Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
SOIL ADDITIVE
Field of the Invention
The present invention relates to a soil additive
comprising a super absorbent polymer particulate and a
growth-promoting additive absorbed therein. The soil
additive is intended for addition to soil in low
concentrations to promote growth of plants, especially to
assist in facilitating growth of plants in a sustained
manner during dry periods. In particular embodiments,
the present invention relates to a controlled release
fertilizer that is based on slow release of plant
nutrients encapsulated in sodium polyacrylate polymer,
formed by incorporation of the nutrients into the polymer
when it is in a water swollen gel state, after which the
product is dried.
Background to the Invention
Controlled release fertilizers have been available
for some time. Typically they are composed of chemical
fertilizer granules with a porous coating which in moist
soil allows diffusion of plant nutrients (ions) into the
adjacent soil environment. An example is the controlled
release fertilizer available from Scotts Co. under the
trademark "Osmocote". By varying the nature and/or
thickness of the coating, nutrient availability over a
range of time periods can be achieved. However, as the
moisture environment around the granules in the soil is
controlled by the moisture content of the soil, under dry
conditions the transfer rate of nutrients to the roots
from the fertilizer granules tends to be greatly reduced.
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Technology for increasing the retention of moisture
in soils is also known. Both natural products, e.g. peat
moss and the like, and synthetic water absorbing polymers
are used in horticultural/agricultural applications.
S Examples of such polymers are those available under the
trademarks "Liqua-Gel" and "SuperSorb". Such synthetic
water absorbing polymers utilized in agricultural end-
uses absorb high volumes of water as soon as they are
placed in soils.
Adequate moisture supply is critical to roots,
especially to plants whose growing medium is subject to
long periods of moisture deficiency. Various
superabsorbent polymer (SAP) gels have been offered
commercially to address the problems of inadequate
moisture supply to roots. So called agricultural SAP
chemicals, which are acrylamides or acrylamide
copolymers, are non-ionic or have a very low anionic
character. As a consequence of the non-ionic state,
there tends to be a relative insensitivity to the
presence of cations in the soil and hence the degree of
swelling of the agricultural SAP tends to remain constant
over repeated wet/dry cycles. In contrast, anionic SAP's
which are normally sodium polyacrylate, tend to lose
their ability to absorb large quantities of water in a
cyclic wet/dry environment because of exchange of cations
from the surrounding soil, particularly from clay soils.
During dry periods, sodium polyacrylate tends to
condense and form crosslinks that inhibit re-swelling
when it is re-wetted. Even when used in situations where
a limited number of wet/dry cycles are experienced,
sodium polyacrylate inhibits plant growth or in some
cases is toxic to plants. This inhibition of plant
growth or toxicity is believed to arise because the
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sodium ions in the sodium polyacrylate network are
exchangeable and these ions are adsorbed by clay
particles or tend to undergo exchange with cations on the
surface of plant roots. The consequence is a condition
that is analogous to an alkali soil, which generally
tends to adversely affect or inhibit plant growth.
Super absorbent polymers have been studied for_many
years for use as soil additives to increase available
water for plants. R.H. Fikhof et al. Proc. 12th Nat Agr
Plastics Conf. 1974 studied the influence of a
I5
hydrophilic polymer on the water requirements of
container grown plants. Gehring and Lewis reported on
the effect of hydrogel on wilting and moisture stress of
bedding plants, (J. Amer. Soc.. Hort. Sci. 105, 511-14
(1980)). Later, W.G. Pill HortScience 23, 998-1000
(1988) studied the use of acrylamide based polymer gels
as growth media for tomato seedlings.
Sensitivity of hydrogels to the presence of salts
has caused the focus to be on acrylamide-based polymers
rather than ionic polyacrylates, although even
polyacrylamide superabsorbents show a decrease in water
absorption in the presence of soluble salts. Bowman,
Evans and Paul, J. Amer. Soc. Hort. Sci. 115: 382-86
(1990) reported that divalent cations at a concentration
of 20 meg/liter reduced water pickup by a polyacrylamide
gel to about 10~ of the level observed in distilled
water. Lamont and O'Connell, reported in Scientia
Horticulture 31: 141-49 (1987) that there was no
improvement in bedding plant dry shoot weight when
polyacrylamide and polyacryiamide copolymer was used,
compared with controls.
U.S. 5,405,425-of Pieh et al relates to the addition
of a sulphonyl group to acrylamide polymers and
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copolymers to reduce the deswelling effects of salts
present in soil. U.S. 4,906,276 and 4,985,062 of Hughes
disclose polymerization of acrylic acid using special
polymerization procedures with potassium and ammonium
ions to provide ion species for plant growth when the
product is swollen in moist soil. U.S. 4,997,192 of
Martinau et al. discloses incorporation of a fine grain
inorganic powder, clay, during polymerization of a cross-
linked water-absorbing polymer or copolymer composed of
acrylic acid and acrylamide.
