Impact of Lamellar Infill and Thickening on the Rigid Fraction of PLLANew Submission

Poly(L-lactic acid) (PLLA) is a well-known semicrystalline polymer, with three distinct phases: the crystalline, mobile amorphous, and rigid phase. The rigid phase, or rigid fraction (RF), is thought to be the layer of polymer chains with properties between that of the crystal phase and mobile amorphous phase, such as restricted mobility. Fast differential scanning calorimetry (Flash DSC) is used to determine the relationship between primary crystallization and the rigid fraction of PLLA, as well as the relationship between secondary crystallization and the rigid fraction. The rigid fraction increases with crystal fraction during primary crystallization, regardless of the temperature of crystallization. Lamellar infill, achieved by crystallizing at one temperature followed by crystallization at a lower temperature, results in an increased rigid fraction content at the same degree of crystallinity relative to primary crystallization alone. The relationship between lamellar thickening, lamellar infill, and the rigid fraction is examined.