Guide to Super Absorbent Polymer (2024)

2024-01-18

    Overview

    SAP (super absorbent polymer) is a functional polymer material. It can absorb water up to several hundred times its own weight.

    History

    The origins of superabsorbent polymer chemistry trace back to the early 1960s when the U.S. Department of Agriculture developed the preferably superabsorbent polymer materials.

    Chemical component

    SAP is a general term for super absorbent polymers, and different types of SAP have different chemical compositions.

    The superabsorbent polymer is usually sodium polyacrylate produced by polymerizing sodium hydroxide and acrylic acid.

    Superabsorbent polymers have large differences in various indicators such as water absorption speed, water absorption capacity, and centrifuge water retention rate, which are realized by changing their composition and production process.

    For example, in order to meet the needs of agriculture, the raw material is changed from sodium hydroxide to potassium hydroxide, so that the product forms a potassium polyacrylate type water-absorbent resin. This not only prevents the risk of soil salinization caused by its decomposition product sodium ions, but also increases the content of potassium in the soil.

    To sum up, the super absorbent polymer is not equal to sodium polyacrylate. It can be sodium polyacrylate or potassium polyacrylate, and it can also refer to various grafted absorbent polymers, such as those specially used for biological Starch-grafted water-absorbing polymers for degradation purposes.


    Types of Super Absorbent Polymer

    In this chapter we will talk about the classification of superabsorbent polymers.

    The classification will be according to the following dimensions: chemical composition and quality.

    The Chemical Composition of SAP

    SAP is mainly divided into two classes:

    And here are the important points on main usages.

    Potassium polyacrylate type SAP

    • Absorbing capacity in soil;
    • Granular size;
    • The photolysis resistance;
    • Period of validity.

    Sodium polyacrylate type SAP

    • Hygiene products (like a diaper, sanitary towel)
      1. Absorbent rate;
      2. Absorption under pressure and retention capacity after centrifugation;
      3. Liquid Permeability;
      4. Residual Monomer.
    • Waterproof tape of cable
      1. Expansion height;
      2. Granular size.
    • Ice bag
      1. Price;
      2. Granular size.
    • Anti-flood bag
      1. Absorbent rate;
      2. The photolysis resistance.
    • Leaking stoppage in drilling
      1. Viscosity;
      2. Coagulation time.

    The Quality Grade of SAP

    As we all know, SAP is a general term for water-absorbent polymers. In addition to the most common sodium polyacrylate, it also includes potassium polyacrylate and grafted SAP.

    Improved SAP

    Improved SAP – Improved on some sides like:

    • Starch-based Grafted SAP – The biodegradable type SAP;
    • Minerals-based Grafted SAP (for plants) – Available in soil for years;
    • SAP with improved catalyst – High expansion ability (for water blocking of cable);
    • Cation type SAP – concrete additive.

    Common SAP

    • Potassium polyacrylate – mainly used in agriculture as a water-retaining agent;
    • Sodium polyacrylate – widely used in industrial production such as Paper diapers, Sanitary napkins, Ice bags, Air fresher, Expanding rubber, etc.

    Defective SAP

    • Recycled SAP: the SAP was used and recycled;
    • Burnt SAP: the SAP was produced at over-temperature.

    Uses of Super Absorbent Polymer

    It is a material that absorbs water quickly and in large quantities and then turns into a hydrogel.

    This chapter will introduce the use of superabsorbent polymers.

