The realization of hierarchical shish‐kebab structures for stereocomplex poly(lactic acid) (PLA) is achieved by the application of a shear flow (100 s–1 for 1 s) mimicking what can be expected during polymer processing. Compared to the normal shearing scenarios, this transient and strong shear flow enables the creation of dense shish precursors in time‐ and energy‐saving manner. The distribution of crystal form associated with the hierarchical structure is revealed by 2D Fourier transform infrared spectroscopy imaging, creating a unique visualization for both spatial resolution and polymorphism identification. Interestingly, in the shear stereocomplex chains are preferentially extended and crystallized as stable central cores with weak temperature dependence, whereas the development of lateral kebabs is defined by the distinct relation to the crystallization temperature. Below the melting point of homocrystals, both homo and stereocomplex crystallization are engaged in lamellar packing. Above that, exclusive stereocomplex crystals are organized into ordered lamellae. Combining the direct observations at multiscale, the ordered alignment of stereocomplex chains is recognized as the molecular origin of fibrillar extended chain bundles that constitute the central row‐nuclei. The proposed hypothesis affords elucidation of shish‐kebab formation and unique polymorphism in sheared stereocomplex PLA, which generates opportunities for engendering hierarchically structured PLA with improved performance.
Abstract The aim of this study was to compare three different test methods for assaying the biodegradability of starch-based materials. The materials tested included some commercial starch-based materials and thermoplastic starch film prepared by extrusion from native potato starch and glycerol. Enzymatic hydrolysis was performed using excess Bacillus licheniformis α-amylase and Aspergillus niger glucoamylase at 37°C. The degree of degradation was assayed by measuring the dissolved carbohydrates and the weight loss of the samples. The head-space test was based on carbon dioxide evolution using sewage sludge as an inoculum. The composting experiments were carried out in an insulated commercial composter bin. The degradation was evaluated visually at weekly intervals, and the weight loss of the samples was measured after composting. Good correlation was found among the three different test methods. 相似文献
The synthetic procedure of lithocholyl-N-(2-aminoethyl)amide yielded a mixture of several forms detected by solid state 13C CP/MAS NMR although the solution state NMR unambiguously ascertained that the compound was pure. By recrystallization from
various solvents one pure polymorph alongside with four solvates were isolated. The structures of the pure polymorph and the
solvates were characterized by 13C and 15N CP/MAS NMR and powder X-ray diffraction (PXRD) methods. Variable contact time and dipolar dephasing experiments were employed
to obtain optimized CP parameters and to distinguish various CHn (n = 0–3) resonances. CSA analyses of spinning side bands at different spinning rates showed small variations in the shielding
tensor values of the carbonyl group between the pure polymorph (recrystallized from acetonitrile, tetrahydrofuran and 1,4-dioxane)
and p-xylene solvate. 相似文献
The title compound, CaCs2[Ag2(SCN)6]·2H2O, forms a continuous structure where the Ag atoms form chains with S atoms in the c‐axis direction. The chains are bonded together through Cs and Ca atoms. The crystal water of the structure is bonded to the Ca atoms, which lie on centers of symmetry. 相似文献
There is a growing body of evidence that oxidative stress plays a major role in Alzheimer's disease (AD) pathogenesis. Identification of oxidatively altered proteins in AD is important for understanding the relationship between protein oxidation, protein aggregation and neurodegeneration. In this communication, we report a method that can be applied to study oxidative changes of individual proteins in brain. In order to analyze protein oxidation by detection of protein-bound carbonyls, cytosolic protein extracts were derivatized with 2,4-dinitrophenylhydrazine (DNPH) and then separated by two-dimensional (2-D) gel electrophoresis. After electrotransfer to polyvinylidene difluoride (PVDF) membranes, proteins were first stained with Sypro Ruby protein stain, and then the oxidized proteins were detected with anti-dinitrophenyl (DNP) antibody. About 150 proteins and more than 100 oxidized proteins were detected and quantified in both AD and control cases by 2-D image analysis. The amount of protein-bound carbonyls was decreased for six and increased for one protein in AD. The amount of protein was increased for three proteins in AD. Furthermore, the degree of oxidation was calculated as the ratio of protein-bound carbonyls to the total amount of an individual protein. Two proteins showed a significant decrease in the degree of oxidation in AD. Our results suggest that the balance of protein oxidation and degradation is altered in AD. 相似文献