Admittedly, the term “polyethylene furanoate (PEF)” doesn’t exactly roll off the tongue. But bottles and packaging materials made from this plastic may soon be coming off assembly lines. Why; Because it is recyclable, and more importantly, it can be made from organic waste like wheat straw instead of petroleum. The hope is that it can, at least to some extent, replace polyethylene terephthalate (PET), the petroleum-derived plastic used to make about 600 billion bottles each year. As a bonus, a “cradle-to-grave analysis” shows that compared to PET production, 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 disaster. The views of beaches with washed up plastic waste, turtles trapped in discarded nets and the giant plastic “garbage patch” in the middle of the Pacific Ocean are very disturbing. So is the knowledge that in the environment, plastics can break down into “microplastics” that can end up in our food supply, and therefore in us. The same is true of certain additives, such as phthalate plasticizers and plastic ingredients 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, which can be identified by the number 1 in the triangular recycling logo. This plastic is made from a polymer of alternating ethylene glycol and terephthalic acid units linked in a long chain. Ethylene glycol is produced from ethylene oxide, which in turn is produced from the “catalytic cracking” of petroleum. The precursor of terephthalic acid is paraxylene which is distilled from petroleum. Both processes require the input of energy derived from burning fossil fuels. One way to “green” PET production is to produce ethylene glycol from a renewable resource, namely bioethanol from sugar fermentation. This is the technology that allowed Coca-Cola to come up with its much-hyped “plant bottle.” In fact, PET is only 30% ethylene glycol by weight, and its production from bioethanol involves many chemical manipulations. Ethanol is first converted to ethylene, then to ethylene oxide, and then to ethylene glycol. There is a significant environmental footprint here. And of course, the terephthalic acid that makes up 70% of plastic comes from petroleum.
This raises the question of finding a non-petroleum alternative to terephthalic acid. And the researchers came up with one! Dicarboxylic acid furan reacts with ethylene glycol just like terephthalic acid to produce polyethylene furanate (PEF), a plastic that can be recycled, allows less carbon dioxide and oxygen to pass through PET and has a higher resistance to mechanical stress meaning that bottles and packaging materials can be made thinner. More importantly, dicarboxylic acid furan is made from plant material such as wheat straw or wood waste through a series of reactions made possible by proprietary metal catalysts. There is, however, one major drawback. Cost! Currently, PEF costs about eight times more to produce than PET. This gap will decrease as PEF production scales up. There is one more matter that needs attention. As mentioned, the ethylene required for the production of ethylene glycol can be produced from bioethanol rather than petroleum, which is a step in the right direction. But regardless of the source, ethylene must be converted to ethylene oxide which is then used to produce ethylene glycol. The point is that ethylene oxide is a reproductive toxin, it is mutagenic and carcinogenic. Indeed, there are concerns that increased cancer rates seen around some chemical plants are due to the release of ethylene oxide into the air. In addition, 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 this be done, but the raw material can be biomass. Through a sequence of reactions, with the help of tungsten-based catalysts, the plant material can be converted into glycolaldehyde which in turn can be hydrogenated to give 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 economically viable. Plastics are here to stay, but the problems with their production and use, especially single-use, must be addressed. Science comes to the fore when backs are against the wall. The elimination of oil as a raw material is not in the near future, but there is no doubt that in the long term research will lead to more biodegradable, recyclable, compostable plastics from renewable sources. You may soon be drinking from a polyethylene furanoate bottle. Of course, one solution to the plastic problem is to not buy that bottled beverage in the first place. @JoeSchwarcz