Semidry synthesis of the poly(acrylic acid)/palygorskite superabsorbent with high-percentage clay via a freeze-thaw-extrusion process

摘要

A problem with the synthesis of polymer/clay composites is the poor compatibility between clay and polymers; this is particularly bad for those with a high percentage of clay. In response, we introduced a freeze-thaw-extrusion process before polymerization to make the best use of the high activation ability of acrylic acid (the monomer) and the exceptional hydration of palygorskite (clay). This processing was powerful for facilitating clay dispersed into the nanoscale and for obtaining good compatibility with the polymer, even for those polymers with high clay contents. The experiment showed that the quality of the consequent superabsorbent was improved significantly. As the dispersion was worked out perfectly by the freeze-thaw-extrusion process, we further explored the effect of the system water content on the water absorptivity of the consequent composite. With synthesis by the improved system, the water absorbency still amounted to 98.2 g/g in a 0.9 wt % NaCl solution for the composite with 35 wt % clay, whereas the water content (55 wt %) was much less than that of general synthesis (ca. 95 wt %). Scanning electron microscopy showed that the composite had a rich pore structure in the range of several hundred nanometers, and the palygorskite was distributed perfectly in the composite on the nanoscale. Fourier transform infrared spectroscopy gave further direct evidence for the reaction between the clay and polymer.