The technical indicators of polyacrylamide are generally molecular weight, hydrolysis degree, ionic degree, viscosity, residual monomer content, so judge the quality of PAM can also be judged from these indicators!
01 Molecular Weight
The molecular weight of PAM is very high and has been greatly improved in recent years. PAM, which was used in the 1970s, had a molecular weight of millions. Since the 1980s, the molecular weight of most efficient PAM was more than 15 million, and some reached 20 million. “Each of these PAM molecules is polymerized from more than one hundred thousand acrylamide or sodium acrylate molecules (acrylamide has a molecular weight of 71, and PAM with one hundred thousand monomers has a molecular weight of 7.1 million).”
In general, PAM with a high molecular weight has a better flocching performance, with a molecular weight of 71 for acrylamide and 7.1 million for PAM containing 100,000 monomers. The molecular weight of polyacrylamide and its derivatives from hundreds of thousands to more than 10 million, according to the molecular weight can be divided into low molecular weight (below 1 million), middle molecular weight (1 million to 10 million), high molecular weight (10 million to 15 million), super molecular weight (more than 15 million).
The molecular weight of macromolecular organic matter, even in the same product is not completely uniform, the nominal molecular weight is its average.
02 Degree of hydrolysis and degree of ion
The ionic degree of PAM has a great impact on its use effect, but its appropriate value depends on the type and nature of the material treated, there will be different optimal values under different circumstances. If the ionic strength of the material treated is higher (containing more inorganic substances), the ionic degree of PAM should be higher, on the contrary, it should be lower. In general, the degree of anion is called the degree of hydrolysis. And ionic degree generally refers to cations.
Ionicity =n/(m+n)*100%
The PAM produced in the early stage was polymerized from a monomer of polyacrylamide, which did not contain the -COONa group. Before use, NaOH should be added and heated to hydrolyze part of the -CONH2 group to -COONa. The equation is as follows:
-CONH2 + NaOH → -COONa + NH3↑
Ammonia gas is released during hydrolysis. The proportion of amide group hydrolysis in PAM is called the degree of hydrolysis of PAM, which is the degree of anion. The use of this kind of PAM is not convenient, and the performance is poor (heating hydrolysis will make the molecular weight and performance of PAM significantly decreased), has been rarely used since the 1980s.
Modern production of PAM has a variety of different anion degree products, the user can according to the need and through the actual test to choose the appropriate variety, do not need to hydrolysis, after dissolution can be used. However, for reasons of habit, some people still refer to the dissolution process of flocculants as hydrolysis. It should be noted that the meaning of hydrolysis is the decomposition of water, which is a chemical reaction. The hydrolysis of PAM has ammonia gas released; Dissolution is only a physical action, no chemical reaction. The two are fundamentally different and should not be confused.
03 Residual monomer content
The residual monomer content of PAM refers to the content of acrylamide monomer in acrylamide polymerization into polyacrylamide in the process of incomplete reaction and ultimately residual in acrylamide products. It is an important parameter to measure whether it is suitable for food industry. Polyacrylamide is non-toxic, but acrylamide has some toxicity. In industrial polyacrylamide, it is hard to avoid residual trace of unpolymerized acrylamide monomer. Therefore, the content of residual monomer in PAM products must be strictly controlled. The amount of residual monomer in PAM used in drinking water and food industry is not allowed to exceed 0.05% internationally. The value of famous foreign products is lower than 0.03%.
04 viscosity
PAM solution is very viscous. The higher the molecular weight of PAM, the greater the viscosity of the solution. This is because PAM macromolecules are long, thin chains that have great resistance to moving through solution. The essence of viscosity is to reflect the size of the friction force in the solution, also known as the internal friction coefficient. The viscosity of the solution of all kinds of polymer organic matter is high and increases with the increase of molecular weight. A method to determine the molecular weight of polymer organic matter, is to determine the viscosity of a certain concentration of solution under certain conditions, and then according to a certain formula to calculate its molecular weight, known as “viscose average molecular weight”.
Post time: Jan-12-2023