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What’s Sodium Polyacrylate?
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.
Basis Info
Melting point
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.
Ph value
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. )
Water absorption
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.
Production Process
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.
How does it work?
You may have been wondering how does sodium polyacrylate work. In fact, the entire water absorption process has undergone complex physical and chemical reactions.
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.
Safety Research
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 Material Safety Data Sheet
How about touching the skin directly?
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).
Food grade sodium polyacrylate
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?
Strictly speaking, the answer can be yes only if sodium polyacrylate meets the food-grade standard.
Conclusion
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.
- If the powder is inhaled, it can irritate the lungs–but that’s not generally a concern.
- When it comes in contact with a large amount of spilled water in an area, it can cause the area to become very slippery.
- If it enters sewer or drainage systems in large quantities, it can cause serious clogging and should be dealt with immediately.
Uses
Sodium polyacrylate has too many uses, and it is still increasing. We can summarize the uses by its actual function:
Summary of uses 01
Sodium polyacrylate can absorb a lot of liquid & lock it firmly.
So the uses can be:
- paper diapers;
- sanitary napkins;
- nursing pad.
Summary of uses 02
Sodium polyacrylate becomes a stable gel after absorbing water.
So the uses can be:
- ice bag;
- hot/cold gel pack;
- growing toys;
- Fragrance carrier.
Summary of uses 03
Sodium polyacrylate’s hydrogel formed after absorbing water can block water.
So the uses can be:
- water blocking tape in cable;
- Water swelling sandbag for flood control.
Summary of uses 04
Sodium polyacrylate’s hydrogel can be made in color and into a spherical shape.
So these sodium polyacrylate beads/balls can be used in:
- Toy gun bullet;
- Transparent vase interior decoration.
Summary of uses 05
Sodium polyacrylate can quickly turn liquid into solid for easy collection and processing.
So it can be used in:
- Human or animal feces and urine collection;
- Wastewater treatment.
Summary of uses 06
Sodium polyacrylate can be modified in the production process.
So it can be used for some special purposes like:
- Artificial snow.
- Fire-retardant gel.
- Additives for drilling lubricants.
- Concrete protection. It can effectively prevent the concrete from drying out during the solidification process.
Summary of uses 07
Some uses that have not been widely used or proven:
- Water bed;
- Thickening agent;
- The drown-free water source for feeder insects.
FAQs
Where to find/get sodium polyacrylate at home?
As I said, you can easily find sodium polyacrylate in sanitary napkins or paper diapers.
Is sodium polyacrylate safe for plants (as fertilizer)?
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.
Can sodium polyacrylate go down the drain?
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.