Synthesis of waterborne polyurethane resin crossli

2022-07-31
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Synthesis of oxidative crosslinked waterborne polyurethane resin (Part 2)

3.3 alcoholysis of vegetable oil and selection of process conditions

in the presence of catalyst, the hydroxyl group and carboxyl group of vegetable oil are redistributed between vegetable oil and glycerin to form glycerol monoester and glycerol diacid. This reaction is reversible. When the reaction reaches equilibrium, the composition of the system, in addition to the product, vegetable oil and glycerin also coexist in it. Considering the subsequent polymerization reaction, only glycerol monoester is the intermediate of dihydroxy functional group, which can be gradually polymerized with diisocyanate to form linear polyurethane resin; Glycerol diacetate is a monohydroxy functional body, which can only produce low molecular weight compounds when reacting with diisocyanate. However, a small amount of glycerol diacetate can be used as a molecular weight regulator in the synthesis of polyurethane resin. Glycerol is a trihydroxy functional body. If the content of glycerol in the system is too high in the experimental process, cross-linking may occur in the polymerization stage. The presence of a small amount of glycerol is conducive to increasing the molecular weight of the polymer and improving the viscosity of the system; The existence of vegetable oil will affect the water solubility of the resin system and the stability of the water-soluble body. According to the reversible reaction characteristics of vegetable oil alcoholysis, through the reasonable selection and control of alcoholysis process conditions, the composition of the alcoholysis end system is mainly glycerol monoester, a small amount of glycerol and glyceric diacid are allowed, and the amount of vegetable oil is as small as possible. Alcoholysis process conditions can be selected according to table 1:

Table 1 alcoholysis process conditions of vegetable oil

normal> Oil: glycerol (mol)

normal> flax oil: tung oil (mol)

normal> catalyst lioh

normal> reaction temperature

normal> reaction time

normal> monoglycerate content%

normal>1:2.5

normal>2:1

normal> 0.04% of the oil content

normal>220 ℃ ~ 240 ℃

n/p>

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