Pampers, Bouncy Baby, Huggies: How do diapers work?

Typical Diapers: Diapers work through osmosis/ Photo: diapers.com

What do infants and seniors have in common? An obvious but careless answer would be that they both wet their pants.  This then would imply that the two groups falling on the extremes of the age continuum find diapers inevitable. This then begs the consequent question on how diapers work. 

Diapers are those pieces of absorbent clothing worn around the bottom and fastened between the legs of infants and adults with bladder control problems to absorb and retain urine and feces. When used on infants, it means that they can absorb several rounds of urine. 

Seniors suffering from incontinence, severe diarrhea and dementia find diapers very resourceful.  Interestingly, when the diapers absorb the liquid, they do not let go. However, this will not hold when the diapers are faulty or they are exposed to excess fluid. How then do diapers perform these tasks? 

Careful scrutiny of diapers reveals that they are made of materials of various weights. In the active region, diapers are heavy. The covering material is fine and almost glossy. Heaviness of the diapers in some regions is because of various layers of materials. Underneath the cloth, diapers have a super-absorbent material. This material is largely sodium polyacrylate, the resulting compound after polymerizing sodium acrylate and acrylic acid. 

Sodium polyacrylate is not completely neutralized. According to Theodore Dolter and Leo Malone in their book Basic Concepts of Chemistry, 50-70% of the acid groups in this polymer are in their original sodium salts. The resulting Sodium polyacrylate molecules have elongated carbon chains intertwined with sodium atoms at their centers. The credit to the working of diapers should go to this material.

Sodium polyacrylate is a highly absorbent polymer. “A 1 g quantity of the polyacrylate can absorb up to 500 g of water,” Malone and Dolter write. This quality alone makes diapers very handy. 

Diapers work through the principle of osmosis. Osmosis is the movement of water molecules from regions in which they are highly concentrated to regions less concentrated with water. Exposing sodium polyacrylate to water causes the water molecules ebbing into the chemical-laden region. This process of absorbing water goes on until its concentration inside and outside the diapers equalizes.

Urine and the fluids of feces provide the water that initiates the absorption process. With the stifled water balance, this water sips into the diapers and remains there. The condition is that the water level inside the diapers should be lower than that outside. This hints one of the reasons why the diapers will snap. 

Failure to change soiled diapers compromises on their functionality. Urine contains an assortment of salts. When the water in the urine gets into the diapers, the inherent salt remains attached to the outside of the diapers. This salt concentration soon stifles the ion balance in the two regions of the diapers. Naturally, therefore, water will find it hard getting into the super absorbent material and instead would tend to get to the salt outside the diapers. This does not matter whether the diapers has attained its absorption limit. 

Besides, pressurizing the water-laden region of the diapers can result to its leaking. To solve this problem, the shell around the absorbent material is engineered to be watertight, leak proof. To solve the problem of reversing of the water flow, advises on frequent changing of diapers once soiled. 

Therefore, the utility of diapers is enabled by the scientific principle of osmosis. The essence of osmosis is that water moves from regions in which it is highly concentrated to regions where its molecules are less. In this case, the water in urine percolates into the sodium polyacrylate, the active ingredient in diapers, and remains there.