WO2017046204A1

WO2017046204A1 - Method for producing a natural rubber

Info

Publication number: WO2017046204A1
Application number: PCT/EP2016/071764
Authority: WO
Inventors: Jérôme DUSSILLOLS; Jean-Luc MERCERON; Katia BARAN
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2015-09-17
Filing date: 2016-09-15
Publication date: 2017-03-23
Also published as: FR3041346B1; FR3041346A1

Abstract

The present invention relates to a method for producing a natural rubber, comprising the addition of a substance selected from the group consisting of proteases, surfactants and the mixtures thereof, to a natural damp rubber coagulum. The method according to the invention allows the production of a natural rubber which provides the rubber composition containing same and reinforced with a filler, with reduced hysteresis, without impairing the processability of the rubber composition.

Description

Process for preparing a natural rubber

The present invention relates to a process for preparing a natural rubber. Natural rubber is an elastomer very widely used in the field of pneumatics because of its remarkable properties. For example, it is used in rubber compositions for the manufacture of semi-finished for vehicles carrying heavy loads, because of the compromise of performance that it can bring to the tire. Indeed, the introduction of natural rubber into a rubber composition reinforced by a reinforcing filler such as a carbon black or a silica gives the rubber composition a very interesting compromise in terms of hysteresis and cohesion which results in terms of performance for the tire by a good compromise between rolling resistance, endurance and tire wear.

The natural rubber used as elastomer in the rubber compositions comes from the rubbery solids of the natural rubber latex, very often extracted from the rubber tree. It is generally recovered according to two major processes. The first is based on the coagulation of spontaneous natural rubber in the bottom of the cup from field latex (bottom of cup), the second on a coagulation of the latex of field with the aid of a chemical agent, preceded or not by centrifugation of the generally stabilized latex (latex route). The unitary steps that constitute each of the processes are far from having no effect on the final chemical composition of the natural rubber, in particular on the structure of the macromolecular chains of the polyisoprene. It is therefore known to those skilled in the art that the chosen preparation process can very strongly impact the properties of natural rubber and therefore those of rubber compositions based on natural rubber.

Moreover, there are numerous published works dealing with natural rubber treatments, for example in its latex form, such as the elimination of proteins or lipids from natural rubber (respectively deproteinization or delipidation in English), the functionalization of polyisoprene chains. These treatments are also described to modify the properties of natural rubber, and hence the properties of rubber compositions based on natural rubber.

However, it is still a constant concern to improve the properties of natural rubber or those of rubber compositions based on natural rubber to increase the performance of tires comprising such compositions. Continuing their efforts, the Applicants have discovered that a specific method of preparation of a natural rubber makes it possible to produce a natural rubber which gives the rubber composition containing it and reinforced by a filler, a reduced hysteresis without deterioration of the setting. processability of the rubber composition; this method has the particularity of understanding the addition of a substance selected from the group consisting of proteases, surfactants and mixtures thereof, to a moist natural rubber coagulum.

Thus, a first object of the invention is a method of preparing a natural rubber which comprises the following step a):

a) adding a substance selected from the group consisting of proteases, surfactants and mixtures thereof to a moist natural rubber coagulum.

Another subject of the invention is a process for producing a rubber composition based on at least one natural rubber and a reinforcing filler, which process comprises the process for preparing the natural rubber as defined above. .

The present invention also relates to the use of a natural rubber in a rubber composition which comprises a reinforcing filler, which natural rubber is prepared by the process for preparing the natural rubber as defined above.

The invention also relates to the use of a natural rubber in a tire rubber component, which natural rubber is prepared by the process for preparing the natural rubber as defined above.

I. DETAILED DESCRIPTION OF THE INVENTION

By the term "composition-based" is meant a composition comprising the mixture and / or the reaction product of the various constituents used, some of these basic constituents being capable of or intended to react with one another, less in part, during the various phases of manufacture of the composition, in particular during its crosslinking or vulcanization. By the term "part by weight per hundred parts by weight of elastomer" (or phr), is meant within the meaning of the present invention, the mass part per hundred parts of elastomer present in the rubber composition considered.

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are percentages (%) by mass. On the other hand, any interval of values denoted by "between a and b" represents the range of values from more than a to less than b (i.e., limits a and b excluded) while any range of values designated by the expression "a to b" means the range of values from a to b (i.e. including the strict limits a and b).

