Activity: Reverse Engineering of Diapers
Summary
Our goal is to discover why these disposable diapers work so well and what
makes them different from the old cloth diapers. This is also a great lesson in the
concept of reverse engineering, which is used by virtually every manufacturing
company in the world, and especially the “big two” diaper manufacturers Kimberly-Clark and Proctor & Gamble.
Engineering Connection
Diapers continue to become thinner and more absorbent. During the 1990s a
modification of the SAP was developed. It uses a surface cross-linker to reduce
the "gel block" problem: If the absorbent is saturated with a liquid, it prevents the
liquid from moving. Independent inventors also are continuing to modify the
diaper. Marlene Sandberg of Stockholm has constructed a diaper that is 70
percent biodegradable. She uses cornstarch in the preparation of the outer layer
of the diaper. This allows her to reduce the amount of polyacrylate used by
designing channels in the fill material that help disperse the urine. Other workers
in the field dispute that the diaper is 70 percent biodegradable: They say the
diapers will not degrade that much in a landfill—their ultimate destination.
Contents
1.
2.
3.
4.
5.
6.
7.
8.
Learning Objectives
Materials
Introduction/Motivation
Vocabulary
Attachments
Procedure
Assessment
Extensions
Grade Level: K-12
Time Required: 30 minutes
Expendable Cost Per Group: US$ 0
Group Size: 2
Keywords: polymer, Reverse Engineering, SAP
Reviews: Read Reviews | Be the First to Write a Review
Related Curriculum:
 Chemistry
Educational Standards:












Oregon Science
Based on observations and science principles, identify questions that can
be tested, design an experiment or investigation, and identify appropriate
tools. Collect and record multiple observations while conducting
investigations or experiments to test a scientific question or hypothesis. (5)
Using science principles describe a solution to a need or problem given
criteria and constraints.(5)
Explain that inventions may lead to other inventions and once an invention
exists, people may think of novel ways of using it. (5)
Describe physical and chemical properties of matter and how they can be
measured. (6)
Based on observation and scientific principals, propose questions or
hypotheses that can be examined through scientific investigation. Design
and conduct an investigation that uses appropriate tools and techniques to
collect relevant data. (6-8)
Define a problem that addresses a need and identify science principals
that may be related to possible solutions. (6-8)
Describe examples of how engineers have created inventions that address
human needs and aspirations. (6)
Explain how new scientific knowledge can be used to develop new
technologies and how new technologies can be used to generate new
scientific knowledge. (7)
Explain how scientific explanations and theories evolve as new information
becomes available. (8)
Evaluate a proposed design solution in terms of design and performance
criteria, constraints, priorities, and trade-offs. Identify possible design
improvements. (8)
Explain how creating a new technology requires considering societal goals,
costs, priorities, and trade-offs. (8)
 Describe how different types and strengths of bonds affect the physical
and chemical properties of compounds. (9-12)
 Explain how chemical reactions result from the making and breaking of
bonds in a process that absorbs or releases energy. Explain how the rate
of a chemical reaction is affected by temperature, pressure, and
concentration. (9-12)
 Explain how energy and chemical elements pass through systems.
Describe how chemical elements are combined and recombined in
different ways as they cycle through the various levels of organization in
biological systems. (9-12)
 Explain how technological problems and advances create a demand for
new scientific knowledge and how new knowledge enables the creation of
new technologies. (9-12)
 Describe how new technologies enable new lines of scientific inquiry and
are largely responsible for changes in how people live and work. (9-12)
 Create and test or otherwise analyze at least one of the more promising
solutions. Collect and process relevant data. Incorporate modifications
based on data from testing or other analysis. (9-12)
 Identify the strengths and weaknesses or a proposed solution to a
problem, and describe how it is better than alternative designs. Identify
further engineering that might be done to refine the recommendations. (912)
Learning Objectives
After this activity, students should be able to:

List reasons disposable diapers sell so well
Describe reverse engineering
Describe other uses of SAP


Materials List
Each student needs:






