Opinion What about
Opinion What about recycling of T he polyhydroxyalkanoate (or PHA) platform consists of products that meet the needs of all known end-oflife options. In this article we shall explain the details behind this statement and its implications. In numerous countries and geographic areas people are rightfully fed-up with the plastic waste streams they see everywhere, including on land and in rivers, lakes and oceans. This plastic waste mountain is growing rapidly year after year, but while the visible part of our plastic waste is readily apparent, the non-visible part is even larger. There are at least two main reasons driving the increased rate of this invisible waste: first, more than 90% of the plastic waste in our water streams sinks to the bottom due to fouling of the plastic waste surfaces; and second, plastic microparticles from our clothes and a large variety of products we use daily not only end up in water streams, but also show up on land and in our food chain in unseen ways. Needless to say, action is long overdue. There are excellent initiatives in place to retrieve plastic waste from oceans and rivers, but that retrieval can lead to a simple recycling of those plastics to make articles that people then throw back into the oceans again. We can subsequently retrieve that waste again from the ocean, and while that is technically a circular economy, it certainly is not one that we should aspire to create. Also, many legislative efforts around the globe aim to curb undesired plastic waste streams. The approach often taken by legislators has been to outright ban the use of large-volume fossil-based polymers for many single-use plastic articles to avoid the visible or environmental harm they can cause on land or in water. Some legislators aim to replace currently used polymers with biodegradable polymers, but they are still in the process of defining what that means. Others tend to only allow the use of natural materials for single-use applications, since those “are biodegradable in nature”. However, natural materials like wood are not biodegradable in water. Wood consists of cellulose and lignin, the latter of which is not biodegradable in a marine environment because it needs fungi to biodegrade, an organism that is not present in water. Consider the fact that wooden shipwrecks lie on the bottom of the ocean for centuries. So the question is: “How can we remedy the challenge lying before us?” In the ideal situation we are looking for innovative, new materials that can be used in a large variety of applications and for which all known end-of-life options are a possibility. After taking steps to reduce use and redesign plastic articles, legislators, manufacturers, retailers and communities should consider the end-of-life options as depictid in table 1. One cannot be selective and use just a few of these end-oflife options; they are all important and critical to ensuring as much material as possible is responsibly recycled, reused or composted. If this can be accomplished with new, innovative materials that account for all these options, then manufacturers can ensure their products minimally impact the environment regardless of whether people are disciplined enough to recycle material the way it is supposed to be. If people instead are purposely or accidentally wasting material by throwing it away on land or in water streams, then full biodegradation is a musthave. For further context, see additional remarks in the box on each of the end-of-life options mentioned in table 1. Polymeric materials that can fully meet a comprehensive combination of end-of-life options include cellulose, a large number of PHA-polymers, and starch or a combination of each of these. All these materials already occur in nature as they are made by biological synthesis through bacteria based on natural nutrients or feedstock. A large variety of micro-organisms are known to make several different PHA-polymers in nature using different sources of nutrients and depending on their environment. These polymers serve as nutrients and energy sources and are known to be part of the metabolism of living organisms including plants, animals and humans. PHA resins are a series of natural bio-benign materials that have appeared in nature for millions of years, similar to other natural materials like wood, other cellulose-based products, proteins and starch. During the last 20-30 years, dozens of initiatives from all over the world have started to make PHA materials viable for durable and structural applications as an alternative to chemically synthesized polymers. This is accomplished by mimicking nature in a consistent way. Table 1: Endf of life options 1. Recycle articles to be used again re-use the article 2. Recycle articles back to the polymer use the polymer for new applications 3. Recycle articles for raw materials use renewable carbon as feedstock 4. Recycle to environment composting industrial or home composting 5. Recycle articles for incineration produce renewable energy 6. Recycle to nutrients for living organisms full biodegradation, denitrification 36 bioplastics MAGAZINE [03/20] Vol. 15
Recycling By: PHA-polymers? Jan Ravenstijn Consultant renewable materials & Co-founder of GO!PHA Meerssen, The Netherlands Phil Van Trump CTO Danimer Scientific Bainbridge, Georgia, USA Today manufacturers have demonstrated the conversion of many different feedstock sources, like gas, liquid or solid waste streams, to PHA polymers. After-use value chains are also being created for several waste streams to fuel PHA production, resulting in a circular economy. PHA materials can substitute petroleum plastics for onetime-use applications that often, whether by design or improper waste management, end up in the environment. This could include micro-beads in cosmetic products, drinking straws and more. Biodegradation of PHA materials in all environments, including compost, soil and water, is comparable to or faster than cellulose (i.e. paper). PHAs can partly substitute any of the traditional fossil-based polymer families, so the accessible market for these materials is vast. Depending