Celebrating 100 years of the CELL Division
The CELL Division is now more than 100 years old! To both celebrate this longevity and to document the history of the worldwide community of cellulose and renewable materials, a detailed presentation has been created by Gary Patterson, as overall editor, and many members of CELL, a Division of the ACS. In this 11-part series, we will cover the evolution of cellulose and CELL division over the last 100 years. While such an endeavor must be inherently incomplete, it is hoped that the simplified story will still capture the “Soul of CELL”.
Cellulose in the 17th and 18th Centuries
Brave souls emigrated from England to North America in search of religious and political freedom. But, the Massachusetts Bay Company was a commercial enterprise. It was important that the new society be financially viable. One of the most attractive aspects of New England was the almost unlimited supply of trees. They allowed the Colonists to construct ships that could compete in the Atlantic trade. But, ships require more than just wood. One of the most enterprising souls in 17th century New England was John Winthrop, Jr., FRS (1606-1676). He learned from the Native Americans how to harvest and process “pine knots” into good tar. He presented this knowledge to the Royal Society of London in a fashion appreciated by the Natural Historians of this august body. The Royal Society appreciated the importance of renewable materials, especially ones based on cellulose!
Cellulose in the 19th Century
“En effet, il y a dans les bois le tissue primitive isomere avec l’amidon, que nous appellerons cellulose, et de plus une matiere qui em remplit les cellules et qui constitue la matiere ligneuse veritable.” Key conclusion of Dumas and the Academie des Sciences (Dumas, 1839)
One of the “by-products’ of cotton ginning is the “linters,” the small strands produced by removing the seeds. A new use for this “raw material” was discovered by Christian Schoenbein (1799-1868). He spilled a mixture of sulfuric and nitric acid on a cotton apron, and as the “product” dried, it burst into flame! Highly nitrated linters were called “guncotton.” As originally formed, it was very dangerous and often exploded unexpectedly. Formulations that were safer were based on gelatinized gun cotton that was extruded into Cordite. When this substance exploded it did not produce the black soot associated with ordinary gun powder, and hence was called “smokeless.”
While this chance discovery eventually revolutionized warfare, the scientific fallout was even greater. Early research established that many nitrocelluloses could be produced. Atomic analysis of the most highly nitrated forms established that up to three nitrate groups could be created per carbohydrate unit. But, it was not known that cellulose was a polymer! Completely nitrated cellulose was not stable and forms with as little as one nitrate per unit were found. Some chemists decided that it was better to consider cellulose to be a tetramer: C24H40O20. Then, up to 11 nitrate groups could be added. The ultimate scientific study of nitrocellulose was reported in the Journal of the American Chemical Society in 1901 by George Lunge (1839-1923) of the ETH Zurich. By adjusting the conditions of nitration, he isolated samples with from 1 to 11 nitrate groups per C24 unit. (No one ever isolated an actual molecule of C24H40O20.)
In addition to determining the atomic composition of cellulose nitrates, Lunge measured the solubility in a standard 2/1 ether-alcohol solvent. Samples with intermediate nitration were almost completely soluble in this mixture. The ability of creating homogeneous solutions of cellulose nitrate revolutionized the applications of this substance. It is called “collodian” in the trade.
The importance of this work for cellulose science cannot be overestimated. Although the results were reported in terms of a cellulose subunit of C24H40O20, Lunge acknowledged that the ultimate size of a cellulose molecule must be much larger. He also looked at his nitrocellulose under the polarizing microscope. The existence of colors for insoluble material is an indication of crystallinity. Actual cellulose fibers are polycrystalline and the “white” color comes from light scattering. Smaller crystals can produce colors due to refraction.
While industrial manufacture of gun cotton was characterized by trade secrets, Lunge’s work was published in the open literature. He revealed all the actual chemistry and materials science of the material and explained the least cost method of obtaining the desired product. The thorough scientific study of this complicated system remains valid today.
Further progress in the understanding of cellulose required a more detailed level of understanding of the atomic structure of sugar oligomers. The key figure in this history is Jacobus van’t Hoff (1852-1911, Nobel 1901). In his classic book, Chemistry in Space (1875), he explained the chiral nature of sugar moieties and adopted a full three dimensional model for molecules. Another major figure in this effort was Emil Fischer (1852-1919, Nobel 1902). He synthesized and explained all 18 hexoses. The model of the two forms of glucopyranose remains true today.
