Vidros e vitrocerâmicos bioativos e antibacterianos dopados com prata

Mestrado em Materiais e Dispositivos BiomédicosO perigo de infeção após cirurgia de implante tem estimulado investigações sobre as potenciais propriedades antimicrobianas de vidros bioativos. O presente trabalho teve como objetivo produzir vidros e vitrocerâmicos bioativos, que, para além de promoverem a regeneração do tecido ósseo, possam destruir localmente de uma forma eficaz invasores patogénicos por libertação de um agente antibacteriano de uma forma controlada e contínua. Um vidro de composição molar 25,43% SiO2 : 32,68% CaO : 10,89% P2O5 : 31,00% MgO e o mesmo vidro dopado com 1 e 2 mol% Ag2O, escolhido como agente antibacteriano, foram preparados pelo método de fusão e vazamento sob a forma de frita e de blocos monolíticos. As amostras foram caracterizadas por DRX, SEM/EDS, FTIR/ATR, ATD e AD. Para obtenção de vidros cerâmicos com diferentes percentagens de fase cristalina, algumas amostras foram sujeitas a tratamentos térmicos adicionais a 785, 800, 815 e 830 ºC, temperaturas escolhidas de acordo com os resultados obtidos por ATD. Estas amostras foram caracterizadas por SEM/EDS, FTIR/ATR, DRX e a quantificação das fases presente foi determinada pelo método de Rietveld. Quer os materiais vítreos quer os vitrocerâmicos foram caraterizados em termos da sua taxa de dissolução, bioatividade em meio fisiológico sintético acelular e atividade antibacteriana contra a Escherichia coli (E. coli). Nos testes de dissolução em água destilada todas as amostras apresentaram um aumento da percentagem de perda de peso com o tempo de imersão, até 168 horas para as fritas e 504 horas para os monolíticos, sem que tenham ocorrido alterações significativas de pH. A introdução de prata e a presença de fase cristalina favoreceram a degradação das amostras nos intervalos de tempo estudados. Nos ensaios de mineralização em SBF, até 168 horas para as fritas e 504 horas para os monolíticos, todos os vidros e vidros cerâmicos desenvolvidos revelaram ser potencialmente bioativos, tendo-se verificado que o desencadear dos processos que levam à formação da camada apatítica ocorreu mais cedo nas amostras vitrocerâmicas. Para estudar as transformações ocorridas na superfície das amostras foram utilizadas as técnicas SEM/EDS, DRX e em algumas amostras FTIR/DRIFT. Durante os intervalos de tempo estudados não ocorreram alterações significativas do pH do SBF. As alterações da concentração iónica do SBF foram monitorizadas por ICP, tendo-se verificado que até às 168 horas de imersão todas as amostras de frita com prata na sua composição libertam esse elemento para o SBF em concentrações iónicas abaixo do limite de toxicidade. A atividade antibacteriana das amostras vítreas e vitrocerâmicas de frita contra a E. Coli foi avaliada de acordo com a norma ASTM E 2149. Verificou-se que para a mesma concentração, a diminuição da granulometria ou o aumento da % de Ag2O adicionado melhoraram as propriedades antibacterianas das amostras vítreas. As amostras vitrocerâmicas estudadas não apresentaram comportamento antibacteriano para a concentração e granulometria utilizadas. Os resultados experimentais obtidos demonstram que os vidros e vitrocerâmicos bioativos dopados com prata estudados são uma abordagem eficaz para minimizar o risco de infeção nos locais de implantação, podendo a sua atividade antibacteriana ser controlada por alteração da composição, da granulometria ou pelo controlo da percentagem das fases presentes.The danger of infection after implant surgery has stimulated the study of the potential antimicrobial properties of bioactive glasses. This study aimed to produce bioactive glasses, which, in addition to promoting the regeneration of bone tissue, can locally destroy pathogenic invaders by release of an antibacterial agent in a controlled and continuous manner. A bioactive glass composition (mol%) 25,43 % SiO2 % : 32,68 % CaO : 10,89 % P2O5 : 31,00 % MgO and the same glass modified with 1 and 2 mol % Ag2O, chosen as antibacterial agent, were prepared by the melting quenching technique under the form of monolithic and frit samples. The samples were characterized by XRD, SEM/EDS, FTIR/ ATR, DTA and dilatometric analysis. Some samples were submitted to additional heat treatment at 785, 800, 815 and 830 ºC, temperatures chosen in accordance with the DTA results, to obtain glass ceramics with different percentages of crystalline phase. These samples were characterized by SEM/EDS, FTIR/ATR, XRD and the quantification of phases was obtained using the Rietveld method. Glassy and glass ceramic materials were characterized in terms of its dissolution rate, bioactivity in a acellular simulated body fluid environment and antibacterial activity against Escherichia coli (E. coli). During the studied time intervals, up to 168 hours to frit and 504 hours for monolithic, all samples showed an increase of the weight loss percentage with the immersion time in distilled water, without the occurrence of significant changes in pH. Weight losses were higher in vitreous silver doped samples and glass ceramic samples. After soaking in SBF, up to 168 hours to frit and 504 hours for monolithic, glasses and glass ceramic samples have proven to be potentially bioactive, starting the formation of the apatite layer early on the glass ceramic samples. SEM/EDS, XRD and, in some samples FTIR/DRIFT, were used to study the surface transformation of the samples. During the studied time intervals there were no significant changes in SBF pH. Changes in ionic concentration of the SBF were monitored by ICP, and it was found that up to 168 hours of soaking all frit samples with silver on their composition release this element to the SBF in ionic concentrations below toxicity values. The antibacterial activity of the glass and glass ceramic frit samples against E. coli was evaluated according to ASTM E 2149 method. It was found that for the same concentration, decreasing the particle size or increasing the % of Ag2O improved the antibacterial properties of the glassy samples. The studied glass ceramic samples at the used concentration and particle size showed no antibacterial behavior. The experimental results show that the studied bioactive glasses and glass ceramics doped with silver are an effective approach to minimizing the risk of infection on implantation sites, and their antibacterial activity may be controlled by changing the composition, the particle size or for controlling the percentage of present phases

