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Thickener thickening mechanism
Release Date:2014-03-27     Source:      Authoradmin
Cellulosic thickener thickening mechanism of the main chain is hydrophobic and the surrounding water molecules through hydrogen bond , the polymer increases the volume of fluid in itself , reduce the space freely movable particles , thereby increasing the viscosity of the system . Viscosity increase can be achieved by molecular chain entanglement , in the performance of a high static and low shear viscosity of the low viscosity at high shear . This is because the static or low shear rate, the cellulose molecular chains in a disordered state and the system exhibits a high viscosity ; while at high shear rate , for molecules parallel to the flow direction of the ordered easily slide against each other , so that the system viscosity decreased .
 Polyacrylic acid thickener thickening mechanism of the thickener is dissolved in water , electrostatic repulsion by sex carboxylate ions , the molecular chain of the helical rod-like extension , thereby increasing the viscosity of the aqueous phase . In addition it by bridging between latex particles and pigments form a mesh structure , increasing the viscosity of the system .
 Made a detailed study of associative polyurethane thickeners AJ Reuvers thickening mechanism of associative polyurethane thickeners . Introduced in the molecular structure of such thickeners hydrophilic group and a hydrophobic group , it exhibits the nature of a surfactant . When its concentration exceeds a certain concentration of the aqueous solution to form micelles, micelles and polymer particles to form a network structure associated enable the system to increase the viscosity . A number of micelles with other molecules , reducing the mobility of water molecules, so that the viscosity of the aqueous phase is improved. Not only to produce such coatings thickener rheological behavior , but also the latex particles are present between the adjacent interaction , if this is too strong , it is easy to cause emulsion layers.
 Bentonite is an inorganic layered silicate thickeners , flocculent material expands to form the absorbent , has good suspension and dispersion, the amount of water in combination with a colloid in water to release the charged particles , increasing large system viscosity.
 Characteristics of various types of thickeners and selection
 High thickening efficiency of the cellulose thickener of a cellulose thickener , especially a thickened aqueous phase ; fewer restrictions on the paint coatings are widely used ; large pH range can be used. But there is poor leveling , roller spatter phenomenon when more bad stability, susceptible to microbial degradation and other shortcomings. Since it is a low viscosity , low shear and static high viscosity under high shear , so the coating is completed , the viscosity increases rapidly to prevent sagging, but on the other hand cause poor leveling. Studies have shown that an increase in the relative molecular mass of thickeners , latex paint spatter increases. Cellulose thickener due to the large molecular weight, so easy to produce spatter. Such thickeners are through the " fixed water" thickening effect is achieved , little pigment and latex particles adsorbed thickener aqueous phase fills the volume expansion , the pigment and latex particles suspended pushed aside , prone to flocculation so poor stability. Because it is a natural polymer , susceptible to microbial attack.
 Polyacrylic thickener polyacrylic thickener with strong thickening and better leveling and good biological stability, but the pH-sensitive , water resistance is poor.
 Associative polyurethane thickeners such associative structure damage under the action of shear viscosity decreases when shear viscosity can be restored to disappear , the construction process to prevent sagging .
 And it has a certain viscosity recovery lag conducive leveling coating . Relative molecular mass of polyurethane thickeners ( thousands to tens of thousands ) is much lower than the previous two types of thickeners relative molecular mass ( several hundred thousand to several million ) , will not contribute to splash. Highly water soluble cellulosic thickeners may affect the water resistance of the coating film , but having a hydrophilic group and a hydrophobic polyurethane thickener molecules and hydrophobic groups of the base film has a strong affinity , can enhance the water resistance of the coating . Because latex particles are involved in the association , no flocculation, a smooth coating can thus have higher gloss. Many polyurethane associative thickener performance than other thickeners , but because of its unique mechanism of thickening micelles , thus the components in the coating formulation that will inevitably impact on the generation of micelle thickening . When this type of thickener used , should fully consider the impact of various factors on the thickening properties , not easily replaced emulsions used in paints , defoamers, dispersing agents , film-forming additives .
 Inorganic thickener thickening aqueous bentonite thickener with strong , good thixotropy wide range of pH values to adapt , good stability . But because the bentonite is an inorganic powder , good absorption , can significantly reduce the surface gloss of the coating , matting agents play a similar role . Therefore , the use of bentonite in bright latex paint , pay attention to controlling the dosage. Nanotechnology realized inorganic nano particles , but also gives some new properties of inorganic thickeners.
 Cellulose ether thickener used its derivatives, alkali-swellable associative thickener and polyurethane thickeners . ( A ) cellulose ethers and their derivatives : cellulose ethers and their derivatives are mainly thickeners hydroxyethyl cellulose, methyl hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, methyl hydroxypropyl based cellulose. Hydrophobically modified cellulose was introduced on a small amount of cellulose hydrophilic matrix hydrophobic alkyl chain length , thus becoming the associative thickener , its thickening effect can be much larger relative molecular mass of cellulose ether thickener varieties quite . ( 2 ) an alkali swellable thickeners : alkali swellable thickeners are divided into two categories: non- alkali swellable associative thickeners and alkali swellable associative thickener .
 ( 3 ) a hydrophobically modified polyurethane thickeners and non- urethane thickener : polyurethane thickener is a hydrophobically modified ethoxylated urethane group of water soluble polymers are nonionic associative thickeners . Environmentally friendly development of associative polyurethane thickeners has received wide attention , in addition to linear associative polyurethane thickeners described above , as well as comb associative polyurethane thickeners .
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