DESTRUCTURED STARCH DERIVATIVES AND ELASTOMER COMPOSITIONS CONTAINING THEM

Abstract

This invention relates to new destructured starch derivatives and elastomer compositions containing them. In particular this invention relates to destructured starch silyl ethers in which at least one oxygen atom of the destructured starch is covalently bonded to at least one silicon atom and/or to at least one compound containing silicon.

Claims

1. A silyl ether of destructurized starch in which at least one Oxygen atom of the destructurized starch is covalently linked with at least one Silicon atom and/or at least one Silicon-containing compound.

2. The silyl ether of destructurized starch according to claim 1 in which said Silicon-containing compound is selected from the group consisting of organosilanes, halosilanes, silanols, silazanes.

3. The silyl ether of destructurized starch according to claim 2, in which said Silicon-containing compound is an organosilane.

4. The silyl ether of destructurized starch according to claim 3, in which said organosilane is selected from the group consisting of compounds having the general formula selected from:
(RO).sub.3SiC.sub.nH.sub.2nS.sub.mC.sub.nH.sub.2nSi(OR).sub.3  (I)
(RO).sub.3SiC.sub.nH.sub.2nX  (II)
(RO).sub.3SiC.sub.nH.sub.2nS.sub.mY  (III) in which “R” represents an alkyl group having from 1 to 4 Carbon atoms, the three R being the same or different; “n” represents an integer from 1 to 6, “m” represents an integer from 1 to 6; “X” represents a mercaptane group, an amine group, a vinyl group, a nitroso group, an imide group, a Chlorine atom or an epoxy group; “Y” represents a cyano group, an N,N-dimethyl thiocarbamoyl group, a mercaptobenzothriazole group, or a methacrylate group.

5. The silyl ether of destructurized starch according to claim 1, obtainable by mixing destructurized starch with at least one Silicon-containing compound at temperatures comprised between 110 and 250° C.

6. The silyl ether of destructurized starch according to claim 5, obtainable by means of a process comprising the steps of: a. preparing destructurized starch; b. mixing said destructurized starch with at least one Silicon-containing compound at temperatures comprised between 110 and 250° C.

7. The silyl ether of destructurized starch according to claim 6, in which said step a. of preparing destructurized starch is performed in presence of 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.

8. The silyl ether of destructurized starch according to claim 6, in which during step a., or after step a. and before step b., at least one crosslinking agent is added.

9. The silyl ether of destructurized starch according to claim 8, in which said crosslinking agent is selected from the group consisting of aldehydes, polyaldehydes and anhydrides.

10. The silyl ether of destructurized starch according to claim 9, in which said crosslinking agent is glyoxal.

11. The silyl ether of destructurized starch according to claim 1, comprising 1-20% by weight of at least one Silicon-containing compound not linked to a oxygen atom of starch.

12. A composition comprising at least one elastomer and at least one silyl ether of destructurized starch according to claim 1.

13. The composition according to claim 12, comprising from 1 to 70 phr of said silyl ether of destructurized starch.

14. The composition according to claim 12, in which said elastomer is selected from the group consisting of natural rubbers and synthetic rubbers.

15. The composition according to claim 14, 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.

16. The silyl ether of destructurized starch according to claim 2, obtainable by mixing destructurized starch with at least one Silicon-containing compound at temperatures comprised between 110 and 250° C.

17. The silyl ether of destructurized starch according to claim 3, obtainable by mixing destructurized starch with at least one Silicon-containing compound at temperatures comprised between 110 and 250° C.

18. The silyl ether of destructurized starch according to claim 4, obtainable by mixing destructurized starch with at least one Silicon-containing compound at temperatures comprised between 110 and 250° C.

19. The silyl ether of destructurized starch according to claim 7, in which during step a., or after step a. and before step b., at least one crosslinking agent is added.

20. The silyl ether of destructurized starch according to claim 2, comprising 1-20% by weight of at least one Silicon-containing compound not linked to a oxygen atom of starch.

Description

EXAMPLES

Methods Used for Characterisation

Extraction in Hexane

[0115] Approximately 2 g of sample ground up to a particle size of less than 500 microns were placed in a 50 ml flask with a magnetic stirrer and a quantity of 25 ml of hexane was added. The mixture then underwent gentle stirring at ambient temperature for one hour. The mixture was then filtered keeping the liquid fraction in a previously weighed 250 ml beaker. The solid fraction underwent further two washes in hexane as described previously.

[0116] At the end of the three washes the solid fraction was placed in a previously weighed weighing filter and dried in a stove at 60° C. for one hour.

