Phosphorus-Containing Polyisocyanurate Elastomers for Flame Retardant Application

Polyurethane (PU) is one of the most common and versatile polymers in many applications especially in the construction and automotive industry where the improvement of thermal stability and flame retardancy is crucial. As polyisocyanaurate (PIR) is well known to have a high decomposition temperature and phosphorus motifs are usually used as flame retardants in polymers, the introduction of PIR and phosphorus motifs in polyurethanes can lead to PUs with high thermal stability and flame retardancy. We investigated a synthetic pathway to introduce polyisocyanurate (PIR) and phosphorus motifs in polyurethanes via co-trimerization of 4,4′-methylene diphenyl diisocyanate (4,4′-MDI) and monoisocyanate, which was synthesized from the reaction between diethyl (hydroxymethyl)phosphonate (DEHP) and 4,4′-MDI. The resulting PIR-DEHP prepolymer was used to prepare PIR-DEHP elastomers in both solvent and solvent-free conditions. The elastomer with polyester polyol and 15 wt % 1,4-butanediol in the polyol component showed high char formation (25.5 wt %) and 55% reduction in the total heat release (THR) relative to the reference elastomer without PIR and phosphorus content. It is expected that the use of the PIR-DEHP prepolymer can be extended to other applications, such as rigid PU foams and compact thermosets where the flame retardancy and bulk reaction conditions are required

A System Dynamics Model of Supply-Side Issues Influencing Beef Consumption in Nigeria

The per capita consumption of beef in Nigeria is reducing amidst a rising population that is dependent on beef as a major source of animal protein. In this paper, a system dynamics (SD) model was developed with the aim of testing exploratory policies aimed at reversing this trend. The simulations of various policy tests showed that, of all the policies tested, having a higher carcass yield seems to be the most efficient solution, but its feasibility faces some steep biological and ecological challenges. However, a combination of policies that cuts across the land–cattle–market nexus is necessary to obtain a consumption level that almost meets the World Health Organization (WHO) standards for recommended animal protein intake. Complex inter-linked systems, like beef production and consumption, require a systemic approach that considers dynamic feedback to avoid fixes that fail or shift the burden when making policy decisions

Synthesis of polyisocyanurate prepolymer and the resulting flexible elastomers with tunable mechanical properties

Polyurethane (PU) is used in a wide range of applications due to its diverse chemical and physical properties. To meet the increasing demands on thermal and mechanical properties of PU materials, polyisocyanurates(PIRs) have been introduced in PU materials as crosslinkers and due to their high decomposition temperature. We prepared a liquid PIR prepolymer with high PIR content by co-trimerization of 4,4’-methylene diphenyl diisocyanate (4,4’-MDI) and mono-isocyanates. The mono-isocyanate was synthesizedvia reaction between a 4,4’-MDI and a 2-ethyl-1-hexanol. The PIR prepolymer obtained was further reacted with long chain polyols and chain extenders in both solvent and solvent-free conditions, leading to PIR elastomers that exhibited good thermal stability with high char formation, and improvedmechanical properties with much higher Young’s modulus. This work demonstrates that the liquid PIR prepolymer can potentially be used in various large-scale industrial applications

Solvent-Free Preparation of Thermally Stable Poly(urethane-imide) Elastomers

Polyurethanes (PUs) are widely used in many applications due to their versatile chemical and physical properties. To meet the increasing demands on PU with respect to intrinsic mechanical and thermal properties, they can be modified with thermally stable aromatic imide structures to form poly(urethane imide) (PUI). However, the preparation of PUI materials has been limited by the need for strong polar solvents, which hinder their industrial scale development. In this work, we prepared imide-containing isocyanate-terminated prepolymers via the reaction of polymeric aromatic or aliphatic isocyanates and pyromellitic dianhydride in completely solvent-free conditions. The subsequent PUI elastomers made from these prepolymers exhibited enhanced char formation and stiffness in comparison to the reference elastomers without imide structures, among which the aromatic PUI elastomer shows improved flame retardancy according to the initial cone calorimetry measurement. This work demonstrates the potential use of imide prepolymers in other PU applications where high thermal stability and flame retardancy are required. The solvent-free synthesis also paves a way for the large-scale production of PUI materials

