PHAs (polyhydroxy alkanoates) are interesting but difficult plastics. Interesting because they are produced in a natural way. From sustainable or waste resources. By microorganisms and not at high temperatures. PHAs are biodegradable. They have widely varying properties. In many applications, they might be the sustainable alternative. But they are also difficult, mainly because of just one problem: their price.
Production by micro-organisms
One of the centres of PHA research is Wageningen Food & Biobased Research in the Netherlands. It has conducted much technological research into the production and use of PHAs for various applications. Recently they summarized their findings, together with Invest-NL. In one sentence, they find that there are ‘many market opportunities for PHAs’. They just need to be developed.
‘PHAs are made by micro-organisms from raw materials such as sugars and vegetable oils,’ says the press release. They can also be produced from various waste streams like food waste and sewage sludge. Market demand is growing, even though production volumes are still limited and production costs are high. But the researchers hope that production costs will go down as production volumes go up.
Three complicating factors
Three factors will complicate this process. Firstly, the production process of PHAs is quite different from that of most other plastics. Polymerization is produced by microorganisms, in a solution, not in a reaction vessel at high temperature. Therefore, this process cannot make use of the body of knowledge built up in the production of other plastics. Optimization of PHA production processes will therefore still require ‘substantial investments and a lot of research’.
Secondly, PHAs vary substantially in properties. This variety is much larger than in any other type of plastic material. In essence, every type of PHA is a separate type of polymer. Moreover, PHA properties often differ substantially from those of other plastics. Therefore, early adopters in each market need to look again into the various types of PHAs and the possible matches with properties required.
Thirdly, often PHAs are more expensive than its alternatives. A problem that might be overcome by growing production volume. Or by making use of other feedstocks. At present, most PHAs are produced from virgin feedstocks like glucose or palm oil. Cost might come down if feedstock with a negative value could be used, such as waste water treatment effluents or various residues. But then, this will require more research, as it is difficult to produce pure products from mixed resources.
But all these drawbacks might be compensated by the single outstanding benefit of PHAs: their sustainability and biodegradability. They may be the perfect material in markets where biodegradability in various natural environments is essential, says Wouter Post, researcher at Wageningen Food & Biobased Research. Therefore, in the roadmap drawn up for PHAs, biodegradability is the main distinguishing factor between the four introduction phases.
These materials may be perfectly suited to markets in which biodegradability is essential, and material properties are of lesser importance (phase 1). Like in paper coating in beverage packaging, that will produce an entirely biodegradable packaging (whereas this is not the case if the plastic coating is made of LDPE). Another application is fertilizer coating. Fertilizer grains need to be coated in order to slow down release into nature. If such a coating would be made of polyurethane, this will remain in the soil; whereas PHA coatings will be biodegraded.
Phase 2 is more difficult already; these applications require biodegradability, whereas material properties are important as well. Yet, there are opportunities for a number of PHA materials. Like in agricultural plastics and nets; here, PHAs will substitute LDPE, that isn’t biodegradable and will release plastic to the soil. Like in plant plugs, that will not have to be removed after having supported the growing seedling. And in artificial reefs, that will support the formation of a natural reef in the beginning, but that will dissolve in the end. Here, PHAs will substitute concrete, that lasts for ages. And finally, in tea bags and coffee cups; these will compost after use together with their contents.
Opportunities become much narrower in phase 3, where material properties are critical. One of the most interesting application categories is plastic tableware such as plates, forks and knifes. These are often developed for single use. Precisely for that reason, they became restricted in the EU in 2019. Unfortunately, biodegradable alternatives are not exempted from the guideline; and a review will not take place before 2027. Plastic bags may be another opportunity; these too are being restricted because they litter the environment. But here, PHA plastic bags do not yet have the same tear strength as those made from LDPE.
In phase 4 (low CO2 footprint), there are no opportunities for PHA at the moment. In liquid and dry food packaging, there are some opportunities that need to be developed. Toys and home appliances could be made from PHAs; but other biobased polymers might in the end have better properties overall.
Slowly, production volume rises
Wageningen Food & Biobased Research currently participates in the European Urbiofin project. This aims to produce PHAs from urban waste for use in packaging materials. They collaborate with Invest-NL in a study on PHA market opportunities. These materials still fight an uphill battle; but slowly, new applications appear and production volumes are on the rise.