BIODEGRADABLE FOAM SUBSTRATE FOR GROWING PLANTS, PLANT SYSTEM PROVIDED THEREWITH, AND METHOD FOR MANUFACTURING SUCH SUBSTRATE

Abstract

A biodegradable foam substrate for growing plants, system provided therewith and method for manufacturing such substrate. The biodegradable foam substrate for growing plants includes a biodegradable polymer and a nucleating agent, where the biodegradable polymer is a polyester and/or an aromatic polymer, and the biodegradable foam substrate provides an open cell structure enabling plant growth.

Claims

1. A biodegradable foam substrate for growing plants, comprising: a biodegradable polymer and a nucleating agent, wherein the biodegradable polymer is at least one of a polyester and an aromatic polymer, and wherein the biodegradable foam substrate includes an open cell structure enabling plant growth.

2. The biodegradable foam substrate for growing plants according to claim 1, wherein the open cell structure comprises an open cell content of at least 50% measured according to mercury porosimetry or gas physisorption.

3. The 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, wherein the cells are interconnected voids.

4. The biodegradable foam substrate for growing plants according to claim 1, wherein the biodegradable polymer is selected from the list consisting of polybutylene sebacate terephthalate and polybutylene adipate terephthalate.

5. The biodegradable foam substrate for growing plants according to claim 1, wherein the biodegradable polymer is selected from the list consisting of polyhydroxyalkanoate, poly(lactic acid), and polybutylene succinate.

6. The biodegradable foam substrate for growing plants according to claim 1, wherein the at least one of said polyester and said aromatic polymer is at least one of branched and crosslinked.

7. The biodegradable foam substrate for growing plants according to claim 1, wherein the nucleating agent is selected from the list consisting of talc, cellulose, hydrotalcite, calcium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, aluminium carbonate, aluminium bicarbonate, calcium carbonate, calcium bicarbonate, calcium stearate, and mixtures thereof.

8. The biodegradable foam substrate for growing plants according to claim 1, wherein the biodegradable foam substrate is an integrally extruded foam.

9. The biodegradable foam substrate for growing plants according to claim 1, 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.

10. The biodegradable foam substrate for growing plants according to claim 1, wherein the total pore volume of the biodegradable foam substrate is in the range of 5-100 cm.sup.3 g.sup.−1.

11. The biodegradable foam substrate for growing plants according to claim 1, wherein the biodegradable foam substrate has a glass-transition temperature of 60° C. or less.

12. The biodegradable foam substrate for growing plants according to claim 1, wherein the foam substrate density is in the range of 10 kg m.sup.−3-200 kg m.sup.−3.

13. The biodegradable foam substrate for growing plants according to claim 1, wherein the weight average molecular weight of the biodegradable polymer is in the range of 10,000 g mol.sup.−1-1,000,000 g mol.sup.−1.

14. The biodegradable foam substrate for growing plants according to claim 1, further comprising an additive, wherein the additive is selected from the list consisting of perlite, vermiculite, nanoclay, salts, cellulose fibres, hemp fibres, cotton fibres, coconut fibres, polyethylene glycol, poloxamers, surfactants, plant nutrients, sugars, and mixtures thereof, wherein cellulose fibres are selected from the list consisting of regular cellulose fibres, ultrafine cellulose fibres, nanocrystalline cellulose fibres, nanofibril cellulose fibres, surface modified cellulose fibres, and mixtures thereof.

15. A plant growing system comprising a holding unit for holding plants and the biodegradable foam substrate according to claim 1, wherein the holding unit is a container.

16. A method for producing biodegradable foam substrate for growing plants, comprising the steps of: providing a mixture of a biodegradable polymer, a nucleating agent, and at least one of a branching agent and a crosslinking agent to form a reagent mixture; heating the mixture; providing a physical blowing agent to the mixture; and substantially completely extruding of the mixture to form the biodegradable foam substrate according to claim 1.

