METHOD FOR PREPARING STARCH BLENDS

Abstract

The present invention relates to a single-stage process for the production of starch blends in a twin-screw extruder or two twin-screw extruders arranged in series, where i) the starch, together with a plasticizer, passes through a wetting section of length 8D to 30D in an extruder or in a wetting section of length 8D to 80D if two extruders are used at temperatures below the gelatinization temperature of the starch, with mixing, where D is defined as the screw diameter of the screw cylinder and the wetting section is defined as starting at that point on the extruder screw at which the starch and the entire or partial quantity of plasticizer encounter one another and ending at that point in the extruder at which the starch is gelatinized and is digested to give thermoplastic starch; ii) in a plastifying section of length 10D to 50D the extruder temperature is adjusted stepwise to above 130° C., where the starch is digested, destructured and thermoplastified, and is dispersed in a starch-immiscible polymer, and a water content below 5%, based on the starch blend, is established before the material leaves the extruder; where the starch-immiscible polymer is added in molten or granular form at any desired point in the extruder, and a mixture of all of the components present is consequently produced.

Claims

1. A single-stage process for the production of starch blends in a twin-screw extruder, where i) the starch, together with a plasticizer, passes through a wetting section of length 8D to 30D in an extruder at temperatures below 85° C., with mixing, where D is defined as the screw diameter of the screw cylinder and the wetting section is defined as starting at that point on the extruder screw at which the starch and the entire or partial quantity of plasticizer encounter one another and ending at that point in the extruder at which the starch is gelatinized and is digested to give thermoplastic starch; ii) in a plastifying section of length 10D to 50D the extruder temperature is adjusted stepwise to above 130° C., where the starch is digested, destructured and thermoplastified, and is dispersed in the starch-immiscible polymer, and a water content below 5%, based on the starch blend, is established before the material leaves the extruder; where the starch-immiscible polymer is added in molten or granular form at any desired point in the extruder, and a mixture of all of the components present is consequently produced.

2. A process for the production of starch blends in two twin-screw extruders arranged in series, where i) the starch, together with a plasticizer, passes through a wetting section of length 8D to 80D at temperatures below 85° C., with mixing, where D is defined as the screw diameter of the screw cylinder and the wetting section is defined as starting at that point on the extruder screw at which the starch and the entire or partial quantity of plasticizer encounter one another and ending at that point in the extruder at which the starch is gelatinized and is digested to give thermoplastic starch; ii) in a plastifying section of length 10D to 50D the extruder temperature is adjusted stepwise to above 130° C., where the starch is digested, destructured and thermoplastified, and is dispersed in the starch-immiscible polymer, and a water content below 5%, based on the starch blend, is established before the material leaves the extruder; where the starch-immiscible polymer is added in molten or granular form at any desired point in the extruder, and a mixture of all of the components present is consequently produced.

3. The process according to claim 1, where the length of the wetting section is at least 12D.

4. The process according to claim 1, where the temperature of the wetting section is kept below 60° C.

5. The process according to claim 1, where the starch-immiscible polymer is added in solid form before the beginning of the wetting section.

6. The process according to claim 1, where the wetting section also comprises, alongside purely conveying elements, additional intensified mixing screw elements, and the starch-immiscible polymer is added only downstream of the additional mixing screw elements of the wetting section.

7. The process according to claim 6, where the polymer is added in solid form.

8. The process according to claim 6, where the polymer is added before the dispersion phase.

9. The process according to claim 1, where the minimal length of the extruder is 44D.

10. The process according to claim 1, where the plasticizer is selected from water, glycerol, sorbitol and oligomerized glycerol and mixtures of these compounds.

11. The process according to claim 10, where the plasticizer comprises an aqueous sorbitol solution with 5 to 80% water content.

12. The process according to claim 11, where the aqueous sorbitol solution has been produced by hydrogenation of an incompletely depolymerized starch solution which still comprises significant proportions of at least 5% of compounds having higher molecular weight than sorbitol, based on the anhydrous mixture.

13. The process according to claim 1, where the polymer comprises an aliphatic or aliphatic-aromatic polyester which comprises, as diol component, 1,4-butanediol and is biodegradable in accordance with EN13432.

14. A starch blend with 39 to 47% by weight of content of thermoplastified starch, based on the entirety of anhydrous starch and of anhydrous plasticizer, and with a lightness value L* in accordance with EN ISO 11664-4/CIE 15:2004 that is greater than 75, obtainable by a process according to claim 1.

