USE OF DESTRUCTURED STARCH DERIVATIVES AS HYSTERESIS REDUCTION ADDITIVES FOR ELASTOMER COMPOSITIONS

Abstract

This invention relates to the use of destructured starch derivatives as hysteresis reduction additive in elastomer compositions and elastomer compositions containing those derivatives.

Claims

1. An elastomeric composition comprising a destructurized and crosslinked starch uniformly dispersed in said elastomeric composition in an effective amount as a hysteresis reduction additive in said elastomeric composition.

2. The elastomeric composition according to claim 1, in which said destructurized and crosslinked starch is added in an amount of from 3 to 70 parts per 100 parts of elastomer (phr) in said elastomeric composition.

3. The elastomeric composition according to claim 1, in which said destructurized and crosslinked starch is obtainable by means of a process in which the starch is destructurized and at the same time mixed with at least one crosslinking agent.

4. The elastomeric composition according to claim 1, in which said destructurized and crosslinked starch is obtainable by means of a process in which the starch is first destructurized and then mixed with at least one crosslinking agent.

5. The elastomeric composition according to claim 1, in which said destructurized and crosslinked starch comprises 1-40% by weight, with respect to the weight of starch, of one or more plasticisers selected from the group consisting of water and polyols having from 2 to 22 carbon atoms.

6. The elastomeric composition claim 1, in which said destructurized and crosslinked starch comprises 0.1-5% by weight, with respect to the weight of starch, of one or more of depolymerizing agents selected from the group consisting of organic acids, inorganic acids, and enzymes.

7. The elastomeric composition according to any one of claims from 1 to 6 claim 1, in which said destructurized and crosslinked starch comprises 0.1-5% by weight with respect to the weight of starch, of one or more crosslinking agents.

8. The elastomeric composition according to claim 7, in which said crosslinking agent is selected from the group consisting of aldehydes, polyaldehydes and anhydrides.

9. The elastomeric composition according to claim 8, in which said crosslinking agent is glyoxal.

10. A composition comprising: i. at least one elastomer; ii. 3-70 phr of a destructurized and crosslinked starch as hysteresis reduction additive.

11. The composition according to claim 10, in which said elastomer is selected from the group consisting of natural rubbers and synthetic rubbers.

12. The composition according to claim 11, in which said synthetic rubbers are selected from the group consisting of dienic homopolymers, block copolymers styrene-butadiene-styrene, random copolymers styrene-isoprene, block copolymers styrene-isoprene-styrene, block copolymers acrylonitrile-butadiene, random copolymers vinylarene-conjugated diene.

13. The elastomeric composition according to claim 2, in which said destructurized and crosslinked starch is obtainable by means of a process in which the starch is destructurized and at the same time mixed with at least one crosslinking agent.

14. The elastomeric composition according to claim 2, in which said destructurized and crosslinked starch is obtainable by means of a process in which the starch is first destructurized and then mixed with at least one crosslinking agent.

15. The elastomeric composition according to claim 2, in which said destructurized and crosslinked starch comprises 1-40% by weight, with respect to the weight of starch, of one or more plasticisers selected from the group consisting of water and polyols having from 2 to 22 carbon atoms.

16. The elastomeric composition according to claim 3, in which said destructurized and crosslinked starch comprises 1-40% by weight, with respect to the weight of starch, of one or more plasticisers selected from the group consisting of water and polyols having from 2 to 22 carbon atoms.

17. The elastomeric composition according to claim 4, in which said destructurized and crosslinked starch comprises 1-40% by weight, with respect to the weight of starch, of one or more plasticisers selected from the group consisting of water and polyols having from 2 to 22 carbon atoms.

18. The elastomeric composition according to claim 2, in which said destructurized and crosslinked starch comprises 0.1-5% by weight, with respect to the weight of starch, of one or more of depolymerizing agents selected from the group consisting of organic acids, inorganic acids, and enzymes.

19. The elastomeric composition according to claim 3, in which said destructurized and crosslinked starch comprises 0.1-5% by weight, with respect to the weight of starch, of one or more of depolymerizing agents selected from the group consisting of organic acids, inorganic acids, and enzymes.

20. The elastomeric composition according to claim 4, in which said destructurized and crosslinked starch comprises 0.1-5% by weight, with respect to the weight of starch, of one or more of depolymerizing agents selected from the group consisting of organic acids, inorganic acids, and enzymes.

Description

EXAMPLES

[0118] Methods Used for Characterisation

[0119] Karl-Fischer Titration

[0120] Karl-Fischer titration (in pyridine) was carried out using a KF Metrohm Titroprocessor 686 titration device controlled by the Dosimat 665 device. The Karl-Fischer reagent was titrated (correction factor) using sodium tartrate dissolved in methanol.

