Supramolecular morphology of two-step, melt-spun poly(lactic acid) fibers

Fibers of poly(lactic acid) produced by two-step melt spinning have been studied. The morphology is elucidated with respect to the thermal and mechanical properties of fibers produced at cold-draw ratios of 1-8. With atomic force microscopy and small-angle X-ray scattering, a fibrillar morphology is found, with microfibril diameters ranging from 30 to 60 nm. Shrinkage properties indicate that, with increasing draw ratio, the fibers undergo a transition from class 2 to class 1 within the classification proposed by Keller. A supramolecular model for the morphology of the fibers is presented that entails a highly oriented skin with a core consisting of microfibrils. The orientation of the crystalline blocks within the microfibrils is similar to what has been reported for nylon fibers. (C) 2002 Wiley Periodicals, Inc.