Water-absorption characteristics of organic-inorganic composite superabsorbent polymers and its effect on summer maize root growth

摘要

Adding inorganic materials in SAPs to synthesize organic-inorganic composite superabsorbent polymers (OICSAPs) can effectively improve salt-tolerance, gel strength, thermal stability, and water retention. However, most researches mainly focus on synthesizing process optimization and new multifunctional products, lacking reports on how ions affected water-absorption characteristics and mechanism of OICSAPs and its influence on summer maize root growth. On the basis of these, we set up laboratory experiments and field cultivation experiment, using environmental scanning electron microscopy (ESEM) and fractal theory to study the questions above. Results show that OICSAPs have better salt-tolerance, while cations and concentration affected its water-absorption characteristics significantly. With higher cation valence, larger ionic radius, and concentration, its water-absorption rate reduced remarkably as Na ~+ < K ~+ < Mg ~(2+) < Ca ~(2+) < Fe ~(2+) < Fe ~(3+) < Al ~(3+) < Cu ~(2+), while the effects of anions could be neglected. The OICSAPs presented typical honeycomb membrane-like 3D crosslinked network structure, but Ca ~(2+), Mg ~(2+), Fe ~(2+), Fe ~(3+), Al ~(3+), and Cu ~(2+) would damage the structure (Cu ~(2+) with the most significant effect) in local microdomain, and changed the complexity of pores. In the experiment, higher concentration could reduce water-absorption rate without changing micromorphological characteristics. Applying OICSAPs will reduce total length, surface area, and volume of summer maize root, while promoting absorbing and transmitting ability by larger root diameter and the proportion of root <0.5 cm. All these results will provide a theoretical basis on application, marketing, and product development of OICSAPs.