Tyre for vehicle wheels

Abstract

The present invention relates to a tyre for vehicle wheels comprising at least one structural element comprising a crosslinked elastomeric material obtained by crosslinking a crosslinkable elastomeric composition comprising a predispersion of natural rubber and lignin obtained by co-precipitation from latex, where said lignin has a concentration of phenolic groups higher than 2 mmol per gram of lignin, and where said predispersion comprises an amount of said lignin such as to provide, in said crosslinkable elastomeric composition, a concentration of lignin equal to or lower than about 25 phr.

Claims

1. A tyre for vehicle wheels comprising at least a structural element comprising a crosslinked elastomeric material obtained by crosslinking a crosslinkable elastomeric composition comprising a predispersion of natural rubber and lignin obtained by co-precipitation from latex, wherein the lignin has a concentration of hydroxyl phenolic groups higher than 2 mmoles per gram of lignin, and wherein the predispersion comprises an amount of the lignin that provides, in the crosslinkable elastomeric composition, a concentration of lignin equal to or lower than about 25 phr.

2. The tyre for vehicle wheels according to claim 1, wherein the predispersion comprises an amount of the lignin that provides, in the crosslinkable elastomeric composition, a concentration of lignin equal to or higher than about 2.5 phr.

3. The tyre for vehicle wheels according to claim 1, wherein the tyre comprises at least a carcass structure, and a tread band applied in a radially outer position with respect to the carcass structure.

4. The tyre for vehicle wheels according to claim 1, wherein the structural element is selected from the group consisting of sidewall inserts, belt structures, sidewall, tread band, bead structures, and a layer of elastomeric material in a radially inner position with respect to the tread band.

5. The tyre for vehicle wheels according to claim 1, wherein the lignin has a concentration of hydroxyl phenolic groups higher than 2.5 mmoles per gram of lignin.

6. The tyre for vehicle wheels according to claim 5, wherein the lignin has a concentration of hydroxyl phenolic groups lower than 6 mmoles per gram of lignin.

7. The tyre for vehicle wheels according to claim 1, wherein the lignin has an number-average molecular weight (Mn) equal to or higher than 1,000 g/mole.

8. The tyre for vehicle wheels according to claim 7, wherein the lignin has an number-average molecular weight (Mn) equal to or lower than 10,000 g/mole.

9. The tyre for vehicle wheels according to claim 1, wherein the elastomeric composition comprises at least 10 phr of the predispersion of natural rubber and lignin obtained by co-precipitation from latex.

10. The tyre for vehicle wheels according to claim 1, wherein the predispersion of natural rubber and lignin comprises an amount of the lignin, that provides, in the crosslinkable elastomeric composition, a concentration of lignin ranging from 5 to 20 phr.

11. The tyre for vehicle wheels according to claim 1, wherein the predispersion of natural rubber and lignin is obtained with a process comprising: (a) adding the lignin to a latex of natural rubber, (b) causing the co-precipitation of the predispersion of natural rubber and lignin from the mixture resulting from step (a), and (c) separating the predispersion of natural rubber and lignin obtained in step (b) from a supernatant residue.

12. The tyre for vehicle wheels according to claim 11, wherein the lignin, before the addition to the latex of natural rubber, is solubilized in an alkaline solution.

13. The tyre for vehicle wheels according to claim 11, wherein the latex of natural rubber has a solid residue ranging from 20% to 70% by weight with respect to the total weight of latex.

14. The tyre for vehicle wheels according to claim 11, wherein the lignin is added in an amount that provides, in the crosslinkable elastomeric composition, a concentration of lignin ranging from 2.5 to 25 phr.

15. A process for preparing a predispersion of natural rubber and lignin, the process comprising: (a) adding the lignin to a latex of natural rubber, (b) causing co-precipitation of the predispersion of natural rubber and lignin from the mixture resulting from step (a), and (c) separating the predispersion of natural rubber and lignin obtained in step (b) from a residual supernatant, wherein the lignin has a concentration of hydroxyl phenolic groups higher than 2 mmoles per gram of lignin.

16. The process according to claim 15, wherein the lignin, before the addition to the latex of natural rubber, is solubilized in an alkaline solution.

17. The process according to claim 15, wherein the co-precipitation occurs by addition of an acid solution.

18. A process for manufacturing a crosslinkable elastomeric composition, the process comprising: feeding at least one mixing apparatus with at least the following components of a crosslinkable elastomeric composition: at least one dienic elastomeric polymer, at least one predispersion of natural rubber and lignin obtained according to claim 15, at least one reinforcing filler, and at least one vulcanizing agent, mixing and dispersing the components to obtain the crosslinkable elastomeric composition, and discharging the crosslinkable elastomeric composition from the mixing apparatus.

