Method for preparing a starch mixture

Abstract

The present invention relates to a method for producing a starch mixture in a single step in a twin-screw extruder or in two twin-screw extruders arranged in series, i) passing starch together with a plasticizer through a wetting section of an extruder having a length of 8D to 30D, or a wetting section of 8D to 80D if two extruders are used, while mixing at a temperature below the gelatinization temperature of the starch, where D is defined as the screw diameter of the screw cylinder, and the wetting section is defined as beginning at a position on the screw of the extruder where the starch and a partial amount of plasticizer meet each other, and ending at a position in the extruder where the starch is gelatinized and digested to form a thermoplastic starch; ii) gradually adjusting the temperature of the extruder to above 130°C in a plasticization section of length 10D to 50D, whereby the starch is digested, broken down, thermoplasticized and dispersed in the starch-immiscible polymer, and a moisture content of less than 5% based on the starch mixture is established before the material exits the extruder; The present invention relates to a method of preparation in which the starch-immiscible polymer is added in a molten or granular state at any point in the extruder, resulting in the production of a mixture of all the components present.

Description

Technical Field

[0001] The present invention relates to a method for producing a starch mixture in a one-step process using a twin-screw extruder or two twin-screw extruders arranged in series, i) a step of passing starch together with a plasticizer through a wet section having a length of 8D to 30D of the extruder or a wet section having a length of 8D to 80D when using two extruders at a temperature lower than the gelatinization temperature of the starch while mixing, where D is defined as the screw diameter of the screw cylinder, and the wet section starts at a position on the screw of the extruder where all or a portion of the total amount of starch and plasticizer encounter each other and ends at a position on the extruder where the starch is gelatinized, digested, and becomes thermoplastic starch; ii) a step of gradually adjusting the temperature of the extruder to above 130°C in a plasticizing section having a length of 10D to 50D, where the starch is digested, disrupted, thermoplastically plasticized, and dispersed in a starch-immiscible polymer, and a water content of less than 5% based on the starch mixture is established before the material exits the extruder; having, A method of adding a starch-immiscible polymer in a molten state or in granular form at any position of the extruder to produce a mixture of all the components present as a result.

Background Art

[0002] Starch mixtures, especially biodegradable starch mixtures, have been known as prior art for decades, and various production methods thereof are described in the literature. Generally, a distinction can be made between a one-step method and a two-step method.

[0003] A one-step method that provides a higher processing capacity (kg / h) and can provide a quality equal to or better than that supplied by the two-step method is highly preferable in terms of processing cost and energy consumption. In the two-step method, starch is digested in a separate process to obtain thermoplastic starch (TPS).

[0004] In the one-step process, the plasticization of starch and the subsequent mixing with additional polymer occur in a single pass in the same machine or in two machines arranged in series, with the operation mainly carried out in a twin-screw extruder. Plasticizers are used for the plasticization of starch and are, for example, glycerol, oligoglycerol, pentaerythritol, and sorbitol, preferably a mixture with water.

[0005] The starting materials can be added in various ways. In direct addition, all starting materials, such as starch, polymer, or optionally further additives and solid plasticizers, form an initial charge in the first zone, and / or liquid plasticizers, such as polyols and / or water, are then added in a downstream zone (e.g., US 2011 / 0177275A1).

[0006] EP 906367A1 and EP 2467418A1 disclose first plasticizing starch with a plasticizer at a temperature above 140 °C. The resulting thermoplastic starch (TPS) is devolatilized, and thus moisture is substantially removed. Only then is additional polymer added in a molten state or as granular solid.

