3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Synthesis, development and characterisation of dehydrated castor oil poly (glyceryl phthalate) alkyd resins(1994) Nzeru, Arnold.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.'