Friday, April 12, 2013

Solvent Spun Rayon: Prof Turbak's view of the early history (Part 1)

Prof. Alban Turbak did ground-breaking work on the dissolution of cellulose during the 1970's while with ITT Rayonier.  As he mentions in this extract of his introduction to non-NMMO cellulose dissolution methods in Regenerated Cellulose Fibres, his 1977 "Solvent Spun Rayon" book  provided one of the stimulii for research work to begin at Courtaulds.  His definition of these fibres as "reconstituted" rather than "regenerated" no longer figures in the nomenclature.

Ever since the discovery of the xanthate process by Cross and Bevan in 1892 and its commercialization in the early 1900’s there have been many efforts to dissolve cellulose directly in non-aqueous solvents which would be both easy to use and readily recoverable. The viscose process produces good quality films and fibers. However, by the mid 1970’s pollution problems and price competition from synthetic films and fibers had seriously eroded the cellophane and rayon markets. In order to remain commercially competitive it was necessary for rayon and cellophane producers to seek simpler less polluting processes.

In the mid 1970’s I.T.T. Rayonier decided that to preserve their pulp markets it would be in their best interest to take the lead in trying to find new ways to make rayon. To their credit, Rayonier’s management authorized a multi-million dollar research effort which ran for a period of 7 years at the I.T.T. Rayonier Eastern Research Division Laboratories. The overall goals were to develop new direct cellulose solvent systems which would require lower investment costs and be readily recovered and recycled in closed loop non-polluting systems.

In order to identify potential previously examined solvent candidates an extensive literature search was made covering 80 years of cellulose solvent reports A close examination and evaluation of these reports from a physical organic viewpoint led to a review paper which, for the first time, delineated all cellulose solvent systems into four simple categories.(1) Subsequently, several other solvent system reviews have been reported (2,3) Rayonier reported some of their preliminary results at an American Chemical Society symposium in New Orleans in 1977.(4) As a result of Rayonier’s stimulus other companies and research universities undertook cellulose solvent research projects.

Concurrently, Franks, McCorsley and Varga at the American Enka Corp were deeply involved in evaluating N-Methyl Morpholine-N- Oxide (NMMO).(5). The Enka NMMO technology was subsequently pursued by Courtaulds in England. As is now well known, Courtaulds’ Tencel® NMMO solvent spun cellulose fiber technology is now a major commercial success and solvent spun cellulose films for food packaging are currently under intense investigation. Tencel® lyocell is actually not a regenerated cellulose fiber but, rather, is a reconstituted cellulose fiber since it was never derivatized.

1. Turbak, A.F., Hammer. R.B., et al, Cellulose Solvents, CHEMTECH, 10,51-57, Jan. 1980
2. Hudson, S.M., and Cuculo, J.A., The Solubility of Unmodified cellulose: A Critique of the Literature, J. Macromol. Sci.,18, (1) 1-82,1980
3. Johnson, D.C., Solvents for Cellulose, Cellulose Chemistry and its Applications, Ellis Harwood, Ltd., Chinchester, 1985
4. Turbak, A.F., Solvent Spun Rayon, Modified Fibers and Derivatives, ACS Symposium # 58, Amer. Chem. Soc., Washington, D.C., 1977
5. Franks, N.E., McCorsley, C.C., and Varga, J.K., U, S. Patent 4,142,913 March, 1979; U.S. Patent4,196,282 April, 1980

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