Biomass Fly Ash Self-Hardened Adsorbent Monoliths for Methylene Blue Removal from Aqueous Solutions

The use of methylene blue (MB) by several industries generates contaminated industrial wastewaters that must be purified before discharge into the environment. Its removal can be achieved by adsorption, and low-cost and easily available materials should be used as adsorbents. Biomass fly ash (BFA) generated from biomass combustion, for heat and power generation, is increasing worldwide since the process is considered CO2 neutral. However, most of the ash is still landfilled. This study aims to evaluate the valorisation of BFA as a low-cost porous bulk adsorbent for MB removal from wastewaters. The monoliths were obtained after 14 days of curing just after adding water and a porogenic agent (aluminium powder) to the BFA, using the self-hardening ability of this waste. The BFA was characterised for chemical (XRF) and mineralogical (XRD) composition, particle size distribution (laser diffraction-COULTER) and morphology (SEM). The monolith sample cured for 14 days was characterised for density, porosity (total and open), microstructure, compressive strength, and MB removal ability (batch tests). The results showed that the addition of aluminium powder (0.09 wt.%) promoted an increase in interconnected porosity and the MB removal efficiency reached 80% for the most porous samples. The equilibrium data for the adsorption process were well characterised by a type 2 Langmuir isotherm equation with a monolayer adsorption capacity (qmax) that ranged from 0.22 to 0.66 mg/g

Valorização de cinzas de caldeiras de biomassa por incorporação em materiais cimentícios e adsorventes para aplicações ambientais

