METHOD FOR EXTRACTING NATURAL RUBBER FROM PLANT MATERIAL

Description

[0001] The invention relates to a method for obtaining natural rubber from plant material, comprising at least the step of grinding the plant material with at least one ball mill with grinding media. Furthermore, the invention relates to the natural rubber obtained according to this method and the use of at least one ball mill with grinding media for grinding plant material in the extraction of natural rubber from plant material.

[0002] Many everyday consumer goods are made from rubber. In terms of durability and quality, natural rubber is often superior to synthetically produced rubber. For a long time, natural rubber was primarily obtained from rubber trees of the genus Hevea, especially from... Hevea braziliensis obtained from a plant species that is mainly cultivated in Asia.

[0003] Recently, efforts have focused on finding suitable alternatives to rubber production, with particular attention paid to plants that thrive in the climatic conditions of Central Europe. Dandelions, especially the Russian dandelion ( Taraxacum kok-saghyz The latter can yield more than 10% (w / w) of the dry mass rubber per plant, and the natural rubber obtained is comparable to that of Hevea braziliensis very similar.

[0004] Methods for obtaining natural rubber from dandelions and other plants, as well as the use of natural rubber for rubber products such as tires, are already known.

[0005] WO 2018036825 A1 describes a process of the type mentioned above, in which dandelion plant parts are crushed and / or squeezed into a pulp, and the pulp is separated into an inulin-rich, gum-poor phase and a gum-rich, inulin-poor phase. The crushing and squeezing can usually be carried out using a bead mill or ball mill.

[0006] DE 10 2013 107 279 A1 also discloses a process for obtaining natural rubber from plant material according to the aforementioned type. Non-metallic linings and / or grinding media with a non-metallic surface are not mentioned in this document.

[0007] The use of ball mills for the treatment of rubber-containing plant parts is also described in US 814,407.

[0008] Ball mills are frequently used, which employ cast iron or steel balls as grinding media in a grinding chamber made of sheet steel with wear plates.

[0009] Natural rubber can be obtained using such ball mills, but it does not always have the desired quality and high aging stability.

[0010] The invention is based on the objective of providing a method for obtaining natural rubber from plant material, comprising at least the step of grinding the plant material with at least one ball mill with grinding media, with which a natural rubber of high quality and improved aging resistance can be obtained.

[0011] This problem is solved according to the invention by the fact that the ball mill has a non-metallic lining and / or the grinding media have at least a non-metallic surface.

[0012] Surprisingly, it has been shown that by eliminating metallic materials from the ball mill that could come into contact with the plant material being ground, a natural rubber can be obtained with improved quality, leading to better and more reproducible products. This natural rubber is also characterized by improved aging behavior (reduced polymer degradation). This is presumably due to the fact that, without metallic materials, no heavy metal ions can enter the rubber, which would otherwise impair its stability and quality.

[0013] Preferably, the non-metallic lining and / or surface of the grinding media is free of heavy and / or transition metals, preferably free of cobalt, iron, copper, manganese, and nickel, and particularly preferably free of iron. Iron has proven to be particularly relevant with regard to impairing aging resistance and should not be present in non-metallic linings and surfaces, for example, in the form of soluble salts.

[0014] According to a preferred embodiment of the invention, the non-metallic lining and / or the non-metallic surface of the grinding media consists of ceramic, glass, minerals, porcelain and / or polymeric materials.

[0015] Particularly good results regarding reduced polymer degradation and thus aging resistance can be achieved when the non-metallic lining and / or the non-metallic surface of the grinding media consists of a ceramic material. These ceramic materials are based, for example, on silicate raw materials, oxide raw materials, or non-oxide raw materials. Preferably, the non-metallic lining and / or the non-metallic surface of the grinding media consists of an aluminum oxide ceramic with, in particular, between 90 and 96% aluminum oxide. Corundum (Al₂O₃) can be used, for example.

