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We present the upgrade and present status of the ultrasmall-angle x-ray scattering ͑USAXS͒ beamline BW4 at the Hamburg Synchrotronstrahlungslabor. In order to extend the accessible scattering vector range, new small-angle setups have been established, making use of the high flux and small divergence of BW4. In standard transmission geometry using a beam size of B = 400 ϫ 400 m 2 ͑horizontalϫ vertical͒, typical small-angle resolution ranges from d max = 90 to 650 nm, depending on sample-to-detector distance. Additionally a new microfocus option has been established. This microfocus option allows reducing the sample size by one order of magnitude. Using parabolic beryllium compound refractive lenses, a new standard beam size of B =65 ϫ 35 m 2 ͑horizontalϫ vertical͒ can be provided. The -SAXS resolution is as high as d max = 150 nm. Using -SAXS in combination with grazing incidence ͑-GISAXS͒ on a standard noble metal gradient multilayer, we prove the feasibility of -GISAXS experiments at a second generation source.

Highly oriented native cellulose fibres (flax) and softwood (pine) have been investigated by means of X-ray diffraction. Local structural information was obtained by using X-ray microbeams. Tensile tests were performed in situ, revealing a change of orientation of cellulose microfibrils in materials with tensile strain. In flax fibres, the microfibrils rotate during the first percent of stretching, into a more parallel orientation with respect to the fibre axis. For wood, a decrease of orientation with the onset of strain hardening is found for the first time.

Uniaxially oriented polypropylene (PP) is molten in the synchrotron beam and crystallized from the quiescent melt, keeping its orientation in order to study the mechanisms of its crystallization. We document the different nanostructures observed as a function of melt-annealing temperature, undercooling, and time. In order to obtain a melt that crystallizes with high preferential orientation again, a melt-annealing temperature between 170 and 176 °C is chosen. Isothermal crystallization at 155 °C results in slow formation of (primary) lamellae placed at random. As the crystallization temperature is decreased (150, 145, and 140 °C), more and more secondary crystallites are observed which develop from a block mesostructure according to Strobl's mechanism. During the isothermal phase the blocks are fusing more or less to form imperfect lamellae. The structure evolution observed in the time-resolved small-angle X-ray scattering (SAXS) data during crystallization and remelting facilitates discrimination between the block structure and another frequently discussed morphology, Keller's cross-hatched structure. While after all our quiescent crystallization experiments most of the crystallites are blocks or incompletely fused lamellae, the hard-elastic precursor material which has been made under extreme gradients of temperature and pressure exhibits the melting of homogeneous and extended lamellae. As we apply a steep temperature gradient (−100 °C/min) to our melt in a nonisothermal crystallization experiment, we initially observe the formation of homogeneous and extended lamellae as well.