In the present application, by natural rubber field latex is meant the latex resulting from the bleeding rubber tree. In the remainder of the description, the term field latex refers to natural rubber field latex. A field latex is an aqueous dispersion comprising several species that can be classified into two families: the natural rubber elastomer present in particle form and the non-rubbery compounds.

In the present application, natural rubber is understood to mean the elastomeric part of the natural rubber latex. In the remainder of the presentation, the name coagulum refers to the coagulum of natural rubber.

In the present application, a moist natural rubber coagulum refers to a natural rubber coagulum before it is dried, in particular according to the drying methods conventionally used in the known processes for manufacturing natural rubber.

The natural rubber coagulum may be from spontaneous coagulation of the field latex (in which case the coagulum is a cup bottom) or caused by the addition of a coagulant to a latex. Preferably, the coagulum is a cup bottom.

The name bottom of the cup is well known to those skilled in the field of the manufacture of natural rubber. At the bleeding of the rubber tree, the fresh field latex flows into a cup called cup in which it coagulates to form a so-called cup lump coagulum. The bottom of the cup is for example the raw material of grade TSR20.

The coagulation of a field latex caused by the addition of a coagulant is widely known and practiced by those skilled in the art in the field of the manufacture of natural rubber, especially in natural rubber mills for grades TSR3L and RSS. Coagulants are well known to those skilled in the art. By way of example, mention may be made of metal ions, carboxylic acids and alcohols. Coagulation caused by addition of a coagulant to a field latex is generally done on a field latex previously stabilized. Field latex stabilization, a unitary operation also known and practiced in natural rubber mills for manufacture of TSR3L and RSS grades, consists in maintaining the pH of the latex at a value greater than the isoelectric point of the field latex, for example by adding an aqueous ammonia solution to the field latex. The substance added to the coagulum is selected from the group consisting of proteases, surfactants and mixtures thereof.

According to one embodiment, the substance is a protease. As a protease, any enzyme capable of breaking peptide bonds, especially those present in the field latex, is suitable. Examples that may be mentioned include acid proteases, neutral proteases and alkaline proteases, in particular papain. Preferably, the protease is papain.

According to another embodiment of the invention, the substance is a surfactant. As surfactant, mention may be made of any surfactant, whether anionic, nonionic or amphoteric, especially those mentioned in patent application EP 624 601. Thus, the anionic surfactants include sulphates, sulphonates, carboxylates, especially of fatty acids, phosphates; among nonionic surfactants, polyethers, among amphoteric surfactants, amino acids, betaines. The surfactant is preferably an anionic surfactant, more preferably a sulfate, even more preferably sodium dodecyl sulfate (SDS).

According to another embodiment of the invention, the substance is a mixture of a protease and a surfactant, preferably a mixture of papain and anionic surfactant, more preferably a mixture of papain and a sulphate.

According to any one of the embodiments of the invention, the sulphate is preferably sodium dodecyl sulphate (SDS). According to a preferred embodiment of the invention, the substance is used in the form of a dispersion, preferably an aqueous dispersion. The use of a dispersion of the substance facilitates the handling of the substance, and ultimately increases the efficiency of the process from the point of view of the amount of the added substance. The concentration of the substance in the aqueous dispersion of the substance is not a critical element in the process. It may be chosen by those skilled in the art so as to optimize the amount of aqueous dispersion of the substance to be added to the coagulum relative to the amount of coagulum to be treated, taking into account in particular the viscosity of the dispersion.

The amount of the substance used should be sufficient to observe an effect on the hysteresis of the natural rubber-reinforced rubber composition. Typically, the added substance level is at least 0.01 g per 100 g of natural rubber. The maximum amount of the substance that can be used is usually limited for economic reasons. This is why the rate of the substance generally does not exceed 5 g per 100 g of natural rubber. Thus the level of the substance added to the coagulum preferably varies in a range from 0.01 g to 5 g per 100 g of natural rubber, more preferably from 0.1 to 3 g per 100 g of natural rubber.