Description

DRAWINGS

(1) The description will be presented hereunder, referring to the appended drawings, supplied purely as a guide and therefore non-limiting, in which:

(2) FIG. 1 illustrates, in transverse half-section, a tyre for motor vehicle wheels according to a first embodiment of the present invention, and

(3) FIG. 2 illustrates, in transverse half-section, a tyre for motor vehicle wheels according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) In FIGS. 1 and 2, “a” indicates an axial direction and “r” indicates a radial direction. For simplicity, FIGS. 1 and 2 show only a portion of the tyre, the remaining portion that is not shown being identical and arranged symmetrically with respect to the radial direction “r”.

(5) Referring to FIG. 1, the tyre 100 for motor vehicle wheels comprises at least one carcass structure, comprising at least one carcass layer 101 having respectively opposite terminal edges engaged in respective annular anchoring structures 102, called bead wires, optionally associated with a bead filler 104. The region of the tyre comprising the bead wire 102 and the filler 104 forms an annular reinforcing structure 103, the so-called bead, intended for anchoring the tyre on a corresponding mounting rim (not shown).

(6) The annular reinforcing structure 103, and in particular the bead filler 104, are advantageously made from the elastomeric composition comprising the predispersion of natural rubber and lignin described above, because these elements are particularly subject to mechanical stresses in conditions of use during rolling of the tyre, as they are directly in contact with the wheel rim, and it is necessary to limit the phenomena of ageing that lead to stiffening of the elastomeric composition.

(7) The carcass structure is usually of the radial type, i.e. the reinforcing elements of the at least one carcass layer 101 are located on planes comprising the rotation axis of the tyre and are substantially perpendicular to the equatorial plane of the tyre. Said reinforcing elements generally consist of textile cords, for example rayon, nylon, polyester (for example polyethylene naphthalate (PEN)). Each annular reinforcing structure is associated with the carcass structure by a backward folding of the opposite side edges of the at least one carcass layer 101 around the annular anchoring structure 102 in order to form the so-called backfolds of the carcass 101a as illustrated in FIG. 1.

(8) In one embodiment, coupling between the carcass structure and the annular reinforcing structure may be provided by a second carcass layer (not shown in FIG. 1) applied in an axially outer position with respect to the first carcass layer.

(9) An antiabrasive strip 105 is arranged in an outer position of each annular reinforcing structure 103. Preferably each antiabrasive strip 105 is arranged at least in an axially outer position with respect to the annular reinforcing structure 103 extending at least between the sidewall 108 and the portion radially below the annular reinforcing structure 103.

(10) Preferably the antiabrasive strip 105 is arranged so as to wrap the annular reinforcing structure 103 along the axially inner and outer regions and regions radially below the annular reinforcing structure 103 so as to be interposed between the latter and the wheel rim when the tyre 100 is mounted on the rim.

(11) Associated with the carcass structure, there is a belt structure 106 comprising one or more belt layers 106a, 106b arranged in radial superposition relative to one another and relative to the carcass layer, having reinforcing cords, typically metallic. These reinforcing cords may have a crossed orientation relative to a circumferential direction of development of the tyre 100. “Circumferential” direction means a direction generally oriented in the direction of rotation of the tyre.

(12) In a radially more outer position with respect to the belt layers 106a, 106b, at least one zero-degrees reinforcing layer 106c may be applied, commonly known as “0° belt”, which generally incorporates a plurality of reinforcing cords, typically textile cords, oriented in a substantially circumferential direction, thus forming an angle of a few degrees (for example an angle between about 0° and 6°) relative to the equatorial plane of the tyre, and coated with an elastomeric material.

(13) The elements of the belt structure are advantageously made from the elastomeric composition comprising the predispersion of natural rubber and lignin described above.

(14) A tread band 109 made of an elastomeric compound is applied in a radially outer position with respect to the belt structure 106.

(15) In addition, respective sidewalls 108 made of an elastomeric compound produced according to the present invention are applied in an axially outer position on the side surfaces of the carcass structure, each extending from one of the side edges of the tread band 109 until flush with the respective annular reinforcing structure 103.

(16) In a radially outer position, the tread band 109 has a rolling surface 109a intended to come into contact with the ground. Circumferential grooves, which are connected by transverse recesses (not shown in FIG. 1) to define a plurality of blocks of various shapes and dimensions distributed over the rolling surface 109a, are generally provided in this surface 109a, which is shown smooth in FIG. 1 for simplicity.

(17) An underlayer 111 is arranged between the belt structure 106 and the tread band 109.