15. The starch blend according to claim 14 and with a lightness value L* in accordance with EN ISO 11664-4/CIE 15:2004 that is greater than 80, and with THF content below 5 ppm.

16. A starch blend consisting to an extent above 50%, of renewable feedstocks, comprising: i) 53 to 61% by weight of a polybutylene adipate-co-terephthalate (PBAT) and/or polybutylene sebacate-co-terephthalate (PBSeT), based on 1,4-butanediol from renewable sources; and ii) 39 to 47% by weight of a thermoplastified starch.

17. A starch blend, comprising: i) 45.4 to 62.95% by weight of a polybutylene adipate-co-terephthalate (PBAT) and/or polybutylene sebacate-co-terephthalate (PBSeT), based on 1,4-butanediol from renewable sources; and ii) 35 to 47% by weight of a thermoplastified starch; iii) 2 to 7% by weight of polylactic acid; and iv) 0.05 to 0.6% by weight of a copolymer which comprises epoxy groups and is based on styrene, acrylate and/or methacrylate.

18. The starch blend according to claim 15, where starch used comprises corn starch, wheat starch or pea starch.

19. The starch blend according to claim 18, where starch used comprises corn starch.

Description

WORKING EXAMPLES

Starting Materials:

[0072] A1) Ecoflex® F Blend C1200, aliphatic-aromatic polyester from BASF with MVR of 3 to 5 cm.sup.3/10 min at 190° C./2.16 kg. [0073] B1) Native corn starch, water content about 12%. [0074] C1) Neosorb 70/70—sorbitol solution with very low susceptibility to crystallization from Roquette, solids content 70%, sorbitol content at least 50%.

Description of Extruders Used:

[0075] E1) ZSK 40 MC corotating twin-screw extruder from Coperion, diameter 40 mm, 14 electrically heatable and water-coolable barrel zones with length respectively 4D, L/D=56 with a wetting section of length 20D, into which three kneading blocks were incorporated. Motor power rating 130 kW, specific torque 11.5 Nm/cm.sup.3.

Description of Blown Film Plants:

[0076] Blown film plant consisting of a single-screw extruder with diameter 30 mm and length 25D, spiral mandrel distributor with 80 mm diameter and die gap 0.8 mm. Blow-up ratio is typically 3.5, resulting in a laid-flat film-bubble width of about 440 mm.

Analysis:

[0077] Determination of water content: The residual water content of the granulates was determined by the Karl Fischer method (Mettler-Toledo InMotion KF).

[0078] Melt volume rate: Melt volume rate was determined in accordance with EN ISO 1133 at the stated temperatures and with the stated weights, and is stated in cm3/10 min.

[0079] Average starch particle diameter: A sample was obtained at −80° C. from the film produced in example 2 by microtome section parallel to the extrusion direction. This sample was studied by atomic force microscopy on portions measuring respectively 15×15 micrometers. The relatively hard TPS phase can be distinguished very easily from the relatively soft polymer phase, and permits precise determination of blend morphology and particle sizes of the starch particles dispersed in the polymer. Evaluation of particle sizes gave an average particle size of 466 nanometers and a maximal particle diameter of only 1488 nanometers; this is evidence of the very fine-particle dispersion of the starch particles in the polymer phase.

[0080] THF determination: The THF determination was carried out by Headspace GC-MS based on DIN 38407-F 43 2014-10 and LA-GC-013.071 (Headspace GC-MS determination of volatile organic substances in low-fat foods). For this, a suitable quantity of the specimen is dissolved in dimethylacetamide and THF-d8 is added as internal standard. The specimen sealed in the glass Headspace GC bottle is heated at 85° C. for 30 min in the Headspace oven in an Agilent HS GC/MS, and then subjected to measurement. Helium is used as carrier gas. The value is externally calibrated on the basis of recovery of the internal standard (THF-d8) and matrix effect control (Matrix Spike).

[0081] Determination of lightness value L* and of b* value: Both values were determined in accordance with EN ISO 11664-4 (CIE 15:2004). The average value was calculated from 4 measurements on granulate grains (size between 3 and 8 mm, in layers of thickness 2 cm in order to ensure that they formed an opaque layer. Between the four measurements, the container was rotated by respectively 90°. A Datacolor 650 was used for the measurement. The measurement was made with spherical geometry, d/8°, with specular component included (SCI), and standard illuminant D65 in combination with the CIE 1963 10° standard observer.

