| In this investigation the roles structural factors play in governing absorbency in air-laid nonwoven webs were examined. Key parameters evaluated were the fluid transport coefficient (specific permeability), the driving force through pores (capillary pressure), and the pore volume (web thickness). Because the webs deform during absorbency, it was necessary that these parameters were assessed during the fluid imbibition period. To facilitate this, specimen cells were designed and built for the Gravimetric Absorbency Testing System (GATS) on which the tests of absorbency were carried out.; The experimental work involved the manufacturing of webs by the air-laying method, needle punching these webs under different conditions, and measuring the absorbent properties on GATS. The webs contained blends of two different fibers, one hydrophobic and the other hydrophilic. The fibers used were polyester, polypropylene, regular rayon, cross-linked rayon, and a superabsorbent fiber. The structure of web was varied further by varying the denier of fiber, the cross-sectional shape of fibers, the intensity and depth of needle penetration, and the pressure under which tests were performed. The fluids used were salines of three different concentrations.; The results showed that all variables of the study produced significant effects. An interesting observation made was that the webs containing superabsorbent fiber behaved very differently from webs containing other fibers. Although the former gave much higher fluid holding capacity than the latter, due to much greater swelling and higher gel strength, it also showed the lowest rate of absorbency, due to gel blocking of the pores. It is shown that the behavior of webs containing regular hydrophilic and hydrophobic fibers can be modelled using modification of the capillary and creeping flow theories of Hagen Poiseuille and d'Arcy. This is an advance over the work of Washburn, whose model has been used extensively in describing absorbency in textiles. The results found with application of the Washburn model are highly qualitative as the predictive values are at least an order of magnitude greater than the values found in practice. Application of the above theories to web containing significant fraction ({dollar}>{dollar}10%) of superabsorbent fibers was not successful. It is assumed that the behavior of the latter was controlled significantly by a diffusion process and to model it diffusion theory, perhaps in combination with capillary flow theories, needed to be utilized. |