(18) A strip consisting of elastomeric material 110, commonly known as a “mini-sidewall”, may optionally be present in the connecting region between the sidewalls 108 and the tread band 109, this mini-sidewall generally being obtained by co-extrusion with the tread band 109 and giving an improvement of the mechanical interaction between the tread band 109 and the sidewalls 108. Preferably the end portion of the sidewall 108 directly covers the side edge of the tread band 109.

(19) The tread band, and/or the underlayer, and/or the mini-sidewall and/or the sidewall may advantageously be made from the elastomeric composition comprising the predispersion of natural rubber and lignin described above, because lower hysteresis means lower dissipation of energy in the form of heat during operation, and consequently lower fuel consumption, and moreover because higher energy at rupture confers higher tearing resistance, and consequently higher strength and durability of the surface of the sidewall and of the tread, which are particularly exposed to harsh mechanical stresses during use (due for example to roughness of the road surface, striking pavements when manoeuvring for parking, and so on).

(20) In the case of tubeless tyres, a layer of rubber 112, generally known as a “liner”, which provides the necessary impermeability to the air for inflating the tyre, may also be provided in a radially inner position with respect to the carcass layer 101.

(21) Self-supporting tyres (100), illustrated in FIG. 2, include a supporting structure that is able to support the load of the vehicle when there is considerable or total loss of pressure. In particular, a sidewall insert (113), made according to the present invention, may be associated with each sidewall. On each side of the self-supporting tyre (100), the sidewall insert (113) extends radially between the relevant bead structure (103) and the corresponding side edge of the tread band (109). Each sidewall insert (113) may be made of one or more portions and is arranged in an axially inner or outer position with respect to the carcass ply. For example, as shown in FIG. 2, the sidewall insert (113) is arranged between the carcass ply (101) and the liner (112).

(22) As an alternative, in the case when there is more than one carcass ply, a sidewall insert (113) may be arranged between two of said carcass plies (not shown in FIG. 2).

(23) As an alternative, a sidewall insert (113) may be arranged between the carcass ply and the sidewall (not shown in FIG. 2).

(24) The sidewall insert is advantageously made of the elastomeric composition comprising the predispersion of natural rubber and lignin described above, because in the working conditions with the tyre deflated it must have good resistance to propagation of tearing (obtainable when there are higher rupture properties, and especially elongation at break), and reduced dissipation of heat (obtainable when there is lower hysteresis).

(25) According to an embodiment that is not shown, the tyre may be a tyre for wheels for heavy vehicles, such as lorries, buses, trucks, vans, and in general for vehicles in which the tyre is subjected to a high load.

(26) Manufacture of the tyres 100 as described above may be carried out by assembling the respective semifinished products on a building drum (not shown), by means of at least one assembly device.

(27) At least a part of the components intended to form the carcass structure of the tyre may be constructed and/or assembled on the building drum. More particularly, the building drum is intended to receive firstly the optional liner, then the carcass structure and the antiabrasive strip. Next, devices that are not shown engage, coaxially around each of the terminal edges, one of the annular anchoring structures, position an outer sleeve comprising the belt structure and the tread band in a position coaxially centred around the cylindrical carcass sleeve and form the carcass sleeve in a toroidal configuration by stretching the carcass structure radially, in order to ensure that it is applied against a radially inner surface of the outer sleeve.

(28) Following building of the raw tyre, a treatment of moulding and vulcanizing is carried out in order to provide structural stabilization of the tyre by crosslinking the elastomeric compound as well as impress a desired tread pattern on the tread band and optionally impress distinctive graphical symbols on the sidewalls.

(29) The present invention will be further illustrated below with a number of examples of preparation, which are supplied purely as a guide and without any limitation of this invention.

Example 1

(30) Characterization of the Lignins Used in the Examples

(31) Five different lignins (Soda Grass, Softwood Kraft, Hardwood Kraft, Wheat Straw and Rice Husk) were tested for carrying out the present invention.

(32) Soda Grass lignin is a lignin extracted from annual plants, for example agricultural waste, by a process that uses sodium hydroxide. The lignin used is marketed by Green Value and is designated Protobind 1000®.

(33) Softwood Kraft lignin is a lignin obtained as a by-product of the Kraft process used for producing cellulose starting from conifers; in particular, a lignin designated Oxifenol® marketed by i-Green srl was used.

(34) Hardwood Kraft lignin is also produced by the Kraft process but using lignocellulosic material obtained from broad-leaved plants.

(35) Wheat Straw lignin is obtained from the purification of a by-product of the process for producing bioethanol starting from annual plants of the Arundo donax or wheat straw type, as described in patent WO 2011/007369 in the name of Chemtex.