Canadian 1,309,070 of Cooke describes a polyacrylate
useful in dry sandy soils to retain moisture. Nutrients
or bacterial strains that increase plant yield can be
absorbed by the swollen gel which is then dried and added
to the soil. The patent is particularly directed to
polymerizing an acrylamide monomer, the polymer product
obtained being subsequently swollen in an aqueous medium
containing additive substances e.g. plant nutrients.
U.S. 4,559,074 of Clarke relates to use of cross-
linked non-ionic polyacryiamide as an additive for a
plant growth medium.
Use of polyacrylamides in horticultural or
agricultural end uses tends to be modest, primarily
because of cost. Although crop yield improvements have
been reported, applications are generally restricted to
some horticultural uses. Inclusion of plant nutrients in
polyacrylamide applications would be expected to further
increase costs.
In preferred embodiments, the present invention
makes use of SAP widely used as absorbents in the
hygienic disposables industry. A process exists for
recovering such SAP, developed by Knowaste Technologies
Inc. of Mississauga, Ontario and illustrated in PCT
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application 4J0 92/07 995 of M.E. Conway et al, published
May 14, 1992. Such SAP may be used in the preparation of
the soil. additives described herein.
Improvements in existing soil additives would be
5 beneficial, especially an increase in water absorption of
super absorbent polymers over repeated wet/dry cycles in
the soil to effect a gradual release of captured nutrient
ions.
Suaaaary of the Invention
A soil additive formed from a super absorbent
polymer and a growth promoting additive has now been
found, which is more effective in producing plant growth
than the super absorbent polymer and the growth-promoting
additive when added separately to the soil.
Accordingly, an aspect of the present invention
provides a soil additive comprising a super absorbent
polymer and a growth-promoting additive, said super
absorbent polymer being a polyacrylate and being in the
form of a particulate and said growth-promoting additive
being absorbed into the super absorbent polymer
particulate, said super absorbent polymer containing
growth-promoting additive having an absorption capacity
index in the range of about 4 to 50, where absorption
capacity index is defined as: (wt of water saturated gel
polymer - polymer dry wt)/polymer dry wt.
In a further aspect, the present invention provides
a soil additive comprising a super absorbent polymer and
a growth-promoting additive, said super absorbent polymer
being a polyacrylate and being in the form of a
particulate and said growth-promoting additive being
absorbed into the super absorbent polymer particulate,
said super absorbent polymer having been treated, when it
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is in a swollen aqueous gel state, with a composition, a
major portion of said composition being inorganic
compounds and at least part of said composition being
growth-promoting additive, said treatment with said
composition effecting shrinkage of the super absorbent
polymer such that the absorption capacity index of said
super absorbent polymer containing growth-promoting
additive is in the range of about 4 to 50, where
absorption capacity index is defined as: (wt of water
saturated gel polymer - polymer dry wt)/polymer dry wt.
In preferred embodiments of the invention, the
growth-promoting additive is urea or a nitrate,
especially ammonium nitrate or calcium nitrate.
In another embodiment of the invention, the super
absorbent polymer is sodium polyacrylate.
In a further embodiment of the invention, the super
absorbent polymer is recycled super absorbent polymer,
especially super absorbent polymer separated from a
process for recovery of components from personal care
products.
In yet another embodiment, the soil additive is
added to soil in an amount of 0.01-0.5 percent by weight.
In another embodiment, the inorganic compound is
calcium nitrate, the growth promoting additive is urea,
the ratio of urea to super absorbent polymer is 0.5-3:1
by weight and the ACI of the superabsorbent polymer,
after urea addition, is in the range of 2-30.
In another aspect of the invention, there is
provided a method of forming a soil additive comprising a
3o super absorbent polymer and a growth-promoting additive,
said super absorbent polymer being a polyacrylate and
being in the form of a particulate and said growth-
promoting additive being absorbed into the super
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absorbent polymer particulate, said method comprising the
steps of treating super absorbent polymer in a swollen
aqueous gel state with a composition, a major portion of
said composition being inorganic compounds and at least
part of said composition being growth-promoting additive,
said treatment with said composition effecting shrinkage
of the super absorbent polymer such that the absorption
capacity index of said super absorbent polymer containing
growth-promoting additive is in the range of about 4 to
50, where absorption capacity index is defined as: (wt of
water saturated gel polymer - polymer dry wt)/polymer dry
wt, and separating said soil additive.
Brief Description of the Drawings
The present invention is illustrated by the
drawings, as follows:
Figure 1 is a graphical representation of results
obtained in Example III; and
Figure 2 is a graphical representation of results
obtained in Example VI.
Detailed Description of the Invention -
The present invention is a granular soil additive,
and the related soil treatment, that incorporates slow
fertilizer release in a specially formulated hydrogel
that undergoes gradual expansion in a wet environment.
