Experimental Parameters Affecting Cross-Linking Density and Free-Thaw Stability of Cross-Linked Porous Starch

Abstract

Cross-linked porous starch has become a subject of research interest recently. The degree of cross-linking and the freeze-thaw stability are critical for cross-linked porous starch with respect to its practical applications. Herein, cross-linked porous corn starch (c-PCS) was prepared by the pre-alkalization of porous corn starch (PCS) using NaCl/NaOH which was then cross-linked using epichlorohydrin (ECH). The effects of key experimental parameters involved in both the pre-alkalization process (i.e., the mass ratio of NaOH to PCS (mNaOH /mpcs), the mass ratio of NaCl to PCS (mNaCl /mpcs), the temperature (Ta), and the reaction time (ta)) and the cross-linking reaction (the ratio of ECH volume to the mass of PCS (VECH/mpcs), the ratio of solution volume to the mass of PCS (Vs /mpcs), pH value, the temperature (Tc), and the reaction time (tc)) on the cross-linking degree and freeze-thaw stability of c-PCS were investigated in details. Results show that optimum conditions for the pre-alkalization and cross-linking reaction to obtain c-PCS are as follows: mNaCl /mpcs is 0.06, mNaOH /mpcs is 0.02, Ta is 40 °C and ta is 1.0 h, VECH/mpcs is 0.003 (mL/g), Vs/mpcs is 7 (mL/g), pH is 10, Tc is 20 °C, and tc is 3.0 h. The morphology, crystalline structure and thermal stability of the as-obtained c-PCS were also investigated, suggesting that the surface became rougher, the crystallinity was decreased, and the thermal stability was enhanced resulting from the cross-linking reaction.