The substance can be added to the coagulum by spraying the coagulum or by soaking the coagulum. Spraying or soaking is chosen by those skilled in the art according to the physical form of the substance. Typically a substance in the form of a dispersion may be added to the coagulum by spraying by spraying the coagulum with the dispersion. Alternatively, the coagulum can be soaked in a liquid containing the substance. Generally, the coagulum and the substance are brought together at a temperature of at least 20 ° C. The required contact time between the coagulum and the substance depends on many factors such as coagulum size, temperature, coagulum concentration and substance, as well as the mode of contact between the coagulum and the substance, ie by spraying or by soaking. It is adjusted by those skilled in the art taking into account these factors. Therefore, the higher the contact temperature, the shorter the contact time.

According to a preferred embodiment, the coagulum is put in the form of granules or foil before step a). This shaping consists of operations widely known and practiced by those skilled in the field of the manufacture of natural rubber, especially in natural rubber mills for the manufacture of grades TSR3L or TSR20 or RSS . These operations are typically carried out in devices comprising at least one creper or at least one granulator (in English "shredder"). By increasing the surface of the coagulum, they make it possible to increase the contact surface between the coagulum and the substance and thus make the addition of the substance more efficient. Those skilled in the art understand that the granulation operation is preferred to the sheet setting operation and that the finer the coagulum is divided, the more effective the process is. During the granulation step, additives to facilitate granulation can be added, such as ricinoleate of soda.

According to one embodiment of the invention, the substance is added to the coagulum previously drained or drained. Draining or wringing are also operations widely practiced by those skilled in the art in natural rubber mills for the manufacture of grades TSR3L or TSR20 or RSS using devices that include screens, crispy for example. This embodiment decreases the risk of leaching of the substance by water and losses of the substance, and thus makes the process more efficient. The water may come from previous washes of the coagulum after harvest before step a). These washes, for example in ponds of water, are typically conducted to rid the coagulum of more or less coarse contaminants, such as twigs, bark or tree leaves. In the present application, the terms "coagulum of treated natural rubber" or "treated coagulum" are used interchangeably to designate the coagulum resulting from step a).

The treated coagulum contains in particular water from the field latex and optionally the aqueous dispersion. Natural rubber is generally dried before being used in a rubber composition, in particular prior to incorporation of the reinforcing filler into the natural rubber. The drying step is an operation widely practiced by those skilled in the field of the manufacture of natural rubber, in particular for use in a tire rubber composition. It can be done by drying under an air or an inert gas, such as nitrogen, or under vacuum. The vacuum drying can be carried out under a stream of an inert gas, such as nitrogen or in the presence of air. The drying can be carried out at a moderate temperature, especially at a temperature of at most 80 ° C, for example from room temperature (23 ° C) to 80 ° C or at a higher temperature, especially greater than 100 ° C. The drying can be carried out under the drying conditions traditionally used in the machining plants (in English "remilling factory") of natural rubber, used in particular in the manufacture of grades TSR or RSS. In this respect, drying is possible under the sole action of the ambient air, with or without smoking (respectively "air drying" and "smoke drying"), drying in machines such as tunnel-type dryers.

Prior to the drying step, an antioxidant may be added to the treated coagulum. This particular embodiment is preferred when the drying is carried out in the presence of air, in particular at temperatures of at least 60 ° C. Alternatively to prevent oxidation of the polyisoprene chains of the natural rubber during its preparation process, for example during drying, the antioxidant may be added to the field latex before coagulation or to the coagulum before step a) .

The polyisoprene chains of natural rubber may be subjected to treatments known to those skilled in the art which are the following:

i. the functionalization of the polyisoprene chains of natural rubber,

ii. removal of proteins, lipids, phospholipids from natural rubber, iii. stabilizing the viscosity of the natural rubber with an additive such as hydroxylamine or one of its salts, with a compound having a hydrazide function CONHNH ₂ . Steps i, ii or iii) can be carried out on the polyisoprene chains before step a) or after step a). They are conducted according to methods well known to those skilled in the art.

The natural rubber prepared according to the process according to the invention can be used in a rubber composition which comprises a reinforcing filler.

The rubber composition is typically prepared by incorporating the reinforcing filler into the natural rubber, especially by kneading, more particularly by thermomechanical kneading.

