High rigidity compound for pneumatic tyres comprising functionalized lignin

Abstract

A rubber compound for making a pneumatic tyre structural component comprising a cross-linkable unsaturated-chain polymer base, a reinforcing filler, a thermosetting resin and a vulcanization system. The thermosetting resin comprises functionalized lignin with —OR groups wherein R is an alkyne group with a number of carbon atoms of between (3) and (18).

Claims

1. A rubber compound for making a pneumatic tyre structural component comprising a cross-linkable unsaturated-chain polymer, a reinforcing filler, a thermosetting resin and a vulcanization system; said compound being characterized in that said thermosetting resin comprises functionalized lignin with —OR groups wherein R is —CH.sub.2CCH, said functionalized lignin is added to the rubber compound during a productive blending step, and said —OR groups derive from the functionalization of 5 to 100% of the hydroxyl phenolic groups of lignin, wherein the pneumatic tyre structural component is a BEAD FILLER.

2. The rubber compound according to claim 1, characterized in that it comprises from 5 to 15 phr of said functionalized lignin.

3. The rubber compound according to claim 1, characterized in that said functionalized lignin derives from Kraft lignin.

4. A pneumatic tyre structural component made with a compound according to claim 1, wherein the pneumatic tyre structural component is a BEAD FILLER.

5. A pneumatic tyre characterized in that it comprises a structural component according to claim 4.

6. A rubber compound for making a pneumatic tyre BEAD FILLER comprising a cross-linkable unsaturated-chain polymer, a reinforcing filler, a thermosetting resin and a vulcanization system; said compound being characterized in that said thermosetting resin comprises functionalized lignin with —OR groups wherein R is —CH.sub.2CCH, the reinforcing filler is carbon black, said —OR groups derive from the functionalization of 5 to 100% of the hydroxyl phenolic groups of lignin, said functionalized lignin derives from Kraft lignin, said rubber compound comprises from 5 to 15 phr of said functionalized lignin, and said functionalized lignin is added to the rubber compound in the preparation of a productive blending step.

Description

EXAMPLES

(1) Four compounds were prepared of which: the first (Compound A) represents a first comparison example and refers to a prior art compound wherein the methylene acceptor compound is added during the first non-productive blending step and the methylene donor compound is added during the productive blending step; the second (Compound B) represents another comparison example, wherein both the methylene acceptor compound and the methylene donor compound are added during the productive blending step; the third (Compound C) represents a still further comparison example, wherein instead of the bi-component resin represented by the methylene acceptor compound and by the methylene donor compound, non-functionalized lignin was used; the fourth (Compound D) represents an example of the invention wherein instead of the bi-component resin, represented by the methylene acceptor compound and by the methylene donor compound, the functionalized lignin according to the invention was used.

(2) The example compounds were prepared according to the procedure reported below.

(3) Preparation of the Compounds

(4) (1.sup.st Non-Productive Blending Step)

(5) Before the start of the mixing, a closed chamber mixer with an internal volume of between 230 and 270 liters was loaded with ingredients listed in Table I, thus reaching a fill factor of between 66-72%.

(6) The mixer was operated at a speed of between 40-60 rpm, and the mixture thus formed was discharged once a temperature of between 140-160° C. had been reached.

(7) (2.sup.nd Non-Productive Blending Step)

(8) The mixture from the previous step was reworked in the mixer operating at a speed of 40-60 rpm and subsequently removed once a temperature of 130-150° C. had been reached.

(9) (Productive Blending Step)

(10) The ingredients listed in Table I were added to the mixture obtained from the previous step, reaching a filling factor of between 63-67%.

(11) The mixer was operated at a speed of between 20-40 rpm, and the mixture thus formed was discharged once a temperature of between 100-110° C. had been reached.

(12) Table I reports the compositions in phr of the five comparison compounds and of the compound of the invention.

(13) TABLE-US-00001 TABLE I A B C D 1.sup.st non-productive blending step NR 75 SBR 25 CB 70 PF Resin 10 — — — ZnO 6 Stearic acid 2 TMQ 1.5 6PPD 0.5 productive blending step PF Resin — 10 — HMMM  3  3 — — Lignin 10 Functionalized lignin — — — 10 Sulfur 8 TBBS 2

(14) NR is a 1,4-cis polyisoprene rubber of natural origin.

(15) SBR is a styrene-butadiene rubber in solution with an average molecular weight comprising, respectively, of between 500-1500×10.sup.3; a styrene content of between 10 and 45%, a vinyl content of between 20 and 70% and an oil content of between 0 and 30%.

(16) CB is carbon black belonging to the class N330

(17) PF resin stands for phenol-formaldehyde resin and constitutes the methylene acceptor compound.

(18) TMQ and 6PPD respectively stand for poly(1,2-dihydro-2,2,4-trimethylquinoline) and N-1,3-dimethylbutyl-N′-phenyl-paraphenylenediamine and constitute two antioxidant agents.

(19) HMMM stands for hexamethoxymethylamine and constitutes the methylene donor compound.

(20) TBBS stands for N-tert-butyl-2-benzothiazyl sulfenamide and constitutes a vulcanization accelerator.

(21) The non-functionalized lignin used is marketed by Sigma Aldrich under the trade name of Alkali Lignin.

(22) The following is an illustrative and non-limiting exemplary embodiment of functionalized lignin according to the invention.

(23) The lignin sample is solubilized in dimethylformamide solution containing a concentration of potassium carbonate that is calculated based upon the content of phenolic hydroxyl and carboxylic acids. The solution is heated to 50° C. and reacted for about 4 hours with the necessary quantity of propargyl Bromide in order to obtain the required functionalization level.

(24) After cooling the solution was precipitated by means of acidification and the solid residue was washed and centrifuged before being recovered.

(25) Each of the compounds reported in Table I was subjected to a series of tests in order to evaluate the viscosity thereof and the dynamic-mechanical properties thereof.

(26) In particular, the measurement of viscosity was performed according to the ASTM D1646 standard, the rheometric properties were measured according to the ASTM D6204 standard, the dynamic-mechanical properties were measured according to the ISO 4664 standard.

(27) Table II reports the results obtained from the test described above.

(28) For more immediate evidence of the benefits relating to the compound of the present invention, the values obtained from the tests were reported in Table II in indexed form against the results obtained from the comparison Compound A.

(29) TABLE-US-00002 TABLE II A B C D Viscosity 100 100 98 105 T50 100 99 100 97 E′1% 100 99 90 115 tanD1% 100 103 110 95

(30) From the values reported in Table II, it is evident that the use of functionalized lignin ensures a better balance between rigidity and hysteresis.

(31) Greater compound rigidity signifies greater BEAD FILLER functionality, while lower hysteresis ensures good resistance to repeated deformation cycles as well as a positive contribution to rolling resistance.

(32) The viscosity and t50 values demonstrate how the use of functionalized lignin does not produce substantial variations in processability.

(33) Finally, the comparison of the results obtained using non-functionalized lignin highlights how the latter is incapable of guaranteeing the rigidity required for the correct function of the Bead Filler.