PHA: As green as it gets

Bio-based polyhydroxyalkanoate (PHA) resins are very green, but still not green enough, says Anindya Mukherjee, a founding member of GO!PHA, the nonprofit initiative created to accelerate the development of the PHA-platform industry.

Bio-based and biodegradable even in the marine environment, PHA seems tailored to supply the demand for sustainable materials created by the ramifications of the upcoming Single-Use Plastics Directive. The European Union, however, sees it differently.

In May 2018, the European Commission proposed a number of new EU-wide rules targeting the 10 single-use plastic products most often found on Europe's beaches and seas, as well as lost and abandoned fishing gear.

Together these items, which include, among others, plastic cotton ear swabs, cutlery, plates and straws, account for some 70 percent of all marine litter. The proposal was adopted in 2019, which means that the deadline for implementation by the EU Member States is this year in July.

The directive is aimed at tackling the problem of marine pollution head on, and it contains various measures to do so. It calls for circular approaches that give priority to sustainable and nontoxic reusable products and reuse systems rather than to single-use products, aiming first and foremost to reduce the quantity of waste generated. Next to outright bans, the directive provides for the introduction of extended producer responsibility schemes to cover the necessary costs of waste management and litter cleanup, as well as the costs of awareness-raising measures to prevent litter in the first place.

Included in the directive is a paragraph explicitly defining the polymer materials covered by the directive and those that are not. And it is here, according to Mukherjee, that the confusion starts.

Plastics are defined as polymeric materials to which additives or other substances may have been added and can function as a main structural component of final products. The directive explicitly states, however, that excepted from this are natural polymers that have not been chemically modified.

On the other hand, the directive emphatically does cover plastics based on modified natural polymers, or plastics manufactured from bio-based, fossil or synthetic starting substances that are not naturally occurring. Examples are polymer-based rubber items and bio-based and biodegradable plastics, regardless of whether they are derived from biomass or are intended to biodegrade over time.

In other words, natural products cannot be equated with products occurring in nature. Any natural polymer or polymers occurring in nature that either are replicated in an industrial process such as fermentation or have been modified are therefore covered by this directive.

The question of whether natural polymers are covered by the term "plastic," and if they may be exempt, is therefore an important one and one that can be answered only by determining what a "natural polymer" is and what exactly is meant by "chemically modified."

The questions are important ones, particularly in relation to polymers such as cellulose derivatives and the PHA family, Mukherjee said. Or, for that matter, wood pulp, starches, cotton and proteins, to name but a few.

"The discussion about cellulose and cellulosics like paper, lyocell and viscose was elucidated in the latest guideline," he said. "A way was found to 'grandfather' in some of these materials like paper and lyocell even though it is clear that paper, for example, is a chemically modified cellulose. However, these materials are now exempt from the directive."

The solution was reached by accepting that a natural polymer does not mean it has to exist in nature in its native form. "It just has to be a part of nature," Mukherjee explained.

But the group of polyhydroxyalkanoates, he added, is less fortunate: These biopolymers are currently covered by the directive, despite being a natural product and despite their outstandingly sustainable credentials.

Bacteria produce PHA as a source of energy and as a carbon stored through the fermentation of renewable feedstocks such as sugars or fatty acids, or any other carbon-containing substrate. This natural process can be mimicked in an industrial setting using feedstocks that can range from wastewater streams to plastic waste, renewable methane and carbon dioxide.

They are a class of natural materials that have existed in nature for millions of years. These materials are both bio-based and biodegradable, similar to other naturals materials such as cellulose, proteins and starch.

According to GO!PHA, PHA products range from amorphous to highly crystalline, and run from high-strength, hard and brittle materials to low-strength, soft and elastic. The versatility of the PHA family accommodates a wide range of market applications, due to their biocompatibility, biodegradability and green credentials.

