Ever wondered why paper beats rock in a game of roshambo? It turns out that cellulose nanocrystals (CNC) derived from wood pulp extract can be used to create one of the strongest materials known to man. Out-toughing even Kevlar and carbon fiber, the material is lightweight, cheap, and abundant. Found in forest by-products such as sawdust and wood chips, CNC could be used to create materials with applications in military defense, engineering, medicine, and consumer products.
The Forest Products Laboratory branch of the US Forest Service has granted $1.7 million towards a pilot plant that will work on the production of cellulose nanocrystals (CNC). One of the most abundant compounds on earth, cellulose can be found in the cell walls of plants and bacteria. Made up of long chains of glucose molecules, cellulose fibers are arranged in a matrix that provides support and strength to everything from a clover leaf to a giant sequoia. Held together by lignin (an easily degraded polymer), cellulose can be extracted from wood byproducts through pulping for use in the production of nanocrystals.
Once the plant material is pulped and rinsed of lignin, the cellulose fibers and water that remain can then be utilized in a process that breaks down the fibers even further into nanofibrils. These extremely small pieces of cellulose are a thousand times smaller than the original fibers. Once they reach the nanofibril stage, the cellulose takes on the form of a three-dimensional stack of unbranched glucose molecules held together by hydrogen bonds. Closely packed next to one another, the glucose molecules are positioned even tighter in their crystalline structure with the help of some strong acid to dissolve the spaces between them.
Currently, the yield for CNC from wood pulp is around 30 percent and it costs about $10 per kilogram to produce. It is hoped that the price could come down to around $1-2 per kilogram when produced on a large scale. CNC has a tensile strength rivaled only by carbon nanotubules, a material that costs almost 100 times more to make.
Of course, CNC is not perfect – it’s biggest drawback lies in how it deals with water. While the hydrogen bonds between the molecules are too strong to simply be dissolved by H2O, the cellulose can become disordered when wet. Since hydrogen bonds with water, a drop can potentially turn CNC into a water-loving substance, soaking up the stuff like a paper towel. This could reduce the strength and greatly increase the weight of the CNC while jostling its microscopic make-up. Researchers exploring ways to develop CNC are striving to overcome its shortcomings with moisture by either adding it to devices that do not come in contact with water, or altering its surface chemistry to repel the molecules.
The Forest Products Laboratory is optimistic that the new plant based in Madison Wisconsin will support the establishment of a new CNC industry, potentially creating a number of jobs and contributing $600 billion to the US economy by 2020.
Lead photo by EMSL