[0007] A common feature of all methods described in the prior art is that the gelatinization / plasticization of starch occurs at a temperature above the gelatinization temperature immediately after the addition of the plasticizer.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] One of the drawbacks of the above one-step method is its low throughput. For example, EP 906367A1 could only achieve 50 - 60 kg / h with a 45 mm extruder, and EP 2467418A1 could only achieve 10 kg / h with a 26 mm extruder. Despite the low throughput, TPS usually only shows coarse particle dispersion in the polymer matrix. EP 2467418A1 could somewhat compensate for this drawback by adding a specific expensive compatibilizer based on maleic anhydride. Finally, the polymer strands of the above-mentioned starch mixture film produced therefrom show high roughness and undispersed particles, which are due to aggregated and poorly dispersed starch particles. Furthermore, the low filling level of conventional extruders leads to unbalanced and very large amounts of energy introduction. Because a relatively high shear load is introduced into a small amount of melt as a result, and therefore, as a result, it becomes relatively hot, which brings about an undesirable discoloration effect from light brown to dark brown in the products manufactured from these starch mixtures.

[0010] Therefore, an object of the present invention is to provide a one-step method with high throughput for producing a mixture having TPS with fine particle dispersion in a polymer matrix and having high whiteness.

Means for Solving the Problems

[0011] Surprisingly, the adopted object is achieved via the method described at the beginning, where the starch is wetted by a plasticizer in a relatively long wet section of the extruder at an internal temperature below the gelatinization temperature of the starch before the starch undergoes digestion.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the method of the present invention will be described in more detail.

[0013] Gelatinization, i.e., digestion of starch granules, occurs at a temperature that depends mainly on the nature of the starch used, in particular its water content, and also on the amount and structure of the plasticizer and its water content (see, for example, Tan et al., Carbohydrate Polymers 2004, 58, 191-204; Taghizadeh & Favis, Carbohydrate Polymers 2013, 92, 1799-1808). Within the range of plasticizer concentrations relevant to the starch mixture, starch gelatinization generally starts above 70 °C and up to 100 °C. Therefore, in step i) of the method of the present invention, it is preferred to set the temperature of the resulting extruder to less than 100 °C, preferably less than 85 °C, particularly preferably less than 60 °C.

[0014] To achieve proper and uniform wetting of the starch with the plasticizer at high throughput, a defined wetting section in the extruder (step i) is required. The wetting section is measured from the position where the starch and the plasticizer or a partial amount of the plasticizer first meet to the position where the temperature of the extruder rises above the temperature at which the starch starts to gelatinize (gelatinization temperature). The length of the wetting section in the extruder is generally 8D (i.e., 8 × the diameter of the screw cylinder), preferably at least 12D. If operating with two extruders arranged in series, generally the first extruder is used for wetting the starch, and its length is usually 8D to 80D, preferably 12D to 60D. An additional residence time of the starch and the plasticizer results in a product with a very low content of undigested agglomerated starch particles. Considering economy, a wetting section longer than 30D for one extruder and longer than 60D when using two extruders can be said to be of relatively low interest.

[0015] In Embodiment A of the method of the present invention, only the conveying screw elements are installed in the wetting section of the extruder. In this mode of operation, it is possible to add the starch-incompatible polymer at any desired position in the wetting section, which may also be in zone 1 at the inlet end of the extruder. The polymer is preferably added in solid form. Embodiment A of that method, in which the polymer in solid form is added early in zone 1 of the extruder, is shown in Example 8 of the present invention.

[0016] In preferred embodiment B, at least one, preferably two or more, screw elements for enhanced mixing are installed in the wet section of the extruder, alongside the conveying screw elements, to further promote the uniform wetting of the starch by the plasticizer and to reduce again the number of agglomerated starch particles in the final product (step i). The expression "screw elements for enhanced mixing" means, for example, kneading blocks, toothed mixing elements, other shearing elements, etc. In embodiment B, it has been proven advantageous to add the starch-incompatible polymer, preferably in solid form, only downstream of these screw elements for enhanced mixing, but upstream of the end of the wet section of the extruder. This preferred mode of operation of embodiment B is shown in Examples 1 to 7 of the present invention.

[0017] The efficient wetting of the starch by the plasticizer in embodiment B has been proven to be successful, in each case, in a mode of operation having a high throughput rate of more than 100 kg / h, in particular more than 120 kg / h, and particularly preferably more than 150 kg / h, based on a twin-screw extruder with a screw diameter of 40 mm and a dry final product (starch mixture). The throughput rate achieved with a twin-screw extruder with a screw diameter of 65 mm is more than 400 kg / h, in particular more than 500 kg / h, and particularly preferably more than 600 kg / h, based on a dry final product.

