Bio-based natural rubber solution

Abstract

The present invention relates to a natural rubber solution obtained by dissolving natural rubber in terpene, a process for obtaining the natural rubber solution, and uses thereof.

Description

[Technical Field]

[0001] The present invention relates to a natural rubber solution obtained by dissolving natural rubber in terpene, a process for obtaining the natural rubber solution, and uses thereof. [Background technology]

[0002] Natural rubber is a polymeric material produced by plants and consists primarily of cis-1,4-polyisoprene. [ka]

[0003] The majority of natural rubber harvested worldwide is used as a key raw material in the manufacture of tires. With over 1.4 billion vehicles on the road worldwide, the demand for natural rubber remains enormous.

[0004] Latex, the aqueous emulsion in which natural rubber is synthesized and stored as droplets, can be harvested from rubber trees or other polyisoprene-producing plants, such as guayule or dandelion. The rubber tree, Hevea brasiliensis, which grows in the tropical regions of West Africa, South America, and Southeast Asia, is the primary source of industrial natural rubber.

[0005] Natural rubber is usually obtained from latex by precipitation and is commercially available in its solid, undissolved form.

[0006] Aqueous latexes can be stabilized, for example, by adding ammonia or ethanolamine to the emulsion, but to date the only known method of obtaining solutions of solid natural rubber is with petrochemical solvents such as benzene, toluene, hexane or chloroform.

[0007] Most petrochemical solvents are toxic and highly flammable, so processes involving petrochemical solvents require increased security measures to protect workers and production plants from harm, which severely limits the manufacturing and application of natural rubber solutions.

[0008] After extensive research in this field, it has now surprisingly been found that terpenes are very good solvating agents for natural rubber, and the resulting natural rubber solutions can be used as viscoelastic liquids or directly to produce natural rubber mixtures. Furthermore, when natural terpenes are used, a completely bio-based natural rubber solution can be obtained without the need for petrochemical-based solvents.

[0009] Patent application WO 2013 / 086407 A1 discloses a water-based adhesive comprising latex, a terpene as a penetrating agent, and a reinforcing filler. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2013 / 086407A1 Brochure Summary of the Invention [Means for solving the problem]

[0011] In one aspect, the present invention provides a natural rubber solution comprising: i) natural rubber; ii) at least one terpene; The present invention relates to a natural rubber solution comprising:

[0012] In a further aspect, the present invention provides a process for obtaining a natural rubber solution as described above or below, comprising the steps of: a. providing natural rubber; b. adding the natural rubber to a liquid terpene to obtain a mixture of solid natural rubber in the liquid terpene; c. incubating the mixture obtained in step b at a temperature in the range of 25°C to 60°C, preferably 30°C to 50°C, more preferably 35°C to 45°C until the natural rubber is dissolved; The present invention relates to a process comprising:

[0013] In another aspect, the present invention provides a process for obtaining crosslinked natural rubber, the process for obtaining a natural rubber solution as described above or as described below, comprising the additional step d. adding a cross-linking agent; e. drying the natural rubber solution containing the crosslinking agent; f. heating the dried natural rubber containing the crosslinking agent obtained in step e.; The process further comprises:

[0014] In yet another aspect, the present invention relates to a crosslinked natural rubber obtainable by the above or below described process for obtaining a crosslinked natural rubber having a glass transition temperature, measured as tan δ in dynamic mechanical analysis, of between −70° C. and −43° C.

[0015] In a final aspect, the present invention relates to the use of a natural rubber solution as defined above or below as a thickener, opacifier, lubricant, paint, as a base for solid natural rubber, and in elastic coatings, elastic joints, elastic moldings, elastic sealings and elastic films. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 shows one aspect of the rheological behavior of the limonene-based natural rubber solutions used in the Examples section as a three-dimensional graph of shear modulus and loss factor versus shear stress. [Figure 2] FIG. 2 shows another aspect of the rheological behavior of the limonene-based natural rubber solutions used in the Examples section as a graph of storage and loss modulus recovery over time after rotational shear. [Figure 3]FIG. 3 shows a third aspect of the rheological behavior of the limonene-based natural rubber solutions used in the Examples section as a graph of dynamic viscosity η versus temperature. [Figure 4] FIG. 4 shows the rheological behavior of the three crosslinked natural rubbers used in the Examples section as graphs of glass transition temperature tan δ, storage modulus G′, and loss modulus G″ versus temperature. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention discloses a natural rubber solution comprising natural rubber and at least one terpene.

