A Simple Experiment to look at Super Water Absorbant Soils
Dr. Skip Rochefort and Norm Fraker
Chemical Engineering Department, Oregon State University
OVERVIEW
SAP is not only used in diapers. Today Super Absorbant Polymers (SAPs) are 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 (see ZEBA discussion below).
Introduction
The beauty of this experiment is that it can be a quick and simple (15 min.) mini-lesson or home
experiment, or integrated into a multiple session learning module on soils, water retention,
erosion, plant growth, etc. This has been tested with 2nd Grade Ashbrook Independent School
students as part of their soils and plants module, and with Benson High School students as a 15
min. fun experiment to demonstrate how a technology developed for one application (the
disposable baby diaper) can have a significant impact in a completely different areas such as:
home gardening; increased crop production in Eastern Oregon; erosion control for prevention of
landslides; and even the production of artificial snow for indoor skiing in Japan (that’s another
lesson for another month!).
NOTE: The Steve Spangler Science link below has a “boat load” of information on these
materials and ideas for how to use them, so I’m just going to cover a simple basic experiment
below. Visit that site….it’s pretty good!
Materials
- Planting soil (or soil from anywhere the kids want to get it)
- Super Absorbant Polymer (SAP): buy a baby diaper, rip it apart and recover the SAP from the
cotton batting – see http://engr.oregonstate.edu/momentum/k12/apr04/index.html for more
details). Contact Dr. Skip if you want a supply of SAP for a larger class or demonstration.
- Cups: two different sizes (small and big) so they can be nestled and you need to be able to poke
holes in the bottom (Styrofoam 10 and 12 oz cups work well).
- graduated cylinders (or anything to measure volume of water added)
- IMAGINATION: find a 2nd grader to help you
Optional additional Experiments
Repeat experiments with commercial planting products available in most plant nurseries.
- SoilMoist -- polyacrylamide based SAP for plants. (http://www.soilmoist.com/)
- ZEBA -- starch-based Super Absorbant Granules (Absorbant Technologies, Inc.)
EXPERIMENT
1. Fill two small cups about half-full with soil (any kind you want). The soil should be DRY
(not bone dry, but not from outside in May showers either). You can make as many pairs of
soil samples as you want to test, but they need to be in pairs.
2. Poke holes (toothpick works well for Styrofoam cups) in the bottom of two large cups (or as
many pairs as you want to use).
3. Place the cups filled with soil inside the cups with holes, making sure that there is enough
space in the nestled cups for water to drain out of the smaller soil filled cup.
4. Mix ½ teaspoon (or less for smaller soil samples) of super absorbent polymer (SAP) into one
of the pair of soil samples (now you see the reason for the pair). Mix in SAP well using a
fork, stick or whatever.
5. Add a known amount of water (100 ml works well) to each soil sample pair and let it sit for a
few minutes (always hard with 2nd graders!).
6. Separate the two cups and measure the amount of water that has drained through the soil.
Compare the soil sample pairs – one normal and one with SAP. What is the observation?
7. Repeat with as many soil samples as you want to test. In the classroom, it is great to have the
kids bring in their own soil samples, either from their yards or their parents planting soils.
Remember, they need to be relatively dry, otherwise the SAP will “clump” when added.
8. Repeat using SoilMoist, ZEBA or some other commercial planting soils SAP additive.
OBSERVATIONS
1. For typical planting soils from a garden shop, when 100 ml of water is added to the soil
sample, approx. 50-70ml will flow right through in a couple of minutes. There should be
little or no water that flows through the same soil sample with SAP added. That is a shocking
observation for the kids. Where did it go?
2. If you haven’t done the diaper lab yet with the kids, you should take the plain SAP and let
them add water to that in a cup. They will quickly see what happened to the water in the soil.
It turned into a polymer gel (hydrogel) and trapped the water in the soil. That’s how it can
help prevent erosion or keep soils moist for a long time by the slow release of water from the
gel particles as they dry out.
3. If you have time, leave the soils out for a week or two and have the kids monitor moisture
content as a function of time. This can be done by sticking something into the soil (like their
fingers, a popsicle stick, etc.) to check how “wet” it is. You should observe that the soil with
SAP added will hold its moisture for a very long time. If you want to sacrifice a plant, you
could also plant something in each cup and watch which one wilts more quickly. This may be
cruelty to plants….I’m not sure about that.
