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Reveal Diapers, How is the Water Absorbed?

A baby's diaper is such a thin layer that it can absorb the amount of urine that the baby urinates several times. No matter how much the baby's little bottom squeezes, the urine does not seep out through the inner surface of the diaper. Mothers not only wonder: how do diapers absorb their babies' urine? The superb absorbency and water retention of diapers is due to their absorbent material and structural design.



A baby's diaper generally has a four-layer structure.

Surface layer: Made of non-woven fabric, it comes into direct contact with the baby's skin, receives the liquid and passes it on to the next layer;

Conductive layer: made of non-woven fabric, which transmits the liquid received by the surface layer evenly to the absorbent layer;

Absorbent layer: made of super absorbent polymer powder (SAP for short) mixed with fluffy fibers, it is the most important functional layer in diapers, used to absorb and store urine;

Bottom layer: made of PE film or PE film + non-woven fabric, the main function is leak-proof.


1.Absorbent substance: super absorbent polymer powder

Many mothers naively believe that the baby's diapers have cotton in them and can absorb water through the cotton. When you uncover the surface of the diaper, you will find that it is a small particle that is mixed with the lint fibers. Although cotton absorbs water, it absorbs water far more quickly and locks in water than polymeric absorbent resins.

Polymer absorbent resin (SAP) is a typical functional polymer material. sap looks like a small bead, only about 0.2 mm in diameter, and can absorb hundreds or even thousands of times its own weight of water and has a high water retention capacity, so it is also called super absorbent or high water retention. sap has super absorbent capacity because high absorbent resin is a low SAP particle size is 100~120mesh (i.e. 0.212mmm~0.254mm), the best absorption ability; when the PH value is 6~8, the absorption rate is the highest. The SAP of diaper absorbent layer is evenly mixed with the fleece fiber. the even mixture of SAP and fleece fiber can make the water absorption evenly, avoid gel adhesion and hard spot piercing the paper surface, and prevent sliding between layers.

super absorbent polymer powder

2.Absorbent principle: layer by layer downward seepage

After knowing the main water-absorbing substances in diapers, what is the process from excretion to absorption of baby's urine by diapers? Let's do further exploration.

The infant expels urine from the body, first receiving it from the surface of the diaper and permeating downward, and then from the infusion layer receiving urine that permeates from the surface layer. Part of the urine is directly absorbed by the next layer of SAP absorbent core along the gap, the rest of the liquid is conducted and diffused longitudinally along the infusion layer to expand the absorbent area of the polymer absorbent core, and finally the urine after diffusion longitudinally along the infusion layer penetrates to the next layer and absorbs the polymer absorbent core evenly. The surface layer of the diaper is in direct contact with the baby's bottom, which is the first layer to receive urine; the infusion layer is to guide the urine that penetrates from the surface to conduct and diffuse along the diaper longitudinally, so that the urine is absorbed evenly by the absorption core, which will not lead to local thickening of the diaper due to multiple absorptions and hinder the subsequent absorption of urine by the absorption core; the SAP absorption core layer is the final layer to absorb and store urine; the bottom layer can effectively prevent leakage.


3.Water locking principle: super absorbent polymer powder has strong water retention capacity

We all know that sponge has strong absorption ability, but if the sponge is slightly squeezed, water will seep out. When the baby pee on the diaper, how to squeeze the small buttocks, the surface of the diaper will not have urine reverse osmosis. How does a baby's diaper lock in moisture? The absorbent substance SAP of the diaper is a SUPER ABSORBENT polymer powder compound, which is linked to many atoms that are accessible to water. Therefore, water molecules are easily attracted to its molecules and squeezed between them, thus swelling and integrating the SAP particles. It can absorb hundreds to thousands of times more water without leaching out.


For example, rice is cooked in water. Although rice grains contain a lot of water, the water does not come out; flour and water are kneaded into dough, and the water inside cannot be squeezed out in any way. Similar to rice and noodles, polymers not only have a strong ability to absorb water, but also have a strong ability to retain water.


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