[0121] The solvent in which the samples were dispersed (N,N-dimethylformamide in molecular sieves—H.sub.2O<0.01% m/m) was titrated to obtain the blank value, which had to be subtracted from the sample measurements.

[0122] The water content of the samples was measured by weighing approximately 1 g of sample in a 27 ml bottle to which were added 20 ml of N,N-dimethylformamide, together with a magnetic stirrer. The bottle was hermetically sealed and heated with gentle stirring to 80° C. on a magnetic plate until the sample had completely disaggregated (approximately 1 hour's mixing). The bottle was then left to cool to ambient temperature. 10 ml of the dispersion in N,N-dimethylformamide were then placed in the titrator cell together with 30 ml of pyridine in order to carry out the titration.

[0123] The water content of the sample was expressed as a percentage, having regard to the volume of Karl-Fischer reagent used with the sample (subtracted from that of the blank), the Karl-Fischer reagent correction factor and the mass of sample used for the measurement.

[0124] HPLC Analysis

[0125] The HPLC analysis was carried out using a Thermo Scientific Accela instrument provided with a refractive index detector and fitted with a Phenomenex Rezex ROA H+ column. An aqueous solution of 0.005 N of sulfuric acid was used as the eluent. The analyses were carried out at 65° C. with a flow of 0.6 ml/min.

[0126] Calibration curves for glycerine and citric acid were produced under the conditions described above using glycerine and citric acid solutions at different concentrations to calculate the instrument response factor.

[0127] In order to measure the citric acid and glycerine content a quantity of approximately 500 mg of sample was weighed and placed in a 100 ml flask containing 25 ml of distilled water for 24 hours at ambient temperature in order to extract the citric acid and the glycerine from the sample. A quantity of 20 μl of this solution was then injected into the system in order to carry out the HPLC analysis. The glycerine or citric acid contents were expressed as m/m percentages.

[0128] Phase Contrast Microscopy

[0129] Phase contrast optical microscopy was carried out using a Leitz Wetzlar Orthoplan optical microscope with a magnification (Polaroid 545) of ×400 with a Phaco 2 EF 40/0.65 objective lens, polarising filter no. 5.

[0130] Approximately 20 mg of sample were placed on an optical microscope slide together with a drop of distilled water. Using a spatula the sample was homogenised with the water until a slightly viscous paste was obtained. A spatula tip of this paste was placed between two optical microscopy slides and gently slid so as to obtain a semi-transparent film which was subsequently analysed.

[0131] SEM Microscopy

[0132] Vulcanised rubber specimens were broken up at ambient temperature, metallised with gold and observed using a FE-SEM ZEISS Supra 40 electron microscope at low magnifications (×200-800 with respect to the Polaroid 545) with secondary electrons at an acceleration potential of 10 kV and a working distance of approximately 8 mm.

[0133] Mechanical Properties

[0134] The vulcanised test specimens were characterised using an Instron 4502 dynamometer equipped with long field extensimeters. The tensile properties were determined in accordance with standard ASTM D412 (type C dumbbell). The fatigue tests were carried out using an Instron 4502 dynamometer equipped with a 100 N load cell on type C ASTM D412 test specimens. The tests were carried out by applying a traversing speed of 250 mm/min with elongations of 10% and 50%.

[0135] The rebound tests were carried out using a Schob type pendulum in accordance with standard ASTM D7121.

Example 1—Preparation of Destructured Crosslinked Starch from Native Starch Preparation of Destructured Starch

[0136] A mixture comprising 80.3 parts by weight of native maize starch (C*GEL 03401, 12% of water), 14.4 parts of glycerol, 3.5 parts of an aqueous solution of glyoxal (40% m/m), and 1.8 parts of citric acid was fed to a dual screw extruder (diameter=21 mm, L/D=40) operating under the following conditions: [0137] rpm (min.sup.−1)=100; [0138] temperature profile (° C.): 60-80-140-170-160-140-110-90; [0139] throughput (kg/h): 2.5; [0140] degassing: closed; [0141] Head temperature (° C.): 91; [0142] Head pressure (bar): 13-17.

[0143] The destructured starch obtained in this way was analysed by phase contrast optical microscopy as previously described in the “Phase contrast microscopy” section and demonstrated that structures which could be related to the native granular structure of the starch were completely absent.

[0144] The destructured crosslinked starch also underwent compositional analysis, being characterised by means of Karl-Fischer titration and HPLC analysis (Table 1).

TABLE-US-00001 TABLE 1 Composition analysis of destructured and crosslinked starch destructured starch (% by weight) Starch 75.5 Glycerol 11.3 Water 9.4 Citric acid 2.3 Glyoxal 1.5

Examples 2-6

[0145] The destructured crosslinked starch according to Example 1 and a commercial complexed starch-based biofiller were used to prepare the compositions in Examples 2-6 respectively shown in Table 2.