Depending on type and grade, PHAs can be used for injection molding, extrusion, thermoforming, foam, nonwovens, fibers, 3D printing, paper and fertilizer coating, glues, adhesives, as additive for reinforcement or plasticization or as building block for thermosets in paints and foams. The main markets where PHAs have already achieved some degree of penetration are packaging, foodservice, agriculture and medical products.

PHA is equally versatile when it comes to the end of life. It can be reused. It can be recycled back to the polymer for new applications. It can be recycled back to raw materials to be used as renewable feedstock. It can be recycled to the environment through industrial or home composting. It can be recycled through incineration, creating renewable energy. And lastly, it can be recycled to nutrients for living organisms through full biodegradation.

PHA may well be a natural polymer, but in the eyes of the EU, it is classified as an artificial or a modified polymer and hence not allowed to be used as a single use plastic replacement.

The reason?

"The basic problem is the fact that PHA is considered to be a fermentation-based product," Mukherjee said.

ECHA considers fermentation — in their REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) Guidelines — to be an industrial process, even though, in the EU Legislation on Flavorings, for example, products produced through fermentation processes are considered to be natural. And what about cheeses, wine and beer, or sauerkraut — should these also be reclassified as artificial? They, too, are all the result of fermentation using living organisms.

"Of course: PHA is the result of a fermentation process. The point here is that fermentation is a natural process — one that occurs everywhere in nature. PHA is a natural polymer that is produced by natural routes in nature, and industrial fermentation processes simply make them economically viable," Mukherjee explained.

For commercial purposes, the process is scaled in order to be able to produce commercial volumes, but it remains a bacterial process that produces a bacterial polyester, he said.

"We have talked to the commission about this, but with disappointing results," he said.

The stance adopted by the European Commission is even more puzzling in view of the fact that Europe has spent more than $100 million sponsoring research into the valorization of waste to produce PHA. One such project, EUROPHA, developed a PHA production process using mixed microbial cultures, enabling the use of low-cost agro-food waste with no market value, no food competition and no price volatility effects. Further research was aimed at developing high quality food-grade biodegradable PHA for packaging that could be disposed of as organic waste.

Moreover, a recently concluded study by the EU expert committee Science Advice for Policy by European Academies on the "Biodegradability of plastics in the open environment," published Dec. 18, 2020, clearly states that the field of biodegradable polymers is one that is rapidly evolving and high-tech and that "policy should avoid placing barriers to future developments and innovations."

Outside Europe, PHA is starting to gain real momentum, with various producers — among them Kaneka, Newlight Technologies and Danimer Scientific — having successfully scaled up production to industrial or even commercial levels. Around the world, it is being used to replace fossil-based plastics in a host of single-use plastic applications such as straws, serviceware and even coffee pods.

The rest of the world, explained Mukherjee, has designated biodegradability as the criterion to ban or exempt use of plastics.

"There are standards for biodegradability — also for marine biodegradability — that are used to certify this. The EU is the only one using this natural polymer criterion to exclude PHA —- but to include cellulose," Mukherjee said.

Yet PHA's biodegradability profile is very similar to cellulose, he pointed out. "Cellulose and PHA have the same order of magnitude biodegradation pattern. All other plastics replacements and biopolymers are several orders of magnitude longer in biodegradation."

It seems odd: Other parts of the world are happy to embrace PHA as a full-fledged biodegradable, sustainable biopolymer and to support and promote its further development and use in single-use applications.

There, the science is straightforward. Europe, however, continues to tenaciously adhere to its own criteria and interpretation of the concept of "natural" — despite what scientists, including EU's own expert panel SAPEA, say.

How this will affect future research and business developments in PHA materials in Europe remains to be seen, but there seems little doubt that not recognizing these materials' potential and eminent suitability for a least some of the products included in the ban, could at least result in Europe's falling out of step with measures taken elsewhere. This is surely not the intention of the directive. Achieving a clean, nonpolluted environment — in the oceans and on land — demands collaborative, coordinated action.

It is time to get on with it.