A comparison study of superabsorbent polymer with microwave - assisted polymerization and free radical solution polymerization: synthesis, kinetics, and applications

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Michael M. Azad (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site: http://library.uncg.edu/
Daniel Herr

Abstract: This purpose of this research is to compare the formation kinetics of two approaches to synthesizing crosslinked polyacrylic acid (x-PAA) superabsorbent polymers (SAP). Specifically, it tests the applicability of the reported general rate expression for free radical solution polymerization to the synthesis of x-PAA SAPs via Microwave-Assisted Polymerization (MAP) and Free Radical Solution Polymerization (FRSP). This study of FRSP and MAP formation kinetics of x-PAA superabsorbent materials provides predictive models and new foundational insights into the rate-limiting steps for these three-dimensional polymerization reactions. These foundational models, based on the observed results from the designed kinetic studies, may help to guide and enable the design of new networked polymers with enhanced functional properties. The published complex mechanism of PAA polymerization, which was assumed to explain the kinetics of superabsorbent polymerization, does not seem to be valid in FRSP and MAP synthesis of PAA SAPs. In fact, for these kinetic studies, the data supported none of the initial hypotheses for all the data in a given reaction. For the FRSP, only a sequential kinetic model, i.e., zero-order followed by the first order in monomer model explains the observed data. For the MAP PAA SAP syntheses, several sequential kinetic models may explain the observed data. A first-order model supports the first-half-reaction, and a zero-order model explains the second-half-reaction. So overall, the key findings show that one cannot conclude with 99% confidence (2s) the existence of a single zero or first-order kinetic process over the entire reaction for each type polymerization, i.e., MAP or FRSP. However, there are regions of sequential zero-order and/or first-order kinetics that explain the dominant mechanistic modes for both types of polymerizations. The MAP reaction, due to its rapid nature, enables a much more uniform distribution of inert material, such as clay, that can be achieved with the FRSP process. Percolation theory provides a way to understand why these interconnected channels help to enhance the movement of a liquid through the PAA SAP’s gel network. This theory could explain why a clay containing polymer made with the MAP process exhibits higher and more consistent permeability than a corresponding system synthesized via the FRSP reaction.

Additional Information

Language: English
Date: 2018
Additive, FRSP, Kinetics, MAP, SAP, Synthesis
Addition polymerization

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