17. The method according to claim 16, further comprising the step of adding an additive prior to the heating step.

18. The method according to claim 16, wherein the physical blowing agent is carbon dioxide, nitrogen, argon, MTBE, air, (iso)pentane, propane, butane, or a mixture thereof.

19. The method according to claim 16, wherein providing the at least one of said branching agent and said crosslinking agent comprises providing dicumyl peroxide, di-tert-butyl peroxide, tert-butyl peroxibenzoate, tert-peroxyacetate, butadiene, butadiene derived polymers, divynylbenzene, benzoquinone, furfuryl sulphide, or a mixture thereof.

20. The method according to claim 17, wherein the step of extruding comprises a single extrusion step to form the integrally extruded foam substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which:

[0052] FIG. 1 shows a plant growing system with the biodegradable foam substrate of the invention;

[0053] FIG. 2 shows an additive supply system;

[0054] FIG. 3 shows a detail of the substrate of FIG. 1 illustrating the sponge-like structure;

[0055] FIG. 4 schematically shows the process of manufacturing the substrate and growing plants thereon;

[0056] FIG. 5 shows a GPC spectrum of the biodegradable polymer;

[0057] FIGS. 6A and 6B show further GPC spectra of the biodegradable polymer;

[0058] FIG. 7 shows a microscopic photo of foam comprising an open cell structure;

[0059] FIG. 8 shows intrusion-extrusion curves of the biodegradable foam substrate according to the invention;

[0060] FIG. 9 shows differential pore size distributions of the samples derived from the intrusion curves in FIG. 8 and mentioned in Table 1;

[0061] FIG. 10 shows further intrusion-extrusion curves of the biodegradable foam substrate according to the invention; and

[0062] FIG. 11 shows differential pore size distributions of the samples derived from the intrusion curves in FIG. 10 and mentioned in Table 2.

DETAILED DESCRIPTION

[0063] Plant growing system 2 (FIG. 1) comprises a tray or gutter 4 for holding biodegradable foam substrate 6. Plants 8 are positioned and fixated in substrate 6 having roots 10 penetrating and growing in substrate 6. Supply 12 provides water and fertilizer (and other relevant components) to substrate 6 and output 14 collects the remaining flow. From output 14 the flow is sent to drain 16 and/or recycled with pump 18 to supply 12.

[0064] In a preferred embodiment the germ root is not able to penetrate the foam substrate.

[0065] From additives supply system 20 one or more additives can be supplied with pump 22 and dosing controller 24 to supply 12. Controller 26 controls the flow rate by controlling pump 18, dosing of additives by controlling pump 22 and the amount of recycling by controlling drain 16.

[0066] It will be understood that alternative systems can also be envisaged in accordance with the present invention.

[0067] Sponge-like structure 30 (FIG. 3) is made from material 32 that defines pores or voids 34 that are interconnected with channels 36. In use, pores or voids 34 are filled with water 38 and the suitable components enabling roots 10 to grow.

[0068] Manufacturing and growing process 102 (FIG. 4) starts with selecting the desired properties for substrate 6 in selection step 104. Mixing step 106 provides the desired mixture of biodegradable polymers and one or more nucleating agents.

[0069] This mixture of biodegradable polymers and nucleating agent(s) is provided to the extruder in supply step 108. Optionally, additives can also be added in adding step 110. In or near the extruder the mixture is heated in heating step 112 to or towards the desired temperature. In the extruder the heated mixture is transported in extrusion step 114, and preferably confronted with a physical blowing agent, such as carbon dioxide in blowing step 116. Then the actual forming of a foam structure in foaming step 118 takes place resulting in the raw end product. If necessary, the raw product is dimensioned in dimensioning step 120. For example, this may involve cutting the raw substrate material into the desired size and shape. Next, the substrate 6 is transported and stored in transport step 122.

[0070] As soon as foam substrate 6 is needed it is installed in installation step 124. After installation plants can grow on and into the substrate in growing step 126. This may also involve degradation of the substrate material at the optional use of its components for the plant growth.

