Effect of comonomer content and annealing on morphological changes in acrylic copolymers and fibers

A better understanding of internal microstructure is necessary to understand various properties of acrylic fibers, such as dyeability, mechanical properties, and comfort. In the present paper, the application of x-ray methods for the investigation of fiber microstructural parameters, namely, crystallinity and crystallite size, is demonstrated. Effect of comonomer incorporation on acrylic copolymer microstructure is assessed in the present work. Influence of annealing aftertreatment on the changes in structure is investigated using the evidence presented by x-ray and DSC studies. Introduction of small amounts of a comonomer (methyl acrylate, MA) results in diminishing crystallinity. Annealing of acrylic copolymers causes the onset of an intramolecular cyclization, as well as an increase in segmental mobility; both these factors lead to an increase in crystallinity and crystallite size. With increasing comonomer content, the exothermic peak in the thermogram is found to shift toward higher temperatures. Some evidence is presented that shows the effect of spinning process variables on acrylic fiber microstructure. The results and findings of the present work have been interpreted in terms of a two-phase structure for acrylic fibers.