Characterization of the Ageing of Glass Fibre-Reinforced Polymers
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Lasikuitulujitteisten polymeerimateriaalien vanhenemisen karakterisointi
This work was carried out as a part of the research in ageing and corrosion of composite materials at Tampere University of Technology. The subject is of great interest for both academia and industry and collaboration with industrial partners is included in the form of materials and even some testing. The aim of this work is to compile and provide information on the chemistry related to the ageing of glass fibre-reinforced unsaturated polyester, vinyl ester and epoxy matrix composites in aqueous environments and to examine suitable methods of observing these processes. The ageing in the polymer matrix is a combination of physical and chemical phenomena, which are determined by the used resin. Hydrolysis, for example, is a major chemical degradation process for all polyester structures; present both in unsaturated polyester and vinyl ester resins. Physical ageing includes plasticizing of the resin, swelling and removal of unreacted resin, all caused by diffusion of water into the structure. Post-curing is likely if the ageing environment has high temperatures. For glass fibres, these environments cause chemical reactions that lead to corrosion of the glass. The severity depends on the composition and structure of the glass, the latter of which is not fully understood. Based on literature review, possible structures of the glass materials are presented and their expected correlation the corrosion is explained. The ageing at the interphase between fibre reinforcements and the resin matrix, in turn, is a complex phenomenon that has been studied with varying success for several decades. It has been shown that the sizing applied on the glass fibre surface has a significant role in the properties of the interphase, but the scope of this work is not sufficient to analyse the role of sizing in detail. The extent of the ageing phenomena, for various materials representing parts of the composite, were examined with several methods. Weighing of the samples during the ageing procedure and optical microscopy and thermal analysis methods after the ageing were used to examine a vinyl ester resin. Scanning electron microscopy and energy-dispersive X-ray spectroscopy, inductively coupled mass spectrometry and mechanical testing were in turn used to examine the changes in glass fibres. Infrared spectroscopy was also utilized to find changes of in the chemical structure of both the resin matrix and the fibre reinforcements. The loss of properties at the interphase was tested with a recently developed microbond tester, developed at Tampere University of Technology. The results of these tests agree with the phenomena found in literature well, but further need for research is identified in many areas of the ageing behaviour.