How to identify the pros and cons of polyacrylamide?

 

At present, the domestic PAM market is relatively chaotic, adulteration is quite common, manufacturers, dealers each solemnly promise that their products are 100% pure goods, but how much is trustworthy?

So how should identify the pros and cons of polyacrylamide, how to spend money to spend worth, buy value for money products?

1. Basic indicators of PAM

Before resolving the quality of polyacrylamide, the molecular weight of polyacrylamide, degree of hydrolysis, ionic degree, viscosity, residual monomer content and other technical indicators are described.

The molecular weight

The molecular weight of PAM is very high and has been improved greatly in recent years. PAM, used in the 1970s, has a molecular weight of several million. After 80's, the molecular weight of most efficient PAM is more than 10 million, some reach 12 million. Each of these PAM molecules is composed of more than 100,000 acrylamide or sodium acrylate molecules polymerized (acrylamide molecular weight 71, containing 100,000 monomer PAM molecular weight 7.1 million), generally, the higher molecular weight PAM flocculation performance is better.

Polyacrylamide and its derivatives molecular weight from hundreds of thousands to more than 10 million, according to the molecular weight can be divided into low molecular weight (less than 1 million), molecular weight (1 million ~10 million), high molecular weight (10 million ~15 million), supermolecular weight (15 million). The molecular weight of a polymer organism is not completely uniform even within the same product; the nominal molecular weight is its average.

Degree of hydrolysis and ionic degree

The ionic degree of PAM has a great influence on its use effect, but its appropriate value depends on the type and nature of the material to be treated, there will be different optimal value under different circumstances. If the ionic strength of the processed material is higher (including more inorganic materials), the ionic degree of PAM should be higher, otherwise it should be lower. Usually, the degree of anion is referred to as the degree of hydrolysis. And the ionic degree generally refers specifically to the cation. Ion = N /(M + N)*100%, the early production of PAM is a monomer polymerization of acrylamide, the original does not contain -Coona group. Before use, heat with NaOH to hydrolyze part of the -ConH2 group into -Coona, and the reaction formula is as follows: -ConH2 + NaOH -→ -Coona + NH3↑. Ammonia is released during hydrolysis. PAM amide group hydrolysis ratio is called PAM degree of hydrolysis, it is anion degree. This kind of PAM is not convenient to use, and the performance is poor (heating hydrolysis will make PAM molecular weight and performance significantly decreased), has been rarely used after the 1980s.

Modern production of PAM has a variety of different anionic degree of products, users can choose the appropriate variety according to the needs and through the actual test, do not need to hydrolyze again, can be used after dissolution. However, for reasons of habit, some people still refer to the process of flocculant dissolution as hydrolysis. It should be noted that hydrolysis means decomposition with water, which is a chemical reaction. Ammonia is released in the hydrolysis of PAM. Dissolution is only a physical action, no chemical reaction. The two are different in nature and should not be confused.

viscosity

PAM solutions are very sticky. The higher the molecular weight of PAM, the greater the viscosity of the solution. This is because PAM macromolecules are long, thin chains with great resistance to movement in solution. The essence of viscosity is to reflect the size of friction force in solution, also known as internal friction coefficient. The viscosity of all kinds of polymer organic solutions is higher 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 calculate its molecular weight according to a certain formula, known as "viscosity average molecular weight".

Residual monomer content

The residual monomer content of PAM refers to the acrylamide monomer content in the polymerization of acrylamide into polyacrylamide, which is not completely reacted and ultimately remains in the polyacrylamide products. It is an important parameter to measure whether it is suitable for the food industry. Polyacrylamide is non-toxic, but acrylamide has some toxicity.

In industrial products of polyacrylamide, it is hard to avoid residual trace of unpolymerized acrylamide monomer. Therefore, the residual monomer content in PAM products must be strictly controlled. The residual monomer content of PAM used in drinking water and food industry should not exceed 0.05%. The figure for famous foreign products is less than 0.03%.

2. Common adulteration means of PAM

Adulterated ideas:

High molecular weight PAM+ filler = low molecular weight PAM

High molecular weight PAM+ filler = low cost high molecular weight PAM

Packing a

Industrial salt, sodium chloride, is low in price, looks similar to PAM, and can achieve the effect of solubilization, that is, to improve the consistency of PAM. However, if the amount added is too large, the solubility of PAM and other substances will be affected.

Packing two

Urea, low price, similar appearance and polyacrylamide, the addition of urea, can reduce the number of hydrogen bonds between the polyacrylamide PAM chain, so PAM dissolved in water, can accelerate its dissolution, reduce agglomeration.

Other packing

Other types of industrial salt such as sodium sulfate, waste PAM such as crosslinked.

3 Identification Methods

Salt can be identified by the following methods

1, depending on the size and color, take 80 or 100 mesh sieve, if too much PAM powder to pay attention to; If the color is not clean, pay attention to it.

2, take a cup of water, evenly sprinkle PAM on the liquid level, due to different specific gravity and water absorption, salt will sink faster, and PAM relatively longer wetting time.

3. Titration of silver nitrate and barium chloride solution

Mixed with ammonium salt can be identified by the following methods

Take a small amount of PAM on the fire to bake for a while, adulterated ammonia will be released.