Non-Isothermal Crystallization Kinetics and Activation Energy for Crystal Growth of Polyamide 66/Short Glass Fiber/Carbon Black Composites.

This study presents the effect of the addition of 0.4 wt.% carbon black (CB) to polyamide 66 (PA66) containing 30 wt.% short glass fibers (GFs) on the behavior of composite thermal crystallization. Composites were studied by differential scanning calorimetry analysis (DSC) at different cooling rates using wide-angle X-ray scattering (WAXS) and scanning electron microscopy (SEM). This thermal crystallization study highlights the nucleation effect of GFs that promote PA66 crystallization by significantly increasing crystallization kinetics and rates. The activation energies (Eas) calculated by model-free (FWO; KAS) and model-fitting (Kissinger method and C-R method) approaches showed that the combination of both GF and CB decreases the activation energy with respect to neat PA66, meaning that the presence of both additives facilitates crystallization. The Coats-Redfern and Criado methods showed that the crystallization of neat PA66 and related composites follows the second-order reaction, i.e., the decelerated reaction, evidencing compatibility between GFs and the matrix.

Natural Cellulose from Ziziphus jujuba Fibers: Extraction and Characterization.

Nowadays, due to their natural availability, renewability, biodegradability, nontoxicity, light weight and relatively low cost, natural fibers, especially lignocellulosic fibers, present attractive potential to substitute non-eco-friendly synthetic fibers. In this study, Ziziphus jujuba fibers were used, thanks to their low lignin content, as an alternative of renewable resource for the production of cellulosic fibers with suitable characteristics and minimal time and energy consumption. In fact, due to their valuable chemical composition, it was possible to remove the amorphous fractions and impurities from the fiber surface by applying ultrasounds coupled with alkaline treatment (80 °C, 5 wt.% NaOH), followed by a bleaching step. The efficient dissolution of the noncellulosic compounds was confirmed by Fourier Transform Infrared Spectroscopy (FTIR). The resulted increase in the crystallinity index (from 35.7% to 57.5%), occurred without impacting the crystalline structure of the fibers. The morphological analysis of the fibers evidences the higher surface area of the obtained fibers. Based on the obtained results, Ziziphus jujuba fibers were found to present a suitable sustainable source for the production of cellulosic fibers.

Disposable non-enzymatic electrochemical glucose sensors based on screen-printed graphite macroelectrodes modified via a facile methodology with Ni, Cu, and Ni/Cu hydroxides are shown to accurately determine glucose in real human serum blood samples.

A three dimensional (3D) non-enzymatic glucose disposable electrochemical sensor based on screen-printed graphite macroelectrodes (SPEs), modified with nickel hydroxide (Ni(OH)2/SPE), copper hydroxide (Cu(OH)2/SPE) and mixed (Ni(OH)2/Cu(OH)2/SPE) microstructures were prepared by a facile and cost-effective electrochemical method for the first time. Their morphologies and structures were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The electrochemical performances of the modified SPEs were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometric measurements. EIS experiments showed lower charge transfer resistance Rct values for the modified SPEs, calculated to be 29.24 kΩ, 22.58 kΩ, 13.27 kΩ and 36.48 kΩ for Ni(OH)2/SPE, Cu(OH)2/SPE, Ni(OH)2/Cu(OH)2/SPE, and SPE, respectively. Under optimal experimental conditions, the results reveal that CV, amperometry and EIS can be readily applied to determine glucose using all of the fabricated sensors, however in terms of an accessible and clinically relevant linear range for the electroanalytical detection of glucose, CV is preferred, where Cu(OH)2/SPE exhibits the largest linear range from 1 µM to 20 mM (R2 = 0.997). In terms of sensitivity and the detection limit however, amperometry appeared to be a better choice of technique, particularly with Ni(OH)2/Cu(OH)2/SPE which demonstrated the highest sensitivity of 2029 µA mM-1 cm-2 and the lowest detection limit of 0.2 µM (S/N = 3). Excellent selectivity was evident against common interfering species, and it was shown to be possible to obtain satisfactory results in human blood serum samples using the as-fabricated sensors. The low cost of the SPEs, the facile preparation and observed clinically relevant analytical sensitivities and limit of detections towards the sensing of glucose make these screen-printed macroelectrode based electrochemical sensing platforms promising for routine human blood serum glucose analysis.

Chitin from Agaricus bisporus: Extraction and characterization.

Chitin was isolated from three main fruit body parts of the Agaricus bisporus mushroom, i.e. pileus, stipes and gills. Chitin was extracted by alkaline treatment of A. bisporus fruit body parts in 1 M NaOH at 80 °C for 2 h.The lyophilized fruit bodies were examined by SEM and exhibited a porous structure that is favorable to polysaccharide extraction. A mild extraction method was adopted to limit the degradation of chitin. The highest extraction yield of chitin was obtained for stipes (7.4% of dry weight). For pileus and gills, yields of chitin were 6.4% and 5.9%, respectively. Chitin extracted from stipes was characterized by thermal analysis, X-ray diffraction, infrared spectroscopy and solid-state 13C NMR. Results showed that the extracted chitin was in the alpha form, with a 63% crystalline index (CrI) and a degree of N-acetylation (DA) of 70%. The presence of proteins and glucans were not observed in the extracted chitin.