[0018] In particular, embodiment B is suitable for the production of a starch mixture having a very fine dispersion of TPS in the polymer matrix or indeed for the production of a co-continuous structure having a very fine lamellar structure. Surprisingly, good dispersion was achieved even with starch mixtures having a high TPS content of more than 29%, more than 39%, and in particular more than 44%.

[0019] In both embodiments, it has been found to be advantageous to introduce the starch-incompatible polymer in solid form (e.g., as granules) before the thermal plasticization of the starch, specifically, at a temperature lower than the gelatinization point of the starch / plasticizer mixture, so that the melting of the polymer and the thermal plasticization of the starch occur simultaneously in the subsequent melting zone.

[0020] As a rule, it is possible to add the starch-immiscible polymer at any position of the extruder (step ii). However, downstream of the polymer addition, there must be an appropriate screw length to allow for the necessary melting of the polymer (when the polymer is added in solid form) and to ensure mixing with the starch (which may or may not already be thermoplasticized) and dispersion of the thermoplasticized starch into the polymer matrix.

[0021] To effect the necessary melting of the starch-immiscible polymer in step ii) and to digest, decompose, thermoplasticize the starch and disperse it in the molten polymer, the internal temperature of the extruder is gradually increased along the plasticizing section to a temperature above 130 °C. The barrel temperature set in the plasticizing section optionally rises up to the discharge die of the extruder and is from 90 °C to 260 °C, preferably up to 230 °C, particularly preferably up to 220 °C, and the temperature of the polymer melt discharged from the die is preferably kept below 250 °C, preferably below 240 °C, particularly preferably below 230 °C.

[0022] The relatively low operating mode in step i) has the advantage that in a further process of the extrusion process, the mixing and homogenization of the melt takes place in the presence of a significant amount of water, generally 1 to 20% by weight, preferably 3 to 15% by weight, particularly preferably 5 to 10% by weight, based on the total amount of the anhydrous final product. Therefore, the starch is very substantially protected from disadvantageous thermal degradation with discoloration. The high water content present at least initially in the plasticization zone promotes a uniform fine particle dispersion of the starch in the polymer matrix. Furthermore, the water present in the mixture, or preferably in the melt, is due to the starch, or the water introduced by the plasticizer or plasticizer mixture used, or separately introduced water, but in step ii) it is reduced, for example, by lateral devolatilization, so that the water content at the time of discharge from the extruder (at the discharge die) is less than 5% based on the starch mixture. When granulating the starch mixture using a water bath pelletizer, it is advantageous to set the water content at the discharge die to less than 3% based on the starch mixture. When using a strand pelletizer, the water content is generally set to less than 2%, preferably less than 1% based on the starch mixture.

[0023] The materials used as components in the process of the present invention are described in more detail below.

[0024] The starch used generally consists of natural starch. Natural starch is in the form of highly crystalline grains (granules) whose melting point is above their decomposition temperature. Generally, natural starch contains a non-negligible proportion of relatively large grains with a diameter of more than 10 μm, and therefore, in an undigested and non-thermoplastic form, it is not suitable for the production of high-quality thin films. Generally, the expression "natural starch" means corn starch, potato starch, wheat starch, pea starch, rice starch, or mixtures thereof. In particular, the expression "natural starch" means wheat starch, and particularly preferably, it means corn starch or potato starch.

[0025] The literature describes numerous low-molecular compounds and relatively high-molecular-weight compounds as plasticizers for starch. Materials that have been proven to be successful in this method are, in particular, water and polyols, and mixtures thereof. Among the polyols, glycerol, sorbitol, sorbitol esters, oligomerized glycerol, and pentaerythritol are preferred, and glycerol, sorbitol, and oligomerized glycerol (oligoglycerol) are particularly preferred. The preferred composition of the oligoglycerol used is described in WO2012 / 017095 and WO2017 / 153431. In particular, in order to very substantially avoid the evaporation of monoglycerol during subsequent film extrusion, the content of monoglycerol in the oligoglycerol is preferably less than 10% by mass.

