Recycling the rigid petrochemical polymers in dashboards, pipes and uPVC window frames remains limited, fragmented and economically challenging. Looking to solve this issue are some innovation-seeking engineers.
For Dr Kala Senathirajah FIEAust CPEng, plastics are legion. When discussing alternatives to conventional plastics, the terminology quickly becomes confusing.
“There’s bioplastics, there’s biodegradable, there’s compostable, there’s biopolymers, there’s bio-derived polymers, there’s bio-based plastics,” she said. “Plastics can mean different things to different people, and I don’t think there’s any clear definition yet.”
Senathirajah, who is Chair of the Engineers Australia College of Environmental Engineering, said her reaction to the prospect of structural bioplastics is one of cautious optimism.
The radical idea is engineering petrochemical polymers into redundancy, designing rigid plastics out of renewable and biodegradable feedstocks while developing enzymes that digest the plastic already in circulation. Before any of that excites an engineer, she wants a word about language, because the ambiguity in those terms is not pedantry.
The categories carry different consequences. According to Senathirajah, some of these materials are genuinely excellent, while others merely defer the problem. A few deepen it, where the additives used to give a material its properties are themselves hazardous, or where a polymer marketed as greener fragments into microplastics earlier than the conventional plastic it replaced.
She warns that no single material should be sold as the ultimate solution. Held against that caution, the engineering that follows reads not as a cure but as a set of uneven, fast-advancing options.
Senathirajah also distinguishes between plastics used primarily for short-lived consumer applications and those embedded in long-life engineered assets. While many packaging and convenience plastics can often tolerate some changes in material performance or design, plastics used in infrastructure, buildings, vehicles and industrial systems are typically specified against stringent safety, durability and performance requirements, making them significantly harder to replace.
A dashboard, a length of PVC pressure pipe or a uPVC window frame is specified against a simultaneous envelope of requirements rather than a single duty.
It has to hold its load-bearing capacity and stiffness, retain dimensional stability across its service temperature range, tolerate UV exposure and remain manufacturable at volume. A petrochemical grade arrives with decades of design data against every one of those axes, and a bio-based candidate doesn’t.
“Replacing these more structural plastics can’t just be a material swap,” Senathirajah said. “Because it’s embedded into systems engineering. Some convenience applications may be redesigned, reduced or replaced through changes in product design and consumer behaviour, whereas infrastructure materials must continue to meet strict engineering specifications throughout their service life.”
What that looks like in practice sits alongside a South Australian power line, in a post-and-rail fence that appears entirely unremarkable. What makes it worth a second look is what it’s made from; half recycled timber, half high-density polyethylene from a kerbside recycling bin, with no metal fixings to risk arcing on the high-voltage line. It’s made by APR Composites, an Adelaide manufacturer, and it points to a change that runs deeper than a single product.
For decades the Australian conversation about plastic has centred on the soft, visible, single-use kind, which has left the harder half of the problem almost untouched.
Five years on from the 2021 National Plastics Plan, around 84 per cent of Australia’s plastic still ends up in landfill, and the figure for plastic packaging recycling sits at roughly 18-20 per cent against a 70 per cent target. Those numbers describe the plastics we can see, while the rigid and structural materials built into our cars, our homes and our infrastructure barely feature.
Simon Modra, Research Lead at APR Composites and a research contact at the University of South Australia, frames the standards barrier bluntly.
“The first to write the standard wins,” he said, pointing to AS/NZS 4766, the polyethylene standard for rotational moulding, which requires an impact test at minus 40 degrees, a benchmark that suits a tank bound for Norway, but tests his material against a cold Australia’s climate will never deliver.
He doesn’t dismiss the standards wholesale, since the benchmarks for an Australian house build, written around pine timber grades, strike him as a fair target. Working in an unconventional material still guarantees friction, which he reframes as the point.
“If it wasn’t a challenge, it would be too easy, and therefore we’d have a market that was already saturated.”
The more radical response is not to source a greener drop-in but to design the polymer from the backbone outward.
Senathirajah frames it as moving past like-for-like replacement towards specifying the architecture itself – the backbone chemistry and molecular weight distribution, tuned so the resin hits a defined mechanical profile and pathway to degradation.