The composition of the invention comprises any type of so-called reinforcing filler known for its ability to reinforce a rubber composition that can be used for the manufacture of tires, for example an organic filler such as carbon black, a reinforcing inorganic filler such as silica to which is associated in a known manner a coupling agent, or a mixture of these two types of filler. Such a reinforcing filler typically consists of nanoparticles whose average size (in mass) is less than one micrometer, generally less than 500 nm, most often between 20 and 200 nm, in particular and more preferably between 20 and 150 nm. Preferably, the content of total reinforcing filler (carbon black and / or reinforcing inorganic filler such as silica) is between 20 and 200 phr, more preferably between 30 and 160 phr, more preferably from 30 to 90 phr. optimum being in a known manner and different according to the particular applications targeted: the level of reinforcement expected on a bicycle tire, for example, is of course less than that required on a tire capable of driving at high speed in a sustained manner, for example a tire motorcycle, a tire for a passenger vehicle or for a commercial vehicle such as a heavy truck.

Suitable carbon blacks are all carbon blacks, especially blacks conventionally used in tires or their treads (so-called pneumatic grade blacks). Among these, the reinforcing carbon blacks of the 100, 200, 300 series or the 500, 600, 700 or 900 series blacks (ASTM grades), for example the blacks N115, N134, N234, N326, are particularly suitable. , N330, N339, N347, N375, N550, N683, N772). These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a carrier for some of the rubber additives used.

"Reinforcing inorganic filler" means any inorganic or mineral filler, irrespective of its color and origin (natural or synthetic), also called "white" filler, "clear" filler or even "non-black" filler. "as opposed to carbon black, capable of reinforcing on its own, with no other means than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tires, in other words able to replace, in its reinforcing function, a conventional carbon black of pneumatic grade; such a filler is generally characterized, in known manner, by the presence of hydroxyl groups (-OH) on its surface.

Suitable reinforcing inorganic fillers are in particular mineral fillers of the siliceous type, preferentially silica (SiO ₂ ). The silica used may be any reinforcing silica known to those skilled in the art, especially any precipitated or fumed silica having a BET surface and a CTAB specific surface both less than 450 m ² / g, preferably between 60 and 300 m ² / g- As highly dispersible precipitated silicas (called "HDS"), there may be mentioned for example the silicas "Ultrasil" 7000 and "Ultrasil" 7005 from the company Degussa, the silicas "Zeosil" 1165MP, 1135MP and 1115MP of the Rhodia company, the "Hi-Sil" silica EZ150G from the company PPG, the "Zeopol" silicas 8715, 8745 and 8755 from the Huber Company, the high surface area silicas as described in the application WO 03/016387. In the present disclosure, the BET surface area is determined in a known manner by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" Vol. 60, page 309, February 1938, specifically according to the French standard NF ISO 9277 of December 1996 (multipoint volumetric method (5 points) - gas: nitrogen - degassing: time at 160 ° C - relative pressure range p / po: 0.05 at 0.17). The CTAB specific surface is the external surface determined according to the French standard NF T 45-007 of November 1987 (method B).

In order to couple the reinforcing inorganic filler to the diene elastomer, an at least bifunctional coupling agent (or bonding agent) is used in a well-known manner to ensure a sufficient chemical and / or physical connection between the inorganic filler (surface of its particles) and the diene elastomer. In particular, organosilanes or at least bifunctional polyorganosiloxanes are used.

In particular, polysulfide silanes, called "symmetrical" or "asymmetrical" silanes according to their particular structure, are used, as described for example in the applications WO03 / 002648 (or US 2005/016651) and WO03 / 002649 (or US 2005/016650).

In particular, polysulphide silanes having the following general formula (I) are not suitable for the following definition:

(I) Z - A - Sx - A - Z, wherein:

x is an integer of 2 to 8 (preferably 2 to 5); - the symbols A, which are identical or different, represent a divalent hydrocarbon group (preferably an alkylene Ci-Ci ₈ or an arylene group C ₆ -Ci2, particularly alkylene Ci-Ci _0, in particular Ci-C ₄ , especially propylene);

the symbols Z, identical or different, correspond to one of the three formulas below:

-

in which:

- the radicals R ^1, substituted or unsubstituted, identical or different, represent an alkyl group _Ci-8 cycloalkyl, C ₅ -C ₈ aryl or C ₆ -C ₈ (preferably alkyl groups -C ₆ , cyclohexyl or phenyl, especially C ₁ -C ₄ alkyl groups, more particularly methyl and / or ethyl).

