CONTROLLED RELEASE AGRICHEMICAL COMPOSITION

Abstract

A granular controlled release agrichemical composition having a matrix including an agrichemical active and a coating for providing controlled release of the agrichemical active from the granular composition, wherein the coating has at least one biodegradable polymer selected from the group consisting of aliphatic polyesters, polyanhydrides, polycarbonates, polyurethanes including aliphatic polyester segments, polyureas including aliphatic polyester segments, copolymers of two or more thereof and mixtures thereof wherein the coating composition includes a Lewis acid in an amount sufficient to enhance degradation of the coating.

Claims

1. A granular controlled release agrichemical composition comprising a matrix comprising an agrichemical active and a coating for providing, controlled release of the agrichemical active from the granular composition, wherein the coating comprises at least one biodegradable polymer selected from the group consisting of aliphatic polyesters, polyanhydrides, polycarbonates, polyurethanes comprising aliphatic polyester segments, polyureas comprising aliphatic polyester segments, copolymers of two or more thereof and mixtures thereof wherein the coating composition comprises a Lewis acid in an amount sufficient to enhance degradation of the coating.

2. A granular controlled release agrichemical composition according to claim 1, wherein the biodegradable polymer is selected from the group consisting of: aliphatic polyesters selected from the group consisting of polylactic acid (PLA), poly(glycolic acid) polycaprolactone (PCL), polyvalerolactone poly(hydroxyl valerate), poly(ethylene succinate), poly(butylene succinate), poly(butylene-succinateadipate), poly(para-dioxanone), polydecalactone, poly(4-hydroxybutyrate), poly(beta-malic acid) and poly (hydroxyl valerate); and polymers selected from polyurethane and polyurea comprising segments of said aliphatic polyesters.

3. A granular controlled release agrichemical composition according to claim 1 wherein the biodegradable polymer comprises an aliphatic polyester.

4. A granular controlled release agrichemical composition according to claim 1, wherein the biodegradable polymer comprises at least one selected from the group consisting of polylactic acid, polycaprolactone, lactic acid caprolactone copolymers and mixtures thereof.

5. A granular controlled release agrichemical composition according to claim 1, wherein the coating extends about at least a part of a core of the matrix comprising the agrichemical active.

6. A granular controlled release agrichemical composition according to claim 1, wherein the biodegradable polymer comprises at least 50% by weight of the coating.

7. A granular controlled release agrichemical composition according to claim 1, wherein the coating further comprises inorganic filler.

8. A granular controlled release agrichemical composition according to claim 7, wherein inorganic filler is a silicate mineral filler present in an amount of up to 30% by weight of the coating.

9. A granular controlled release agrichemical composition according to claim 1, wherein the Lewis acid is selected from the group consisting of metal oxides, metal alkoxides and metal C.sub.8 to C.sub.20 aliphatic acid salts.

10. A granular controlled release agrichemical composition according to claim 1, wherein the Lewis acid is selected from the group consisting of titanium dioxide, titanium chloride, aluminium isopropoxide, aluminium halide and tin dioxide.

11. A granular controlled release agrichemical composition according to claim 1, wherein the amount of Lewis acid is at least 0.1 wt % based on the weight of polymer.

12. A granular controlled release agrichemical composition according to claim 1, wherein the amount of Lewis acid is in the range of from 0.05% to0.5% by weight based on the weight of polymer.

13. A granular controlled release agrichemical composition according; to claim 1, wherein the agrichemical active is selected from pesticides, plant growth regulators and fertilizers.

14. A granular controlled release agrichemical composition according to claim 1, wherein the agrichemical active comprises a nitrogenous fertilizer.

15. A granular fertiliser according to claim 14, wherein the nitrogenous fertiliser comprises urea, ammonium nitrate, calcium nitrate or mixture thereof.

16. A granular fertiliser according to claim 1, wherein the agrichemical active is present in a amount of at least 30% by weight of the granular composition.

17. A granular controlled release agrichemical composition, wherein the coating comprises no more than 15% by weight of the granular composition.

18. (canceled)

19. A granular controlled release agrichemical composition according to claim 1, wherein the matrix further comprises a polymeric binder.

20. A granular controlled release agrichemical composition, according to claim 1, wherein the :molecular weight Mn) of biodegradable polymer is in the range of from 10,000 to 200,000.

21. (canceled)

22. (canceled)

23. (canceled)

24. (canceled)

25. A process for preparing a granular controlled release agrichemical composition according to claim 1, comprising forming a matrix comprising an agrichemical active and coating the matrix with a coating composition comprising at least one biodegradable polymer selected from the group consisting of aliphatic polyesters, polyurethanes comprising aliphatic polyester segments, polyanhydrides, polycarbonates, copolymers of two or more thereof, wherein the coating composition comprises a Lewis acid in an amount sufficient to enhance degradation of the coating.

26. (canceled)

27. (canceled)

28. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0112] Specific embodiments of the invention are described with reference to the attached drawings.

[0113] In the drawings:

[0114] FIG. 1 is a graph showing the degradation profile, presented as GPC Molecular weight distribution curves, for blank samples of Example 1 with varying catalyst loadings, soaked in water after five weeks as described in Example 3.

