If you are scared of chemical terminology, you may think you are in for a bumpy ride. But fear not, you do not need a degree in chemistry to follow this discussion. Buckle up, and let’s go.
Granted, the term “polyethylene furanoate (PEF)” doesn’t exactly roll off the tongue. But bottles and packaging materials made from this plastic may soon be rolling off assembly lines. Why? Because it is recyclable, and more importantly, it can be made from bio-waste such as wheat straw instead of from petroleum. The hope is that it can, at least to some extent, replace polyethylene terephthalate (PET), the petroleum-derived plastic that is used to produce some 600 billion bottles every year. As a bonus, a “cradle-to-grave analysis” shows that compared with the production of PET, PEF is associated with reduced greenhouse gas emissions.
While life today without plastics is unimaginable, their once common description as “miracle materials” needs an asterisk. Most plastics are made from non-renewable petroleum, and their improper disposal has become an environmental calamity. Views of beaches with washed-up plastic waste, turtles snared in discarded fishing nets, and the giant plastic “garbage patch” in the middle of the Pacific Ocean is very disturbing. So is the knowledge that in the environment, plastics can degrade into “microplastics” that can end up in our food supply, and therefore in us. Ditto for some additives such as phthalate plasticizers and plastic components such as bisphenol A (BPA), which has raised various health concerns. The plastics industry, aware of these problems and the associated adverse publicity, is taking steps to address these issues. But there are many challenges.
Let’s start by doing an autopsy of a PET bottle, identifiable by the number 1 in the triangular recycling logo. This plastic is made of a polymer of alternating units of ethylene glycol and terephthalic acid linked in a long chain. Ethylene glycol is made from ethylene oxide, which in turn is made by the “catalytic cracking” of petroleum. The precursor of terephthalic acid is para-xylene which is distilled from petroleum. Both processes require the input of energy that comes from burning fossil fuels. One way to “green up” PET production is to derive the ethylene glycol from a renewable resource, namely bioethanol from the fermentation of sugar. This is the technology that allowed Coca-Cola to come up with its much-hyped “plant bottle.” Actually, PET is only 30% ethylene glycol by weight, and its production from bioethanol involves a lot of chemical manipulation. The ethanol is first converted into ethylene, then into ethylene oxide, and then into ethylene glycol. There is a significant environmental footprint here. And of course, the terephthalic acid that makes up 70% of the plastic comes from petroleum.
That raises the question of finding an alternative to terephthalic acid that does not come from petroleum. And researchers have come up with one! Furan dicarboxylic acid reacts with ethylene glycol just like terephthalic acid does and produces polyethylene furanoate (PEF), a plastic that can be recycled, allows less carbon dioxide and oxygen to pass through than PET, and has higher resistance to mechanical strain which means that bottles and packaging materials can be made thinner. Most importantly, furan dicarboxylic acid be made from plant material such as wheat straw or wood waste through a sequence of reactions made possible by proprietary metal catalysts. There is, however, one big drawback. Cost! Currently, it costs roughly eight times as much to produce PEF than PET. That gap will be reduced as the manufacture of PEF is scaled up.
There is yet another issue that needs attention. As mentioned, the ethylene needed to make ethylene glycol can be produced from bioethanol rather than from petroleum, which is a step in the right direction. But regardless of the source, the ethylene has to be converted into ethylene oxide which is then used to produce ethylene glycol. The issue is that ethylene oxide is a reproductive toxin, is mutagenic and carcinogenic. Indeed, there are concerns that the increased cancer rates seen around some chemical plants are due to the release of ethylene oxide into the air. Furthermore, the production of ethylene oxide releases large amounts of carbon dioxide.
So, can ethylene glycol be made without going through ethylene oxide as an intermediate? Not only can that be done, but the starting material can be biomass. Through a sequence of reactions, with the aid of tungsten-based catalysts, plant material can be converted into glycolaldehyde which in turn can be hydrogenated to yield ethylene glycol. The whole process releases less carbon dioxide than the production of ethylene oxide. Is there a fly in the ointment? So far, the synthesis of ethylene glycol by this process is only at the pilot plant stage and it remains to be seen whether it can prove to be practically and financially viable.
Plastics are here to stay, but problems with their production and use, particularly single-use, have to be addressed. Science comes to the fore when backs are against the wall. Elimination of petroleum as a source material is not in the near future, but there is no question that in the long run research will lead to more biodegradable, recyclable, compostable plastics made from renewable resources. You may soon be drinking from a polyethylene furanoate bottle. Of course, one solution to the plastic problem is not to buy that bottled beverage in the first place.