Interface driven magnetoelectric effects in granular CrO2

Antiferromagnetic and magnetoelectric Cr2O3-surfaces strongly affect the electronic properties in half metallic CrO2. We show the presence of a Cr2O3 surface layer on CrO3 grains by high-resolution transmission electron microscopy. The effect of these surface layers is demonstrated by measurements of the temperature variation of the magnetoelectric susceptibility. A major observation is a sign change at about 100 K followed by a monotonic rise as a function of temperature. These electric field induced moments in CrO3 are correlated with the magnetoelectric susceptibility of pure Cr2O3. This study indicates that it is important to take into account the magnetoelectric character of thin surface layers of Cr2O3 in granular CrO2 for better understanding the transport mechanism in this system. The observation of a finite magnetoelectric susceptibility near room temperature may find utility in device applications.Comment: Figure 1 with strongly reduced resolutio

Worldwide food recall patterns over an eleven month period: A country perspective.

<p>Abstract</p> <p>Background</p> <p>Following the World Health Organization Forum in November 2007, the Beijing Declaration recognized the importance of food safety along with the rights of all individuals to a safe and adequate diet. The aim of this study is to retrospectively analyze the patterns in food alert and recall by countries to identify the principal hazard generators and gatekeepers of food safety in the eleven months leading up to the Declaration.</p> <p>Methods</p> <p>The food recall data set was collected by the Laboratory of the Government Chemist (LGC, UK) over the period from January to November 2007. Statistics were computed with the focus reporting patterns by the 117 countries. The complexity of the recorded interrelations was depicted as a network constructed from structural properties contained in the data. The analysed network properties included degrees, weighted degrees, modularity and <it>k</it>-core decomposition. Network analyses of the reports, based on 'country making report' (<it>detector</it>) and 'country reported on' (<it>transgressor</it>), revealed that the network is organized around a dominant core.</p> <p>Results</p> <p>Ten countries were reported for sixty per cent of all faulty products marketed, with the top 5 countries having received between 100 to 281 reports. Further analysis of the dominant core revealed that out of the top five transgressors three made no reports (in the order China > Turkey > Iran). The top ten detectors account for three quarters of reports with three > 300 (Italy: 406, Germany: 340, United Kingdom: 322).</p> <p>Conclusion</p> <p>Of the 117 countries studied, the vast majority of food reports are made by 10 countries, with EU countries predominating. The majority of the faulty foodstuffs originate in ten countries with four major producers making no reports. This pattern is very distant from that proposed by the Beijing Declaration which urges all countries to take responsibility for the provision of safe and adequate diets for their nationals.</p

Critical exponents at the ferromagnetic transition in tetrakis(diethylamino)ethylene-C60_{60} (TDAE-C60_{60})

Critical exponents at the ferromagnetic transition were measured for the first time in an organic ferromagnetic material tetrakis(dimethylamino)ethylene fullerene[60] (TDAE-C$_{60}$). From a complete magnetization-temperature-field data set near $T_{c}=16.1\pm 0.05,$ we determine the susceptibility and magnetization critical exponents $\gamma =1.22\pm 0.02$ and $\beta =0.75 \pm 0.03$ respectively, and the field vs. magnetization exponent at $T_{c}$ of $\delta =2.28\pm 0.14$. Hyperscaling is found to be violated by $\Omega \equiv d^{\prime}-d \approx -1/4$, suggesting that the onset of ferromagnetism can be related to percolation of a particular contact configuration of C$_{60}$ molecular orientations.Comment: 5 pages, including 3 figures; to appear in Phys. Rev. Let