The soil additive is formed from a sodium or potassium
polyacrylate super absorbent polymer (SAP) that has been
treated in its gel state with growth-promoting additives.
The treatment is adjusted to produce a controlled degree
of gel deswelling. After it is dried, and during use in
soil, the soil additive undergoes slow reswelling in a
moist soil and the trapped growth-promoting additive is
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released slowly over time. Typically during a growing
season, soils undergo repeated wet/dry cycles. During
each cyclic wetting, there is an additional release of
growth-promoting additives into the soil.
As noted above and illustrated herein, the present
invention relates to a soil additive comprising a super
absorbent polymer and a growthpromoting additive, and use
thereof. The growth-promoting additive is absorbed into
the super absorbent polymer, and is not merely an
admixture of super absorbent polymer and growth-promoting
additive.
Anionic super absorbent polymers are preferred as
the SAP used in the preparation of the soil additive of
the present invention, especially because their level of
swelling in aqueous solutions tends to be dependent upon
the cation concentration of the solutions. Potassium and
sodium polyacrylates are especially preferred and
furthermore have the advantage of being available
commercially because they are widely used for absorption
of body fluids in hygienic disposable products, e.g. baby
diapers, sanitary napkins, adult incontinence products
and the like.
Super absorbent polymers that are acrylate polymers
are normally cross-linked during the manufacturing
process. Any cross-linking referred to herein is in
addition to cross-linking that may have occurred in the
processes for the manufacture of the polymer.
The super absorbent polymer may be virgin polymer,
but it is particularly intended that the super absorbent
polymer would be such polymer that has been recovered
from another process, one example of which is recovery
from used disposable diapers or other absorbent sanitary
paper products, also referred to herein as personal care
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products, during processes for recycling and recovery of
components of such processes for future use.
In embodiments of the invention, dry solid sodium
polyacrylate is swollen in water, using ratios of about
1:25 to 1:300 of sodium polyacrylate: water. At ratios
below about 1:75, the gel absorbs essentially all of the
water, and dry ionic solids or even slightly soluble
molecules such as calcium hydroxide or water-soluble
organic molecules such as urea may be added directly to
the gel. The solids essentially dissolve in the bound
water in the gel, which undergoes extensive deswelling.
As a result of inherent water absorbent properties,
superabsorbent polymers tend to swell on contact with
water. The super absorbent polymer, after treatment for
use in the soil additive of the present invention,
preferably has an absorption capacity index (ACI) that is
in the range of about 4-50, especially in the range of
about 10-45. As noted above, ACI is defined as: (wt of
water saturated gel polymer - polymer dry wt)/polymer dry
wt. The measurement of ACI is described herein.
The ACI of an anionic super absorbent polymer, such
as the polyacrylate polymers, may be decreased by cross-
linking of the polymer with cations. Examples of
chemical compounds that may be added to the aqueous
solution to effect cross-linking include soluble salts of
at least one of an alkaline metal, an alkaline earth
metal, aluminum, copper (II), iron (III) and zinc.
Examples of such salts include calcium chloride, calcium
nitrate, dicalcium phosphate, tricalcium phosphate,
magnesium chloride, magnesium nitrate, magnesium sulphate
potassium nitrate, dipotassium phosphate, superphosphate,
disodium phosphate, barium chloride, barium nitrate,
disodium phosphate, trisodium phosphate, sodium nitrate,
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aluminum sulphate, aluminum nitrate, zinc sulphate and
zinc nitrate. In addition, salts of ammonium ions, e.g.
diammonium phosphate, triammonium phosphate and
especially ammonium nitrate may be used. Calcium
5 hydroxide may also be included to aid in deswelling the
SAP. In preferred embodiments of the present invention
the cation used is potassium, calcium or ammonium or a
combination of these cations, and the anion is nitrate.
The amounts of cross-linking agent and growth-
10 promoting additive are adjusted so that the absorption
capacity index (ACI) of the super absorbent gel polymer
is preferably in the range of about 4-50, as indicated
above. This is substantially less than ACI typically
characteristic of super absorbent polymers, which is
substantially above 100.
The particulate gel super absorbent polymer that has
been treated as described herein is separated from the
aqueous solution and subjected to drying procedures,
preferably in a heated air stream at about 60°C or lower.
In embodiments, drying is allowed to proceed until a hard
solid of about 1-10% moisture content is obtained, which
is then ground to size for adding to soil.
The growth-promoting additives that may be used
herein include the nitrate and phosphate compounds
mentioned herein as cross-linking agents, as such
compounds may function as both cross-linking agents to
deswell the SAP and as growth-promoting agents. Urea is
another growth-promoting additive that can be
incorporated into the super absorbent gel matrix to
produce a delayed release fertilizer. Urea is a water
soluble organic compound that is slightly basic.
However, it is not cationic, and thus it does not deswell
anionic super absorbent polymer gels.
