Numerical and experimental analyses of biocomposites reinforced with natural fibres

n the last decades the biocomposites have been widely used in the construction, automobile and aerospace industries. Not only the interface transition zone (ITZ) but also the heterogeneity of natural fibres affects the mechanical behaviour of these composites. This work focuses on the numerical and experimental analyses of a polymeric composite fabricated with epoxy resin and unidirectional sisal and banana fibres. A three-dimensional model was set to analyze the composites using the elastic properties of the individual phases. In addition, a two-dimensional model was set taking into account the effective composite properties obtained by micromechanical models. A tensile testing was performed to validate the numerical analyses and evaluating the interface condition of the constitutive phases.

Drilling delamination outcomes on glass and sisal reinforced plastics

Nowadays, fibre reinforced plastics are used in a wide variety of applications. Apart from the most known reinforcement fibres, like glass or carbon, natural fibres can be seen as an economical alternative. However, some mistrust is yet limiting the use of such materials, being one of the main reasons the inconsistency normally found in their mechanical properties. It should be noticed that these materials are more used for their low density than for their high stiffness. In this work, two different types of reinforced plates were compared: glass reinforced epoxy plate and sisal reinforced epoxy plate. For material characterization purposes, tensile and flexural tests were carried out. Main properties of both materials, like elastic modulus, tensile strength or flexural modulus, are presented and compared with reference values. Afterwards, plates were drilled under two different feed rates: low and high, with two diverse tools: twist and brad type drill, while cutting speed was kept constant. Thrust forces during drilling were monitored. Then, delamination area around the hole was assessed by using digital images that were processed using a computational platform previously developed. Finally, drilled plates were mechanically tested for bearing and open-hole resistance. Results were compared and correlated with the measured delamination. Conclusions contribute to the understanding of natural fibres reinforced plastics as a substitute to glass fibres reinforced plastics, helping on cost reductions without compromising reliability, as well as the consequence of delamination on mechanical resistance of this type of composites.

Processing of continuous fibre reinforced thermoplastics

Towpregs based on different fibres and thermoplastic matrices were processed for highly demanding and more commercial applications by different composite processing technologies. In the technologies used, compression moulding and pultrusion, the final composite pr ocessing parameters were studied in order to obtain composites with adequate properties at industrial compatible production rates. The produced towpregs were tested to verify its polymer content and degree of impregnation. The obtained results have shown t hat the coating line enabled to produce, with efficiency and industrial scale speed rates, thermoplastic matrix towpregs that may be used to manufacture composites for advanced and larger volume commercial markets.

Drilling of fibre reinforced plastic laminates

The use of fibre reinforced plastics – FRP’s – in structures is under a considerable increase. Advantages of their use are related with their low weight, high strength and stiffness. The improvement of the dynamic characteristics has been profitable for aeronautics, automobile, railway, naval and sporting goods industries. Drilling is a widely used machining technique as it is needed to assemble parts in a structure. This is a unique machining process, characterized by the existence of two different mechanisms: extrusion by the drill chisel edge and cutting by the rotating cutting lips. Drilling raises particular problems that can reduce mechanical and fatigue strength of the parts. In this work, quasi-isotropic hybrid laminates with 25% of carbon fibre reinforced plies and 4 mm thickness are produced, tested and drilled. Three different drill geometries are compared. Results considered are the interlaminar fracture toughness in Mode I – GIc –, thrust force during drilling and delamination extent after drilling. A bearing test is performed to evaluate tool influence on the load carrying capacity of the plate. Results consider the influence of drill geometry on delamination. A correlation linking plate damage to bearing test results is presented.