Inventive Examples

Examples 1 to 7 (Extruder E1, Embodiment B)

[0082] Gravimetric metering systems were used for addition of all starting materials. The native starches B were added in powder form into zone 1 of the extruder. A gravimetrically controlled gear pump was used to add the plasticizer(s) C, for example in the middle of zone 2. The starting material A was added by way of a side feeder (ZSB) in granulate form in zone 6 of the extruder. Between the plasticizer-addition point in zone 2 and the polymer-addition point in zone 6 there were not only conveying elements installed but also 1-5 mixing elements (neutral kneading blocks and/or toothed reverse-conveying mixing elements). Excess water was removed in zone 13 via a 40 mm lateral devolatilization unit, and the product was extruded by way of a die plate in the form of strands, which were cooled in a water bath and granulated.

[0083] The polymer granules were then dried at 70° C. to the residual moisture levels stated in the table.

Example 8 (Extruder E1, Embodiment A)

[0084] Gravimetric metering systems were used for addition of all starting materials. The native starches B and the starting material A were added in zone 1 of the extruder by way of 2 separate gravimetric metering systems. The plasticizer(s) C was/were added in liquid form approximately in the middle of zone 2 by using a gravimetrically controlled gear pump. Zones 1-6 used exclusively conveying screw elements. Excess water was removed in zone 13 via a 40 mm lateral devolatilization system, and the product was extruded by way of a die plate in the form of strands, which were cooled and granulated in a water bath.

[0085] The polymer granulates were then dried at 70° C. to the residual moisture levels stated in the table.

TABLE-US-00001 Example 1 Example 2 Example 3 Example 4 Example 5 Extruder E1 E1 E1 E1 E1 Rotation rate 350 350 350 350 350 rpm Temperature  .sup. Set/actual  .sup. Set/actual  .sup. Set/actual  .sup. Set/actual  .sup. Set/actual profile/° C. Zone 1 WC*/31 .sup.  Water WC*/34 .sup.  WC*/31 .sup.  WC*/32 .sup.  cooling WC*/33 .sup.  Zone 2 30/38 30/39 30/38 30/36 30/37 Zone 3 30/42 30/46 30/46 30/43 30/44 Zone 4 30/46 30/48 30/49 30/43 30/44 Zone 5 30/56 30/57 30/58 30/49 30/49 Zone 6 30/57 30/97 30/98 30/50 30/51 Zone 7 60/57 120/119 120/121 60/62 60/60 Zone 8 140/137 140/141 140/144 140/138 140/143 Zone 9 160/158 160/160 160/160 160/160 160/160 Zone 10 160/160 160/160 160/160 160/160 160/160 Zone 11 160/178 160/179 160/178 160/186 160/180 Zone 12 160/160 160/160 160/160 160/164 160/163 Zone 13 160/159 160/160 160/160 160/160 160/162 Zone 14 160/173 160/175 160/171 160/177 160/168 Zone 15 160/164 160/164 160/161 160/167 160/161 (head) Wetting section ** 20D 20D 20D 20D 20D *WC = water cooling, not controllable ** defined as distance from addition of plasticizer (all or part) to beginning of starch melting zone/plastifying zone in multiples of the extruder diameter D.