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As will be shown in an example, addition of urea to
a SAP gel, that was previously treated with an inorganic
compound such that the SAP gel had an ACI in the 5 to 50
range, results in absorption of the urea into the SAP
gel, dissolving in the bound water within the gel. There
is no further deswelling with this treatment, and it is
believed that all of the urea is retained within the gel.
The preferred ionic deswelling agents are compounds
that contain ions beneficial to plant growth, e.g.
ammonium, potassium, nitrate, phosphate etc. It is
preferred that the resulting dry solid have a controlled
reswelling characteristic i.e. the first expansion in the
presence of water is moderate and subsequent wetting with
pure water brings on an increase in swelling over several
cycles. This behavior may be achieved with divalent ions
such as calcium or magnesium. Thus, for example, calcium
salts can be used with ammonium salts. Relatively
insoluble calcium compounds can be used e.g. calcium
hydroxide. Water soluble organic compounds may be
introduced into the gel network either before or after
the deswelling agent is added. In embodiments,
sufficient urea is added, for example, to yield a final
product with more than 32% nitrogen. In other
embodiments, when the sodium polyacrylate:water ratio is
in the range of 1:30-50, urea dissolves in the bound
water in the gel with little or no deswelling of the gel.
A high concentration of urea in the sodium polyacrylate
increases its rewet ACI. By incorporation of high urea
concentration in the gel structure it is possible to
achieve nitrogen levels not achievable using super
absorbent polymer polymerization processes with use of
nitrogen containing salts.
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For processes for recovery of SAP after use, in
which it is swelled and mixed with other ingredients, for
example, in a process for recovery of components of
soiled hygienic disposable products, such as that
described in the aforementioned PCT application WO
92/07995 of M.E. Conway et al, a multi-step process as
described above has certain advantages. The first
treatment, using the aforementioned cross-linking agents,
reduces the ACI of the swollen gel to a desirable level
for its separation from the other recycle products.
Introducing fertilizer ingredients at this point in such
a process causes a significant amount of the fertilizer
ingredients to be lost since it remains in the slurry
from which the dewatered gel SAP is recovered. Also, the
process waste water would likely be unacceptably high in
nitrogen for most municipal sewage treatment operations;
if nitrogen is part of the fertilizer composition.
Multivalent, low pH salts are disclosed in the
aforementioned PCT application of M.E. Conway et al. that
do not create sewage disposal problems. Alternatively,
basic compounds such as calcium hydroxide or calcium
carbonate may be used to dewater the gel SAP.
While a growth-promoting additive may be added in a
separate step, it is preferred that the treatment and
formation of the particulate form of the super absorbent
polymer and addition of the growth-promoting additive be
carried in one step by utilizing a cross-linking agent
that is in itself also a growth-promoting agent.
Nonetheless, it is to be understood that for practical
reasons it may be necessary to utilize two or more steps
to effect deswelling and incorporation of a growth-
promoting additive. As an example, use of ammonium
nitrate for both deswelling and as growth-promoting
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additive may require the use of environmentally- ,
unacceptable amounts of ammonium nitrate. If the growth
. promoting additive has nitrogen, phosphorus and potassium
components, it may be preferable to utilize a three-step
process to formulate the soil additive.
The soil additive of the invention is added to soil,
for instance by using techniques typically used for the
addition of fertilizers to soil. The amount of soil
additive added to soil may be varied over a wide range of
concentrations. Nonetheless, a concentration of soil
additive that is sufficient to effect promotion of growth
of plants within the soil but not substantially in excess
of such a concentration should be used, .for practical
reasons. For example, typical concentrations may be in
the range of 0.05-0.5% based on the dry weight of soil,
with a preferred range of 0.1-0.4%, although it should be
understood that the concentration to be used will depend
on the concentration of the growth-promoting agent used,
the soil composition and the type of plants grown.
The invention discloses a novel way to provide a
growth-promoting additive that is released slowly over
time into soil as the soil undergoes alternate wet and
dry periods. As these growth-promoting additives are
released, they are in an environment of relatively high
moisture content which surrounds each gel super absorbent
polymer particulate. As the soil dries out, the zone
surrounding the super absorbent particulate better
retains its moisture and this zone also has a greater
concentration of the growth-promoting additive. Thus, it
is believed that a more desirable environment is created
for the plant roots in these zones. The particulate of
this invention undergoes an increase in absorption
capacity index when subjected to alternate wet and dry
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cycles; therefore, additional amounts of growth-promoting
additive are released over time to the soil for
absorption by plant roots. For this mechanism of
diffusion of growth-promoting additives out of the SAP
particulate into the soil to take place over repeated wet
and dry cycles, it is necessary that the SAP not swell to
its maximum extent when it is first placed in water. On
the other hand, it is believed that some increase in
swelling must occur over time in order for the growth-
promoting additives to diffuse out of the particulate.
