Description:DESCRIPTION
U.S. Pat. No. 3,798,836 discloses a water insoluble open celled foamed polyurethane matrix having dispersed therein thermoplastic particles.

U.S. Pat. No. 3,889,417 makes a hydrophilic foam by reacting a prepolymer with a high amount of water. This foam may be used in horticultural applications. The water index applied is 1300–78000. A similar process has been disclosed in WO 96/16099 wherein no special guidance as to the iso-cyanate index and the water index has been given; in the examples the water index was more than 1700 and the isocyanate index was less than 6. The prepolymers used are made from polyols having a molecular weight of at least 1000.

U.S. Pat. No. 3,970,618 discloses a substrate for cultivating plants which Substrate is a hydrophilic polyurethane foam made by reacting a polyisocyanate and a polyol at a low NCO index, the polyol having an hydroxyl value of 900-1800 and the polyisocyanate being a toluene diisocyanate (TDI) type polyisocyanate. U.S. Pat. No. 5,155,931 uses a foam as plant mat, which foam is made by reacting an organic isocyanate, which preferably is TDI, and a polyol at an NCO-index of 90-120. U.S. Pat. No. 6,479,433 discloses a horticultural growing medium made by reacting a prepolymer and water in the presence of a selected filler material. US 2005/013 1095 discloses a process for making polyure thane foams, including flexible ones, at an NCO-index of 40-150. No special attention has been given to the water index; in the examples the NCO-index was between 85-106 and the water index varied between 93-120.

A process for making flexible polyurethane foams at a low isocyanate index using a low and a high amount of water respectively. Surprisingly, polyurethane foams could be further 50 improved regarding the foam stability at 100% water saturation and the water buffer capacity together with a high compression load deflection at low density.
Surprisingly we also have found a novel process to make such novel polyurethane foams. Therefore, the present invention is concerned with a flexible polyurethane foam having a density of 25-70 kg/m, a com pression load deflection at 40% (CLD) of 5-15 kPa, a volume increase at water saturation of at most 25% and a water buffer capacity of 40-60%. Further the present invention is concerned with a process for making such a flexible polyurethane foam, which process comprises reacting at an isocyanate index of 20-70 and at a water index of 200-400.
, Claims:1. A flexible polyurethane foam having a density of 25-70 kg/m, a compression load deflection at 40% (CLD) of 5-15 kPa, a volume increase at water saturation of at most 25%, and a water buffer capacity of 40-60% obtained by reacting at an isocyanate index of 20-70 and at a water index of 200-400.
2. 2. The foam according to claim 1 wherein the density is 26-60kg/m, the CLD is 5-12 kPa and the volume increase at water saturation is at most 15%.
3. A process for making a flexible polyurethane foam having a density of 25-70 kg/m, a compression load deflection at 40% (CLD) of 5-15 kPa, a volume increase at water saturation.
4. 4. A process for making a flexible polyurethane foam according to claim3 wherein the foam is made according to a free rise process or a restricted free rise process.
5. A plant growth medium, green wall, or green roof com prising the flexible polyurethane foam according to claim 1.
6. The flexible polyurethane foam according to claim 1 wherein the polyol used to form the prepolymer.