[0016] In the design of the ball mill, the lining and surface of the grinding media can be made of different materials, which should be as abrasion-resistant as possible. The grinding media should at least have a non-metallic surface. However, they can also be made entirely of non-metallic material.

[0017] To minimize mutual wear, it has proven advantageous if the non-metallic lining and the non-metallic surface of the grinding media are made of the same material, for example corundum.

[0018] In the process according to the invention, at least one ball mill is used. It is also possible to use several ball mills, preferably in series, with different dimensions, grinding media, and linings. According to a preferred embodiment of the invention, the ball mill is a drum mill or a tube mill, or the ball mills are drum mills and / or tube mills. These mill types enable a continuous process for grinding the plant material.

[0019] The plant material is ground in the ball mill in the presence of a liquid, preferably water. This allows the natural rubber to be efficiently extracted from the plant material.

[0020] To ensure proper processing of the plant material and obtain the purest possible natural rubber, it has proven advantageous to clean the plant material, preferably by washing it with water, before grinding it in the ball mill. This removes substances adhering to the surface, such as sand, loam, and clay. Cleaning can be carried out using standard equipment, methods, and cleaning agents commonly used for cleaning plant material.

[0021] To shorten the dwell time of the plant material in the ball mill, it has proven beneficial to pre-shred the plant material before grinding it in the ball mill. This pre-shredding can be carried out using conventional cutting or crushing methods such as cutting machines, hammer mills, or similar equipment.

[0022] The process according to the invention can be applied to all plants suitable for natural rubber production. The plant material is particularly preferably derived from the dandelion genus. (Taraxacum). The plant material of this genus can be ground particularly well using this method.

[0023] To obtain a particularly high proportion of natural rubber from the plant material, the plant material comes from the Russian dandelion species ( Taraxacum kok-saghyz ) or offspring (hybrids) of this.

[0024] When using dandelions, the entire plant can be ground up in the process. Preferably, however, the plant material consists mainly of the roots and hypocotyl of the dandelion, as these parts contain the highest proportion of natural rubber.

[0025] The invention also encompasses the natural rubber obtained by the process. Due to its low heavy metal ion content, the natural rubber is characterized by good quality and improved aging resistance. The natural rubber can be used to manufacture a wide variety of rubber products, preferably tires. Products made from this natural rubber, such as vehicle tires, are characterized by good and age-stable mechanical and dynamic properties. The natural rubber obtained by the process can be used for this purpose like conventional rubber produced from Hevea braziliensis Natural rubber is extracted and processed into vulcanizates by mixing and vulcanization, together with common mixture components such as fillers, antioxidants, plasticizers, sulfur and vulcanization accelerators.

[0026] The invention further relates to the use of at least one ball mill with grinding media for grinding plant material in the extraction of natural rubber from plant material, wherein the ball mill has a non-metallic lining and / or the grinding media have at least a non-metallic surface.

[0027] The invention will now be explained in more detail using comparative and exemplary embodiments, with Table 1 listing the linings and grinding media used and the analysis results obtained.

[0028] 1–4 kg of fresh Russian dandelion roots, cleaned with water, were boiled in 5 to 10 times the volume of water for 20 to 60 minutes, separated from the boiling water, and transferred to a ball mill (KM 30, 30 L nominal volume, 30 kg grinding balls (1.5 to 6 cm diameter)) with 3 to 10 times the volume of fresh water. The ball-root-water mixture was then ground at a speed of 0.5 to 0.75 * n (critical) for 1 to 4 hours. The exact grinding parameters depend on root quality (size, etc.); the optimal grinding result is characterized by the formation of rubber flakes approximately 0.5 to 5 cm in diameter within a homogeneous plant pulp. The mill lining and grinding media were varied according to Table 1. The resulting suspensions were, for example,The material was filtered through a perforated plate with a 5 mm hole diameter (other filter screens, devices, or rakes are also possible and suitable; flotation can also be used for separation). The filter cake contains the rubber flakes formed during the grinding process. The rubber flakes were washed several times with water and then dried at room temperature. The grinding balls could be separated using a ball trap when emptying the mill.