The absorption capacity index (ACI) test used herein
was as follows: l.Og of the dried particulate product was
placed in 200 ml of water for a period of time. The
resultant gel was collected on a fine mesh screen and the
weight of the gel was measured, from which the ACI
value was calculated. The procedure was repeated, after
discarding the water not absorbed in the gel, using a
further 200 ml of water and the ACI value was re-
calculated. This procedure was repeated for 5 or more
cycles. This testing cycle was used as a simulation
of the moisture behaviour found in soil. For instance,
under wet soil conditions, where there is runoff and/or
loss to the water table in the soil, the SAP should
experience swelling similar to immersion in water. As
the soil dries out, water diffuses out of the SAP along
with trapped salts and it will reach the moisture content
measured in the "gel" state. Nonetheless, it is
understood that in actual conditions in a soil, further
soil drying will also reduce the water content of the
SAP, but this loss will be influenced by the osmotic
forces developed in the soil. This was deemed to be
outside the scope of measurement in laboratory tests used
to assess the present invention.
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The present invention is illustrated by the
following examples.
Example I
5 Table 1 contains a summary of the composition and
properties of a series of formulations of super absorbent
polymer compositions. The same super absorbent polymer
source, Stockhausen Favor "Fam" sodium polyacrylate, was
used in all of the formulations in the Table.
10 The columns showing water ratios list the
solid/water ratio for each of the ingredients. A value
of zero indicates that the solid was added as a dry salt.
When two or more salts were added sequentially, with
filtration and collection of the gel between addition of
15 the salts, the second salt is shown in the column "SLT
2". When two salts were added without an intermediate
filtration of the gel, both salts are listed in "SLT 1"
along with their respective weights.
The footnote to the Table shows the names of the
compounds that were used. ACI values were measured as
described herein. "Rewet ACI" shows the ACI values of
the formulations after having been rewet 1, 2, 3 or "n"
times.
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16
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- ~ I~ u~ o m~ u~Ino 0 0 0 0 0
E-~ o 0 0
",3 U7 f-1 d'rl M MM M M M M N
l'~7 M M M
O O
dl
I I I
b
O N M Lf)l0(~ O rl N M O
H d' CO d'
01
(1','Z,N N N N NN N M M M M U ~ ~ x
N N N M
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The first step in the procedure used in the Runs of
Table 1 above was to dissolve the SAP in water. In Runs
1-12 and 14-23, large quantities of water (150:1 to
300:1) were used so that there was excess of water i.e.
free water, present with the swollen gel. In Runs 24-34,
lower water quantities were used (20:1 to 35:1). In
these Runs, the gels obtained were semi-solid i.e. there
was not free water present with the gel. Run 13 was a run
in which granular SAP was added to a higly concentrated
calcium nitrate solution, without addition of water.
The quantity of water presen~ with the gel during
the subsequent deswelling by ionic salts affected salt
concentration, which in turn influenced the ACI values
that were obtained. Thus, the ACI values recorded in
Runs 1-12 and 14-23 were greater than those obtained in
Runs 24-34.
In a number of Runs, the composition had
water: calcium nitrate in a ratio of 1:0.6. The runs with
the higher water content viz. Runs 12, 17, 19, 23, showed
higher ACI values than the Runs with the lower water
content viz. Runs 24, 25, 27 and 34.
The data show that reversing the order of addition
of two salts can affect polymer reswelling
characteristics and the amount of nitrogen in the final
product (see for example Runs 15 and 17).
When urea used in Run 17 was substituted with sugar
(Run 19), the rewet values were similar. These organic
and essentially nonionic compounds appear to sterically
hinder the collapse of the gel network and subsequent
crosslinking of the SAP by the calcium ion during drying.
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As a result, on rewetting a larger amount of water is
absorbed.
The anion present in the calcium salt also affects
rewet characteristics. A large hydrated ion reduces
crosslinking which results in higher rewet values after
the treated SAP has been dried. For instance, Run 1 used
calcium nitrate whereas Run 5 used calcium hydroxide. The
initial rewet of Run 1 is low, but it increases with
repeat cycles. In contrast, in Run 5, use of calcium
hydroxide resulted in a treated SAP that essentially does
not reswell. Similarly, in Run 16 a high concentration
of calcium nitrate (15 g of calcium nitrate with 10 g
SAP) after addition of 40 g of urea, showed an initial
rewet with a low ACI (3), but on subsequent rewet cycles
the ACI value increased significantly.
Example II
Two compositions from Table 1, Runs 16 and 31, were
investigated for their retention of nitrogen compounds,
ammonium ions and nitrate ions, when the compositions
were immersed in water. The procedure used was to place
2.0 g of each composition in 400 ml of water and then
analyze the water from each composition for ammonium and
nitrate ions after various periods of time.
