Routes to halogen‐free flame‐retardant polypropylene wood plastic composites

Developing halogen‐free flame retardants with reasonably high efficiency, which thus function at limited loadings in polypropylene‐based wood/plastic composites (WPC), is still a challenge. Cost‐effective flame‐retarded WPC have been identified as a way to open the door to an interesting, broader spectrum of application in the building and transportation sectors. This work imparts a systematic comprehensive understanding and assessment of different basic routes to halogen‐free flame‐retarded WPC, taking into account economic and environmental considerations. Cheap, halogen‐free single‐component flame retardants and their multicomponent systems are investigated at reasonable filling grades of 20 wt%. The basic routes of promising synergistic multicomponent systems are discussed, and their potential and limits assessed. Optimizing the consistency of fire residue; closing the surface of inorganic‐organic residual layers; the thermal stabilization and design of the residue, eg, synergistic combination of ammonium polyphosphate and expandable graphite; and the combination of different flame‐retardant mechanisms, eg, intumescence and flame inhibition, are proposed as promising routes to boost the flame‐retardant efficiency.     

Black Phosphorus Cytotoxicity Assessments Pitfalls: Advantages and Disadvantages of Metabolic and Morphological Assays

Black phosphorus (BP) belongs to a group of 2D nanomaterials and nowadays attracts constantly increasing attention. Parallel to the growing utilization of BP nanomaterial increase also the requirements for the thorough comprehension of its potential impact on human and animal health. The aim of this study was to compare and discuss five assays commonly used for the cytotoxicity assessments of nanomaterials with a special focus on BP nanoparticles. A comprehensive survey of factors and pitfalls is provided that should be accounted for when assessing their toxicity and pointed to their inconsistency. BP might introduce various levels of interference during toxicity assessments depending on its concentration applied. More importantly, the BP toxicity evaluation was found to be influenced by the nature of assay chosen. These are based on different principles and do not have to assess all the cellular events equally. A commercial assay based on the measurement of protease activity was identified to be the most suitable for the BP toxicity assessment. Further, the benefit of time-lapse quantitative phase imaging for nanomaterial toxicity evaluation was highlighted. Unlike the conventional assessments it provides real-time analysis of the processes accompanying BP administration and enables to understand them deeper and in the context.     

Stochastic modelling and simulation of a kidney transplant waiting list

We created a dynamic stochastic model to evaluate the performance of a kidney transplantation system. Our model is applicable in the context of a small country where the legislation requires that a kidney from a deceased donor should be used whenever available. Using a systematic design of simulation experiments, we performed a complex simulation study based on real medical data to explore the impact of factors representing different rates of deceased kidneys harvesting, the proportion of patients with a willing living donor and different allocation policies. On the basis of careful statistical analysis carried out by two different statistical methodologies, ANOVA and bootstrap, we draw some important conclusions about the effects of these factors and recommendations for the medical community. The results of the study clearly demonstrate that in addition to increasing the numbers of kidney donors, deceased as well as living, the introduction of a kidney exchange program leads to further expansion of the numbers of donations and to shortening of waiting time for transplantation. Moreover, we observed that the largest and most counter-intuitive effect on waiting time and transplantation probability was obtained by replacing the currently implemented first-come-first-transplanted allocation policy to a policy that prioritizes the most vulnerable group of patients. This change has led to shortening the waiting time of these patients by enormous 28 months on average while leaving the waiting time of other patients practically the same.

     

Trace Element Determination in Diesel Particulates by Total-Reflection X-Ray Fluorescence Analysis

 Particulate matter of Diesel emissions collected from diluted exhaust during standard test runs with two Diesel fuels of different sulfur content was analysed by total-reflection X-ray fluorescence (TXRF). The trace elements determined were S, Ca, Cr, Mn, Fe, Ni, Cu, Zn and Pb. Additionally, some filter materials were tested with respect to their applicability for sample collection. Quartz fibre filters were found to be most suitable, both from a technical and a chemical point of view. A clear reduction of total particulate emissions during the whole test was observed when the fuel with very low sulfur content was used. In addition, it was found that the wear metal content of particulate matter emitted by a cold engine was higher than that observed during normal engine working temperature. Received September 10, 1998. Revision March 2, 1999     

Systematic generation of relativistic gaussian basis sets

A method for the Gaussian basis set generation for molecular relativistic Dirac-Fock calculations is proposed. The basis set exponents are obtained in the process of stochastic optimization (a hybrid of simplex and simulated annealing optimization techniques has been employed) of a functional defined as the sum of squares of differences between the numerical relativistic atomic wave functions and the wave functions obtained using the Gaussian function expansion. After this pre-optimization step the exponents are refined by ordinary gradient energy-functional based procedure. The present method seems to be very effective and robust. As an example the optimized basis sets of atoms from H (Z=1) to Ar (Z=18) are presented. Results of the Dirac-Fock calculations for all atoms under study are presented and compared with the numerical Dirac-Fock results and results obtained using the Gaussian basis sets according to Okada et al.: J. Chem. Phys.93 (1990) 5013. Slovak Grant Agency has funded the work reported in this paper, project No. 1/4205/98.     

Synthesis,Characterization, and Crystal Structure of [ReO(Me4tu)4](PF6)3 (tu = thiourea)

A new Re^V oxo complex with tetramethylthiourea, [ReO(Me₄tu)₄](PF₆)₃, has been synthesized by reduction of perrhenate with tin(II) chloride in strongly acidic solution in the presence of excess tetramethylthiourea. The complex has been characterized by elemental analysis and electronic and FTIR spectroscopy. The molecular structure of the compound was determined by X‐ray diffraction methods. The coordination polyhedron is a regular square pyramid with the substituted thiourea sulfur atoms in the equatorial positions [d(Re–S) = 2.339(3) Å] and the oxo ligand located in the summit [d(Re–O) = 1.63(2) Å]. Computational methods were employed to analyze the geometric and electronic structures of tetramethylthiourea and thiourea. Quantum mechanical studies suggest steric hindrance as the reason for the stabilization of the ReO³⁺ center instead of the Re^III one.     

Polymers of carbonic acid. XXVII. Macrocyclic polymerization of trimethylene carbonate

2,2-Dibutyl-2-stanna-1,3-dioxepane (DSDOP) was used as cyclic initiator for the polymerization of trimethylene carbonate (TMC). The polymerizations were either conducted in concentrated chlorobenzene solution at 50 and 80°C or in bulk at 60 and 120°C. With monomer/initiator ratios ≤100 the conversion was complete within 2 h at 80°C and within 12 h at 50°C. Variation of the reaction time revealed that the rapid polymerization is followed by a relatively rapid (backbiting) degradation even at 80°C. The polymerizations in bulk at 60°C were somewhat slower than those at 80°C in solution, but the influence of degradation reactions was less pronounced. With optimized reaction time the number average molecular weight (M_n) roughly parallels the monomer/initiator ratio and M_n's up to 100,000 were obtained. In contrast to a classical living polymerization broader polydispersities (1.5–1.7) were found. In the case of 5,5-dimethyltrimethylene carbonate rapid degradation and chain transfer reactions prevented the formation of high molecular weight polymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2179–2189, 1999