[0071] Analysis of the biodegradable polymer by GPC (FIG. 5) shows that a weight average molecular weight of the biodegradable polymer in the range of 10,000 g mol.sup.−1-1,000,000 g mol.sup.−1 was achieved. The measurement was performed as shown in FIG. 5. The weight average molecular weight was determined according to ISO 13885-1. The weight average molecular weight in g mol.sup.−1 (shown on the x-axis) was plotted against the PSS SECcurity RI (shown on the y-axis).

[0072] A further analysis of the biodegradable polymer by GPC (FIGS. 6A and 6B) show that a biodegradable polymer with a molecular weight of respectively 106,379 g mol.sup.−1 and 121,898 g mol.sup.−1 is achieved. The weight average molecular weight was determined according to ISO 13885-1. The retention volume (mL, shown on the x-axis) was plotted against the weight average molecular weight (Mw, shown on the y-axis). The calibration line of FIGS. 6A and 6B comprises the values of 3.053×10.sup.6 g mol.sup.−1, also known as 3,053,000 g mol.sup.−1, 956,000 g mol.sup.−1, 327,300 g mol.sup.−1, 139,400 g mol.sup.−1, 74,800 g mol.sup.−1, 30,230 g mol.sup.−1, 21,810 g mol.sup.−1, 10,440 g mol.sup.−1, 4,730 g mol.sup.−1, 1,920 g mol.sup.−1, 1,320 g mol.sup.−1, 575 g mol.sup.−1. These polymers were used as biodegradable foam substrate for growing plants. It was noted that such substrate provided efficient and effective plant growth, in particularly the growth of the root of the plant.

[0073] It can be concluded that the GPC analysis of abovementioned samples showed consistency of the samples.

[0074] FIG. 7 shows a microscopic photo of foam comprising an open cell structure. The foam is provided using the method according to the invention. The average size of the pores is 0.70 mm. The majority of the cells comprise a size which is at least 0.5 times the average size of the pores and at most 2 times the average size of the pores. The sizes of the pores are determined by the open source software ImageJ including Fiji plugin.

[0075] Experiments have shown that a combination of biodegradable polymers can be used advantageously to provide the desired characteristics for a specific plant or plant variety. In some of these experiments, polybutylene sebacate terephthalate or polybutylene adipate terephthalate is effectively used in combination with polyhydroxyalkanoate or polybutylene succinate in a ratio of about 80-20. An amount of about 1-3%, preferably 2%, talc and cellulose is used as nucleating agent and filler. This provides sponge-like structure 30 with an open cell content of about 75 to 85%. After the manufacturing process the average size of the pores or voids is about 500 micron. The foam density is about 50 kg m.sup.−3. Optionally, some additives are provided, such as ultrafine cellulose fibres. In the manufacturing process about 2.5 wt % CO.sub.2 is used for foaming the mixture. Branching and/or crosslinking agent is provided in the range of between 0-4 wt %, preferably 1 wt %. Optionally, CaCO.sub.3 is used in a range of 2.5-3% as an additional filler in the substrate matrix.

[0076] Experiments showed that the substrate in use can have a water uptake of about 20 times the dry weight of the substrate. In use, the substrate showed good fixation possibility and plant root growth potential. After use the material degraded and was optionally composted after which its components were used in the process, thereby contributing to the sustainable character of the biodegradable foam substrate according to the invention.

[0077] Experiments showed that the porosity of the foam is at least 76% comprising a total volume of 2.49 cm.sup.3 g.sup.−1. The porosity was determined by mercury intrusion porosimetry over three samples. For the measurement cubes of about 10×8×8 mm were used. The samples were degassed in vacuum at about 25° C. for about 16 hours. Subsequently, the intrusion and extrusion curves were recorded on a Micrometrics Autopore 9505 analyser, applying pressures from 0.002 MPa to 220 MPa. The mass loss obtained upon pre-treatment has been recorded and the dry mass has been used in the calculations.