Dimers of glucose are also capable of forming different molecules. Two of the most important forms are maltose and cellobiose. Polymers of maltose are called starch; those based on cellobiose are called cellulose! There were still many aspects of cellulose structure to be determined, and there were many experimental techniques that needed to be invented. But, with the work of these world famous chemists, a sound basis for cellulose science had been created. These developments also illustrated how progress in industrial chemistry can facilitate the realization of fundamental issues that can be pursued by academic chemists with both precision and breadth.
Cellulose used for fabrics was improved greatly by John Mercer (1791-1866, FRS, FSC). He subjected cotton fabric to treatment with caustic soda, the process now called “mercerization.” The attempt to provide a detailed understanding of mercerized cotton continues today. The original patent is from 1850: “For improvements in the preparation of cotton and other fabrics and fibrous materials. Textile science has always been a part of CELL and remains so today. Mercer is a good example of a cellulose scientist. He was the most knowledgeable inorganic chemist of his age, even though he never even went to secondary school. He was able to converse with the academic chemical community at a level that earned him Fellowship in both the Royal Society and the Chemical Society. He combined his encyclopedic knowledge of calico printing with a dogged pursuit of both technological success and coherent understanding.
Pure cellulose is “insoluble” in pure water, but it does adsorb water and can transport it by capillary action. One of the goals of cellulose technology in the 19th century was to find a “solvent” that would dissolve cellulose and allow it to be processed in the fluid state. One of the great stories in cellulose history is the discovery and development of “Viscose.” It is documented in the classic book by C.F. Cross (1855-1935) and E.J. Bevan (1856-1921): Cellulose: An Outline of the Chemistry of The Structural Elements of Plants with reference to their Natural History and Industrial Uses (1910).
While cellulose binds a limited amount of water, the overall structure is retained, and the individual molecules do not separate into fully solvated entities. Some change in the conditions at the pyranose level is required to promote solubilization. One of the simplest solvents is concentrated(40%) aqueous zinc chloride. Cross and Bevan were sophisticated enough to understand the role of charge in the solubilization of aqueous solutions. Apparently, pyranose units can bind zinc to produce a polyelectrolyte. This will decompose the cellulose crystals and allow discrete polymers to exist in solution. Another important solvent for cellulose is created from concentrated ammonia and cupric oxide. This solution was eventually used to study the molecular weight of native cellulose. But, the most famous solution associated with Cross and Bevan was created with alkali cellulose and carbon disulfide: “Viscose.” It is called cellulose xanthate. After the solution has been homogenized, the native cellulose can be regenerated in many ways to yield the desired product. This regenerated cellulose is much more “active” in both chemical reactions and in processing.
While extremely pure cotton is essentially pure cellulose, and the finest Swedish filter paper has almost no residual ash, such expensive raw materials cannot be used for mundane purposes. The most abundant source of inexpensive cellulose is trees. But, separating the cellulose from the raw wood was a major problem. An early leader in this industry was Benjamin Chew Tilghman (1821-1901).
In 1867 he patented a process to separate the lignin and other non-cellulose components of soft-wood pulps (US Patent 70487). The heartwood was chipped and suspended in a solution of calcium bisulfite and excess sulfur dioxide at elevated temperatures (150oC) and contained in a pressure vessel. The recovered solid material is mostly cellulose, but also contains other carbohydrates and impurities. It is still colored and is used to make “brown paper.” Further processing often includes bleaching and extraction with organic solvents to produce a white cellulose, suitable for high quality paper.
One of the branches of this diagram outlines the process of wood distillation. During the ancient process of making charcoal, the early exhalations of the pile are merely discarded until the dehydration of the remaining carbohydrate to produce charcoal is started. Lee Fred Hawley (1882-1959) of the Forest Products Laboratory in Madison, Wisconsin published a detailed account of Wood Distillation. Now the full benefit of the wood could be obtained, including fuel for the overall process. The industrial process of wood distillation was scaled up to enormous size and very little documentation existed before Hawley. The wood was loaded into large metal retorts mounted on an overhead conveyor belt. During the volatile products phase, both tar and pyroligneous acid were obtained. These could also be further refined to produce acetates and alcohols.
CELL division has always been a vibrant mixture of industrial, engineering and fundamental scientific activities. This arose because the worldwide cellulose community contained a critical mass of people devoted to its success and future. This remains the case today.
Coming up soon
A survey of human activities that were important in the late 19th century, when the American Chemical Society was formed.