Preparation of films and nonwoven composites from fungal microfibers grown in bread waste

Sammanfattning: Unsold bread makes up a signification fraction of waste occurring in Swedish supermarkets. This thesis seeks to address the problem of food waste, by cultivating filamentous fungi on bread waste and producing chitinous films and nonwovens from them. Rhizopus delemar was cultivated on bread waste in liquid-state fermentation in order to obtain mycelia biomass. The biomass was processed by alkali or protease treatments to disrupt the fungal cells and remove proteins and fats. Afterwards it was subjected to a bleaching treatment to remove lignin fractions of bread residues. The treated biomass was then subjected to a grinding treatment for a homogeneous dispersion of mycelial fibers, where the dispersion was confirmed by microscopic images. The chemically and mechanically processed biomass was used for the preparation of films and nonwoven composites by employing a wet-laid papermaking process. The films exhibited plastic-like features, due to their brittleness and their smooth upper surface. Films and nonwoven composites were characterized on their tensile properties, surface water contact angle and their surface morphology by scanning electron microscopy. Treating fungal biomass by alkali and then bleaching resulted in films with atensile modulus of 3.38 GPa and an ultimate tensile strength of 71.50 MPa. These are the highest reported tensile properties for mycelia derived films to date. Water contact angle measurements confirmed a hydrophobic quality of mycelial films. Scanning electron microscopy showed a very dense and even surface without an obvious fibrous morphology. Fungal biomass and viscose fibers together form a rigid nonwoven composite, in which fungal biomass takes over the role of a natural eco-friendly binding matrix. Flexural rigidity measurements were out of bounds and need to be confirmed by future studies. Additionally, a second strain of fungi, Fusarium venenatum, was cultivated on bread particles in water suspension in order to determine optimum growth conditions for future scale-up investigations.