Global awareness about environmental issues has led to the increasing use of renewable and sustainable sources of energy, as substitutes for fossil fuels, being the combustion of biomass one of the most used alternative sources of energy. Kraft pulp and paper plants are equipped with biomass cogeneration facilities to produce steam and power that are used in the pulp manufacturing processes and, in some cases, they also have biomass power stations to produce electricity. Industrial by-products from the production process and forestry residues are commonly used as fuel. However, this process produces large quantities of biomass fly ash (BFA) that is essentially landfilled, although in the context of the circular economy concept it should be recycled. This thesis investigates the potential of using BFA in the production of cement-based materials or as dye adsorbent. For this purpose, eight different types of biomass typically present in the fuel mixtures at the mill were combusted and the properties of the ash they generate were determined. These biomass ashes cannot be used alone as secondary raw material for clinker production since they exhibit low concentrations of Al₂O₃ and Fe₂O₃ and a CaO/SiO₂ mass ratio that is, in general, too high. Nevertheless, according to EN197–1:2011 and the value of Na₂O(eq), they can be used in cementitious formulations, with the incorporation amount depending on the biomass type. This knowledge will allow, in the future, optimizing biomass blends to be used as fuel aiming to generate ash with suitable properties for a better incorporation in cement-based materials. The possibility of using BFA as secondary raw material in a commercial screed mortar formulation, as filler (5.0, 7.5 e 10.0 wt.%), or as a cement substitute (17.0, 50.0 e 67.0 wt.%), was fully tested. Some simple pre-treatment processes were applied, such as milling and sieving, aiming to adapt ash characteristics to maximize its incorporation rate. The valorisation of 7.5 wt.% of BFA in the asreceived condition or up to 10.0 wt.% after grinding and sieving (<63 μm) as fillers, and the substitution of 17 wt.% of cement by as-received BFA proven to be technically feasible. Furthermore, the select formulations showed resistance to 25 consecutive freeze-thaw cycles. Additionally, it was verified that these recycling solutions provide an economic benefit of up to 8.85 €/tmortar and 1.11 €/tmortar for the mortar and the pulp and paper producers, respectively. Exploring a completely different valorisation route, BFA-based highly porous monoliths were prepared and used as adsorbents for methylene blue removal from aqueous solutions, demonstrating a high-added value potential. The monoliths were prepared with a sort of as-received BFA, taking advantage of its hydraulic potential. The total porosity was increased up to 72.7% by adding 0.09 wt.% of aluminium powder. The achieved dye maximum uptake (0.66 mg/g) was inferior to that of BFA powdered samples. However, once exhausted, monoliths removal from solutions is much easier and practical, and facilitates their use in continuous flow systems. The results obtained in this thesis demonstrate that BFA can be utilized in the production of low-cost and environmentally friendly adsorbents. Furthermore, it opens the way to scale-up the production of more sustainable screed mortars in which cement and natural non-renewable resources are substituted by an abundant residue.A consciencialização global sobre questões ambientais tem levado ao uso crescente de fontes de energia renováveis como alternativa aos combustíveis fósseis, sendo a combustão de biomassa uma das mais utilizadas. As fábricas de produção de pasta e papel pelo processo Kraft estão equipadas com centrais de cogeração a biomassa para produzir vapor e energia elétrica que são utilizados no processo de fabrico e, em alguns casos, também possuem centrais termoelétricas para produção de eletricidade. Subprodutos industriais do processo de produção e biomassa resultante de operações de limpeza florestal são comumente utilizados como combustível. Este processo produz grandes quantidades de cinzas volantes de biomassa (CVB), normalmente depositadas em aterro, mas que no contexto da economia circular devem ser recicladas. Esta tese investiga o uso de CVB na produção de argamassas e de materiais para adsorção de corantes. Com este intuito, foram incineradas oito tipologias de biomassa tipicamente presentes nas misturas de combustível utilizadas na fábrica e as cinzas geradas foram devidamente caracterizadas. Verificou-se que as cinzas obtidas não podem ser individualmente utilizadas como matéria-prima para a produção de clínquer, pois apresentam uma relação mássica CaO/SiO₂ em geral muito alta e possuem baixos teores de Al₂O₃ e Fe₂O₃. No entanto, de acordo com os pressupostos da EN197–1:2011 e o valor de Na₂O(eq), podem ser utilizadas em formulações cimentícias com o teor de incorporação a depender do tipo de biomassa utilizada. Este conhecimento permitirá, no futuro, otimizar as misturas de biomassa com o objetivo de produzir cinzas com propriedades adequadas para incorporação em materiais à base de cimento. A possibilidade de utilização de CVB como matéria-prima secundária na formulação de uma betonilha comercial, como filler (5,0, 7,5 e 10,0% em massa) ou em substituição de cimento (17,0, 50,0 e 67,0% em massa), foi também testada. Com o intuito de adequar as características das cinzas e assim maximizar a sua percentagem de incorporação, foram testados processos simples de pré-tratamento como moagem e peneiração. A valorização de 7,5% de CVB como recebidas ou até 10.0% após moagem e peneiração (<63 μm) como filler, ou como 17% de substituto do cimento como recebidas foi provada ser tecnicamente viável. Além disso, as formulações selecionadas demonstraram ser resistentes a 25 ciclos de gelo/degelo. Adicionalmente, verificou-se que estas soluções de reciclagem podem proporcionar um benefício económico, de até 8,85 €/tbetonilha para a empresa produtora da betonilha e 1,11 €/tbetonilha para a fábrica produtora de pasta e papel. Explorando uma alternativa de valorização completamente diferente, foram preparados monólitos com elevada porosidade à base de CVB como recebidas, que foram utilizados como adsorventes para remoção de azul de metileno de soluções aquosas. Os monólitos foram preparados aproveitando o potencial hidráulico de uma tipologia de CVB e a porosidade total foi incrementada até 72,7% pela adição de 0,09% em massa de pó de alumínio. A adsorção máxima alcançada (0,66 mg/g) foi inferior à verificada em amostras de CVB em pó. No entanto, uma vez exaustos, a remoção de monólitos das soluções é muito mais fácil e prática para além de simplificar a sua aplicação em sistemas de fluxo contínuo. Os resultados obtidos demonstram que as CVB podem ser utilizadas na produção de adsorventes ecológicos e de baixo custo. Além disso, este estudo abre caminho para a produção de betonilhas mais sustentáveis, em que cimento e recursos naturais não renováveis podem ser substituídos por um resíduo.Programa Doutoral em Biorrefinaria