The samples of composition in water were stirred at
a moderate level using a Sybron N/4 stirrer. Ion
concentrations in Table 2 are reported in mg/L.
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Diffusion of Ions into Solution Over Time
Table 2
5 Time, min Run 16 Run 31
NH4' NO, NHQ' N03
_
1 1.0 90 8.6 20.6
10 0.3 12.8 9.7 44.7
1000 8.6 24.9 14.9 49.7
Ion diffusion out of the gel of Run 16 is lower than
the diffusion from the gel of Run 31, which could be.
expected from its lower ACI value. Also, diffusion of
the nitrate ion from the gels is greater than ammonium
ion diffusion. Even after 1000 min of stirring, the
nitrogen remaining in the gel of Run 31 is estimated at
over 90% based on a total nitrogen measurement of the
original compound.
Example III
The product of Run 34 was used in a plant trial to
determine the effect of the superabsorbent polymer
product on plants, and especially on the roots of plants.
"Red Robin" tomato seedlings were grown in a 50/50
spagnum moss/vermiculite medium in 6" pots containing the
product of Run 34, using 250g of medium and 10g of the
treated SAP of Run 34. After a period of 45 days, the
test was terminated.
It was found that the plants had an average fresh
weight of 2828. The sphagnum moss/vermiculite medium was
examined at the end of the trial and a number of swollen
SAP gels of >2mm diameter were observed. Most of the
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gels were penetrated by roots and in some cases the roots
also exited i.e. passed right through, the gels.
It was concluded that the roots were not adverse to
' the presence of the treated SAP product, and actually
sought out the nutrients and water absorbed within the
product. It is believed that the roots have the
capability of extracting nutrients such as nitrate,
phosphate and potassium ions directly from the treated
gels of the SAP product.
Example IV
A series of compositions of super absorbent polymers
and plant growth promoting additives is shown in Table 3.
The method of preparation of each composition is given,
together with the ACI of the product prior to 5 drying.
"Favor'Sodium polyacrylate polymer, FAM type, from
Stockhausen was used as the starting material for all
compositions.
Table 3
Sample No. Preparation
1 45 g NH4N03 in 1 liter water added to 20 g.
SAP in 3 liters water followed by 5 g
Ca(NO,), in 500 ml water. Gel was filtered
(ACI = 35.6) and dried.
2 12.5 g Ca(N03)z granules added to 20 g SAP
in 3 liters water, Gel collected (ACI =
34.6) Add 20 g NH4 N03 to gel. Collected
dewatered gel (ACI = 5.0) and dried.
3 20 g SAP granules added to 80 g Ca((N03)a
in 100 ml water. Collected gel (ACI = 1.1)
and dried.
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4 50 g Ca((N03)Z in 1 liter water added to 20
g SAP in 3 liters water. Gel collected
(ACI = 2.4) and dried.
20 g Ca(OH)2 in 200 ml water added to 10 g
SAP in 3 liters water. Granular material
collected and dried.
Note: Samples 1, 2, 4 and 5 are Runs 3, 12, 1 and 6
respectively of Table 1.
The rate and degree to which these products reswell
in water are shown in Figure 1. The ACI vs Water
Treatment is also shown for the SAP polymer used in
preparation of the above compositions, identified as
untreated SAP in Figure 1, which is believed to be
typical of polyacrylate polymers used in hygienic
disposable products. Measurable swelling in water is
very rapid, taking place in less than one minute. An
unmodified commercial sodium polyacrylate polymer would
not be a satisfactory medium for controlled, delayed
release of growth promoting substances in soil.
Samples 1-4 when placed in water, for the ACI test,
show a markedly slower rate of swelling than the
untreated SAP. The rate and degree of reswelling
correlates with the ACI values shown in Table 1.
Sample 3 had a very low (1.1) ACI which is
attributed to its method of manufacture. In the
preparation of the sample, granular SAP rather than water
swollen SAP, was introduced into a highly concentrated
Ca(N03)2 solution and it is believed that the SAP never
became fully hydrolyzed.
Sample 5 did not swell or take on gel
characteristics after repeated ACI tests. This
formulation would not be a suitable candidate for slow
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release, into soil, of a growth-promoting additive
because it is believed that diffusion of trapped ions
(nutrient) out of the composition would be insufficient
to benefit plants. However, lower concentrations of
Ca(OH)2 combined with SAP did yield products that
reswelled in water.
Sample 5 demonstrates that sodium polyacrylate
polymer has a high affinity for Ca++ ion since it absorbs
this ion from dilute solution causing most of the calcium
hydroxide, which has a low solubility product, to
dissolve. The calcium ion concentration in Sample 5 is
actually lower in the SAP than it is in Sample 4, yet
Sample 4 shows greater reswelling properties in water.
