If you’re afraid of chemical terminology, you might think you’re in for a bumpy ride. But fear not, you don’t need a degree in chemistry to follow this discussion. Buckle up and let’s go.
Admittedly, the term “polyethylene furanoate (PEF)” does not exactly leave the language. But bottles and packaging materials made from this plastic could soon roll off the assembly lines. Why? Because it is recyclable, and more importantly, it can be made from bio-waste such as wheat straw instead of 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 to PET production, PEF is associated with reduced greenhouse gas emissions.
While life today without plastic is unimaginable, their once-common description of “miracle materials” requires an asterisk. Most plastics are made from non-renewable petroleum and their improper disposal has become an environmental calamity. The sights of beaches with plastic waste washed up, turtles trapped in abandoned fishing nets, and the giant plastic “trash can” in the middle of the Pacific Ocean are very disturbing. So does 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 certain additives such as phthalate plasticizers and plastic components like bisphenol A (BPA), which have raised various health concerns. The plastics industry, aware of these issues and the associated negative publicity, is taking steps to address these issues. But the challenges are many.
Let’s start by doing the autopsy of a PET bottle, identified 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 by a long chain. Ethylene glycol is made from ethylene oxide, which in turn is made by the “catalytic cracking” of petroleum. The precursor to terephthalic acid is para-xylene which is distilled from petroleum. Both processes require the input of energy from the combustion of fossil fuels. One way to “green” PET production is to derive ethylene glycol from a renewable resource, namely bioethanol from the fermentation of sugar. It’s the technology that allowed Coca-Cola to come up with its much publicized “vegetable bottle”. In fact, PET contains 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, 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 an alternative to terephthalic acid that is not derived from petroleum. And the researchers found one! Furan dicarboxylic acid reacts with ethylene glycol just like terephthalic acid to produce polyethylene furanoate (PEF), a plastic that can be recycled, passes less carbon dioxide and oxygen than PET and has greater resistance to mechanical stress, which means that bottles and packaging materials can be made thinner. More importantly, furan dicarboxylic acid must be made from plant materials such as wheat straw or wood waste through a sequence of reactions made possible by proprietary metal catalysts. There is, however, a big drawback. Cost! Currently, it costs about eight times more to produce PEF than PET. This gap will be reduced as PEF manufacturing increases.
There is yet another matter which deserves our attention. As mentioned, the ethylene needed to make ethylene glycol can be produced from bioethanol rather than petroleum, which is a step in the right direction. But regardless of the source, the ethylene must be converted into ethylene oxide which is then used to produce ethylene glycol. The problem is that ethylene oxide is a reproductive toxin, it is mutagenic and carcinogenic. Indeed, it is feared that the increase in cancer rates seen around some chemical plants is due to the release of ethylene oxide into the air. Additionally, the production of ethylene oxide releases large amounts of carbon dioxide.
So, can ethylene glycol be made without using ethylene oxide as an intermediate? Not only can this be done, but the starting material can be biomass. Through a sequence of reactions, using tungsten catalysts, 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 producing ethylene oxide. Is there a fly in the ointment? To date, the synthesis of ethylene glycol by this process is only at the pilot stage and it remains to be seen whether it will prove to be practically and financially viable.
Plastics are here to stay, but issues around their production and use, especially single-use, need to be addressed. Science comes to the fore when the back is against the wall. The elimination of petroleum 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 and compostable plastics made from renewable resources. You will soon be able to drink from a bottle of polyethylene furanoate. Of course, a solution to the plastic problem isn’t to buy that bottled drink in the first place.
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