Background Research – Nappy absorption

Since becoming a father I have been very interested in the effectiveness of different brands of nappies. I am particularly interested in the absorption rates of these nappies as this would impact on the overall cost of nappies over a period of time. I.e. the better the absorption the less often a babies nappy needs to be changed, therefore less money being spent.

I am also conscious of the impact disposable nappies have on our environment. Our family would prefer to use reusable nappies but are they more absorbent?

I have heard that disposable nappies have a chemical called polymer in them. What is the purpose of polymer? Is it more effective than cloth to absorb moisture?

An overview of the types of nappies

There are three main categories that you can choose between:

Traditional cloth nappies, known as flat or square nappies Disposable nappies

Modern cloth nappies which are pre-shaped and re-usable.

Cloth Nappies

Modern cloth nappies are now easy to use and just as easy to clean. Cloth nappies are made up of three layers: a waterproof shell, an absorbent core, and a fabric next to the skin that allows moisture to pass through, keeping your baby’s skin dry.

Cloth nappies halve the ecological footprint of disposable nappies. Every child adds a minimum of 6,500 disposable nappies to our landfills which take upwards of 500 years to decompose. Included in the soiled nappies are

many pounds of raw fecal matter. Viruses found in the feces can pose a threat to our water supplies and wildlife by seeping through cracks that sometimes develop in landfills.

Further, the 30 billion disposable nappies that get thrown out in the World annually consume approximately 150,000 tons of plastic and 1,200,000 tons

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of tree pulp every year. Now compare that to the natural resources used to make and clean three to five dozen cloth nappies.

Then there’s the question of what’s hidden in some disposable nappies, such as dioxin (a by-product of bleaching the pulp) which has been linked to cancer, as well as other chemicals and fragrances that can irritate sensitive baby skin.

On average, parents spend $4,000 (US) on disposable nappies per child. Compare that to an average of $900 (that includes laundering expenses) for your first child's nappy years using cloth nappies. A second and third child will cost much less since cloth nappies can be re-used for more than one child.

Cloth nappies use premium quality 100% natural cotton fibre in their cloth nappies for softness, absorbency and durability.

Many cloth nappies have inserts that fold easily and are sized to fit perfectly a nappy cover. They can be folded in a variety of ways to accommodate boys, girls and smaller babies as required, and 'boosted' with optional booster pads for heavy wetters or night time use.

What’s in a disposable nappy?

70% - Core containing fluff pulp and absorbent material10% - Polypropylene topsheet to protect against wetness13% - Polyethylene backsheet to prevent leakage7% - Other, including tapes, elastics and adhesives

Baby Nappy Polymer

Description

Modern baby diapers contain polyacrylic acid, a super-absorbent polymer. When some of this polymer was added to a beaker with water and stirred, it absorbed many times its weight in water.

Explanation

Polyacrylic acid is a polymer made from the monomer acrylic acid. These long chains contain thousands of monomer units, and the polymer also has some cross-linking between the chains. Many polymers, such as polyethylene and polystyrene (used in trash bags, plastic bottles, and Styrofoam®, for example) are hydrophobic, meaning they repel water. Polyacrylic acid, however, is very hydrophilic - it attracts water. That's because of the carboxylic acid groups (COOH) in the polymer, which can hydrogen-bond to water molecules.

Nappies contain a small amount (4-5 grams) of polyacrylic acid in a powder form, which is mixed into the fluff in the middle layer of the diaper. The inside layer of the diaper allows water to pass through it into the absorbent middle layer, and the outer layer is waterproof, so both baby and mommy stay dry. Polyacrylic acid can absorb about 30 times its weight in water, or about 30 mL (1 oz) of water per gram, so a typical nappy can absorb 120-150 mL of water (about a half cup). That's about how much a baby... um... pees.

Summary of nappies

From this research I believe disposable nappies that contain polymer would be more absorbent than reusable cloth nappies. I’m still not convinced that this will be enough to stop me from using reusable nappies as I believe the cost to the environment is more paramount.

Bibliography

http://www.coolscience.org/CoolScience/KidScientists/babydiaper.htm

http://www.thenappynetwork.org.nz/

http://www.realnappies.co.nz/real-nappies-prefold-cloth-diaper-system

http://www.kiwifamilies.co.nz/articles/nappy-overview/

http://news.bbc.co.uk/2/hi/science/nature/4562613.stm