Influence of the Polyvinyl Pyrrolidone Concentration on Particle Size and Dispersion of ZnS Nanoparticles Synthesized by Microwave Irradiation

Zinc sulfide semiconductor nanoparticles were synthesized in an aqueous solution of polyvinyl pyrrolidone via a simple microwave irradiation method. The effect of the polymer concentration and the type of sulfur source on the particle size and dispersion of the final ZnS nanoparticle product was carefully examined. Microwave heating generally occurs by two main mechanisms: dipolar polarization of water and ionic conduction of precursors. The introduction of the polymer affects the heating rate by restriction of the rotational motion of dipole molecules and immobilization of ions. Consequently, our results show that the presence of the polymer strongly affects the nucleation and growth rates of the ZnS nanoparticles and therefore determines the average particle size and the dispersion. Moreover, we found that PVP adsorbed on the surface of the ZnS nanoparticles by interaction of the C–N and C=O with the nanoparticle’s surface, thereby affording protection from agglomeration by steric hindrance. Generally, with increasing PVP concentration, mono-dispersed colloidal solutions were obtained and at the optimal PVP concentration (5%), sufficiently small size and narrow size distributions were obtained from both sodium sulfide and thioacetamide sulfur sources. Finally, the sulfur source directly influences the reaction mechanism and the final particle morphology, as well as the average size.     

Optimized Catalytic Bleaching Sequences for Eucalyptus Kraft Pulp

Contemporary multi-stage bleaching processes partially remove residual lignin and hexenuronic acid from cellulosic pulps. The reactions in the steps could be faster and consume smaller amounts of chemicals. Catalytic bleaching (H_cat), utilizing hypochlorite (H), triethylenediamine (DABCO) and its derivative N-carboxymethyl triethylenediamine (CM-DABCO), is a new discovery that has the potential to improve the chemical and energetic efficiency of bleaching processes in chemical pulp mills, e.g. through reducing the reaction time of the bleaching processes. The objective of this study was to clarify if new kraft pulp bleaching sequences with initial stage of chlorine dioxide (ClO₂; D) and an intermediate stage of H_cat could provide fully bleached pulps. The bleaching sequences of the studied eucalyptus pulps include D₀E_(OP)H_cat(Q)P and H_catZ/DP, which attained a final brightness of 88 and 89% ISO, respectively. H_catZ/DP showed to be the best sequence for the catalytic bleaching of eucalyptus kraft pulps. This study may open new doors to future bleaching of cellulose pulps with fewer towers and decreased use of chemicals.     

A bi-objective location-inventory model with capacitated transportation and lateral transshipments

We integrate location and inventory decisions in a three-echelon distribution network model with multiple products, capacitated in-house fleet and proactive transshipments between depots. The problem was originally motivated by the real-life case of a leading company in consumers’ household goods. The company offers a wide range of products which are different from demand pattern and shortage viewpoints. One of the product groups has seasonal trend with possibly lost sales during high seasons and backlog in low seasons, while the others lack any seasonal trend and get backlogged if any shortage occurs. A two-step process consisting of a new practical customer classification framework and a new mathematical model is developed. Total profit and customers’ dissatisfaction in the form of a new service-level measure are considered as the objective functions. To study the effects of transportation capacity on the network’s performance, a second scenario with inclusion of third-party transportation resources is presented. Due to unavailability or insufficiency of required objective data about production capacities and demands, they are assumed to be imprecise (i.e. possibilistic). After converting the original fuzzy model to its equivalent crisp formulation, an interactive solution procedure is applied to deal with the trade-off between the conflicting objectives. Useful managerial insights are also derived from the numerical experiments.     

