EXTRACTION OF POLYISOPRENE WITH HIGH MOLAR MASS

Abstract

The invention relates to a method for extracting high-quality polyisoprene by grinding plants via rotary shearing using a device comprising at least one rotor and at least one stator, into particles of size smaller than 1 mm, or grinding at a pH higher than 3 and lower than 8. This method is implemented in aqueous phase and allows the preparation of a dispersion of polyisoprene in water having a weight average molecular weight (M.sub.W) higher than 800 000 g/mol. The polyisoprene is extracted from plants and in particular from guayule (Parthenium argentatum). It is a method that is particularly heedful of the environment.

Claims

1. A method for extracting polyisoprene having a weight-average molecular weight (M.sub.W) higher than 800 000 g/mol, in the form of a dispersion in water, comprising: grinding, via rotary shearing using a device comprising at least one rotor and at least one stator or grinding at a pH higher than 3 and lower than 8, at least one plant, plant part or plant derivative selected from the group consisting of guayule (Parthenium argentatum), spurge (Euphorbia lathyris), argan (Argania spinosa), mariola (Parthenium incanum), rubber rabbitbrush (Chrysothamnus pinifolius), showy milkweed (Asclepias speciosa), pale Indian plantain (Cacalia atripikifolia), rubber vine (Cryptostegia grandiflora), Russian dandelion (Taraxacum koksaghyz), scorzonera (Scorzonera sp.), hoary mountain mint (Pycnanthemum incanum), Canada germander (Teucrieum canadense) and Tall Bellflower Campanula americana in a volume of water or in an aqueous solution ranging from 1 to 15 L/kg of plant, into particles of size less than 1 mm; and separating solid residues from the dispersion.

2. The method according to claim 1, wherein the grinding is performed at a pH higher than 3 and lower than 8, via shearing alone or shearing with flexion.

3. The method according to claim 1, wherein the grinding is performed at a pH higher than 3 and lower than 11, or at a pH higher than 3 and lower than 8 via rotary shearing using a device comprising at least one rotor and one stator.

4. The method according to claim 1, subsequently comprising concentrating of the dispersion of polyisoprene in water (latex), and stabilizing of the polyisoprene in the form of a dispersion in water, or coagulating the polyisoprene and separating the rubber.

5. (canceled)

6. The method according to claim 1, wherein grinding leads to particles of size smaller than 500 m, or wherein at least one step is performed in the presence of at least one agent selected from the group consisting of a polyisoprene extracting agent, a polyisoprene stabilising agent, and a polyisoprene concentrating agent; or comprising at least two additional steps of grinding and separating; or comprising a prior pre-treatment step of the harvested plant.

7. (canceled)

8. (canceled)

9. (canceled)

10. The method according to claim 1, wherein: the plant is guayule (Parthenium argentatum); or the whole plant is used; or the plant is previously pre-treated; or only the roots, branches and leaves of the plant are used; or only the branches and leaves of the plant are used; or only the branches of the plant are used; or only the leaves of the plant are used; or only the roots of the plant are used; or only the fruit of the plant is used; or only the woody biomass of the plant is used; or only the wood of the plant is used; or only the bark of the plant is used.

11. The method according to claim 1, wherein the extracted polyisoprene has a weight-average molecular weight (M.sub.W) higher than 1,000,000 g/mol or higher than 2,000,000 g/mol or higher than 2,500,000 g/mol.

12. The method according to claim 1, wherein the weight-average molecular weight (M.sub.W) of the extracted polyisoprene is 50 to 100 of the value of the weight-average molecular weight (M.sub.W) of the polyisoprene in the plant before extraction.

13. The method according to claim 1, wherein the polydispersity index of the extracted polyisoprene is lower than 3 or the polydispersity index of the extracted polyisoprene ranges from 1.6 to 3, or from 1.6 to 2, or from 1.8 to 3 or from 1.8 to 3.

14. The method according to claim 1, wherein the dispersion obtained of polyisoprene in water comprises 5 to 65 by weight of dry rubber content (DRC).

15. The method according to claim 1, wherein the extraction yield of polyisoprene having a weight-average molecular weight (M.sub.W) higher than 800 000 g/mol is greater than 50 by weight of polyisoprene in the plant after harvesting.

16. The method according to claim 1, wherein the grinding is performed less than 6 months after harvesting.

17. The method according to claim 1, wherein the grinding is performed at a pH higher than 3 and lower than 7.8, or at a pH higher than 3 and lower than 7.5, or at a pH higher than 3 and lower than 7, or at a pH higher than 4 and lower than 7.8, or at a pH higher than 4 and lower than 7.5, or at a pH higher than 4 and lower than 7.

18. The method according to claim 1, wherein the grinding is performed at a temperature lower than 60 C.

19. The method according to claim 1, wherein the grinding is performed after soaking the plant after harvesting in an aqueous solution comprising at least one agent selected from the group consisting of a polyisoprene extracting agent, a polyisoprene stabilizing agent, a polyisoprene concentrating agent.