[0115] FIG. 2 is a graph showing the influence of humidity level applied using a controlled chamber on the molecular weight (Mp) of compositions of Example 1 with differing amounts of catalyst in accordance with the test protocol of Example 3.

[0116] FIG. 3 includes two column charts (3a and 3b) showing the molecular weight (Mn in left column Mw in right hand column) for PLA-PCL films with different amounts of catalyst after exposure for one month (FIG. 3a) and two months (FIG. 3b) in accordance with the testing protocol described in Example 4.

[0117] FIG. 4 includes two column charts (4a and 4b) showing the effect of different Lewis acid catalysts on the hydrolytic degradation of films of PCL-PLLA after 44 days in accordance with Example 5. FIG. 4a showing molecular weight and FIG. 4b showing polydispersity against a polystyrene standard.

[0118] FIG. 5 includes two column charts (5a and 5b) showing the affect of different amounts of the Lewis acid aluminium isopropoxide on the hydrolytic degradation of films of PCL-PLLA after 44 days in accordance with Example 6.

[0119] FIG. 6 shows the testing assembly used to assess urea release from extruded biodegradable polymer containing different Lewis acid catalyst loadings.

[0120] FIG. 7 is a graph showing the urea transport across a range of membranes compositions of thickness 120 microns at 22 C. and 50 C.

[0121] FIG. 8 is a graph showing the variation of urea transport with time across a 160 micron membrane of a composition containing 70% PLLA 30% PCL with 0.5% w/w catalyst (three left hand side plots) and without catalyst (three right hand side plots).

[0122] FIG. 9 is a graph of variation of urea transport across polymer membranes with time for three membranes with 70PLLA30PLC of 160 micron thickness and no catalyst (upper three plots) and 70PLLA30PCL with 200 micron thickness (lower two plots).

[0123] FIG. 10 is a schematic longitudinal section showing an extruder for coextrusion of nutrient matrix within a continuous polymer tube.

[0124] FIG. 11 shows a schematic longitudinal section showing intermediates in preparing pellets of one embodiment of FIG. 11 including (a) the tube containing spaced nutrient matrix segments, (b) segment of tube cut between discrete nutrient matrix portions and (c) completed pellets in which ends of cut tube segments are closed so that the tube polymer envelops the nutrient matrix.

[0125] FIG. 12 is a longitudinal cross section of one embodiment of a pellet formed in accordance with the invention.

[0126] FIG. 13 shows a schematic longitudinal section showing intermediates in preparation of pellets of an alternative process in which alternating polymer and nutrient matrix portions are coextruded within the tube (a) and tube is cut between spaced nutrient portions and through polymer portions to provide a tube of polymer having and outer tube, central nutrient matrix within the tube and ends of the tube sealed with polymer (b).

[0127] FIG. 14 is a graph showing the percentage of urea lost with time from urea prills coated with PCL as described in Example 13.

[0128] FIG. 15 includes two graphs showing the change in molecular weight of PCL-PLLA films containing different amounts of aluminium isopropoxide catalyst from day 0 to day 31 of placement in clayloam soil. FIG. 15(a) shows change in Mn and FIG. 15(b) shows change in Mp.

[0129] FIG. 16 is a graph showing the average molecular weight (Mw) of PC film of samples numbers 2, 3 and 4 referred to in Example 17 initially and after 10, 35 and 55 days of being buried in wet tropical soil.

[0130] FIG. 17 is a graph showing the average molecular weight (Mn) of PCL film of samples numbers 2, 3 and 4 referred to in Example 17 initially and after 10, 35 and 55 days of being buried in wet tropical soil.

[0131] FIG. 18 is a graph showing the polydispersity (PD) of PCL film of samples numbers 2, 3 and 4 referred to in Example 17 initially and after 10, 35 and 55 days of being buried in wet tropical soil.

[0132] FIG. 19 is a graph showing the molecular weight (Mn and Mw) and polydispersity (PD) of granules of Sample number 1 of Example 17 initially and after 10, 35 and 55 days of being buried in wet tropical soil.

[0133] In one embodiment of the process the pellets are formed by coextrusion of a thermoplastic tube, such as formed of a polycaprolactone-polylactic acid copolymer, with spaced portions of a core matrix, such as a paste comprising a urea composition, clay and ionic polyurethane. Referring to FIG. 10 there is shown a longitudinal section of a coextruder (10) for coextrusion to form of an intermediate coextruded structure (FIG. 11a) from which individual pellets may be formed (FIG. 11b). The coextruder comprises a number of interlocking parts (11-14) providing tube resin inlet (15) for feeding polymer tube resin under pressure to an annular extrusion port (16) and a matrix extrusion channel (17) in which discrete portions of matrix may be conveyed in a sleeve (18) of air. In one embodiment the portions of matrix may be separated by a resin for forming the ends of the pellets as shown in FIG. 13.

