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Composites of poly(L-lactide) (PLA) with hemp fibers (Cannabis sativa), prepared by batch mixing and plasticized with poly(ethylene glycol) (PEG; weight-average molecular weight ¼ 600 g/mol), were examined by polarized optical microscopy, scanning electron microscopy, wide-angle X-ray scattering, differential scanning calorimetry, thermogravimetric analysis, and mechanical tests. The properties of both fully amorphous and semicrystalline samples of PLA/hemp and PLA-PEG/hemp composites were analyzed as a function of the fiber amount. The cold-crystallization kinetics of PLA in amorphous composites were investigated under isothermal conditions within the range of 70-1308C. For PLA/hemp samples, the bulk crystallization rate displayed a maximum near 1108C, whereas for plasticized samples, a higher and almost constant crystallization rate was observed over the entire temperature range, independently of the hemp amount. The kinetics were then analyzed on the basis of the Avrami model. The effect of fibers on the growth morphology of PLA spherulites, as well as the influence of the plasticizer on the melting behavior of PLA crystals and their reorganization during heating, was also examined. The thermogravimetric analysis of the composites, carried out in both nitrogen and air, showed that the degradation process of fiber-filled systems started earlier than that of plain PLA, independently of the presence of the plasticizer. Mechanical tests showed that the modulus of elasticity of the composites markedly increased with the hemp content, reaching 5.2 GPa in the case of crystallized PLA reinforced with 20 wt % hemp, whereas the elongation and stress at break decreased with an increasing amount of fiber for all examined systems. Plasticization with PEG did not improve the tensile properties of the composites.

A dispersion of isotactic polypropylene (PP) nanoparticles was produced by interfacially‐driven breakup of PP nanolayers. Layer‐multiplying coextrusion was used to fabricate an assembly of 257 alternating PP nanolayers about 12 nm thick sandwiched between thicker polystyrene (PS) layers. Characterization by thermal analysis and wide‐angle X‐ray diffraction (WAXD) confirmed that PP crystallized primarily in the smectic form when confined as nanolayers. When the layered assembly was heated into the melt, the PP nanolayers broke up to form a dispersion of PP droplets in a PS matrix. After solidification, particle size analysis revealed that 90% of the PP was present as 30 nm nanoparticles. The particles were small enough and numerous enough that most did not contain a primary nucleus. When cooled from melt at 10 °C min−1, the droplets crystallized by homogeneous nucleation at 40 °C. The droplets were found to be in the smectic form by WAXD. Because crystallization occurred below the temperature of the smectic to α‐form transformation, the intermediate smectic form was stable and did not convert to the α‐form until heated above 70 °C. This result provided direct evidence for an intermediate smectic phase in the process whereby homogeneous nucleation leads to α‐form crystals in confined nanoparticles. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1795–1803, 2006