Micromorphology of Macromolecular Superabsorbent Polymer and its Fractal Characteristics

摘要

Superabsorbent polymer (SAP) can absorb a solution of 10-folds to 1000-folds as much as its own weight. Its micromorphology directly affects its water absorption mechanism and absorption characteristics. In this work, we selected three types of polymer products for research analysis: KH (sodium polyacrylate-type), HLM (polyacrylamide-type), and AS (polyacrylamide-kaliumcrylic acid-crosslinking-copolymer-type). The environmental scanning electronic microscope (ESEM) method and the fractal theory are applied for studying the micromorphology of the three types of SAPs. The results show that KH possesses the highest water absorption multiplying factor and HLM possesses the lowest one. Under the condition of repeated water absorption and water release, the structure of FILM hydrogel transfers from gridding membrane to network structure. Various types of cation solutions significantly affect the characteristics of micromorphology of HLM hydrogel, and both uniqueness and diversity prevail. Under the condition of repeated water absorption and water release, the swelling multiplying factor of HLM in deionized water abides by an "inverted U" distribution. The water absorption multiplying factor for the third time is the largest one. This is primarily caused by both reduction of resilience of crosslinking network and dissolution of polymer on the surface of hydrogel under the condition of repeated water absorption and water release. The boundary of hydrogel pore network of the three types of SAPs possesses fractal characteristics. The number of fractal dimensions is as follows: fractal dimension of HLM < fractal dimension of AS < fractal dimension of KH. With the increase of the number of repeated water absorption and water release, the number of fractal dimensions of cross-sectional pore boundary reduces, that is, T1 (1.3848) > T3 (1.2100) > T5 (1.1226).