Aqueous polyuethane (PU) colloids, like many other water-borne polymer
colloids, have become an increasingly important class of materials in the surface
coating industry. Three processing stages, the pre-dispersion, dispersion and postdispersion
stages, are generally involved in the production of aqueous PU colloids.
However, existing researches have neglected the importance of the dispersion stage.
The present study aims to develop better understanding of the dispersion stage during
the production of aqueous PU colloids. Non chain-extendable PU pre-polymer (PUp)
is used to enable independent study of the dispersion stage and the phase inversion
process is chosen due to its widespread industrial usage.
Valid drop size characterisation techniques and phase inversion detection
methods have been developed in this project. Three different dispersion regions have
also been identified by changing the ionic group content of PUp. Each dispersion
region is associated with a particular dispersion type. Those are (I) Stable aqueous
emulsions that contain small PUp-in-water drops. They were produced using PUp
with more than 0.2 mmole/g of ionic groups. (2) Aqueous PUp colloids with 0.05 ~ 0.2 mmole/g of ionic groups. These emulsions contain a mixture of drop structures,
including simple drops and different multiple drops. (3) Aqueous PUp dispersions
containing less than 0.05 mmole/g of ionic groups. These dispersions are not stable
and the resultant dispersions separated when agitation was stopped. Modified phase
inversion maps are introduced to represent the occurrence of all three dispersion
regions. The modified phase inversion maps are partly analogous to those of
conventional non-ionic-surfactant-water (nSOW) systems. The three dispersion
regions have also been "reproduced" successfully using external surfactants as
substitutes for the internal stabilising groups. A new catastrophic phase inversion
mechanism is proposed to explain the existence of all three dispersion regions. Other
variables studied during this project include different neutralising agents. different
amount of carboxylic acid groups, operating temperatures and material addition rates.
In conclusion, this project shows that the phase inversion process is a feasible
route for producing aqueous polymer dispersions with little or no added external
surfactants. Stable PUp-W dispersions can also be produced below the minimum ionic
group content reported in existing literatures.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.