Thermal and microbial degradation of alginate-based superabsorbent polymer

Abstract

In this study, an alginate-based superabsorbent polymer (SAP), alginate- graft-poly[acrylamide- co-(itaconic acid)- g-(acrylic acid)] or Alg- g-P(AM- co-IA- g-AA), was prepared to examine its thermal and microbial degradation properties through Thermogravimetric Analysis (TGA), and soil supernatant test (with and without added nutrient) and soil burial test, respectively. The TGA thermogram of the SAP showed three degradation steps. The first degradation step was due to the thermal degradation of alginate and decomposition of the functional groups of PAM, PIA and PAA; whereas the second degradation step occurred as a result of the decomposition of PAM, PAA and PIA chains. Further decomposition of PIA contributed to the third degradation step. Among all the soil samples [tropical forest soil (TF), former tin mine lake soil (TM), peanut farm soil (PF), indigenous microorganism soil from an organic vegetable farm (OF), and oil palm plantation soil (OP)] tested, OF soil degraded the polymer sample most effectively, with the highest weight loss of 82.6% (with added nutrient) and 82.8% (without added nutrient) in soil supernatant tests, and 63.5% in soil burial test. Morphological observation under an Illuminated Stereo Microscope showed some holes and weak topographical spots on the surface of the polymer material after it had been incubated in OF solution for 40 days. Meanwhile, the intrinsic viscosities, [ η], of NaAlg and the Alg-based SAP solutions were 2.62 and 2.75 respectively.