[0117] The beaker containing the three liquid fractions was exposed to a gentle flow of air to cause the hexane to evaporate and on completion of the operation it was placed in a stove to dry at 60° C. for one hour. The mass of residue obtained is equivalent to the fraction of unreacted silane.

Karl-Fischer Titration

[0118] 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.

[0119] The solvents 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.

[0120] 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.

[0121] 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.

HPLC Analysis

[0122] 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.

[0123] 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.

[0124] 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.

Phase Contrast Microscopy

[0125] Phase contrast optical microscopy was carried out using a Leitz Wetzlar Orthoplan optical microscope with a magnification (Polaroid 545) of x 400 with a Phaco 2 EF 40/0.65 objective lens, polarising filter no. 5.

[0126] 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.

SEM Microscopy

[0127] 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.

UATR Analyses

[0128] The UATR analyses were carried out using a Perkin Elmer Spectrum 2 FT-IR/UATR spectrophotometer equipped with an accessory for high resolution reflection analyses. Approximately 20 mg of the ground sample (if solid) or a drop of liquid were placed on the diamond-coated accessory, subjected to a suitable pressure using the instrument's torque and scanned under MIR (medium infrared) radiation between 4000 and 450 cm.sup.−1 carrying out 16 scans with a resolution of 4 cm.sup.−1 for each spectrum.

.SUP.1.H-NMR

[0129] .sup.1H-NMR analyses were carried out using a Bruker Avance 500 MHz Ultrashield spectrometer at 25° C. using a pulse time (pl) of 7.6 μs, a relaxation time (dl) of 3 s, and an acquisition time (aq) of 1.7 s and 64 scans.

[0130] Approximately 10 mg of sample were dissolved in 0.8 ml of dmso-d6 and the sample was analysed under the conditions reported above.

Mechanical Properties

[0131] 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%.

[0132] The rebound tests were carried out using a Schob type pendulum in accordance with standard ASTM D7121.

Density

[0133] Density was measured at 23° C. in ethanol in accordance with standard ASTM D792.

Examples 1-3—Preparation of Destructured Starch Silyl Ethers from Native Starch

Preparation of Destructured Starch

[0134] 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: [0135] rpm (min.sup.−1)=100; [0136] temperature profile (° C.): 60-80-140-170-160-140-110-90; [0137] throughput (kg/h): 2.5; [0138] degassing: closed; [0139] die temperature (° C.): 91; [0140] die pressure (bar): 13-17.

[0141] 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.

Preparation of Silyl Ethers in Accordance with Examples 1-3

[0142] The destructured starch so obtained was used in three reactive extrusion processes adding different quantities of bis(3-trioxysilylpropyl)tetrasulfide (Si-69, produced by Evonik). The reactive extrusion processes were carried out in a twin screw extruder (diameter=21 mm, L/D=40) under the operating conditions shown in Table 1 below.

TABLE-US-00001 Example 1 Example 2 Example 3 Destructured starch 95 90 85 (% by weight) Si-69 (% by weight) 5 10 15 rpm (min.sup.−1) 100 150 150 Temperature profile 60-120-160 × 60-120-160 × 60-120-160 × (° C.) 4-155-150 4-155-150 4-155-150 Throughput (kg/h) 2.0 2.0 2.0 Degassing closed closed closed die temperature (° C.) 149 151 150 die pressure (bar) 3-4 3-4 4

[0143] The silyl ethers of destructured starch and the destructured starch used for their preparation were subjected to compositional analysis, being characterised by Karl-Fischer titration, HPLC analysis and extraction in hexane (Table 2).

TABLE-US-00002 TABLE 2 Analysis of the composition of the destructured starch and the silyl ethers according to examples 1-3 Destructured starch Example 1 Example 2 Example 3 (% by (% by (% by (% by weight) weight) weight) weight) Starch 75.5 70.6 70.0 65.7 Glycerol 11.3 13.8 10.3 10.0 Water 9.4 7.1 5.1 4.6 Citric acid 2.3 1.9 2.2 2.0 Reacted Si-69 0 3.7 7.9 10.3 Unreacted Si-69 0 1.5 3.1 6.1 Glyoxal 1.5 1.4 1.4 1.3

[0144] The hexane-soluble fractions were also analysed by H1-NMR spectrometry dissolving the samples in dmso-d6. The silyl ethers according to Examples 1-3 revealed the presence of a signal at 1.06 ppm attributed to the three protons of the ethoxy group of the silane CH.sub.3—CH.sub.2—O—Si.

