Influence of the size and amount of cork particles on the toughness of a structural adhesive

The inclusion of particles (nano or micro) is a method to improve the mechanical properties such as toughness of structural adhesives. Structural adhesives are known for their high strength and stiffness but also for their low ductility and toughness. There are many processes described in the literature to increase the toughness, being one of the most common the use of rubber particles. In the present study, natural micro particles of cork are used with the objective to increase the toughness of a brittle epoxy adhesive. The idea is for the cork particles to act like as a crack stopper leading to more energy absorption. The influence of the cork particle size and amount were studied. Particles of cork ranging from 38 to 250 µm were mixed in the epoxy adhesive Araldite 2020 from Huntsman. The amount of cork in the adhesive was varied between 1 and 5% in weight. Surface treatment (low pressure plasma) was applied to the cork powder to assess the effect of the interaction adhesive-cork with several degrees of adhesion

Use of seawater to improve the static strength and fatigue life of bonded coated steel joints

La industria de la construcción naval exige soluciones adhesivas para unir componentes a sustratos pintados, ya que las tecnologías de soldadura tradicionales requieren operaciones de procesamiento costosas y que requieren mucho tiempo. Sin embargo, este tema rara vez se considera en la literatura. El objetivo del presente estudio es investigar la influencia de la exposición en disoluciones de cloruro de sodio en la resistencia estática y el rendimiento a la fatiga de juntas de acero pintadas unidas con adhesivo. Para ello, se utilizó un adhesivo epoxídico frágil de dos componentes para fabricar uniones a solape de aceros pintados unidos con adhesivo. Se realizaron ensayos estáticos y de fatiga tras envejecer las uniones mediante inmersión en soluciones cloradas durante diferentes periodos de tiempo. Las pruebas adicionales realizadas incluyeron pruebas FTIR, análisis de la temperatura de transición vítrea y pruebas de tracción de muestras de adhesivo envejecidas y sin envejecer, estudios experimentales y de simulación FEM de la absorción de agua, y análisis de la superficie de fractura de las juntas. Los resultados muestran, sorprendentemente, que tanto las propiedades mecánicas estáticas como las de fatiga de las juntas aumentan significativamente con el envejecimiento durante el primer mes de exposición. La difusión de agua que tuvo lugar durante el primer mes en las juntas a solape mejoró más del 30% tanto la resistencia estática como la resistencia a la fatiga de las juntas fabricadas con este adhesivo relativamente rígido. La tasa de absorción de agua del adhesivo también se calculó utilizando las relaciones de la ley de Fick. Los resultados se utilizaron para simular numéricamente el nivel de humedad absorbida por la capa de adhesivo de las uniones. La presente investigación demuestra que el fenómeno de absorción de humedad no conduce a resultados negativos para todas las uniones adhesivas. Para uniones adhesivas frágiles, como la analizada aquí, el contenido de agua reduce la concentración de tensiones en los extremos de unión, proporcionando una distribución de tensiones más uniforme a lo largo de la línea de unión. Este fenómeno permite que la unión sostenga niveles de carga más altos. Este comportamiento mecánico mejorado relacionado con la diferente distribución del contenido de agua puede considerarse una estrategia novedosa en el diseño de juntas, ya que puede reducir los costos del servicio y también puede reducir el peso total de la estructura adherida. Para aplicaciones navales, este estudio sugiere que la junta adhesiva considerada se puede utilizar en un entorno no sumergido. En este caso, la absorción de agua se desarrollará a un ritmo menor respecto a los resultados obtenidos, manteniendo su rendimiento durante un periodo mayor. Sin embargo, se deberían realizar más investigaciones para analizar este comportamiento. Esta contribución constituye la publicación más relevante de la Tesis Doctoral Industrial con mención internacional de Dª M. Ortega-Iguña, tesis dirigida por el solicitante (J.M Sánchez-Amaya), y defendida en 2023

