Structural dependence of the molecular mobility in acetylated starch

In this study, the molecular mobility of acetylated starch (AS) with degree of substitution (DS) 1.5 and 3, representing partial and complete substitution of hydroxyl groups with acetyl groups, was investigated. The glass transition region and the onset of long-range cooperative molecular motions were examined using temperature-modulated-DSC (TMDSC). A potential analogy between the relaxation time of hole formation and the alpha-relaxation time was observed. The deviation in the temperature dependence of the alpha-relaxation time from the Arrhenius relationship, obtained with the fragility index, revealed differences according to DS. The cooperative rearranging region (CRR) characteristics differed according to DS and estimation method. Smaller size of the CRR for AS with DS 3 compared to AS with DS 1.5 suggest disruption of hydrogen bonds at high acetylation level. TMDSC experimental data at moderate temperature and predictions and SS-NMR results at ambient temperature, indicate different mobility of AS according to DS and temperature conditions.