[0018] The natural rubber may be selected from the group consisting of Standard Malaysian rubber, Standard African rubber, and Standard Thai rubber, Standard Indonesian rubber, Standard Nigerian rubber, Standard Vietnamese rubber, Standard Chinese rubber, dandelion rubber, guayule rubber, and combinations thereof.

[0019] Preferably, the natural rubber is selected from standard Malaysian rubber, standard African rubber and standard Thai rubber and combinations thereof.

[0020] The natural rubber solution preferably contains natural rubber in an amount of 0.01 to 99 parts by weight per 100 parts by weight of terpene, preferably 0.1 to 25 parts by weight per 100 parts by weight of terpene, and more preferably 1 to 10 parts by weight per 100 parts by weight of terpene.

[0021] Terpenes are organic compounds built from isoprene subunits and are found primarily in plants. Natural rubber is also built from isoprene subunits, so it is classified as a polyterpene.

[0022] To obtain a natural rubber solution, at least one terpene is added to the natural rubber, preferably a liquid terpene is used as the solvating agent.

[0023] Preferably, the terpene is selected from the group consisting of polylimonene, limonene, carvone, α-pinene, citral, 1,8-cineole, eucalyptol, citronellol, geraniol, geranylgeraniol, citronellene, terpinen-4-ol, borneol, camphor, guayule resin, farnesene, and combinations thereof.

[0024] More preferably, the terpene is selected from the group consisting of limonene, carvone, α-pinene, citral, 1,8-cineole, eucalyptol, citronellol, geraniol, geranylgeraniol, citronellene, terpinen-4-ol and farnesene.

[0025] Most preferably, the terpene is limonene.

[0026] Terpenes and terpene resins that are solid at normal ambient temperatures and pressures can be liquefied by increasing the temperature and / or reducing the pressure before adding the natural rubber.

[0027] Anti-aging agents Preferably, the solution further comprises at least one antioxidant.

[0028] Because natural rubber and most terpenes contain alkene moieties that are easily oxidized, the shelf life of natural rubber solutions can be extended by using antioxidants as additives. Antioxidants are materials that inhibit or slow the oxidation / aging process of materials by being oxidized themselves. Therefore, natural rubber solutions containing antioxidants remain unchanged for longer periods in oxidizing environments, such as air.

[0029] Antiaging agents include butylated hydroxytoluene (BHT); at least one stereoisomeric form of vitamin E, such as tocopherol and tocotrienol, or derivatives thereof; N-Ci-i2 alkyl-N'-phenyl-p-phenylenediamines, such as N-isopropyl-N'-phenyl-p-phenylenediamine, N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (6PPD), N-1,4-dimethylpentyl-N'-phenyl-p-phenylenediamine (7PPD), N,N'-bis-1,4-(1,4-dimethylpentyl)-p-phenylenediamine (77PD), diaryl-p-phenylenediamine (DTPD), 4,4'-bis(Ci-i2-alkylamino)triphenylamine; 7,8-dimethylisoalloxazine or derivatives thereof, such as riboflavin; p-phenylenediamine;p-Di(nitroso)arenes such as poly-p-di(nitroso)benzene, oligomerized 2,2,4-trimethyl-1,2-dihydro-quinoline (TMQ), styrenated diphenylamine (DDA), cumylated diphenylamine, zinc salts of 4- and 5-methylmercaptobenzimidazole, zinc salts of di-n-butyldithiocarbamic acid, 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,2'-methylene-bis(6-tert-butyl)-p-cresol, poly(dicyclopentadiene-co-p-cresol), n-octadecyl-β-(4-hydroxy-3,5-di-tert-butyl-phenyl)-propionate, 2,2'-methylene-bis-( 4-methyl-6-tert-butylphenol) (BPH), 2-methyl-4,6-bis(octylsulfanylmethyl)phenol, thiobisphenol, 4,4'-bis-(1,1-dimethylbenzyl)-diphenylamine (CDPA), octylated diphenylamine (ODPA), phenyl-α-naphthylamine (PAN), phenyl-β-naphthylamine (PBN), tris(nonylphenyl)phosphite, sodium hypophosphite, 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), 2-mercaptobenzimidazole (MBI), methyl-2-mercaptobenzimidazole (MMBI), and a mixture of the reaction products between p-cresol and dicyclopentadiene corresponding to formula (I); [ka] (wherein n is an integer of 1 to 9), or a combination of these You can choose from:

