As promised, this week I’m going to write about the common resin systems that are used in composite manufacturing, what their chemistry and manufacture has done to the environment in the past and how the industry is changing and has changed to reduce or eliminate the long lived pollutants that were created and dispersed into our environment from the manufacture of these resin systems.
I thought that I would start the resin discussion with epoxies, since they are the most prevalent resin system in advanced composites today. To begin the discussion, we need to understand what chemistry makes up the precursors for epoxies, and how the resins are manufactured. So I will start there.
Your typical bisphenol-A based epoxy starts with a molecule that most of us – especially those in the industry or that have been reading my newsletters know rather well – phenol or the alcohol of benzene. Again, it is this 6-sided carbon ring that makes epoxy resin as strong and stiff as it is. Phenol itself is most commonly industrially produced through the refinement of petroleum. Since crude oil is a big mixture of all sorts of hydrocarbons and lots of other things, refinement of it into products that are useful for both the transportation fuels and in the materials industry. It is the materials industry that is of interest here, because the precursors for epoxies occur naturally in petroleum. I have written about this before, but since crude oil is predominantly prehistoric plants and the plant kingdom prefers the 6-sided benzene ring for making its structural materials (think trees, leaves, etc.), there are lots of phenolic compounds naturally occurring in crude oil.
The other compound that is required to make an epoxy resin is epichlorohydrin, which is a fairly simple organic acid (has some oxygen in the backbone along with an OH group) that has a chlorine atom attached to it to replace a hydrogen atom. This again is usually synthesized using a fairly simple three carbon chain with some oxygen as well as an OH group attached to it which is either reacted with hydrochloric acid or hypochlorous acid (has an oxygen atom in it). In other words, the manufacture of epichlorohydrin requires reacting a fairly simple oxidized organic with a highly toxic acid.
Getting back to the base or backbone of the epoxy – bisphenol-A – again what is used are two simple phenols that are connected together with an acetone molecule by the use of concentrated hydrochloric or sulfuric acid. Again, we have toxic chemistry just in the manufacture of bisphenol-A.
Bisphenol-A also has a bad rap because even though it does not occur in nature at all it can mimic critical enzymes in the body and play all sorts of havoc in humans. It has been linked to loss of cognitive function especially in younger people, may contribute to ADHD, anxiety, and depression, it can contribute to all sorts of metabolic disorders like obesity, diabetes, and heart disease, and can also contribute to the development of cancers.
Of course, once these compounds are made into a solid epoxy resin, they are so tightly bound chemically that they can no longer cause any harm. The potential for trouble, however, occurs when there are industrial leaks of these compounds into the atmosphere or water supply where they can contribute to human exposure.
This is what has led to the banning of most of these chemicals in food packaging. The epoxies that were used to line cans for food prior to the discovery that BPA was harmful unfortunately exposed people to BPA. This compound has also been found in the bloodstream of most humans, especially in the developed industrial world.
These chemicals are also used, especially BPA, in modern plastics that are used for food packaging, plastic tableware, children’s toys, plastic containers, and the list goes on. In fact the microplastics that are polluting our atmosphere, fresh water supply (including in the atmosphere incorporated into the snow on the mountains here in California), and the ocean are predominantly made using these chemicals as well as the ones I am going to be talking about next week which are the polyesters.
And the problem with this is that even though people think of these plastics in much the same way we talk about the fluorinated hydrocarbons we call PFAS or forever chemicals, neither PFAS nor microplastics are truly forever materials. All organics break down when exposed to the outdoors which includes of course air with all of its gases including water vapor. Seawater exposure is even a bit more onerous because the salts in seawater can accelerate this decomposition, especially as the ocean gets more acidic because of the carbon dioxide that is being dissolved in it from human activity. Exposing water to carbon dioxide creates carbonic acid, which is what gives soda water its acidic taste. So your scotch and soda gets its bite not only from the scotch but also from the carbonic acid.
Sunlight also breaks down plastics because the ultraviolet light from the sun that makes it down to earth and gives you a sunburn is in about the right frequency band (or wavelength if you prefer) to crack the bonds in most plastics. That is why plastic sheeting has to have UV absorbers included in the plastic to prolong the life of the plastics. But anyone that has ever used a common polyethylene sheet like you can buy at Home Depot knows that they only last a year or two when exposed to the sun before you have to collect all of the little pieces of plastic, throw them in the trash, and cover with a new sheet of plastic.
It is those little bits of degraded plastic that are one of the major sources of the microplastics that are everywhere, including in all of us. And the microplastics are breaking down in the ocean as we speak, which is going to give the “Pacific Garbage Patch” as it is called whereas of 2017 had something like 9 billion tons of mostly plastic garbage floating in what are called the “horse latitudes”.
All of this from just pumping crude oil out of the ground. And while you can argue that it isn’t just the pumping of oil out of the ground that is the problem, really it is what we are doing with that crude oil that is causing quite a bit of the environmental problems we face today. And I’m not just talking about global warming and carbon dioxide in the upper atmosphere, what I am talking about is all of the toxic chemistry and microplastics that pervades our environment and is being incorporated into our bodies as we speak. And we have no idea what the long term effects of this are. But I am certain that we will find out.
The good news is that this problem has finally entered into the public consciousness. The EU has banned a number of these organic chemicals, starting with BPA. And the plastics industry itself is evolving to more of a sustainable future because they are beginning to understand that we are going to eventually run out of oil. More importantly, long before that happens the cost of their precursors will effectively mean the end of cheap plastics and will devastate their industry. This can be seen in some of the latest news articles where polymer chemists working for companies like DuPont and BASF are furiously working on plant-based substitutes for all of their petrochemical precursors. This is in addition to the realization that crude oil is just prehistoric plants and animals, so the chemistry of big oil is all biologically based to start with.
In other words, the light at the end of this tunnel is not an oncoming train. We do have a lot of work to clean up our past sins, but that is the nature of the human race. When it comes to our very survival we wake up as a species and do what is needed to survive. This one is coming on us fast, so my hope is that we aren’t waking up too late.
That’s about it for this week. This is the next installment of this multi-part series on this topic. It follows directly from the subject of my second book on composites sustainability, so I’m treating this as a natural progression of this newsletter.
As always, I hope everyone that reads these posts enjoys them as much as I enjoy writing them. I will post this first on my website – www.nedpatton.com – as then on LinkedIn. And if anyone wants to provide comments to this, I welcome them with open arms. Comments, criticisms, etc. are all quite welcome. I really do want to engage in a conversation with all of you about composites because we can learn so much from each other as long as we share our own perspectives.
My second book is now completely in the hands of my publisher. Most of you know that it is about what I have been writing in these newsletters for the last 6 months or so – sustainability of composites and a path to the future that does not include using fossil fuels for either the raw materials or the process energy to make composites. The title of the book, at least for now, is “Close the Circle, A Roadmap to Composite Materials Sustainability.” It truly is a roadmap which I hope that at least at some level the industry will follow. Only time will tell.
Finally, I still need to plug my first book, so here’s the plug. The book pretty much covers the watershed in composites, starting with a brief history of composites, then introducing the Periodic Table and why Carbon is such an important and interesting element. The book was published and made available last August and is available both on Amazon and from McFarland Books – my publisher. However, the best place to get one is to go to my website and buy one. I will send you a signed copy for the same price you would get charged on Amazon for an unsigned one, except that I have to charge for shipping. Anyway, here’s the link to get your signed copy: https://www.nedpatton.com/product-page/the-string-and-glue-of-our-world-signed-copy. And as usual, here’s a picture of the book.
Comments