[0134] Referring to FIG. 11(a) there is shown the intermediate structure (20) comprising a length of an outer tube (21) of the thermoplastic such as polycaprolactone-polylactic acid copolymer, with coextruded spaced portions of a core matrix (22).

[0135] Referring to FIG. 11(b) the individual pellets may be formed by cutting the tube between portions (22) of matrix and collapsing the tube (21) to form ends (23) of pellets (24) formed of the tube polymer. This operation may be performed in separate steps as shown in FIG. 11 or the separation of the pellets may be carried out in a process step in which the tube is collapsed between portions of matrix and cut in a process continuous with the collapsing action, for example using opposed blades.

[0136] Referring to FIGS. 13(a) and 13(b) an alternative process in shown in which the length of coextruded structure (25) comprises a length of tube (21), spaced portions of matrix (22) and portions of resin (26) between portions of matrix (FIG. 13(a)). The tube is cut through portions of the resin (26) to separate the pellets and provide pellet ends (27) formed of the resin (FIG. 13(b)).

[0137] The invention will now be described with reference to the following examples. It is to be understood that the examples are provided by way of illustration of the invention and that they are in no way limiting to the scope of the invention.

EXAMPLES

[0138] Method

[0139] Particle size was measured by Wyatt Dyna Pro Plate Reader Wyatt Technology Corporation, 6300 Hollister Ave, Santa Barbara, Calif. 93117-3253. The viscosity of polymer solution was measured by Brookfield digital rotary viscometer, model 94800-0.

[0140] Tetrahydrofuran (THF) was used as eluent and solvent in GPC measurements, using WATERS 2695 Separations module, WATERS 2414 Refractive Index, four PLGel columns (35 m MIXED-C AND 13 M Mixed-E) in a series with flow 1.0 mL/min. Molecular weight was determined according to calibration on polystyrene standards.

[0141] DSC was performed on a Mettler Toledo DSC821 using samples (5 mg weight) at a heating rate of 10 C./min under nitrogen purge The samples were stored for 48 h under a vacuum at room temperature (RT) (0.1 Torr) prior to analysis. Tensile testing was performed on an Instron Model 4468 universal testing machine following the ASTM D 882-02 test method at ambient temperature (23 C.) with a humidity of around 54%.

[0142] The 1H-NMR, 13C NMR and COSY techniques were used for the characterization of polymer structure. 1H-NMR spectra were recorded on Bruker Advance II Spectrometer, Germany operating at 400 MHz. 13 C NMR and COSY spectroscopic measurements were performed with 500 MHz in all NMR analyses CDCl.sub.3 was used as solvent.

[0143] Fourier transform infrared (FTIR) spectra were collected on a Perkin Elmer Spectrum 2000 FTIR instrument in attenuated total reflectance (ATR) mode using diamond as the background reference. The infrared data were recorded in wavenumbers (cm.sup.1) with the intensity of the absorption (vmax) specified as either strong (s), medium (m), weak (w) and prefixed broad (b) where appropriate.

[0144] Biodegradation Test Method for Film

[0145] Assessment of the rate of degradation of the test samples exposed to soil or compost was carried out under simulated test conditions, by measuring the amount of carbon dioxide evolved from bioreactors containing the test samples. The theoretical amount of carbon dioxide THCO.sub.2, in grams per bioreactor,which the test material can produce was calculated using following equation:

[0146] THCO.sub.2=MTOTCTOT44/12 where, MTOT is the total dry solids, in grams, in the test material at the start of the test, CTOT is the proportion of total organic carbon in the total dry solids in the test material, in grams per gram, 44 and 12 are the molecular mass of carbon dioxide and the atomic mass of carbon, respectively. From the cumulative amounts of carbon dioxide released, calculate the percentage biodegradation lit, of the test materials for each measurement interval using following equation:

Dt=((CO.sub.2) T(CO2) B/THCO.sub.2)100 [0147] where. (CO.sub.2) T is the cumulative amount of carbon dioxide evolved in each bioreactor containing test material, in grams per bioreactor. Solvent cast samples of films containing the polymer were prepared.

[0148] Biodegradation Test in Soil in Field Condition

[0149] Solvent cast samples of films PCL films containing varying concentrations of catalyst were hot melt pressed into 0.3 mm thick sheets at 120 C. Samples of 1 g (film) placed in regular pantyhose having, an internal support frame made of PC tubing, 11 cm diameter, 1 cm high with 0.4 cm thick walls. Free ends of the pantyhose were sealed with cable ties. The complete arrangement was then buried in sandy loam soil at a depth of approximately 10 cm. M.Wt. determinations were made at regular interval.

[0150] Measurement of Rates of Fertiliser Release from Polymer Coated Matrix and Pellets

[0151] The laboratory methods use incubation to determine either the time taken until a specified amount of nutrient is released (e.g. time for 75% release) or the amount released over a specified time (Carson and Ozores-Hampton, 2012). For the commercial, tubular, granular CRF sample (0.3 to 0.4 g) was mixed with 10 g of acid-washed fine sand and transferred to a 10 ml syringe. For coated urea pellets, 8 pellets weighing 0.4-0.6 g were used. A disc of fibreglass glass filter paper (Whatman GF/C) was placed at the bottom of the syringe to prevent loss of sand and clogging. Another disc was placed on top of the sand to distribute input solution across the surface.

