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

Cross-linked porous starch has become a subject of research interest recently.The degree of cross-linking and the freezethaw 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 crosslinked 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 (m NaOH /m pcs ), the mass ratio of NaCl to PCS (m NaCl /m pcs ), the temperature (T a ), and the reaction time (t a )) and the cross-linking reaction (the ratio of ECH volume to the mass of PCS (V ECH /m pcs ), the ratio of solution volume to the mass of PCS (V s /m pcs ), pH value, the temperature (T c ), and the reaction time (t c )) 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: m NaCl /m pcs is 0.06, m NaOH /m pcs is 0.02, T a is 40 °C and t a is 1.0 h, V ECH /m pcs is 0.003 (mL/g), V s /m pcs is 7 (mL/g), pH is 10, T c is 20 °C, and t c 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.