Characterization of a Polypropylene/Super-Absorbent Web by NMR Diffusion Studies

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Abstract
Super-absorbent fiber has the property of absorbing moisture up to several thousand times its original weight, undergoing significant expansion, and eventually becoming a gel. The hydrophilic super-absorbent fiber is usually blended with hydrophobic polymer fiber to form a polymer web with the ability to attract fluid and also to hold it under pressure. Because of the confining influence of pore boundaries on molecular translation, restricted diffusion measurements on fluids in porous systems, such as the super-absorbent web, contain important information about the pore morphology. In this work, we studied the diffusion of water in a web of super-absorbent polyacrylate and polypropylene fiber. We observed restricted diffusion of the water by means of the pulsed-field-gradient spin-echo (PFGSE) NMR technique. Several mathematical models were used to interpret the data and yield estimates of the gross pore dimensions and the surface-to-volume ratio of the pores.