Occupational stress and coping resources in physiotherapists: a survey of physiotherapists in three general hospitals

Objectives - To identify occupational stressors and coping resources in a group of physiotherapists, and to analyse interactions between subjective levels of stress, efficacy in stress resolution and coping resources used by these professionals. Design - A sample of 55 physiotherapists working in three general hospitals in Portugal completed the Coping Resources Inventory for Stress, the Occupational Stressors Inventory and two subjective scales for stress and stress resolution. Main results - Most physiotherapists perceived that they were moderately stressed (19/55, 35%) or stressed (20/55, 36%) due to work, and reported that their efficacy in stress resolution was moderate (25/54, 46%) or efficient (23/54, 42%). Issues related to lack of professional autonomy, lack of organisation in the hierarchical command chain, lack of professional and social recognition, disorganisation in task distribution and interpersonal conflicts with superiors were identified as the main sources of stress. The most frequently used coping resources were social support, stress monitoring, physical health and structuring. Perceived efficacy in stress resolution was inversely related to perceived level of occupational stress (r = −0.61, P < 0.01). Significant correlations were found between several coping resources and the perceived level of stress and efficacy in stress resolution. Associations between problem solving, cognitive restructuring and stress monitoring and both low levels of perceived stress and high levels of perceived efficacy were particularly strong. Implications for practice - The importance of identifying stressors and coping resources related to physiotherapists’ occupational stress, and the need for the development of specific training programmes to cope with stress are supported.

Drilling tool geometry evaluation for reinforced composite laminates

In this work, a comparative study on different drill point geometries and feed rate for composite laminates drilling is presented. For this goal, thrust force monitoring during drilling, hole wall roughness measurement and delamination extension assessment after drilling is accomplished. Delamination is evaluated using enhanced radiography combined with a dedicated computational platform that integrates algorithms of image processing and analysis. An experimental procedure was planned and consequences were evaluated. Results show that a cautious combination of the factors involved, like drill tip geometry or feed rate, can promote the reduction of delamination damage.

Analyzing objects in images for estimating the delamination influence on load carrying capacity of composite laminates

The use of fiber reinforced plastics has increased in the last decades due to their unique properties. Advantages of their use are related with low weight, high strength and stiffness. Drilling of composite plates can be carried out in conventional machinery with some adaptations. However, the presence of typical defects like delamination can affect mechanical properties of produced parts. In this paper delamination influence in bearing stress of drilled hybrid carbon+glass/epoxy quasi-isotropic plates is studied by using image processing and analysis techniques. Results from bearing test show that damage minimization is an important mean to improve mechanical properties of the joint area of the plate. The appropriateness of the image processing and analysis techniques used in the measurement of the damaged area is demonstrated.

Increasing the wear resistance of molds for injection of glass fiber reinforced plastics

Abrasion by glass fibers during injection molding of fiber reinforced plastics raises new challenges to the wear performance of the molds. In the last few decades, a large number of PVD and CVD coatings have been developed with the aim of minimizing abrasion problems. In this work, two different coatings were tested in order to increase the wear resistance of the surface of a mold used for glass fiber reinforced plastics: TiAlSiN and CrN/CrCN/DLC. TiAlSiN was deposited as a graded monolayer coating while CrN/CrCN/DLC was a nanostructured coating consisting of three distinct layers. Both coatings were produced by PVD unbalanced magnetron sputtering and were characterized using scanning electron microscopy (SEM) provided with energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), micro hardness (MH) and scratch test analysis. Coating morphology, thickness, roughness, chemical composition and structure, hardness and adhesion to the substrate were investigated. Wear resistance was characterized through industrial tests with coated samples and an uncoated reference sample inserted in a feed channel of a plastic injection mold working with 30 wt.% glass fiber reinforced polypropylene. Results after 45,000 injection cycles indicate that the wear resistance of the mold was increased by a factor of 25 and 58, by the TiAlSiN and CrN/CrCN/DLC coatings, respectively, over the uncoated mold steel.

