Description

The present invention relates to an adhesive composition for providing a culture substrate for plants wherein the adhesive composition is comprised of colophony and a vegetable- based wax. The present invention further relates to a culture substrate for plants comprised the adhesive composition mixed with a growth substrate and a method for the production of the culture substrate for plants.

Greenhouse and ornamental horticulture are evolving rapidly, increasing in scale and related automation. The automation of the process from growth to transport of the plants places higher demands on the stability of the growing substrates. For example, bound plugs are indispensable as growing plugs for growing young plants. This also applies to the greenhouse vegetables with the bound cultivation mats and blocks.

Cultivating of plants and especially young plants is often performed using various types of growth substrates concentrated into a container, also known as plant plugs. Cultivating young plants using plant plugs have shown to improve yields, and produce healthy plants at locations that have a limited space for plant growth in soil. It also provides an easier system for cultivation of seedlings that are difficult to cultivate, since the plug has a potentially greater capacity to withstand pests, disease and drought due to the more contained and controlled environment during plant cultivation. Plug plants grow more consistently.

Plant plugs are produced by pressing and gluing of organic substrate under use of an adhesive composition to form a plug in a container for holding a plant or to form a growing block and /or slab for cultivation of plants. These plug or growth systems are popular systems in horticulture since the cultivated plant, when ready, can easily be removed from the system comprising a tray holding the plug and plant, without damaging the young roots. However, a main issue that occurs during harvesting of the grown plant is that plant plug holding the growth substrate falls apart upon being removed from the container or when the plants are to be transferred to a larger cultivating bed. Therefore plugs are being damaged during the process and may further lead to damage to the plant roots.

Plant plugs, growing blocks and/or cultivation or growing slabs are all being produced, stabilized and held together by an adhesive product. To date, these adhesive products have been synthesized through use of bio based materials originating from corn, wheat, potato and/or petroleum. However, a drawback of these synthesized products is that they no longer resemble organic starting products and are therefore also not regarded as organic and cannot actually be recognized as an organic product. Furthermore environmentally harmful by-products are often released during synthesis of these adhesive products. To prevent a negative impact of these synthesized products on the environment, new compositions need to be used that must at least meet conditions of; 100% organic origin, and not being synthesized after harvest, fully biodegradable and the product extracted from nature must be able to return to nature in their original chemical structure.

Several types of adhesives are known that may comply with the conditions as indicated; especially the natural resins may be very suitable. These resins are hot melts with different melting temperatures. The advantage of these hot melts is that no chemical reaction is required to obtain a gluing effect of the product. The glued effect is purely a physical reaction, mechanically binding the fibres of the organic composition together. However, in the industry such resins are used in combination with synthetic (not fully biodegradable) binders due to its adhesive strength.

These resins are in solid form at room temperature and are often very brittle, which negatively affect the durability of the product produced via the adhesive composition. In order to obtain a less brittle, more elastic adhesive the hot melts may be mixed with unsaturated fat or wax (e.g. beeswax or paraffin), thereby lowering the melting point of the adhesive composition and increasing the adhesive strength. However, the drawback is that such adhesives due to the mixture with wax become highly water repellent which is not very suitable for use in the production of plant plugs for holding and cultivating young plants.

Considering the above, there is a need in the art for an adhesive composition for providing a culture substrate for plants which is fully biodegradable, 100% organic, has improved water absorbance properties and provides an increased durability to the culture substrate for plants comprising the adhesive composition. In addition, there is a need in the art for an adhesive composition that has improved adhesive and elastic properties, and at the same time has hydrophilic properties.

It is an object of the present invention, amongst other objects, to address the above need in the art. The object of present invention, amongst other objects, is met by the present invention as outlined in the appended claims.

Specifically, the above object, amongst other objects, is met, according to a first aspect, by the present invention by an adhesive composition for providing a culture substrate for plants, said adhesive composition is comprised of at least 80 wt% colophony and at most 20 wt% vegetable-based wax based on the weight of the adhesive composition, wherein the vegetable- based wax is comprised of at least 55 wt% saturated fatty acids. The adhesive composition of present invention is fully plant based and 100 % bio renewable. Furthermore mixing the colophony with the vegetable -based wax results in lowering of the melting point and an improved water adhesive capacity of the colophony (much less water repellent). Culture substrate for plants, like plant plugs or cultivation mats, produced with the adhesive composition of present invention are also more flexible due to the elastic properties of the adhesive mixed with the organic substrate that forms these products.

