Wheat-gluten silica foams

Abstract

Consulta en la Biblioteca ETSI Industriales (9178)

[EN] This work presents an alternative to polymer insulators by performing hybrid wheat gluten-silica foams. Nowadays, most of commercial insulators are made from petroleum-based polymers and blowing agents that contribute to the greenhouse effect. Wheat gluten (WG) is a potential and interesting choice to achieve materials with promising insulation properties and environmental agreement. A second inorganic phase, silica, has been added to the gluten foam structure in order to achieve this insulation material with additional stability and lifetimes under moisture conditions. Foams have been made by freeze-drying, changing the conditions (temperature, concentration and kind of precursor, mainly) of the process for obtaining different samples. Two kind of precursors have been used to get silica by sol-gel technique: tetraethoxysilane (TEOS) and (3-Mercaptopropyl)trimethoxysilane (MTMOS). A re-heating step on the samples is essential to get these not dissolving water foams. Densities of the foams are strongly affected by gluten/silica concentration and temperature: 120 kg/m3 to 195 kg/m3 (139 kg/m3 for only WG foams). MTMOS foams with a re-heating step have higher densities, with large open pores with long ¿sheets¿ cell walls. However, both precursor foams have similar cell structure for the same conditions. Furthermore, stiffness has upper values with upper concentrations and upper process temperature, although WG-Silica foams have not excellent mechanical properties with low E-modulus values in the re-heated samples. WG-Silica foams have outstanding thermal and combustion properties and an excellent behavior when they are burnt, being classified as V-0 materials according to the standards of the UL 94 test. Thermal conductivity values were between 1 and 1.3 J/(g ºC), which are closed to other commercial closed cell insulation materials as polystyrene and polyurethane (ca. 1.4 J/(g ºC)).