| Summary: | Dissertation (Ph.D.)--Stellenbosch University, 2001. === ENGLISH ABSTRACT: Self-emulsifiable and self-assembling nano-particle phosphated and siloxane-modified
polyurethane dispersions, for use in metal coatings, were synthesised from a new
phosphate monomer, a carboxylate monomer, a polysiloxane macroglycol and a
. cycloaliphatic diisocyanate, and characterised.
Crosslinked nano-particles of acrylic-modified, self-assembling, phosphated polyurethane
dispersions with better water swell resistance were obtained using the phosphated nanoparticles
as the 'seed' to polymerise monofunctional and multifunctional acrylic monomers
in the dispersed phase. This was done by reacting 2-hydroxyethyl methacrylate end-capped
polyurethane with monofunctional and multifunctional acrylate monomers in the dispersed
phase.
Phase inversion of the polyurethane resin from an organic solvent into dispersion was
accompanied by three stages, as studied by viscosity and conductivity measurements.
In an attempt to modify existing synthesis procedures of the traditional polyurethane
acrylic dispersions for which organic solvents are used, polymerisable acrylic monomers
were used as diluents during the urethane-forming reaction. This resulted in overcoming
the limitations of the existing process.
Particle-size analysis indicated that the above dispersions had smaller particle sizes,
narrower distributions and better hydrophobicity than any reported to date. Aqueous vinylterminated
phosphated polyurethane dispersions were studied for their viscosity behaviour
under shear and showed Newtonian behaviour.
The polyurethane dispersions were evaluated for their hydrolytic stability with respect to
the location of the ionic groups on the segments. Greater hydrolytic stability was obtained
when the ionic groups were on the urethane hard segment. The polyurethane dispersionsresponded well to UV curing, a curing technique that has not received much attention to
date.
The surface and interface analyses of the self-assembling coatings obtained from the
phosphated and siloxane-modified polyurethane dispersions showed increased silicon
enrichment at the coating/air interface and phosphorus enrichment at the metal/coating
interface. Results of dynamic contact angle studies proved the poor wettability of the
coatings, as shown by the increase in contact angle by probe liquids.
Dynamic thermogravimetry studies of the phosphate-containing polyurethanes showed a
decrease in activation energy with increasing phosphate content. This is a good indication
that phosphate-containing polyurethanes could be used as fire retarding coatings that
comply with fire limit regulations. === AFRIKAANSE OPSOMMING: Self-emulgeerbare en selfsamestellende, nanopartikel, fosfaat- en siloksaanbevattende
poliuretaandispersies, vir gebruik as deklae vir metale, is gesintetiseer en gekarakteriseer.
Die uitgangstowwe vir die ~ bereiding was 'n splinternuwe fosfaatmonomeer, 'n
karboksilaatmonomeer, 'n polisiloksaanglikol en 'n siklo-alifatiese diisosianaat.
Deur die polimerisasie van die monofunksionele en multifunksionele akriel-monomere in die
dispergeerde fase in te ent met die fosfaat-bevattende nanopartikels, is kruisgebinde
nanopartikels van akrielgemodifiseerde, selfsamestellende, fosfaatbevattende poliuretaandispersies
met goeie waterswelweerstand berei. Dit is bewerkstellig deur poliuretaan,
met reaktiewe hidroksietiel-endgroepe, te reageer met monofunksionele
akrilaatmonomere in die gedispergeerde fase.
Fase-omkering van die poli-uretaanhars uit die organiese oplosmiddel, tot in dispersie, het in
drie stappe plaasgevind. Dit is bepaal deur viskositeit en konduktiwiteit.
Bestaande metodes van sintese Vir tradisionele poli-uretaanakrieldispersies, waarvoor
organiese oplosmiddels gebruik is, is gewysig om die beperkinge van die bestaande metodes
te oorkom. Suskes is behaal met die gebruik van polimeriseerbare akrielmonomere as
verdunningsmiddels in die uretaanvormingsreaksie.
Partikelgrootte-analises het getoon dat die verkreë dispersies kleiner partikelgroottes, nouer
verspreidings en beter hidrofobisiteit gehad het as enige wat tot dusver beskryf is. Die
viskositeit van die wateroplosbare, vinielgetermineerde, fosfaatbevattende poliuretanandispersies
is onder afskuiwing bepaal en het Newtoniese gedrag getoon.
Die hidrolitiese stabiliteit van die poli-uretane, met betrekking tot die posisie van die ioniese
groepe in die segmente, is bepaaL ..Die polimere met die ioniese groepe in die harde segment
van die poli-uretaan het hoër hidrolitiese stabiliteit vertoon. Kruisbinding (verharding) deur middel van UV, wat tot dusver min aandag geniet het, was
baie suksesvol.
Analises van die oppervlakte en die tussenvlak van die selfsamestellende deklaag, wat van
die fosfaat- en siloksaanbevattende dispersies berei is, het verhoogde siloksaanverryking by
die deklaag/lug tussenvlak en verhoogde fosfaatverryking by die metaal/deklaag tussenvlak
getoon. Resultate van dinamiese kontakhoekstudies het bewys dat die deklae swak benat is,
dws daar was 'n toename in die kontakhoek deur peilvloeistowwe.
Termogravimetriese studies het getoon dat daar 'n afname was in die aktiveringsenergie van
die fosfaatbevattende poli-uretane met 'n toenemende fosfaatinhoud. Hierdie feit dui daarop
dat hierdie poli-uretane moontlik as brandvertragende deklae gebruik kan word.
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