Combined effect of seawater and load on methacrylate adhesive

[Abstract]: Although the shipbuilding industry is constantly demanding new advanced joining solutions, adhesive technology is not as developed in the marine as compared to other industries. The main reason is the lack of specific knowledge that guarantees the durability of the bonded joints in optimal conditions during the life cycle of a ship. This work simulates in the laboratory a marinelike environment by immersing an adhesive in seawater and subjecting it to constant loading. The objective is to characterize the seawater absorption behavior and its consequences on the mechanical, thermal, and chemical properties of the adhesive after this aging process. Seawater ingress was determined through gravimetric tests at several load conditions of the tensile strength of the adhesive. Besides, absorption process was studied using Fick’s Law, determining the diffusion coefficients. The thermal behavior was monitored with differential scanning calorimetry (DSC) and the chemical degradation was analyzed using Fourier transform infrared spectroscopy (FTIR). Also, the mechanical properties were determined by tensile tests. The surface of the adhesive (dried) was studied by Scanning Electron Microscopy (SEM) technique and the porosity was measured by physisorption with a high-performance adsorption analyzer. A numerical simulation was developed using Darcy’s Law combined with continuity equation. The results show that application of loads and immersion in seawater until full saturation of seawater improve the mechanical properties of the adhesive, but it affects negatively to the glass transition temperature. This should be considered when designing adhesive bonding joints on ships.Xunta de Galicia; ED431C-2020-14The research of Javier Tarrío Saavedra has been supported by the Ministerio de Ciencia e Innovación grant PID2020-113578RB- 100, the Xunta de Galicia (Grupos de Referencia Competitiva ED431C-2020-14), and by the CITIC, also funded by the Xunta de Galicia through the collaboration agreement between the Consellería de Cultura, Educaci´on, Formaci´on Profesional e Universidades and the Galician universities for the reinforcement of the research centers of the Galician University System (CIGUS)

Bradyrhizobium ingae sp. nov., isolated from effective nodules of Inga laurina grown in Cerrado soil

Root-nodule bacteria were isolated from lnga laurina (Sw.) Willd. growing in the Cerrado Amazon region, State of Roraima, Brazil. The 16S rRNA gene sequences of six strains (BR 10250(T), BR 10248, BR 10249, BR 10251, BR 10252 and BR 10253) showed low similarities with currently described species of the genus Bradyrhizobium. Phylogenetic analyses of sequences of five housekeeping genes (dnaK, gyrB, recA and rpoB) revealed Bradyrhizobium iriomotense EKO5(T) to be the closest type strain (97.4% sequence similarity or less). Chemotaxonomic data, including fatty acid profiles [with the major components C-16:0 and summed feature 8 (C-18:1 omega 6c/C-18:1 omega 7c)], the slow growth rate and carbon compound utilization patterns supported the assignment of our strains to the genus Bradyrhizobium. Results from DNA DNA hybridizations and physiological traits differentiated our strains from the closest related species of the genus Bradyrhizobium with validly published names. Sequences of symbiosis-related genes for nodulation (nodC) and nitrogen fixation (nifH) grouped together with those of B. iriomotense EKO5(T) and Bradyrhizobium sp. strains BR 6610 (used as a commercial inoculant for Inga marginata in Brazil) and TUXTLAS-10 (previously observed in Central America). Based on these data, the six strains represent a novel species, for which the name Bradyrhizobium ingae sp. nov. is proposed. The type strain is BR 10250(T) (=HAMBI 3600(T))

The fraction of cancer attributable to ways of life, infections, occupation, and environmental agents in Brazil in 2020

Many human cancers develop as a result of exposure to risk factors related to the environment and ways of life. The aim of this study was to estimate attributable fractions of 25 types of cancers resulting from exposure to modifiable risk factors in Brazil. The prevalence of exposure to selected risk factors among adults was obtained from population-based surveys conducted from 2000 to 2008. Risk estimates were based on data drawn from metaanalyses or large, high quality studies. Population-attributable fractions (PAF) for a combination of risk factors, as well as the number of preventable deaths and cancer cases, were calculated for 2020. The known preventable risk factors studied will account for 34% of cancer cases among men and 35% among women in 2020, and for 46% and 39% deaths, respectively. The highest attributable fractions were estimated for tobacco smoking, infections, low consumption of fruits and vegetables, excess weight, reproductive factors, and physical inactivity. This is the first study to systematically estimate the fraction of cancer attributable to potentially modifiable risk factors in Brazil. Strategies for primary prevention of tobacco smoking and control of infection and the promotion of a healthy diet and physical activity should be the main priorities in policies for cancer prevention in the country. \ua9 2016 Azevedo e Silva et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited