Publicações

This set of articles describes the behaviour of formulated polyvinylchorides in various conditions of photoageing, including exposition in artificial and in natural conditions. In this article, the modification of the infrared and UVvisible spectra of PVC films irradiated with a xenon light are reported

One major problem encountered with polymeric materials is their sensitivity to outdoors weathering. Exposure to outdoors conditions leads to a degradation of the use properties of the material. This set of articles describes a comparison of the behavior of several stabilised polyvinylchlorides exposed to various conditions of ageing including light and temperature. The first article focusses on the effect of thermal ageing on the infrared and UV-visible characteristics of the selected samples.

Neste artigo apresenta-se resultados de um estudo experimental, ainda em curso, sobre a durabilidade em ambientes marítimos de perfis pultrudidos de GFRP, constituídos por resinas de poliéster insaturado e viniléster reforçadas com fibra de vidro. Diversos provetes foram submetidos a imersão durante 12 meses em (i) água desionizada e (ii) água salgada, a diferentes temperaturas (20 ºC, 40 ºC e 60 ºC), e a (iii) nevoeiro salino durante 2000 horas, após o que as suas propriedades físicas, químicas, mecânicas e estéticas foram avaliadas.

To assess the quality of polyethylene pipes compounded with recycled polyethylene for applications in drainage and sewerage, several analysis techniques were applied, some of them being not previewed in the performance characteristics standards. The measured physical, chemical and mechanical properties of raw-materials, intermediate compounds and final products, were used to evaluate the performance of the different formulations, allowing to an understanding of the thermo-mechanical effects of the several transformation processes. The analysis of the results will help us to optimising the manufacture parameters and to check the formulations, in view of its upgrading. The effect of a nanoclay was also studied. INTRODUCTION

Neste artigo é abordado o tema da utilização de materiais compósitos de matriz polimérica reforçados com fibras na reabilitação de estruturas. Procuraram-se sistematizar os motivos que têm conduzido ao sucesso da aplicação desta família de materiais, designadamente por darem aos projectistas a possibilidade de construir soluções “por medida” que se adeqúem aos requisitos específicos de uma dada aplicação.

Neste artigo apresentam-se resultados da apreciação da resistência a variações térmicas de dois tipos de perfis estruturais fabricados por pultrusão e reforçados com fibras de vidro, que diferem na natureza da sua matriz: poliéster insaturado e viniléster. Este trabalho encontra-se inserido num projecto de investigação em curso, cujo objectivo é analisar a durabilidade deste tipo de produtos, utilizados em aplicações estruturais na Engenharia Civil.

In most of polymer ageing studies conducted at laboratory, there is a trend to underestimate some of the parameters involved in natural exposure, leading to poor simulation results and low reliability of the real world phenomena. Moreover, the nature of polymer and its formulation should be taken into account due to possible synergies and antagonisms between environment and polymer additives. Among the underestimated parameters, we can stress the role of ambient humidity and inorganic fillers. These additives are usually considered to be inert regarding the degradation induced by radiation. In this work, four different PVC formulations, designed for outdoor applications, in the form of calendered films were submitted to artificial accelerated ageing under different radiation sources, without and with spray of water, and to natural exposure. The influence of the different photo-oxidation conditions was evaluated by means of Xray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIRS). The photo-oxidation of PVC can be studied by FTIR measurements following the formation of oxidation products of carbonyl type, due to radical attack to the double bonds in the molecular structure of PVC, enhanced by radiation and temperature. Results have shown that relative rates of PVC degradation reactions are different under different photo-oxidative conditions. XPS results show that, in technical PVC formulations, the fraction of chloride ion trapped in the inorganic filler is a better parameter to measure the PVC degradation (measured by the yellowing index variation) than the amount of total remaining (or lost) chlorine in the surface. When the ageing method includes water jets, the top superficial layer made from the inorganic filler and the organic products from the PVC degradation is removed and leaves behind a much more homogeneous layer which is more resistant towards ageing than the “as processed” one that contains defects introduced by the calendering process. XPS also makes clear that zinc-calcium additive is a better thermal stabilizer than the dibutyltinmaleate and the presence of the tinuvin P retards the PVC degradation. The best simulation of the natural weathering of such PVC materials in laboratory conditions needs to consider, besides the light, the intervention of water jets and/or humidity as well as the existence of light and dark periods.

