Materials and processes pitches

July 6th, 2023

Hydrothermal Liquefaction of Plastic-Lignin Binary Mixtures [pdf not available for download] – Chye Yi Leow (The University of Adeliade)

Hydrothermal liquefaction (HTL) is a unique process that exploits the properties of water near its critical point to break-down macromolecular bonds to form intermediate complexes and products. This presents a strong potential for HTL to be employed as an generic recycling technology for contaminated plastic wastes. In this study batch HTL investigations were undertaken at a scale, utilising plastic-lignin mixtures in a water medium at a reaction temperature of 350°C. The plastics evaluated were polyethylene, polystyrene, and polyethylene terephthalate. The HTL products were separated then analysed and quantified using GC-MS and thermogravimetric analysis. Preliminary findings indicate significant variations in susceptibility to decomposition via HTL for the range of plastics, with the catalytic effect of lignin affecting the extent of decomposition. By employing GC-MS, the characterisation of the products was achieved providing insight of the HTL of plastic-lignin binary mixtures.

Plastic Waste and its potential role in the future of green energy [pdf] – Laila Halim, Matthew Hill and Leonie van’t Hag (Monash University and CSIRO Applied Porous Materials Team)

Plastic pollution represents one of the biggest man-made challenges of our time. Advanced ‘plastic-to-plastic’ recycling techniques are highly beneficial solutions; however, a downside is that these methods can only be performed a few times before properties become undesirable. What if we established an improved circular economy and recycled into products with significantly longer lifetimes? And what if this fit into the picture of green energy: another colossal challenge facing humanity? Namely, plastic waste can be depolymerised into oils that could be employed as liquid organic hydrogen carriers – compounds that can be reused to sustainably transport hydrogen. Depolymerisation products could also be utilised to create separators in next generation batteries, or to form key components in solar panels. The applied porous materials team is working towards the development of membranes to separate out useful plastic breakdown products which could then form these exciting opportunities within the green energy sector.

Bio recycling – a promising waste innovation [pdf] – Chris Rinke (The University of Queensland)

Plastic recycling rates remain low in Australia, mainly due to a lack of know-how to convert plastic waste into valuable end products. Our research aims to change the status quo and to provide experimentally verified, well-characterised, and efficient plastic degrading enzymes. We use advanced microbial genomics, molecular biology, and metabolic engineering workflows to discover, characterise, and optimise microbial proteins for plastic depolymerisation. The resulting enzymes will be applied to break down plastics into their building blocks, followed by the production of new plastic products, equal in quality to fossil-fuel derived virgin plastics. Alternatively, this biorecycling approach can be combined with microbial biosynthesis of high-value chemicals, such as bioplastics, to shift towards natural polymers. Overall, enzyme based biorecycling will help to valorise plastic waste and to transform circular economy principles into practice.

Investigating the Feasibility of Recycled Polyethylene Terephthalate Glycol-modified as a Viable Printing Material for 3D Printing [pdf not available for download] – Jojibabu Panta (Western Sydney University)

This research presents an investigation on the feasibility of recycled polyethylene terephthalate glycol-modified (rPETG) using 3D printing for applications. The study focuses on the effects of processing parameters on mechanical properties of rPETG printed parts using Fused particle fabrication (FPF) 3D printing technology. The mechanical properties of FPF printed parts are evaluated using tensile tests according to ASTM D638 standard. The effects of the main 3D printing parameters such as layer thickness, infill density and number of contours on the mechanical properties of printed parts are studied. The morphology of the printed layers and their interlayer bonding of printed parts is also evaluated using scanning electron microscopy (SEM). Fourier transformation infrared (FTIR) spectroscopy is used to analyse the chemical structure of the printed parts. The results indicate that rPETG is a feasible material for 3D printing and that the mechanical properties of printed parts can be improved by optimising the processing parameters. The FTIR analysis confirms the presence of characteristic peaks for PET in the printed parts, suggesting that rPETG is a viable material for 3D printing. The study demonstrates the potential of rPETG as a sustainable alternative to virgin materials and provides insights into the optimal processing conditions for achieving high-quality 3D printed rPETG parts.

Fully Bio-based & compostable coffee thermosets Brett Pollard (Australian National University)

Spent coffee grounds are a massively underutilised waste product from both an industrial and commercial standpoint. We have employed spent coffee grounds at a practical scale for the preparation of a polymeric system with real-world applications. We report our development of a novel and entirely green thermoset using sustainably sourced chia seed oil (selected for its high iodine value) which underwent epoxidation before cross-linking through catalyst- and solvent-free esterification with kelp-derived alginic acid at mild reaction temperatures (90 – 120 °C). The developed material showed reprocessability owing to the molecular rearrangements produced by thermally activated, catalyst free transesterification reaction of β-hydroxyester groups. Further, the composite is completely composted under backyard conditions within 3-4 months, providing a sustainable end-of-life strategy. The resultant suite of materials have potential industrial applications, and, to demonstrate this, several functional prototypes have been developed.

Are all bioplastics biodegradable in the sea? [pdf] – Tracey Read (The University of Queensland)

More than 10 Mt of non-degradable commodity plastic leaks into seas and waterways each year. To combat this, there is an increased demand for bioplastic to replace problematic products. But not all bioplastics are equal, and judiciousness in material choices in circular economy planning is required. To understand the complex behaviour of bioplastics in waterways, 3 commonly known bioplastics (polyhydroxyalkanoate (PHA), polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT)) were placed in four representative aquatic environments in Moreton Bay, Brisbane, over an 18-month field trial. The effects of processing (cast/injection moulded/extruded), as well as additives, product thickness, and surface versus benthic exposure, are being assessed, through exhaustive testing (not just mass loss). Preliminary results show that PHA – a natural polyester produced by bacteria – biodegrades faster than PBAT – a fossil fuel-based bioplastic – and that PLA – derived from corn starch or sugar cane – is showing very limited mass loss.