<p> High molecular weight poly(ethylene oxide) (PEO) is used in conjunction
with a cofactor such as phenol formaldehyde resin (PFR) as flocculants for
newsprint manufacture. The objectives of the work described in this thesis were
to prepare flocculants superior to PEO and to determine the flocculation
mechanism. A series of novel comb copolymers consisting of a polyacrylamide
backbone with short pendant poly(ethylene glycol) (PEG) chains was prepared
and characterized. Additionally, polymerization conversion curves and reactivity
ratios were measured. An interesting finding was that the reactivity of the
macromonomer in free radical copolymerization decreased with PEG chain
length. </p> <p> Flocculation results with both model latex dispersions and commercial
wood pulp suspensions showed that copolymer chain length was the most
important variable ; molecular weights greater than 3 million were required for
good flocculation. On the other hand, the PEG pendant chains could be as short
as 9 ether repeat units. Also, only 1 to 2 PEG chains for every 100 acrylamide
backbone moieties were required. </p> <p> No published flocculation mechanisms could predict all the behaviors of the PEO or copolymer system. A new mechanism called complex bridging was
proposed. According to this mechanism PEO or copolymer chains aggregate in
the presence of cofactor to form colloidally dispersed polymer complex which
heteroflocculates with the colloidal particles. </p> <p> Given in this work is the first explanation of the requirement for extremely high PEO or copolymer molecular weights for flocculation. It is proposed that polymer chains with molecular weights less than 106 collapse in the presence of
PFR to an inactive precipitate before flocculation can occur whereas complexes
based on very high molecular weight PEO collapse slowly enough to permit
flocculation. </p> <p> Published mechanistic studies are hindered by the fact that PFR has
poorly defined structures. It is shown for the first time in this work that welldefined,
linear, poly(p-vinyl phenol) (PVPh) is an effective cofactor. </p> / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/19534 |
| Date | 12 1900 |
| Creators | Xiao, Huining |
| Contributors | Pelton, Robert H., Hamielec, Archie E., Chemical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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