Effect Of Epoxy Soybean Oil On Water Resistance Of Waterborne Polyurethane Adhesive Film
Effect of epoxy soybean oil on water resistance of waterborne polyurethane adhesive film
In the process of preparing anionic waterborne polyurethane, due to the introduction of hydrophilic groups so that the water resistance of polyurethane film decreased, through the epoxy soybean oil in the internal cross-linking of polyurethane molecular chain formed part of the cross-linking structure, and the introduction of long chain hydrophobic chain segment, improve its water resistance, solvent resistance performance. Each epoxy soybean oil molecule has ~4 epoxy group, which can form some cross-linked reticular structure with-nco reaction, and improve the overall performance. When the content of epoxy soybean oil increased, the crosslinking degree of polyurethane system increased, and the mechanical properties and water resistance of waterborne polyurethane increased. However, the introduction of cross-linked structure will cause the early viscosity of the system to increase too quickly, prone to the formation of gel phenomenon.
Fig. 3 is when the content of Dmpa is 5%, the water absorption rate of waterborne polyurethane film varies with the content of epoxy soybean oil. It is shown that the water absorption rate of polyurethane film is greatly decreased with the increase of epoxy soybean oil content. This is because with the increase of the amount of epoxy soybean oil, the crosslinking degree of polyurethane molecular chain increases, the greater the crosslinking degree, the more difficult the water molecule to penetrate into the plastic film, so the water absorption rate is reduced, the resistance of the film is significantly improved. But the amount of epoxy soybean oil is too large, will cause the prepolymer viscosity increase, the operation is inconvenient, the emulsification is difficult, can not get the stability emulsion with finer particle size. When the amount of epoxy soybean oil reaches more than 8%, it is very easy to gel in the process of Prepolymer. Therefore, the amount of epoxy soybean oil should not be too large, to 4%~6% as well.
Effect of 2.4 Epoxy soybean oil on adhesive properties of waterborne polyurethane adhesives
Epoxy soybean oil has cross-linking effect on polyurethane, epoxy soy oils molecule contains 3~4, epoxy base can react with isocyanate, improve the crosslinking degree of polyurethane molecule, and improve the cohesion of waterborne polyurethane.
Table 2 The effect of the dosage of epoxy soybean oil on the adhesive properties of waterborne polyurethane adhesives.
As can be seen from table 2, the T-peel strength increases with the increase of the amount of epoxy soybean oil, and then decreases. This is because epoxy soybean oil improves the crosslinking degree of polyurethane molecular chain, the cohesion of the adhesive is increased, and the adhesion strength of the adhesives is increased, but with the increase of the amount of epoxy soybean oil, the Prepolymer emulsification is difficult and the stability of the emulsion decreases, which leads to the decrease of the adhesive strength of the polyurethane adhesive. On the other hand, due to the addition of epoxy soybean oil, the viscosity of waterborne polyurethane adhesive is decreased, which is beneficial to the wetting of the substrate and the adhesive strength of waterborne polyurethane adhesives. To sum up, when the epoxy soybean oil content is 4%~6%, the polyurethane adhesive bonding ability is better.
T-peel strength is a measure of the bonding strength between layers of composite films. In order to ensure that the composite film is not stratified, the peel strength of interlayer adhesion shall not be lower than 100n/m. It can be seen from table 2 that when the dosage of epoxy soybean oil is 4%~6%, the peel strength of waterborne polyurethane adhesive to different films is greater than 100n/m, which shows that the adhesive can be used for bonding of various composite film materials.