Note: Descriptions are shown in the official language in which they were submitted.
S. M. Bille-N. F. Cardarelli
104~27Z l-l
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This invention relates to a slow release fertil~
izer and to a process for its preparation.
Nitrogen, phosphorus and potassium are the pri~
mary essential elements for plant growth, and commercially
available fertilizers invariably comprise either or both
an organic and an inorganic compound containing one or
more of these elements in ~ome form. Agronomically, most
commercially available fertilizer materials are marked by
~,.
one notably detrimental phy~ical property - high water
solubility. Thus, treatment of plants with highly water
soluble fertilizer materials, particularly nitrogen-
containing, can be undesirable because the fertilizers are
readily solubilized, thereby releasing nutrients in the
soil at high concentrations. This results in luxury con-
sumption and nutrient imbalances. If the release of nutr~-
ents were controlled to more closely match actual plant
:.,
; re~uirements, a number of adva~tages would accrue. Eval-
uated from the viewpoint of plant physiology, controlled-
` release fertilizers, as compared to many conventional
; 20 fertilizers, maintain a more optimum concentration of
` nutrient in the root zone over a longer part of the plant
growth period. Particularly in the case of turfgrass,
controlled-release fertilizers applied in a single appli-
cation provide a more even rate of growth than split
applications of a soluble fertilizer at comparable rates.
- Other advantages of controlled-release fertilizers are
minimization of nutrient losses due to runoff or
;
iO47272
S.M. Bille - N.F. Cardarelli
. .
s volatilization, reduction of application costs through re-
duction in frequency of applications and prevention of veg-
etation burning or seedling damage.
Many attempts to control nutrient release to
plants have been made with varying degrees of success.
These efforts have focused on two broad areas: (1) devel-
opment of polymeric or discrete chemical compounds that
have limited water solubility, and (2) altering soluble
compounds in some manner to retard their release in the
soil-~solution, as by coatings or matrices which are water-
insoluble. A number of patents have issued on the results
of these effort~, many of which are directed to matrices
for fertilizers.
U. S. Patents 3,417,181 and 3,639,583 disclose
the use of a vulcanizable elastomeric matrix for the con-
trolled release of toxicants. ~owever, the mechanism of
rèlease of the active agent in the~e patents depends upon
a solubility equilibrium system requiring that the toxi-
,. .
cants be soluble in the matrix but have only limited water
solubility. Fertilizers, on the other hand, are normally
insoluble in elastomeric matrices and highly soluble in
wa~er. Moreover, because of elastomer solubility require-
ments, the elastomeric matrix of the aforementioned patents
must be present in large proportions, well over 80% of the
- 25 weight of the product. In the case of fertilizers, cost
among other considerations would normally preclude the use
of a product containing such large proportions of matrix.
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10~7272
proportions of matrix. Coatings or matrices intended to slow or control the
release of fertilizers should be effective at relatively low percentages in
order to provide the greatest fertilizer benefit and the lowest cost per unit
weight of product.
We have discovered that a vulcanizable elastomeric material forms
a highly effective matrix for the slow release of water soluble fertilizers. -
The proportion of active agent in the matrix, the manner of incorporation of
the fertilizer in the matrix and its method of release is totally different
from that set forth in the aforementioned patents. In the compositions of
the invention, the fertilizers are distributed throughout the elastomeric
matrix in which the fertilizer is insoluble and they are slowly and continu- -
ously released from the matrix in the presence of water by a leaching process.
Accordingly~ the present invention provides a slow release fertil-
izer composition comprising a water permeable~ biodegradable~ organic
vulcanizable elastomeric matrix material and a water soluble organic or
inorganic fertilizer distributed throughout said matrix, said matrix being
present in an amount of from 5 to 50% of the fertilizer weight, said
fertilizer being substantially insoluble in the matrix and adapted in the
presence of water to be slowly leached therefrom.
The present invention also provides a process of preparing a slow
release fertilizer composition comprising blending a water soluble organic or
inorganic fertilizer with from 5 to 50% by weight of the fertilizer of a water
permeable, biodegradable~ organic ~ulcanizable elastomeric material to
distribute the fertilizer throughout the matrix, forming shaped rods, sheets
or other forms of the blended composition, vulcanizing and comminuting the
` shaped composition to produce a finely divided composition in which the
fertilizer is substantially insoluble in the matrix and adapted in the pre-
sence of water to be slowly leached therefrom.
The vulcaniza~le elastomers use~ul in the invention retain higher
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~ 10~7Z72
loadings of active ingredients than the toxicants of the aforementioned patents
because the fertilizer or other active ingredient is retained in the matrix
as discrete particles rather than in solution. When placed in the soil,
water molecules from the external environment gradually permeate the surface
area of the elastomeric pellets or granules and contact the water soluble
fertilizer molecules. The latter pass into solution and move out of the
elastomer body in accordance with the law of solution kinetics. Removal of
` the fertilizer molecules or aggregates of molecules leads to the growth of a
fine pore structure within the pellet, thus facilitating water contact with
internal fertilizer
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1~ - 4a -
S.M. Bille - N.F. Cardarelli
1 ~047~72 1-l
5 -
with internal fertilizer molecules, which in turn pass
through the pore structures into the elastomer - water ~ "--
interface and hence to the external environment.
