56 research outputs found

    Effects of environmental conditions on the micro-mechanical properties of formulated waterborne coatings

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    Waterborne colloidal polymer coatings are widely used in architectural and agricultural applications where they are subject to challenging environments, such as extremes of temperatures and relative humidities (RH). This research investigates the effects of adding two common co-formulants, poly(acrylic acid) (PAA) and xanthan gum (XG), to waterborne polymer composite coatings in these environments. The mechanical properties of the resulting coatings are of particular interest. Hardness, creep and tack properties of thick (similar to 400 mu m) formulated model coatings were characterized using a micro-indentation technique operating in a single cycle within a bespoke environmental chamber. Measurements were made at three temperatures (16, 20 and 30 degrees C), which span the glass transition temperature (T-g) of the acrylic copolymer binder, and over three RH values of 10%, 43%, and 90%. The creep data were analysed using the Burgers model to extract characteristic viscoelastic properties. The tack was found by recording the force when withdrawing the probe from the sample and using it to obtain nominal stress (knowing the indentation depth and probe geometry) during the indenter's withdrawal and hence the work of adhesion (W-Adh) to detach from the coating. Tack adhesion is completely lost below the binder's T-g but increases when the ambient temperature increases. In formulated coatings, both the tack and creep deformation increase as the relative humidity increases, and this trend is observed at each temperature. There is no evidence from thermal analysis for plasticization of the acrylic polymer by moisture sorption, but the two co-formulants are hydrophilic. The observed softening of the coatings at high RH can be attributed to water sorption in the components. The presence of glassy PAA has the effect of raising the hardness of glassy coatings, but only at low RH when there is no plasticization by water. The addition of hydrophilic XG surprisingly reduces tack adhesion while also raising the viscosity of the coating. These findings will inform the formulation of waterborne colloidal coatings to function in a range of environments.work was funded by EPSRC (Grant EP/L016788/1) through the Doctoral Training Centre in Micro- and NanoMaterials and Technology (MiNMaT). We benefited from useful discussions with Dr. Marco Ram- aioli (INRAE, AgroParisTech - Center de Massy) and Dr. Nicholas Ballard (University of the Basque Country). We thank Violeta Doukova and Dave Jones (University of Surrey) for laboratory assistance and Dr. Agata Gajewicz-Jaromin for performing DSC and TGA analyses. We also thank Dr. James Adams (Cubica Technology) for his assistance in writing data analysis scripts. We thank Richard Turner (Acal BFI UK Ltd.) for the relative humidity and temperature probes, and for his assistance with their setup

    The Norwich Patellar Instability Score:validity, internal consistency and responsiveness for people conservatively-managed following first-time patellar dislocation

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    Background: This paper assessed the validity, internal consistency, responsiveness and floor-ceiling effects of the Norwich Patellar Instability (NPI) Score for a cohort of conservatively managed people following first-time patellar dislocation (FTPD).  Methods: Fifty patients were recruited, providing 130 completed datasets over 12 months. The NPI Score, Lysholm Knee Score, Tegner Level of Activity Score and isometric knee extension strength were assessed at baseline, six weeks, six and 12 months post-injury.  Results: There was high convergent validity with a statistically significant correlation between the NPI Score and the Lysholm Knee Score (p < 0.001), Tegner Level of Activity Score (p < 0.001) and isometric knee extension strength (p < 0.002). Principal component analysis revealed that the NPI Score demonstrated good concurrent validity with four components account for 70.4% of the variability. Whilst the NPI Score demonstrated a flooring-effect for 13 of the 19 items, no ceiling effect was reported. There was high internal consistency with a Cronbach Alpha value of 0.93 (95% CI: 0.91 to 0.93). The NPI Score was responsive to change over the 12 months period with an effect size of 1.04 from baseline to 12 months post-injury.  Conclusions: The NPI Score is a valid tool to assess patellar instability symptoms in people conservatively managed following FTPD.  Level of evidence: Level I

    Global age-sex-specific fertility, mortality, healthy life expectancy (HALE), and population estimates in 204 countries and territories, 1950–2019: a comprehensive demographic analysis for the Global Burden of Disease Study 2019

