RESUMO
Biomass-based hydrogel is a promising flame-retardant material and has a high potential for applications in transportation, aerospace, building and electrical engineering, and electronics. However, rapid vat photopolymerization (VP) 3D printing of biomass-based hydrogels, especially that of all-natural ones, is still rare. Herein, a new class of VP 3D-printed hydrogels with strong covalent networks, fabricating using fully biomass materials and a commercial liquid crystal display (LCD) printer assembled with low-intensity visible light is presented. Encouragingly, the highly ordered layer-by-layer packing structures provided by VP 3D printing technology endow these hydrogels with remarkable flame retardancy, exceptional temperature resistance, advantageous combustion behaviors, and favorable mechanical strength, in particular, giving them a better limit oxygen index (83.5%) than various biomass-based hydrogels. The proposed approach enables the green design as well as the precise and efficient preparation for flame-retardant materials, paving the way for the future flame-retardant materials toward attaining green sustainability.
RESUMO
Isotactic polypropylene (iPP)-based multilayered composites containing alternating layers of pure iPP and α-nucleating agents (α-NAs)-filled iPP (αPP) were fabricated through layer-multiplying co-extrusion technology. With the manipulation of layer number, a tunable multilayered distribution of α-NAs was achieved and its effect on the crystallization behavior and optical properties of iPP was investigated. When the thickness of an individual iPP layer, which is equal to the distance between adjacent αPP layers, was large, the crystallization process of iPP was governed by homogeneous nucleation, although the crystallization of areas near the layer interfaces was induced by α-NAs. As a result, most iPP formed big spherulites thus a poor clarity. By decreasing the layer thickness via multiplying the layer number, the nucleation of iPP was gradually transformed from a homogeneous mode to a heterogeneous mode because of the more and more strong influence of αPP layers on the crystallization process of adjacent iPP layers. Consequently, iPP exhibited similar crystallization behavior compared with αPP. The polarized optical microscopy results further demonstrated that the size of spherulites in iPP was significantly reduced with the increase of layer number, which contributed to the enhancement of transmittance and decline of haze. Accordingly, this work developed a novel approach to tailor the crystallization behavior and optical properties of iPP.
RESUMO
OBJECTIVE: To analyze the clinical value of dual-source CT (DSCT) in the diagnosis of coronary artery disease. METHODS: Fifty-five patients with suspected coronary heart disease underwent both DSCT coronary angiography (DSCTCA) and selective coronary angiography (CAG) examination, and the diagnostic sensitivity, specificity and accuracy of the DSCTCA was evaluated. RESULTS: The sensitivity, specificity, positive and negative predictive value, and accuracy of DSCT in the diagnosis of coronary heart disease were 97.7%, 72.6%, 93.5%, 88.9% and 92.7% by the number of patients, respectively; by calculating the coronary arteries, the sensitivity, specificity, positive and negative predictive value, accuracy were 94.9%, 95.8%, 92.5%, 97.1%, 95.5%, respectively. According to the lesion segment, these values were 88.2%, 96.9%, 90.5%, 96.1%, 94.7%, respectively. DSCTCA showed no significant difference from CAG for a diagnostic purpose, nor did their vessel sensitivity, specificity, positive and negative predictive value, and accuracy in different coronaries differ significantly. CONCLUSION: DSCT has a diagnostic accuracy of coronary heart disease close to that CAG and can on some occasion serve as an alternative to CAG in the screening of coronary artery disease.
