A biorefinery approach using Rhododendron residues

The increasing global demand for sustainable materials has accelerated the transition from fossil fuel-based polymers to renewable approaches that harness natural resources. This research focuses on the development of biopolymers from plant biomass, specifically using the invasive Rhododendron ponticum species, to model a sustainable and eco-friendly alternative to traditional polymer production. Biorefining involves the sustainable processing of biomass to produce marketable products and energy, prioritising economic, environmental, and sustainability considerations. These facilities can take the form of individual plants or integrated clusters, optimising resource use and sustainability through collaborative processes. Our objective is to utilise Rhododendron waste materials as a renewable resource within this biorefinery framework, aiming to investigate the viability of production of innovative products that stimulate extraction processes and add value to otherwise underutilised biomass. By harnessing these residues, we contribute to the development of sustainable value chains that align with the principles of the bioeconomy. R. ponticum, a shrub with leathery leaves, was introduced to Ireland in the 18th century from Asia for ornamental purposes. However, it has since spread rapidly and become a major threat to the peatlands in western Ireland. The Ph.D. research centres on the concept of a biorefinery, with a focus on exploring alternative methods for reusing the endemic species Rhododendron in a variety of applications. The main strand of the research is the production of nanofibrillated cellulose (NFC) and microfibrillated cellulose (MFC) from this biomass. For the production of NFC, two chemical processes, bleaching and TEMPO oxidation, were applied, along with two mechanical processes for defibrillation, using a twin-screw extrusion (TSE) and grinding with a super mass colloid (Massuko). The primary focus was on characterising the fibres produced in each process while assessing the impact of varying degrees of cellulose defibrillation through different chemical pre-treatments and mechanical defibrillation methods. The best material was selected for the production of scaffolds using PCL (Polycaprolactone) in a 3D printer. The addition of 1% NFC significantly enhanced the mechanical properties compared to pure PCL. Moreover, NFC exhibits non-toxic characteristics, making these materials particularly promising for biomedical applications.
For the production of MFC, the same chemical treatments were applied (bleaching and TEMPO), with the addition of the cryocrush process before the TSE. Following this, MFC with the highest TSE steps was used for mycelium growth. These MFC-fungus composites offer promise for sustainable packaging and biodegradable plastics.
Other potential products in the biorefinery model proposed in this work include the use of extracts from leaves and wood for the production of films utilising polyvinyl alcohol (PVA) for wound healing, as well as the pyrolysis of wood for the production of biochar with a high surface area. Rhododendron extract from leaves and wood was found to contain numerous potentially valuable antioxidant compounds. Cell tests and wound healing assays confirmed the healing capacity of these extracts. In the biorefinery model, biochar is a valuable by-product of the biomass conversion process into a variety of renewable products. Here, the goal of this research was to investigate the effects of thermochemical treatments on activated biochar production and evaluate the efficacy of activated biochar in removing acetylsalicylic acid (aspirin) from water. Biochar was produced through biomass pyrolysis and was used for aspirin removal from water. In summary, the Ph.D. emphasises the various opportunities associated with this plant, given its abundant availability and the need to manage this invasive species in Ireland. By exploring innovative approaches for the reuse of the endemic species Rhododendron, this research addresses the question of finding alternative methods for its utilisation, ultimately contributing to sustainable practices and enhancing local ecosystems.