Recycling mussel shells as secondary sources in green construction materials: a preliminary assessment

This paper reports the development of novel green bio-composite mortars obtained by reusing mussel shells, a waste from the fish canning industry, as recycled aggregate, used for the first time in total substitution to the traditional sand. It suggests that this is a valid alternative to their usual disposal in landfills because the organic matter is potentially dangerous to humans and the environment. Different waste-based cementitious mixes were tested and compared to a traditional OPC mortar. The manufacturing process was performed at ambient conditions (20 ◦C, 65% RH) with highly sustainable results and consisted of simple operative steps reproducible in a real building site. The engineering performance was investigated to preliminarily assess the novel material potentials in construction. The main results showed that recycling mussel shells as aggregate while considerably decreasing the mechanical resistance (up to 60% in bending and 50% in compression), mixes could still find proper building applications (either structural, light partition, and plastering) according to the relevant standards. Moreover, the bulk density resulted up to 30% lower and the energy behavior was improved up to 40%, making the developed mortars highly suitable for promising energy-saving uses. Finally, the waste recycling about halves the materials cost and could also grant further financial saving for the fish industry. To conclude, the large amount of reused bio-waste not only represents a valid alternative to their usual disposal in landfills, but also makes the considered mortars suitable for building applications and promising candidates for the Minimum Environmental Criteria certification, in light of the EU Green Transition, and in line with the principles of the circular economy

Recycling Mussel Shells as Secondary Sources in Green Construction Materials: A Preliminary Assessment

