Preparation
Based on the different raw materials used in the synthesis of alkyd resins, the preparation methods of alkyd resins can be divided into the fatty acid method and the alcoholysis method.
Fatty Acid Method
The raw material used in the fatty acid method is fatty acid. Since polyols, polyacids, and fatty acids are miscible, the reaction can proceed in a homogeneous state. Therefore, when preparing alkyd resins using the fatty acid method, polyols, polyacids, and fatty acids can be directly mixed together for reaction.
Alcoholysis Method
Since polyols, polyacids, and vegetable oils are immiscible, direct mixing will result in phase separation, with one phase being a mixture of alcohol and acid, and the other phase being vegetable oil. If they are allowed to react directly in a phase-separated state, the alcohol and acid will react to form polyester, while the vegetable oil hardly participates in the reaction. It will gel after polymerization to a certain extent, so direct mixing for reaction is not possible. To allow the reaction to proceed in a homogeneous state, the alcoholysis method must be used. Alcoholysis is performed first, followed by esterification. That is, the vegetable oil and polyol are first transesterified into monoglycerides through alcoholysis, and then a polyacid is added for esterification. The fatty acid method offers greater formulation selectivity than the alcoholysis method, allowing for the use of various fatty acids in the reaction; however, the reaction apparatus is prone to corrosion and costs are higher. The alcoholysis method uses vegetable oils directly, resulting in a wider availability of raw materials and lower costs. Furthermore, the structures of the resins produced by the fatty acid method and the alcoholysis method differ, necessitating a rational selection based on specific circumstances.
Uses
Alkyd resins are used as vehicles in exterior house paints, marine paints, and baking enamels. Molded alkyd resins are used for electrical components, distributor caps, encapsulation, and a variety of similar applications.
Definition
A thermosetting coating polymer, chemically similar to polyester resins, conventionally made by condensation and polymerization of a dihydric or polyhydric alcohol (ethylene glycol or glycerol) and a polybasic acid (phthalic anhydride), usually with a drying oil modifier. The process requires heating at 230–250C for up to 12 hours. A new and quite different method utilizes epoxy addition polymerization, in which a mixture of glycidyl esters and organic acid anhydrides is heated with a metallic catalyst at 100C or less for only 2–4 hours. Cost and energy savings and improved application performance are realized by this process.