- the radicals R ^2, substituted or unsubstituted, identical or different, represent an alkoxy group or Ci-Ci ₈ cycloalkoxy, C ₅ -C ₈ (preferably a group selected from alkoxyls and C ₈ cycloalkoxyls C ₅ -C ₈ , more preferably still a group selected from C ₁ -C ₄ alkoxyls, in particular methoxyl and ethoxyl).

The content of coupling agent is advantageously less than 20 phr, it being understood that it is generally desirable to use as little as possible. Typically the level of coupling agent is from 0.5% to 15% by weight relative to the amount of inorganic filler. Its level is preferably between 0.5 and 12 phr, more preferably in a range from 3 to 10 phr. This level is easily adjusted by those skilled in the art according to the level of inorganic filler used in the composition.

The rubber composition may furthermore comprise all or part of the usual additives normally used in elastomer compositions intended to constitute mixtures of finished articles of rubber such as tires, in particular treads, such as, for example, plasticizers. or extender oils of aromatic or nonaromatic nature, pigments, protective agents such as antiozone waxes, chemical antiozonants, anti-oxidants, anti-fatigue agents, reinforcing resins (such as resorcinol or bismaleimide), acceptors (for example phenolic novolac resin) or methylene donors (for example HMT or H3M) as described for example in application WO 02/10269, a crosslinking system based on of sulfur, either of sulfur and / or peroxide and / or bismaleimide donors, vulcanization accelerators or retarders, vulcanization activators.

The rubber composition may contain, in addition to the natural rubber resulting from the process according to the invention, another diene elastomer. By "diene" elastomer (or indistinctly rubber) is to be understood in known manner an elastomer consisting at least in part (ie, a homopolymer or a copolymer) of monomeric diene units (monomers carrying two carbon-carbon double bonds, conjugated or not). As an elastomer, mention may be made of those conventionally used in the tire, such as polybutadienes (BR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers, and mixtures of these elastomers.

According to any of the embodiments of the invention, the rubber composition can be manufactured in mixers using two successive preparation phases well known to those skilled in the art: a first phase of work or thermomechanical mixing (phase so-called "non-productive") at high temperature, up to a maximum temperature of between 110 ° C and 200 ° C, preferably between 130 ° C and 185 ° C, followed by a second mechanical working phase (so-called "Productive") to a lower temperature, typically less than 120 ° C, for example between 40 ° C and 100 ° C, finishing phase during which is incorporated a crosslinking system.

By way of example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the constituents of the rubber composition are introduced into a suitable mixer such as a conventional internal mixer. exception of the crosslinking system. The total mixing time, in this non-productive phase, is preferably between 2 and 10 min. After cooling the mixture thus obtained during the first non-productive phase, the low temperature crosslinking system is then incorporated, generally in an external mixer such as a roll mill; the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 min.

The first kneading step is generally carried out by incorporating the reinforcing filler with the elastomer, in this case natural rubber and, if appropriate, other diene elastomers, in one or more times by thermomechanically kneading. In the case where the reinforcing filler, in particular carbon black, is already incorporated wholly or partly into the elastomer in the form of a masterbatch, it is the masterbatch which is directly kneaded and, if appropriate, incorporates other elastomers or reinforcing fillers present in the composition which are not in the form of masterbatch, as well as additives other than the crosslinking system. The final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for a characterization in the laboratory, or else extruded in the form of a rubber profile that can be used, for example, as a tread. tire for passenger vehicle.

The rubber composition may be in the green state (before crosslinking) or in the fired state (after crosslinking). The rubber composition may be used in a tire, especially as a composition of one of the constituent elements of the tire. These constituent elements may be a rubber component such as a tread, a sheet or a filling compound. Thus, the natural rubber prepared according to the process according to the invention can be used in a tire rubber component.

The aforementioned features of the present invention, as well as others, will be better understood on reading the following description of several embodiments of the invention, given by way of illustration and not limitation.

II. EXAMPLES OF CARRYING OUT THE INVENTION

ll-l. Preparation of natural rubbers:

The seven natural rubbers NR1 to NR7 are prepared according to the methods of preparation described hereinafter. Table I lists the differences in the treatment of natural rubbers NR2 to NR7 with natural rubber NR1, as well as the drying conditions of natural rubbers NI to NR7.

