HORTICULTURAL GROWTH MEDIUM AND METHOD FOR PREPARING THE GROWTH MEDIUM

Abstract

A horticultural growth medium includes a filler and a binder. The binder is a moisture-cured, isocyanate-terminated quasi-prepolymer made from an organic polyisocyanate that includes a large proportion of 4,4-diphenylmethane diisocyanate. This binder system provides excellent curing properties and imparts excellent physical properties to the growth medium.

Claims

1. A horticultural growth medium comprising: a) 10 to 99 weight percent, based on the combined weights of components a) and b), of a particulate filler, wherein the particulate filler is embedded in b) 90 to 1 weight percent, based on the combined weights of components a) and b), of a porous polyurethane-urea polymer formed by moisture-curing an isocyanate-functional quasi-prepolymer, which isocyanate-functional quasi-prepolymer is a reaction product of at least one hydroxyl-terminated polymer of ethylene oxide with an excess of an organic polyisocyanate that includes at least 80 weight-% diphenylmethane diisocyanate of which diphenylmethane diisocyanate at least 60 weight-% is 4,4-diphenylmethane diisocyanate, wherein the isocyanate-functional quasi-prepolymer has prior to moisture curing an isocyanate content of 5 to 15% by weight and contains 35 to 50 weight percent of oxyethylene units, based on the weight of the isocyanate-functional quasi-prepolymer.

2. The horticultural growth medium of claim 1 wherein the isocyanate-functional quasi-prepolymer has prior to moisture curing an isocyanate content of 6 to 15% by weight.

3. The horticultural growth medium of claim 2 wherein the organic polyisocyanate contains at least 95% by weight of diphenylmethane diisocyanate.

4. The horticultural growth medium of wherein at least 80% of the diphenylmethane diisocyanate is 4,4-diphenylmethane diisocyanate.

5. The horticultural growth medium of claim 1 wherein the particulate filler constitutes 10 to 75 weight percent of the combined weight of components a) and b).

6. The horticultural growth medium of claim 1 wherein the filler includes one or more of sand, clay, a hydrated silica, biotite, phlogopite, polymer foam particles, limestone, gypsum, mica, hydrated obsidian, diatomaceous earth, carbon black, graphite, soil, moss, ground or chopped plant matter, manure, plant fiber, garbage, ground tree bark, wood shavings, sawdust, coffee grinds, humus, charcoal, coke or coal.

7. The horticultural growth medium of claim 1 further comprising a plant seed or fungal spore.

8. The horticultural growth medium of claim 1 further comprising a growing plant or fungus rooted therein.

9. A method of making a horticultural growth medium, comprising: A. forming a mixture containing a) 10 to 99 weight percent, based on the combined weights of components a) and b), of at least one particulate filler, b) 90 to 1 weight percent, based on the combined weights of components a) and b), of an isocyanate-functional quasi-prepolymer, which isocyanate-functional quasi-prepolymer is a reaction product of at least one hydroxyl-terminated polymer of ethylene oxide with an excess of an organic polyisocyanate that includes at least 80 weight-% diphenylmethane diisocyanate of which diphenylmethane diisocyanate at least 60 weight-% is 4,4-diphenylmethane diisocyanate, wherein the isocyanate-functional quasi-prepolymer has prior to moisture curing an isocyanate content of 5 to 15% by weight and contains 35 to 50 weight percent of oxyethylene units based on the weight of the isocyanate-functional quasi-prepolymer, and c) 10 to 90 weight percent water, based on the combined weights of components a), b) and c) and B. solidifying the mixture obtained in step A by moisture-curing the isocyanate-functional quasi-prepolymer to form a porous polyurethane-urea polymer in which the particulate filler is embedded.

10. The method of claim 9 wherein the isocyanate-functional quasi-prepolymer has prior to moisture curing an isocyanate content of 6 to 15% by weight.

11. The method of claim 10 wherein the organic polyisocyanate contains at least 95% by weight of diphenylmethane diisocyanate.

12. The method of claim 11 wherein at least 80% of the diphenylmethane diisocyanate is 4,4-diphenylmethane diisocyanate.

13. The method of claim 9 wherein the particulate filler constitutes 10 to 75 weight percent of the combined weight of components a) and b).

14. The method of claim 9 wherein the filler includes one or more of sand, clay, a hydrated silica, biotite, phlogopite, polymer foam particles, limestone, gypsum, mica, hydrated obsidian, diatomaceous earth, carbon black, graphite, soil, moss, ground or chopped plant matter, manure, plant fiber, garbage, ground tree bark, wood shavings, sawdust, coffee grinds, humus, charcoal, coke or coal.

15. A method for growing a plant or fungus, comprising embedding a plant seed, plant seedling, cutting, callus culture, growing plant and/or fungus spore in a horticultural growing medium of claim 1 and cultivating the plant seed, plant seedling, cutting, callus culture, growing plant and/or fungus spore in the horticultural growing medium to produce a plant or fungus rooted in the horticultural growing medium.