[0029] The natural rubbers obtained in this way were analyzed with regard to the following parameters: The iron content (Fe content) of the rubber is determined via the 550 °C ash (100–150 mg) using XRF (X-ray fluorescence spectroscopy) directly in XRF SpectroMicro Sample Cups (6.1 mm ID) with PROLENE film from Spectro using the SPECTRO XEPOS instrument. The number-mean molar mass Mn and weight-mean molar mass Mw of the natural rubber are determined by gel permeation chromatography (GPC) with tetrahydrofuran (THF) as the eluent against a polystyrene standard according to DIN 55672-1. Table 1 Explanation Mahlkörper Fe Content of Rubber [%] M n [g / mol] M w [g / mol] Edelstahl Edelstahl 0,98 270000 1200000 Edelstahl Corundum (Al 0,11 580000 1900000 Corundum (Al Corundum (Al 0,05 680000 2100000

[0030] Table 1 shows that the use of non-metallic material as a lining and / or for the grinding media can significantly reduce polymer degradation and thus the aging of the natural rubber. It is particularly advantageous if the lining and grinding media are made of corundum.

Claims

1. Process for obtaining natural rubber from plant material containing at least the step of milling the plant material with at least one ball mill comprising milling media, characterized in that the ball mill has a nonmetallic lining and / or the milling media have at least a nonmetallic surface.

2. Process for obtaining natural rubber from plant material according to Claim 1, characterized in that the nonmetallic lining and / or the nonmetallic surface of the milling media is / are free of heavy metals and / or transition metals.

3. Process for obtaining natural rubber from plant material according to Claim 2, characterized in that the nonmetallic lining and / or the nonmetallic surface of the milling media is / are free of iron.

4. Process for obtaining natural rubber from plant material according to at least one of the preceding claims, characterized in that the nonmetallic lining and / or the nonmetallic surface of the milling media consist(s) of ceramic, glass, minerals, porcelain and / or polymeric materials.

5. Process for obtaining natural rubber from plant material according to at least one of the preceding claims, characterized in that the nonmetallic lining and / or the nonmetallic surface of the milling media consist(s) of a ceramic material, preferably an aluminium oxide ceramic.

6. Process for obtaining natural rubber from plant material according to at least one of the preceding claims, characterized in that the nonmetallic lining and the nonmetallic surface of the milling media consist of the same material.

7. Process for obtaining natural rubber from plant material according to at least one of the preceding claims, characterized in that the ball mill is a drum mill or tube mill or the ball mills are drum mills and / or tube mills.

8. Process for obtaining natural rubber from plant material according to at least one of the preceding claims, characterized in that the plant material is milled in the ball mill in the presence of a liquid, preferably water.

9. Process for obtaining natural rubber from plant material according to at least one of the preceding claims, characterized in that the plant material has been cleaned, preferably washed with water, before milling in the ball mill.

10. Process for obtaining natural rubber from plant material according to at least one of the preceding claims, characterized in that the plant material has been subjected to precomminution before milling in the ball mill.

11. Process for obtaining natural rubber from plant material according to at least one of the preceding claims, characterized in that the plant material originates from the plant genus dandelion (Taraxacum).

12. Process for obtaining natural rubber from plant material according to Claim 11, characterized in that the plant material originates from the plant species Russian dandelion (Taraxacum kok-saghyz) or offspring (hybrids) thereof.

13. Process for obtaining natural rubber from plant material according to Claim 11 or 12, characterized in that the plant material essentially comprises the roots and the hypocotyl.

14. Use of at least one ball mill comprising milling media for milling plant material when obtaining natural rubber from plant material, characterized in that the ball mill has a nonmetallic lining and / or the milling media have at least a nonmetallic surface.