Since this article is long and will be updated continuously, if you are interested in SAP (Super absorbent polymer), it is recommended to bookmark it. (press “Ctrl”+”D” to add bookmark)
For more details about Super absorbent polymer, you can visit our Guide.
First of all, it should be clear that not all sodium polyacrylates have the function of water absorption.
Sodium polyacrylate can be divided into two categories according to the molecular weight, namely water-soluble and water-swellable.
Sodium polyacrylate is a kind of super absorbent polymer (also called SAP).
It is a functional polymer used in a variety of common products such as paper diapers, pets pads, water-retaining material (to help the soil retain water), instant snow, and so on. It is known for its superior absorbency:
Sodium polyacrylate can absorb hundreds of times its own weight in water. It starts out as a powder and as it comes into contact with moisture, it swells into its gel form.
Unlike other absorbent materials, it’s not easy to squeeze the moisture out of this gel. This is what makes it perfect for use in paper diapers — your baby can sit on it, roll around, and sleep for hours in a wet diaper without leaks.
So we can simply sort out sodium polyacrylate as the main function of water-absorbing polymer.
|CAS Registry Number
|Usually white powder or granules
It’s 150℃. In addition, after sodium polyacrylate absorbs water and becomes a hydrogel, it will be easily melted and photodegraded at a lower temperature (such as 40°C). This is one of the reasons why sodium polyacrylate cannot be used as a water-retaining agent for agriculture and forestry.
Generally speaking, sodium polyacrylate is weakly acidic because it has very little acrylic residue. (Sodium polyacrylate is formed by the polymerization reaction of acrylic acid and sodium hydroxide. )
As the strongest water-absorbing material at present, sodium polyacrylate can absorb up to several thousand times its own weight of pure water.
In addition, whether the water is pure or not directly affects the absorption of sodium polyacrylate. If salt is added to the water, the water absorption will be greatly reduced. The concentration of water ions in the soil is extremely high, and the water absorption of sodium polyacrylate is greatly reduced — This is one reason why it is not suitable for use as a water-retaining agent.
Why is the water absorption of sodium polyacrylate related to the brine concentration of the liquid?
After a careful study of the entire saline absorption process of sodium polyacrylate, we will find:
Sodium polyacrylate polymer itself is a semi-permeable membrane. The semi-permeable membrane only allows water molecules to pass through, and the semi-permeable membrane wraps sodium chloride to form small spheres. Outside the membrane is a low concentration. When the sodium polyacrylate polymer comes into contact with water, because the concentration of the solution inside and outside the small ball is very different, a large amount of water penetrates from the low concentration solution outside the small ball into the high concentration solution inside the small ball, until the inner and outer solutions are The concentrations are equal. This is called isotonicity.
Based on the principle of osmosis, the amount of water absorbed by a water-absorbing polymer depends on the type of external solution. If it is distilled water, it can absorb 800 times the weight of the polymer itself. If it is tap water, because it contains more ions, it can only absorb 300 times its own weight.
In copolymer chemistry, there’re 3 ways to produce sodium polyacrylate: gel polymerization, solution polymerization, and suspension polymerization.
Here’s the common process picture for your conference:
As you see, sodium polyacrylate is not a natural product.
ps: there is one kind of sodium polyacrylate produced by starch grafting. The manufacturer claims that it is a “natural product” as a gimmick.
You may have been wondering how sodium polyacrylate work. In fact, the entire water absorption process has undergone complex physical and chemical reactions. (It is generally believed that physical reactions account for most of the effects.)
Simply speaking, there are network molecular chains in the molecular structure of sodium polyacrylate. Its electrolysis occurs immediately after encountering water and dissociates into positively and negatively charged ions. The positively and negatively charged ions have a strong affinity with water. Therefore, it has strong water absorption and water retention capabilities.
Sodium polyacrylate is white granular, is a water-absorbing polymer, and the main chain contains -COONa. When water intervenes, it dissociates into -COO- and Na+. Due to the mutual repulsion between the -COO- anions, the originally curved chain expands into a straight chain.