Its resistance to reswelling is attributed to steric
effects. In the case of Sample 4, the presence of the
larger nitrate anion in the gel vs the hydroxyl anion in
Sample 5, is believed to prevent the SAP network from
condensing as much during drying and it is more amenable
to subsequent swelling in water. This test result
demonstrates that difficultly-soluble salts can be
incorporated into water swollen SAP in appreciable
quantities. Thus, it is believed that growth-promoting
substances with low solubility can be incorporated into
the gel structure if they have an ionic character.
Example V
The SAP used in preparation of the samples of
Example IV was treated as in Table 3. 70 g Ammonium
nitrate in 1.5 liters of water was added to 30 g SAP in 6
liters of water to give a gel ACI of 45 (Run 3 of Table
' I). This sample was coded SAP/AN. The composition was
tested as a soil additive, and compared with the use of
each component separately as a soil additive viz. the use
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of each of sodium polyacrylate and ammonium nitrate as a
soil additive, as well as addition of a mixture of SAP
and ammonium nitrate in admixture i.e. in which the
ammonium nitrate was merely admixed with the SAP but not
absorbed therein.
Two week old "Orangeade" Marigold (Burpee)
transplants were grown in 500g of growing medium in 16 oz
(473m1) plastic containers under experimental conditions
shown in Table 11. Two soil types were used: 100% garden
soil (S) and a 50/50 soil/sand mix (SS). Two levels of
water application were employed in each watering cycle:
High (H) and Low (L). All soil treatments were given
equivalent water volumes in each cycle but the amount of
water did not remain constant throughout the cycles
because of different degrees of soil dryness and the
amount of water transpired by the plants as their root
mass changed. Thus soil treatment was studied under four
conditions: high and low water addition in soil and high
and low water addition in the soil/sand mix.
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Table
4
Run Treatment Soil Water Soil Recipe, g
No. Code Type Addition SAP AN SAP/AN
5
SAP S H 1.5
36 SAP SS H 1.5
37 SAP S L 1.5
38 SAP SS L 1.5
10 39 SAP/AN S H 2.25
SAP/AN SS H 2.25
41 SAP/AN S L 2.25
42 SAP/AN SS L 2.25
43 CONTROL S H
15 44 CONTROL SS H
CONTROL S L
46 CONTROL SS L
47 SAP+AN S H 1.5 0.75
48 SAP+AN SS H 1.5 0.75
20 49 SAP+AN S L 1.5 0.75
SAP+AN SS L 1.5 0.75
51 AN S H 0.75
52 AN SS H 0.75
53 AN S L 0.75
25 54 AN S L 0.75
In the Table, Control to samples that were
refers
watered were
but not
which treated
with
SAP
and/or
AN
in
any form. SAP/AN refers to the
modified
SAP of
Example
30 III i.e. samples f the whereas SAP+AN refers
o invention,
to SAP dmixture only.
addition and
of AN
the in
a
Plant height was r time. Table 5 shows
measured
ove
the average results from the four testing conditions
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applied to the five soil treatments over the indicated
period of time.
Table 5
Run No. Test Condition Growth (cm) Growth (cm)
Three Weeks Four Weeks
55 SAP 13 19
56 SAP/AN 23 30
57 CONTROL 14 18
58 SAP+AN 18 26
59 AN 18 28
The marigold plants grown in containers with the
treatment of the present invention, SAP/AN, showed the
greatest growth. This growth was superior to use of the
known fertilizer, ammonium nitrate (AN) or to the use of
an admixture of SAP and AN. The treatment of SAP alone at
this concentration, 0.03 weight %, resulted in plant
growth that was indistinguishable from the untreated
control.
Example VI
"Aztec" Hybrid Sweet Corn (Ferry Morse) kernels were
germinated directly in a 50/50 soil sand mix in 16 oz
plastic containers. Three modified SAP samples of Example
1, in which ammonium nitrate and calcium nitrate were
added, were compared with: (1) a treatment consisting of
separate additions of granules of super absorbent polymer
and ammonium nitrate, [coded SAP + AN], and (2) untreated
soil controls. The treatments are shown in Table 4.