20. The method according to claim 1, wherein the separating is done by filtration.

21. The method according to claim 4, wherein the concentrating is obtained by mechanical centrifugation or by mechanical centrifugation in the presence of at least one creaming agent.

22. The method according to claim 1, wherein the grinding is conducted: in a volume of water or aqueous solution ranging from 3 to 7 L/kg or from 4 to 5 L/kg of plant, or in a volume of aqueous solution comprising an antioxidant ranging from 3 to 7 L/kg or from 4 to 5 L/kg of plant.

23. (canceled)

24. The method according to claim 1, wherein the grinding is performed in the presence of at least one surfactant selected from the group consisting of: an anionic surfactant; a cationic surfactant; a non-ionic surfactant; and a zwitterionic surfactant.

25. The method according to claim 1, also comprising: prior cutting of the plant in a wet medium, in an aqueous solution or in water, into pieces of size ranging from 0.5 to 100 mm or 60 mm; or prior cutting of the plant in a wet medium, in an aqueous solution or in water, into pieces of size ranging from 0.5 to 50 mm followed by storage of the plant pieces in a wet medium, in an aqueous solution or in water.

Description

EXAMPLE 1

Extraction of Polyisoprene from Guayule Plants (Parthenium argentatum) Using Different Grinders

[0050] Guayule plants were harvested to extract polyisoprene therefrom with the method of the invention. Harvesting comprised reaping the guayule plants two years after planting. After harvesting, the leaves and inflorescences of the guayule plants were separated. The biomass thus prepared was treated in accordance with the method of the invention. Measurements of weight-average molecular weight (M.sub.W) and extraction yield were performed on the extracted polyisoprene. Comparative measurements in relation to these same variables were performed on the polyisoprene content of the plant before extraction in accordance with the method of the invention.

[0051] The extraction yield of polyisoprene (weight %) is the ratio of the weight of polyisoprene extracted, dried and coagulated with an acid, recovered after two successive extraction steps, to the weight of polyisoprene contained in the sample of biomass used for the extraction test, multiplied by 100. Each extraction test and each measured value are the mean of three tests with a standard deviation lower than 10% in relative value.

[0052] Several samples of biomass were treated. Samples were prepared from 100 g of guayule biomass mixed with 500 mL of aqueous phase. Other samples were prepared from 10 kg of guayule biomass mixed with 40 L of aqueous phase.

[0053] The different samples were treated by grinding followed by separation of the solid residues via filtration. A grinder A equipped with a rotor and stator (Silverson L4RT grinder) and a grinder B equipped with blades (Fryma Koruma MZ or ML grinder) were used. The size of the particles obtained after grinding was smaller than 150 m. The results obtained are given in Table 1.

TABLE-US-00001 TABLE 1 Weight-average molecular weight (M.sub.w) of Extraction yield of Test Grinder extracted polyisoprene (g/mol) polyisoprene (%) 1 A 2 700 000 72 2 B 2 600 000 70 3 B 2 800 000 87

[0054] The method of the invention therefore allows the extraction of polyisoprene having a weight-average molecular weight (M.sub.W) that is much higher than 1 000 000 g/mol or 1 500 000 g/mol and even higher than 2 000 000 g/mol.

EXAMPLE 2

Extraction of Polyisoprne from Guayule Plants (Parthenium argentatum) as a Function of pH

[0055] The biomass prepared according to Example 1 was used to evaluate the influence of pH when polyisoprene is extracted with grinder A. The variation in pH from 3 to 10 was obtained by adding hydrochloric acid or ammonia to the aqueous phase when grinding. The results obtained are given in Table 2. They were obtained as a function of initial pH of the aqueous phase used for extraction.

TABLE-US-00002 TABLE 2 Weight-average molecular weight (M.sub.w) of extracted Extraction yield of pH polyisoprene (g/mol) polyisoprene (%) 3 1 900 000 25 4 2 300 000 64 5 2 100 000 73 6 2 400 000 72 7 2 500 000 70 8 2 500 000 72 11 2 200 000 67

[0056] The method of the invention allows the extraction of polyisoprene having high weight-average molecular weight (M.sub.W), including at neutral or acid pH, thereby avoiding the addition of a base.

EXAMPLE 3

Extraction of Polyisoprene from Guayule Plants (Parthenium argentatum) in the Presence of a Surfactant

[0057] The biomass prepared according to Example 1 was used to evaluate the influence of a non-ionic surfactant (polyethylene sorbitol esterTween 80 product) contained in low concentration (0.01 weight %) in the aqueous phase when grinding. The results are given in Table 3.

TABLE-US-00003 TABLE 3 Weight-average molecular weight (M.sub.w) of Extraction yield of Test extracted polyisoprene (g/mol) polyisoprene (%) without 2 000 000 60 surfactant with 2 000 000 74 surfactant

[0058] It is ascertained that the weight-average molecular weight of polyisoprene is identical to the value measured in the absence of added surfactant. However, the percent extraction of polyisoprene obtained in the presence of the non-ionic surfactant in low concentration is much higher. The presence of this surfactant therefore allows an increase in the performance level of the extraction method of the invention, without having any negative impact on the quality of the extracted polyisoprene.