Mechanical behavior and localized failure modes in a porous basalt from the Azores

Basaltic rocks are the main component of the oceanic upper crust, thus of potential interest for water and geothermal resources, storage of CO2 and volcanic edifice stability. In this work, we investigated experimentally the mechanical behavior and the failure modes of a porous basalt, with an initial connected porosity of 18%. Results were acquired under triaxial compression experiments at confining pressure in the range of 25-200 MPa on water saturated samples. In addition, a purely hydrostatic test was also performed to reach the pore collapse critical pressure P*. During hydrostatic loading, our results show that the permeability is highly pressure dependent, which suggests that the permeability is mainly controlled by pre-existing cracks. When the sample is deformed at pressure higher than the pore collapse pressure P*, some very small dilatancy develops due to microcracking, and an increase in permeability is observed. Under triaxial loading, two modes of deformation can be highlighted. At low confining pressure (Pc < 50 MPa), the samples are brittle and shear localization occurs. For confining pressure > 50 MPa, the stress-strain curves are characterized by strain hardening and volumetric compaction. Stress drops are also observed, suggesting that compaction may be localized. The presence of compaction bands is confirmed by our microstructure analysis. In addition, the mechanical data allows us to plot the full yield surface for this porous basalt, which follows an elliptic cap as previously observed in high porosity sandstones and limestones.

Delamination analysis of carbon fibre reinforced laminates: evaluation of a special step drill

Drilling of carbon fibre/epoxy laminates is usually carried out using standard drills. However, it is necessary to adapt the processes and/or tooling as the risk of delamination, or other damages, is high. These problems can affect mechanical properties of produced parts, therefore, lower reliability. In this paper, four different drills – three commercial and a special step (prototype) – are compared in terms of thrust force during drilling and delamination. In order to evaluate damage, enhanced radiography is applied. The resulting images were then computational processed using a previously developed image processing and analysis platform. Results show that the prototype drill had encouraging results in terms of maximum thrust force and delamination reduction. Furthermore, it is possible to state that a correct choice of drill geometry, particularly the use of a pilot hole, a conservative cutting speed – 53 m/min – and a low feed rate – 0.025 mm/rev – can help to prevent delamination.

Tool geometry evaluation for carbon reinforced composite laminates

The use of composite laminates in complex structures has increased significantly. However, there are still some issues when considering their use, mainly related with machining, leading to some difficulties and lack of acceptance. In this work, a methodology to evaluate drill geometry and feed rate based on thrust force and delamination extension is presented.

The influence of geometric factors on the wall shear stress distribution in realistic human coronary arteries

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para a obtenção do grau de Mestre em Engenharia Biomédica. A presente dissertação foi desenvolvida no Erasmus Medical Center em Roterdão, Holanda

Evaluation of tools and cutting conditions on carbon fibre reinforced laminates

The distinctive characteristics of carbon fibre reinforced plastics, like low weight or high specific strength, had broadened their use to new fields. Due to the need of assembly to structures, machining operations like drilling are frequent. In result of composites inhomogeneity, this operation can lead to different damages that reduce mechanical strength of the parts in the connection area. From these damages, delamination is the most severe. A proper choice of tool and cutting parameters can reduce delamination substantially. In this work the results obtained with five different tool geometries are compared. Conclusions show that the choice of an adequate drill can reduce thrust forces, thus delamination damage.

Contributo para o estudo da influência do stress na resposta imunitária à vacina contra a gripe em profissionais de saúde