16. An isocyanate-terminated quasi-prepolymer which is a reaction product of at least one hydroxyl-terminated polymer of ethylene oxide with an excess of an organic polyisocyanate that includes at least 80 weight-% diphenylmethane diisocyanate of which diphenylmethane diisocyanate at least 60 weight-% is 4,4-diphenylmethane diisocyanate, wherein the isocyanate-functional quasi-prepolymer has prior to moisture curing an isocyanate content of 5 to 15% by weight and contains 35 to 50 weight percent, based on the weight of the isocyanate-functional quasi-prepolymer, of oxyethylene units.

Description

EXAMPLES 1-5 AND 3-A AND COMPARATIVE SAMPLES A-C

A. Quasi-Prepolymer Formation

[0062] Quasi-Prepolymers (QPs) 1-5 and Comparative Quasi-Prepolymers A-C are made in the following general manner, from ingredients as indicated in Table 1. The polyol(s) are dried to a moisture content of less than 250 ppm by heating them to 100 C. overnight with stirring under nitrogen. A trace of benzoyl chloride is added to the dried polyols and stirred in. The polyisocyanate(s) are separately heated to 50 C. and combined with the polyol(s). The resulting reaction mixture is heated at 75 C. under nitrogen until a constant isocyanate content is obtained. The quasi-prepolymer is then cooled to room temperature and stored under nitrogen.

[0063] The NCO content is measured according to ASTM D5155. The oxyethylene content of the quasi-prepolymer is calculated from that of the starting materials. The p,p- (4,4-) content of the isocyanate(s) is calculated from those of the starting isocyanates. The resulting values are as reported in Table 1.

[0064] Polyol A is a copolymer of ethylene oxide and propylene oxide having a nominal hydroxyl functionality of 2 and a number average molecular weight of approximately 2,400 g/mole. It contains 64% oxyethylene groups. Polyol A is commercially available as UCON PCL-270 polyol from The Dow Chemical Company.

[0065] Polyol B is a copolymer of ethylene oxide and propylene oxide having a nominal hydroxyl functionality of 3 and a number average molecular weight of approximately 5,000 g/mole. It contains 75% oxyethylene groups. Polyol B is commercially available as VORANOL CP-1421 polyol from The Dow Chemical Company.

[0066] Polyol C is a 1000 molecular weight, nominally difunctional homopolymer of ethylene oxide. It contains 100% oxyethylene groups. Polyol C is commercially available as Carbowax 1000 polyol from The Dow Chemical Company.

[0067] Polyol D is trimethylolpropane.

[0068] Isocyanate A is a mixture of 98% 4,4-MDI and 2% 2,4-MDI. It has an isocyanate content of 33.5%. Isocyanate A is available from The Dow Chemical Company as ISONATE 125M polyisocyanate.

[0069] Isocyanate B is a mixture of 50% 4,4-MDI and 50% 2,4-MDI. It has an isocyanate content of 33.5%. Isocyanate B is available from The Dow Chemical Company as ISONATE 50 O,P polyisocyanate.

[0070] Isocyanate C is a mixture of 80% 2,4-toluene diisocyanate and 20% 2,6-toluene diisocyanate.

TABLE-US-00001 TABLE 1 Parts By Weight QP-1 QP-2 QP-3 QP-4 QP-5 QP-A* QP-B* QP-C* Ingredient Polyol A 66.2 63.8 62 56.5 51.6 0 65 0 Polyol B 7.4 7.1 7 6.3 5.7 0 0 0 Polyol C 0 0 0 0 0 52 0 58 Polyol D 0 0 0 0 0 13 0 4 Isocyanate A 15.9 17.5 19 22.4 25.6 21 0 0 Isocyanate B 10.6 11.7 12 14.9 17.1 14 35 0 Isocyanate C 0 0 0 0 0 0 0 38 Properties NCO Content, 6.4% 7.4% 8% 10.3% 12.4% 7% 9.3% 9.8 % Oxyethylene 48% 46 45% 41% 37% 65% 42% 58 content 4,4-MDI 80% 80% 80% 80% 80% 80% 50% N/A isomer content *Comparative.

B. Preparation of Horticultural Growth Media

[0071] Horticultural Growth Media Examples 1-5 and Comparative Media A-C are made from Quasi-Prepolymers 1-5 and A-C, respectively.

[0072] Surfactant Solution A is an ethylene oxide/propylene oxide block copolymer having a molecular weight of about 2500 and a nominal hydroxyl functionality of 2, diluted with water at a ratio of 1 part of the copolymer to 9 parts water.

[0073] Surfactant Solution B is a 1:9 mixture of an ethylene oxide/propylene oxide/ethylene oxide triblock copolymer and water. The central poly(propylene oxide) block of the copolymer has a molecular weight of 1750. The outer poly(ethylene oxide) blocks constitute 80% of the total weight of the copolymer. The copolymer has a nominal hydroxyl functionality of 2.

[0074] The Filler is a physical mixture of sphagnum peat moss, perlite, and limestone, commercially available from SunGro Horticulture.

