Just as an explanation for why I haven’t posted in a couple of weeks, I’ve been on hiatus trying to get moved out of my house in Sunnyvale and into an apartment in San Diego. Moving out of a house is lots of work, but getting rid of the stuff you haven’t used in a long time is quite cathartic. So, this is sort of a pleasure / pain time. We are very excited about the move to San Diego. Life is going to settle down for us a little bit once this transition period is over with.
Anyway, my wife and I were talking about my newsletter and what I like to write about and asked me a question that I did not have an answer for. I talk about plant-based precursors for composites a lot, and I talk about particular plants or plant types quite a bit in this newsletter. And I talk about the future of composites and how we need to move over to plant or bio-based chemistry for all of our composite material precursors (with the singular exception of glass fiber). We also need to use renewable energy sources for processing the precursors into fibers and resins. Basically, we have to move from a petroleum based linear economy for composites to a circular bio-based economy.
So, the question she asked is “What plants are going to be used in the future?” At the time I didn’t have a good answer. There are the usual suspects like agricultural and forest products waste, flax fiber, bamboo, coconut coir, etc. What are we going to grow for composites in the future. Can the development of precursors for the materials of our future be integrated with our agricultural food supply? It certainly can’t compete for arable land with the requirement to feed our burgeoning population on this planet.
What I decided to write about here are the thoughts that came to mind when I sat down to think about it a bit. What is going to be important of course are the two most abundant organic molecules on the planet, namely cellulose and lignin. Hemicellulose also to a lesser extent because it tends to be more of a branched molecule than cellulose. If you have read some of my previous posts, you will understand the organic chemistry behind these two molecules. Cellulose is what is called a long chain polysaccharide which is basically a bunch of benzene rings (6-carbon rings) all stuck together with a bunch of OH groups attached to the carbons – that is, a bunch of simple sugars all stuck together on long chains. Lignin on the other hand is what is called an aromatic which is again a bunch of benzene rings all stuck together with a single OH group or a couple of OH groups depending on what version of lignin it is, plus some other stuff as well that makes it sticky and makes it Lignin. In other words, lignin is the glue that holds the cellulose together in all plants.
Of course, a good internet search if you know what you’re looking for provides a wealth of information. Here are a few samples:
“The cellulose content in vegetables ranges from 1 to 21%; fruits range from 0.6 to 4.2%; seeds range from about 2 to 12%; agricultural residues range from 31 to 59%; wood ranges from 41 to 53%; flax and hemp have about 70% cellulose; and cotton (the purest natural cellulose) has about 95% cellulose.” (https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/cellulosic-material). This is pretty much as expected and includes the usual suspects – ag waste, forest products waste, flax and hemp. All of these things have been used as building materials ever since man started building mud brick huts to live in.
What about food sources? Here’s one I found – “High levels of cellulose are found in root and leafy vegetables, legumes, and some fruits such as pears and apples. Lignin content is highest in fruits, particularly strawberries and peaches, whereas pectin levels are highest in citrus fruits and apples.” Now we’re getting somewhere. Root and leafy vegetables – things like potatoes, sweet potatoes, radishes, turnips, and kale, collards, beans, etc. are all sources high in cellulose. And lots of fruits are high in lignin. So, what that means to me is that the tops of these root vegetables and the stalks and potentially leaves and stalks of things like broccoli, cauliflower, beans and other legumes, would all be high in cellulose content, so the waste from these crops could be as valuable as grain straw, flax fiber, and other crops that are usually grown mostly for their fiber.
Lignin is the other organic that we are looking for. Here’s a snippet from MDPI – “High density feedstocks such as the drupe fruit endocarps (shells) of olives, eastern black walnut and coconut have the highest lignin content of all known plant organs, and the energy derived from the endocarp is comparable to coal [16].” (https://www.mdpi.com/1996-1073/8/8/7654) This is from an article that is looking for the energy content of the waste products from particular plants. This is because lignin is an aromatic compound (series of benzene rings with a few OH groups - i.e alcohols) that is quite sticky in its native form and is the probable prehistoric source of coal tar. Coal and petroleum are after all fossilized plants. And again, this is a particular type of agricultural waste that is very probably going to be quite valuable as we move into a plant-based future for composites.
Here’s a table I found that has the cellulose content of some agricultural products. Fairly interesting list and something to ponder.
It appears that cabbage, celery, lettuce, and peas have lots of cellulose, and cabbage and lettuce have quite a bit of lignin. So that would mean to me that broccoli stalks, Brussels Sprout stalks, cabbage outer leaves, the leaves of cauliflower, etc. would be great sources of not only high nutritive content in the food itself, but also for use as a source of material to make composite material precursors. Bottom line – grow some cruciferous vegetables and have lunch as well as make yourself some carbon fiber / epoxy parts.
And of course, depending on where you are in the world, there are prime examples of useful food plants whose waste or shells or stems, or in the case of coconut the coir or outer husk that can and should be used for both the fiber and the resin components of composites. What I am advocating here is that entrepreneurs in less developed countries, where agriculture is the main industry, develop processes to convert their agricultural waste stream into very valuable precursors for use in manufacturing composites. This is the future of this industry, and those that adopt this and adapt their way of thinking about this problem will be the ones that make the money and build successful and sustainable industries right in their own back yard.
That’s about it for this week. I hope everyone that reads these posts enjoys them as much as I enjoy writing them. As usual I will post this first on my website – www.nedpatton.com – as well as 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.
I also wanted everyone to know that I am working on my second book. This one 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. Stay tuned to this space and I will let everyone know about my progress as I write this one. I’m about three chapters into it at this point and I know what I want to write. And now that life is settling down a little bit – at least it will as of the first of next month – I will have time to devote to just writing.
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, except that I charge $8 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, for those of you just tuning in.
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