    As mentioned at the beginning of this article, a superabsorbent polymer is a material that absorbs water quickly and in large quantities, and then turns into a hydrogel. Taking advantage of its characteristics, we try to classify its uses as follows:

    • Super strong absorbent material for inorganic liquids. In fact, it is the water-absorbing material with the highest absorption rate of inorganic liquids that can be found so far. The efficiency of absorbing pure water can reach thousands of times its own weight.
    • Non-toxic and environmentally friendly gel material. It is widely used in new ice packs. In addition, the modified sodium polyacrylate absorbs water to form a spherical hydrogel, which is widely used in indoor landscape potted plants, toy gun bullets, etc.
    • Waterproof material for special purpose. The hydrogel after sodium polyacrylate absorbs water is insoluble in water and can effectively isolate water. It is widely used as waterproof material for the exterior of cables and water-blocking material for lightweight flood-proof sandbags.
    • Oxygen barrier fire extinguishing material. Sodium polyacrylate can quickly absorb water and expand in volume when it meets water. According to this principle, it can be used as an efficient cooling and oxygen barrier material in fire extinguishers.

    There are so many uses of superabsorbent polymers that we cannot list them all in this article, so this article only lists some of their commonly used uses and does not introduce them in detail.

    SAP for Plants

    Usually, the hydrogel formed after the superabsorbent polymer absorbs water can firmly hold the water and no longer let the water escape from the hydrogel. But we can set the osmotic pressure of the superabsorbent polymer hydrogel to be lower than the water absorption osmotic pressure of plant roots by processing.

    In this way, we get a very, very magical “mini reservoir in the soil”, which can:

    • After irrigation After irrigation or rain, it absorbs water hard and forms hydrogel to store excess water in the soil.
    • When the soil is relatively dry, the water in the hydrogel is released to the roots of the plants.

    As the type of superabsorbent polymer for plants, it is a unique superabsorbent granule, which acts to provide increased moisture availability to plants.

    What can super absorbent polymer do for plants exactly?

    Agriculture grade SAP ( potassium polyacrylate ) can be widely used in agriculture, forestry, and gardening, such as soil water retention agent, seed coating, soil-less cultivation, artificial turf, etc.

    • Improve seed germination and emergence to give plants an early, healthy start,
    • Save the irrigation, increase crops and fruit yield,
    • It contains Potassium, Phosphorus Nitrogen and releases fertilizer efficiency slowly.

    Important indicators are as follows,

    • Absorbing capacity in soil. The water absorption capacity in the soil is relatively high, which involves water absorption under high pressure and high ion concentration. At the same time, the temperature in the soil will also affect its water absorption capacity.
    • Granular size. The particle size also determines the water retention capacity of potassium polyacrylate in soil. For example, the larger the particle, the stronger the viscose, which can resist the pressure in the soil, but reduces its maximum water absorption.
    • The photolysis resistance. Potassium acrylate usually undergoes photolysis over a long period of time in soil. Photolysis resistance determines the lifetime of potassium polyacrylate in soil.
    • Period of validity. Potassium polyacrylate usually has a very long Period of validity before use. So if you purchase this product in large quantities, it is recommended to transport it by sea.

    Usage for farming

    Application Ways

    • Dry Application
      • Mix it with fertilizer and soil evenly and then apply the mixture to the ground by using a fertilizer applicator.
      • For the confined area (less than 20 square meters), it is recommended to apply manually.
      • Completely turn over the ground by using a tillage machine (require it at depth of 20cm).
      • Trampling the ground.
      • Watering the ground.
    • Wet Application
      • Let SAP absorb 200 times water, and become gel form.
      • Put into the sowing furrow.
      • For the confined area (less than 20 square meters), it is recommended to apply manually.
      • Put surface soil in order before planting.

    For example, in the farming of rain-fed sugar cane, significant increases in yield of approx. 25% are observed.

    • When replanting a field, put SAP in the furrows where the cane shoots are placed.
    • SAP may be applied at the same time as a fertilizer.
    • Cover the shoots with soil by earthing them up.

    Usage for arboriculture

    • Dig a hole about three times the volume of the root system.
    • Mix 1 to 2 kg of SAP per m³ into the earth fill.
    • Place the root ball of the plant at the bottom of the hole and fill in the hole with the treated soil. Make sure that the product is distributed evenly around the roots. Then cover the surface with 5 cm of untreated soil to prevent degradation of the polymer by ultraviolet rays and stagnation of water on the surface.
    • Be especially careful not to put the unmixed dry product at the bottom of the hole. After hydration, the product would destabilize the plant.

