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

The phase content and crystallinity of initially amorphous amylose-water mi xtures (70/30 W/W) have been changed by slow cycles of dissolution and recr ystallization from T-max with 50 degrees C < T-max < 120 degrees C. Analysi s 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. T he DSC technique, which gives the temperature of disappearance of long-rang e order, is unable to quantitatively follow the growth of crystallinity ach ieved by treating the samples. In highly interactive polymer-solvent system s, 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 t o 147 J/g when T-max increases. The other conclusion is that strain-melting and the network phase, characterized first in polyolefins has a more promi nent role in the characterization of H-bonded polysaccharide-water mixtures . Correlation is achieved between the concentration of bands in the C-O str etching region, the fraction of single and double helices, and the three en dotherms found on the slow T-ramp dissolution traces. FTIR spectra show tha t chains in the network cannot be disentangled by quenching but can be orga nized during a slow cooling. The B and V crystalline modifications are obse rved in the treated samples. Quenched treated amylose and enzyme-resistant amylose seem to contain a comparable amount of double-helical/strainable fr action. (C) 2000 John Wiley & Sons, Inc.