Alkyd resins quality control

FIGURE 2-17. Contribution of molecular weight to polymer properties, (a) Molecular weight distribution profile of a typical polymer. (b) Quality control of an alkyd resin. It was determined that a good paint resulted only when the ratio of the peak heights was between 0.6 and 0.8. Detector refractive index. 

Quality control in the manufacture of alkyd resins involves appropriate rapid tests to determine the acid number, viscosity of solutions of known concentrations in mineral spirits or xylene (Gardner-Holdt viscosity tubes used for comparison), color (Gardner 1933 Color Standards), and cure time. A target range 2-5 units above the acid number units of gelation is desirable. Most manufactured alkyd resins have an acid value (number of mg of potassium hydroxide required toneutralize 1 gm of resin) of less than 15. 

Higher quality, higher performance alkyds are produced in the fatty acid process where the composition of the resulting resin can be more precisely controlled. In this process the following are combined and cooked together until the product has achieved a predetermined level of viscosity. 

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