    Usage for bare-root dipping

    • Mix 1 kg of SAP in 150-200 liters of water. (Amounts vary depending on the salinity of the water)
    • Slowly pour in the product while stirring the water to obtain a dressing without dumping particles.
    • Let the dressing stand for 15 minutes, the time needed for SAP to reach its maximum absorption. It is important to obtain a dressing that will adhere completely to the roots. The longer the maturation time, the thicker the dressing will be, and the better it will adhere to the roots.
    • A water-soluble nematocide and/or fungicide may also be added to the preparation to protect plants against nematode and fungal attacks.

    Usage for bare-root dipping

    SAP in the form of the hydrogel may be placed in sealed plastic pouches. Once frozen, the pouches are often used in the transport of heat-sensitive plant products such as cut flowers. The hydrogel has excellent resistance to heat shock and does not leak after thawing.


    Usage for hydroseeding

    The other advantage of SAP is that it prevents cellulose mulch from becoming hardpan during a dry spell. The mulch remains aerated and allows the seeds to sprout quickly. SAP also makes it possible to reduce the amount of mulch.

    • SAP must be added last to the hydroseeder tank, after the other components: seeds, fertilizers, mulch, etc.
    • Stir for at least 15 minutes before spreading.

    SAP for Production

    With each passing day, SAP is being employed in more and more industries and applications due to its increasing popularity and efficiency in water deterrence.

    Some applications are as follows,

    For hygiene products

    In fact, the application of superabsorbent polymers on plants accounts for only a small part of its use. More than 90% of super absorbent polymers are used in sanitary products such as diapers and sanitary napkins as absorbent materials.

    With its awesome properties of liquid absorption and locking it has found very useful applications in products prone to moisture like:

    • Diapers,
    • Sanitary napkins,
    • Nursing pads and
    • Pet pads.

    In the use of sanitary products, the product parameters of SAP are different from those of plant use.

    Important indicators are as follows,

    • Absorbent rate;
    • Absorption under pressure and retention capacity after centrifugation;
    • Liquid Permeability;
    • Residual Monomer.

    For Waterproofing cables

    Not only can SAP quickly absorb water, but the gel formed after absorbing water can effectively block water. So it also occupies a place in many water-blocking materials.

    SAP is a highly coveted product as far as the manufacture of water-proof tapes and ointments for all sorts of cables are concerned; even, optical fiber cables use SAP. The extent and the speed of absorption are quite high and so are the overall inflation rate and its quantum of inflation upon encountering water.

    Important indicators are as follows,

    • Expansion height;
    • Granular size.

    Used in Cable

    • Fine powder,
    • Fast absorption,
    • Well inflation is under pressure ≥15mm/1 min ≥18mm/3 min
    • Good stability to light, heat, acid, and alkali.

    Used in water-blocking tape

    • Fine powder with uniform size,
    • Well resistant to cold and high temperature,
    • Good stability to light, heat, acid, and alkali.

    For Ice Bags

    Compared with ordinary ice packs, the ice packs produced by SAP have many advantages, such as soft texture, quick ice crystal formation, and prevention of water overflow.

    Freshwater is directed at the individual sheets of ice packs to activate them; Superabsorbent Polymer instantly starts absorbing the water and converting it to a Gel by placing them under fresh tap water; in about 20 minutes time it is seen to soak up enough water to form small cushion-shaped Ice Cubes. They are now ready for use by placing them in the freezer.

    Important indicators are as follows,

    • Hydration time;
    • Price;
    • Granular size.

    For Inflatable anti-flood sandbags

    SAP has this unique application in Disaster Management where it is used in preparing sandbags which, when coming in contact with water, quickly absorb it and expand to form a barrier to the advancing water. Though we call them Sandbags, they actually do not contain any sand; they are so-called because that is how they have been known traditionally.