[0152] A leaching solution of 2 mM CaCl.sub.2 was applied at the rate of 50 mL daily to the centre at the top of the columns using multichannel peristaltic pumps. Leaching was collected by gravity and measured by weight initially twice daily and then at 24 h intervals. Measurements were carried out in triplicate and in an incubation set at 55 C.

[0153] The laboratory method also included extruded with active urea core were placed in sealed pill bottles containing water. This assembly was then placed in a constant temperature oven until the water was sampled for urea in solution. Multiple pill bottles were uses so a range of time intervals could be investigated. Detection of urea in water solution was carried out by UV-VIS spectroscopy using a colourant (p-dimethylaminobenzaldehyde) to activated the urea. A calibration cure is first constructed to yield a ppm vs absorbance level at 420 nm. For those concentration falling outside the calibration limits, dilutions of the original solution are made accordingly.

Reference: Spectrophotometric Method for Detection of Urea. G. W Watt and J. D. Chrisp, Analytical Chemistry. Vol: 26. No. 3, March 1954. pp 452-453.

[0154] Materials

[0155] Natural latex rubber (Water emulsified, Sprayable Latex with 40.2% solids content was received from Barnes, Sydney. Sodium Alginate was received as powder from Melbourne Food Depot, Victoria, PolyurethanesAs synthesised. Bentonite clay was received from Aldrich and used as received. Commercial PLA was supplied by NatureWorks (PLA 7000D) from Cargill-Dow UK with. Monomer Epsiloncaprolactone (99%) obtain from Fluka, was used, Monobutyltin oxide (BuSnOOH) was use as catalyst, provided from Arkema Inc, Philadelphia. Polymer Polycaprolactone (PCL) was purchased from Solvay, England. Carbon black HIBBLACK 890 was purchased from Korea Carbon Black Co Ltd and used as received.

[0156] Abbreviation [0157] PCL=Polycaprolactone polymer [0158] PLLA=Poly-1-lactic acid polymer [0159] PU=Polyurethanes

EXAMPLE 1

Biodegradable Polymer Synthesis and Composition: PCL-PLLA Copolymer Synthesis

[0160] Granules of PLA were ground and dried for two hours in nitrogen own at 100 C. before use. The -caprolactone was dried on oil bath at temperature 100 C. under vacuum pump. Synthesis of copolymer with c-caprolactone 15 and 20% by weight were prepared as follows:

[0161] PCL-PLLA polymer was synthesized by ring opening polymerisation using reactive extrusion.

##STR00002##

Synthesis Scheme of PCL-PLLA Polymer

[0162] The actual polymerization time (depending on the amount of catalyst added and the temperature conditions used) varies between two hours and up to two days. It has to be noted that the limitation in finalizing the polymerization is the time needed for the remaining monomer to diffuse through the already formed high viscous polymer in order to reach the reactive sites. The polymer obtained with such a process often has a low thermal stability in melt processing. The polymerization time was in this case two hours for samples as well for blanks.

[0163] The kinetics of bulk polymerization of PLA with -caprolactone in the presence of BuOSn as catalyst was studied with 0.08, 0.05, 0.03, 0.01 and 0.005% w/w catalyst and results are summarised in Table 1.

[0164] The results show that samples with different amount of catalyst after two hours of reaction have lower molecular weight than starting material PLA 7000D. Peak molecular weight of starting polymer PLA measure by GPC was 187661 with polydispersity (PDI) of 1.6 and melt flow index (MFI) at 210 C. of 7.5. After two hours the molecular weight is lower and the polymer has a PDI value of 1,8.

[0165] increasing catalyst levels lowers the molecular weight of resultant polymers and a lower amount of monomer (c-caprolactone) in reactions will result in lower molecular weight in comparison with the use of higher amounts of monomer in reactions.

TABLE-US-00001 TABLE 1 Mn, Mp and polydispersity (PDI) value for non-processes samples from bulk reactors after two hours of synthesis. - caprolactone Catalyst [%] [%] Mn Mp PDI SAMPLES 20% 0.08 33911 66798 1.8 0.05 42683 82130 1.77 0.03 51530 93459 1.78 0.01 55145 97769 1.77 0.005 59295 104536 1.83 15% 0.08 25553 48871 1.9 0.05 37957 76119 1.82 0.03 46532 89490 1.8 0.01 51615 93528 1.8 0.005 51755 100155 1.9 BLENDS PLA7000D 110249 165743 1.8 PLA7000D + 0.08% fascat 66070 113309 1.8 PLA7000D + CAPPA 6800 79511 119685 1.7 PLA7000D + 15% -caproloctone 78630 128159 1.84 PLA7000D + 20% -caproloctone 75644 129635 1.9 PLA7000D + 50% -caproloctone 106919 135991 1.51 PLC 76047 114381 1.63 -caproloetone + 0.08% catalyst 27671 59038 2.09

EXAMPLE 2

Synthesis of PCL-PLLA Polymer Blend by Extrusion

[0166] PCL and PLLA blends were prepared by extrusion process using granules of both PCL and PLLA polymers with different loading of the catalyst BuOSn in amounts of 0.5, 1, 1.5, 2 and 3% by weight of the polymer respectively. PCLPLLA polymers were compounded at temperatures between 160-190 C. by using a Haake twin screw extruder. The extruded blends were pelletized into pellets in order to feed to the extrusion of films process. PCL/PLA blends were feed into the hopper of a film extrusion process with temperature profile 160-180 C. Three films were prepared of thickness 120, 160 and 200 micron.