[0030] Preferably, the antioxidant is a bio-based antioxidant, and more preferably, the antioxidant is butylated hydroxytoluene (BHT).

[0031] In order for the antioxidant to exhibit the desired protective effect, the total content of the antioxidant should be at least 0.01 phr (w / w), preferably 0.05-5 phr (w / w), more preferably 0.1-3.5 phr (w / w), even more preferably 0.25-2 phr (w / w), and most preferably 0.4-1.0 phr (w / w), based on the amount of natural rubber.

[0032] The unit phr(w / w) is used to describe parts by weight per 100 parts by weight of rubber.

[0033] According to the disclosed invention, the dissolved natural rubber has a solubility of 1.0 to 10.0 × 10 as determined by thermal field-flow fractionation (ThFFF) measurement. 7 g / mol (mol), preferably 1.15 to 5.0 × 10 7 g / mol, most preferably 1.4 to 3.5 × 10 7 The polymer may have a weight average molecular weight Mw of g / mol.

[0034] The resulting polydispersity index PD, which is the Mw / Mn ratio, is preferably 5.0 to 20.0, preferably 5.5 to 17.5, most preferably 6.0 to 15.0, determined by ThFFF measurements.

[0035] The z-average molecular weight, Mz, was determined by ThFFF measurement and ranged from 5.0 to 35 × 10 7 g / mol, preferably 7.5 to 30 × 10 7 g / mol, most preferably 10.0 to 25.0 × 10 7 g / mol.

[0036] The weight average radius of gyration Rw can be 10 to 110 nm, preferably 20 to 100 nm, and most preferably 30 to 90 nm, as determined by ThFFF measurement.

[0037] Furthermore, the natural rubber solution has a 50 s shear strength of 2300 to 2700 mPas when measured by dynamic shear measurement at a temperature of 20 to 40°C. -1 The viscosity may have a dynamic shear viscosity at a constant shear rate of 0.05 to 0.15.

[0038] The natural rubber solution preferably contains natural rubber, terpene, and optionally an antioxidant in a total amount of more than 90% by weight, more preferably in the range of 95 to 100% by weight, based on the total weight of the natural rubber solution.

[0039] Process for obtaining natural rubber solution A natural rubber solution having the above properties can be obtained directly under mild conditions.

[0040] The process for obtaining the natural rubber solution of the present invention comprises the following steps: a. providing natural rubber; b. adding the natural rubber to a liquid terpene to obtain a mixture of solid natural rubber in the liquid terpene; c. incubating the mixture obtained in step b at a temperature in the range of 20°C to 60°C, preferably 30°C to 50°C, more preferably 35°C to 45°C until the natural rubber is dissolved. Includes:

[0041] To reduce the time for dissolving the natural rubber, it is advantageous to chop the natural rubber into small pieces before adding it to the liquid terpene in step b.

[0042] The incubation in step c) can be carried out in any known mixing device using any known mixing technique. Preferably, the mixture is mixed in a roller mixer or drum mixer, more preferably in a roller mixer.

[0043] Terpenes and terpene resins that are solid at normal ambient temperatures and pressures can be liquefied by increasing the temperature and / or reducing the pressure before adding the natural rubber.