[0078] The samples comprise relatively large cubes, re-organisation of (loose) powder particles followed by fulling of inter-particle porosity is not applicable. The fact that at relatively low pressures the intrusion curve of the samples displays substantial intrusion should thus be attributed to the presence and filling of large intra-particle voids.

[0079] The intrusion-extrusion curves of the samples are shown in FIG. 8 and the properties of the sample are incorporated in Table 1. The intrusion curves is represented by the open marks, and the extrusion curves are represented by the solid marks. The sample of entry 1 comprises a biodegradable foam substrate with a water capacity of 40% and a diameter of the top surface of 25 millimetres. The sample of entry 2 comprises a biodegradable foam substrate with a similar water capacity of 40% and a diameter of the top surface of 25 millimeters. The sample of entry 3 comprises a biodegradable foam substrate with a water capacity of 65% and a diameter of the surface of 20 millimeters. In FIG. 8 the lower line at 10 MPa relates to entry 2 of Table 1, the middle line at 10 MPa relates to entry 3 of Table 1, and the upper line relates to entry 1 of Table 1.

[0080] The first intrusion step occurs over a relatively broad pressure range from a pressure of about 0.002 MPa up to approximately 1 MPa where a plateau is reached. A second intrusion step can be seen at a pressure which ranges from about 60 MPa to 220 MPa, this attributes to the elastic compression of the large cubes rather than actual pores. It will be understood that this is the case due to the fact that the extrusion curves are reversible to the intrusion curves, which is not the case when porosity is present.

TABLE-US-00001 TABLE 1 Properties samples analysed by mercury porosimetry at a pressure of 60 MPa. Mass Mass loss V.sub.total Prosity ρ.sub.apparent Entry g m/m % cm.sup.3 g.sup.−1 % g cm.sup.−3 1 0.1487 1.7 4.12 83 1.19 2 0.1844 0.9 2.49 76 1.28 3 0.1375 0.8 3.98 84 1.31

[0081] The skeletal density of entry 1 of Table 1 has been determined using helium pycnometry and was about 1.26 g cm.sup.−3. It will be understood that the differences could be induced by a high degree of porosity and low sample mass used could result in somewhat inaccurate sample volume, and thus porosity, determinations.

[0082] The pore size distributions derived from the intrusion curves (FIG. 8) are displayed in FIG. 9. In FIG. 9 the lower line at about 300 μm relates to entry 2 of Table 1, the middle line at about 300 μm relates to entry 1 of Table 1, and the upper line at about 300 μm relates to entry 3 of Table 1.

[0083] Difference could be observed in the intrusion curves at lower pressure (larger pores) between the samples. The distributions of samples also show these differences. For example, the sample of entry 3 comprises a distribution with a very high contribution of similar sized pores, ranging from about 10 μm to about 700 μm with a mode around 265 μm. The distributions of the samples of entry 1 and 2 are slightly broader and lower, while the range of and modes are similar to the sample of entry 3, ranging from about 10 μm to about 700 μm with a mode around 265 μm. The minor contribution noticed at very small pores size can be attributed to the elastic compression of the samples.

[0084] Therefore, it can thus be concluded that the three samples mainly comprise large intra-particles pores.

[0085] The intrusion-extrusion curves of further samples are shown in FIG. 10 and the properties of the sample are incorporated in Table 2. The intrusion curves are represented by the open marks, and the extrusion curves are represented by the solid marks. The sample of entry 1 comprises a biodegradable foam substrate with a water capacity of 55% and a diameter of the top surface of 23 millimeters. The sample of entry 2 comprises a biodegradable foam substrate with a water capacity of 75% and a diameter of the top surface of 23 millimeters. In FIG. 10 the lower line at 10 MPa relates to entry 1 of Table 2, and the upper line relates to entry 2 of Table 2. The samples were prepared as mentioned above.