Example 3

Hydrolytic Degradation of PCL-PLLA Co-Polymer

[0167] The films prepared with different amount of catalyst in Example 1 were soaked in water at ambient temperature and showed various degradation profile shown in FIGS. 1 and 2.

[0168] FIG. 1 shows the GPC Molecular weight distribution curves for the blank soaked in water after five weeks. Samples with increasing amount of -caprolactone and lower level of catalyst have higher Mp than those synthesized with higher amount of catalyst.

[0169] FIG. 2 shows Influence of increasing humidity on degradation of samples and blends in controlled chamber.

EXAMPLE 4

Hydrolytic Degradation of PCL-PLLA Blend Film

[0170] Strips of the film composition prepared in Example 2 with different levels of tin catalyst were subject to degradation by immersion in distilled water (20.0 g) sealed in a glass vile and places in bench top oven at 50 C. Samples were removed at 2 month interval, dried and 5-10 mg of polymer was dissolved in a small 2 mL vial with N,N-Dimethylacetamide (DMAC) and placed in a 50 C. oven for several hours until fully dissolved. This solution was filtered through 40 m syringe filter into 1 mL gel permeation chromatography (GPC) vial with rubber septum. The degradation profile of the films are summarised in FIG. 3 which showed polymer degradation was dependent on catalyst concentration.

[0171] FIG. 3 shows the hydrolytic degradation of PLA-PCL films with varying amounts (% w/w) of Sn catalyst after a) 1, and b) 2 months. The number average molecular weight (g/mole) is determined against a polystyrene standard.

EXAMPLE 5

Hydrolytic Degradation of PCL-PLLA Blend Film Containing Different Catalysts

[0172] Five different PCL-PLLA copolymers were prepared using 0.5 wt % of different catalyst Aluminium isopropoxide (AIPO), Titanium butoxide (TBO), Titanium isopropoxide (TIPO), Monobutyltin oxide (MBTO) and Zinc acetate (ZnAc) following the procedure described in Example 1. The samples were each compressed moulded into thin films and evaluated in hydrolytic degradation tests as described in Example 4. All polymer samples showed significant reduction in molecular weight after 44 days and are results summarised in Table 2 and FIGS. 4(a) and 4(b). In each group of columns in FIG. 4(a) the columns from left to right in the group show Mn at time 0 (Mn_T0), Mw at time 0 (Mw_T0), Mn at 44 days (Mn_44D) and Mw at 44 days (Mw_44D).

TABLE-US-00002 TABLE 2 PCL-PLLA degradation profile with different catalyst Time 1 = CATALYST TIME 0 44 days PL-AIPO Aluminium 94095/156830/1.66 13531/27367/1.77 isopropoxide PL-TBO-Titanium butoxide 78652/118265/1.46 13050/25662/1.96 PL-TIPO-Titanium 106839/173887/1.62 16524/35089/1.68 isopropoxide: PL-MBTO -Monobutyltin oxide 105387/167996/1.59 14602/33116/1.75 PL-ZnAc Zinc acetate 104674/161903/1.54 15109/31975/2.11

[0173] FIG. 4 shows the hydrolytic degradation of PLA-PCL films with varying catalyst after 44 days a). Number average molecular weight Mnand weight average molecular weight (Mw) (g/mole) b) Polydispersity (PD) against a polystyrene standard at time 0 (PD_T0and at 44 days (PD_T0).

EXAMPLE 6

Hydrolytic Degradation of PCL-PLLA Blend Film Containing Different Concetration of Aluminium Isopropoxide (AIPO)

[0174] PCL-PLLA copolymers containing five different concentration of Aluminium isopropoxide (AIPO), were prepared following the general procedure described in Example 1. The samples were compress moulded into thin films and hydrolytic degradation was evaluated in accordance with tests described in Example 4. The polymer showed significant reduction in molecular weight in all samples containing different amount of catalyst after 31 days and results are summarised in FIG. 5.

[0175] FIG. 5: Hydrolytic degradation of PLA-PCL films with different concentration of catalyst Aluminium isopropoxide (ALISO in FIG. 5(a) and (b)) after 0 days in the left hand column of each pair and 31 days in the right hand column of each pair of columns. FIG. 5(a) compares molecular weight (Mn-) and FIG. 5(b) compares polydispersity (PD).

EXAMPLE 7

Urea Permeation Across PLLA-PCL Membranes

[0176] A series of PLLA-PCL (90:10 wt ratio or 70:30 wt ratio) prepared in Example 2 with different loading of catalysts were evaluated as membranes for urea release. The rate of urea transport across the films was measured as a function of time. The films were placed within the testing assembly shown schematically in FIG. 6.

