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EP-3890471-B1 - BIODEGRADABLE FOAM SUBSTRATE FOR GROWING PLANTS, PLANT SYSTEM PROVIDED THEREWITH, AND METHOD FOR MANUFACTURING SUCH SUBSTRATE

EP3890471B1EP 3890471 B1EP3890471 B1EP 3890471B1EP-3890471-B1

Inventors

  • TIETEMA, Martin
  • BELJAARS, Martijn
  • VAN ASSEN, Vincent
  • STANKUTE, Ineta

Dates

Publication Date
20260506
Application Date
20191206

Claims (14)

  1. Biodegradable foam substrate for growing plants, comprising a biodegradable polymer and a nucleating agent, wherein the biodegradable polymer is a polyester and/or an aromatic polymer, characterised in that the polyester and/or aromatic polymer is branched and/or crosslinked, such that the biodegradable foam substrate includes an open cell structure enabling plant growth, in that the biodegradable foam substrate is an integrally extruded foam, in that the open cell structure comprises an open cell content of at least 50% measured according to mercury porosimetry or gas physisorption, and in that the cells are interconnected voids.
  2. Biodegradable foam substrate for growing plants according to claim 1, further comprising an overall average cell size in the range of 0.001 - 3.0 millimetres, preferably in the range of 0.01 - 2.0 millimetres, more preferably in the range of 0.01 - 1.5 millimetres.
  3. Biodegradable foam substrate for growing plants according to any one of the preceding claims, wherein the biodegradable polymer is chosen from the group of polybutylene sebacate terephthalate and/or polybutylene adipate terephthalate.
  4. Biodegradable foam substrate for growing plants according to any one of the preceding claims, wherein the biodegradable polymer is one or more of the group polyhydroxyalkanoate, poly(lactic acid), polybutylene succinate.
  5. Biodegradable foam substrate for growing plants according to any one of the preceding claims, wherein the nucleating agent is chosen from the group of talc, cellulose, hydrotalcite, calcium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, aluminium carbonate, aluminium bicarbonate, calcium carbonate, calcium bicarbonate, calcium stearate, or a mixture thereof.
  6. Biodegradable foam substrate for growing plants according to any one of the preceding claims, wherein the biodegradable foam substrate is free of solvent.
  7. Biodegradable foam substrate for growing plants according to any one of the preceding claims, wherein the open cell structure, comprises an open cell content wherein the open cell content of the biodegradable foam substrate is at least 70% measured according to mercury porosimetry or gas physisorption, preferably the open cell content of the biodegradable foam substrate is at least 80% measured according to mercury porosimetry or gas physisorption, more preferably the open cell content of the biodegradable foam substrate is at least 90% measured according to mercury porosimetry or gas physisorption, most preferably the open cell content of the biodegradable foam substrate is at least 95% measured according to mercury porosimetry or gas physisorption.
  8. Biodegradable foam substrate for growing plants according to any one of the preceding claims, wherein the total pore volume of the biodegradable foam substrate is in the range of 5 - 100 cm 3 g -1 , preferably in the range of 5 - 50 cm 3 g -1 , more preferably in the range of 5 - 25 cm 3 g -1 , preferably wherein the biodegradable foam substrate has a glass-transition temperature of at most 60 °C or less, preferably a glass-transition temperature of at most 30 °C or less, more preferably a glass-transition temperature of at most 0 °C or less, most preferably a glass-transition temperature of at most -20 °C or less, preferably wherein the foam substrate density is in the range of 10 kg m -3 - 200 kg m -3 , more preferably the foam substrate density is in the range of 20 kg m -3 - 90 kg m -3 , even more preferably the foam substrate density is in the range of 30 kg m -3 - 70 kg m -3 , and most preferably the foam substrate density is about 50 kg m -3 , preferably wherein the weight average molecular weight of the biodegradable polymer is in the range of 10.000 g mol -1 - 1.000.000 g mol -1 , preferably the weight average molecular weight of the biodegradable polymer is in the range of 10.000 g mol -1 - 500.000 g mol -1 , more preferably the weight average molecular weight of the biodegradable polymer is in the range of 20.000 g mol -1 - 250.000 g mol -1 , most preferably the weight average molecular weight of the biodegradable polymer is in the range of 30.000 g mol -1 - 150.000 g mol -1 .
  9. Biodegradable foam substrate for growing plants according to any one of the preceding claims, further comprising an additive, wherein the additive is chosen from the group of perlite, vermiculite, nanoclay, salts, cellulose fibres, hemp fibres, cotton fibres, coconut fibres, polyethylene glycol, poloxamers, surfactants, plant nutrients, sugars, or a mixture thereof, preferably wherein cellulose fibres are chosen from the group of regular cellulose fibres, ultrafine cellulose fibres, nanocrystalline cellulose fibres, nanofibril cellulose fibres, surface modified cellulose fibres, or a mixture thereof.
  10. Plant growing system (2) comprising a holding unit (4) for holding plants (8) and biodegradable foam substrate (6) according to any one of the claims 1 - 9, wherein the holding unit (4) preferably is a container and more preferably is a container having at least one open end.
  11. Method (102) for producing biodegradable foam substrate for growing plants, comprising the steps of: - providing (108) a mixture of biodegradable polymer wherein the biodegradable polymer is a polyester and/or an aromatic polymer, nucleating agent and a branching agent and/or crosslinking agent to form a reagent mixture; - heating the mixture (112); - providing (116) a physical blowing agent to the mixture; and - substantially completely extruding (114) of the mixture to form the biodegradable foam substrate according to any one of the claims 1 to 9.
  12. Method according to claim 11, further comprising the step of adding (110) an additive prior to the heating step.
  13. Method according to any one of the claims 11 or 12, wherein the physical blowing agent is carbon dioxide, nitrogen, argon, MTBE, air, (iso)pentane, propane, butane, and the like or a mixture thereof, preferably wherein providing the branching agent and/or crosslinking agent comprises providing dicumyl peroxide, di- tert -butyl peroxide, tert -butyl peroxibenzoate, tert- peroxyacetate, butadiene, butadiene derived polymers, divynylbenzene, benzoquinone, furfuryl sulphide, and the like or a mixture thereof..
  14. Method according to any one of the claims 11 - 13, wherein the step of extruding comprises a single extrusion step to form the integrally extruded foam substrate.