[0044] Process for obtaining natural rubber solution containing anti-aging agent Since a natural rubber solution containing additional antioxidants has beneficial properties with respect to the shelf life of the natural rubber and terpene, an antioxidant may be introduced into the mixture of solid natural rubber in liquid terpene in step b.

[0045] Therefore, the process for obtaining a natural rubber solution containing an antioxidant comprises the following steps: a. providing natural rubber; b. adding the natural rubber to a liquid terpene to obtain a mixture of solid natural rubber in the liquid terpene; b1. adding an antioxidant to the mixture obtained in step b; c. incubating the mixture obtained in step b1 at a temperature in the range of 25°C to 60°C, preferably 30°C to 50°C, more preferably 35°C to 45°C until the natural rubber is dissolved; Includes:

[0046] The antioxidant added may consist of only one of the antioxidants listed above, or may be a combination of antioxidants.

[0047] Process for obtaining crosslinked natural rubber Crosslinking alters the physical properties of each polymeric material by linking polymer chains together through covalent or ionic bonds. These bonds increase the stiffness of the polymeric material and therefore raise its glass transition temperature.

[0048] Oxidative crosslinkers are capable of forming covalent bonds between polymer chains by oxidizing double bonds.

[0049] To obtain crosslinked natural rubber according to the present invention, a crosslinking agent can be added to the natural rubber solution obtained after step c in one of the above processes.

[0050] Therefore, the process for obtaining crosslinked natural rubber comprises the following steps: a. providing natural rubber; b. adding the natural rubber (and optionally an antioxidant) to liquid terpene to obtain a mixture of solid natural rubber in liquid terpene; b1. Optionally, adding an anti-aging agent to the mixture obtained in step b; c. incubating the mixture obtained in step b or step b1 at a temperature in the range of 25°C to 60°C, preferably 30°C to 50°C, more preferably 35°C to 45°C until the natural rubber is dissolved; d. adding a cross-linking agent; e. drying the natural rubber solution containing the crosslinking agent; f. heating the dried natural rubber containing the crosslinking agent obtained in step e.; Includes:

[0051] The crosslinking agent can be selected from elemental sulfur, elemental selenium, elemental tellurium, sulfur compounds, peroxides, quinone compounds, amine compounds, resin compounds, metal oxides and isocyanates. In a preferred embodiment, the crosslinking agent is a peroxide, more preferably dicumyl peroxide.

[0052] The crosslinking agent is added in an amount of preferably 0.01 to 3 phr (w / w), more preferably 0.5 to 1.5 phr (w / w), based on the natural rubber.

[0053] Depending on the amount of crosslinking agent added, a crosslinked natural rubber can be obtained that has a glass transition temperature of -70°C to -43°C, as measured as tan δ by dynamic mechanical analysis (DMA).

[0054] Crosslinking of the natural rubber occurs in step f during heating of the dried natural rubber containing the crosslinking agent obtained in step e.

[0055] The heating in step f is preferably carried out at a temperature in the range of 50°C to 250°C, preferably 100°C to 200°C, more preferably 130°C to 180°C. [Example]

[0056] Experimental Procedures and Examples Measurement method Rheological behavior Experimental characterization of the rheological behavior of the natural rubber solutions was carried out on an Anton Paar MCR 302 rheometer. The rheometer was equipped with a Peltier plate and hood temperature control for high-temperature uniformity. A cone-plate measuring system with a diameter of 50 mm, a cone angle of 1°, and a truncated cone of 102 μm was selected. Viscosity curves were obtained at different temperatures (20–40 °C) and from 0.1 to 1000 s. -1 The shear rate was obtained.