Since the hydrogen atom in the H2O (H-O-H) molecule is slightly positively charged, and the oxygen atom is slightly negatively charged, the attraction between the slightly positively charged hydrogen atom and the negatively charged -COO- produces hydrogen bonds, so the polymer Sodium acrylate can absorb water.
But sodium polyacrylate is not dissolved in water but forms a colloidal substance. The reason is that when the degree of cross-linking is high, water cannot enter the polymer, and its water absorption capacity is reduced. On the other hand, in the case of a low degree of crosslinking, water molecules easily penetrate into the polymer, and the resin swells, further hydrophilic and gelatinized, and becomes a state of high water absorption.
Tip: When the crosslink density is too low, it may dissolve in water.
Sodium polyacrylate, also known as waterlock or superabsorbent polymer (SAP), is a highly water-absorbent polymer that is widely used in various industries. It is a sodium salt of polyacrylic acid, which is a polymer composed of acrylic acid monomers. In this article, we will discuss the uses of sodium polyacrylate in various industries and applications.
More than 90% of the world’s sodium polyacrylate is used as water-absorbent material to produce diapers. Therefore, the safety of sodium polyacrylate has always attracted the attention of the society. In fact, sodium polyacrylate is safe and harmless, and its only acrylic acid content that may cause skin discomfort is almost an index strictly tested by every diaper production factory.
Excellent water absorption capacity, as well as the characteristics of firmly locking urine after absorbing water, make diapers produced by sodium polyacrylate help keep babies’ skin dry and prevent rashes.
For the same reason, sodium polyacrylate has always been the best choice for water-absorbing materials for women’s sanitary products in view of its strong absorption capacity and water-locking capacity of physiological saline. Compared with general traditional materials, such as cotton or wood pulp, sodium polyacrylate can firmly lock menstrual fluid and prevent leakage, greatly improving the comfort of women’s physiological products.
Sodium polyacrylate is widely used in the medical industry. Not only can it be used as a wound dressing to absorb body fluid exuded from the wound, but it can also be used to absorb body fluid during and after surgery, which greatly simplifies the difficulty of medical waste disposal.
The sodium polyacrylate that has absorbed the liquid is in the solid state of gel, which can be easily collected and disposed of, and can be degraded in the natural environment without pollution to the environment.
Sodium polyacrylate can not only absorb the moisture in the humid air, but its hydrogel can also be used as solid water during the transportation of plants and flowers, preventing or delaying the withering and death of plants during transportation.
Sodium polyacrylate has been widely used in water treatment industry. After special treatment, sodium polyacrylate is produced, which can already be used as a flocculant to help particles in wastewater aggregate and settle, preventing fouling from forming on plumbing equipment.
As a commonly used thickener and emulsifier, sodium polyacrylate can be used in personal care products.
Sodium polyacrylate has two main uses in the mining industry.
One application is that in oil and gas extraction, the viscosity of the drilling fluid can be controlled, and the pores of the rock can be blocked in time to prevent the drilling fluid mud from losing into the porous rock formation.
The second use is that there will be relatively shallow waste liquid sludge during the mine mining process. This waste liquid is difficult to use, and it is difficult to pump it out and transport it out of the mine in other ways. At this time, it is a very economical and time-saving method to sprinkle sodium polyacrylate to fully absorb it, and then transport it out of the mine in the form of solid.
The material inside the Gel Ice Pack is sodium polyacrylate. This material is extremely water-absorbent, and after absorbing water, it can swell quickly to form a hydrogel, which is soft in texture, and the whole material is completely non-toxic.
In conclusion, sodium polyacrylate is a versatile polymer that is used in a wide range of industries and applications. Its excellent water-absorbent properties make it ideal for use in disposable diapers, feminine hygiene products, and other absorbent products.
It is also used in medical applications, packaging and transportation, water treatment, personal care products, and the oil and gas industry. As new applications are developed, the demand for sodium polyacrylate is expected to continue to grow.
Is sodium polyacrylate safe?
Yes. According to various material safety data sheets (documents created by the U.S. Occupational Safety and Health Administration that list potential hazards of chemicals in great detail), sodium polyacrylate is totally safe.