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    Background: Accurate and up-to-date assessment of demographic metrics is crucial for understanding a wide range of social, economic, and public health issues that affect populations worldwide. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 produced updated and comprehensive demographic assessments of the key indicators of fertility, mortality, migration, and population for 204 countries and territories and selected subnational locations from 1950 to 2019. Methods: 8078 country-years of vital registration and sample registration data, 938 surveys, 349 censuses, and 238 other sources were identified and used to estimate age-specific fertility. Spatiotemporal Gaussian process regression (ST-GPR) was used to generate age-specific fertility rates for 5-year age groups between ages 15 and 49 years. With extensions to age groups 10–14 and 50–54 years, the total fertility rate (TFR) was then aggregated using the estimated age-specific fertility between ages 10 and 54 years. 7417 sources were used for under-5 mortality estimation and 7355 for adult mortality. ST-GPR was used to synthesise data sources after correction for known biases. Adult mortality was measured as the probability of death between ages 15 and 60 years based on vital registration, sample registration, and sibling histories, and was also estimated using ST-GPR. HIV-free life tables were then estimated using estimates of under-5 and adult mortality rates using a relational model life table system created for GBD, which closely tracks observed age-specific mortality rates from complete vital registration when available. Independent estimates of HIV-specific mortality generated by an epidemiological analysis of HIV prevalence surveys and antenatal clinic serosurveillance and other sources were incorporated into the estimates in countries with large epidemics. Annual and single-year age estimates of net migration and population for each country and territory were generated using a Bayesian hierarchical cohort component model that analysed estimated age-specific fertility and mortality rates along with 1250 censuses and 747 population registry years. We classified location-years into seven categories on the basis of the natural rate of increase in population (calculated by subtracting the crude death rate from the crude birth rate) and the net migration rate. We computed healthy life expectancy (HALE) using years lived with disability (YLDs) per capita, life tables, and standard demographic methods. Uncertainty was propagated throughout the demographic estimation process, including fertility, mortality, and population, with 1000 draw-level estimates produced for each metric. Findings: The global TFR decreased from 2•72 (95% uncertainty interval [UI] 2•66–2•79) in 2000 to 2•31 (2•17–2•46) in 2019. Global annual livebirths increased from 134•5 million (131•5–137•8) in 2000 to a peak of 139•6 million (133•0–146•9) in 2016. Global livebirths then declined to 135•3 million (127•2–144•1) in 2019. Of the 204 countries and territories included in this study, in 2019, 102 had a TFR lower than 2•1, which is considered a good approximation of replacement-level fertility. All countries in sub-Saharan Africa had TFRs above replacement level in 2019 and accounted for 27•1% (95% UI 26•4–27•8) of global livebirths. Global life expectancy at birth increased from 67•2 years (95% UI 66•8–67•6) in 2000 to 73•5 years (72•8–74•3) in 2019. The total number of deaths increased from 50•7 million (49•5–51•9) in 2000 to 56•5 million (53•7–59•2) in 2019. Under-5 deaths declined from 9•6 million (9•1–10•3) in 2000 to 5•0 million (4•3–6•0) in 2019. Global population increased by 25•7%, from 6•2 billion (6•0–6•3) in 2000 to 7•7 billion (7•5–8•0) in 2019. In 2019, 34 countries had negative natural rates of increase; in 17 of these, the population declined because immigration was not sufficient to counteract the negative rate of decline. Globally, HALE increased from 58•6 years (56•1–60•8) in 2000 to 63•5 years (60•8–66•1) in 2019. HALE increased in 202 of 204 countries and territories between 2000 and 2019. Interpretation: Over the past 20 years, fertility rates have been dropping steadily and life expectancy has been increasing, with few exceptions. Much of this change follows historical patterns linking social and economic determinants, such as those captured by the GBD Socio-demographic Index, with demographic outcomes. More recently, several countries have experienced a combination of low fertility and stagnating improvement in mortality rates, pushing more populations into the late stages of the demographic transition. Tracking demographic change and the emergence of new patterns will be essential for global health monitoring. Funding: Bill & Melinda Gates Foundation. © 2020 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 licens