[0086] From FIG. 10 it becomes clear that the first intrusion step occurs over a relatively broad pressure range of about 0.002 MPa to about 1 MPa where a plateau is reached. It can be concluded that the porosity is available in a rather broad pore size range of relatively large pores. Furthermore, the sample from entry 1 of Table 2 has a lower intruder volume compared to the sample of entry 2 of Table 2. From about 50 MPa and up the plateau is not changing, it can therefore be concluded that all porosity of >6 nm has adequately assessed.

TABLE-US-00002 TABLE 2 Properties samples analysed by mercury porosimetry at a pressure of 220 MPa. Mass Mass loss V.sub.total Porosity ρ.sub.apparent Entry g m/m % cm.sup.3 g.sup.−1 % g cm.sup.−3 1 0.3014 0.3 4.00 84 1.29 2 0.3517 0.5 4.31 84 1.22

[0087] From Table 2 it becomes clear that the mass loss obtained upon pre-treatment is slightly different as for the sample of entry 1 0.3 m/m % is removed and for the sample of entry 2 0.5 m/m % is removed. Furthermore, Table 2 lists that the intruder volume of the sample of entry 1 of Table 2 is indeed the lowest at 4.00 cm.sup.3 g.sup.−1, while that of the sample entry 2 of Table 2 is higher at 4.31 cm.sup.3 g.sup.−1. The porosities of both samples are similar, about 84%, while there are some minor differences between the calculated apparent densities. A maximum relative difference of 6% is obtained, which is considered good for the mercury intrusion technique if it is expected that both samples are composed of the same material. The skeletal density of the samples has been determined using helium pycnometry and was determined at approx. 1.26 g cm.sup.−3.

[0088] It can be concluded that a good match between apparent densities of the samples, and it can therefore be stated that all porosity has been adequately assessed.

[0089] The differences could be induced by the following: a high degree of porosity and low sample mass used could result in somewhat inaccurate sample volume (and thus porosity) determinations. Since the apparent density calculation also involves the solid volume, this data should also be treated with some care.

[0090] The pore size distributions derived from the intrusion curves (FIG. 10) are displayed in FIG. 11. In FIG. 11 the lower line at about 300 μm relates to entry 1 of Table 2, and the upper line at about 300 μm relates to entry 2 of Table 2.

[0091] The distributions of the samples show pores ranging from about 5 μm to about 700 μm, and both samples show a mode around 300 μm. The intensity of the distribution of the sample of entry 2 of Table 2 is higher compared to that of the sample entry 1 of Table 2 in the range from about 180 μm to about 700 μm, while the intensity from about 5 μm to about 180 μm shows the opposite trend. The higher initial intensity of the sample entry 2 of Table 2 is responsible for the higher total intruded volume, while the higher intensity of the sample of entry 1 of Table 2 indicates that this sample has a larger contribution of smaller pores.

[0092] Therefore, it can thus be concluded that both samples mainly comprise large intra-particles pores.

[0093] Experiments showed that the biodegradable foam substrate according to the invention comprises a foam substrate density a mentioned in Table 3.

TABLE-US-00003 TABLE 3 maximum and minimum value biodegradable foam substrate density. Entry 1 2 3 4 5 6 7 8 9 Max 96.548 91.222 96.548 89.239 89.239 85.948 97.810 96.548 96.548 density Min 66.606 58.781 67.242 76.753 76.753 76.753 71.409 60.286 66.606 density

[0094] In a further experiment PBAT, pigment, branching agent and a nucleating agent, wherein the nucleating agent is one or more selected from the group of talc, cellulose, and calcium carbonate, are added to the first zone of the extruder and mixed. The mixture is heated to about 200° C. in order to melt the PBAT, to homogenise the mixture and to react the branching agent and PBAT. In the following zone an about 70° C. pre-heated surfactant is added to the mixture. In further zones the reaction mixture is slowly cooled down and CO.sub.2 is injected. In the final zone of the extruder the mixture is mixed using a static mixer and is provided to the die. As a result, a continuous open cell foam substrate is achieved.

[0095] The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims, within the scope of which many modifications can be envisaged.