Deep Thinking on Recycling
Updated: Nov 19, 2021
Should plastics be compostable, recyclable - mechanically or chemically – or just good for incineration or landfill?
(A defense of plastics mechanical recycling)
(By Dr. Mario Grimau, SPRING Materials Science SME)
In the long term, biomaterials will probably be the best materials we can aspire to. Meanwhile, it is very likely that we should settle and be very happy with the much simpler, but quite effective synthetic materials that we have today. Thus, we must look for the best ways to deal with their possible end of life. To do so, no physical or chemical method should be ruled out, since all of them can be improved and adjusted to our current needs.
When it comes to the structural materials used to build life, Nature has made rather different choices than we have. Although carbon is always present as a structural element, both in nature and in the synthetic world, the "nature choices" seem too complex for our present capacities. The preferences of materials in nature also show us that our choices and needs are not very similar to those choices suitable for the construction of life, despite fulfilling some quite similar functions. This is because, in general, our needs are much simpler and humbler than those of the natural world.
Natural biomaterials have several highly successful attributes, among which self-healing and self-repairing are two of the most interesting -- especially in relation to our inability to reuse much of the materials we use and need today. The capacity for self-healing seems, in many ways, much more interesting than the capacity for the self-destruction that natural materials have at the end of their life, too, when they are in the right environment. In particular, the latter is worth noting when it comes to composting, which is a self-destructive alternative at the end of life from the material’s perspective. In any case, it is clear that composting does not seem to be the best solution we could aspire to.
However, for now we are not able to master either self-healing, or natural self-repairing skills to build materials much less uncomfortable for the environment and our conscience. But to be fair, most of the work done so far on self-destructing synthetic materials seems to be going in the right direction: After the glycosidic bonds in biomacromolecules needed for the formation of living matter, the ester bonds in synthetic materials appear to be the most promising route for their self-healing and self-repairing.
Still, at this time, especially on an industrial and business scale, what seems more likely and rational is that it is much better to source reduce and recognize that, for the end-of-life of plastics, both mechanical recycling and chemical recycling still have a lot to give us if we know how to use them well. Above all, we must adjust them to what we really need. Nevertheless, it will not be in the short term when we achieve mechanical and/or chemical recycling of plastics or biomaterials that adapt to all our expectations, as well as to our misbegotten dreams and desires. In all three cases, it is an unfinished task.
In reality, and contrary to what is generally accepted in many of the current debates about the best method of treating post-consumer plastics, the fact of assuming that the current technologies for the mechanical recycling of plastics are the most successful technological expression and almost the last to which we could aspire is, in any case, very far reality. So, as a result of the misinterpretation above, the inability of our current mechanical recycling technologies to achieve significant recycling rates, or worse, rather unrealistic recycling targets in the nearest future, is dooming mechanical recycling of plastics be a failure as an end-of-life management method for plastic waste.
The reality, however, is far from this conclusion. The mechanical recycling of plastics is in its infancy, compared to the recycling of metals, glass or paper and cardboard. In addition, the disproportionate and misplaced social, political and environmental pressures have done much more to condemn a technology that is just taking its first steps, which by the way, has had very important achievements in a very, very short time: the bottle-to-bottle recycling process of PET.
Most industrial plastics recycling being done today is a very artisanal enterprise, which has lately been adorned with very high performance state-of-the-art optical sorting technologies. These technologies only confirm one of the most immense distortions of the mechanical recycling of post-consumer plastics: the idea that to recycle plastics successfully we must collect, sort and separate the largest possible volume of plastics, when that has never been the reality of successful recycling processes.
Meanwhile, plastics reprocessing processes during recycling have been completely neglected for over thirty years, by settling for a worse or second-rate version of virgin polymers extrusion processing. It seems that just having an extruder is enough to do the job ... or not having it, simply ... to be able to enter the business of recycling plastics, and thus calm the anguish of all those who dream of an improbable world without waste, or at least no plastic waste. But the reality, however, is quite far from that.
As a matter of fact, it is not that collecting large volumes of post-consumer plastics is not essential. It is also essential to separate, sort and clean them almost perfectly to achieve a business that produces real benefits and generates added value. All these stages are, in fact, essential and must be executed prominently.
The huge problem, however, is that the entire plastics recycling business has been designed by underestimating the importance of plastics reprocessing, thus subordinating the processing of new recycled pellets to having first many tons of plastic garbage of the best quality and in the largest possible quantity. It is very likely that in this last stage the final blow to the constant and inevitable devaluation of post-consumer plastics as truly secondary materials will be added: the infamous downcycling.
In fact, excellence in each of the stages throughout the mechanical plastics recycling process can be seen as fundamentally necessary conditions, while none of them alone is sufficient. Therefore, we will never be able to produce actual secondary materials from post-consumer plastics despite achieving the huge volumes of clean and well-sorted plastic waste; which we all seem to now consider a holy grail. The latter, in fact, will not help us if we are not able to process these large volumes properly and with high quality. On the contrary, with the current way of mechanically recycling plastics, in general, we are only degrading them a little more (or not so little) and thus condemning recycled plastics to an endless devaluation. The only exception to this fatal rule seems to be almost the entire PET bottle-to-bottle recycling procedure -- but the reality is a little more painful.
If we really want to recycle more, we must learn to recycle mechanically much better. We must overcome once and for all the quasi-artisanal and informal state of industrial plastic recycling worldwide that is concentrated only on the large volumes of plastic garbage. We must also provide the mechanical recycling of plastics with the next generation of engineering and scientific assistance that it sorely needs.
This will not be an easy task at all. There is much to do and many to convince, in addition to rethinking a science that until now has not been able to do its job well enough. It is a long way to go, but still shorter than that required for self-healing biomaterials of our best dreams. There is no time to wait.
Dr. Mario Grimau is a materials engineer and experienced teacher with a proven track record of work in the higher education industry. He specializes in materials science and polymer structure, renewable energy, sustainable development, mechanical and dielectric spectroscopy, X-ray diffraction and chemical and physical properties in polymers and plastics. Dr. Grimau is a strong professional researcher with a Ph.D. focused on Polymer Physics from Simón Bolívar University (Caracas) and a M.Sc. in Polymer Physics from Paul Sabatier University (Toulouse). He was previously a Full Professor at Simón Bolívar University.