[0057] Molecular weight distribution and radius of gyration The molecular weight distribution of poly(cis-1,4-isoprene) in the extract was determined using a TF2000 temperature gradient field-flow fractionation (ThFFF) system coupled to a MALS and ELS detector (Postnova Analytics, Germany). The extract was dissolved in toluene or limonene at 40 °C to a final concentration of 5 mg / ml. The sample was then centrifuged at 1000 g for 60 min, and the supernatant was diluted 1:3 with toluene. Fractionation was performed using an injection volume of 100 μl and toluene as the carrier liquid at a flow rate of 0.2 ml / min. The signals obtained from the ELS detector and the MALS angle of 28–156° were used for calculations with the following parameters: random coil as the calculation type, dn / dc value of 0.104 ml / g, and extinction coefficient of 0.62 ml / g. -1 cm -1 .

[0058] Glass transition temperature Dynamic mechanical analysis of shear deformation was performed on striped specimens on an Anton Paar MCR 501 TwinDrive using the following parameters: specimen dimensions: 10 mm (width) × 2 mm (depth) × 25 mm (height), measurement frequency: 10 rad s -1 , Deformation amplitude: 0.05%, Temperature range: -80~60℃, Heating rate: 3K / min.

[0059] General Procedure 0.5cm of Standard Malaysian Rubber (SMR) 3 The natural rubber was then shredded into small pieces having a volume of 0.001g and added to the solvating agent in an amount of 6.625 parts by weight per 100 parts by weight of the solvating agent. Butylated hydroxytoluene (BHT) was added to the above mixture in an amount of 0.5 phr (w / w) based on the amount of natural rubber. The resulting mixture was heated to 40°C and mixed on a roller mixer for 48 hours.

[0060] [Table 1]

[0061] SMR1 and SMR2 ​​are standard Malaysian rubber from different commercial batches.

[0062] The natural rubber solution with limonene was honey-like, highly viscous, and non-polar.

[0063] The measured average molar masses, i.e., number-average molar mass (Mn), mass-average molar mass (Mw) and Z-average molar mass (Mz), of the natural rubber solutions in limonene were higher compared to the comparative natural rubber solutions in toluene, indicating a higher ability of the terpene to dissolve longer polymer chains.

[0064] When limonene was used as a solvating agent, the radius of gyration (number-average radius of gyration Rn, mass-average radius of gyration Rw, and Z-average radius of gyration Rz) of the rubber solution was reduced. This effect may be due to the reduced swelling of polyisoprene in limonene compared to toluene.

[0065] Figure 1 Rheological studies of limonene-based natural rubber solutions (SMR1 in limonene) showed that the shear modulus of loss modulus G" is higher than the storage modulus G' for shear forces between 0.1 and 100 Pa. This demonstrates the absence of gelation and that the natural rubber solution is essentially a viscoelastic liquid, since for a gel the ratio of G" to G' (loss factor) is less than 1, whereas for a viscoelastic liquid it is greater than 1.

[0066] This study further shows a linear viscoelasticity (LVE) range between 0.1 and 10 Pa.

[0067] Since the storage modulus begins to decrease after 10 Pa, the yield point, which marks the limit of elastic behavior and the onset of plastic behavior, can be determined to be approximately 10 Pa.

[0068] Figure 2 Furthermore, crosslinking of the viscoelastic limonene-based natural rubber solution (SMR1 in limonene) is not observed, as the recovery rates of the storage modulus G' (>80% recovery) and loss modulus G" (100% recovery) were approximately 20 s after rotational shear.

[0069] Figure 3 50s in the temperature range of 20℃ to 40℃ -1 Dynamic viscosity measurements at a constant shear rate of 1000 rpm showed a temperature dependence, with a minimum value around 29°C.

[0070] Natural rubber solution containing crosslinking agents (NRCLS) 0.5cm of solid natural rubber (SMR) 3 The mixture was chopped into small pieces having a volume of 1000g and added to the solvating agent. Butylated hydroxytoluene (BHT) was added to the mixture. The resulting mixture was heated to 40°C and mixed on a roller mixer for 48 hours. After cooling, dicumyl peroxide was added and the blend was mixed for an additional 5 minutes.

[0071] [Table 2]

[0072] The mixture was then poured into a mold and the natural rubber solution containing the crosslinker was allowed to dry.

