What does Dietary Fiber have to do with Composites?

So, I’ve talked a bit about Strings and Glues – aka Fibers and Resins – for Composites in previous posts in this newsletter. So, I thought this post I would chat a bit about what dietary fiber is and how it is connected (or not?) with composite materials. As in, what does dietary fiber have to do with composite string and glue or composite fibers and resins.

First, what is dietary fiber and why are there different types of dietary fiber. As it turns out, there is what is called “soluble” fiber, and “insoluble” fiber. Soluble fiber is dietary fiber that will dissolve in water. If you have ever taken chia seeds and put them in water, what you get is a sort of a gummy looking mixture. This gummy stuff is the soluble fiber that is in chia seeds. And, the wheat gluten that holds bread together is also a soluble fiber.

Insoluble fiber is stuff like the stringy part of a stalk of celery or the crunchy central vein in a leaf of romaine lettuce. You have to chew it up to swallow it, and it doesn’t dissolve in water. If it did, the lettuce leaf wouldn’t have any structure, and the celery stalk would be a limp, gummy mess. It is the insoluble fiber that gives plants their structure and holds the leaves together.

And, what’s a picture of a tree doing in a newsletter about dietary fiber and composite string and glue? Well, like I have said in previous posts, a tree is a wonderful example of Mother Nature being a clever engineer and using soluble and insoluble fiber to make her structures.

The insoluble fiber in a tree is the cellulose fiber that provides the structure to the tree. And, the glue that holds the tree together – lignin and sap – is actually a soluble fiber if we go by the dietary fiber definition.

Now, if you think we don’t eat cellulose, think again. Cellulose is the major component of the strings in celery and the ribs and parts of the leaf of romaine that we chew up in our lunch salads. And it is cellulose that makes up the majority of the cell walls in plants.

As for the soluble fiber, that’s the majority of the protoplasm of the plant cell that is inside of the cellulose casing that makes up a plant cell. That is in fact where the lignin and sap comes from, and it is also where the gummy, gooey stuff that chia seeds become comes from.

So, there you have it, when you eat a plant, you are eating some string and some glue. And most of it is pretty tasty. And, as long as the cellulose cell walls of the plant that you are eating aren’t as stiff as wood, you will probably be able to eat it and your gut will thank you for doing so.

I wanted to go on about this topic for a while, because composites have had a bit of a problem for some time, since both the majority of the high strength fibers (I’m thinking carbon fiber here) and nearly all of the resins that are used in the business have come from the petroleum business. And that means that they are definitely not “green”, nor is that business sustainable for the long term because at some point we are going to run shy of the raw petroleum to make these things.

That is why there is such a push now to move to natural fibers or fibers derived from natural sources of cellulose. It is also why there is an enormous research effort going on now to derive high performance resin systems – mostly epoxies – from entirely plant based sources. Once we make it to the point where composites are entirely made from plant based sources, we can make structural material for our modern existence as long as we can grow plants.

So, this is a good lead in to some of the next newsletters where I plan to talk in a little more detail about some of the work that is being done now to develop high performance resins for the composites industry entirely from plant based sources. There are a few success stories that I want to highlight that I didn’t cover in my original post on natural fibers and resins.

So, until then, and the next time you eat a salad or some broccoli, think about the string and the glue that you are eating and how they are the insoluble and soluble fiber that is in what you’re crunching up and feeding to all of those wonderful bacteria in your gut.