TABLE-US-00002 Example 1 Example 2 Example 3 Example 4 Example 5 Quantity of A1 65.0/Z6 65.0 (Z6) 60.0 (Z6) 65/Z6 60.0/Z6 added & zone (kg/h) Quantity of B1 29.5 29.5 33.7 29.5 33.7 added (kg/h) Quantity of C1 13.0 13.0 14.0 11.5 14.0 added (kg/h) Total report/kg/h 107.5 107.5 107.7 105.5 107.7 Melt temperature 209 213 205 210 201 (at die exit in ° C.) TPS content in final 35.0 35.0 39.7 34.4 39.7 product/% Residual moisture 850 720 860 1910 2490 level after drying (ppm) MVR after drying 4.5 4.5 3.6 4.8 4.1 (190° C., 5 kg) Film extruder Rotation rate (rpm) 80 80 80 80 80 Temperature profile (° C.) Intake zone water- water- water- water- water- cooled cooled cooled cooled cooled Zone 1 120 120 120 120 120 Zone 2 170 170 170 170 170 Zone 3 170 170 170 170 170 Flange 170 170 170 170 170 Elbow 170 170 170 170 170 Spiral mandrel 170 170 170 170 170 distributor Die 170 170 170 170 170 Blow-up ratio 1:3.5 1:3.5 1:3.5 1:3.5 1:3.5 Film thickness 14.9 14.9 15.4 14.9 14.6 and (μm, from weight 9.0* per unit area) Film thickness 16 17 19 17 18/11 (μm, via film gauge) Visual assessment 1 1 1 1 1 of film ** L* (lightness — — — — 83.04*** value) b* (blue-yellow — — — — 18.2*** value) THF content for — — — — 2.3 ppm drying *The maximal possible take-off velocity of the film plant B2 of 30/min limits the minimal achievable film thickness to 9 micrometers - the quality of the starch blend would also allow production of even thinner films. ** 1: few, and only small, undispersed particles, no holes 2: few undispersed particles, some of which are somewhat larger, no holes 3: more undispersed particles, also occasional medium- to large-sized undispersed particles, occasional holes 4: many medium- and some larger-sized undispersed particles, regular occurrence of holes, film only just runnable 5: many medium- and also some large-sized undispersed particles, frequent holes, stable running of film not achievable over a prolonged period 6: many medium-sized and large undispersed particles, holes constantly occurring, film continually collapses ***a blend made of 60 kg/h of A1, 33.7 kg/h of B1 and 14.0 kg/h of C1 was produced in the extruder E1 by a method based on the extruder configuration from example 1 in EP 2467418A1. At a rotation rate of 350 rpm, the melt temperature at the die exit was 248° C. The resultant blown films had a considerably higher number of starch agglomerates than in example 5, and could not be drawn to thicknesses below about 25 micrometers, because of constant occurrence of holes. The product moreover exhibited brownish discoloration. The lightness value L* of the granulate was as low as 72.96, and the b* value was 24.29, i.e. the granulate was significantly darker than the granulate of the invention from example 5, and had a higher yellow value.

TABLE-US-00003 Example 1 Example 2 Example 3 Example 4 Example 5 TPS content in 35 35 40 34  40 blend/% Film thickness (μm, 14.9 14.9 15.4 14.9 14.6/9.0  from weight per unit area) Film thickness (μm, 16 17 19 17 18/11 via film cage) Tensile test in machine direction Modulus of elasticity/ 144 131 162 175 146/142 MPa Tensile stress at — — — — —/— yield/MPa Tensile strain at — — — — —/— yield/% Tensile strength/ 27.8 25.5 23.3 30.9 21.5/23.4 MPa Tensile strain at 338 419 318 409 317/168 max. tensile strength/% Tear strength/MPa 22.9 23.8 18.8 29.7 18.7/14.7 Tensile strain at 347 424 326 414 328/181 break/% Tensile test in transverse direction Modulus of elasticity/ 132 160 161 157 163/120 MPa Tensile stress at — 9.2 — 8.8 —/— yield/MPa Tensile strain at — 17.0 — 22.1 —/— yield/% Tensile strength/ 21.2 22.0 17.7 22.8 16.6/15.7 MPa Tensile strain at 498 535 434 492 421/392 max. tensile strength/% Tear strength/MPa 20.2 20.5 17.2 22.0 16.3/14.4 Tensile strain at 502 539 438 494 425/399 break/[% Dart drop W.sub.F/g 198 210 156 141 135 Tear propagation 1415 1359 1906 2054 1605/525  resistance in machine direction/mN Tear propagation 4105 3687 5024 4506 4318/2278 resistance in transverse direction/mN

TABLE-US-00004 Example 6 Example 7 Example 8 Extruder E1 E1 E1 Rotation rate, rpm 300 350 400 Temperature profile/° C.  .sup. Set/actual  .sup. Set/actual  .sup. Set/actual Zone 1 water cooling water cooling WC/29 .sup.  WC*/29 .sup.  WC*/31 .sup.  Zone 2 30/32 30/33 30/29 Zone 3 30/29 30/31 30/29 Zone 4 30/28 30/31 30/29 Zone 5 30/33 30/37 30/31 Zone 6 30/38 30/41 50/51 Zone 7 30/42 30/46 140/142 Zone 8 140/117 140/132 160/163 Zone 9 160/160 160/160 160/160 Zone 10 160/160 160/161 160/160 Zone 11 160/160 160/169 160/185 Zone 12 160/170 160/165 160/150 Zone 13 160/162 160/158 160/166 Zone 14 160/150 160/157 160/193 Zone 15 160 (head)/161      160 (head)/161      160/178 Wetting section ** 22D 22D 18D *WC = water cooling, not controllable ** defined as distance from addition of plasticizer (all or part) to beginning of starch melting zone/plastifying zone in multiples of the extruder diameter D.

