A+-+properties+of+disposable+diapers

Carolyn Ko, Period A Friday, November 5th, 2010. Mr.Lindhala

=**//"What properties of disposable diapers enable them to hold so much liquid? What impact has the widespread use of disposable diapers had on the environment?" //**= = = = ﻿ = media type="youtube" key="TpvNEZCvk84?fs=1" height="385" width="480" align="center"

· Average baby uses __//7- 10//__ diapers a day in their first year.

· The first disposable diapers were created b/c during WWII, there was a cotton shortage. (cloth diapers usually made of cotton)

**__ So, what makes disposable diapers so absorbent? Let’s take a look at the major components of a diaper: __**

1) **__Inside layer__** that comes in contact with baby’s skin: a hydrophilic layer make of polypropylene allows water to pass through into the absorbent filler beneath.

2) **__Outer layer__**: usually made of polyethylene. This plastic prevents liquid from leaking out of diaper.

3) **__Cellulose filler__**: processed from pine trees and milled into “**fluff pulp**”. The pulp consists of long cellulose fibres that provide a strong capillary effect, which helps draw in liquids.

4) **__sodium polyacrylate:__**  · Aka sodium prop-2-enoate (it’s an ester!); SAP “super absorbent polymer”    · Distributed throughout fluff pulp.    · When dry, appears as a white crystalline powder, or clear beads. When wet, the water soaked polymer crystals become a frosty/clear gel.    · Amazing water absorber (holds 200-300 times its mass in water)    · How it’s formed: acrylic acid and sodium hydroxide react to form sodium acrylate and water. C2H3COOH + NaOH à C2H3COONa + H2O (acid-base rxn)    · sodium acrylate then is polymerized into long chains of sodium polyacrylate.    · sodium polyacrylate chains have **cross-links** (these covalent bonds link one polymer to another), which create a 3D structure that holds liquids in place.

Sodium Polyacrylate- Taken from Scientific American

· When sodium polyacrylate comes in contact with water, the Na+ detaches itself, leaving negatively charged carboxyl ions, which attract H2O molecules. (H-bonding) · The negatively charged carboxyl ions repel one another, so the polymer unwinds as it absorbs water.

· Ability to absorb water depends on electrolytes in the water (ex. Salt minerals in urine). **__Osmosis:__** forces water into the solid polymer lattice of diaper in attempt to get equilibrium. Remember, water moves from areas of lower electrolyte concentration to areas with higher electrolyte concentration. Therefore, very concentrated urine is not absorbed as well as more dilute urine.

**__ Environmental Impact – Disposable Diapers a threat to the environment __**

· Diapers account for up to 2% of total volume of landfills. · Estimated 500 yrs for a disposable diaper to decompose. · Only some materials are biodegradable (wood pulp “fluff pulp”, and sodium polyacrylate) Polyethylene, elastic, polypropylene (tape) are not biodegradable · Eco-diapers are made with some recycled plant materials, but they don’t break down much faster than regular disposable diapers. · Dirty diapers – possible groundwater contamination --Sodium Polyacrylate linked to skin irritations and Toxic Shock Syndrome.

**__ Bibliography __** Banks, Catherine H. Chemistry Explained //Disposable Diapers// Copyright © 2010 Advameg. Inc [] Calder, Vince Argonne National Laboratory ( Summer 2009) //Sodium Polyacrylate and Water Absorption// Retrieved October 28,2010 [] Ed. Stacey L. Blachford. Gale Cengage, 2002 //"Disposable Diaper." How Products are Made.// __eNotes.com__. 2006. 30 Oct, 2010 [] Redtails ADISC (November 8, 2008) //The Chemistry Behind Diapers// Retrieved October 28, 2010. [] Richer Investment Diaper Consulting Services (2007) //What are the components of a typical disposable diaper?// Retrieved October 28, 2010. []