Abstract
Acrylic polymer is a superabsorbent for water and widely used in diapers, in which its swelling behavior can be significantly affected by several factors, i.e., the time, temperature, pH, and salt concentration, and thus the product performance in the applications. In this work, the water absorption behavior of acrylic superabsorbent polymers by each of these individual factors was investigated. The results showed that the water absorbency increases with the pH in the range of 2 to ~7 and decreases when the pH continues to increase. However, it decreases with the increases in NaCl concentration in the solution. Moreover, more water can be absorbed by the acrylic polymers at the higher temperature. Based on a previously developed kinetic swelling model and the information from the above investigations, a semiempirical model for predicting the swelling behavior of superabsorbent polymers (SAPs) under different conditions has been developed. Data showed that the model can predict (with a relative error of <4.5%) the amount of water absorbed by acrylic SAPs under different swelling conditions. The model would be very helpful to the practical application in both product design and its performance evaluation.
Highlights
Acrylic superabsorbent polymers (SAPs) are materials with hydrophilic networks that retain huge amounts of water or aqueous solutions, up to 100,000% their own weigh
Modern diapers are typically composed of fluff pulp, acrylic SAP materials, and other materials making up the nonwoven sheets [3, 4]
Three models have been developed to describe the kinetics of swelling of acrylic SAPs; i.e., a second-order equation [16, 18,19,20], a power function of Fickian diffusion and Case II transport [16, 21, 22], and a Voigt-based viscoelastic model [23]
Summary
Acrylic superabsorbent polymers (SAPs) are materials with hydrophilic networks that retain huge amounts of water or aqueous solutions, up to 100,000% their own weigh. Because of the variation of urine’s salt ions and pH and temperature in the micro environment (between the skin and diaper), it affects the actual water absorption behavior of acrylic SAPs and the product’s performance in applications [1, 7,8,9]. The comprehensive information of these variables on the swelling behavior of acrylic SAPs would be very helpful to the polymer synthesis/control, product design, and the performance evaluation in the diaper-related applications. There is a need to have a model that can accurately predict the swelling behavior of SAP materials
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