Freeze-Dried Wheat Gluten-Based Foams

Sammanfattning: This thesis presents wheat gluten foams as an alternative to the available commercialfoams. Polymeric foams, like all plastics, are mostly made from petroleum, and this isaffecting the environment negatively with the emission of greenhouse gases and generation oflandfills. During the past decades, there has been a drive to replace petroleum-based plasticswith alternatives made from renewable resources. Wheat gluten has interesting and promisingproperties as an alternative resource. As a large by-product in Europe from the biofuelindustry it is largely available and at a low price.In order to develop an insulation material based on this renewable resource, foammaterials have been made by freeze-drying frozen mixtures consisting of either acommercially available wheat gluten powder or various protein rich fractions of gliadins orglutenins extracted from the commercial powder. Some of the foams were further modifiedwith the addition of glycerol as plasticizer or bacterial cellulose as a reinforcing fiber. Theresulting cellular structure was shown to depend on the initial gluten concentration, and thefraction and type of additive used. The wheat gluten foam materials contained mainly an openpore structure with average pore diameters ranging from 20 to 70 μm.The addition of glycerol and/or bacterial cellulose changed the foam structure, theprotein structure and the mechanical properties. The addition of 20 wt.% glycerol wassufficient to plasticize the foam and to achieve a low modulus and a high strain recovery, butwith glycerol the average pores size increased due to the difference in freezing conditions.The bacterial cellulose gave a small and insignificant increase in stiffness and also a moreuniform cell structure. In addition, the glycerol-containing samples had a more polymerizedprotein structure, whereas the foams containing fibers had a lower degree of polymerization.Foams made from a glutenin rich fraction were much stiffer and stronger than gliadinrich foams. The glutenin rich foams had a higher degree of polymerization than the latter,foam the relatively mild heat treatment.The gluten foams were promising as insulation materials. The thermal conductivityvalues were 0.04-0.05 (W/m⋅°C), and were close to that of commercially available closed cellpolystyrene and polyurethane foams, that both have values at ca. 0.03 (W/m⋅°C).The wheat gluten foams showed also promising combustion properties with longignition times, no material dripping and a large content of residual char. The glycerolcontainingfoam however, exhibited a more rigorous bubbling and a larger flame.