Description

The present invention relates to a biodegradable foam substrate for growing plants. In practice, substrates are used for growing plants in stead of using soil. Such substrates for growing plants are known from hydroponic, semi-hydroponic, hydroculture and similar systems, wherein plants are grown in an alternative medium that transports water, fertilizer and other relevant components. Such (growing) systems can be applied in glasshouses/greenhouses, for example. In practice, substrate material is made from a synthetic material, such as rockwool made from an inorganic fibre material or peat/PUR, or is made from degradable/compostable material, such as compressed cocos plugs or compost plugs with a polymer sheet. The roots of the plant penetrate into the substrate and fixate the plant. Often, feed systems provide water, fertilizer and other relevant components to the plant roots to enable plant growth. US 9,521,814 B2 discloses a growth substrate for plants including polylactic acid, wherein the polylactic acid is particulate polylactic acid foam. A method for preparing a growth substrate for plants including polylactic acid foam, the method including providing particulate expandable polylactic acid and exposing the particulate expandable polylactic acid to predetermined temperature and pressure conditions to obtain particulate polylactic acid foam. US 2013/0180173 A1 discloses a composition and method for preparing artificial seeds of plantlets that can be developed into grown plants for propagation in the field. In one embodiment, the artificial seeds are developed in degradable containers. WO 02/076187 A2 discloses a culture medium that is suitable for growing plants and that comprises a filler and a polymer. The culture medium is characterised in that it is made of a polymerised mixture containing a biologically degradable polymer and the filler. One of the problems with such synthetic substrates relates to the fact that these substrates may contain undesired (agro) chemicals that render it difficult to dispose of this substrate material. Furthermore, plugs of synthetic substrates are often too wet for optimal root growth. In addition, in practice one is confronted with the non sustainability of such materials of this substrate material and the fact that the material is often easily damaged. Specific problems of rockwool, is that rockwool can cause root diseases and that it is harmful during manual handling. Peat/PUR is known to potentially clog the water infrastructure and has a complicated nutrient composition. Problems with such degradable/compostable substrates relates to the fact that these substrates may contain an undesired composition which is hard to define that render it difficult to fulfil the nutrients needs of the roots. These degradable/compostable substrates contaminate the water infrastructure. Furthermore, plugs of degradable/compostable substrates are often dimensionally unstable. The present invention has for its object to provide a substrate that obviates or at least reduces one or more of the aforementioned problems. This is achieved with the biodegradable foam substrate according to claim 1. It is noted that in this application substrate and foam substrate are used interchangeably and refer to the same subject. The foam substrate according to the present invention comprises a biodegradable polymer which is a polyester and/or an aromatic polymer. In the context of this invention biodegradable relates to the degradation resulting in a loss of properties from the action of microorganisms such as bacteria, fungi and algae. By manufacturing the biodegradable foam substrate according to the invention from a biodegradable polymer an environmentally friendly substrate for growing plants is achieved. This significantly reduces the environmental footprint of growing plants and plant substrates in glasshouses/greenhouses, for example involving hydroponic plant systems or other suitable systems. As a further effect of the use of the biodegradable products the substrate is preferably also compostable. In the context of this invention compostable relates to degradation by biological processes resulting in the yield of CO2, water, inorganic compounds and biomass. Therefore, the biodegradable polymer in the foam substrate according to the invention is capable of being degraded such that the water infrastructure and/or water treatment plants are prevented from clogging. Furthermore, the biodegradable polymer in the foam substrate according to the invention is dimensional stable which prevents accumulation of the foam substrate causing blockages. As a further advantage of the use of these biodegradable polymers the plants may even profit from the degradation of the substrate material. This results in the substrate having both a stabilizing/fixation effect and in addition thereto a growing effect due to the use of the degradation products for plant growth. This renders the substrate material according