    Global burden of 87 risk factors in 204 countries and territories, 1990�2019: a systematic analysis for the Global Burden of Disease Study 2019

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    Background: Rigorous analysis of levels and trends in exposure to leading risk factors and quantification of their effect on human health are important to identify where public health is making progress and in which cases current efforts are inadequate. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 provides a standardised and comprehensive assessment of the magnitude of risk factor exposure, relative risk, and attributable burden of disease. Methods: GBD 2019 estimated attributable mortality, years of life lost (YLLs), years of life lived with disability (YLDs), and disability-adjusted life-years (DALYs) for 87 risk factors and combinations of risk factors, at the global level, regionally, and for 204 countries and territories. GBD uses a hierarchical list of risk factors so that specific risk factors (eg, sodium intake), and related aggregates (eg, diet quality), are both evaluated. This method has six analytical steps. (1) We included 560 risk�outcome pairs that met criteria for convincing or probable evidence on the basis of research studies. 12 risk�outcome pairs included in GBD 2017 no longer met inclusion criteria and 47 risk�outcome pairs for risks already included in GBD 2017 were added based on new evidence. (2) Relative risks were estimated as a function of exposure based on published systematic reviews, 81 systematic reviews done for GBD 2019, and meta-regression. (3) Levels of exposure in each age-sex-location-year included in the study were estimated based on all available data sources using spatiotemporal Gaussian process regression, DisMod-MR 2.1, a Bayesian meta-regression method, or alternative methods. (4) We determined, from published trials or cohort studies, the level of exposure associated with minimum risk, called the theoretical minimum risk exposure level. (5) Attributable deaths, YLLs, YLDs, and DALYs were computed by multiplying population attributable fractions (PAFs) by the relevant outcome quantity for each age-sex-location-year. (6) PAFs and attributable burden for combinations of risk factors were estimated taking into account mediation of different risk factors through other risk factors. Across all six analytical steps, 30 652 distinct data sources were used in the analysis. Uncertainty in each step of the analysis was propagated into the final estimates of attributable burden. Exposure levels for dichotomous, polytomous, and continuous risk factors were summarised with use of the summary exposure value to facilitate comparisons over time, across location, and across risks. Because the entire time series from 1990 to 2019 has been re-estimated with use of consistent data and methods, these results supersede previously published GBD estimates of attributable burden. Findings: The largest declines in risk exposure from 2010 to 2019 were among a set of risks that are strongly linked to social and economic development, including household air pollution; unsafe water, sanitation, and handwashing; and child growth failure. Global declines also occurred for tobacco smoking and lead exposure. The largest increases in risk exposure were for ambient particulate matter pollution, drug use, high fasting plasma glucose, and high body-mass index. In 2019, the leading Level 2 risk factor globally for attributable deaths was high systolic blood pressure, which accounted for 10·8 million (95 uncertainty interval UI 9·51�12·1) deaths (19·2% 16·9�21·3 of all deaths in 2019), followed by tobacco (smoked, second-hand, and chewing), which accounted for 8·71 million (8·12�9·31) deaths (15·4% 14·6�16·2 of all deaths in 2019). The leading Level 2 risk factor for attributable DALYs globally in 2019 was child and maternal malnutrition, which largely affects health in the youngest age groups and accounted for 295 million (253�350) DALYs (11·6% 10·3�13·1 of all global DALYs that year). The risk factor burden varied considerably in 2019 between age groups and locations. Among children aged 0�9 years, the three leading detailed risk factors for attributable DALYs were all related to malnutrition. Iron deficiency was the leading risk factor for those aged 10�24 years, alcohol use for those aged 25�49 years, and high systolic blood pressure for those aged 50�74 years and 75 years and older. Interpretation: Overall, the record for reducing exposure to harmful risks over the past three decades is poor. Success with reducing smoking and lead exposure through regulatory policy might point the way for a stronger role for public policy on other risks in addition to continued efforts to provide information on risk factor harm to the general public. Funding: Bill & Melinda Gates Foundation. © 2020 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 licens

