Enhanced Surface Wettability of Rice Straw with Alkaline Pretreatment

ABSTRACT

To improve the surface wetting properties of rice straw, effects of distilled water and four alkali pretreatment on the straw surface wettability were analyzed. The straw surface contact angle at different time points was measured by JC2000A contact angle measuring apparatus, optical microscope (OM) and scanning electron microscopy (SEM) combined with a linear regression technique for parameter extraction. The results show that the surface wettability of rice straw obtained significant improvement after alkali treatment and the contact angle decreases until it reaches equilibrium (force balance, heat balance and chemical equilibrium) over time. The contact angle has the maximum rate of change at the mass fraction of l% in 10min by NaNH2 pretreatment of the rice straw with the contact angle decrease gradient of 20.64%. The contact angle has the smallest decrease gradient of 3.6% by CaH2 pretreatment of the rice straw under the same conditions, however, a large number of CaCO3 formation lead to the contact angle which does not change significantly over time. When smooth wax inside and outside the straw surface is removed, there has been similar to the “etched” phenomenon with wettability improved obviously by SEM image analysis. The optimum conditions of processing technology were obtained through orthogonal test: concentration of NaOH is 0.6%, solvent ratio 1:3.5 and reaction time 12h.