Morphology and tensile properties of acrylic fibers with different manufacturing histories have been investigated. Acrylic fibers that have been partially drawn undergo appreciable plastic deformation after passing through a yield point and exhibit "crazing" over the entire surface. On the other hand, acrylic fibers that have been fully drawn and annealed display no yield point or crazing and have a lower modulus and con siderably reduced elongation-to-break. SEM photomicrographs of tensile fractures in dicate that the former acrylic fibers show a straight fracture along a transverse section, while the latter invariably fail by axial splitting. The morphological structure of acrylic fibers develops and is perfected as a consequence of the manufacturing process, which alters the fibers' response to applied tensile stress.
SynopsisA better understanding of internal microstructure is necessary to understand various prop erties 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 asseased 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 twephase structure for acrylic fibers.
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