Resumo: Os profissionais de saúde podem estar expostos a vários factores indutores de stress crónico nomeadamente de natureza profissional destacando-se, entre os seus possíveis efeitos, a diminuição da resposta de anticorpos após administração de vacinas, entre as quais, a vacina contra a gripe. Uma vez que os trabalhadores da saúde estão expostos a factores indutores de stress e, simultaneamente, a agentes biológicos cujos efeitos poderão ser prevenidos pela vacinação, é pertinente estudar a influência do stress na resposta imunitária à vacina contra a gripe em enfermeiros. Constituíram objectivos deste trabalho: (1) estudar a associação entre a presença de stress crónico em enfermeiros hospitalares e a “insuficiente” resposta imunitária à vacina contra a gripe, avaliada um mês após a vacinação (T1); (2) estudar a associação entre a presença de stress crónico em enfermeiros hospitalares e a redução dos títulos de anticorpos dirigidos às hemaglutininas seis meses após a vacinação (T6) e (3) identificar algumas características das unidades de internamento e do trabalho dos participantes que possam estar associadas à presença de stress crónico e estudar a sua possível associação com a resposta imunitária à vacina contra a gripe. Realizou-se um estudo caso-controlo incorporado num estudo de coortes e a amostra em estudo foi constituída por 136 enfermeiros saudáveis (83,8% sexo feminino; média de idades de 33anos) de um hospital universitário. Realizaram-se entrevistas individuais e aplicaram-se as versões portuguesas dos questionários The General Health Questionnaire (GHQ12) e Maslach Burnout Inventory – Human Services Survey (MBI-HSS) para determinação da presença de stress crónico pelo método da triangulação, no início do estudo (T0) e realizou-se a recolha de dados relativos à caracterização de elementos de trabalho nas unidades de internamento. Foi administrada a vacina contra a gripe e determinou-se os títulos de anticorpos dirigidos às hemaglutininas de cada estirpe componentes da vacina contra a gripe utilizada em 2007, antes da vacinação, um mês e seis meses após a vacinação. Não se encontrou associação, ao nível de significância de 5%, entre a presença de stress e a “insuficiente” resposta à vacina contra a gripe, avaliada pela taxa de indivíduos que apresentaram um aumento, ao fim de um mês, inferior a quatro vezes os títulos de anticorpos antes da vacinação. No entanto, encontrou-se uma maior proporção de indivíduos com stress no grupo de participantes em que ocorreu uma diminuição do título de anticorpos dirigidos à hemaglutinina AH1 (ac AH1) em T6, quando comparado com o respectivo grupo controlo. A diferença entre grupos foi estatisticamente significativa, quando se avaliou a presença de stress pelo método da triangulação usando a entrevista (p=0,006), pelo método da triangulação usando o GHQ12 (p=0,045) e ainda usando a combinação dos três critérios (p=0,001). Após análise multivariada, verificou-se que a associação entre a presença de XXVI stress e a redução dos ac AH1 em T6 manteve significado estatístico (respectivamente, p= 0,010, p= 0,042 e p=0,002) e apresentou odds ratio ajustados, em função de cada um dos métodos de avaliação da presença de stress, de 3,643, de 2,733 e de 5,223. A quantidade de trabalho percepcionada como sobrecarga constituiu o factor indutor de stress mais vezes referido (58,8% da amostra e 61,8% dos enfermeiros de unidades de internamento), seguida dos conflitos entre profissionais. O contacto com o sofrimento e a morte de doentes foram identificados em quarto lugar pela amostra, mas em segundo pelos enfermeiros de unidades de internamento. Nesses, verificou-se uma associação positiva entre trabalhar em Serviços onde o número de doentes falecidos foi muito elevado e a presença de stress, medido pelo método da triangulação usando a entrevista (p=0,039), usando o GHQ12 (p=0,019), usando a escala de exaustão emocional do MBI-HSS (p=0,012) e pela combinação dos três métodos (p=0,014). Verificou-se também uma associação positiva entre a presença de stress, identificada pelo método da triangulação usando a escala de exaustão emocional do MBI-HSS, e o trabalho em serviços de internamento onde a percentagem de doentes idosos (p=0,025) e a taxa de letalidade (p=0,036) foram elevadas. Contudo, não se encontrou associação entre a exposição muito frequente ao sofrimento e à morte de doentes e a redução do título de ac AH1 em