NRl natural rubber is prepared according to the following method:

- harvest of coagulum in the cup 3 days after bleeding

- 5 passages in crepe

- 2 passages in a shredder

- spraying with sodium ricinoleate at a rate of 1.5 g per 100 g of natural rubber

- 2 passages in crepe

- 1 passage in a shredder

drying of the granules under air at 125 ° C. for 1 h 30 min (air drying)

Natural rubbers NR2 to NR7 are prepared as NR1 with the following differences: a step of dipping the granules in an aqueous dispersion of papain (Aldrich, reference P3375), sodium dodecyl sulphate (SDS) (Aldrich, reference 05030) or their mixture precedes the drying step, for 2 hours at 54 ° C., the drying is under vacuum under a stream of nitrogen at 65 ° C for 48 hours for NR2, NR4 and NR6 (nitrogen drying).

The content of the substance brought into contact with the granules is, per 100 g of natural rubber, 0.7 g of papain, 0.3 g of SDS and a mixture containing 0.7 g of papain and 0.3 g of SDS. Only natural rubbers NR2 to NR7 are prepared according to the process according to the invention. NR1, prepared according to a process not according to the invention due to the absence of the addition of the substance to the coagulum, corresponds to a grade TSR20.

11-2. Characterization of natural rubbers:

Mooney plasticity was measured for each of the prepared natural rubbers NR1 to NR7. To measure the Mooney plasticity, an oscillating consistometer is used as described in the French standard NF T 43-005 (1991). The Mooney plasticity measurement is carried out according to the following principle: the raw composition (i.e., before firing) is molded in a cylindrical chamber heated to 100 ° C. After a minute of preheating, the rotor (of small size) rotates within the test tube at 2 revolutions / minute and the useful torque is measured to maintain this movement after 4 minutes of rotation. Mooney plasticity (MS 1 + 4) is expressed in "Mooney unit" (UM, with 1 MU = 0.83 Newton meter).

The drying of the natural rubbers of NR3, NR5 and NR7 being conducted under air, it is found that the addition of the substance to the coagulum has the advantage of not inducing a penalty of the processability of the natural rubber: no increase in the plasticity of NR3, NR5 and NR7 natural rubbers compared to NR1 is observed. Furthermore, it is observed that when the process combines the addition of papain and / or SDS to drying under air, it leads to natural rubbers of lower Mooney plasticity. This embodiment of the invention could be of advantage in terms of cost, since it dispenses operations of peptization or plasticization of natural rubber generally necessary in the manufacturing process of rubber compositions to reduce the plasticity of natural rubber. 11-3. Preparation of rubber compositions

Rubber compositions C1 to C7 are prepared according to the method described below with the content of the constituents expressed in phr in Table II: In an internal mixer (final filling rate: about 70% by volume), the initial temperature of the tank is approximately 80 ° C., successively the natural rubber elastomer, the reinforcing filler, and the various other ingredients. with the exception of the vulcanization system. Thermomechanical work (non-productive phase) is then carried out in one step, which lasts a total of about 3 to 4 minutes, until a maximum temperature of "fall" of 165 ° C is reached. The mixture thus obtained is recovered, cooled and then sulfur is incorporated and the sulfenamide type accelerator on a mixer (homo-finisher) at 70 ° C., mixing the whole (productive phase) for a suitable time (for example 3 hours). at 4 minutes).

The compositions are then calendered in the form of a plate with a thickness ranging from 2 to 3 mm or thin rubber sheets for the measurement of their physical or mechanical properties.

The rubber compositions differ in the nature of the natural rubber used in the rubber composition. The rubber compositions C1 to C7 respectively contain the natural rubbers NR1 to NR7.

The rubber composition C1 is a control rubber composition, since it contains as a natural rubber a grade TSR20; the rubber compositions C2 to C7 are rubber compositions prepared according to the process according to the invention, since the natural rubbers NR2 to NR7 are prepared by dipping the coagulae in an aqueous dispersion of papain and / or SDS.

11-4. Rubber results:

For each of the compositions vulcanized at 150 ° C., the Mooney plasticity, the properties at break and the dynamic properties are measured under the test conditions described below. The composition Cl is taken as a control. The results are shown in Table III. Mooney plasticity (MS) of natural rubbers and rubber compositions:

An oscillating consistometer is used as described in the French standard NF T 43-005 (1991). The Mooney plasticity measurement is carried out according to the following principle: the raw composition (i.e., before firing) is molded in a cylindrical chamber heated to 100 ° C. After a minute of preheating, the rotor (of small size) rotates within the test tube at 2 revolutions / minute and the useful torque is measured to maintain this movement after 4 minutes of rotation. Mooney plasticity (MS 1 + 4) is expressed in "Mooney unit" (UM, with 1 MU = 0.83 Newton meter).

