The thickening mechanism of hydroxyethyl cellulose is to increase the viscosity through the formation of intermolecular and intramolecular hydrogen bonds, as well as hydration and chain entanglement of molecular chains. Therefore, the thickening method of hydroxyethyl cellulose can be divided into two aspects: one is the role of intermolecular and intramolecular hydrogen bonds. The hydrophobic main chain associates with the surrounding water molecules through hydrogen bonds, which improves the fluidity of the polymer itself. The volume of the particles reduces the space for free movement of the particles, thereby increasing the viscosity of the system; second, through the entanglement and overlapping of molecular chains, the cellulose chains are in a three-dimensional network structure in the entire system, thereby improving the viscosity.
Let’s look at how cellulose plays a role in 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 interaction of cellulose chains The lap entanglement forms a cross-linked network or separate area between the pigments, fillers and emulsion particles, which prevents settling.
It is the combination of the above two modes of action that enables hydroxyethyl cellulose to have a very good ability to improve storage stability. In the production of latex paint, the HEC added during beating and dispersing increases with the increase of external force, the shear velocity gradient increases, the molecules are arranged in an orderly direction parallel to the flow direction, and the lap winding system between the molecular chains is destroyed, which is easy to Sliding with each other, the system viscosity decreases. Since the system contains a large amount of other components (pigments, fillers, emulsions), this orderly arrangement cannot restore the entangled state of cross-linking and overlapping even if it is placed for a long time after the paint is mixed. In this case, HEC only relies on hydrogen bonds. The effect of water retention and thickening reduces the thickening efficiency of HEC, and the contribution of this dispersion state to the storage stability of the system is also reduced accordingly. However, the dissolved HEC was uniformly dispersed in the system at a lower stirring speed during letdown, and the network structure formed by the cross-linking of HEC chains was less damaged. Thus showing higher thickening efficiency and storage stability. Obviously, the simultaneous action of the two thickening methods is the premise of efficient thickening of cellulose and ensuring storage stability. In other words, the dissolved and dispersed state of cellulose in water will seriously affect its thickening effect and its contribution to storage stability.
Post time: Apr-25-2024