[0177] Referring to FIG. 6 the testing assembly (1) includes two inclined tube sections (2,3) separated by a membrane (4) in a V configuration with urea solution (5) in a tube section (2) on one side of the membrane (4) and distilled water (6) in the tube section (3) on the other side of the membrane from the urea solution (5).

[0178] The method used is as follows:

Step Process

[0179] 1. Prepare a solution of urea (1080 g/L). [0180] 2. Select an area of film with no/minimal defects and cut roughly 62 mm diameter segment and place in test jig of FIG. 6. [0181] 3. Add 30 mL of urea solution to one side and 30 mL of DI water to the other side. [0182] 4. Plug opening to each side with a rubber stopper to prevent evaporation. [0183] 5. Record date and time. [0184] 6. Sample at regular intervals determine the transport across he membrane.

[0185] Thee release profiles of urea are summarised in FIGS. 7-9.

[0186] FIG. 7 shows urea transport across membranes at 22 C., 35 C. and 50 C.

[0187] FIG. 7 demonstrates that PLLA-PCL films with a thickness of 120 m allow minimal transport of urea across the film at ambient (22 C.) temperature. Once increased to 35 C. (see dashed line at 40 days) there was a systematic increase in the rake of urea transport across the films. After 70 days total testing, the temperature was increased to 50 C., resulting in considerable increase in urea transport across the film and more rapid breakdown or failure of the films. Urea transport across membranes at showing that addition of catalyst leads to the early onset of film degradation and decrease of zero release period.

[0188] Subsequent testing has been carried out at 50 C. FIG. 8 shows urea transport across 160 m thick films with the addition of 0.5 wt % monobutyltin oxide (BuOSn) catalyst (three left hand side plots) and without the addition of 0.5 wt % monobutyltin oxide (BuOSn) catalyst (three right hand side plots).

[0189] FIG. 9 shows the impact of increasing thickness of the film on urea transport rates. The results for urea transport across membranes at 50 C. show that increased thickness of the coating leads to a slightly increased zero release period and slower rate of transition to total failure of the coating.

EXAMPLE 8

Polymer Coated Matrix: Co-Extrusion of Urea Matrix with PCL Polymer

[0190] Urea/bentonite clay matrix as prepared in Example 10 is flowable at ambient temperature. The slurry coextruded into polymer tube successfully using low molecular weight polycaprolactone (PCL) (Mn-68,000 Da) polymer in varying ratios 1:2, 1:1 and 2:1 of slurry: PCL (FIG. 10) and then pelletized manually.

[0191] The co-extrusion of the filled polymer tubing was carried out with an annular extrusion die (Guill Tool & Engineering Co. Guill 812 crosshead) using three feeds. A 16 mm co-rotating screw extruder (Prism Eurolab 16) fitted with a gear-driven melt pump (Barrel) delivering the molten polymer for the outer layer, compressed air to keep the internal aperture open and control wall thickness and the nutrient matrix which was delivered via a syringe protruding through the extrusion die into the forming tube supplied by a piston pump (Teledynelsco 500D).

[0192] The tubing was cooled either with air or by passing through a water bath and taken off with a conveyor belt. The tubing wall thickness and overall diameter was varied by altering the polymer feed rate, melt temperature, nutrient matrix feed rate, air flow and haul off rate.

[0193] Example extruder conditions; Extruder temp profile 20-90 C. die temp 110 C., screw speed 120 rpm, polymer feed rate 45%, melt pump 20%, nutrient feed rate 2 mL/min.

[0194] In formulations used to co-extrude with PLA/PCL polymers, only bentonite clay and urea solution were used to prepare the matrix. Formulation being 1:5.4; of bentonite:50% urea/water solution.

[0195] Co-extrusion of urea with PCL polymer may be conducted in accordance with the scheme shown in FIGS. 11(a) and 11(b) to provide pellets shown in FIG. 12.

EXAMPLE 9

Co-Extrusion Processes

[0196] In an alternative process to that shown in FIG. 11 and FIG. 12 the urea could be coextruded with biodegradable polymer using the pellet co-extrusion process shown in FIGS. 13(a) and 13(b) in which portions of a resin are coextruded into the tube between the urea to provide pellet ends by cutting the extrusion through portion of the resin between portions of urea.

EXAMPLE 10

Urea Matrix: Urea-Bentonite Clay Matrix Composition

Method 1

[0197] Commercial urea prills (Richgro) were prepared to a 50% (wt/wt) solution with water. This was spatulated with bentonite clay 20 wt % until a thick, homogeneous paste was made. To this a biodegradable polyurethane emulsion (of Example 11) was also incorporated in the final formulation by spatulation.

Method 2

[0198] Commercial urea prills (Richgro) were prepared to a 50% (wt/wt) solution with water. This was spatulated with bentonite clay 20 wt % (as the sodium salt, high AR grade) and 1 wt % hydroxyethyl cellulose until a thick, homogeneous paste was made. To this a biodegradable polyurethane emulsion prepared according to Example 11 was also incorporated in the final formulation by spatulation. The final composition of the core matrix composition is shown in Table 3 below.

