The Morphology of Regenerated Cellulose

Abstract

The morphotogy of three different regenerated celluloses has been investigated using electron microscopy. Fortisan rayon consists entirely of microlihrils, ∼40-50 nm in width, which are usually aggregated into larger fibers. The sub structure of the microfibrils is a parallel array of protofibrils ∼1.5-4.0 nm in width. The cellulose regenerated from a solution of dimethylsulfoxide and paraformaldehyde (DMSO/PF cellulose) exhibits a predominaritly fibrous morphology, but the microfibrits are often less, perfect than those observed for Fortisan. In addition, unoriented mats composed of short rodlets (∼12 nm wide) are occasionaly observed. The cellulose regenerated fromhydrazine (N2H4/H2O cellulose) consists primarily of unoriented mats of rodlets and occasional fihers. Both the mats and fibers are shown to be assemblies of the rodlets. High-magnification micrographs of the latter suggest that they are tiny cellulose crystals of approximate dimensions 2 × 6 × 25 nm. The differences observed in the morphology of the three regenerated celluloses are thought to be more a result of the processing conditions than the chemistry of the regeneration. The morphology of Fortisan is consistent with extended chains, althuugh chains having long, irregular fold periods are also a possibility. The morphologies of the UMSO/PF cellulose and N2H4/H2O cellulose are consistent with chain-folded crystallites, in which case the fold period would be ∼25 nm.