A Dissertation Submitted to the Faculty of Science, University of the
Witwatersrand, Johannesburg, in fulfillment of the requirements for the
Degree of Master of Science in Polymer Chemistry. / The dissertation studies the synthesis, formulation development, crosslinking
and spectral characterisation of dehydrated castor oil poly(glyceryl
phthalate) alkyd resins for use as air-dry surface coating vehicles.
Synthesis of alkyd resins involves simultaneous dehydration, alcoholysis
and polyesterification reactions. Dehydration of castor oil is achieved in situ
under phthalic anhydride catalysis. Alcoholysis of dehydrated castor oil by
glycerol is also achieved in situ to form predominantly the monoglyceride.
Polyesterification of the resultant mono- and diglycerides is realised through
interaction with phthalic anhydride. The reaction is carried out at 280°C for
3 hours and at 225°C for 2 hours under azeotropic distillation with xylene.
The parent poly(glyceryl phthalate) alkyd resin is synthesized by reaction of
castor oil, glycerol and phthalic anhydride to a predetermined acid value.
Formulation development experiments were carried out to study the effect
of variations in the dibasic acid to polyol/oil and polyol to oil ratios on alkyd
resin properties. Model formulations exhibiting the best alkyd performance
were developed. Predictive model formulation equations were derived from
model formulation data and their limits of reliability and applicability
established. The formulation of water soluble alkyd resins is modified to
introduce pendant carboxylic acid groups along the polymer skeleton. Water
solubility is achieved by neutralisation of the residual pendant carboxylic
acid groups by 'fugitive' amines to yield water soluble alkyd soaps. The
effect of variations in the nature and level of incorporation of amine is
investigated. Alkyd resin solubilisation and resin acidity guide formulae were
studied and developed.
Cross-linking chemistry of alkyd resins, both in the reactor (gelation) and on
application (film formation) is investigated. Gelation manifested itself in two
different forms, thermoplastic and thermosetting. An important alkyd
constant, K, was established as an indispensable tool in control of
premature gelation and in the prediction of resin drying characteristics.
Autooxidation and solvent evaporation are the two competing curing
mechanisms encountered in film formation. The nature and influence of
each curing mechanism on the rate of cure and film characteristics is
highlighted. Catalysis experiments were conducted with metallic driers (Co2
Mn2 and Pb2} to bring the rate of drying of resin films to economically
feasible limits and catalyst addition levels were established.
New spectral characterisation techniques based on Fourier Transform
Infrared spectroscopy were investigated. An extensive study was carried out
on FT IR spectral data to establish qualitative and quantitative relationships
between transmission peak ratios and alkyd resin composition. Series
dependent and series independent correlation equations, useful in
quantifying alkyd resin components were derived. A new FT IR
spectroanalytic characterisation method for dibasic acids is proposed. The
method, if adopted, affords both qualitative and quantitative characterisation
of the dibasic acid component in the alkyd resin matrix and it is envisaged
the technique will supersede conventional methods in terms of speed and
simplicity.' / Andrew Chakane 2021
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/31338 |
| Date | January 1994 |
| Creators | Nzeru, Arnold. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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