Method 3

[0199] Commercial urea prills (Richgro) were prepared to a 50% (wt/wt) solution with water. This was spatulated with bentonite clay 20 wt % (as the sodium salt, high AR grade) and 1 wt % hydroxyethyl cellulose until a thick, homogeneous paste was made. To this a biodegradable polyurethane emulsion of Example 11 was also incorporated in the final formulation by spatulation and extruded as a solid component through a pressurised syringe pump and thrown into water bath containing calcium chloride solution (5 wt %) to crosslink the polyurethane polymer.

Method 4

[0200] Commercial urea prills (Richgro) were prepared to a 50% (wt/wt) solution with water. This was spatulated with bentonite clay (as the sodium salt, high AR grade) until a thick, homogeneous paste was made. To this composition a biodegradable polyurethane emulsion was also incorporated by spatulation. The resulting matrix paste was then sprayed with calcium chloride 2- 5wt % solution to crosslink the biodegradable polyurethane polymer.

TABLE-US-00003 TABLE 3 Core matrix composition Component Component Percentage Bentonite Clay 25 Urea/water solution (50% wt/wt) 51 Biodegradable ionic polyurethane (BPU) of Example 11 11 Water 13

[0201] The above matrix formulation of bentonite-urea-BPU-water was extruded (by syringe) into 2% CaCl.sub.2 solution to provide crosslinked polyurethane. The matrix was dried at 90 C. for under nitrogen for 72 h.

[0202] Incorporation of polyurethane in the matrix composition provides a hydrophobic coating on the matrix and hinders easy access to water to hydrolytically sensitive matrix and slow down the release of urea. The ionic crosslinking of polyurethane film with CaCl.sub.2 solution will further improve the hydrolytic stability, biodegradation and mechanical integrity to thermosets polyurethane film.

EXAMPLE 11

Polymer Formulation

[0203] A biodegradable ionic polyurethane was prepared by two step solution polymerisation methods in water. Following precursors were used in the polymer.

[0204] PCL (MW 1000, 20.00 g), IPDI (8.20 g), BMPA (0.432g), TEAe (0.309 g), EDA (0.774 g Polyol and pre-dried BMPA (0.43g). The mixture was accurately weighed into a three neck flask equipped with mechanical stirrer, dropping funnel and nitrogen inlet. The mixture was heated with stirring to 100 C. for one hour until all BPM dissolved. The reaction temperature was lowered to 90 C. and IPDI (8,20 g) was added to the above polyol mixture and reacted for another 4 h at the 90 C. The flask was cooled down to 60 C. and anhydrous Triethylamine (0.309g) was added and reaction continued for 30 mins. Thee flask was further cooled down to 0 C. using an ice bath. Deionised water (44.0 ml) containing 2 wt % SDDS was quickly added to this pre-cooled prepolymer mixture and was stirred vigorously to yield an emulsified opaque solution. Chain extension agent EDA (0.76 g) was added drop wise to this solution and stirring continued for 30 mins. The reaction flask was later warmed to 25 C. and the stirring continued until. NCO peak disappeared. The low viscous stable aqueous dispersion of polyurethanes thus obtained was stored in an air tight container at ambient temperature.

[0205] The polymer showed an average particle size distribution of 42553 nm with a viscosity of 625 mPa.Math.s. The molecular weight of polymer was M.sub.n=74961, M.sub.w=226290 and PD=3.01.

EXAMPLE 12

Urea Release from Urea/Bentonite Clay Matrix at Room Temperature

[0206] Thee bentonite-urea-BPU matrix prepared in Example 10, 3.31 g was placed in a sintered glass crucible (No 1 porosity) on a plinth allowing the crucible to be surrounded by water (600 mL) at RT. Total available urea in the oven dried matrix was 0.78 g or 1400 ppm in the body of water. Ultraviolet (UV) light spectroscopy was used to determine the amount of urea released into a body of water over a period of time (see Table 2). The results showed almost 54% loss in 4 days. The concentration exceed the calibration curve accuracy after this time period.

TABLE-US-00004 TABLE 4 Concentration of urea leached form oven dried matrix formulation. Time Concentration of released urea (h) (ppm) 6 None Detected 24 None Detected 48 240 72 618 96 (4 D) 760

EXAMPLE 13

Urea Release From Low Mw PCL Coated Urea Prill

[0207] Urea prills (average weight 22 mg) were rolled and coated in molten PCL (MW. 10K) at 100-150 C. The coated prill was then d rapped into cold water from approximately 1.2 m height. Prills were retrieved from the water and patted dry with tissue paper. A single coated prill was then placed in 25.00 mL of water in a sealed pill bottle and left at room temperature until tested. Testing was carried out by calibrated UV-VIS interpolation by taking 2.00 mL of immersion water made up to 15 mL followed by a colourant of p-climethylaminobenzaldehyde for free urea in water. The test showed the loss of 100% urea in 8 days. A coating with a mixture of different MWs of PCL in different ratios is also achieved using above method to control the release of urea from the coating.