(36) However, Rice Husk lignin has been extracted in the laboratory from rice husks, a by-product of the food and agriculture industry.

(37) Table 1 below summarizes the main characteristics of the lignin used.

(38) TABLE-US-00001 TABLE 1 Soda Softwood Hardwood Wheat Rice Lignin Grass Kraft Kraft Straw Husk Molecular weights (g/mol) Number-average 1000 4700 3700 4400 5500 molecular weight (Mn) g/mol Molecular weight of 700 1450 2500 2000 2100 the most abundant fraction (Mp) g/mol Polydispersity index 2.5 5.7 2.1 2.7 3.5 (D) Functional groups (mmol/g) Aliphatic alcohols 1.69 2.23 1.24 1.84 1.95 Total phenols 3.46 4.83 2.57 1.77 0.94 Carboxylic acids 1.07 0.59 0.48 0.51 0.52

(39) The molecular weights were characterized by GPC (gel permeation chromatography). The lignins were functionalized chemically (acetylation) to make them soluble in the solvent used in the instrument (THF), then the various fractions were separated by a column with variable porosity, and the molecular weight of the various fractions was quantified by comparing with a standard of known molecular weight. The parameter most used for describing the distribution of the molecular weights of a polymer is the number-average molecular weight M.sub.n, which is the average of the molecular weights of the polymer chains calculated as follows:

(40) $M_n=\frac{\Sigma M_i{N}_i}{\Sigma N_i}$

(41) where M.sub.i represents the molecular weight and N.sub.i the number of chains.

(42) The functional groups were characterized by .sup.31P-NMR. The various hydroxyls of the lignin are functionalized by reaction with TMDP (2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane) and quantified by NMR analysis.

Example 2

(43) Preparation of the Predispersion of Natural Rubber Containing Lignin

(44) Various predispersions of natural rubber were prepared containing 15 phr of various types of lignin (Soda Grass, Softwood Kraft, Hardwood Kraft, Wheat Straw and Rice Husk) and different amounts (7, 15 and 45 phr) of Softwood Kraft lignin.

(45) The procedure comprises a first step of dissolution of the lignin at room temperature in alkaline solution, followed by the step of adding the lignin solution thus obtained to latex of natural rubber, and finally the step of coagulation by adding organic or inorganic acids.

(46) Dissolution of the lignin was effected with a 0.1M solution of sodium hydroxide (NaOH), in an amount of about 10 ml per gram of lignin. Dissolution was carried out at room temperature (about 20° C.), adding the lignin to the alkaline solution, with stirring. When all the lignin had been added, the mixture was stirred until the lignin had dissolved completely.

(47) The latex of natural rubber was prepared separately. The latex used, of Thailand provenance, consisted of a latex concentrated by centrifugation to 60% of solid rubber residue and stabilized with ammonia, produced and marketed by the company Von Bundit Co., Ltd.

(48) The latex was stirred at room temperature for several minutes in a suitable vessel, and then, while still stirring, the lignin solution previously obtained was poured in slowly.

(49) The mixture thus obtained was stirred vigorously at room temperature for a period of time ranging from 1 to 2 hours.

(50) At the end of this period, the coagulation step was started by acidifying the solution by adding a 10% solution of sulphuric acid (H.sub.2SO.sub.4). Acidification causes co-precipitation of the natural rubber and lignin, leaving a relatively clear and transparent supernatant.

(51) The precipitate of natural rubber and lignin was filtered and washed to remove the residual salts and the excess acid, then reduced to a thin foil, about 1 cm thick. The foil was then dried by exposure to the air at room temperature away from the light for 24 hours, and then dried in the stove at 35° C. under vacuum for 12 hours.

(52) Following the procedure described above, the predispersions were prepared with the amounts of natural rubber and the amounts and types of lignin shown in Table 2 below.

(53) TABLE-US-00002 TABLE 2 Amount of Amount of Predispersion natural rubber Type of lignin lignin 1 100 Rice Husk 15 2 100 Wheat Straw 15 3 100 Hardwood Kraft 15 4 100 Soda Grass 15 5 100 Softwood Kraft 15 6 100 Softwood Kraft 7 7 100 Softwood Kraft 45

Example 3

(54) Preparation of the Compounds Using the Predispersions of Natural Rubber Containing Lignin Prepared in Example 2

(55) The predispersions described above were used, as crude pastes, for preparing the compounds in Table 3, which also describes a reference compound (R) comprising only natural rubber, and a comparative compound (C) with pure natural rubber added, after coagulation from latex, with 15 phr of Softwood Kraft lignin directly, both in the mixing step.