TABLE-US-00005 Example 6 Example 7 Example 8 Quantity of A1 65/Z6 78/Z6 105/Z1 added & zone (kg/h) Quantity of B1 added 29.5 35.4 37.8 (kg/h) Quantity of C1 13 15.6 16.8 added (kg/h) Total throughput/ 107.5 129 159.6 kg/h Melt temperature (at 198 200 220 die exit in ° C.) TPS content in final 35.0 35.0 30.0 product/% Residual moisture 2400 2170 760 level after drying (ppm) MVR after drying 3.2 5.4 4.0 (190° C., 5 kg) Film extrusion Rotation rate (rpm) 80 80 80 Temperature profile (° C.) Intake zone water cooling water cooling water cooling Zone 1 120 120 120 Zone 2 170 170 170 Zone 3 170 170 170 Flange 170 170 170 Elbow 170 170 170 Spiral mandrel distributor 170 170 170 Die 170 170 170 Blow-up ratio 1:3.5 1:3.5 1:3.5 Film thickness (μm, 15.3 15.8 15.3 from weight per unit area) Film thickness (μm, 21.5 18.0 17.8 via film gauge) Visual assessment of 2 1 1 film* ** 1: few, and only small, undispersed particles, no holes 2: few undispersed particles, some of which are somewhat larger, no holes 3: more undispersed particles, also occasional medium- to large-sized undispersed particles, occasional holes 4: many medium- and some larger-sized undispersed particles, regular occurrence of holes, film only just runnable 5: many medium- and also some large-sized undispersed particles, frequent holes, stable running of film not achievable over a prolonged period 6: many medium-sized and large undispersed particles, holes constantly occurring, film continually collapses

TABLE-US-00006 Example 6 Example 7 Example 8 TPS content in blend/% 35.0 35.0 30.0 Film thickness (μm, 15.3 15.8 15.3 from weight per unit area) Film thickness (μm, 21.5 18.0 17.8 via film gauge) Tensile test in not determined machine direction Modulus of elasticity/MPa 153 142 Tensile stress at yield/MPa — — Tensile strain at yield/% — — Tensile strength/MPa 22.6 29.2 Tensile strain at max. 266 381 tensile strength/% Tear strength/MPa 21.9 26.5 Tensile strain at 269 385 break/% Tensile test in not determined transverse direction Modulus of elasticity/MPa 165 127 Tensile stress at yield/MPa — — Tensile strain at yield/% — — Tensile strength/MPa 16.5 19.6 Tensile strain at max. 365 465 tensile strength/% Tear strength/MPa 15.9 19.3 Tensile strain at 368 468 break/% Dart drop W.sub.F/g 123 381 not determined Tear propagation 1235 1304 not determined resistance in machine direction/mN Tear propagation 3009 4051 not determined resistance in transverse direction/mN

Example 9

[0086] With parameters the same as those in example 5, a blend was compounded from 54.8% of partially biobased Bio-PBAT (the same as A1, but with 100% biobased bio-BDO produced by fermentation instead of fossil BDO), 5% of polylactic acid 4043D from Natureworks, 0.2% of Joncryl ADR 4468, 33.7% of 61 and 14.0% of C1. The polylactic acid and the Joncryl were added together with the bio-PBAT. MVR after drying was 2.8 (190° C./5 kg), the lightness value L* was 83.64 and the b* value was 17.8. The compounded material could be processed without difficulty with parameters the same as those of example 5 to give a thin film of thickness 10 micrometers which was practically free from undispersed particles while having good mechanical properties sufficient for a fruit and vegetable bag (in particular in respect of tear-propagation behavior perpendicular to machine direction), with biobased .sup.17C content of about 60%, higher than in example 5.