Colophony is a resin that is produced by conifers and pine trees with high adhesive strength. At room temperature colophony is very brittle and has a melting point of around 80 - 90 ° Celsius. Colophony by itself cannot be used in horticulture since the culture substrate for plants, such as plant plugs, that are glued have to absorb water and colophony by itself has water repellent properties. However, we have found that when combined with a saturated fatty acid (for example stearic acid), that has bi-functional properties with a polar and a non-polar part, such a mixture become much less water repellent. The effect of the addition of saturated fatty acids is that the culture substrate for plants produced using the adhesive composition of present invention will be able to absorb water after gluing with the colophony / saturated fatty acid mixture. Furthermore, due to the adhesive composition a reduction in melting point, better adhesive strength and better elastic properties are obtained, than when only colophony is being used as adhesive. The saturated fatty acids are added to the colophony in the form of vegetable wax, preferably soy wax.

According to a preferred embodiment, the present invention relates to the adhesive composition, wherein the vegetable-based wax is comprised of at least 65wt% saturated fatty acids, preferably at least 75wt%, more preferably at least 85wt%, even more preferably at least 95 wt%, most preferably 100 wt%. In case the vegetable based wax comprises less than 65 wt% of saturated fatty acids, the wax has a low melting point and becomes too soft and fluid at room temperature (i.e. about 18 - 23 °C), and becomes unsuitable as adhesive composition for the for providing a culture substrate for plants. In greenhouse conditions the temperatures may often be around or above 18 C, which in turn would lead to weakening or even disintegration of a for example a plant plug produced via the adhesive composition of present invention.

According to another preferred embodiment, the present invention relates to the adhesive composition, wherein the adhesive composition comprises between 9 to 15 wt% vegetable-based wax, preferably between 10 to 13 wt%. Above 15 wt% of vegetable-based wax , although beneficiary for the water absorbent properties, the melting point of the adhesive composition becomes too low such that the composition becomes too flexible and adversely affects the adhesive properties. Below 9 wt% vegetable -based wax in the adhesive composition the melting point becomes too high, the composition has reduced adhesive properties, becomes to hard and brittle, and does not mix properly with the organic substrate when producing a culture substrate for plants using the adhesive composition of present invention.

According to yet another preferred embodiment, the present invention relates to the adhesive composition, wherein the vegetable-based wax is a wax ester comprising saturated fatty acids having a backbone comprising at least 14 carbon atoms, preferably at least 16 carbon atoms, and wherein the wax ester is solid at room temperature. A wax ester is an ester of a fatty acid and a fatty alcohol. Various types of wax esters exist comprising (un)saturated fatty acids. Preferably the the wax ester comprising saturated fatty acids has a backbone comprising between 16 to 22 carbon atoms, more preferably between 18 to 20 carbon atoms. The wax esters in the composition of present invention are high in saturated fatty acids content having at least 14 C atoms in their backbone, resulting in that the wax ester remains solid at room temperature, preferably remain solid at temperatures above 40 or 45° C.

According to a preferred embodiment, the present invention relates to the adhesive composition, wherein said saturated fatty acids is one or more selected from the group consisting of stearic acid, palmitic acid, or a mixture thereof, preferably stearic acid.

According to another preferred embodiment, the present invention relates to the adhesive composition, wherein the vegetable based wax is selected from the group consisting of soy wax, palm wax, preferably soy wax. Soy wax is made from hydrogenated soybean oil and is a 100% renewable product, produced from fast-growing crops and does not comprise further toxic chemicals of by product (in contrast to paraffin wax which contains for example petroleum). Soy wax is comprised of a mixture of saturated and unsaturated fatty acid vegetable lipids predominantly containing triglycerides, diglycerides and monoglycerides, and mainly stearic acids. Linseed wax has been shown to adversely affect the adhesive properties when mixed with colophony, whereas especially soy wax improved the adhesive properties of such a mixture.

