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  • Writer's pictureNed Patton

Cellulose and Lignin – Our Wonderful Friends

They are in every plant, and are the most abundant organic polymers on the planet. And the wonderful part of that is that they are the most useful organic polymers in the plant kingdom to use as precursors for composites.

So, this week I am going to introduce everyone to these two wonderful long chain organic polymers and talk a little bit about what they are, how much of this stuff is around us, and how they can be used to make sustainable composites. But first, let’s see what these two plant polymers look like. First let’s take a look at cellulose.

This is a snippet from Wikipedia that shows that cellulose is basically a long chain sugar or polysaccharide. So, from sunlight, carbon dioxide and water, plants start by making glucose and then stick a whole bunch of glucose molecules together to make whatever they need – in this case cellulose. It actually isn’t quite that simple, but you get the message. Everything starts with carbon dioxide, water and sunlight.

In the image above the dark grey atoms are carbon, the red ones are oxygen, and the light gray or white ones are hydrogen. An actual cellulose molecule has on average a molecular weight on the order of 10,000, which is like nearly 1000 atoms of glucose all stuck together to make one long chain. And the chain ends up being straight because of the 6-sided rings which are all Benzene rings with one of the carbons replaced with an oxygen atom.

So, cellulose makes long strings that are very strong, so this is the string part of the plant’s string and glue composite material that we call wood or stems or leaves.

But, what is the glue part? Well, the other part of the plant that provides stiffness and strength to the cellulose fiber is lignin. It is also an organic polymer, but rather than being a long string of simple sugars tied together it is more of a network of phenols, so it is effectively an organic alcohol or what we would consider a phenolic compound. Here is something of what it looks like – again from Wikipedia. This is an idealized structure, but it does show how this stuff sticks together the cellulose fibers.

There are actually three different common varieties of lignin that plants make. The one shown in the pic above is from a softwood or conifer tree. The precursor to this is called “coniferyl alcohol”. The other two are “paracoumaryl alcohol” and “sinapyl alcohol”. Note all three of these are simple organic alcohols that start with phenol which is benzene with an O-H group attached to one of the 6 carbons.

So, this stuff is very much like the phenolic resins that were the first of the composite resins that started all of this reinforced plastic revolution that we call composite materials.

The major source of lignin in industry is from the paper making process where the lignin is removed from wood pulp to leave only the cellulose which is then bleached and processed into the paper that all of us write on or that goes through our printers. Wood that is ground up to use for paper has about 25% lignin and the rest is mostly cellulosic materials – the fiber that is used to make the paper. The lignin is therefore a waste product of the paper making industry, and is readily available to be used for composites.

So, what are composites researchers and companies that make composite precursors doing with cellulose and lignin? As it turns out quite a bit. Both of these materials are abundant and very inexpensive compared to petroleum. Lignin especially because it is a waste byproduct of the paper making industry is being studied intensively for making carbon fibers. That is because of the string of phenols (benzene rings) that make up lignin.

There is a group in Sweden that is actively working on wet spinning lignin and cellulose into long fibers that they can then pyrolyze into carbon fibers.(1) And while the mechanical properties of the resultant fibers are not as good as those made from polyacrylonitrile derived from petroleum, it is really more a matter of time before these materials become the norm for precursors for both carbon fiber and also the resins used to stick the fibers together to make a composite.

There are of course more groups working on this as I write this, and I would like to bring everyone’s attention to a new microsite being put together by Composites World that is intending to bring all of the work being done on composites sustainability to one place. The URL for that site is:

I will be talking more about sustainability of composites in future posts and maybe if there is enough interest I will focus more fully on issues and updates in composites sustainability in this space. So, stay tuned for the latest. And I also want everyone to know that I will be giving two talks at the Composites World sponsored Carbon Fiber Conference in Salt Lake at the end of this month. One is about sustainability of composites and the other has to do with the Titan tragedy, so if you’re interested please attend that conference. I’m certain that it will be worth your time.

That’s about enough for this week. Finally, for those of you that have not heard, my book has been published and is for sale. 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: And as usual, here’s a picture of the book, for those of you just tuning in.


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