[0208] FIG. 14: shows the urea percentage loss from urea prill coated with PCL 10,000 dalton at room temperature.

EXAMPLE 14

Urea Release from Extruded PCL Polymer Tube Filled with Urea Matrix at Different Temperatures

[0209] Hot melt sealed tablets were prepared by method given in Example 6 using PCL polymer 6800 with no catalyst. The hot sealed tablets were tested prior to the test by squeezing to make sure the matrix did not move within the extruded tablet. Four single pellet (average 0.13 g)) was placed in 25.00 miL water sealed in a pill bottle. This was placed in a constant temp oven at 50 C. A 2 mL sample of this water was then taken at regular time intervals for UV-VIS analysis for free urea in solution. The table shows mg of free urea lost (from a possible 22 mg contained in the pellet). There are some inconsistencies in free urea detection, likely from the contamination during pellet preparation, however, after 69 days there was only a trace loss from all tablets (see Table 5).

[0210] The same samples were also subjected to different temperature at 60 and 75 C. The samples at 75 C. degrade overnight while sample in oven at 60 C. released only 11 mg (25.36%) in 49 days. The results are summarised in table.

TABLE-US-00005 TABLE 5 Urea % loss from extruded PCL polymer coated urea matrix Urea Release Sample Days Temperature (ppm) PCL-Matrix 69 25 2 (1%) PCL-Matrix 1 75 45 (100%) PCL-Matrix 49 60 .sup.11 (25.36%)

EXAMPLE 15

Urea Release from Extruded PCL Polymer Containing BuOSn Catalyst Tube Filled with Urea Matrix

[0211] Hot melt sealed tablets were prepared by method given in Example 6 using PCL polymer 6800 with 0.5 wt % catalyst. The hot sealed tablets were tested prior to the test by squeezing to make sure the matrix did not move within the extruded tablet. Four single pellet (average 0.13 g)) was placed in 25.00 mL water sealed in a pill bottle. This was placed in a constant temp oven at 50 C. A 2 mL sample of this water was then taken at regular time intervals for UV-VIS analysis for free urea in solution. The table shows mg of free urea lost (from a possible 135 mg contained in the pellet).

TABLE-US-00006 TABLE 6 Urea % loss from extruded PCL polymer g BuOSn catalyst tube filled with urea matrix. Urea Release Sample Days Temperature (ppm) PCL-Matrix 42 50 29 ppm (21%)

EXAMPLE 16

Degradation of PCL-PLLA Films With and Without Catalyst Films in Soil

[0212] Degradation of PCL-PLLA films containing different concentration of Aluminium isopropoxide (AIPO), was carried out using strips of polymer film in clay loam soil in field conditions. Polymer degradation was monitored by GPC and results are shown in FIG. 15.

[0213] FIG. 15 shows GPC results of polymer samples from soil test after 0 days (left hand column in each group) and 31 days (right hand column in each group) where FIG. 15a) shows the number average molecular weights (Mn-) and in FIG. 15b) the polydispersity (PD) is shown).

EXAMPLE 17

PCL Degradation and Urea Release from PCL Coated Urea in Field Conditions

[0214] Samples of the coated fertiliser and biodegradable film listed in Table 7 were subjected to field trials in sugarcane fields in three different locations within the wet tropics. In the trials, plastic mesh bags each having a number of separate pouches were used to retain samples of coated urea pellets and polymer film strips and were buried to examine degradation of the samples in tropical conditions.

TABLE-US-00007 TABLE 7 Sample No Description 1 coated fertilisers granules of Example 15 2 Coated fertiliser of Example 19 3 Example 5 PCL film with no Catalyst (TBO) 4 Example 5 PCL film with 0.05 wt % catalyst (TBO) 5 Example 5 PCL film with 0.5 wt % catalyst (TBO) PSL strips were of dimensions 6 cm 1 cm thickness of approximately 0.5 mm.

[0215] The mesh bags were retrieved at regular interval and the results up to 55 days are summarized in the graphs referred to below. The retrieved samples were analysed by GPC for their average molecular weight (Mn and Mw) and polydispersity.

[0216] FIG. 16 is a graph showing the average molecular weight (Mw) of PC film of samples numbers 2, 3 and 4 referred to in Example 17 initially and after 10, 35 and 55 days of being buried in wet tropical soil.

[0217] FIG. 17 is a graph showing the average molecular weight (Mn) of PCL film of samples numbers 2, 3 and 4 referred to in Example 17 initially and after 10, 35 and 55 days of being buried in wet tropical soil.

[0218] FIG. 18 is a graph showing the polydispersity (PD) of PCL film of samples numbers 2, 3 and 4 referred to in Example 17 initially and after 10, 35 and 55 days of being buried in wet tropical soil.

[0219] FIG. 19 is a graph showing the molecular weight (Mn and Mw) and polydispersity (PD) of granules of Sample number 1 of Example 17 initially and after 10, 35 and 55 days of being buried in wet tropical soil.