(56) The compounds were prepared in a Brabender internal mixer with a cubic capacity of 50 cm.sup.3 and a filling factor of 0.9. The chamber and the rotors of the mixer were set at an initial temperature of 60° C., and the rotary speed of the rotors was set at 70 rpm.

(57) At zero minute (0′), loading of the appropriate predispersion or natural rubber, depending on the compound, was begun. In the case of compound (C), at the third minute (3′) the lignin was added in the form of powder. At the fourth minute (4′), the vulcanizing agents were added, consisting of soluble sulphur, stearic acid, zinc oxide and CBS (N-cyclohexyl-2-benzothiazole sulphenamide), according to the formulations given in Table 3 below. At the eighth minute (8′) the compound was discharged and left to cool.

(58) TABLE-US-00003 TABLE 3 Compounds 1 2 3 4 5 6 7 R C Predispersion 1 2 3 4 5 6 7 — — Natural rubber 100 100 100 100 100 100 100 100 100 Lignin 15 15 15 15 15 7 45 0 15 Sulphur 2 2 2 2 2 2 2 2 2 ZnO 5 5 5 5 5 5 5 5 5 Stearic acid 2 2 2 2 2 2 2 2 2 CBS 2 2 2 2 2 2 2 2 2

(59) Measurements by MDR (Moving Die Rheometer) were performed on the crude compounds to verify their crosslinking kinetics. MDR rheometry analysis was carried out using a Monsanto MDR rheometer. The test was performed at 170° C. for 20 minutes with an oscillation frequency of 1.66 Hz (100 oscillations per minute) and an oscillation amplitude of ±0.5°. The values of minimum torque (ML) and maximum torque (MH) were measured. The results obtained are given in Table 4.

(60) The crude compounds were then vulcanized at 151° C. for 30 min and then Dumbbell test specimens were punched out.

(61) The static mechanical properties according to standard UNI 6065:2001 were measured at different elongations (10%, 50%, 100% and 300%) on the aforementioned Dumbbell test specimens. The results obtained are given in Table 4.

(62) TABLE-US-00004 TABLE 4 Compounds 1 2 3 4 5 6 7 R C MDR MEASUREMENTS ML [dN m] 1.17 1.3 1.16 1.25 1.35 0.91 0.92 1.08 0.86 MH [dN m] 7.87 8.9 9.06 6.72 8.06 9.74 3.33 9.16 6.63 TS2 [min] 2.94 3.36 6.4 2.5 2.66 8.81 4.2 3.7 1.71 T90 [min] 5.5 6.72 10.46 5.74 6.25 13.41 4.99 7.33 3.99 T100 [min] 12.42 13.59 16.98 59.95 18.93 24.62 11.43 29.58 9.6 % RET [%] 4.48 7.63 10.63 0.18 4.17 9.06 22.41 6.56 6.93 STATIC MECHANICAL PROPERTIES Ca0.1 [MPa] 0.29 0.29 0.30 0.28 0.29 0.26 0.55 0.23 0.27 Ca0.5 [MPa] 0.75 0.77 0.75 0.74 0.75 0.69 1.33 0.68 0.72 Ca1 [MPa] 1.16 1.24 1.16 1.17 1.18 1.04 2.06 1.07 1.08 Ca3 [MPa] 4.07 4.95 4.25 4.32 4.5 3.06 5.25 3.25 3.23 CR [MPa] 17.21 15.67 23.25 20.78 23.76 22.95 15.77 15.00 14.39 AR [%] 497.15 486.51 591.84 571.79 577.3 595.5 541.44 586.00 521.09 ENERGY[J/cm.sup.3] 23.26 23.2 39.16 36.81 40.53 33.95 32.2 — 20.98

(63) It can be seen from the results of the tensile tests presented in Table 4 that the best results were obtained with predispersions 3, 4 and 5 comprising respectively 15 phr of Hardwood Kraft, Soda Grass and Softwood Kraft lignin, and that good results are also obtained with predispersion 6 comprising 7 phr of Softwood Kraft lignin. These lignins endow the compounds with excellent rupture properties and superior resilience and reinforcement.

(64) The best properties are obtained with Softwood Kraft lignin, contained in compounds 5 and 6. Hardwood Kraft lignin, contained in compound 3, gave it similar but slightly poorer characteristics, while Soda Grass, contained in compound 4, maintained a good result in elongation, but gave it a lower breaking load.

(65) On the contrary, it was observed from the results of the tensile tests on predispersions 1 and 2, comprising 15 phr of Rice Husk and Wheat Straw lignin respectively, that such lignins had an adverse effect on the rupture properties of the compound.

