Zinc‐based compounds as smoke suppressant agents for an aerospace epoxy matrix

Smoke is considered to be the main hazard of fires involving epoxy resins but its production depends on many variables, principally the chemical character and the burning rate of the polymer plus the availability of oxygen. The work reported aimed to study the smoke suppressant effect and flammability performance of zinc‐based compounds (FR system) in epoxy matrix composites used in the aerospace and aeronautical industry. The flammability performance of neat and FR‐loaded systems was screened using microcombustion calorimetry, while smoke generation, in terms of carbon monoxide (CO) and carbon dioxide (CO₂) production, was analysed under dynamic conditions using cone calorimetry. Final results indicate that the dispersion of zinc borate and zinc hydroxystannate (ZHS) into epoxy matrices leads to a significant variation in flame retardant properties reducing both total heat release by about 25 and 30%, respectively, and heat release capacity by about 30 and 50%, respectively. The system containing ZHS shows an enhancement in all smoke suppressant properties; both tin compounds (zinc stannate (ZS) and ZHS) give a reduction of CO₂/CO ratio from 41 to 25 for ZS and from 41 to 36 for ZHS compared to neat matrix. Copyright © 2010 Society of Chemical Industry     

Effect of nanofillers on the flame retardant properties of a polyethylene–calcium carbonate–silicone elastomer system

This study shows the effects of three different nanofillers on the viscosity properties and fire behavior of a halogen‐free flame retardant system. The original system, based on ethylene‐acrylate copolymer, calcium carbonate, and a silicone elastomer, shows good flame retardant properties. One of the nanofillers, montmorillonite (MMT), significantly increases the viscosity above 250^°C, resulting in reduced dripping and decreased heat release rate. The ash residue, however, is very brittle, indicating poor interactions between the MMT and other components of the system. The second nanofiller, sepiolite, shows no improvement on the flame retardant properties of the system. Reduced dripping is observed when a small amount of the third nanofiller, polyhedral oligomeric silsesquioxane, POSS, is incorporated into the system. In this case, high silica content on the surface indicates char formation originating from the POSS. However, an increased heat release is observed when POSS is used in the system. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrochemical reduction of tert-butyl chloride—Computational study

In this work kinetics of the electrochemical reduction of the tert-butyl chloride molecule are studied. The two-dimensional potential surface E(x, y) was obtained from the Hamiltonian model used earlier [1] to study quantum effects on the reaction rate of the same reaction. In series of molecular dynamics simulations two different models, isotropic (γ_x = γ_y) and anisotropic (γ_x > γ_y), of the friction parameters for the solvent (γ_x) and for the C-Cl bond (γ_y) were considered. An influence of several factors, such as an overpotential, a solvent friction coefficient and a temperature, on the rate constants k obtained with the two models are presented and compared to the results obtained for the non-adiabatic mechanism. It is shown, that the anisotropic model predicts generally much smaller rates when compared to those calculated with the isotropic model and also with the non-adiabatic model. On the curves k(γ_x) the turnover region is very well defined for relatively low frictions in the isotropic case, while for the anisotropic case it is shifted towards much higher γ_x values. In all simulations the saddle point avoidance phenomenon was observed and its extent for different models and reaction conditions is discussed. Transfer coefficients α obtained for adiabatic and non-adiabatic reaction mechanisms as a function of the overpotential and temperature are also presented.     

Effects of a Protic Ionic Liquid on the Reaction Pathway during Non-Aqueous Sol–Gel Synthesis of Silica: A Raman Spectroscopic Investigation

The reaction pathway during the formation of silica via a two-component “non-aqueou” sol-gel synthesis is studied by in situ time-resolved Raman spectroscopy. This synthetic route is followed with and without the addition of the protic ionic liquid 1-ethylimidazolium bis(trifluoromethanesulfonyl)imide (C₂HImTFSI) in order to investigate its effect on the reaction pathway. We demonstrate that Raman spectroscopy is suitable to discriminate between different silica intermediates, which are produced and consumed at different rates with respect to the point of gelation. We find that half-way to gelation monomers and shorter chains are the most abundant silica species, while the formation of silica rings strongly correlates to the sol-to-gel transition. Thus, curling up of linear chains is here proposed as a plausible mechanism for the formation of small rings. These in turn act as nucleation sites for the condensation of larger rings and thus the formation of the open and polymeric silica network. We find that the protic ionic liquid does not change the reaction pathway per se, but accelerates the cyclization process, intermediated by the faster inclusion of monomeric species.     

Application of Molecular Dynamics Simulations in the Analysis of Cyclodextrin Complexes

Cyclodextrins (CDs) are highly respected for their ability to form inclusion complexes via host–guest noncovalent interactions and, thus, ensofance other molecular properties. Various molecular modeling methods have found their applications in the analysis of those complexes. However, as showed in this review, molecular dynamics (MD) simulations could provide the information unobtainable by any other means. It is therefore not surprising that published works on MD simulations used in this field have rapidly increased since the early 2010s. This review provides an overview of the successful applications of MD simulations in the studies on CD complexes. Information that is crucial for MD simulations, such as application of force fields, the length of the simulation, or solvent treatment method, are thoroughly discussed. Therefore, this work can serve as a guide to properly set up such calculations and analyze their results.     

Genetic Background of Fetal Growth Restriction

Fetal growth restriction (FGR) is one of the most formidable challenges in present-day antenatal care. Pathological fetal growth is a well-known factor of not only in utero demise in the third trimester, but also postnatal morbidity and unfavorable developmental outcomes, including long-term sequalae such as metabolic diseases, diabetic mellitus or hypertension. In this review, the authors present the current state of knowledge about the genetic disturbances responsible for FGR diagnosis, divided into fetal, placental and maternal causes (including preeclampsia), as well as their impact on prenatal diagnostics, with particular attention on chromosomal microarray (CMA) and noninvasive prenatal testing technique (NIPT).     

The role of iron(III) oxide in chloroprene and butadiene rubber blends’ cross-linking,structure, thermal and mechanical characteristics

Iranian Polymer Journal - The role of iron(III) oxide (Fe2O3) in the cross-linking process, structure and functional properties of chloroprene and butadiene rubber (CR/BR) blends was studied. The...     

Electrocardiographic motion artifact versus electrode impedance

We degraded electrocardiographic electrodes by exposing them to air for four days and evaluated them on 12 subjects. After application, we recorded the electrocardiogram (including motion artifact), missed QRS detections and electrode impedance during 5 min of arm and body movements. Missed QRS detections increased with electrode impedance but correlation was poor. Increased electrode impedance was not a reliable predictor of a poor electrode and the need to replace it.