Exploring spinifex biomass for renewable materials building blocks

Abstract

Triodia pungens is one of the 69 species of an Australian native arid grass spinifex which covers approximately 27 % (2.1 million km 2 ) of the Australian landmass. The use of fibrous and resinous components of spinifex has been well documented in traditional indigenous Australian culture for thousands of years. In this thesis the utility of both the cellulosic and resinous components of this abundant biomass for modern applications, and a potential economy for ourAboriginal collaborators, were explored. One part of this study was focused on the optimisation of a resin extraction process using solvent, and the subsequent evaluation, via a field trial, of the potential use and efficacy of the resin as a termiticide. Termiticidal performance was evaluated by re-dissolving the extracted resin in acetone and coating on pine timber blocks. The resin-coated and control blocks (uncoated timber) were then exposed to a colony of Mastotermes darwiniensis termites, which are the most primitive active and destructive species in subterranean areas, at a trial site in northeast Australia, for six months. The results clearly showed that spinifex resin effectively protected the timber from termite attack, while the uncoated control samples were extensively damaged. By demonstrating an enhanced termite resistance, it is shown that plant resins that are produced by arid/semi-arid grasses could be potentially used as treatments to prevent termite attack.In the other part of this study it has been demonstrated that very small diameter and unprecedentedly high aspect ratio cellulose nanofibrils (NFC) can be readily isolated from spinifex biomass using unrivalled mild pulping coupled with minimal mechanical energy by any of three methods; high pressure homogenizer, ultrasonication, and milling. After washing, delignification and bleaching steps, the mechanical defibrillation of fibres was optimized by varying the specific processing conditions of each of these three mechanical treatment methods. Cellulose nanofibres with an extremely low average diameter (below 10 nm) and high aspect ratio (~500) were produced, even after applying very low energy processing. Similarly, acid hydrolysis at lower temperatures and acid concentrations with respect to the published contemporary protocols yielded high aspect ratio cellulose nanocrystals (CNC), for which the average lengths were found to be unaffected by further ultrasonic treatments. We hypothesize that the chemical and morphological origins for this surprisingly low energy input requirement for isolating high aspect ratio nanofibers from Triodia pungens is directly related to the plant's unique morphology and composition, which contains unusually high amounts of hemicellulose. It is also hypothesised that these unique traits are a result of this species' evolution, which has been heavily influenced by an extreme semi-arid climate.Polyurethane and spinifex CNC nanocomposites were also prepared via twin-screw reactive extrusion and solvent casting. Twin-screw reactive extrusion offer...