This paper reports the development of novel green bio-composite mortars obtained by reusing mussel shells, a waste from the fish canning industry, as recycled aggregate, used for the first time in total substitution to the traditional sand. It suggests that this is a valid alternative to their usual disposal in landfills because the organic matter is potentially dangerous to humans and the environment. Different waste-based cementitious mixes were tested and compared to a traditional OPC mortar. The manufacturing process was performed at ambient conditions (20 °C, 65% RH) with highly sustainable results and consisted of simple operative steps reproducible in a real building site. The engineering performance was investigated to preliminarily assess the novel material potentials in construction. The main results showed that recycling mussel shells as aggregate while considerably decreasing the mechanical resistance (up to 60% in bending and 50% in compression), mixes could still find proper building applications (either structural, light partition, and plastering) according to the relevant standards. Moreover, the bulk density resulted up to 30% lower and the energy behavior was improved up to 40%, making the developed mortars highly suitable for promising energy-saving uses. Finally, the waste recycling about halves the materials cost and could also grant further financial saving for the fish industry. To conclude, the large amount of reused bio-waste not only represents a valid alternative to their usual disposal in landfills, but also makes the considered mortars suitable for building applications and promising candidates for the Minimum Environmental Criteria certification, in light of the EU Green Transition, and in line with the principles of the circular economy

Valorization of Fly Ashes and Sands Wastes from Biomass Boilers in One-Part Geopolymers

Fly ash (FA) and exhausted bed sands (sands wastes) that are generated in biomass burners for energy production are two of the wastes generated in the pulp and paper industry. The worldwide production of FA biomass is estimated at 10 million tons/year and is expected to increase. In this context, the present work aims to develop one-part alkali-activated materials with biomass FA (0–100 wt.% of the binder) and sands wastes (100 wt.% of the aggregate). FA from two different boilers, CA and CT, was characterized and the mortar’s properties, in the fresh and hardened conditions, were evaluated. Overall, the incorporation of FA decreases the compressive strength of the specimens. However, values higher than 30 MPa are reached with 50 wt.% of FA incorporation. For CA and CT, the compressive strength of mortars with 28 days of curing was 59.2 MPa (0 wt.%), 56.9 and 57.0 MPa (25 wt.%), 34.9 and 46.8 MPa (50 wt.%), 20.5 and 13.5 MPa (75 wt.%), and 9.2 and 0.2 MPa (100 wt.%), respectively. The other evaluated characteristics (density, water absorption, leached components and freeze–thaw resistance) showed no significant differences, except for the specimen with 100 wt.% of CA. Therefore, this work proved that one-part geopolymeric materials with up to 90 wt.% of pulp and paper industrial residues (FA and sand) can be produced, thus reducing the carbon footprint associated with the construction sector

Characterization of ashes produced from different biomass fuels used in combustion systems in a pulp and paper industry towards its recycling

In the boilers of pulp mills the fuel blends used vary because they are essentially composed of residual forest biomass. Consequently, the physical-chemical properties of the produced ash streams can exhibit high temporal variability, making their proper management and recycling difficult. This study aims to characterize the ash from the incineration of biomass samples used as fuel in order to understand its influence on the properties of the generated ash fluxes. This can anticipate suitable blending procedures that minimize the variability of the ash characteristics. For this purpose, typical biomass samples (eucalyptus bark, treetops and knots, pine treetops, silver wattle, Sydney golden wattle, white poplar, and grey willow) were incinerated (at 550 and 825 °C) and the resulting ashes were characterized. The thermal behavior of the biomass was evaluated by TG/DTA and the generated ash content was determined. The particle size distribution (laser diffraction), morphology (SEM), mineralogy (XRD), and chemical composition (XRF) were other evaluated properties. From the results obtained it is concluded that the ashes cannot be used as raw materials for clinker production. However, they can be used in concrete and mortar formulations, as a cement substitute or as filler. The maximum incorporation amount depends on the type of biomass used, ranging from 54 wt% for pine treetops to 100 wt% for eucalyptus bark. This knowledge is fundamental to understand how to optimize the biomass blends used in industrial combustion systems to obtain ashes with suitable properties to be used as secondary raw materials in building materials formulations.publishe

Architectural technologies for life environment: Spent coffee ground reuse in lime-based mortars. A preliminary assessment for innovative green thermo-plasters