According to yet another preferred embodiment, the present invention relates to the adhesive composition, wherein the adhesive composition is in the form of a powder having a particle size of between 20 to 300 pm, preferably between 30 to 220 pm, more preferably between 50 to 180 pm. A particle size within these ranges leads to an increased contact surface for interactions between the organic fibres and the colophony/vegetable-based wax particles.

However, when the particle size becomes too small (i.e. <50um), the particles have been shown to have a decreased adhesive effect having difficulty interacting with the organic fibres.

According to yet another preferred embodiment, the present invention relates to the adhesive composition, wherein the composition is 100% biodegradable. The adhesive composition is comprised fully of plant based organic products and therefore complies with afore mentioned conditions of organic origin, and not being synthesized after harvest, and that the product extracted from nature must be able to return to nature in their original chemical structure. In addition to biodegradability, oxidation of the adhesive composition may also take place in case the conditions for biodegradability are not optimal.

The present invention, according to a second aspect, relates to a culture substrate for plants comprised of an adhesive composition of present invention mixed with a growth substrate, wherein the culture substrate for plants comprises between 10 to 65 wt% dry weight of the adhesive composition, preferably between 15 to 45 wt%, more preferably between 20 to 40 wt%, based on the total dry weight of the culture substrate for plants.

According to a preferred embodiment, the present invention relates to the culture substrate for plants, wherein the growth substrate is one or more selected from the group consisting of peat or peat soil, rock wool, wood wool, coconut fiber, cellulose fibers, perlite, clay, hemp fiber, and cotton fibers, preferably of peat or peat soil.

According to a preferred embodiment, the present invention relates to the culture substrate for plants, wherein the culture substrate for plants is one or more selected from the group of a plant plug, growing block and/or growing slab. In horticulture cultivation of younglings using plant plug, growing blocks and/or cultivation or growing slabs have shown to improve yields and provides an system for cultivation of seedlings that are difficult to cultivate, since the plug has a potentially greater capacity to withstand pests, disease and drought due to the more contained and controlled environment during plant cultivation.

The present invention, according to a third aspect, relates to a method for providing a culture substrate for plants having improved water absorbance and increased durability properties, comprising the steps of a) providing at least one organic substrate selected from the group consisting of peat or peat soil, rock wool, wood wool, coconut fibre, cellulose fibre, perlite, clay, hemp fibre, and cotton fibre, preferably of peat or peat soil, b) mixing the organic substrate with the adhesive composition according to present invention for obtaining an homogenous mixture, c) moulding of the organic substrate for plants from the homogenous mixture and subsequently heating of the moulded organic substrate to at least 70° C, preferably at least 80 ° C for adhering the fibres of organic substrate together by the adhesive composition and providing a stabilized culture substrate for plants, and d) optionally, let the moulded culture substrate cool down to room temperature.

The culture substrate according to present inventions (such as a plant plug) are produced by pressing and gluing of organic substrate under use of the adhesive composition of present invention to form a stabilized culture substrate for cultivation of plants. The resulting culture substrate is 100% organic origin fully biodegradable having improved water absorbance properties and increased durability as compared to substrates without adhesive or synthetic adhesives.

The present invention, according to a third aspect, relates to use of the adhesive composition of present invention for the production of the culture substrate for plants of present invention.

The present invention will be further detailed in the following examples: Examples

Example 1- Mixtures of soy wax and colophony

One of the main reasons for developing a adhesive composition comprised of a mixture of soy wax and colophony is that present hot melts are being mixed with wax or oil (such as beeswax) which have a strong negative impact on the water uptake of the bonded substrate (i.e. the culture substrate for plants being used for plant cultivation). Therefore various mixtures of soy wax (89 wt% stearic acid and 11 wt% palmitic acid) and colophony according to an adhesive composition of present invention were prepared and subsequently tested for their melting point, moulding and elastic properties.

As a control 100 gr Colophony (100%) was also included. The control composition has a melting point at about 70° Celsius. Below 60° C the composition remains solid and hard, and is non-elastic, brittle and rigid.

100 g Colophony + 10 g Soy wax (~9 wt%): Melting point at about 40° C. At 38 ° C the product is easily malleable and long thin threads can be pulled from the mixture. The composition is clearly much more elastic than the control compound (100% colophony).

