The alkaline extraction of hemicelluloses from a mixture of three varieties of wheat straw (containing 40.1% cellulose, 20.23% xylan, and 26.2% hemicellulose) was analyzed considering the following complementary pre-treatments: freeze–thaw cycles, microwaves, and ultrasounds. The two cycles freeze–thaw approach was selected based on simplicity and energy savings for further analysis and optimization. Experiments planned with Design Expert were performed. The regression model determined through the response surface methodology based on the severity factor (defined as a function of time and temperature) and alkali concentration as variables was then used to optimize the process in a multi-objective case considering the possibility of further use for pulping. To show the properties and chemical structure of the separated hemicelluloses, several analytical methods were used: high-performance chromatography (HPLC), Fourier-transformed infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H-NMR), thermogravimetry and derivative thermogravimetry analysis (TG, DTG), and scanning electron microscopy (SEM). The verified experimental optimization result indicated the possibility of obtaining hemicelluloses material containing 3.40% glucan, 85.51% xylan, and 7.89% arabinan. The association of hot alkaline extraction with two freeze–thaw cycles allows the partial preservation of the hemicellulose polymeric structure.
The main result and characterizing aspect of the research consists of the effectiveness of novel ZnO-linen fibrous composites synthesized by means of hydrothermal deposition of zinc oxide onto linen fibers, with the assistance of two surfactants. This has a direct implication on the relationship between the morphological, structural and chemical attributes and water vapor sorption-desorption behavior. Methodology consists of the hydrothermal synthesis of zinc oxide onto linen fibrous substrates previously grafted with MCT-β-CD (MonoChloroTriazinyl–β-CycloDextrin) via a hydrothermal process. The morphological, structural and chemical properties of the samples were examined, in terms of a co-assisted investigation system: SEM images for the morphology, EDX analysis for surface composition, FTIR spectroscopy and X-ray diffractometry for structural samples features. Dynamic vapor sorption (DVS) analysis will complete this study. According to the results provided by the characterization technique, the uniformity of the fabric coated with ZnO powder hydrothermally synthesized with assistance of CTAB (Cetyl TrimethylAmmonium Bromide) is better than that of ZnO powder hydrothermally synthesized in the presence of Pluronic P123 and possesses good washing fastness. X-ray diffraction results have indicated that the composites exhibited a more ordered structure and higher water vapor sorption-desorption capacity (obtained by DVS analysis) compared with those of the reference fibrous linen supports.
Plasma nitriding has significant advantages: very low running costs (reduced consumption of energy and gases); optimized structure and layers; and nitriding of stainless steels. Plasma nitriding is totally safe and has no poisonous gas emissions and no negative environmental impact. However, conventional plasma nitriding has a number of well-known difficulties, including the direct application of plasma on the parts to be treated, the risk of arcing, hollow cathodes, white layers, non-homogenous batch temperature and the impossibility to mix parts of different geometries in the chamber made this technology to be almost forgotten. In the last years, due to the ecofriendly character of the technology, several atempts were made in order to establish an improvement in this technique in terms of batch damages. Active screen plasma nitriding technology is a new industrial solution that enjoys all the advantages of traditional plasma nitriding but does not have its inconveniences. A comparative study regarding quality surface and formed layer properties between conventional plasma nitriding and active screen plasma nitriding was conducted, in order to highlight the advantages that comes with this relatively new technique.
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