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Analysis of the reasons for the influence of different hydroxyethyl cellulose addition methods on the emulsion paint system:
The thickening mechanism of hydroxyethyl cellulose is through the formation of intermolecular and intramolecular hydrogen bonds, as well as hydration and chain entanglement of molecular chains to achieve high JIA viscosity.
The thickening method of hydroxyethyl cellulose is divided into two aspects:
One is the role of intermolecular and intramolecular hydrogen bonds. The hydrophobic backbone and surrounding water molecules associate through hydrogen bonds, as shown in Figure 1 (left), which increases the fluid volume of the polymer itself and reduces the space for particles to move freely. , Thereby increasing the viscosity of the system;
The second is to make the cellulose chain present a three-dimensional network structure in the entire system through the entanglement of molecular chains, thereby achieving an increase in viscosity.
Let's look at how cellulose affects the storage stability of the system:
First, the role of hydrogen bonds restricts the flow of free water, plays a role in water retention, and contributes to preventing water separation;
Second, the overlapping and entanglement of the cellulose chains forms a cross-linked network structure or independent area between the pigments and fillers and the emulsion particles, which plays a role in preventing sedimentation. It is the combination of the above two modes of action that makes hydroxyethyl cellulose have a good ability to improve storage stability. In the production of latex paint, the HEC added during beating and dispersion increases with the increase of external force and the increase of the shear rate gradient. The molecules are arranged in an orderly parallel to the flow direction, and the lap winding system between the molecular chains is destroyed, which is easy to Sliding with each other is manifested as a decrease in the viscosity of the system. Because the system contains a large number of other components (pigments, fillers, emulsions), this orderly arrangement cannot restore the entangled state of crosslinking and lap even after the paint is left for a long time. In this case, HEC only relies on hydrogen bonding The role of water retention and thickening, so that the thickening efficiency of HEC is reduced, and the contribution of this dispersion state to the storage stability of the system is correspondingly reduced. However, the dissolved HEC is evenly dispersed in the system at a lower stirring speed when the paint is let down, and the network structure formed by the cross-linking of the HEC chain is less damaged. Thus showing higher thickening efficiency and storage stability. Obviously, the simultaneous action of the two thickening methods is the prerequisite for efficient thickening of cellulose and storage stability. In other words, the dissolution and dispersion state of cellulose in water will seriously affect its thickening effect and its contribution to storage stability.
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