PLA/WOOD BIOCOMPOSITES: IMPROVING COMPOSITE STRENGTH BY CHEMICAL TREATMENT OF THE FIBERS

A resol type phenolic resin was prepared for the impregnation of wood particles used for the reinforcement of PLA. A preliminary study showed that the resin penetrates wood with rates depending on the concentration of the solution and on temperature. Treatment with a solution of 1 wt% resin resulted in a considerable increase of composite strength and decrease of water absorption. Composite strength improved as a result of increased inherent strength of the wood, but interfacial adhesion might be modified as well. When wood was treated with resin solutions of larger concentrations, the strength of the composites decreased, first slightly, then drastically to a very small value. A larger amount of resin results in a thick coating on wood with inferior mechanical properties. At large resin contents the mechanism of deformation changes; the thick coating breaks very easily leading to the catastrophic failure of the composites at very small loads

The Dialectic of Values and Globalisation Virtual Communities and Identity Construction

This study is part of a body of research that seeks to understand an individual's social and cultural identity through their intensive use of social media and membership of virtual communities. It explores the impact of this engagement on their religious, moral and social values. The researcher drew on a variety of specialist references to uncover this social phenomenon. It was found that virtual communities represent a parallel social life to real society, serving as an alternative space. Individuals have begun to replace their real communities with virtual ones, where they find fulfilment of their desires and achievement of their social aspirations, often neglecting their social values. This shift leads to the globalisation of their ideas and beliefs, resulting in the formation of a new identity with unclear characteristics

PLA/Lignocellulosic fiber composites: particle characteristics, interfacial adhesion and failure mechanism.

PLA composites were prepared using six lignocellulosic fibers with widely varying particle characteristics. The composites were characterized by tensile testing, scanning electron (SEM) and polarization optical (POM) microscopy. Micromechanical deformation processes during loading were followed by acoustic emission measurements. Interfacial adhesion was estimated by three independent methods. Contrary to most claims published in the literature, interfacial adhesion between PLA and natural fibers was found to be rather strong, a result confirmed by the quantitative estimation of adhesion strength, acoustic emission measurements and SEM study. Strong interfacial adhesion results in weak dependence of the extent of reinforcement on the particle characteristics of the reinforcing fibers. Both acoustic emission measurements and microscopy indicated that the dominating micromechanical deformation process is the fracture of the fibers and close correlation was found between the initiation stress of fiber fracture, reinforcement and the ultimate strength of the composites

Tributyl citrate as an effective plasticizer for biodegradable polymers: effect of plasticizer on free volume and transport and mechanical properties

The effectiveness of tributyl citrate (TbC) as a plasticizer for polylactide and polyhydroxybutyrate was analysed in order to improve the ductility of these polymers and make them good candidates for food packaging applications. Although the thermal and mechanical properties have been widely studied in the literature, the effect of the plasticizer on free volume and transport properties has not been deeply analysed. The free volume was characterized using positron annihilation lifetime spectroscopy observing its linear increase with TbC content. The permeability to water vapour, oxygen and carbon dioxide was determined and the obtained results were related to the changes in glass transition temperature, level of crystallinity of the samples and free volume. This work would allow a better understanding of the effect of the plasticizer on the barrier and mechanical properties of polymers allowing the development of competitive materials for packaging applications. (c) 2018 Society of Chemical Industr

Nanostructured Biomaterials for Tissue Engineered Bone Tissue Reconstruction

Bone tissue engineering strategies are emerging as attractive alternatives to autografts and allografts in bone tissue reconstruction, in particular thanks to their association with nanotechnologies. Nanostructured biomaterials, indeed, mimic the extracellular matrix (ECM) of the natural bone, creating an artificial microenvironment that promotes cell adhesion, proliferation and differentiation. At the same time, the possibility to easily isolate mesenchymal stem cells (MSCs) from different adult tissues together with their multi-lineage differentiation potential makes them an interesting tool in the field of bone tissue engineering. This review gives an overview of the most promising nanostructured biomaterials, used alone or in combination with MSCs, which could in future be employed as bone substitutes. Recent works indicate that composite scaffolds made of ceramics/metals or ceramics/polymers are undoubtedly more effective than the single counterparts in terms of osteoconductivity, osteogenicity and osteoinductivity. A better understanding of the interactions between MSCs and nanostructured biomaterials will surely contribute to the progress of bone tissue engineering

Synthesis of four-arm star poly(L-lactide) oligomers using an in situ-generated calcium-based initiator

Using an in situ-generated calcium-based initiating species derived from pentaerythritol, the bulk synthesis of well-defined 4-arm star poly(L-lactide) oligomers has been studied in detail. The substitution of the traditional initiator, stannous octoate with calcium hydride allowed the synthesis of oligomers that had both low PDIs and a comparable number of polymeric arms (3.7 – 3.9) to oligomers of similar molecular weight. Investigations into the degree of control observed during the course of the polymerization found that the insolubility of pentaerythritol in molten L-lactide resulted in an uncontrolled polymerization only when the feed mole ratio of L-lactide to pentaerythritol was 13. At feed ratios of 40 and greater, a pseudo-living polymerization was observed. As part of this study, in situ FT-Raman spectroscopy was demonstrated to be a suitable method to monitor the kinetics of the ring-opening polymerization (ROP) of lactide. The advantages of using this technique rather than FT-IR-ATR and 1H NMR for monitoring L-lactide consumption during polymerization are discussed

Improving the estimation of the spatial distribution of atmospheric aerosols using satellite observations and machine learning

