Modification of the Cuticle and Primary Wall of Cotton by Corona Treatment

Abstract

Transmission electron microscope studies of the surface of air-corona and air-chlorine corona treated cotton fibers reveal essentially no topographical changes. Air-chlorine coronas apparently modify the wax, causing increased wettability, and C-chlorination occurs in about one of every three carbon atoms in the cuticle. About one half of the chlorine that reacts with cotton is covalently bonded to carbon in the wax, the remainder to nonextractable constituents of the cuticle or the primary wall. The secondary wall remains essentially unchanged by corona treatment as indicated by tenacity, crystallinity, solubility in cupriethylenediamine hydroxide, iodine uptake, and moisture regain (the latter may be marginally decreased). Increased accessibility of the fiber interior or secondary wall component to swelling reagents such as caustic, and yarn setting reagents such as benzyltrimethylammonium hydroxide, indicates that corona treatments modify the surface layer or primary wall in such a way as to weaken it and possibly to increase its permeability. However, marginally diminished regain and unchanged iodine sorption values do not support such conclusions. Corona treated cotton exposed to an electron beam develops cracks several thousands of angstroms deep, parallel to the spiral ridges— further evidence of a weakened surface layer. Potential practical applications of corona treatmemt are indicated by improved mercerization, better yarn stretch and setting properties, increased dyeability, and the localized heating indicated by the generation of free radicals which may make possible heat-induced localized polymerization.