[0026] Sorbitol is particularly preferred as the plasticizer, and here, in particular, an aqueous sorbitol solution with a water content of 5 to 80%, preferably 5 to 50%, particularly preferably 10 to 35% is preferred.

[0027] An aqueous sorbitol solution produced using an incompletely depolymerized starch solution and still containing a significant proportion of a compound having a higher molecular weight than sorbitol of at least 5%, preferably more than 10%, particularly preferably more than 15% based on the anhydrous mixture has been specified as a particularly preferred plasticizer.

[0028] The plasticizer (excluding moisture) is generally used in a proportion of 5 to 40% by mass, preferably 10 to 30% by mass, particularly preferably 15 to 25% by mass, based on the natural starch (excluding moisture).

[0029] The water content present in the extruder mixture before devolatilization and obtained from water introduced by the starch, by the plasticizer or plasticizer mixture used, or by separate introduction into the extruder is generally 1 to 20% by weight, preferably 3 to 15% by weight, particularly preferably 5 to 10% by weight, based on the total of the anhydrous final product. Advantageous mixtures for optimizing the water content in the extruder and preventing this water content from becoming excessive contain, in each case, an aqueous sorbitol solution having an oligoglycerol, based on the quantitative ratio of the amount of the anhydrous sorbitol solution containing any higher oligomers present, calculated as the ratio to the anhydrous oligoglycerol mixture, in a sorbitol:oligoglycerol ratio of 15:85 to 75:25.

[0030] The expression "starch immiscible polymer" means, for example, polyethylene or polypropylene, here in particular polymers manufactured from renewable resources, polystyrene, particularly preferably polyesters, which are preferably biodegradable in accordance with DIN EN 13432.

[0031] Among the latter, there are in particular the diol dicarboxylic acid type polyesters, where an aliphatic polyester consisting of an aliphatic diol and an aliphatic diacid and an aliphatic aromatic polyester consisting of an aliphatic diol and an aliphatic diacid and an aromatic diacid are distinguished. A common feature of these polyesters is that they are biodegradable in accordance with DIN EN 13432.

[0032] Among the biodegradable aliphatic aromatic polyesters, particularly preferred are the linear non-chain-extended polyesters of the type described as an example in WO92 / 09654, preferably the chain-extended and / or branched polyesters of the type described as an example in WO96 / 15173, WO-A2006 / 097353 or WO98 / 12242. In particular, the expression "aliphatic aromatic polyester" means products such as ecoflex® (BASF SE) and Origo-Bi® (Novamont).

[0033] Among the particularly preferred aliphatic aromatic polyesters, the polyester contains as substantial components A) an acid component comprising a1) 30 to 99 mol%, preferably 30 to 70 mol% of an aliphatic C4-C 18 dicarboxylic acid, for example, preferably succinic acid, adipic acid, sebacic acid, azelaic acid, brassilic acid, or their ester-forming derivatives, or mixtures thereof, or a mixture of sebacic acid and adipic acid or succinic acid, and a2) 1 to 70 mol%, preferably 30 to 70 mol% of terephthalic acid, furandicarboxylic acid, or their ester-forming derivatives, or mixtures thereof, and an acid component consisting of; B) based on acid component A, 98.5 to 100 mol% of a C2-C6 diol component, for example, preferably 1,3-propanediol and 1,4-butanediol, particularly preferably 1,4-butanediol produced from renewable resources; and C) based on acid component A, 0 to 1.5 mol%, preferably 0.01 to 1 mol% of c1) a compound having at least three groups capable of forming esters, c2) a di- or polyisocyanate, c3) a di- or polyepoxide, or a mixture of c1) to c3) a component selected from and contains.