T6. Possivelmente, a exposição a esse factor indutor de stress, apesar de estar relacionada com a presença de stress nos enfermeiros de serviços de internamento, não foi suficientemente intenso para, por si só, estar associada à redução do título de ac AH1 em T6. A associação encontrada entre a presença de stress crónico e a redução do título de anticorpos AH1 em T6 vem apoiar a resposta à questão de investigação inicialmente colocada de que o stress poderá influenciar negativamente a manutenção dos títulos de anticorpos, mesmo em indivíduos adultos não idosos. Assim, o risco de um enfermeiro com stress apresentar redução do título de anticorpos dirigidos à hemaglutinina da estirpe AH1N1 – A/Solomon Islands/3/2006 ao fim dos seis meses do estudo, foi 3,6, 2,7 ou 5,2 vezes superior ao de um enfermeiro sem stress, consoante o critério de stress ter sido determinado, respectivamente, pelo método da triangulação usando a entrevista, pelo método da triangulação utilizando o GHQ12 ou pela combinação dos três critérios. Summary: Health workers may be exposed to various factors causing chronic stress namely those related directly to their activity, in particular the decrease in the capacity of the response of antibodies after the administration of the vaccines, amongst others the Influenza vaccine. Since health workers are exposed to factors causing stress and at the same time biological agents, whose effects may be prevented through vaccination, it is important to study the influence of stress in the immunity response to the Influenza vaccine on nurses. The aims of this study are: (1) to examine the relation between chronic stress in hospital nurses and the “insufficient” immunity response to the Influenza vaccine, assessed at one month after vaccination (T1); (2) to examine the relation between chronic stress in hospital nurses and the decrease of the hemagglutinin titles of antibodies six months after vaccination (T6); (3) to identify some characteristics of internment units and the work of the participants that may be related to the presence of chronic stress and to study its possible relation with the immunity response to the Influenza vaccine. A control-case study, integrated in a coortes study, was carried out and the sample under analysis consisted of 136 healthy nurses (83,8% female; average age 33 years old) from a university hospital. Several individual interviews were conducted and the portuguese versions of General Health Questionnaire (GHQ12) and Maslach Burnout Inventory – Human Services Survey (MBI-HSS) was applied in order to determine the presence of chronic stress, using the triangulation method at the beginning of the study (T0). Data concerning the particular features of the internment units was collected. The Influenza vaccine was administered and the titles of hemagglutinin antibodies of each strain composing the Influenza vaccine used in 2007, before vaccination, and a month and six months after vaccination, were determined. There was no statistically relevant (5%) relation between stress and the “insufficient” immune response to the Influenza vaccine, according to the rate of individuals that showed, after a month, a level of antibodies concentration lower than four times the level prior to the vaccination. Nevertheless, there was a greater number of individuals with stress in the group of participants in which there was a decrease of the hemagglutinin titles of antibodies AH1 (ac AH1) in T6, when compared to the control group under study. The difference between groups was statistically relevant when assessing the presence of stress by triangulation method using the interview (p=0,006), by triangulation method using the GHQ12 (p=0,045) and by the combination of the three criteria (p=0,001). After multivariate analysis, it was verified that the XXVIII relation between the presence of stress and the reduction of the ac AH1 in T6 was statistically relevant (respectively, p= 0,010, p= 0,042 and p=0,002) and the odds ratio were, according to each of the methods used to assess the presence of stress, 3,643, 2,733 and 5,223. Overwork was the most emphasised stress-causing factor (58,8% of the sample and 61,8% of the nurses working in the Internment Units), followed by conflicts arousing among co-workers. Witnessing the suffering and death of patients was ranked as the fourth cause of stress, but the second by the nurses of the internment units. The former revealed