Cotton squares (1” x 1”) typically used for face cleansing.
One disposable diaper (per group of four people)
One Ziploc bag, gallon size and Scissors
Two small containers, like Petri dish halves
One syringe, pipette or graduated cylinder (10 ml size)
Water (approx. 200 mL per group) and Salt Water (approx. 50 ml per
group)
Introduction/Motivation
Over 20 billion disposable diapers are sold and used each year. This is enough
diapers to cover a football field 3 miles deep. Within the last 10 years the
average age to “potty train” children has increased from 2 years to 3 years old.
There is a reason that so many homes use so many disposable diapers; they
work so well!
But where do they all go? To your local landfill…which just keeps getting bigger
and bigger each day!
This activity is an example of a common engineering practice called “reverse
engineering”. By disassembling a product and making a schematic diagram with
careful notes, engineers at company A can determine the design of a product by
company B. For example, if you worked for Proctor and Gamble (manufacturers
of Pampers diapers) you could cut into a Huggies diaper (manufactured by
Kimberly-Clark) and see how engineers at Kimberly-Clark have designed their
product, which just happens to be your biggest competitor.
Vocabulary/Definitions:
Polymer: a long chain of repeating molecules. There are many common
polymers derived from algae, such a carrageen, xanthan gum, and gelann
gum.
SAP: Super-Absorbent Polymer
Reverse Engineering: Making a diagram of a product by disassembling it and
taking careful notes
Attachments




Disposable Diaper Handout
Diaper Evolution
Disposable Diaper Chemistry
Example Data
Procedure
Disposable Diaper Reverse Engineering (groups of 2)
1. Examine your disposable diaper. Think about form and function, why and
how does it work? Cut the diaper in half down its length and give one-half
of the diaper for each group of two people. As you examine your diaper,
create a cross-sectional schematic diagram of the important parts (see
Fig.1 as a basic example). Make sure to note ALL the parts. Does the
cotton feel like normal cotton?
INSIDE
Figure 1
Schematic
crosssectional
OUTSIDE
diagram of
2. Remove the cotton batting from the diaper and place ait baby
in the plastic bag.
3. Cut (or break-off) an approx. 1” x 1” square piece anddiaper
put it(very
aside for later
basic).
use.
4. Break-up the batting in the bag and separate the grainy crystals from the
cotton. After breaking up the cotton some white crystals (they look like salt
granules) will collect in the bottom of the bag. These are the “white
gold”, Super Absorbant Polymer (SAP).
Absorbancy
1. Obtain a “cotton square” from the teacher. This is the type of cotton
typically used for cleansing your face. Place the cotton square in a petrie
dish and add 10ml of DIW. Place the 1” square you recovered from your
diaper in a petrie dish and add 10ml of DIW. This is an example of the
difference between a cloth diaper (physical absorbancy) and the
disposable diaper with SAP (chemical absorbancy). Make some
observations, note the differences and arrive at an explanation for the
difference between physical and chemical absorbancy.
2. Weigh out approximately 0.25 grams of your recovered SAP into a petrie
dish and record the exact mass. These crystals are called Super
Absorbent Polymer (SAP). SAP is a dehydrated particle (powder) that will
rapidly pick up water.
3. In small increments, roughly 5 mL, add deionized water (DIW) to the SAP
in the plastic dish. Note how the crystals rapidly absorb the water. Allow
30-60 sec. for the SAP to absorb the water. Continue adding water in small
increments until the SAP appears to be “saturated”. The best test for test is
what we call the “snail trail test”. Slowly tilt the petrie dish and watch to see
if the SAP slides and leaves a slight liquid trail (like a snail moving) on the
plastic dish. Once you see the “snail trail” wait about 60 sec. and then
repeat the test. If it is gone, add a bit more water. When you see the “snail
trail” repeatedly, you are done. This is a subjective determination, so
have both partners agree when the experiment is complete!
Assessment
Post-Activity Assessment
Informal discussion: After completing this experiment, and seeing the amazing
properties of the SAP, it is clear why kids want to be in diapers longer! They
stay dry and end up with a nice gel pad for softer landings! SAP is not only
used in diapers. Today SAP is used in a wide range of applications, such as:
clean-up of all types of spills, including oil spills; as a fire retardant squirted on
the roofs of homes to prevent destruction in wildfires; as artificial snow in indoor
ski hills, predominantly in Japan; in garments (hats and bandanas) that can be
soaked and worn to prevent overheating; and in planting soil to keep overhead
plants from dripping or to decrease the frequency of watering; to prevent
erosion of topsoil in some of the worlds’ leading food producing areas.
Activity Extensions
Absorbancy Extensions for high school/college
1. Record the volume of water that was absorbed by your SAP.
2. Calculate the Absorbancy Ratio (AR) = ml DIW/g SAP
3. Repeat steps 2-5 using salt water with 0.5 g SAP.
4. Calculate AR = ml Salt Water/g SAP.
5. REPEAT steps 2-5 for the commercial ChemSol SAP supplied by your
teacher
6. REPORT your DATA for DIW and SALT WATER to the teacher. This data
will be later shared with the class for an analysis of the average absorbancy
ratio (AR) and experimental error (standard deviation).
Owner
Dr. Skip Rochefort, Chemical Engineering Department, Oregon State University
Last modified: 8/18/09