Microscopical Studies of Cottons Reacted in Vapor Phase

Morphological effects of the modification of cotton by vapor-phase treatments were studied by light and electron microscopy. Observations were made of etherified, grafted, and cross-linked cottons. The uniformity of reaction was followed by swelling whole fibers in cupriethylenediamine hydroxide (Cuene) solution and observing the swelling and dissolution along the length of the fiber. In addition, ultrathin sections were prepared and dissolution characteristics of the sections, after immersion in Cuene, were observed with the electron microscope. Observations of cotton cross-linked with methanol hemiformal in the presence of SO₂, in an open constant-volume reactor, gave indications that little reaction had occurred; reacted areas observed were at the periphery of the fiber. Samples of cotton cross-linked with vapors of paraformaldehyde, with formic acid as catalyst, appeared to be cross-linked throughout the fine structure of the fiber; when HCl or SO₂ was used as the catalyst in this reaction, peripheral crosslinking was observed. When fabrics were treated for long periods of time with formalin in the presence of SO₂, the reaction seemed to penetrate the entire structure of the fiber; after short periods of treatment it was peripheral. Large amounts of HCl with formalin resulted in some limited cross-linking of the fiber. When cotton was treated in a closed, constant-pressure reactor with formalin in the presence of SO₂, the cellulose was reacted throughout the fiber. Observations of a series of cottons impregnated with 2-hydroxyethyl carbamate exposed to butanol hemiformal vapor indicated that the degree of penetration of the cross-linking agent was dependent upon the length of time the samples were exposed to the cross-linking agent in the vapor phase. Examination of sections from cotton grafted with acrylic acid revealed that the material remaining after solution in Cuene was not fibrillar, but rather one of spongy character. Hydroxyethylation made the fiber sensitive to a dimethylolethylene urea (DMEU) cross-linking treatment.