Surface photo-crosslinking of corn starch sheets

Surface of corn starch sheets was modified by cross-linking through ultra violet (UV) irradiation. Sodium benzoate was used as photosensitiser and induced into sheet surface layer by soaking the sheets in the photosensitiser aqueous solution. Photo-crosslinking kinetics was investigated and it was found that the cross-linking reaction at the starch sheet surface was very fast initially (during the first 20 J/cm2 irradiation), and the irradiation dose was the primary factor to affect the crosslink extent. Afterwards, concentration of photosensitiser aqueous solution became the dominant factor to affect the crosslink extent. The concentration of 0.75% of sodium benzoate aqueous solution gave rise to the highest crosslink extent in the investigated range, 0.1–2.0%. The results of water contact angle measurements and moisture absorption measurements showed that surface photo-crosslinking modifications significantly reduced the hydrophilic character of the starch sheet surface and enhance water resistance of the starch sheets.