This section studies and compares 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 (2σ) 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.
|Advisor:||Herr, Daniel J.C.|
|Commitee:||Ryan, James, Wei, Jianjun, Zheng, Lifeng|
|School:||The University of North Carolina at Greensboro|
|Department:||Nanoscience and Nanoengineering|
|School Location:||United States -- North Carolina|
|Source:||DAI-B 80/06(E), Dissertation Abstracts International|
|Subjects:||Polymer chemistry, Nanoscience, Nanotechnology|
|Keywords:||Additive, FRSP, Kinetics, Map, SAP, Synthesis|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be