A revised morphological model for the crimp structure of tendon is presented. The 300-500 mu diameter tendons of the mature rat tail are comprised of from one to more than ten substructures, called fascicles, of 80-320 mu diameter. Fascicles each possess a "crimp structure" demonstrable in the polarizing microscope and neighboring fascicles within a tendon usually exhibit crimp registry. The fascicle itself is shown to be a cylindrical array of planar-zig-zag crimped 500-5000 A diameter collagen fibrils. The approximate cylindrical symmetry of the fascicle is domonstrated by SEM not equal to and polarizing optical microscopy. A method of replacing native water with other liquids of refractive index near to that of collagen is utilized to reduce or eliminate light diffusion and therby greatly improve OM observations. Small bunches of collagen fibrils removed from the tendon are shown to exhibit the simple planar zig-zag morphology described in previous literature. The planar crimping of collagen fibrils and their assemblage into cylindrically symmetric fascicles is verified by small angle X-ray diffraction.

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Plane strain compression in a channel die is kinematically very similar to drawing; however, the possibility of void formation is limited due to a compressive component of stress. In drawing, voids were detected by small-angle X-ray scattering (SAXS) and density measurements in poly(methylene oxide) (POM), polypropylene (PP), and high-density polyethylene (HDPE), but no voiding was found in polyamide 6 (PA 6), low-density polyethylenes (LDPEs), and ethylene-octene copolymer (EOC). The slope and shape of the initial elastic part of true stress-true strain curves are similar in tension and in channel die compression. When drawn samples of POM, PP, HDPE, and PA 6 already show yielding, the channel die compressed samples still undergo elastic deformation to a much larger deformation and respond with a much larger stress. Channel die compressed POM, PP, HDPE, and PA 6 exhibit strong and rapid strain hardening up to 400 MPa in contrast to their behavior in tension. The difference in strain hardening is related to preservation of chain entanglement density in channel die compression and disentanglement in tensile drawing. True stress-true strain curves for polymers having crystals with low plastic resistance and not cavitating are very similar in channel die compression and in tension. In tensile drawing there is a competition between cavitation and activation of crystal plasticity. Cavitation occurs in polymers with crystals of higher plastic resistance, while plastic deformation of crystals in polymers with crystals of lower plastic resistance. The necessary conditions for cavitation and for plastic deformation of crystal are defined. They explain why the cavitation is observed in POM, PP, and HDPE but not in LDPEs. In PA 6 negative pressure causes cavitation but the cavities, due to their small sizes and healing action of surface tension, are unstable, close quickly, but leave the traces of a structural damage. A model of plastic deformation of crystalline polymers accounting for cavitation is outlined.

The design and fabrication of ultrathin polymer layers are of increasing importance because of the rapid development of nanoscience and nanotechnology. Confined, two-dimensional crystallization of polymers presents challenges and opportunities due to the long-chain, covalently bonded nature of the macromolecule. Using an innovative layer-multiplying coextrusion process to obtain assemblies with thousands of polymer nanolayers, we discovered a morphology that emerges as confined polyethylene oxide (PEO) layers are made progressively thinner. When the thickness is confined to 20 nanometers, the PEO crystallizes as single, high-aspect-ratio lamellae that resemble single crystals. Unexpectedly, the crystallization habit imparts two orders of magnitude reduction in the gas permeability.

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Polylactide (PLA)/clay nanocomposites loaded with 3 wt % organomodified montmorillonite and PLA/clay microcomposites containing 3 wt % sodium montmorillonite were prepared by melt blending. We investigated the morphology and thermal properties of the nanocomposites and microcomposites and compared them with unfilled PLA, keeping the same thermomechanical history. The influence of the processing temperature on the structural characteristics of the investigated systems was determined. The investigations were performed with differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), size exclusion chromatography (SEC), and polarized light microscopy (LM). XRD showed that the good affinity between the organomodified clay and the PLA was sufficient to form intercalated structure in the nanocomposite. The microcomposite featured a phase-separated constitution. DSC and LM studies showed that the nature of the filler affected the ordering of the PLA matrix at the molecular and supermolecular levels. According to TGA, the PLAbased nanocomposites exhibited improvement in their thermal stability in air. Reduced flammability, together with char formation, was also observed for nanocomposites, compared to the microcomposites and pure PLA.

The process of cavitation during tensile deformation of polypropylene was studied. It was shown that in injection-molded polypropylene samples cavities appear in the center of a sample shortly before yielding. With increasing deformation the cavities change their size, number, and orientation from elongated perpendicular to parallel to deformation. The cavitation process is visible also as a rapid increase of volume of deformed material. The cavitation could be suppressed by changing internal morphology of polypropylene by fast cooling. The samples prepared by compression molding followed by quenching, with less perfect crystals, were able to deform by plastic deformation of crystals without cavitation. However, for faster draw rate the cavitation in amorphous phase was preferred again due to stronger response of crystals.