Crystal Orientation of Poly(l-Lactic Acid) Induced by Magnetic Alignment of a Nucleating Agent

The orientation of poly(l-lactic acid) (PLLA) crystals was controlled through crystal growth from a magnetically oriented nucleating agent, phenylphosphonic acid zinc (PPAZn). The one-dimensional magnetically oriented microcrystal array of PPAZn microcrystals revealed the relationship between the magnetization and crystallographic axes in the PPAZn crystal. The PPAZn microcrystals were homogeneously dispersed in PLLA via melt mixing, which decreased the molecular weight of the PLLA component due to degradation. The PPAZn microcrystals in the molten PLLA were uniaxially aligned under an 8-T static or rotating magnetic field. The wide-angle X-ray diffraction and small-angle X-ray scattering patterns of the PPAZn/PLLA composite films crystallized under each magnetic field showed that the PLLA lamellae grew from the surface of the PPAZn microcrystals, which were uniaxially oriented along the easy- or hard-magnetization axis, with the c-axis of PLLA parallel to the bc-plane of PPAZn. It was also suggested that the greater nucleating effect of PPAZn on PLLA was derived not from geometrical matching, but from factors such as favorable interactions and/or the plate-like shape of the microcrystal.