Traction tests The tensile tests make it possible to determine the elastic stress and the properties at break. Unless otherwise indicated, they are carried out in accordance with the French standard NF T 46-002 of September 1988. Traction data processing also makes it possible to draw the modulus curve as a function of elongation. The nominal secant modulus calculated at the initial elongation of the test specimen (or apparent stress, in MPa) at 100% and 300% elongation noted MSA100 and MSA300 respectively is measured at first elongation. The breaking stresses (in MPa) and the elongations at break (in%) are measured at 60 ° C. Dynamic Properties

The loss factor tan (δ) max is measured on a viscoanalyzer (Metravib VA4000) according to ASTM D 5992-96. The response of a sample of vulcanized composition (in the form of 2 test pieces 2 mm thick and 10 mm in diameter) is recorded, subjected to sinusoidal stress in alternating simple shear, at the frequency of 10 Hz, at 60 °. C according to ASTM D 1349-99. A strain amplitude sweep is performed from 0.1% to 50% (forward cycle) and then from 50% to 0.1% (return cycle). The result exploited is the loss factor tan (δ). For the return cycle, the maximum value of tan (δ) observed, denoted tan (δ) max, is indicated. The C2 to C7 rubber compositions made according to the process according to the invention are less hysteretic than the control composition, without there being a substantial change in the breaking properties and plasticity of the rubber compositions.

Table I

Table II

(1) "Wingstay 100" (mixture of N, N '- (phenyl and benzene-1,4-diamines),

(2) N-1,3-dimethylbutyl N-phenylparaphenylenediamine

(3) N-cyclohexyl-2-benzothiazylsulfenamide Table III

Constraint deformation

Tanô _m ax MS (1 + 4)

Composition Rupture (%) Rupture (MPa)

at 60 ° C 100 ° C to 60 ° C to 60 ° C

Cl 612 26.21 0.24 56

C2 500 19.75 0.21 55

C3,617 26.55 0.22 58

C4,640 27.28 0.21 53

C5 613 26.40 0.23 55

C 587 24.83 0.22 56

C7,631 26.98 0.22 52

Claims

A process for preparing a natural rubber which comprises the following step:

The method of claim 1 wherein the substance is a protease, preferably papain.

3. The process of claim 1 wherein the substance is a surfactant, preferably an anionic surfactant, more preferably a sulfate.

4. Process according to claim 1, in which the substance is a mixture of a protease and a surfactant, preferably a mixture of papain and an anionic surfactant, more preferably a mixture of papain and a sulphate. .

5. Process according to any one of claims 1 to 4 wherein the substance is in the form of a dispersion, preferably aqueous.

6. Process according to any one of claims 1 to 5 wherein the substance is added to the coagulum by spraying or soaking the coagulum.

7. Method according to any one of claims 1 to 6 wherein the level of the added substance is in a range from 0.01 g to 5 g per 100 g of natural rubber, preferably from 0.1 to 3 g per 100 g. of natural rubber.

The method of any one of claims 1 to 7 wherein the coagulum is a cup bottom.

9. A process according to any one of claims 1 to 8 wherein the coagulum is formed into granules or sheets prior to step a).

10. Method according to any one of claims 1 to 9 wherein a dewatering step or dewatering of the coagulum is performed before step a).

11. A method according to any one of claims 1 to 10 which comprises after step a) a drying step of the coagulum.

12. The method of claim 11 wherein the step of drying the coagulum is carried out in air or under nitrogen.

13. A method of manufacturing a rubber composition based on at least one natural rubber and a reinforcing filler, which process comprises the steps of the method as defined in claim 1 to 12.

14. The method of claim 13 which comprises the incorporation of the reinforcing filler in the natural rubber, preferably by kneading, more preferably by thermomechanical kneading.

15. Use of a natural rubber in a rubber composition which comprises a reinforcing filler, which natural rubber is prepared according to the steps of the method defined according to any one of claims 1 to 12.

16. Use of a natural rubber in a tire rubber component, which natural rubber is prepared according to the steps of the method defined in any one of claims 1 to 12.