Double-helical network in amylose as seen by slow calorimetry and FTIR

The phase content and crystallinity of initially amorphous amylose–water mixtures (70/30 W/W) have been changed by slow cycles of dissolution and recrystallization from Tmax with 50 °C < Tmax < 120 °C. Analysis of the treatment-induced changes is made by X-ray diffraction, FTIR, fast T-ramp DSC and slow calorimetry. Our interest was to follow the relaxation of the network phase and its consequence on the growth of crystallinity. The DSC technique, which gives the temperature of disappearance of long-range order, is unable to quantitatively follow the growth of crystallinity achieved by treating the samples. In highly interactive polymer–solvent systems, order is unmeltable in a fast T-ramp due to strain developed during the ramp. In a 6 K/h T-ramp, the order becomes meltable and grows from 21 J/g to 147 J/g when Tmax increases. The other conclusion is that strain-melting and the network phase, characterized first in polyolefins has a more prominent role in the characterization of H-bonded polysaccharide–water mixtures. Correlation is achieved between the concentration of bands in the CO stretching region, the fraction of single and double helices, and the three endotherms found on the slow T-ramp dissolution traces. FTIR spectra show that chains in the network cannot be disentangled by quenching but can be organized during a slow cooling. The B and V crystalline modifications are observed in the treated samples. Quenched treated amylose and enzyme-resistant amylose seem to contain a comparable amount of double-helical/strainable fraction.