Figure 3e shows the effect of temperature on the Q values of hydrogels after the pasting reaction. The Q values increased and then decreased with increasing temperature, and reached to the maximum at 50 °C. Less free radicals could be produced at such a low temperature, and thus may decrease the rate of grafting reaction, resulting in low Qs. With increasing temperature, more free radicals could be produced and the monomer reactivity may increase; therefore, the grafting and chain growth rate increased [16], thereby increasing the Q values of the hydrogels. When the temperature was >50 °C, the excessive free radicals generated from the decomposition of initiator increased the reaction rate, thus decreased the grafting molecular weight and were …show more content…
In the first 15 min, the swelling ratio of the hydrogels increased fast. After 15 min, the increasing rate decreased, and the swelling achieved equilibrium at ∼20 min. Compared to the control hydrogel (SH-0), the swelling ratios and swelling rates of SH-2 hydrogel (25% pretreated corn straw) and SH-9 hydrogel (14% pretreated corn straw) both increased. With more corn straw, there would be more grafting g points, favoring the grafting reaction, forming a 3D network, thus increasing the water absorptivity. However, the swelling rate and ratio of SH-9 (14% pretreated straw) were higher than those of SH-2 (25% prereated straw), indicating that the increased amount of corn straw may not result in better water absorptivity of hydrogels, because besides cellulose, corn straw contains a lot of lignin and hemicellulose. The phenol units in lignin can inhibit the polymerization, indicating that too excess corn straws would make the grafting reaction difficult and thus inhibit the formation of a 3D network. The swelling dynamics of the hydrogels agreed with the following exponential variation equation …show more content…
Figure 5a shows that the parallel fibers compacted and ordered into a fiber bundle. The micropores were closed and many reactive hydroxyls were sealed. Figure 6b shows that after the pretreatment by NaOH and H2O2, the surface morphology of the corn straw significantly changed. The fiber structure became loose; the specific surface area of cellulose increased; some micropores were observed on the fiber extension surface, thus decreasing the degree of crystallinity. All these factors enhanced the surface wettability of cellulose to reagent and improved its