Polyacrylamide synthesis is a typical free radical polymerization, monomer acrylamide is a, β unsaturated amine, with two active centers (a vinyl group and an amine group), the elementary reaction can be divided into: Chain initiation, chain growth and chain termination reactions. In addition to the three elementary reactions, it is often accompanied by a chain transfer reaction, which terminates the growth of the molecular chain. Therefore, acrylamide can react with a variety of compounds to produce many derivatives of polyacrylamide, and these street organisms have a variety of properties, such as flocculation, thickening (thickness), surface activity and so on. Polyacrylamide products can be divided into three categories according to ionic form, nonionic, anionic and cationic.
The interaction between non-ionic polyacrylamide and rubber compound HSiO; depends on hydrogen bonding.
The action mechanism of the polyacrylamide double electric layer is based on the coagulation physics theory, focusing on the electrostatic effect of inorganic salts on colloidal particles, compressing the diffusion layer, reducing the zeta potential, thereby reducing or eliminating the repulsive potential energy peak, and causing the colloidal particles to agglomerate. It focuses on neutralizing colloidal particle charge destabilization, ignoring the charge change sign and re-stabilization. The adsorption bridging mechanism focuses on the strong adsorption between the colloidal particles and the polymer. The adsorption bridging promotes particle aggregation and flocculation. These two effects reflect the typical effects of coagulation and flocculation, in practice the two are often inseparable.
According to the above-mentioned flocculation mechanism, a polymer structure can be obtained, which has an important influence on the flocculation process, such as relative molecular mass and its distribution, ionization, molecular shape, etc.
Many studies have pointed out that HPAM has the largest flocculation effect when the degree of hydrolysis is 3%. The higher the relative molecular mass, the greater the flocculation capacity. PAM and HPAM studies on clay flocculation show that the relative molecular mass is less than (1 ~ 3) x 10* Except for independence, the effect is very poor, and when the relative molecular mass is equal to (7~13) x 10*, the flocculation effect can be increased by 2~8 times compared with the former. However, as the relative molecular mass increases, the range of the optimal effective addition amount becomes narrower, which will bring difficulties to the application. Especially for the sludge dewatering rate, it decreases with the increase of the relative molecular mass after the maximum value appears. Many works have pointed out that the relative molecular mass may not always be higher and more favorable.
The effect of the relative molecular mass distribution of the flocculant on the flocculation effect shows that the high molecular weight fraction in the product plays a leading role in flocculation. When the added amount is below the optimal dosage range, the dispersion of the low relative molecular mass fraction is not obvious; when the added amount is greater than the optimal dosage range, the low relative molecular mass fraction will play a role in dispersion protection. In addition, in order to achieve a high turbidity removal rate, for low-molecular-weight products, the dosage range will increase as the relative molecular weight increases. After a certain limit, the relative molecular weight will increase and the dosage range will decrease, so the overall situation will be It is advantageous that the relative molecular mass distribution is wider. For some occasions (such as drilling fluids treated with HPAM), deliberately choose low and high relative molecular masses that differ widely
The compatibility of HPAM, and the application of narrow distribution (such as HPAM for paper reinforcement) are special technical needs. When the average relative molecular mass is equivalent, long straight-chain macromolecules have better flocculation ability than branched-chain macromolecules.
Since Lamer proposed the adsorption bridging model, the theoretical research on the role of polymer flocculants has not made much progress so far, but there is much work in combination with practical applications. Practice has shown that the flocculation process is complicated, and the structure and performance of the polymer also change a lot. The two are combined-there are many factors that need to be carefully analyzed and studied, such as the hydrophilic-lipophilic ratio of the polymer flocculant. , Temperature, the influence of inorganic salts on the morphology of macromolecules (in turn affecting the role of macromolecules), the influence and utilization of magnetism, the exclusive adsorption of functional groups on macromolecules to certain objects, etc. These aspects are all receiving attention and research. . These works will promote the continuous development and improvement of polymer flocculation theory, and lead to the emergence of some new flocculants and flocculation technologies, such as heat-sensitive flocculants and magnetic flocculation.