At 32° C, kneading is still possible, but pulling the threads becomes more difficult. The wires become thicker but are still flexible. At 26° C, the product is hard, hardly elastic and becomes more brittle again.

100 g Colophony + 15 g Soy wax (~ 13 wt%): Melting point at about 35 ° C. At 40 ° C, very malleable and easy to pull thin long threads of the mixture. At 25 ° C it is still malleable, but pulling threads becomes more difficult, thicker but still flexible. At 20 ° C, the product clearly loses its flexibility, and becomes brittle. Some bendability is present but breaks quickly. At 13° C the product is hard and tough.

100 gr Colophony + 20 gr Soy wax (17 wt%): Melting point is below 25 ° C and can also be molded at a lower temperature. At this point the composition is unsuitable as adhesive composition, since already at low temperatures the composition will become soft and very flexible, leading to an increased chance of disintegration of loosening of an fibrous product that has been glued together using such an adhesive composition. An adhesive composition of present invention having more than 15 wt% Soy Wax is difficult to use for substrate bonding when producing a culture substrate for plants, as temperatures of 30 degrees in the greenhouse are very common in the summer and this will lead to softening and loosening of the fibres comprising the culture substrate for plants (i.e. a plant plug).

Example 2 - Production of culture substrate for plants

Next the stability is tested of a culture substrate for plants that has been produced using the various adhesive compositions of present invention and to test when and if the bonding between fibers will break and/or the plant plug tends to become soft due to the melting of the glue. It was tested that a good workable amount is around 10 to 14 wt%, preferably 12 to 13 wt% soy wax in the mixture (B). As a control a colophony/beeswax composition was prepared (A), to further test the water repellent/absorption effect of a culture substrate for plants prepared with the adhesive composition. Colophony is mixed with Beeswax to make the glue more elastic. The Colophony itself is moderately water-repellent, but the addition of wax (unsaturated fat), for example bees-wax makes it highly water-repellent. As a further control (C) a culture substrate for plants was used that was produced using no adhesive composition, to observe the adverse affects of using an adhesive composition on the water absorption of the culture substrate for plants.

Culture substrate for plants A: A mixture was prepared comprising 25 g growth substrate (peat substrate comprising 17,8 g water and 7,2 g dry matter) and approximately 3 g (= 40wt% on basis of total weight of dry matter of culture substrate) of an adhesive composition comprised of colophony / beeswax (colophony + 13 wt% beeswax). This mixture was mixed with water and growth substrate to form a plug of 6.6 gr. The plug is heated in microwave for 12 seconds and subsequently cooled to room temperature. The plug was then subjected to water for 30 seconds. The final weight of the plug after water absorption is 14.4 gr. The plug remained intact and fibres were well glued.

Culture substrate for plants B : The above test with A was repeated with a colophony / soy wax mixture (13 wt% soy wax). The final weight of the plug after water absorption is 20.0 gr. The plug remained intact and fibres were also well glued.

Culture substrate for plants C: The final weight of a 6.6 gr non-glued plug of the same peat substrate (no glue) after water absorption is 21.2 gr. The plug became soft and had a somewhat disintegrated fibrous structure. The plug of B absorbed almost 40% more water, when an adhesive composition according to present invention is being used, and was only slightly below the amount of water absorption of a plug produced without any adhesive composition. The reason that the non-glued plug absorbs slightly more water than the glued plug with mixture 2 is that the non-glued plug can swell, thus enlarging pores, and thus absorbing slightly more water. Furthermore, the glued plug of B absorbed a lot of water and also tended to lose its strength. This is because the peat fibres swell and become weaker. As soon as the plug dried a little, the glued plug becomes stronger again.

What can be observed is that the plug with colophony / soy wax glue is just as strong the plug with colophony / beeswax glue while the plug A contains a lot less water, due to the water repellent properties of the beeswax. The plug with the mixture A should have been firmer. The conclusion can be drawn that binding strength of the colophony / soy wax mixture is greater than the colophony / beeswax mixture. An additional reason not to use beeswax in the mixture is the possible presence of pesticides in the beeswax. This is mentioned repeatedly in the literature.