TABLE-US-00002 TABLE 2 Compositions of Examples 2-6 Example 3 Example 4 Example 2 (comparative) (comparative) Example 5 Example 6 phr phr phr phr phr SBR rubber.sup.1 100 100 100 100 100 Destructured crosslinked 9.6 — 2 3.8 7.5 starch (Example 1) Biofiller.sup.2 — 9.6 — — — Silica.sup.3 54 54 67.1 64.5 59 Silane.sup.4 5.80 5.80 5.70 5.75 5.90 Stearic acid 1.5 1.5 1.5 1.5 1.5 Extender oil.sup.5 17 17 17 17 17 Antidegradation agent.sup.6 1.5 1.5 1.5 1.5 1.5 ZnO 2.6 2.6 2.6 2.6 2.6 Sulfur 1 1 1.0 1.0 1.0 Vulcanising agent 1.sup.7 1.3 1.3 1.3 1.3 1.3 Vulcanising agent 2.sup.8 1.5 1.5 1.5 1.5 1.5 .sup.1SBR1502 (Versalis Europrene), .sup.2Mater-Bi 1128RR (starch complexed with poly(ethylenevinyl alcohol), produced by Novamont S.p.A.), .sup.3Zeosil 1165 MP (Rhodia), .sup.4Si-69 (Evonik), .sup.5TDAE (Repsol Extensoil), .sup.6Vulkanox HS/LG (Lanxess), .sup.7Vulkacite DM/MG (Lanxess), .sup.8Vulcacite D-EG/C (Lanxess)

[0146] The compositions in Examples 2-6 were prepared and vulcanised in accordance with the following method.

[0147] SBR rubber was loaded into a 300 cm.sup.3 Banbury Pomini Farrel mixer and mixed at 80 rpm for 30 seconds at T=133° C. The quantities of SBR rubber and the other components used were selected so as to obtain a final volume filling the mixer chamber to 86%. The silica and the extender oil were added to the SBR rubber in three equal aliquots, mixing the system for 30 seconds between one addition and the next. The silane was added together with the second aliquot of silica and extender oil, while the other components (apart from the vulcanising agents) were added together with the third aliquot of silica and extender oil. The mixture was then further mixed until a chamber temperature of 160° C. was reached. Once this temperature had been reached stirring was reduced to 60 rpm and mixing continued under these conditions for a further two minutes.

[0148] The mixture so obtained was discharged and underwent a further stage of mixing (known as remill) in the 300 cm.sup.3 Banbury Pomini Farrel mixer set to 140° C., 80 rpm (chamber filling volume 86%). The mixture was allowed to mix for the time necessary to reach 160° C. and then again discharged. The purpose of the remill operation is to ensure a uniform distribution of all the components in the volume of the mixture.

[0149] The mixture finally underwent vulcanisation. The mixture was again loaded into the 300 cm.sup.3 Banbury Pomini Farrel mixer (chamber filling volume 86%) and mixed at 70° C., 60 rpm for 30 seconds. The vulcanising agents were then added and after two minutes of further mixing, the mixture together with the vulcanising agents was discharged and vulcanised at 160° C. for 30 minutes.

[0150] The vulcanised composition so obtained was then mechanically characterised (Table 4).

TABLE-US-00003 TABLE 4 Mechanical characterisation of the compositions according to Examples 2 and 3 (comparative) 10% 50% deformation deformation hysteresis hysteresis σ.sub.b ε.sub.b E.sub.100 E.sub.200 Rebound (mJ) (mJ) Examples (MPa) (%) (MPa) (MPa) (%) cycle I cycle V cycle I cycle V 2 16.6 276 4.0 5.0 51.9 1.5 1.1 35.6 18.4 3 (comp.) 18.6 314 3.3 4.6 49.6 1.9 1.2 44.5 22.3 4 (comp.) 18.8 360 2.7 3.5 45.0 2.6 1.8 50.5 27.1 5 18.9 351 2.9 3.9 45.3 2.4 1.6 49.8 25.8 6 15.8 324 2.8 3.7 46.8 2.1 1.4 43.6 23.7

[0151] As will be seen, the composition according to the invention in Example 2 demonstrates σ.sub.b, ε.sub.b, E.sub.100, E.sub.200, and Rebound mechanical properties which are substantially equivalent to those of comparative Example 3, and further shows improved hysteresis properties, as will be seen from the lower dissipated energy values (in mJ) in both deformation-recovery stress cycles I and V. Comparative Example 4, furthermore, shows the hysteresis reducing effect of the additive according to the invention is significantly lower below 3 phr.