VAE emulsions are environmentally friendly products. Vinyl groups are embedded in the polyvinyl acetate molecular chain, giving the polymer emulsion a low film-forming temperature and excellent film-forming properties. They exhibit strong adhesion to difficult-to-adhere materials such as PET, PVC, PE, and PP. The polymer film produced is very water and weather resistant. It also holds up well to scrubbing and remains flexible even at low temperatures. The thickness of VAE emulsions is impacted by a number of things.
1. Effect of Solids Content on Viscosity
We conducted extensive testing on the formulations and process conditions of VAE Emulsion DA-180L and VINNAPAS 400, respectively. The data in the following tables are derived from these tests. The relationship between solids content and viscosity is shown in Table 1.
As shown in Table 1, higher solids content increases viscosity. This is because higher solids content increases the number of colloidal particles in the same emulsion mass, reduces the amount of aqueous phase, and increases the total surface area of the particles. This enhances interparticle interactions and resistance to motion, resulting in higher viscosity.
2. Effect of Protective Colloids on Viscosity
In emulsion polymerization, protective colloids are often used as emulsion stabilizers to improve emulsifier stability and adjust viscosity. The emulsion stability of partially hydrolyzed PVA is also related to the distribution of acetyl groups on the polymer chain. A higher degree of blockiness in the acetyl group distribution results in greater surface activity, better emulsion stability, and smaller and more viscous emulsions. The higher the PVA degree of polymerization, the higher the viscosity of the polyvinyl alcohol aqueous solution before polymerization, and the higher the viscosity of the VAE. The higher the degree of alcoholysis of PVA, the lower the viscosity of the VAE. PVA's protective colloid ability increases with increasing degree of polymerization. Low-degree PVA forms coarser latex particles and has lower viscosity. An increase in the degree of polymerization improves both the protective and dispersing capabilities. To maintain the dispersion and protective properties of PVA during emulsion polymerization, while only adjusting the viscosity, the total amount of PVA is typically kept constant, with only the ratio between the two adjusted. With other conditions remaining unchanged, adding 4.54 kg of PVA Polyvinyl Alcohol 088-20 will increase the viscosity of each batch by 100 mPa·s. Table 2 lists the molecular weight and molecular weight distribution of high- and low-viscosity VAE emulsions.
Table 2 shows that the low-viscosity emulsion has a higher molecular weight, coarser particles, and a wider particle size distribution than the high-viscosity emulsion, resulting in lower viscosity.
3. Effect of Initial Initiator on Viscosity
The initiator has a main influence on the speed of polymerization. The more initiator is used, the faster the polymerization reaction is, and the reaction is difficult to control. After the polymerization conditions and the type of initiator are determined, the amount of initiator can be used to adjust the molecular weight of the polymer. The more initiator is used, the smaller the molecular weight of the polymer is, and the viscosity of the emulsion increases, and vice versa. Among them, the amount of initial initiator (ICAT) added has the greatest impact.
These data clearly show that the more initial initiator is added, the higher the viscosity of the emulsion. This is because the more initial initiator is added, the more difficult the monomer is to react or the reaction rate is slow in the initial stage, and the resulting polymer has a smaller molecular weight, smaller particle size, and higher viscosity.
4. Conclusions
(1) The higher the solid content of the emulsion, the greater the viscosity.
(2) The higher the degree of polymerization of the protective colloid PVA, the greater the viscosity of the emulsion, and vice versa.
(3) The viscosity of the emulsion when PVA is used as a protective colloid is higher than that when cellulose or surfactant is used as a protective colloid.
(4) With the same degree of polymerization, the higher the degree of alcoholysis, the lower the viscosity of the emulsion.
(5) The more initial initiator and total amount of initiator added, the higher the viscosity of the emulsion.
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