Crystallite Size in Natural Cellulose

Abstract

NATURALLY occurring long thin threads of cellulose, the so-called microfibrils, vary in width from about 100 Å in bacterial, most algal and all higher plants, to more than 200 Å in some marine algae (for example, Valonia and the Cladophorales). Two schools of thought have developed concerning the internal structure of microfibrils. Ranby¹, Preston² and Ellefsen et al.³ conclude from electron microscopy, qualitative X-ray analysis and various chemical treatments that each microfibril contains a single crystalline core, the same order of size as the microfibril. Although the smaller microfibrils, for example of higher plants, may well fasciate to give broader structures, the broad microfibrils of the exceptional seaweeds are not multiples of narrower fibrillar bodies. Frey-Wyssling and Mühlethaler^4–6 and Manley⁷, on the other hand, maintain that electron microscopical evidence points to the presence in microfibrils of linear bodies 35 Å wide which they call “elementary fibrils”. They conclude that the thickness of microfibrils differs in steps of 35 Å, dependent on the number of included elementary fibrils. The reliability of this evidence has already been called into question by Colvin⁸. We have attempted to resolve the controversy by determining crystal dimensions in a variety of microfibrils of different sizes in conditions closely resembling those in the living organism. Our findings, mostly using the method of X-ray high-angle line-broadening, but supported by low-angle scattering and electron microscopy, are presented here, and the details will be published elsewhere.