[0034] In particular, the following aliphatic aromatic polyesters are preferred: Polybutylene sebacate-co-terephthalate (PBSeT), polybutylene azelate-co-terephthalate (PBAzT), polybutylene adipate-co-terephthalate (PBAT), polypropylene adipate-co-terephthalate (PPrAT), polybutylene succinate-co-terephthalate (PBST), or polybutylene sebacate-co-adipate-co-terephthalate (PBSeAT), or polybutylene sebacate-co-succinate-co-terephthalate (PBSeST), or a mixture of two or more of the above polyesters. The above aliphatic-aromatic polyesters preferably contain 1,4-butanediol from renewable resources as the diol component.

[0035] Preferred aliphatic-aromatic polyesters are characterized in that the molar mass (Mn) is in the range of 1,000 to 100,000, particularly in the range of 9,000 to 75,000 g / mol, preferably in the range of 10,000 to 50,000 g / mol, and the melting point is in the range of 60°C to 170°C, preferably in the range of 80°C to 150°C.

[0036] The meaning of the expression "aliphatic polyester" includes polyesters composed of aliphatic diols and aliphatic dicarboxylic acids, for example, polybutylene succinate (PBS), polybutylene adipate (PBA), polybutylene succinate adipate (PBSA), polybutylene succinate sebacate (PBSSe), polybutylene sebacate (PBSe), or the corresponding polyesters having a partial polyester amide structure or a partial polyester urethane structure. This aliphatic polyester is, for example, sold by Mitsubishi as BIUOPBS. WO-A2010 / 034711 describes the more recent development status.

[0037] Mixtures of aliphatic and aliphatic-aromatic polyesters, or the above-mentioned mixtures of aliphatic or aliphatic-aromatic polyesters can also be used. The latter used includes polybutylene adipate-co-terephthalate (PBAT), polybutylene sebacate-co-terephthalate (PBSeT), and mixtures of PBAT and PBSeT, and contains up to 44.99% by mass, preferably 1-29.9% by mass, and particularly preferably 1-10% by mass of other biodegradable polymers selected from the group consisting of polylactic acid (PLA), polycaprolactone (PCL), polypropylene carbonate, and polyhydroxyalkanoate.

[0038] Compatibilizers, for example, a) copolymers based on styrene, acrylate and / or methacrylate having epoxy groups, and / or b) fatty acid amides, fatty acid esters, or natural oils having epoxy groups can be added to the polymer mixture, particularly to the mixture containing polylactic acid.

[0039] The expression "copolymer based on styrene, acrylate and / or methacrylate having epoxy groups" means the following structure a). The unit having an epoxy group is preferably glycidyl (meth)acrylate. Copolymers that have been proven to be advantageous have a glycidyl methacrylate content in the copolymer of more than 20% by mass, particularly preferably more than 30% by mass, and particularly preferably more than 50% by mass. The epoxy equivalent weight (EEW) of these polymers is preferably 150-3000 g / equivalent, and particularly preferably 200-500 g / equivalent. The average molecular weight (weight average) M W of the polymer is preferably 2000-25000, particularly 3000-8000. The average molecular weight (number average) M nis preferably from 400 to 6000, particularly from 1000 to 4000. The polydispersity (Q) is generally between 1.5 and 5. The copolymers of the above type having epoxy groups are, for example, sold under the trademark Joncryl® ADR by BASF Resins B.V. Joncryl® ADR 4368, Joncryl ADR 4468C or Joncryl ADR 4468HP are particularly suitable as compatibilizers.

[0040] The addition amount of the compatibilizer a) is 0 to 2% by mass, preferably 0.05 to 0.6% by mass, based on the total mass of the starch mixture.

[0041] Fatty acid amides, fatty acid esters, or (epoxidized) natural oils containing epoxy groups can be further used as the compatibilizer b). The expression "natural oil" means, for example, olive oil, linseed oil, soybean oil, palm oil, peanut oil, coconut oil, seaweed oil, cod liver oil, or a mixture of these compounds. In particular, epoxidized soybean oil (for example, Merginat® ESBO from Hobum in Hamburg, or Edenol® B 316 from Cognis in Düsseldorf) is preferred. The compatibilizers of structural types a) and b) can also be combined, for example, Joncryl® ADR 4368 (structural type a)) and Merginat® ESBO (structural type b)).

