Polyester Polyol includes conventional polyester polyols, polycaprolactone
polyols and polycarbonate diols, which contain ester groups or carbonate groups,
but in fact, polyester polyols usually referred to are composed of dicarboxylic
acids and dicarboxylic acids. Polyester polyol obtained by polycondensation
reaction such as alcohol.
Polyester polyol is one of the main raw materials of polyester polyurethane. According to whether it contains a benzene ring, it can be divided into aliphatic polyol and aromatic polyol. Among them, the aliphatic polyol is mainly adipic acid polyester diol.
The preparation of polyester polyol adopts batch method.
The first stage combines polyols (ethylene glycol, propylene glycol, diethylene glycol, trimethylolpropane, pentaerythritol, 1,4-butanediol, etc.) with dibasic acids (phthalic acid, adipic acid, Halogenated phthalic acid, etc.) or acid anhydride (phthalic anhydride, etc.) are esterified and polycondensed at 140-200°C, and the top temperature of the fractionation tower is controlled at 100-102°C, and most of the side-effects produced are removed by atmospheric pressure. After the product water, keep it at 200～230℃ for 1～2h, at this time the acid value has generally been reduced to 20～30mg KOH/g.
In the second stage, vacuum is applied, and the degree of vacuum is gradually increased, and the trace water and excess glycol compounds are removed under reduced pressure, so that the reaction proceeds in the direction of generating low acid value polyester polyol, which can be called "vacuum melting method". Inert gas such as nitrogen can also be continuously introduced to bring out water, which is called "carrier gas melting method". It is also possible to add an azeotropic solvent such as toluene to the reaction system, and use a water trap to slowly take out the water generated when toluene is refluxed. This method is called "azeotropic distillation".
Different varieties of polyester polyols have different properties due to different types or different preparation processes. Several important indicators for polyester polyols are hydroxyl value, acid value, moisture, viscosity, molecular weight, density, and color. .
Polyester polyols are not classified as dangerous goods. The materials of storage and transportation containers can be carbon steel, aluminum, stainless steel, polyethylene or polypropylene. Liquid polyester will occasionally appear turbid in long-term storage at low temperature. This phenomenon can be eliminated by heating at about 80°C for a short time without affecting the quality. Polyester polyols are easy to absorb moisture, so the moisture in the atmosphere should be avoided in storage and transportation. In order to reduce the reverse reaction, the temperature should not exceed 120°C. The product should be stored in a sealed barrel that is insulated from air at room temperature, or stored in a container heated at 70-110°C and filled with nitrogen.
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