Aerogels synthesised from Canola seed meal protein: processing-structure-property relationships

Novel bioaerogels produced via the gelation of protein extracts from canola seed meal (CSM) are described for the first time, adding to the scant collection of aerogels that are derived from plant-based biotechnology. Aerogels are incredibly valuable and versatile advanced materials with unique uses in aerospace, construction, laboratory science, medicine, pharmaceuticals, environmental clean-up, high-energy physics, sporting equipment, and clothing. Bioaerogels are modernising this field by addressing questions of sustainability and eco-friendliness and further broadening application potential in industries such as food, medicine, and biosciences. Proteins are one of the least researched precursor materials for bioaerogel production, yet they are often untapped sources of biomass and can provide unique biochemical attributes. Canola seed meal protein is a lower-value co-product of the food industry that can be upcycled for materials production and possesses chemistry amenable to aerogel manufacture. The central aim of this thesis was to use canola protein as a precursor polymer for developing aerogels. The resulting novel protein aerogels had their morphologies and properties characterised for comparison with other bioaerogels. Biochemical analyses examined whether the canola protein possesses bioactivity for unique application potential and permitted an understanding of the chemistry responsible for gelation. Finally, elucidating the relationship between processing parameters, aerogel morphologies, and aerogel properties revealed the tailorability of these aerogels to specific target applications. The CSM protein aerogels were successfully synthesised by manipulating aqueous chemical parameters of the protein solution to form gels, and subsequently drying the gels using freeze drying or supercritical carbon dioxide drying. Gelation success and gel properties were dependent in the first instance on protein concentration and solution pH. Substantial gel viscosities (up to 80,000 mPa.s) were achieved when CSM protein gels (10 wt%) were manipulated to an optimum pH (8.0 ± 0.2) and/or strengthened with heating (to 95 °C), CaCl2 (20 mmol/L) or fibrous biomolecules (chitin and collagen). CaCl2 and pH limits proved essential tools for the development of supercritically dried aerogels, while freeze dried gels were possible from a broader range of CSM protein solutions. The CSM protein aerogels were comprised of a particulate-based gel network formed after denatured canola proteins were driven to gelation by the formation of hydrophobic and electrostatic interactions. The resulting freeze dried gels (or cryogels) demonstrated an average density of 0.13 g/cm3 and competitive density-specific mechanical properties (specific compressive strengths up to 4.5 kPa/(kg/m3), specific compressive moduli up to 0.15 MPa/(kg/m3)). Supercritically dried CSM protein aerogels experienced a slight increase in density (0.2 g/cm3) with a corresponding shift in pore size distribution that permitted a mesoporous (Barrett-Joyner-Hallett) pore volume of 0.5 cm3/g and a Brunauer-Emmett-Teller specific surface area of 113 m2/g. Gelation of canola protein extracts using pH, CaCl2, and heating has shown how these bioaerogels are manufacturable and tailorable using environmentally friendly chemical techniques. Thus, ensuring the final aerogel products are likely environmentally safe, biocompatible, and potentially bioactive. Tailorable pore sizes and gel morphologies were identified after variations to protein concentration, solution pH, and drying methods. Variations to morphological features consequently influenced aerogel properties such as strength-to-weight ratios and specific surface areas. Owing to fundamental structural differences, supercritically dried and freeze dried gels (‘aerogels’ and ‘cryogels’, respectively) demonstrated distinct property differences, therefore possessing different application potentials. Additionally, unique biochemical potential, optical features, and controllable degradation rates suggest this novel system of bioaerogels has potential uses in food, cosmetic, and biopharmaceutical applications