Molecular designs
The engineering payoff is the avoidance of regrettable substitutions, where a regulated hazard is swapped for an unregulated analogue that shares the same liability: bisphenol flagged as an endocrine disruptor, then replaced by BPS and BPF analogues with comparable activity behind a BPA-free label, or long-chain PFAS giving way to short-chain homologues that are just as persistent.
“These regrettable substitutions can be avoided with molecular engineering, because it lets us design materials at the molecular level,” she said.
It’s the engineering expression of the caution she opened with, since designing a polymer deliberately is how you avoid recreating the hazard you set out to remove.
The polymer family in this context is the polyhydroxyalkanoates (PHAs), microbially synthesised polyesters that bacteria accumulate intracellularly as carbon reserves and recover by fermentation rather than petrochemical synthesis.
The mechanical envelope splits along chain length. Short chain-length grades, three to five carbons in the repeat unit, are highly crystalline, stiff and brittle. Medium chain-length grades run low in crystallinity with a depressed glass transition and high elongation, behaving as elastomers. That compositional control is why no single number describes a PHA, though all are biodegradable, non-toxic and water-insoluble.
The canonical-grade, poly-3-hydroxybutyrate or P3HB, sits close to commodity polypropylene on the headline numbers, with a tensile strength near 40 MPa and a Young’s modulus around 3.5 GPa, yet it fails an engineer on the properties that do not make the datasheet headline.
Its elongation at break sits near 6 per cent and the brittleness is time-dependent. P3HB crystallises above 50 per cent, its glass transition sits near room temperature and low nucleation density produces large spherulites that crack between themselves – while secondary crystallisation and physical ageing over days to weeks embrittle a part that tested adequately when moulded. A narrow processing window adds chain-scission risk near the melt temperature.
Each failure mode has a lever, copolymerising with 3-hydroxyvalerate depresses melting point and crystallinity, trading tensile strength toward 20 MPa for elongation near 50 per cent; nucleating agents suppress cracking; plasticisers slow ageing; sub-150-degree annealing restores ductility.
The published range runs from under 1 MPa to roughly 190 MPa, and documented modifications have raised tensile strength by 330 per cent – so the unsolved work is process control and economics, not feasibility.
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Australian effort
The clearest Australian demonstration that PHA chemistry can scale is Uluu, a Perth company that grows its polymer from farmed seaweed rather than food waste.
Red Gracilaria seaweed is hydrolysed with enzymes into sugars, which saltwater microbes ferment and store internally as PHA, harvested as white pellets. The grade is PHBV, the copolymer that tempers P3HB’s brittleness. It drops into existing injection-moulding and extrusion equipment, removing the capital barrier that kills most material substitutions.
The marine-biodegradable, microplastic-free pellets have already been prototyped with Audi and Quiksilver, and funding is moving from a 100 kg-per-year pilot to a 10 t demonstration plant.
Much of the national effort to carry that capability towards production runs through the Bioplastics Innovation Hub, a collaboration between CSIRO and Murdoch University that couples microbiology, synthetic biology and biochemical engineering to advanced manufacturing, aiming to move PHA work from pilot scale to full production.
Its lead industry partnership is a co-investment with Ecopha Biotech, that has completed its R&D stage and filed several patents on PHA production, fermenting sugars and lipids recovered from food-industry waste into polymer, the upstream feedstock economics any rigid-grade product depends on.
Australia has excellent research, but it tends not to translate into application as readily as other regions, such as Europe.
“Currently we put the burden on ‘Prove to me that it’s not safe,’” Senathirajah said. “We need to shift that mindset. The burden should be on demonstrating safety and sustainability up front, rather than managing unintended consequences after deployment.”
The proof that this chemistry survives a real structural specification comes from BARBARA, a Horizon 2020 project coordinated by the Aragonese technology centre Aitiip.
It targeted engineering-grade feedstock for fused filament fabrication, extracting polysaccharide fractions from corn by-products, starch from broken corn and arabinoxylan from corn fibre, and compatibilising them with engineered polyamide and polyester resins, with reinforcing additives recovered from agro-food waste including almond shells and pomegranate.