(66) Comparing the results for compound 5, comprising the predispersion with co-precipitated Softwood Kraft lignin, with the results for the comparative compound C, comprising an equal amount of Softwood Kraft lignin that was not co-precipitated, but added to the coagulated rubber in the mixing step, it was observed that the co-precipitation method gave compounds with definitely superior properties.

(67) Comparing the results for compounds 5, 6 and 7, comprising the predispersions with variable amounts of Softwood Kraft lignin, it was observed that by increasing the loading from 7 to 15 phr there is an improvement of the loads at the various strains and a decrease of little significance in elongation at break. If, however, the loading is increased excessively, to 45 phr, deterioration of the mechanical properties is observed instead, which can be linked to non-optimum vulcanization, evidenced by the low torque values (MH) obtained during the vulcanization step.

Example 4

(68) Preparation of a Compound for a Tyre Sidewall Insert Using a Predispersion of Natural Rubber Containing Softwood Kraft Lignin

(69) A predispersion of natural rubber containing 15 phr of Softwood Kraft lignin prepared as predispersion 5 in example 2 was used for preparing compounds 1 and 2 in Table 5.

(70) The reference compound R comprised only natural rubber coagulated from latex, 17 phr of carbon black and a complete antioxidant system comprising 1 phr of TMQ and 1.5 phr of 6PPD.

(71) The comparative compound C comprised only natural rubber, 11 phr of carbon black (6 phr less than reference R) and a complete antioxidant system comprising 1 phr of TMQ and 1.5 phr of 6PPD.

(72) The compound used for the purposes of the invention 1, comprised 60 phr of natural rubber, 46 phr of predispersion 5 (40 phr of natural rubber and 6 phr of Softwood Kraft lignin), 11 phr of carbon black (6 phr less than reference R), and a complete antioxidant system comprising 1 phr of TMQ and 1.5 phr of 6PPD.

(73) The compound used for the purposes of the invention 2, comprised 60 phr of natural rubber, 46 phr of predispersion 5 (40 phr of natural rubber and 6 phr of Softwood Kraft lignin), 11 phr of carbon black (6 phr less than reference R), and an antioxidant system comprising only 0.5 phr of TMQ and 0.5 phr of 6PPD.

(74) The complete composition of the four compounds is presented in Table 5 below.

(75) The four compounds illustrated in Table 5 were prepared as follows (the amounts of the various components are given in phr), working in a 1.6-litre Banbury mixer.

(76) All the components of the first phase were mixed in the Banbury mixer. As soon as the temperature reached 140°±5° C., the elastomeric composition was discharged. After it had been left to stand for a day, the compound was put back in the Banbury, adding the components of the second phase, and discharging when the temperature reached 120°±5° C. Finally, the ingredients of the third phase were added, discharging at a temperature not above 120° C.

(77) TABLE-US-00005 TABLE 5 COMPOUND INGREDIENTS R C 1 2 FIRST PHASE BR 60 60 60 60 TESPT(50%) 2.4 2.4 2.4 2.4 N550 18 18 18 18 SiO2 20 20 20 20 NR 40 40 — — PREDISPERSION 5 — — 46 46 BIMODAL WAX 1 1 1 1 N550 17 11 11 11 SECOND PHASE ZINC OCTOATE 2.66 2.66 2.66 2.66 ZINC OXIDE 80 5.0 5.0 5.0 5.0 TMQ 1.0 1.0 1.0 0.5 6PPD 1.5 1.5 1.5 0.5 THIRD PHASE TESPT(50%) 2.4 2.4 2.4 2.4 TiBTD 1.0 1.0 1.0 1.0 TBBS 80% 1.88 1.88 1.88 1.88 RHENOCURE IS90G 2.00 2.00 2.00 2.00 BR is a polybutadiene rubber SKD with neodymium catalyst having more than 97% of cis butadiene TESPT(50%) is a silane tetrasulphide of the Si69 type supported on carbon black SiO2 is Zeosil 1115 MP precipitated silica with surface area of 101 m.sup.2/g from Solvay NR is natural rubber coagulated from latex concentrated to 60% of solid rubber PREDISPERSION 5 is the predispersion of natural rubber coprecipitated with 15 phr of Softwood Kraft lignin as described in example 2 BIMODAL WAX is the antiozonant wax N550 is carbon black (Cabot Corporation) ZINC OCTOATE is a vulcanizing agent ZINC OXIDE 80 is a dispersion of natural rubber with 80% of zinc oxide TMQ is the antioxidant 2,2,4-trimethyl-1,2-diidroquinoline (Nord Chemie) 6PPD is the aromatic amine antioxidant N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (Lanxess Deutschland GmbH, Germany) TiBTD is the accelerant tetraisobutylthiuram disulphide TBBS 80% is a dispersion of N-tert-butyl-2-benzothiazole sulphenamide (Vulkacit ® NZ/EGC, Lanxess Deutschland GmbH, Germany) RHENOCURE IS90G is insoluble sulphur (Lanxess Deutschland GmbH, Germany)

(78) Rheometric measurements were performed on the crude compounds at 170° C. for 10 minutes with the RPA 2000 instrument from ALPHA TECHNOLOGIES (Rubber Processing Analyzer). The results obtained are given in Table 6.

