Early oriented isothermal crystallization of polyethylene studied by high-time-resolution SAXS/WAXS

During cooling from the quiescent melt of a highly oriented polyethylene rod, highly oriented proto-lamellae are formed first, which are not crystalline. This is shown in scattering data which are recorded on two-dimensional detectors with a cycle time of 1 s and an exposure of 0.1 s. In the experiments small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) are registered simultaneously during the first 3 min after quenching to a crystallization temperature. A non-uniform thickness between 20 and 100 nm is characteristic for the ensemble of proto-lamellae. During the first minute of isothermal treatment the number of proto-lamellae slowly increases without a change of the thickness distribution. As crystallization starts, the crystallites are not oriented in contrast to the proto-lamellae. During crystallization the layer thickness distribution narrows. The number of lamellae rapidly increases during the following 2 min of isothermal treatment (at 128 degrees C and 124 degrees C). The results are obtained by interpretation of the WAXS and of the multidimensional chord distribution function (CDF), a model-free real-space visualization of the nanostructure information contained in the SAXS data.

Correlation between Solid-State Structures and Enzymatic Degradability of Cocrystallized Blends

Solid-state structures and enzymatic degradability have been investigated for cocrystallized blends between poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [PHBV] and poly(3-hydroxybutyrate-co-3-hydroxypropionate) [PHBP]. From wide-angle X-ray diffraction patterns, small-angle X-ray scattering data, and the comparison of the enzymatic degradability of these blends, the solid-state structures of PHBV/PHBP blend samples, in which the PHBV component has higher isothermal crystal growth rate (G) value than the PHBP one, might be similar to those of the component PHBVs; while those of the PHBP/PHBV blend samples, in which PHBP component has higher G value, were similar to the component PHBPs. Normalized one-dimensional correlation functions gamma(x) of PHBV/PHBP binary blends crystallized at 90 degrees C.

Experiências simultâneas de espalhamento de raios X e calorimetria diferencial de varredura (SAXS/WAXD/DSC) com resolução temporal utilizando radiação síncrotron

Neste trabalho apresentamos uma nova instrumentação instalada na linha de SAXS do LNLS. Este equipamento permite a realização de experimentos simultâneos e resolvidos no tempo de espalhamento de raios X a baixos e altos ângulos (SAXS/WAXD) e calorimetria diferencial de varredura (DSC). O dispositivo de DSC mostrou-se comparável a equipamentos convencionais, com taxas de variação de temperatura de até 60 °C/min e uma precisão de 0.1 °C. O uso de uma fonte de radiação síncrotron e de detetores de raios X sensíveis à posição permitiu a obtenção de dados com uma resolução temporal de 30 s. A aplicação deste arranjo experimental no estudo da cristalização isotérmica e da fusão em materiais poliméricos é mostrada para o caso da policaprolactona (PCL) e suas blendas com polietileno clorado (PCL/PECl). As experiências mostraram a formação simultânea da estrutura cristalina e da morfologia lamelar nos diferentes estágios da cristalização assim como mudanças na cinética do processo com o tratamento isotérmico e a composição da blenda. Finalmente cabe destacar que experimentos simultâneos de SAXS/WAXD/DSC permitem o estudo de distintos processos abrangendo não apenas os de cristalização, mas também a formação de colóides e géis ou as transições de fase estruturais em diversos materiais.