Examples 4-8

[0145] The silyl ethers according to Examples 1-3, a commercial complexed starch-based biofiller as well as a mixture of starch and plasticizer were used to prepare the compositions shown in Table 3.

TABLE-US-00003 TABLE 3 Compositions in Examples 4-8 Exam- Exam- ple 7 ple 8 Exam- Exam- Exam- (compar- (compar- ple 4 ple 5 ple 6 ative) ative) phr phr phr phr phr SBR rubber.sup.1 100 100 100 100 100 Silyl ether 11.05 — — — — (example 1).sup.2 Silyl ether — 11.05 — — — (Example 2).sup.2 Silyl ether — — 11.05 — — (Example 3).sup.2 Biofiller.sup.3 — — — 9.6 Starch/water (75/25) 11.05 Silica.sup.4 54 54 54 54 54 Silane.sup.5 4.32 4.32 4.32 5.8 6.04 Stearic acid 1.5 1.5 1.5 1.5 1.5 Extender oil.sup.6 17 17 17 17 17 Antidegradation 1.5 1.5 1.5 1.5 1.5 agent.sup.7 ZnO 2.6 2.6 2.6 2.6 2.6 Sulfur 1 1 1 1 1 Vulcaniser 1.sup.8 1.3 1.3 1.3 1.3 1.3 Vulcaniser 2.sup.9 1.5 1.5 1.5 1.5 1.5 .sup.1SBR1502 (Versalis Europrene), .sup.2Density of the silyl ethers = 1.45 g/cm.sup.3, .sup.3Mater-Bi 1128RR (starch complex with poly(ethylenevinyl alcohol) produced by Novamont S.p.A. - density 1.26 g/cm.sup.3), .sup.4Zeosil 1165 MP (Rhodia), .sup.5Si-69 (Evonik), .sup.6TDAE (Repsol Extensoil), .sup.7Vulkanox HS/LG (Lanxess), .sup.8Vulkacite DM/MG (Lanxess), .sup.9Vulcacite D- EG/C (Lanxess)

[0146] In the compositions in Examples 4-6 the quantities of silyl ethers and biofiller added were modulated so as to obtain equal volumes of additives, having regard to their respective densities. In addition to this, the quantity of silane added at this stage was modulated to obtain a total quantity of silane equal to that in Example 7, taking into account the unreacted silane present in the destructured starch silyl ethers.

[0147] The compositions in Examples 4-7 were prepared in accordance with the following method. 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 composition of Example 8 (reported in Table 3) was instead prepared in accordance with the following method: 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 mixture of starch and water was added to the SBR rubber in two equal aliquots, mixing the system for 30 seconds between one addition and the next. 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.

[0149] The mixtures obtained in Examples 4-8 were all 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 mixtures were 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.

[0150] The mixtures finally underwent vulcanisation. The mixtures were 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 mixtures together with the vulcanising agents were discharged and vulcanised at 160° C. for 30 minutes by compression molding.

[0151] The vulcanised compositions so obtained were then mechanically characterised (Table 4).

TABLE-US-00004 TABLE 4 Mechanical characterisation of the compositions according to Examples 4-6 and 7 and 8 (comparative) 10% 50% deformation deformation hysteresis hysteresis (mJ) (mJ) σ.sub.b ε.sub.b E.sub.100 E.sub.200 E.sub.300 Rebound cycle cycle cycle cycle Examples (MPa) (%) (MPa) (MPa) (MPa) (%) I V I V 4 15.8 317 3.1 4.0 4.8 52 1.3 0.9 31.4 16.3 5 17.4 331 3.2 4.1 5.0 51.7 1.2 0.8 29.4 16.3 6 15.9 298 3.4 4.3 5.4 50.3 1.5 0.9 34 18.4 7 (comp.) 18.6 314 3.3 4.6 5.7 49.6 1.9 1.2 44.5 22.3 8 (comp.) 11.0 280 2.9 3.5 — 45.2 5.5 2.4 102 37.8

[0152] As will be seen, the compositions according to the invention in Examples 4-6 demonstrate σ.sub.b, ε.sub.b, E.sub.100, E.sub.200, E.sub.300 and Rebound mechanical properties which are substantially equivalent to those of comparative Example 7, and further show improved hysteresis properties, as will be seen from the lower dissipated energy values (in mJ) in both deformation-recovery stress cycles I and V. The composition according to comparative Example 8, instead, shows the worst mechanical and hysteresis properties.