    These Sand-less Sandbags are quite small in size and light in weight initially but they soak up the water to assume a solid shape. They are much easier to store and transport and take up lesser space when unused.

    Important indicators are as follows,

    • Absorbent rate;
    • The photolysis resistance.

    For Concrete protection

    Concrete needs to absorb water continuously during the setting process, otherwise it will dry out and damage the appearance and firmness. After properly adding the specially formulated SAP when mixing concrete, the SAP hydrogel can buffer the expansion difference during the concrete solidification process, effectively preventing the concrete from cracking.

    • Its permeability happens to be quite low; it totally shuts out the water content,
    • Due to its fibrous texture, it can be stored to form a vertical barrier,
    • Since it is an effective sealant, it finds application in Cement-based items.

    For Sewage Treatment

    SAP is a cost-saving alternative to other bulk solidifiers, including Portland cement, kiln dust, corn-cobs, sawdust, or other commodity absorbents.

    The unique characteristic of SAP is its ability to absorb water or organic fluids, reject oil, and resist bio-degradation while retaining liquid under pressure. This makes it an ideal stabilizing medium for waste disposal in landfills.

    Industrial waste streams vary by salinity, temperature, and chemical composition, so it’s necessary to offer multiple grades of polymer to match the economic and performance requirements for each industrial solidification project.

    Advantages

    • Chemically bonds with water and won’t release liquid,
    • Minimizes waste volume because typical expansion is less than 1%,
    • Mixes quickly to improve production efficiency,
    • Reduce waste transportation and disposal costs compared to other bulking agents.

    For Drilling

    In oil or gas well drilling, lost circulation occurs when drilling fluid, known commonly as “mud”, flows into one or more geological formations instead of returning up the annulus. Lost circulation can be a serious problem during the drilling of an oil well or gas well.

    SAP Drilling Mud Additive which is a new environmental protection product with good water-absorbable and swellable properties, can effectively against lost circulation.

    What is lost circulation?

    In oil or gas well drilling, lost circulation occurs when drilling fluid, known commonly as “mud”, flows into one or more geological formations instead of returning up the annulus. Lost circulation can be a serious problem during the drilling of an oil well or gas well.

    Consequences

    1. Blowout

    If the amount of fluid in the wellbore drops due to lost circulation (or any other reason), hydrostatic pressure is reduced, which can allow gas or fluid which is under higher pressure than the reduced hydrostatic pressure to flow into the wellbore. An influx of gas or fluid into the wellbore, known as a” kick”, can lead to a blowout.

    1. Dry Drilling

    Dry drilling occurs when fluid is completely lost from the wellbore without actual drilling coming to a stop. The effects of dry drilling range from as minor as destroying a bit too as serious as major damage to the wellbore requiring a new well to be drilled. Dry drilling can also cause severe damage to the drill string, including snapping the pipe, and the drilling rig itself.

    Solution of lost circulation

    The Traditional Solution to lost circulation

    There are some options are available when lost circulation occurs, depending on the severity: Increasing the viscosity of the fluid with bentonite or with the addition of other additives, which typically include organic plant particles.

    SAP Drilling Mud Additive – A better solution for lost circulation

    It is a new environmental protection material with good water-absorbable, thickening property and swellable properties, which can effectively against lost circulation.


    Other Applications

    It finds extensive usage in a number of species of products due to its amazing properties; some of them may be listed here:

    • As an additive for functional coating in many specific applications,
    • As an additive in Air fresheners,
    • For expanding rubber requirements,
    • Absorption of wastewaters from industries,
    • In the mining industry for disaster management and normal seepages,
    • In certain cosmetics.

    Due to its awesome capacity to act on moisture, SAP (Superabsorbent Polymer) is finding newer purposes for which it is being employed.


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