An analysis of the correlation between structural anisotropy and dimensional stability for drawn poly(lactic acid) films

The anisotropic structures found in drawn poly(lactic acid) films are strongly correlated to their overall dimensional stability. Several aspects of this relationship can be efficiently characterized by Raman spectroscopy. We determined the degree of orientation in these drawn films by measuring the relative intensity of the polarized and depolarized components and the shift in the relative band positions. The bandwidth and specific band frequency also correlated well with the degree of sample crystallinity. These aspects make the Raman method amenable for the online monitoring of orientation and crystallinity in commercial processes. A molecular understanding of heat setting to reduce film shrinkage is also proposed. Raman data from films that were heat-set while physically constrained suggest that amorphous-phase relaxation does not occur during heat setting. Rather, the level of crystallinity increases substantially, indicating that the cause of low shrinkage in the films was due to crystalline network formation rather than amorphous-phase relaxation. (C) 2001 John Wiley & Sons, Inc.