Influence of hot-melt extrusion and compression molding on polymer structure organization, investigated by differential scanning calorimetry

A blend of a pullulan polymer and 1,2,6-hexanetriol as a plasticizer were used to study the effect of melt processing techniques on the physical properties of the resulting materials. The main advantage of pullulan is its linear polysaccharide chain model structure. Hot-melt extrusion and compression molding were performed under the same temperature and pressure conditions. The materials obtained were analysed by differential scanning calorimetry. For the first time, the comparative effect of the two processing techniques, i.e., extrusion and compression molding, on the polymer arrangement is reported. Endothermic events resulted from the melt extrusion process were shown to be related to different structures of oriented populations of macromolecules and to microphase separation. Orientation was enhanced by cooling the extrudate at the die exit, with a corresponding increased enthalpy from 34.7 to 51.4 J/g. In contrast, when using compression molding, the endotherm was less marked (11.9 J/g), suggesting less orientation, but the shape of the thermogram was quite similar to that of the extrudate. In both cases, we observed a loss of orientation when the molded materials were milled. A semiquantitative kinetic study of the disorientation process of the extrudate upon isothermic tempering suggests that a disorientation phenomenon occurs at the same time as a swelling process due to the presence of microphase separation. The extrudate was shown to be stable at 25 degreesC. (C) 2001 John Wiley & Sons, Inc.