Low pressure drop respirator gas filters using adsorbent hollow fibres as an alternative to granular adsorbents

Respirator users experience a physiological burden, one aspect of which is associated with breathing resistance from the filter. The current best practice of gas filters is to provide protection using 3adsorbent granule filled filters which, as the particle size decreases, have better adsorption kinetics, and hence longerbreakthrough times. However this comes at the price of an increasing pressure drop and hence greater breathing resistance. In this paper, adsorbent hollow fibres for use in respirator filters are presented as a potential alternative to the conventional granular cartridges. A comparison of hollow fibre and granular filter modules was carried out using scanning electron microscopy and dynamic ammonia challenge (800 ppm, 1 L/min). In addition the pressure drop was measured at flow rates between 0.5-5 L/min, and using these data,pressure drops at higher flow rates were predicted. The hollow fibres were demonstrated to compare favourably to a granular module of equal volume in terms of pressure drop, adsorption kinetics and breakthrough loading,although improvements still need to be made to hollow fibre breakthrough time, which is slightly lower than an equal volume pellet module as a result of the lower density of the hollow fibre filters. The qualities of hollow fibres will provide several options for novel filter design

Preparation and characterization of benzoxazine based nanocomposites: comprehensive study in curing kinetics and enhanced thermal stabilities

Several bisphenol-A benzoxazine (BEN) based nanocomposites incorporated with several polyhedral oligomeric silsesquioxane (POSS), carbon nanotubes (CNTs), and clays, were prepared successfully. The influences of the nanofillers on curing kinetics, network formation, and thermal stability of the BEN were investigated comprehensively. The addition of the nanofillers showed different influence on curing kinetics of BEN. Furthermore, the incorporation of the nanofillers showed good improvement on thermal stability of BEN. An increase of 70 and 336°C at the onset and the half-life decomposition temperature were observed with the addition of 5 wt % 30B clay in nitrogen atmosphere. With the incorporation of 5 wt % POSS, the half-life of decomposition and char yield enhanced by 280°C and 13 wt % in nitrogen atmosphere. For the 4 wt % MWCNT-COOH/BEN nanocomposite, the half-life of decomposition and char yield at 800°C increased by 286°C and 14 wt % in nitrogen atmosphere, respectively

Exploring the thermal degradation mechanisms of some polybenzoxazines under ballistic heating conditions in helium and air

The degradation behaviour of five polybenzoxazines (PBZs) is studied using pyrolysis-GC/MS. Upon heating to 800 °C in helium the PBZs generate a variety of similar pyrolysis products including aniline (the major product in all cases), substituted phenols, acridine, and 9-vinylcarbazole. During the initial stages of heating (200–300 °C) aniline is the dominant pyrolysis product; from 350 °C onwards substituted phenols are released, particularly 2-methylphenol and 2,6-dimethyl phenol. The same major species are produced on heating in air, but in addition isocyanatobenzene is observed which results from the oxidation of Mannich bridges, along with a number of sulphurous species from the monomer containing a thioether bridge. This suggests that sulphur is more likely to be retained in the char in a helium atmosphere, but takes part in oxidative reactions to form pyrolysis fragments in air. During the ramped temperature cycles in both air and helium atmospheres the release of aniline was observed to rise, fall and then to rise again. This may be due a combination of the very high heating rate, poor thermal conduction of the polymer and the availability of the Mannich bridges to undergo breakdown

Exploring Structure–Property Relationships in Aromatic Polybenzoxazines Through Molecular Simulation

A series of commercial difunctional benzoxazine monomers are characterized using thermal and thermo-mechanical techniques before constructing representative polymer networks using molecular simulation techniques. Good agreement is obtained between replicate analyses and for the kinetic parameters obtained from differential scanning calorimetry data (and determined using the methods of Kissinger and Ozawa). Activation energies range from 85 to 108 kJ/mol (Kissinger) and 89 to 110 kJ/mol (Ozawa) for the uncatalyzed thermal polymerization reactions, which achieve conversions of between 85% and 97%. Glass transition temperatures determined from differential scanning calorimetry and dynamic mechanical thermal analysis are comparable, ranging from BA-a (151 °C, crosslink density 3.6 × 10−3 mol cm−3) containing the bisphenol A moiety to BP-a, based on a phenolphthalein bridge (239 to 256 °C, crosslink density 5.5 to 18.4 × 10−3 mol cm−3, depending on formulation). Molecular dynamics simulations of the polybenzoxazines generally agree well with empirical data, indicating that representative networks have been modelled

The Use of Single-Sided NMR to Study Moisture Behaviour in an Activated Carbon Fibre/Phenolic Composite

Nuclear Magnetic Resonance (NMR) has been shown to be a useful technique to study the form and content of water in polymer composites. Composites using activated carbon fibres with phenolic resin have complex water absorption behaviour which would benefit from such investigation; however, the presence of the conductive fibres can make NMR problematic. In this study, single-sided NMR has been successfully used on such material by developing a method for sample-to-sample compensation for the effect of conductivity. Transverse relaxation curves showed water to be primarily in two states in the resin, corresponding to "bound" and "mobile" molecules. In addition, two much less bound states were identified in the composite, associated firstly with water adsorbed on to the fibre surface and secondly with clusters of water molecules moving more freely within the fibre pores