Les particules de matière (PM) en suspension dans l’air appelées aérosols atmosphériques sont connues pour leurs effets nocifs sur la santé et l’environnement en plus de la perturbation du système climatique. Afin de connaître le cycle de vie des aérosols, il faut étudier leurs origines, leurs réactivités, et la manière dont ils sont transportés par le vent. Différentes méthodes plus ou moins précises existent pour estimer l’abondance des PM. Les approches satellitaires fournissent classiquement des observations estimant les PM en 2D, c’est-à-dire la distribution horizontale ou les profils verticaux. Les modèles de chimie-transport simulent la distribution 3D des particules, mais une grande incertitude est liée à ces simulations, surtout en régions qui manquent d’instruments de mesures in situ pour contraindre la modélisation.L’objectif de ma thèse est d’améliorer les estimations existantes de la distribution spatiale des aérosols en exploitant les données satellitaires, les modèles de chimie-transport et l’intelligence artificielle. Pour cela, la première partie de mes travaux de thèse ont permis le développement de la première méthode capable d’observer la distribution 3D des particules fines. L'algorithme appelé AEROS5P utilise les parties visible et proche infrarouge des spectres de réflectance terrestre mesurés par l’instrument satellitaire TROPOMI afin de déduire des profils d'extinction des aérosols. Ces derniers sont comparables avec des mesures indépendantes de haute résolution verticale issues de la télédétection active lidar.Dans une deuxième partie, j’ai développé une méthode combinant les avantages du modèle chimie-transport CHIMERE et des observations satellitaires pour réduire les biais des champs simulés de l’épaisseur optique des aérosols. Cette correction est appliquée a posteriori à l'aide de modèles d'apprentissage automatique (Machine Learning) et des observations de l’instrument satellitaire MODIS. Les nouvelles estimations de l’AOD sont plus proches des observations indépendantes de MODIS et des stations d’observations AERONET.Particles of matter (PM) suspended in the air called atmospheric aerosols are known for their harmful effects on health and the environment in addition to the disruption of the climate system. In order to know the life cycle of aerosols, it is necessary to study their origins, their reactivity, and the way in which they are transported by wind. Different methods exist to estimate the abundance of PM. Satellite approaches typically provide observations estimating PM in 2D, i.e. horizontal distribution or vertical profiles. Chemistry-transport models simulate the 3D distribution of particles, but large uncertainty may be linked to them, especially in regions lacking ground stations monitoring instruments to constrain the modeling.The objective of my thesis is to improve existing estimates of the spatial distribution of aerosols by exploiting satellite data, chemistry-transport models and artificial intelligence. For this, the first part of my thesis is the development of the first method capable of observing the 3D distribution of fine particles. The algorithm called AEROS5P uses the visible and near infrared parts of the terrestrial reflectance spectra measured by the satellite instrument TROPOMI in order to deduce aerosol extinction profiles. These are comparable with independent measurements of high vertical resolution from active lidar remote sensing.In the second part, I developed a method combining the advantages of the CHIMERE chemistry-transport model and satellite observations to reduce the biases of the simulated fields of the optical thickness of aerosols. This correction is applied a posteriori using machine learning models and observations from the MODIS satellite observations. The new AOD are found to be closer to the independent MODIS observations and AERONET stations measurements

Causas genéticas e ambientais da hipoplasia do esmalte: revisão narrativa

A hipoplasia do esmalte (HE) é um defeito parcial ou completo do esmalte, associado a um distúrbio da fase secretora da amelogénese. Esta condição é identificada visualmente por uma redução localizada na espessura do esmalte apresentando limites regulares com esmalte saudável, que está presente antes da erupção do dente. Esta patologia aumenta o risco de cáries e danos dentários que geralmente ocorrem em fossas, sulcos ou linhas dentro do dente. Para além das fossas e sulcos nos dentes, os sinais e sintomas da HE também incluem manchas castanhas-amareladas que se desenvolvem sob a camada de dentina exposta. Na vida quotidiana, estes pacientes podem sentir dor ao consumir alimentos ou bebidas devido à maior sensibilidade ao frio ou ao calor. O maior impacto no dia a dia é não sorrir por causa da aparência dos dentes, o que pode afetar negativamente a autoconfiança do indivíduo. As opções de tratamento são baseadas em muitos fatores, como a gravidade da condição, idade do paciente e localização da hipoplasia. Pode ser utilizada uma restauração em compósito, uma coroa, um branqueamento e nos casos mais severos a extração dentária. O principal objetivo desta revisão narrativa é relembrar os fatores etiológicos, o diagnóstico, as características clínicas da hipoplasia dentária para melhor compreender a sua origem.Enamel hypoplasia (EH) is a partial or complete defect of enamel associated with a disorder of the secretory phase of amelogenesis. This condition is visually identified by a localized reduction in enamel thickness, showing regular boundaries with healthy enamel, that is present before tooth eruption. This pathology increases the risk of caries and dental damage that usually occur in pits, grooves or lines inside the tooth. Besides pits and grooves in the teeth, signs and symptoms of EH also include yellowish- brown spots that develop under the exposed dentin layer. In everyday life, patients may experience pain when consuming food or drinks due to their higher sensibility to cold or heat. The biggest impact in everyday life is not smiling because of the way teeth look, which can affect negatively the self-confidence of the individual. Treatment options are based on many factors, such as the severity of the condition, age of the patient, and location of the hypoplasia. A composite restoration, a crown, a bleaching and in the most severe cases a tooth extraction can be performed. The main objective of this narrative review is to recall the etiological factors, the diagnosis, the clinical features of dental hypoplasia to better understand its origin