Polyvinyl alcohol/chitosan/carbon nanotubes electroactive shape memory nanocomposite hydrogels

Shape memory nanocomposite hydrogels are intelligent soft materials in which, the nanoparticles can impart desirable mechanical properties to the polymeric matrix. The main challenge is the capability to program from permanent to temporary shapes and vice versa under the direct and indirect thermal stimuli. In this work, carbon nanotubes (CNT) with a high modulus of 1 TPa, was used to mechanically reinforce polyvinyl alcohol (PVA) and polyvinyl alcohol/chitosan (PVA/Cs) hydrogel networks. Adding appropriate amount of conductor component enables the system to be electrically activated, which leads to achieving the original permanent shape without applying mechanical external force. The PVA/Cs/CNT hydrogel containing 0.25 wt% of CNT, showed electrical conductivity greater than 9 mS cm⁻¹. Because of the presence of CNT, the shape memory behavior of PVA and PVA/Cs hydrogels was improved by 170 and 260%, respectively. The electroactive shape memory nanocomposite hydrogels exhibited complete recovery under indirect stimulation by generating Joule heating in the system.     

Conductive shape-memory polyurethane/multiwall carbon nanotube nanocomposite aerogels

Smart nanocomposite aerogels have promising applications. In this work, different percentages of multiwall carbon nanotube (MWCNT) added into synthesized polyurethane (PU) gel in the molten state, using a two-roll mill. By soaking the PU/MWCNT nanocomposite gel into the water, PU/MWCNT hydrogels containing more than 90 wt % of water were prepared. The obtained hydrogels were freeze-dried to produce aerogel counterparts. The aerogels were fully characterized using mercury porosimetry, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FE-SEM). The electrical percolation threshold of conductive aerogel system was measured. The shape-memory behavior of PU/MWCNT nanocomposite aerogels was evaluated by dynamic mechanical thermal analysis (DMTA). The results of the DMTA showed that by adding 2.75 wt % of MWCNT, the recovery ratio and storage modulus of the PU/MWCNT nanocomposite aerogel increased 42 and 180%, respectively. The electrical conductivity of the system also increased three orders of magnitude at the percolation threshold. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48602.     

Corrosion Behavior of Pure Copper Surrounded by Hank’s Physiological Electrolyte at 310 K (37 °C) as a Potential Biomaterial for Contraception: An Analogy Drawn Between Micro- and Nano-grained Copper

This work aims to evaluate the corrosion behavior of pure copper from the microstructural viewpoint for a biomedical application, namely intrauterine devices. For this purpose, Tafel polarization and electrochemical impedance spectroscopy (EIS) techniques were used to evaluate the corrosion behavior of annealed pure copper (with the average grain size of 45 ± 1 µm) and nano-grained microstructure in physiological electrolyte of Hank at 310 K (37 °C). Pure copper in nanoscale grain size, typically an average of 90 ± 5 nm, was successfully made by eight-cycle accumulative roll bonding process at room temperature. On the basis of Tafel polarization results, it was revealed that nano-grained sample had lower corrosion current density and more noble corrosion potential for prolonged exposure in Hank’s physiological solution at 310 K (37 °C). In addition, the EIS results showed that the nano-grained sample had more corrosion resistance compared to the coarse-grained one for long-time immersion.     

Effects of Sodium-Glucose Co-Transporter 2 Inhibitors on Vascular Cell Function and Arterial Remodeling

Cardiovascular disease is the leading cause of morbidity and mortality in diabetes. Recent clinical studies indicate that sodium-glucose co-transporter 2 (SGLT2) inhibitors improve cardiovascular outcomes in patients with diabetes. The mechanism underlying the beneficial effect of SGLT2 inhibitors is not completely clear but may involve direct actions on vascular cells. SGLT2 inhibitors increase the bioavailability of endothelium-derived nitric oxide and thereby restore endothelium-dependent vasodilation in diabetes. In addition, SGLT2 inhibitors favorably regulate the proliferation, migration, differentiation, survival, and senescence of endothelial cells (ECs). Moreover, they exert potent antioxidant and anti-inflammatory effects in ECs. SGLT2 inhibitors also inhibit the contraction of vascular smooth muscle cells and block the proliferation and migration of these cells. Furthermore, studies demonstrate that SGLT2 inhibitors prevent postangioplasty restenosis, maladaptive remodeling of the vasculature in pulmonary arterial hypertension, the formation of abdominal aortic aneurysms, and the acceleration of arterial stiffness in diabetes. However, the role of SGLT2 in mediating the vascular actions of these drugs remains to be established as important off-target effects of SGLT2 inhibitors have been identified. Future studies distinguishing drug- versus class-specific effects may optimize the selection of specific SGLT2 inhibitors in patients with distinct cardiovascular pathologies.     