(79) The crude compounds were then vulcanized at 170° C. for 10 min, then Dumbbell test specimens were punched out according to UNI 6065:2001.

(80) The static mechanical properties were measured at different elongations (10%, 50%, and 100%) as described for example 3, on samples of the compounds immediately after crosslinking at 170° C. for 10 minutes, and after thermal ageing at 70° C. for 7 days (168 hours) in an air stove. The results obtained are given in Table 6.

(81) The dynamic mechanical properties E′ and Tan delta were measured using an Instron model 1341 dynamic tester in tension-compression conditions according to the following methods. A testpiece of crosslinked material (170° C. for 10 minutes) having a cylindrical shape (length=25 mm; diameter=14 mm), preloaded in compression to a longitudinal strain of 25% relative to the initial length and maintained at the set temperature (23° C. or 70° C.) throughout the test, was subjected to a dynamic sinusoidal stress having an amplitude of ±3.5% with respect to the length under pre-load, with a frequency of 100 Hz. The dynamic mechanical properties are expressed in terms of values of dynamic elastic modulus (E′) and Tan delta (loss factor). The Tan delta value was calculated as the ratio of the viscous dynamic modulus (E″) to the elastic dynamic modulus (E′). The results obtained are given in Table 6.

(82) TABLE-US-00006 TABLE 6 Compound Properties R C 1 2 RPA MEASUREMENTS ML [dN m] 2.33 2.13 2.60 2.64 MH [dN m] 23.15 21.22 22.30 23.02 TS2[min] 0.74 0.79 0.78 0.79 T30[min] 0.89 0.93 0.92 0.96 T90[min] 1.88 2.00 1.99 1.81 STATIC MECHANICAL PROPERTIES ON THE FRESH MATERIAL Ca0.1[MPa] 0.62 0.56 0.62 0.65 Ca0.5[MPa] 1.80 1.56 1.71 1.87 Ca1[MPa] 3.63 2.95 3.35 3.76 CR[MPa] 12.97 13.64 13.36 14.69 AR[%] 252.94 300.03 274.56 268.79 ENERGY[J/cm.sup.3] 14.60 18.04 16.33 17.63 STATIC MECHANICAL PROPERTIES AFTER AGEING Ca0.1[MPa] 0.73 0.66 0.70 0.74 Ca0.5[MPa] 2.12 1.89 1.98 2.14 Ca1[MPa] 4.44 3.85 4.04 4.48 CR[MPa] 12.39 11.39 12.20 12.21 AR[%] 203.74 218.90 218.52 212.73 ENERGY[J/cm.sup.3] 10.24 10.76 11.44 11.27 Δ Ca0.5 [%] +17.7 +21.1 +15.7 +14.4 Δ AR [%] −19.4 −27.0 −20.0 −20.8 DYNAMIC MECHANICAL PROPERTIES E′[MPa] 23° C., 100 Hz 8.444 7.523 8.057 8.194 Tan.Delta[—] 0.111 0.104 0.105 0.104 E′[MPa] 100° C., 100 Hz 7.975 7.124 7.581 7.717 Tan.Delta[—] 0.077 0.070 0.071 0.070

(83) The results obtained in the static tests in Table 6 demonstrated that compounds 1 and 2, prepared using the predispersion of lignin where part of the black is replaced with equal amounts of lignin, gave values of elongation and especially loads at rupture higher than the reference R, predictive of improved tearing resistance.

(84) At the same time, the results obtained in the ageing tests in Table 6 demonstrated that the presence of lignin, introduced via the predispersion, makes it possible to guarantee a good level of resistance to thermal oxidative ageing, evidencing of similar or lower variation of the static mechanical properties after ageing.

(85) Moreover, compounds 1 and 2 showed values of the static moduli substantially in line with the reference, and dynamic properties even better then the reference. In particular, compounds 1 and 2 showed lower hot hysteresis, which indicates a longer tyre life when running flat (run-flat) with the tyre deflated, allowing colder processing of the sidewall insert material.

Example 5

(86) Preparation of a Tyre Sidewall Compound Using a Predispersion of Natural Rubber Containing Softwood Kraft Lignin

(87) The procedure in example 4 was repeated with a second compound with the reference R′, a second comparative compound C′, and a compound 3 prepared using the predispersion of lignin and comprising an antioxidant system comprising only 0.5 phr of 6PPD and free from TMQ.