a positive connection between working in the services, where there was a high rate of deaths, and the presence of stress, when assessing the presence of stress by triangulation method using the interview (p=0,039), the GHQ12 (p=0,019), the MBI-HSS emotional exhaustion scale (p=0,012) and by the combination of the three criteria (p=0,014).There was also a connection between the presence of stress, identified by the method of triangulation using the MBI-HSS emotional exhaustion scale, and working in the internment units, where the percentage of elderly people (p=0,025) and the mortality rate (p=0,036) were high. However, there was no connection between frequent exposure to suffering and death in patients and the reduction of ac AH1 titles, in T6. Although one can establish a connection between stress in nurses working in the internment units and the aforementioned stress-causing factor, the exposure to that factor was not, per se, intense enough to reduce the ac AH1 title in T6. The relation found between the presence of chronic stress and the reduction of AH1 antibodies titles in T6, corroborates the hypothesis that stress can negatively influence the title of antibodies, even in non-elderly adults. Thus, and according to the criteria used to define stress, by the triangulation method using the interview, by the triangulation method using the GHQ12 or the combination of the three criteria respectively, the risk of a nurse suffering from stress showing a reduction in the title of hemagglutinin antibodies for the strain AH1N1 – A/Solomon Islands/3/2006 six-month after Influenza vaccine was 3,6, 2,7 or 5,2 times greater than on a nurse suffering from no stress at all. Résumé: Les professionnels de la santé peuvent être exposés à différents facteurs inducteurs de stress chronique de nature professionnelle. On remarque, parmi les effets possibles, une baisse de la réponse des anticorps après l´administration de vaccins, comme en particulier, le vaccin de la grippe. Lorsque les professionnels de la santé ont été exposés à des facteurs inducteurs de stress, et de manière simultanée, à des agents biologiques dont les effets pourront être prévenus par la vaccination, il est pertinent d´étudier l´influence du stress dans la réponse immunitaire au vaccin de la grippe chez les infirmiers. Ils ont constitué des objectifs d´études et de discussion : (1) étudier l´association entre la présence de stress chronique chez les infirmiers, en milieu hospitalier, et la “insuffisant” réponse immunitaire au vaccin de la grippe, vérifiée à un mois après la vaccination (T1); (2) étudier l´association entre la présence de stress chronique chez les infirmiers, en milieu hospitalier, et la réduction de la teneur des anticorps dirigé à la hémaglutinina six mois après la vaccination (T6) (3) identifier certaines caractéristiques des unités d´internement, et étudier les aspects du travail des participants, qui puissent être associée à la présence de stress chronique et étudier sa possible association avec la réponse immunitaire au vaccin de la grippe. Une étude cas-contrôle incorporée dans une étude de groupe a été réalisée et un échantillon, pour étude, a été constitué par 136 infirmiers sains (83,8% de sexe féminin, âge moyen 33 ans) travaillant dans un hôpital universitaire. Des entretiens individuels ont été réalisés et les versions portugaises des questionnaires de General Health Questionnaire (GHQ12) et Maslach Burnout Inventory- Human Service Survey (MBI-HSS) ont été utilisés pour déterminer la présence de stress chronique grâce à la méthode de triangulation, au début de l´étude (T0) et un relevé de données relatives à la caractérisation d´éléments de travail dans les unités d´internement a été fait. Le vaccin de la grippe a été administré et les teneurs en anticorps dirigés aux hémaglutininas de chaque composant du vaccin de la grippe pour 2007 ont été déterminés, avant la vaccination et un mois et six mois après. On n´a pas trouvé d´association, à un niveau significatif de au moins 5%, entre la présence de stress et la “insuffisant” réponse au vaccin de la grippe, évaluée par le taux d´individus qui ont présenté une augmentation, à la fin du mois, inférieur à quatre fois la teneur des anticorps par rapport à avant la vaccination. Cependant , on a trouvé une plus grande proportion d´individus victimes de stress dans le groupe des participants où il y a eu une baisse de la teneur des