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Table 6
R~ Relative
No. Treatment Plant Size
60 SAP+AN (0.26g SAP, 0. 1 5g AN); No Leaching 20
61 SAP/AN (0.418 SAP/AN); No Leaching 1
62 Control; No Leaching g
63 SAP/AN+CN (0.41g SAP/AN+CN); No Leaching 3
64 SAP/CN+AN (0.41g SAP/CN+AN); No Leaching 8
65 SAP+AN (0.26g SAP, 0.15g AN); Leaching 13
66 SAP/AN (0.418 SAP/AN); Leaching 5
67 Control; Leaching 10
68 SAP/AN+CN (0.41g SAP/AN+CN); Leaching 2
69 SAP/CN+AN (0.41g SAP/CN+AN); Leaching 4
70 SAP+AN (0.26g SAP, 0. 1 5g AN); No Leaching 14
71 SAP/AN (0.41g SAP/AN); No Leaching 12
72 Control; No Leaching 16
73 SAP/AN+CN (0.41g SAP/AN+CN); No Leaching 6
74 SAP/CN+AN (0.41g SAP/CN+AN); No Leaching 18
75 SAP+AN (0.26g SAP, 0. 1 5g AN); Leaching 15
76 SAP/AN (0.418 SAP/AN); Leaching 11
77 Control; Leaching 17
78 SAP/AN+CN (0.41g SAP/AN+CN); Leaching 7
79 SAP/CN+AN (0.41g SAP/CN+AN); Leaching 19
In the Table, "Leaching" indicates that the amount
of water added in each cycle was sufficient to cause
drainage from the container and salts were leached from
the soil, whereas "No Leaching" indicates that the amount
of water added was insufficient to cause drainage from
the container. The plants were compared and rated for
overall size, (1 for largest and 20 for smallest) after 6
watering cycles, at which time they were becoming
rootbound.
The average of the four measurements for each
treatment indicates that modified SAP, when its ACI is
above 3.0, results in increased corn growth. The
results, in which the lower number indicates better
results, were as follows:
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Run No. Treatment Avg. Size Rating
80 SAP/AN+CN 4.5
81 SAN/AN 7.3
82 SAP/CN+AN 12.3
83 No Treatment 13.0
84 SAP+AN 14.3
The growth results from the five treatments fall
into two groups. Plants grown with modified SAP
treatments, SAP/AN+CN and SAP/AN, were substantially more
vigorous than those grown with the other treatments. At
the low concentration of the treatments used in this
test, the treatments SAP+AN and SAP/CN+AN were little
different from the Control. In the case of the SAP/CN+AN
treatment this is attributed to its low, 3.0, ACI value
which indicated it did not, under the test conditions
used, provide sufficient moisture and nutrients to the
plants.
Example VII
In this Example, a series of experiments were
conducted to illustrate the effect on gel SAP properties -
of the order of addition to gel SAP of an ionic nitrogen
containing compound (calcium nitrate) and a covalent
organic nitrogen compound (urea). Two concentration
levels of the nitrogen- containing compounds were used.
In particular, the effect of the order of addition and
compound concentration was determined for: (i) the
ACI of the gel SAP, (ii) the nitrogen concentration in
the dried SAP products, and (iii) the reswelling
characteristics of the dried SAP products.
In Step 1 of each experiment, 10.0 g of Stockhausen
"Favor' Fam type sodium polyacrylate were mixed with 1.5
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liters of water. The resulting gel had no free water
present. After about 30 minutes, the first nitrogen
containing compound was added. After a further one hour,
the dewatered SAP gel was filtered from any free water.
The gel obtained was weighed and the ACI calculated.
In Step 2, the other nitrogen containing compound
was added to the gel from Step 1. The gel was filtered
from any free water present. The gel was then weighed
and the ACI calculated. Subsequently, the gel was dried
at about 770°C.
Measurement of the nitrogen content of the dried gel
was made using the Dumas test. Rate of reswelling in
water was measured using the ACI test procedure described
above.
Further details and the results obtained are
summarized in Table 5 and Figure 2. The data in Figure 2
was obtained in the same manner as that in Figure 1 Note
that Runs 85-88 correspond to Runs 15-18 of Table 1.
Table 7
Run No. 85 86 87 88
SAP, g 10 ZO 10 10
1st nitrogen
Compound (g) U* 20 U 40 CaN* 6 CaN 15
gel ACI, first
treatment 152 154 26 2
. 30 2nd nitrogen
Compound (g) CaN, 6 CaN, 15 urea, 20 urea, 21**
gel ACI, 2nd
treatment 24 3 27 5
Nitrogen content,
dried gel % 13.4 NM*** 30,4 29.1
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* CaN = calcium nitrate
U = Urea
** This is the maximum quantity of urea that would
5 dissolve in the gel SAP.
*** Not measured.
These results show that gel deswelling only occurs
when the calcium ion is added. With Samples 87 and-88,
10 there was no water loss in the second treatment, so the
gel weight increased by the weight of the urea added, and
therefore the ACI value increased.
As urea does not dewater the gel SAP in the second
processing step, all of the urea remains in the SAP after
15 it is dried. Samples 87 and 88 showed retained nitrogen
levels of about 30~ which indicates urea concentration in
the dried final product of 65~ by weight.
The reswellability of sample 88, (see Figure 2) is
in contrast to Sample 86 when its low ACI after the
20 second treatment is considered, ACI=5 c.f. ACI=3. It is
believed that Sample 88 contained sa much urea that in
the final dry state of the SAP the calcium ions were not
as effective crosslinkers as in earlier tests where the
anion concentration within the deswollen gel SAP was
25 lower. Sample 88 has the added feature, vs sample 87, of
lower drying costs because there is less water to
evaporate from the gel.
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