The project produced eight qualified materials and validated them in prototypes including door handles and a dashboard fascia produced with Centro Ricerche Fiat, alongside a starch-and-polyamide matrix upscaled for a load-bearing construction mould.
“It shows that structural bioplastics are not just a hypothetical wishlist,” Senathirajah said.
While it doesn’t resolve the local problems of scale and standards, it removes the open question of whether bio-based resins can meet automotive and construction performance, which lets the Australian conversation move from “whether” to “how soon”.
Designing new polymers is only half of the redundancy argument, since the other half is digesting the petrochemical plastic already in circulation. Engineered PET hydrolases now achieve at least 90 per cent depolymerisation in 10 hours, and a 2025 closed-loop process from the University of Portsmouth has put recycled PET at $2.19 dollars a kilogram against $2.71 for virgin – the first signal that enzymatic recycling can compete on cost.
Filling the consumer and precision-parts gap, much of it imported, is Biolastics, a Western Australian materials and design firm that distributes the Tecnaro lignin-based family, whose three grades map onto a property ladder.
Arboform, the original liquid wood, combines lignin with natural fibres and injection-moulds at 150-170 degrees with thermal stability to around 95 degrees, below the 140-degree automotive bar. Arbofill lifts impact strength and thermal resistance into ABS territory and is visually indistinguishable from petrochemical plastic.
Arboblend, the most capable, is formulated from blends that can include PHA, PLA and bio-polyamides, engineered for high impact strength, flame retardancy and full biodegradability, and its PHA content makes it the direct commercial bridge to the resin chemistry the Perth researchers are scaling.
APR Composites, meanwhile, is working on the structural edge.
Its wood-plastic composite runs roughly 50 per cent recycled high-density polyethylene against 50 per cent recycled timber, with a UV stabiliser, masterbatch and lubricant making up the balance. It performs strongly in compression, which suits retaining-wall and post-and-rail duty, and turns up in coastal and park infrastructure, in the dunnage that cushions the curved precast concrete segments of Melbourne’s Metro Tunnel, in vehicle crossing pads over rail lines, and in the non-conductive post-and-rail systems supplied to SA Power Networks.
Modra, of APR Composites, is proud of that last product, the VAB, which carries no metal fixings and so removes the arcing and work-health-and-safety exposure metal hardware introduces. His framing of the feedstock is the sharpest line in the argument.
“Plastic is eminently recyclable. It’s the waste part of plastic that’s a problem, until we treat it as precious, which it is, because it’s a petrochemical,” he said.
The trade-off in the composite is real, because adding a hydrophilic timber fibre to a hydrophobic polyolefin raises stiffness but opens a moisture-uptake pathway the neat polymer would not have.
APR’s answer is a hemp-plastic composite, developed with the University of Melbourne to improve impact performance and crystallinity while making the matrix markedly more hydrophobic, with an explicit target: match MGP10 and MGP12, the machine-graded pine that frames most Australian houses. Clear that bar, Modra said, and APR has early state-government interest in mandating 20 per cent recycled content in structural components of new builds.
“The structure would be using up plastic, and that is a good thing,” he said.
The path there is less a breakthrough than a grind of externally ratified weathering, span and bend testing. Automotive dashboards and electronics casings fall outside APR’s focus, and while the technology is transferable, the company is staying with architectural and water infrastructure, leaving the rigid consumer and automotive frontier to the materials that will claim it.
Part of what keeps that frontier open is economics.
APR’s own costs rose by around a third on oil price volatility, a reminder that petrochemical plastic remains hostage to a market the bio-based alternatives can in principle escape, while bioplastics, still dearer today, track down a double-digit growth curve as oil extraction grows more expensive.
The two cost curves are converging, and a full substitution of fossil-based plastics would represent a market turnover of roughly 250 million tonnes a year.
With the foundational science proven and macroeconomic tides turning, the challenge now shifts from the laboratory to the unglamorous mechanics of industrial adoption.
Factors like rewriting conservative regulatory codes, generating long-term performance data and scaling production lines. This pivot won’t happen overnight, and as Senathirajah said, it can’t be treated as a singular silver bullet.
But on the factory floors where Australia’s new material architecture is actively being developed, the future has already begun.
This article was originally published in the August 2026 edition of create with the headline “The plastics pivot”.