anticorps dirigé à la hémaglutinina AH1 (ac AH1) en T6, après comparaison avec le respectif groupe de contrôle. La différence entre les groupes a été statistiquement significative lorsqu´on a vérifié la présence de stress grâce à la méthode de triangulation, en utilisant l´entretien (p=0,006), par la méthode de triangulation en utilisant le GHQ12 (p=0,045) et en utilisant aussi la combinaison des trois critères (p=0,001). Après une analyse XXX multivariée, on a vérifié que l´association entre la présence de stress et la réduction des ac AH1 en T6 a conservé un signifié statistique (respectivement, p=0,010, p=0,042 et p=0,002) et a présenté des odds ratio ajustés, en fonction de chacune des méthodes de vérification de la présence de stress de 3,643, de 2,733 et de 5,223. La quantité de travail perçue comme une surcharge constitue le facteur inducteur de stress le plus souvent cité (58,8% de l´échantillon et 61,8% des infirmiers des unités d´internement), suivi par les conflits entre professionnels. Le contact avec la souffrance et la mort des patients a été placé en quatrième position par l´échantillon, mais en deuxième position par les infirmiers des unités d´internement. Dans ces cas, on a vérifié une association évidente entre le fait de travailler dans des services où le nombre de patients décédés a été très élevé et la présence de stress, identifiée par la méthode de triangulation, en utilisant l´entretien (p=0,039), le GHQ12 (p=0,019), l´échelle de fatigue émotionnelle du MBI-HSS (p=0,012) et en utilisant aussi la combinaison des trois critères (p=0,014). On a aussi vérifié une association positive entre la présence de stress, identifiée par la méthode de triangulation, en utilisant l´échelle de fatigue émotionnelle du MBI-HSS et le travail dans des services d´internement où le pourcentage de malade âgés (p=0,025) et le taux de mortalité ont été élevés (p=0,036). Malgré tout, on n´a pas trouvé d´association entre l´exposition très fréquente à la souffrance et à la mort des patients et la réduction de la teneur de ac AH1 en T6. Probablement l´exposition à ce facteur inducteur de stress, bien qu´elle soit liée à la présence de stress chez les infirmiers des services d´internement, n´a pas été suffisamment intense pour, en elle-même, être associée à la réduction de la teneur ac AH1 enT6. L´association trouvée entre la présence de stress chronique et la réduction de la teneur des anticorps AH1 en T6 vient renforcer l´hypothèse que le stress pourra influencer négativement la manutention des teneurs en anticorps même chez les individus adultes jeunes. Donc le risque qu´un infirmier stressé présente une réduction de la teneur en anticorps dirigés à la hémaglutinina de le composant AH1N1-A/Solomon Island/3/2006 à la fin des six mois d´études a été 3,6, 2,7 ou 5,2 fois supérieure à celui d´un infirmier sans stress, après avoir déterminé le critère de stress, respectivement par la méthode de triangulation utilisant l´entretien, par la méthode de triangulation utilisant le GHQ12 ou par la combinaison des trois critères.

New recycling approaches for thermoset polymeric composite wastes – an experimental study on polyester based concrete materials filled with fibre reinforced plastic recyclates

In this study, a new waste management solution for thermoset glass fibre reinforced polymer (GFRP) based products was assessed. Mechanical recycling approach, with reduction of GFRP waste to powdered and fibrous materials was applied, and the prospective added-value of obtained recyclates was experimentally investigated as raw material for polyester based mortars. Different GFRP waste admixed mortar formulations were analyzed varying the content, between 4% up to 12% in weight, of GFRP powder and fibre mix waste. The effect of incorporation of a silane coupling agent was also assessed. Design of experiments and data treatment was accomplished through implementation of full factorial design and analysis of variance ANOVA. Added value of potential recycling solution was assessed by means of flexural and compressive loading capacity of GFRP waste admixed mortars with regard to unmodified polymer mortars. The key findings of this study showed a viable technological option for improving the quality of polyester based mortars and highlight a potential cost-effective waste management solution for thermoset composite materials in the production of sustainable concrete-polymer based products.