Hydrolytic ageing of syntactic foams for thermal insulation in deep water: degradation mechanisms and water uptake model

This paper focuses on a novel syntactic foam formulation based on a model diepoxy-diamine matrix with a controlled architecture, discusses the factors governing the long-term performance of these materials and gives a predictive model to assist in the design of efficient and safe insulating systems.Hygrothermal ageing in deionized water at 20°C, 60°C, 100°C and 120°C over 18 months (with no additional pressure) is followed by both gravimetric and impedance measurements. This original protocol provides the evolution with time of both mass gain and intrinsic material conductivity. Attention is paid to the degradation phenomenon observed after the matrix has reached saturation and the corresponding increase of both mass gain and conductivity. The latter suggests the occurrence of ionic extraction from the microsphere glass undergoing water leaching.A model of mass gain is proposed to explain the gravimetric data and predict the long-term mass gain that governs the mechanical and thermal performances. The temperature dependence of fitting parameters follows an Arrhenius law and activation energies calculated support the scheme of glass corrosion by water during hygrothermal ageing, with respect to the literature.