Influence of monomeric and polymeric structure on the physical properties of thermoplastic polyesters derived from hydroxy fatty acids

The physical properties of three vegetable oil derived medium and long chain poly(ω‐hydroxy fatty ester)s (P(Me‐ω‐OHFA)s), namely poly(ω‐hydroxynonanoate) [P(Me‐ω‐OHC9)], poly(ω‐hydroxytridecanoate) [P(Me‐ω‐OHC13)] and poly(ω‐hydroxyoctadecanoate) [P(Me‐ω‐OHC18)] (n = 8, 12 and 17, respectively), of the [?(CH₂)_n?COO–]_x polyester homologous series are presented. The effect of M_n (M_n 10–40 kg mol^?1) and n on the crystal structure and thermal and mechanical properties of the P(Me‐ω‐OHFA)s were investigated by wide‐angle X‐ray diffraction (WAXD), TGA, DSC, dynamic mechanical analysis (DMA) and tensile analysis and are discussed in the context of the [?(CH₂)_n?COO–]_x polyester homologous series, contrasted with linear polyethylene (PE). For all P(Me‐ω‐OHFA)s the WAXD data indicated an orthorhombic crystal phase reminiscent of linear PE with crystallinity (X_c = 50%?80%) depending strongly on M_n. The glass transition temperature and Young's modulus for P(Me‐ω‐OHFA)s increased with X_c. The DSC, DMA and TGA studies for P(Me‐ω‐OHFA)s (n = 8, 12 and 17) indicated strong correlations between the melting, glass transition and thermal degradation behavior and n. The established predictive structure relationships can be used for the custom engineering of polyester materials suitable for specialty and commodity applications. © 2014 Society of Chemical Industry     

Phase Controlled Monodispersed CdS Nanocrystals Synthesized in Polymer Solution Using Microwave Irradiation

Cadmium sulfide (CdS) nanocrystals were synthesized in aqueous solution of polyvinyl pyrrolidone (PVP) via the simple and rapid microwave irradiation method. It is revealed that sulfur source is a key factor in controlling the phase formation of the resulting nanocrystals. The hexagonal and cubic structure of CdS nanocrystals could be obtained with varying sulfur sources of thioacetamide and sodium sulphide respectively. The interaction mechanism of PVP with precursor ions of cadmium and sulfur sources in the preparation process was proposed. It is found that PVP compounded the CdS nanoparticles and protected them from agglomerating. With increasing of PVP concentration, the average particle size of CdS nanocrystals increased and subsequently their optical band gap decreased. At the appropriate dosage of PVP, well isolated nanoparticles with relatively narrow size distribution were obtained for both sulfur sources. Moreover the stability of CdS nanoparticles enhanced after coating with polymer.     

Using game theory for analysing pricing models in closed-loop supply chain from short- and long-term perspectives

Closed-loop supply chain (CLSC) management is an environmental approach to supply chain management that aims to prevent hazardous material from entering the nature by means of creating a reverse flow. This paper studies the short- and long-term behaviour of agents in implementing the appropriate collecting strategy in a two-echelon CLSC. In short-term, based on the Stackelberg game, several novel pricing models for different collecting strategies are proposed and compared. Then, the optimal policies of the pricing decisions are determined for each model. The long-term behaviour of companies in implementing collecting process is examined by evolutionary game theory and the most stable strategy is selected. Furthermore, a numerical example is presented to compare the different collecting structures. Finally, a managerial insight is provided to indicate the effect of key parameters such as remanufacturing rate, marketing elasticity and government subsidies on selecting the appropriate strategy.