on the type and grade, PHA materials can be used for injection molding, extrusion, thermoforming, foam, non-wovens, fibers, 3D-printing, paper and fertilizer coating, glues and adhesives. It can additionally be used as an additive for reinforcement or plasticization or as a building block for thermosets in paints and foams. Also, their use in medical applications like sutures and wound closures is already commercially viable because the material is bioresorbable. A variety of PHA-polymers are currently made at industrial scale and these polymers have been demonstrated in at least 24 product-market combinations. Although PHA polymers cannot replace all existing fossil-based polymers, they technically fit in a large number of applications as a first step. The PHA-platform is an emerging new polymer platform and the major world producers today are small to mid-size enterprises. Industrialization of this new polymer platform started in 1992 and currently moves from the embryonic to the early-growth stage, while several companies around the globe have built and are building new large-scale manufacturing capacities. www.gopha.org | www.danimerscientific.com 1. Recycle articles to be used again Many plastic articles are already re-used on a regular basis, such as large soft drink bottles, sturdy plastic shopping bags, beer crates and many others. Although it is beneficial to re-use these articles many times, the wear on these items all the time will generate primary micro-plastics that often end up in the world’s oceans. A good example of this can be found in the use of synthetic fibers for products like T-shirts. T-shirts are used and re-used on a regular basis, but every time they are washed in the laundry, they lose fibers to the waste water stream. According to the International Union for Conservation of Nature, synthetic fibers are responsible for 35% of the primary micro-plastics that end up in the world’s oceans. This adds up to many thousands of metric tons of plastic every year. When products need to be re-used often, they should be made from a material that is biodegradable in case the micro-plastics they produce end up in the ocean. 2. Recycle articles back to the polymer Recycling to polymer is common for polymer-based articles that are sold in very large volumes, and the logistics to funnel these used articles back into a polymer processing plant are worth organizing. In the recycling process, the polymeric material is melted and put into a different form. An example of this in action is how polyethylene terephthalate (PET) in bottles can be recycled and then used for spinning synthetic fibers. All thermoplastics can be recycled this way provided they are obtained in a relatively pure form. The issue is that polymers become weaker and less pure after they are re-melted and re-processed more than 2 or 3 times. Every time they are recycled, the polymer molecular weight reduces, and their physical properties will deteriorate. Eventually, the material will need to be disposed of in another manner. 3. Recycle articles for raw materials This form of recycling can be done for all carbon-containing materials, including most thermoplastic and thermoset polymers. Even if a material is “contaminated” with other organic waste streams, it can be used as feedstock for manufacturing chemicals. This source of renewable carbon is called “Renewable Carbon from the Techno-sphere” in a report from the nova Institute, written by Michael Carus. Several global companies have developed technology and built manufacturing plants to produce renewable chemicals from these recycling streams. Contaminated plastic waste pulled from oceans can be used as a source for this process. 4. Recycle to environment composting Composting may refer to industrial or home settings. Industrial composting takes place at elevated temperatures and was originally developed to manage agricultural, forestry and garden waste streams by turning them into a useful product: compost. Standards have been developed to demonstrate whether polymers are industrially compostable, and they typically define a part thickness for the material that is tested. It should be noted that thicker parts take much longer to fully biodegrade. Home composting is done at ambient temperatures, which means that materials that biodegrade under industrial composting conditions may not biodegrade under these milder conditions. To account for this there are separate standards for home compostable material. Polymers that qualify for composting are usually aliphatic polyesters, cellulose and starch. However, some limited aromatic structure can be allowed in the polyesters. 5. Recycle articles for incineration If there is no option to recycle polymeric materials according to any of the abovementioned methods, one can always use the energy captured in these polymers for making electricity. A similar principle to recycling articles for raw material applies here, albeit that in this case the results are not new chemicals, but energy instead. The downside to this method is that it can produce more carbon in the atmosphere. If done in a controlled way, the generated CO2 from this process can be used as raw material again. If not, non-carbon sources, like sun, wind, tidal, white water or nuclear, are more preferred sources of energy. 6. Recycle to nutrients for living organisms Living organisms like bacteria and fungi feed on nutritious materials, so when polymeric materials end up on land or in water streams, either by design or accidental, they could serve as nutrients for these organisms. There are several polymers that biodegrade on land, but the number of polymers that also biodegrade in fresh and salt water is limited. Polymers such as PHAs that are currently produced industrially meet this requirement. There is an additional functionality of PHA polymers that minimizes their environmental impact: they can denitrify waste water streams, because they act as a solid-state carbon source that converts nitrogen compounds, like nitrates, nitrites and ammonia, into nitrogen gas (cf. article on p 38) bioplastics MAGAZINE [03/20] Vol. 15 37