In most of polymer ageing studies conducted at laboratory, there is a trend to subestimate some of the parameters involved in natural exposure, leading to a poor simulation results and low reliability of the real world phenomena. Moreover the nature of polymer and its formulation should be taken into account due to possible synergies and antagonisms between environment and polymer additives. Among the subestimated parameters, we can stress the role of ambient humidity and inorganic fillers. These last additives are usually considered to be inert regarding the degradation induced by radiation. In this work we used X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIRS) to evaluate the influence of the different photo-oxidation conditions. Different PVC formulations, designed for outdoor applications, in the form of calendered films, were submitted to artificial accelerated ageing under different radiation sources, with and without water spray, and also to natural exposure in Lisbon. Usually, PVC degradation is evaluated by dosing evolved chlorine under the form of HCl or Cl2. XPS results show that, in technical PVC formulations, the fraction of chloride ions trapped in the inorganic filler is a better parameter to measure the PVC degradation (measured by the yellowing index variation) than the total lost (or remaining) chlorine in the surface. FTIRS measurements were used to follow the formation of oxidation products of the carbonyl type, which are due to radical attack on the double bonds in the molecular structure of PVC. Results show that relative rates of PVC degradation reactions are different under different photo-oxidative conditions. Combination of XPS and FTIRS analyses have shown that the best simulations of the natural weathering of such PVC materials under laboratory conditions needs to consider, besides the light, the intervention of water jets and/or humidity as well as the existence of light and dark periods.

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An experimental program was undertaken to evaluate the durability of three commercial epoxy adhesives used for bonding repairing and strengthening Carbon Fibre Reinforced Plastics (CFRP) to concrete structures. The changes in physical and mechanical properties after exposure for up to 18 months under different environmental conditions are reported and discussed.

No presente relatório apresentam-se os dados meteorológicos do ano de 2007, recolhidos na estação meteorológica existente no Núcleo de Materiais Orgânicos do Departamento de Materiais do LNEC, em Lisboa.

Os resultados experimentais, obtidos através da medição de propriedades dos materiais e produtos, requerem tratamento específico e adequado, de forma a garantir a sua qualidade. É por isso muitas vezes necessário recorrer a métodos estatísticos para fazer a análise do tipo de distribuição dos resultados, proceder à deteção de valores suspeitos num conjunto de observações e à eventual rejeição de resultados anómalos. Este tipo de tratamento estatístico é principalmente adequado a ensaios de intercomparação, quer do foro metrológico (comparação de valores de padrões ou materiais de referência, mediante medição efetuada por operadores de diferentes laboratórios metrológicos, com incerteza variável), quer do âmbito dos laboratórios de ensaio. Os ensaios de Comparação Interlaboratorial realizados por laboratórios de ensaio, constituem uma ferramenta de garantia da Qualidade e são utilizados para a validação de métodos de ensaio (incerteza e robustez) e como um meio para a determinação das características de desempenho dos laboratórios, nomeadamente da reprodutibilidade e da repetibilidade. Nesta publicação faz-se uma descrição dos vários parâmetros que devem ser determinados em ensaios interlaboratoriais do tipo “Intercomparações com valor de consenso” e respetivos métodos de cálculo. A estatística aqui apresentada pode, numa boa parte dos casos, ser também aplicada à análise de resultados de medições experimentais correntes.

The main purpose of this Paper is to present a state of the art about weathering and polymer degradation. This review was presented during a training course promoted by the 5th European Weathering Symposium EWS (XXVIIth Colloquium of Danubian Countries on Natural and Artificial Ageing of Polymers), which was held in Lisbon on September 21 - 23, 2011, organised on behalf of CEEES (Confederation of European Environmental Engineering Societies) by the German Management Society for Environmental Engineering GUS (Gesellschaft für Umweltsimulation e.V.) and supported by SOPSAR (Sociedade Portuguesa de Simulação Ambiental e de Avaliação de Riscos), APIP (Associação Portuguesa da Indústria de Plásticos) and LNEC (Laboratório Nacional de Engenharia Civil). The main topics of this review are the weathering of polymers and composites, the determination, simulation and effects of relevant climatic quantities, innovative polymer additives, new test procedures and devices, instrumental methods of analysis to evaluate polymer degradation, recent developments in polymeric materials and composites designed for outdoor applications and methods for service-life prediction.

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