Water permeation of the elastomer base, pore
growth and solution and movement of the fertilizer are ~`
time dependent occurrences so that the 1098 of fertilizer
is continuous and 810w. Noreovex, the rate of fertilizer
release may be adjusted to achieve a specific desired
level by choice of add tives, process of compounding and
u~e of vulcanization.
The matrices useful in the practice of the in-
vention are organic elastomeric materials capable of being
'~ crosslinked or vulcanized. A particularly preferred class
't~ of rubbers useful as matrice~ are natural rubber, synthetic
; 15 natural rubbers (polyisoprene), cis-polybutadiene rubber,
ethylene-propylene and styrene-butadiene copolymers. The
foregoing elastomers are water-permeable, biodegradable,
;,
;; permit high loading of fertilizer and are relatively inex-
~f.` pensive. Other useful elastomers such as butyl rubber
(isobutylene/isoprene copolymer) and ethylene-propylene-
~
- dicyclopentadiene terpolymers may also be used. Polyure-
thane and polychloroprene type elastomers are also useful
~; although their cost is somewhat greater than those mentioned
above. The matrix may be used in an amount corresponding
.~;
to 5 to 50% of the fertilizer weight. The crosslinking of
vulcanization is carried out in a manner well known in the
rubber compounding art. Measured amounts of sulfur, sulfur
- bearing materials, metal oxides, peroxides, amines or other
-- 5 --
~ S. M. Bille/N. F. Cardarelli ~
~047272
known vulcanization elements, as they are known to the
trade, are added and the formulations are then exposed
to a time-temperature cycle to crosslink the elastomeric
molecules which in turn provide the proper matrix-~
geometry.
Virtually any water soluble organic or inorganic
fertilizer material may be used in the invention. Exam-
; ples are urea, ammonium sulfate, ammonium nitrate,
monoammonium phosphate, potassium chloride, potassium
sulfate and other well known plant nutrients.
In addition to the elastomer, the fertilizer and
the vulcanizing agent(s), a number of additives may be pre-
sent in the formulations. Powdered carbon or carbon black
is instrumental in controlling the release rate of the
active agent. This additive is entrained within the
matrix and serves to impede the progress of ingressing
water and the flow of water solution of the agent outward,
carbon blacks vary in geometry from course to very fine,
the more highly structured blacks, ranging from 20 to
40 millimicrons in diameter being superior in usage. The
carbon black may be used in amounts of 1 to 25 parts by
weight per hundred parts of elastomer.
Other additives may be added to the elastomer/
fertilizer systems in order to enhance specifically de-
sirable properties. Such additives include organic sub-
; stances that aid in the retardation of pore structure
growth, thus slowing the leaching system, such as waxes
and oils; or other polymers that in effect "coat" the
, agent retarding solubilization in water. This latter
"
S. M. Bille/N.F. Cardarelli- 1-1
1047272
class of materials is typified by polymers that bond
through H-O}~ attraction with urea - such as polyvinyl
acetate, polyamides, cellulose acetate and polyvinyl
alcohols. In addition, lubricants such as stearic
acid, anti-oxidants such as phenyl-beta-naphthylamine
and cure accelerators such as benzothiazole disulfide,
mercaptobenzothiazole and tetramethylthiuram disulfide
may also be added.
The compositions may be formulated by known
' 10 rubber blending techniques in conventional rubber pro-
,......................................................................... .
cessing equipment. Mixing may be carried out on two-
roll rubber mills or internal-type mixers. The compo-
sitions may then be sheeted off of a rubber mill or a
rubber calender or extruded as a rod of varying diameter.
It may then be vulcanized by placing between heated
plates, at the desired time - temperature, e.g. from
240 to 310F for from 15 minutes to 2 hours, or by pass-
ing through a hot air oven at the stated conditions.
After vulcanization, the sheets, rods or other shapes
may be chopped or otherwise comminuted into pellets,
granules, powder flakes or other finely divided form.
The formulations are then ready for application to the
soil, normally at a rate providing from 40 to 250
lbs/acre of nitrogen.
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The following examples illustrate the practice
:
; of the invention. All parts are by weight unless other-
'~ wise identified.
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S. M. Bille~N. F. Cardarelli - 1-1
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Example 1
The folluwing formulation was prepared, based
upon parts by weight of each ingredient.