[0075] 14.3 parts of the Filler, 7.2 parts of Surfactant Solution A, 3.1 parts of Surfactant Solution B and 629 parts of water are combined at room temperature. The quasi-prepolymer (12.5 parts) is then added at room temperature. No urethane catalyst is present. The resultant mixture is mixed with a high-speed mixer for 16 seconds and then allowed to react and foam in an open box mold. The resulting horticultural growth medium in each case is allowed to condition overnight at room temperature.

[0076] Horticultural Growth Medium 3-A is made in the same manner, using Prepolymer 3, except that the surfactant solutions are omitted. The reaction mixture contains 14 parts of Quasi-Prepolymer 3, 16 parts of the Filler and 70 parts of water.

[0077] The curing characteristics of these formulations each are evaluated by measuring tack-free time and rise time. Tack-free time is determined by periodically pressing a tongue depressor against the top surface of the foaming reaction mixture. The time that elapses from the start of visible foaming until the reaction mixture no longer sticks to the tongue depressor is the tack-free time. The time that elapses from the start of visible foaming until the foam height ceases to increase is the rise time.

[0078] Water uptake is measured by cutting the cured growth media into 1 inch1 inch2 inch (2.54 cm2.54 cm5.08 cm) test specimens. The test specimens are dried at 80 C. for a minimum of 16 hours and immediately weighed. The dimensions of the dried specimen are measured in each case and used to calculate the dried specimen volume. The dry density is obtained by dividing the measured weight by calculated volume.

[0079] The weighed specimens are placed into an 800 mL tripor filled with 300 mL of water and allowed to soak overnight. The soaked specimens are removed from the water and allowed to sit under ambient conditions until water stops dripping from them. The specimens are then patted down with a paper towel to remove surface water and weighed. Percent water uptake is calculated as:

Water Uptake (%)=((Weight.sub.pat,dryWeight.sub.dry)/Weight.sub.dry)*100

wherein Weight.sub.pat,dry indicated the weight of the soaked specimen after removing surface water and Weight.sub.dry is the weight of the dried specimen before soaking. Wet density is then determined by measuring the dimensions of the soaked specimen, calculating its volume and dividing Weight.sub.pat,dry by the calculated volume.

[0080] Wet tear strength is measured according to ASTM D3574, Test F on sliced specimens having dimensions 6 inch1 inch1 inch (15.24 cm2.54 cm2.54 cm) with a 1.5 inch (3.81 cm) slit, using a crosshead travel speed of 500 mm/min. The test specimens are prepared for testing by equilibrating them in a constant temperature/constant humidity room overnight, immersing them in deionized water for 5 minutes and patting them dry for 30 seconds. Results of the foregoing testing are as indicated in Table 2.

TABLE-US-00002 TABLE 2 Property Example or Comparative Sample Designation Quasi- Ex. 1 Ex. 2 Ex. 3 Ex. 3-A Ex. 4 Ex. 5 A* B* C* Prepolymer QP-1 QP-2 QP-3 QP-3 QP-4 QP-5 QP-A QP-B QP-C QP Isocyanate 6.4 7.4 8.0 8.0 10.3 12.4 7.0 9.3 9.8 Content QP oxyethylene 65% 42% 58 content MDI p,p-content 80 80 80 80 80 80 80% 50% N/A Tack-free time, 2:15-2:33 2:15-2:33 2.50-3.00 2:35-2:45 2:20-2:35 2:45-3:00 1:35-1:45 4:50-5:10 3:10 minutes:seconds Rise time, 4:50-5:00 5:00-5:15 5:15-5:25 5:20-5:30 6:00-6:10 6:50-7:00 3:45-3:50 19:00-20:00 5:00-5:20 minutes:seconds Dry density, 0.19 0.17 0.16 0.19 0.14 0.16 0.17 0.12 0.13 g/cm.sup.3 Wet density, 0.57 0.67 0.61 0.70 0.63 0.69 0.78 0.60 0.61 g/cm.sup.3 Water uptake, % 545 703 627 633 692 670 611 851 644 Wet tear 2.66 (465) 1.94 (339) 1.92 (336) 2.51 (439) 1.23 (215) 1.34 (234) ** 1.09 (191) 0.25 (44) strength, lb-f/in (N/m) *Not an example of the invention. ** Sample has too little mechanical strength to measure.

[0081] Comparative Sample C represents a typical, toluene diisocyanate (TDI)-based formulation. Its tack-free and rise times are well adapted to industrial bound growth media processing, and it wet density and water uptake reflect industry targets.

[0082] Comparative Sample B shows the effect of using an MDI with high o,p-content. The system cures very slowly compared to the TDI-based system (Comp. C), and is not suitable for industrial application.

[0083] Comparative Sample A shows the effect of using an MDI-prepolymer having a very high oxyethylene content. The system cures much faster than the TDI-based system, which makes processing difficult. Despite the fast cure, this growth medium fails to develop sufficient mechanical strength. Its mechanical properties are so poor that tear strength cannot be measured using the ASTM method.

[0084] Examples 1-5 exhibit an excellent balance of reactivity and properties. Tack-free and rise times are closely in line with those of the TDI-based control, as are dry densities and water uptakes. Tear strength is very much improved relative to the TDI-based control, being some 5 to 10 times greater. This allows for more robust handling, facilitates using automated handling equipment and prolongs useful life.