[0073] Cross-linked natural rubber (CLNR) The resulting samples of natural rubber (NRCL) containing the crosslinker were pressed at 160°C to crosslink the polymer, and subsequent dynamic mechanical analysis was performed on the crosslinked natural rubber (CLNR).

[0074] [Table 3]

[0075] Figure 4 Dynamic mechanical analysis showed parallel courses of elastic modulus and loss modulus of the resulting crosslinked natural rubbers CLNR1-3, with the maximum values ​​of tan δ at −55°C for CLNR1 (A), −50°C for comparative CLNR2 (B), and −58°C for CLNR2 (C).

[0076] Comparative CLNR2 exhibits a substantially higher glass transition temperature than the two inventive crosslinked natural rubbers CLNR1 and CLNR3.

[0077] Furthermore, the amount of crosslinking agent used directly affects the glass transition temperature of the resulting crosslinked natural rubber. The difference between CLNR1 and CLNR3 is the amount of dicumyl peroxide, which results in a 3°C difference in glass transition temperature.

Claims

1. A natural rubber solution comprising: i) natural rubber; ii) at least one terpene; A natural rubber solution comprising:

2. 2. The natural rubber solution according to claim 1, characterized in that the natural rubber is selected from the group consisting of standard Malaysian rubber, standard African rubber and standard Thai rubber, standard Indonesian rubber, standard Nigerian rubber, standard Vietnamese rubber, standard Chinese rubber, dandelion rubber, guayule rubber and combinations thereof, preferably standard Malaysian rubber, standard African rubber and standard Thai rubber and combinations thereof.

3. The natural rubber solution according to claim 1 or 2, wherein the at least one terpene is selected from the group consisting of polylimonene, limonene, carvone, α-pinene, citral, 1,8-cineole, eucalyptol, citronellol, geraniol, geranylgeraniol, citronellene, terpinen-4-ol, borneol, camphor, guayule resin, farnesene, and combinations thereof, preferably selected from the group consisting of limonene, carvone, α-pinene, citral, 1,8-cineole, eucalyptol, citronellol, geraniol, geranylgeraniol, citronellene, terpinen-4-ol, and farnesene, and more preferably limonene.

4. 4. The natural rubber solution according to claim 1, wherein the solution contains natural rubber in an amount of 0.01 to 99 parts by weight, preferably 0.1 to 25 parts by weight, and more preferably 1 to 10 parts by weight per 100 parts by weight of terpene.

5. The natural rubber solution according to claim 1 , wherein the solution further comprises at least one antioxidant.

6. The antioxidants include butylated hydroxytoluene (BHT); at least one stereoisomer of vitamin E, such as tocopherol and tocotrienol, or a derivative thereof; N-C1-12 alkyl-N'-phenyl-p-phenylenediamine, such as N-isopropyl-N'-phenyl-p-phenylenediamine, N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (6PPD), N-1,4-dimethylpentyl-N'-phenyl-p-phenylenediamine (7PPD), N,N'-bis-1,4-(1,4-dimethylpentyl)-p-phenylenediamine (77PD), diaryl-p-phenylenediamine (DTPD), 4,4'-bis(C1-12-alkylamino)triphenylamine; 7,8-dimethylisoalloxazine or a derivative thereof, such as riboflavin; p-phenylenediamine;p-Di(nitroso)arenes such as poly-p-di(nitroso)benzene, oligomerized 2,2,4-trimethyl-1,2-dihydro-quinoline (TMQ), styrenated diphenylamine (DDA), cumylated diphenylamine, zinc salts of 4- and 5-methylmercaptobenzimidazole, zinc salts of di-n-butyldithiocarbamic acid, 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,2′-methylene-bis(6-tert-butyl)-p-cresol, poly(dicyclopentadiene-co-p-cresol), n-octadecyl-β-(4-hydroxy-3,5-di-tert-butyl-phenyl)-propionate, 2,2′-methylene-bis-( 4-methyl-6-tert-butylphenol) (BPH), 2-methyl-4,6-bis(octylsulfanylmethyl)phenol, thiobisphenol, 4,4'-bis-(1,1-dimethylbenzyl)-diphenylamine (CDPA), octylated diphenylamine (ODPA), phenyl-α-naphthylamine (PAN), phenyl-β-naphthylamine (PBN), tris(nonylphenyl)phosphite, sodium hypophosphite, 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), 2-mercaptobenzimidazole (MBI), methyl-2-mercaptobenzimidazole (MMBI), and a mixture of the reaction products between p-cresol and dicyclopentadiene corresponding to formula (I); 【Chemistry 1】 (wherein n is an integer of 1 to 9), or a combination thereof, preferably, the antioxidant is a bio-based antioxidant, and more preferably, the antioxidant is butylated hydroxytoluene (BHT).

