Polymer matrix composites represent an interesting alternative for equipment design and structural applications. The attractive properties of thermosetting composite materials reinforced with glass fibres call the attention of industrial sectors according to competitive price, excellent mechanical and specific properties, high corrosion resistance behaviour and reduced maintenance.

Nowadays, these materials are being used in important sectors like aerospace, air, terrestrial and naval transport; leisure and sport. Civil engineering has shown a growing interest for this type of materials, for structures, restoration and as concrete reinforcement. In chemical industry we can find these materials in pipes, storage tanks, etc., which are in contact to chemical environments for long times. For these reasons, service behaviour, material durability and determination of degradation mechanisms are the main objectives of the present research.

In this thesis, orthophthalic polyester and vinylester of bisphenol A resins reinforced with three different fabrics of E-glass fibre were studied. The composites were obtained by means of hand-lay up process. Four chemical environments, water, sodium chloride, sodium hydroxide and sodium hypochlorite were experimented in order to study the degradation effects for long immersion times. This permits us to study the materials chemical resistance under service conditions and times, avoiding accelerated experiments with synergetic effects.

Although the evaluation of mechanical properties of these materials is one of the most important aspects due to their numerous applications, composite chemical resistance becomes a critical item in applications in contact to environments with different chemical character for long term periods. Therefore, the degradation behaviour study of these composites was carried out through the mechanical characterisation by means of flexural, tensile, impact and hardness techniques for different immersion times in each environment. Moreover, analysis of water uptake as a function of immersion time, fracture morphological analysis with Scanning Electron Microscopy (SEM) and thermal analysis techniques as MDSC and TGA and degradation surface analysis contribute to understand this behaviour.

The analysis of mechanical results as a function of immersion times, allowed us to find a mechanical behaviour that followed a predictive model according to an exponential decay, with excellent correlation levels. The most severe degradation conditions takes place for immersion in high pH solutions, alkaline environments. Ester groups hydrolysis in resins, leaching of small soluble segments, reinforcement fibre attack and interphase failure are the responsible of sodium hydroxide being the most aggressive environment.