The efficacy of whole human genome capture on ancient dental calculus and dentin

Objectives: Dental calculus is among the richest known sources of ancient DNA in the archaeological record. Although most DNA within calculus is microbial, it has been shown to contain sufficient human DNA for the targeted retrieval of whole mitochondrial genomes. Here, we explore whether calculus is also a viable substrate for whole human genome recovery using targeted enrichment techniques. Materials and methods: Total DNA extracted from 24 paired archaeological human dentin and calculus samples was subjected to whole human genome enrichment using in-solution hybridization capture and high-throughput sequencing. Results: Total DNA from calculus exceeded that of dentin in all cases, and although the proportion of human DNA was generally lower in calculus, the absolute human DNA content of calculus and dentin was not significantly different. Whole genome enrichment resulted in up to fourfold enrichment of the human endogenous DNA content for both dentin and dental calculus libraries, albeit with some loss in complexity. Recovering more on-target reads for the same sequencing effort generally improved the quality of downstream analyses, such as sex and ancestry estimation. For nonhuman DNA, comparison of phylum-level microbial community structure revealed few differences between precapture and postcapture libraries, indicating that off-target sequences in human genome-enriched calculus libraries may still be useful for oral microbiome reconstruction. Discussion: While ancient human dental calculus does contain endogenous human DNA sequences, their relative proportion is low when compared with other skeletal tissues. Whole genome enrichment can help increase the proportion of recovered human reads, but in this instance enrichment efficiency was relatively low when compared with other forms of capture. We conclude that further optimization is necessary before the method can be routinely applied to archaeological samples

Hydrolytic stability in hemilabile metal–organic frameworks

Highly porous metal–organic frameworks (MOFs), which have undergone exciting developments over the past few decades, show promise for a wide range of applications. However, many studies indicate that they suffer from significant stability issues, especially with respect to their interactions with water, which severely limits their practical potential. Here we demonstrate how the presence of ‘sacrificial’ bonds in the coordination environment of its metal centres (referred to as hemilability) endows a dehydrated copper-based MOF with good hydrolytic stability. On exposure to water, in contrast to the indiscriminate breaking of coordination bonds that typically results in structure degradation, it is non-structural weak interactions between the MOF’s copper paddlewheel clusters that are broken and the framework recovers its as-synthesized, hydrated structure. This MOF retained its structural integrity even after contact with water for one year, whereas HKUST-1, a compositionally similar material that lacks these sacrificial bonds, loses its crystallinity in less than a day under the same conditions

Ciliary Neurotrophic Factor Protects Striatal Neurons against Excitotoxicity by Enhancing Glial Glutamate Uptake

Ciliary neurotrophic factor (CNTF) is a potent neuroprotective cytokine in different animal models of glutamate-induced excitotoxicity, although its action mechanisms are still poorly characterized. We tested the hypothesis that an increased function of glial glutamate transporters (GTs) could underlie CNTF-mediated neuroprotection. We show that neuronal loss induced by in vivo striatal injection of the excitotoxin quinolinic acid (QA) was significantly reduced (by ∼75%) in CNTF-treated animals. In striatal slices, acute QA application dramatically inhibited corticostriatal field potentials (FPs), whose recovery was significantly higher in CNTF rats compared to controls (∼40% vs. ∼7%), confirming an enhanced resistance to excitotoxicity. The GT inhibitor dl-threo-β-benzyloxyaspartate greatly reduced FP recovery in CNTF rats, supporting the role of GT in CNTF-mediated neuroprotection. Whole-cell patch-clamp recordings from striatal medium spiny neurons showed no alteration of basic properties of striatal glutamatergic transmission in CNTF animals, but the increased effect of a low-affinity competitive glutamate receptor antagonist (γ-d-glutamylglycine) also suggested an enhanced GT function. These data strongly support our hypothesis that CNTF is neuroprotective via an increased function of glial GTs, and further confirms the therapeutic potential of CNTF for the clinical treatment of progressive neurodegenerative diseases involving glutamate overflow

Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial

Background Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy

Variants at multiple loci implicated in both innate and adaptive immune responses are associated with Sjögren’s syndrome

Sjögren’s syndrome is a common autoimmune disease (~0.7% of European Americans) typically presenting as keratoconjunctivitis sicca and xerostomia. In addition to strong association within the HLA region at 6p21 (Pmeta=7.65×10−114), we establish associations with IRF5-TNPO3 (Pmeta=2.73×10−19), STAT4 (Pmeta=6.80×10−15), IL12A (Pmeta =1.17×10−10), FAM167A-BLK (Pmeta=4.97×10−10), DDX6-CXCR5 (Pmeta=1.10×10−8), and TNIP1 (Pmeta=3.30×10−8). Suggestive associations with Pmeta<5×10−5 were observed with 29 regions including TNFAIP3, PTTG1, PRDM1, DGKQ, FCGR2A, IRAK1BP1, ITSN2, and PHIP amongst others. These results highlight the importance of genes involved in both innate and adaptive immunity in Sjögren’s syndrome