    A Critical and Quantitative Review of the Stratification of Particles during the Drying of Colloidal Films

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    For a wide range of applications, films are deposited from colloidal particles suspended in a volatile liquid. There is burgeoning interest in stratifying colloidal particles into separate layers within the final dry film to impart properties at the surface different to the interior. Here, we outline the mechanisms by which colloidal mixtures can stratify during the drying process. The problem is considered here as a three-way competition between evaporation of the continuous liquid, sedimentation of particles, and their Brownian diffusion. In particle mixtures, the sedimentation of larger or denser particles offers one means of stratification. When the rate of evaporation is fast relative to diffusion, binary mixtures of large and small particles can stratify with small particles on the top, according to physical models and computer simulations. We compare experimental results found in the scientific literature to the predictions of several recent models in a quantitative way. Although there is not perfect agreement between them, some general trends emerge in the experiments, simulations and models. The stratification of small particles on the top of a film is favoured when the colloidal suspension is dilute but when both the concentration of the small particles and the solvent evaporation rate are sufficiently high. A higher ratio also favours stratification by size. This review points to ways that microstructures can be designed and controlled in colloidal materials to achieve desired properties

    Determination of parameters for self-stratification in bimodal colloidal coatings using Raman depth profiling

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    In waterborne mixtures of colloidal particles with differing sizes, the spontaneous stratification of one species of particle in a coating – driven by diffusiophoresis - offers the possibility to tailor the surface properties. However, despite strong research interest in stratification in recent years, the acceptable range of experimental parameters has not been fully explored, and the extent of stratification that is achievable has not yet been quantified. Here, we study the stratification of bimodal mixtures of waterborne polyurethane particles mixed with larger acrylic particles. We use ultra-low angle microtoming to prepare cross-sections of coating samples and analyse compositions quantitatively with Raman mapping. We use this method to obtain high-resolution depth profiles of the polyurethane phase in the coating with spacing between measurements corresponding to a few tens of nm. We experimentally test a model of diffusiophoresis and observe stratification when the processing parameters (evaporation rates, film thickness, and volume fraction of small particles) fall within the required range. Samples that exhibit stratification have top layer thicknesses on the order of tens of μm, which is a significant depth for exploitation in coatings aiming to modify surface properties. To guide the design of coatings in applications, we draw on the model to define the range of parameters in which self-stratification is expected. Our results provide a fundamental understanding that will enable the fabrication of tailored coatings in which the properties of the surface differ from the bulk material

    Water sorption in polymer network films synthesised from PEO oligomers containing acrylic and vinyl ether functionalities

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    Poly(ethylene oxide) oligomers, with end groups that have either acrylic or vinyl ether functionalities, were photopolymerised by UV radiation to create polymer networks in the form of thin films. Moisture sorption of the polymers, determined by microgravimetric analysis, was correlated to the oligomer structure, i.e. to the PEO chain length and to the type of unsaturation. The data can be described with a Fickian diffusion model using diffusion coefficients of water in the polymer networks on the order of 1 × 10−12 m2/s. The total amount of water sorption at equilibrium saturation increases with an increasing number of EO units in the oligomer used to synthesise the network. The number of absorbed water molecules associated with each EO unit increases with the number of these units in the oligomer until it reaches two water molecules per EO unit, for acrylated-PEO oligomers (PEGDA) having at least 30 EO units. The type of interactions between the polymer network and water were evaluated by means of thermal analysis performed on the hydrated films. It was found that all water is present as bound rather than mobile water

    Humidity sensing using PMMA-PMTGA-PMMA polymer in low coherence interferometric system

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    The authors describe a new optical humidity sensing system based on a multiplexed low coherence dual interferometric system allowing an absolute measurement at four different locations. The sensor is composed of a PMMA-PMTGA-PMMA polymer that combines good sensitivity and reproducibility for an overall accuracy of 1.21% relative humidity at equilibrium
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