Spent coffee ground, the residue obtained from the brewing process, is the primary unavoidable (inedible) waste from the coffee consumption. As coffee production and beverage consumption are increasing worldwide, a more sustainable waste management is required since the usual disposal in landfill is a liability to both humans and the environment. This paper is aimed at showing a possible alternative reuse of coffee ground wastes in novel green building materials intended for thermo-plastering applications in construction, in a circular economy context. Coffee waste was used in various percentages (up to 17.5%) to assess the engineering performance of the pro- duced bio-composite mortars. The main results showed that just a little amount of coffee waste determines a bulk density decrease up to 15.4% (making the products comparable to a structural lightweight conglomerate or a light plastering mortar), an extensive drop in mechanical performance (still maintaining acceptable values for the considered plastering application) and in thermal conductivity (up to 47%). Moreover, a multi-criteria analysis, not only able to consider the materials performance, but also aspects related to the environmental impact and the economic drawback, has been implemented resulting that the preferable mix would contain 10% waste. Finally, preparatory virtual energy simulations were implemented to analyse the performance of that mix in a simplified architectural model, revealing a sufficient energy improvement and a more efficacy in cold cli- mates. All considering, coffee waste can be effectively reused to manufacture green bio-composite thermo- plasters with adequate energy performance considering the main requirements of a building application

Waste-Based One-Part Alkali Activated Materials

Ordinary Portland Cement is the most widely used binder in the construction sector; however, a very high carbon footprint is associated with its production process. Consequently, more sustainable alternative construction materials are being investigated, namely, one-part alkali activated materials (AAMs). In this work, waste-based one-part AAMs binders were developed using only a blast furnace slag, as the solid precursor, and sodium metasilicate, as the solid activator. For the first time, mortars in which the commercial sand was replaced by two exhausted sands from biomass boilers (CA and CT) were developed. Firstly, the characterization of the slag and sands (aggregates) was performed. After, the AAMs fresh and hardened state properties were evaluated, being the characterization complemented by FTIR and microstructural analysis. The binder and the mortars prepared with commercial sand presented high compressive strength values after 28 days of curing-56 MPa and 79 MPa, respectively. The mortars developed with exhausted sands exhibit outstanding compressive strength values, 86 and 70 MPa for CT and CA, respectively, and the other material’s properties were not affected. Consequently, this work proved that high compressive strength waste-based one-part AAMs mortars can be produced and that it is feasible to use another waste as aggregate in the mortar’s formulations: the exhausted sands from biomass boilers

Development of energy-saving innovative hydraulic mortars reusing spent coffee ground for applications in construction

This paper reports the development of green bio-composite mortars, obtained reusing spent coffee ground (SCG), an agri-food residue, in the light of the Circular Economy approach. This process can boost the sustainability in Construction and proposes an alternative to SCG disposal in landfill, potentially dangerous to humans and the environment. For the first time, specimens were produced and compared using different blends of conventional hydraulic binders (ordinary Portland cement and natural hydraulic lime); SCG partially substituted sand (up to 15 wt.%, with a 2.5% increment) for the aggregate mix. The manufacturing process was performed at ambient conditions (20°C, 65% RH) resulting highly sustainable, and consisted of simple operative steps reproducible in a real building site. The prepared mixes were fully characterised to assess their technological potentials in construction. Morphology analysis, performed by Scanning Electron Microscopy (SEM), showed SCG addition led to a more compact structure. Considering the functional properties, results widely range on binder blend base, offering various concrete applications; it was observed that with SCG addition, despite a decrease in the bulk density (up to 26%), the mechanical performance still remained suitable for proper masonry applications, according to the relevant standards (class of resistance M2.5-M10). A light water imbibition increase was registered (about 5%) while a significant decrease of the capillarity index was seen. Moreover, a robust thermal conductivity reduction was observed (up to 72%), making the mortars highly suitable for energy-saving uses in building. Finally, a reduction in the manufacturing cost (up to 8%) was calculated, granting significant financial saving in light of the industrial symbiosis. These encouraging results showed that reusing SCG not only provides numerous benefits to the overall building performance and management but it is also a valid alternative to usual SCG disposal. The high amount of reused bio-waste significantly widens the knowledge of greener and more efficient building sector, making the prepared mortars promising candidates for the Minimum Environmental Criteria certification, in light of the recent EU regulations, and in line with the principles of the Circular Economy