As we learn more about the environmental influences of human activity, materials that contribute measurable negative impacts develop a less savory reputation. Plastic is one such material. Despite its practicality, durability, and low cost, plastic is increasingly viewed as problematic due to its petrochemical origin, contributions to a burgeoning waste stream, and health-affecting chemical composition. To be fair, “plastic” is an umbrella term encompassing many different types of polymers and composites that do not all exhibit these characteristics. Nevertheless, plastic’s increasingly troublesome reputation, based on the performance of the most commonly used polymers, has become associated with the material in general.
One of the most intriguing contributions of materials science is the potential to transform substances beyond our expectations—including the invention of new variants that can reshape common knowledge. Plastic is a category ripe for experimentation, and biopolymers represent an opportunity for this kind of redefinition. Bioplastics—plastics made from biomass sources rather than petrochemicals—come in two primary forms: polylactic acids (PLA) and polyhydroxyalkanoates (PHA). PLA is made from sugars derived from plants like corn or sugarcane, whereas PHA is produced via microbial fermentation. PLA, which thus far has received more industry attention, has raised concerns due to its use of edible feedstocks that could otherwise be consumed as food. PLA also does not readily biodegrade and must be composted via industrial processes. PHA, meanwhile, exhibits superior biodegradability compared with PLA, but unfortunately, the material is expensive and slow to produce.
However, a recent breakthrough points to a more viable future for PHA, now the so-called “dream plastic.” Scientists at Colorado State University in Fort Collins have been developing methods of preparing a functional polymer from biorenewable feedstocks. To date, PHA (like PLA) plastics have been brittle, making them less desirable than the more robust petroleum-based polymers. In addition, PHAs have exhibited thermal instability, making them difficult to melt in order to reprocess the material without degradation. (This thermal instability has been a significant reason for the high processing cost of PHA.) Nevertheless, CSU chemistry professor Eugene Chen and his research team have devised a solution for both limitations. The answer lies in replacing volatile hydrogen atoms with more durable methyl compounds. This fundamental change in chemistry imparts much-improved stability and robustness in the resulting material, which is tougher than common high-density polyethylene and polypropylene. The new PHA can also be remelted easily (and repeatedly) into new material. “We are adding three key desired features to the biological PHAs, including closed-loop chemical recycling, which is essential for achieving a circular PHA economy,” Chen said in a CSU press release.
PHA is still in the early stages of commercialization, and—like PLA—its initial consumer applications have been low-risk, small-format products such as disposable containers and packaging materials. However, to achieve measurable positive environmental impacts, PHA should be developed for more robust, larger-scale applications in the automotive and building construction industries. One promising area of inquiry is wood-PHA composites. Wood plastic composites, made from a combination of wood flour and thermoplastics, have gained popularity as a form of engineered lumber exhibiting high durability and low maintenance. The market for WPCs is currently $5.7 billion in the U.S. and is expected to more than double by 2030. Example WPC building applications include decking, flooring, cladding, fencing, railings, and outdoor furniture. As a team of researchers from Australia’s University of Queensland has determined, PHA can serve as a high-functioning substitute for petroleum-derived plastics in WPCs. However, the development of such exterior-grade products will likely be slow as more research is required to determine the long-term performance of wood-PHA composites in harsh environmental conditions. Ironically, one of PHA’s most significant advantages—that it naturally biodegrades in ambient contexts (e.g., oceans)—undermines the goal of long-term durability. Additives and compatibilizers—polymer blends that add stability—can be used to extend material service life, but the long-term environmental effects of these substances require further study.
As we face the grim realities of our oil-based plastic problem, PHA offers an enticing solution that promises to reduce the quantity of global plastic waste, petrochemical dependence, and adverse human health effects. If PHA can be successfully commercialized at scale and in durable industries such as building construction, its mass substitution for traditional polymers could redefine plastic as a much more environmentally responsible material. However, such an achievement poses an intriguing quandary: Oil-based plastic perseveres by design, based on our undisputed goal of longevity for products. but this long-term aim is inherently shortsighted. We need only contemplate the Great Pacific Garbage Patch to appreciate that products should not be designed to outlive their usefulness. Of course, what constitutes a useful lifespan will remain a matter of ongoing debate as we increasingly confront the innate uncertainty of future scenarios. But the consideration of end-of-life possibilities also represents a significant environmental design opportunity. PHA is an optimal material for such an exploration, and it could change the very character of plastic. The question is: As we interrogate the materialistic culture that drives product accumulation, are we ready to change ourselves?
The views and conclusions from this author are not necessarily those of ARCHITECT magazine or of The American Institute of Architects.
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