Natural Rubber 100
Sulfur 1.5
Stearic Acid .2
Benzothiazole Disulfide0.~
Mercaptobenzothiazole0.7
Carbon Black 15
Zinc Oxide
Urea 150
The natural rubber was masticated and banded on
a rubber mill and the remaining materiala added gradually
while the milling continued. The remaining materials were
added in the following order: carbon black, stearic acid,
sulfur and zinc oxide, urea and finally the sulfide and
thiazole accelerators. The resulting formulation was then
vulcanized between heated plates at 240 for 60 minutes
and the resulting sheets were chopped into pellets.
.~
~ 20 Examples 2 - 4
i The following additional formulations were pre-
pared in accordance with the procedure of Example 1.
Example 2 used Ameripol-SN-600* (synthetic polyisoprene
rubber) as the matrix; Example 3 used Ameripol-CB-220*
(ci~polybutadiene rubber); and Example 4 used Ameripol-
1510* lnon-pigmented cold styrene-butadiene rubber).
*Trademarks
- 8 -
10'~72~Z
S. M. Billie/N. F. Cardarelli ~
_ 9 _ - ,
Example 2 Example 3 Example 4
.
Styrene-butadiene 100
Polyisoprene 100
Cis-polybutadiene 100
Sulfur 1.5 1.5 1.5
Stearic Acid 0.2
Benzothiazole
Disulfide 0.7
Mercaptobenzothiazole O.7 1.O 1.0
Phenyl-beta-
napthylamine 1.0
Carbon Black 20
; Carbon Black 20 20
~ .
~" Zinc Oxide 1.0
~i 15 Urea 130 150 150
i~ A series of greenhouse tests were run on the
coated products of Examples 1 - 4. The tests were run
on plots of Windsor Kentucky bluegrass seedlings con-
~ taining adequate levels of phosphorous and potassium.
;~1 20 These evaluations were conducted on all plots at the
r~ same time to eliminate variablessuch as light intensity,
~ air temperatures and the like from affecting the results.
"
~ In addition, for comparison, a gras~ plot was also given a
;i; single initial application with straight urea. A final
control plot was left untreated. Table I sets forth
fresh weight of grass clippings on the indicated day after
treatment. Clipping weights are a conventional indicator
of nutrient uptake by a test plant, and therefore of
,
fertilizer release charact:eristics.
;, 7} _ 9 _
1047272 s . M. Bille-N . F . Cardarelli
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-- S. N. Bille/N. F. Cardarelli - 1-1
1047Z72
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Table II shows the results of color observa-
tions of the same test plots at the indicated intervals
after treatment. The results are on a O to 10 scale
with the best color being 10.
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1047272 ~. N. F~ille/N. F. Cardarelli
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Table III records the results of turf quality
of the same test plots at the indicated intervals. Turf
quality ~as evaluated on a 1 to 10 scale with best quality
being 1.
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Example 5 (SE-36D)
A formulation was prepared from the following
constituents in parts by weight:
Ethylene proplene dimer (Epcar* 5465) 100
. 5 Sulfur 0.75
Stearic Acid 0.5
. Mercaptobenzothiazole 0.75
, Carbon Black 20
Tetramethylthiuram disulfide 0.4
, 10 Urea 100
t The formulation was mixed and w lcanized as
set forth in Example 1. Field tests of this composition
: at 5 lbs./1,000 sq. ft. application rate indicated very
good turf color and essentially no phytotoxicity.
Example 6
~;; A formulation was prepared and vulcanized as
;,
.~ in Example 1 containing (NH412SO4 as the fertilizer
source in place of urea. The elastomer was the ethylene-
. propylene dimer of Example 5. The formulation was as
... 20 follow~:
.. Ethylene-Propylene Dimer 100
' Sulfur
Mercaptobenzothiazole
,.. ~
Carbon Black 15
' 25 Zinc Oxide 1.5
;; Ammonium Sulfate 100
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. *Trademark
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S. M. Bille-N. F. Cardarelli
1047Z72 1-l ~
- 16 -
Example 7
Example 6 was repeated substituting 100 parts of
the styrene-butadiene rubber used in Example 4 as the elas-
tomer. The formulation was otherwise the same.
.~ -
S Example 8
Example 6 was repeated substituting 100 parts of
natural rubber as the elastomer.
Release rate studies were performed on the ammonium
sulfate compositions of example 6 to 8 to determine the
percent of nitrogen loss at intervals over a thirteen week
period. The release rate tests were conducted by immersing
duplicate samples of the compositions tested in water for
specified periods of time and then analyzing the water for
the amount of nitrogen present. The results of these tests
are set forth in Table IV.
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S. M. Bille/N. F. Cardarelli
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The test results of Table IV show that after a
relatively high initial release rate, the materials level
off to a fairly continuous nitrogen release over testing
- period. The compositions incorporating ammonium sulfate in
natural rubber (Example 8) display the most steady and con-
tinuous release during the 13 week period.
Test results similar to those described above were
, carried out with ammonium nitrate as the fertilizer in
place of ammonium sulfate. The results indicate that am-
monium nitrate acts similarly to ammonium sulfate in the
compositions of the inventions.
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