Convenient Method for Enhancing Hydrophobicity and Dispersibility of Starch Nanocrystals by Crosslinking Modification with Citric Acid

Abstract This study investigated the chemical, wettability, thermal and structural properties of starch nanocrystals (SNCs) modified through crosslinking modification using citric acid in aqueous medium. The results of Fourier transform infrared spectroscopy analysis suggested that new interactions occurred between starch and citric acid after modification and an increase of the reaction time increased the degree of substitution. X-ray diffraction analysis showed that the crystalline structure of SNCs was maintained after the crosslinking modification by adjusting the pH to 3.5, and destroyed after the modification by pretreatments without adjusting the pH of the citric acid solution. Crosslinking modification decreased the size and aggregation of SNCs and longer reaction time gave rise to the smaller particle size of SNCs modified by the pretreatments of adjusting the pH of the citric acid solution. The crosslinked SNCs had lower polarity and showed stronger hydrophobicity and dispersion stability which allowed them be used as reinforcements in hydrophobic polymer matrices.