We can also know more through the MSDS (Material Safety Data Sheet) documents like this:
Sodium polyacrylate itself is not irritating to the skin. As a polymer, it sticks together in long chains that are way too large to be absorbed through the skin.
But some kind of sodium polyacrylate is mixed up with small amounts of acrylic acid, a leftover from the manufacturing process.
In theory, acrylic acid in large doses could be harmful to a baby’s skin. But according to a 2009 report in the Journal of Toxicology and Environmental Health, there isn’t nearly enough acrylic acid in disposable diapers to raise concern. (The study was funded by Procter & Gamble, a major manufacturer of diapers.) Another side, sodium polyacrylate suppliers should test the acrylic acid value and make sure it is less than 300 ppm (part per million).
Although the claim of “food-grade sodium polyacrylate” has existed for many years, no manufacturer has claimed to be able to produce it. This may be related to the production process.
*ps: this content is updated in 2021.
Is sodium polyacrylate toxic to dogs/animals/insects?
Normally, sodium polyacrylate has a very low content of acrylic acid, a harmful substance, and will not pose a toxic effect on the human body. But for small animals and even insects, exposure to too much sodium polyacrylate can be harmful.
Sodium polyacrylate is safe — non-toxic and free from any major safety risks.
But, it can pose certain dangers if not handled properly. But please be sure to take notes of the following hazards and take precautions to avoid any injury or mishaps when handling sodium polyacrylate.
According to the average data of Alibaba.com in 2022, the price of sodium polyacrylate, which is mainly used as absorbent material for diapers, is US$1,500-2,200 per ton. The price of special purpose sodium polyacrylate will be much higher than this price.
Yes for sodium polyacrylate gel. It’ll slowly be decomposed into the water, carbon dioxide, and some sodium ions, which will not cause environmental pollution.
PS: Sodium polyacrylate powder has a strong water swelling property. This will cause the toilet to block.
At this point, the properties of sodium polyacrylate are different.
Ordinary sodium polyacrylate cannot be reused. For example, sodium polyacrylate used in diapers will be discarded after absorbing urine.
For the sodium polyacrylate used in some special purposes such as water-absorbing expansion flood control bags, the manufacturer will carry out special post-processing. The sodium polyacrylate after these special treatments can become solid particles after a certain period of time after absorbing water. State, can repeatedly absorb moisture.
It is generally believed that physical reactions account for most of the effects.
Sodium polyacrylate is not a natural substance, but a macromolecular structure of organic synthesis, so it is difficult to be biodegraded in natural soil.
But it is worth mentioning that sodium polyacrylate can be decomposed naturally in the soil.
We can confirm this conclusion through a very simple experiment. For example, the gel after absorbing water with sodium polyacrylate will melt under the sunlight for a week.
In addition, in some countries, diaper manufacturers have begun to research and produce sodium polyacrylate types that can be naturally degraded by biotechnology. The principle is that the process of sodium polyacrylate production is grafted with starch or other substances so that it can be decomposed by living microorganisms.
Although the price of sodium polyacrylate is much lower than potassium polyacrylate, it’s whimsical to use it as a water-retaining agent.
List a few reasons why you should NOT use sodium polyacrylate for plants:
As a water-retaining agent, sodium polyacrylate can hardly absorb water underground causing the high ion concentration of soil leachate.
The water gel from sodium polyacrylate is easily melted and photodegraded at a lower temperature (such as 40°C).
Sodium polyacrylate is decomposed into a large number of sodium ions that cannot be absorbed by plants, which leads to increased soil salinization.
Note: different from A, B, which is specially designed for the water-retaining agents, effectively solves the above three problems.
Sodium polyacrylate is not toxic. In the process of synthesizing sodium polyacrylate, the content of acrylic acid can be strictly controlled and is not harmful to the human body.
In fact, sodium polyacrylate has been widely used as an important water-absorbing component of baby diapers.
Although sodium polyacrylate is harmless to the skin, you should see a doctor as soon as possible after your baby or your dog ingests it. This is because it swells so fast that it can cause gastrointestinal discomfort after accidental ingestion.
As I said, you can easily find sodium polyacrylate in sanitary napkins or paper diapers.