7. 7. The natural rubber solution according to claim 5 or claim 6, wherein the total content of the antioxidants is at least 0.01 phr (w / w), preferably 0.05 to 5 phr (w / w), more preferably 0.1 to 3.5 phr (w / w), even more preferably 0.25 to 2 phr (w / w), and most preferably 0.4 to 1.0 phr (w / w), based on the amount of natural rubber.

8. The dissolved natural rubber is subjected to the following parameters: 1.0-10.0 x 10 as determined by temperature gradient field-flow fractionation (ThFFF) measurements ７ the weight average molecular weight Mw in g / mol, and / or a polydispersity index PD of 5.0 to 20.0 Mw / Mn ratio determined by ThFFF measurements, and / or 5.0 to 35 × 10 determined by ThFFF measurement ７ the Z-average molecular weight Mz in g / mol, and / or A weight average radius of gyration Rw of 10 to 110 nm, preferably 20 to 100 nm, most preferably 30 to 90 nm, as determined by ThFFF measurement and / or The natural rubber solution has a 50 s viscosity of 2300 to 2700 mPas as measured by dynamic shear measurement at a temperature of 20 to 40°C. －１ having a dynamic shear viscosity at a constant shear rate of The natural rubber solution according to any one of claims 1 to 7.

9. A method for obtaining the natural rubber solution according to any one of claims 1 to 8, comprising the steps of: a. providing natural rubber; b) adding the natural rubber to a liquid terpene to obtain a mixture of solid natural rubber in the liquid terpene; c. Incubating the mixture obtained in step b at a temperature ranging from 25°C to 60°C, preferably from 30°C to 50°C, more preferably from 35°C to 45°C until the natural rubber is dissolved. A method comprising:

10. 10. The method of claim 9, wherein the natural rubber is chopped into small pieces before being added to the liquid terpene in step b, and / or at least one antioxidant is added to the mixture of solid natural rubber in the liquid terpene obtained in step b.

11. The method of claim 9 or claim 10, further comprising the additional step of: d. adding a cross-linking agent; e. drying the natural rubber solution containing the crosslinking agent; f. heating the dried natural rubber containing the crosslinking agent obtained in step e.; A method for obtaining crosslinked natural rubber, further comprising:

12. 12. A process for obtaining crosslinked natural rubber according to claim 11, characterized in that the crosslinking agent is added in step d in an amount of 0.01 to 3 phr (w / w), preferably 0.5 to 1.5 phr (w / w), based on the amount of natural rubber, and / or characterized in that the crosslinking agent is dicumyl peroxide.

13. The method for obtaining crosslinked natural rubber according to claim 11 or claim 12, characterized in that the heating in step f is carried out at a temperature in the range of from 50°C to 250°C, preferably from 100°C to 200°C, and more preferably from 130°C to 180°C.

14. 14. A crosslinked natural rubber obtainable by the method according to any one of claims 11 to 13, which has a glass transition temperature, measured as tan δ in dynamic mechanical analysis, of -70°C to -43°C.

15. Use of the natural rubber solution according to any one of claims 1 to 10 as a thickener, opacifier, lubricant, paint, as a base for solid natural rubber, and in elastic coatings, elastic joints, elastic moldings, elastic sealings and elastic films.

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