(88) The complete composition of the three compounds is described in Table 7 below.

(89) The three compounds illustrated in Table 7 were prepared as follows (the amounts of the various components are given in phr), working in a 1.6-litre Banbury mixer.

(90) All the components of the first phase were mixed in the Banbury mixer. As soon as the temperature reached 140°±5° C., the elastomeric composition was discharged. After it had been left to stand for a day, the compound was put back in the Banbury, adding the components of the second phase, and discharging when the temperature reached 120°±5° C. Finally, the ingredients of the third phase were added, discharging at a temperature not above 120° C.

(91) TABLE-US-00007 TABLE 7 COMPOUND INGREDIENTS R′ C′ 3 FIRST PHASE BR 60 60 60 TESPT(50%) 2.4 2.4 2.4 N550 18 18 18 SiO2 20 20 20 NR 40 40 — PREDISPERSION 5 — — 46 BIMODAL WAX 1 1 1 N550 17 11 11 SECOND PHASE ZINC OCTOATE 2.66 2.66 2.66 ZINC OXIDE 80 5.0 5.0 5.0 TMQ 1.0 1.0 — 6PPD 1.5 1.5 0.5 THIRD PHASE TESPT(50%) 2.4 2.4 2.4 TiBTD 1.0 1.0 1.0 TBBS 80% 1.88 1.88 1.88 RHENOCURE IS90G 2.00 2.00 2.00

(92) The crude compounds were submitted to MDR (Moving Die Rheometer) rheometric measurements using a Monsanto instrument at 170° C. for 20 minutes as described in example 3. The Mooney viscosity ML (1+4) at 100° C. was measured according to standard ISO 289-1:2005. The results obtained are given in Table 8.

(93) The crude compounds were then vulcanized at 170° C. for 10 min, and then ring specimens according to UNI 6065:2001 were punched out.

(94) The static mechanical properties were measured at different elongations (50% and 100%) as described for example 3. The results obtained are given in Table 8.

(95) The dynamic mechanical properties E′ and Tan delta were measured using an Instron model 1341 dynamic tester in tension-compression conditions as described in example 4. The results obtained are given in Table 8.

(96) The hardness in degrees IRHD (at 23° C.) was measured according to standard ISO 48:2007, on samples of the compounds immediately after crosslinking at 170° C. for 10 minutes, and after thermal ageing in the air stove at 70° C. for 168 and 336 hours. The results obtained are given in Table 8.

(97) TABLE-US-00008 TABLE 8 Compound R′ C′ 3 Mooney ML (1 + 4) 100° C. 71.5 65.5 76.4 MDR MEASUREMENTS ML[dN m] 2.47 2.16 2.76 MH[dN m] 27.76 25.08 27.88 TS2[min] 1.11 1.13 1.14 T90[min] 3.47 3.57 3.71 T100[min] 19.98 19.99 19.97 % RET[%] 0.04 0.04 0.04 STATIC MECHANICAL PROPERTIES Ca0.5[MPa] 2.04 1.76 1.98 Ca1[MPa] 4.31 3.55 4.05 CR[MPa] 9.00 8.59 9.37 AR[%] 182.87 203.35 192.08 ENERGY[J/cm.sup.3] 7.16 7.53 7.94 IRHD 71.9 69.4 72.9 DYNAMIC MECHANICAL PROPERTIES E′[MPa] 23° C., 100 Hz 8.765 7.762 8.892 Tan.Delta[—] 0.109 0.103 0.100 E′[MPa] 100° C., 100 Hz 8.361 7.492 8.566 Tan.Delta[—] 0.075 0.070 0.069 ACCELERATED AGEING IRHD after 168 hours, 70° C. 76.4 73.9 76.6 IRHD after 336 hours, 70° C. 78.3 75.4 78.6 ΔIRHD 168 hours +6.20% +6.4% +4.80% ΔIRHD 336 hours +8.90% +8.6% +7.20%

(98) The results obtained in the static tests in Table 8 demonstrated that compound 3, prepared using the predispersion of lignin where part of the black is replaced with equal amounts of lignin, gives values of elongation and especially loads at rupture higher than the reference R′, predictive of improved tearing resistance.

(99) At the same time, the results obtained in the ageing tests in Table 8 demonstrated that the presence of lignin, introduced via the predispersion according to the invention, makes it possible to guarantee a good level of resistance to thermal oxidative ageing, with evidence of lower variation of hardness after ageing, even with greatly reduced amounts of antioxidants (TMQ and 6PPD).