhance the comprehensive performance, the double network composed of different monomers was introduced. A novel double network nanocomposite hydrogel consisting of the first network of PAAm using laponite as a crosslinker and the second network of PAA using MBAM as a crosslinker was synthesized by two-step solution polymerization. The resulting PAAm-PAA double network nanocomposite hydrogels showed an excellent swelling capacity of 1219 g/g in deionized water, 124 g/g in 0.9 wt% NaCl solution while 21.5 KPa high compressive stress in a high water content of 99.58% was achieved when 5 wt% laponite and 0.05 wt% MBAM were used during the polymerization respectively. But the time to reach swelling equilibrium is shorter than hydrogel with two crosslinkers.Based on PAAm-PAA double network nanocomposite hydrogels, PAAm-PAMPS hydrogels were prepared by different methods by which the first network of PAAm was denser in contrast to the one in PAAm-PAA. The results showed the hydrogel had a high compressive stress of 87.58 KPa in high water content of 99.3% while the swelling capacity in deionized water is 195.2 g/g when the contents of laponite and MBAM were 13.8% and 1.8%, respectively..