For more information or to obtain some super absorbent polymer (SAP) contact:
Skip.rochefort@oregonstate.edu
Reference Web Sites (there are many others)
Best general site to visit: http://www.stevespanglerscience.com/experiment/00000038
Water absorbing Soil polymers: http://www.aquadiamonds.com/
SoilMoist superabsorbant granuales: http://www.soilmoist.com/
ZEBA Superabsorbant Granules: http://www.soilmoist.com/
ZEBA Superabsorbant Granules (Absorbant Technology Incorporated- ATI)
A Smart New Way to Grow Crops
Zeba, a new soil amendment from Absorbent Technologies, Inc. (ATI), offers growers nextgeneration technology that delivers higher-quality crops with greater yields, more cost-effective
input use, and more dependable plant germination and growth.With its proprietary
starch-based formulation, Zeba help plants maximize water usage and creates a healthy
microenvironment in the root zone that promotes vigorous plant growth and greater yields.
The core technology behind Zeba was developed by ATI advisor William Doane, Ph.D., and his
research group during his 32 years with the U.S. Department of Agriculture (USDA). Doane, an
authority on starch polymer chemistry, and the USDA team are credited with key scientific
breakthroughs, including several patents in superabsorbent technology. After eight years of
subsequent development, ATI has evolved these initial research concepts into a broad range of
new discoveries and patents, developing a commercial product that will change grower
production practices across the globe.
Chemical Composition
Zeba is based on natural cornstarch, making it an environmentally friendly, biodegradable,
nontoxic and virtually odorless granule. To understand why Zeba succeeds in the field where
synthetic petroleum-based polymers have failed, it is necessary to look at its chemical
composition.
• Starch-based. Zeba is formed by hydrolyzed starch-polyacrylonile graft copolymers. Zeba
copolymers are highly absorbent, but are water-insoluble. As a starch-based polymer, Zeba is
made up of glucose molecules, which are linked together chemically to become a waterinsoluble, net-like matrix in the form of a hydrogel that holds and releases water and nutrients.
There are no active ingredients in the hydrogel.
• Massive absorption. The immense size and weight of its molecular structure are what set Zeba
apart. These anionic units are able to absorb water, swelling up to 400 times their original
weight, until reaching maximum absorbency.
• Controlled release. The Zeba hydrogel slowly releases just the right amount of captured
moisture to plant roots in response to capillary action (suction) of the root hairs. The hydrogel
easily rehydrates and stores more water as moisture enters the soil. This process is repeated
over and over again for a year or more before the hydrogel loses effectiveness. Other factors
that affect moisture diffusion include soil moisture content and soil microbial activity.
• Potassium benefits. Zeba contains potassium as its positive ion instead of sodium, which is
used in other products, including synthetic polyacrylates and polyacrylamides. Plants benefit
from the addition of potassium as a nutrient. Increased amounts of sodium in the soil can limit
plant growth, especially in soils with high alkalinity levels.
• Soil enhancement. Zeba has high water-absorption and storage properties in a wide range of
water qualities and soil types. Because it is starch-based, Zeba particles are an attractive food
source for soil microorganisms. Over time, the microbes consume the hydrogel molecules,
creating a richer soil environment than before Zeba was added.
• No phytotoxicity. Zeba, a natural, starch-based product, is biodegradable and does not harm
plants or soil.
The difference between Zeba and diaper SAPs based on polyacrylates
Zeba is totally different from other water-preservation products, including any of the synthetic
polyacrylate and polyacrylamide formulations (e.g., PAMs) currently available. These synthetic
polymers are superabsorbents made with petroleum-based formulations and typically use the
active material found in disposable diapers. These synthetic polymers hold water tightly—a good
thing for diapers, but not for plants that compete with the polymers for moisture, which explains
why these formulationsare less effective in growing plants.
Zeba is a natural, starch-based formulation. It is nontoxic, biodegradable, pH-neutral and safe for
all plants. Many synthetic polymers typically contain significant amounts of sodium, petroleum
derivatives and other fillers, which can be detrimental to food crops. Zeba was developed to hold
400 times its weight in water, although a Zeba granule could be produced to hold as much as
5,000 times its weight. The Zeba particle has been developed to deliver the optimal balance of
water and nutrients to benefit plants in agriculture. The most important factor is not total
absorbency, but the ability of any superabsorbent to release the greatest amount of water as
the plant needs it.
In this vital area, Zeba is unmatched. Virtually all synthetic polyacrylates and polyacrylamides
are formulated by large chemical manufacturers and are repackaged by distributors under such
trade names as Terra-Sorb®, Soil Moist®, HydroSource®, Solid H20,
STOCKOSORB®,Tramsorb, Watersorb®, WaterSmart Crystals and WaterGel Spikes.