[0042] The addition amount of the compatibilizer b) is generally 0 to 6% by mass, preferably 0.3 to 3% by mass, based on the total mass of the starch mixture.

[0043] Particularly when using the compatibilizer b), it is possible to further add an organic acid to the reaction mixture, examples of which include malic acid, lactic acid, tartaric acid or citric acid. The acid is generally used at a concentration of 0.01 to 0.45% by mass, preferably 0.05 to 0.3% by mass, based on the total mass of the starch mixture.

[0044] Mineral fillers can also be added to the starch mixture, for example, chalk, graphite, gypsum, conductive carbon black, iron oxide, calcium phosphate, dolomite, kaolin, silicon dioxide (quartz), sodium carbonate, titanium dioxide, silicate, wollastonite, mica, or montmorillonite. The general amount of mineral filler used is 0.1 to 20% by mass, preferably 2 to 15% by mass, based on the total mass of the starch mixture.

[0045] The starch mixture of the present invention can usually contain further additives known to those skilled in the art. Here, for example, additional substances conventionally used in plastic technology, such as stabilizers, nucleating agents such as the above-mentioned mineral fillers and also crystalline polylactic acid; lubricants and mold release agents such as stearates (especially calcium stearate); surfactants such as polysorbate, palmitate or laurate; antistatic agents, ultraviolet absorbers; ultraviolet stabilizers; anti-fogging agents, or colorants (for example, graphite). The additives are usually used at a concentration of 0 to 2% by mass, particularly 0.1 to 2% by mass, based on the total mass of the starch mixture.

[0046] Instead of using the above-mentioned mixture of biodegradable polyester or polycarbonate, it is also possible to add these polyesters or polycarbonates to the extruder at different positions. Therefore, it is possible to add a polyester susceptible to hydrolysis, such as polybutylene succinate, polyhydroxyalkanoate, or polylactic acid, at a position in the extruder where the water content of the polymer melt has already decreased after prior devolatilization.

[0047] The above-mentioned polymer can further contain additional additives known to those skilled in the art. These examples are additional substances conventionally used in plastic technology, such as stabilizers, antiblocking agents, lubricants, nucleating agents, antistatic agents, ultraviolet absorbers; plasticizers such as citroflex, or anti-fogging agents such as atomers, compatibilizers, for example, copolymers based on styrene, acrylate and / or methacrylate having epoxy groups, or colorants. Of course, additives conventionally used in starch mixtures, such as organic acids and fatty acid esters described in EP0947559 and by Zhang et al., Polm. Adv. Technol. 2018, pages 1-11, can also be used. The concentrations generally used for these additives are 0 to 2% by weight, particularly 0.1 to 1% by weight, based on the polyester mixture of the present invention.

[0048] The above-mentioned additives or auxiliaries can also be fed into the extruder separately from the starch-incompatible polymer.

[0049] The one-step process of the present invention has a number of advantages. The non-aggressive and efficient wetting of the starch by one or more plasticizers in the wet section of the extruder results in non-aggressive gelatinization / thermal plasticization of the starch and non-aggressive incorporation of the TPS into the matrix of the starch-incompatible polymer in a further process in the plasticization section. Compared to the processes described in the prior art, the process under consideration is generally carried out in the presence of a significant amount of water, generally 1 to 20%, preferably 3 to 15%, particularly preferably 5 to 10%, based on the total amount of the anhydrous final product, in the plasticization section. Therefore, the starch is very substantially protected from adverse thermal degradation, including discoloration. At the same time, fine particle dispersion of the starch in the polymer matrix becomes possible, resulting in high processing capacity and high starch content in the polymer. Furthermore, in order to achieve dispersion of the TPS in the polymer, it is possible to avoid the addition of certain expensive compatibilizers mainly added in the prior art.

[0050] Therefore, by the method of the present invention according to claims 1 to 12, preferably 10 to 12, for the first time it has become possible to produce on an industrial scale a starch mixture having a lightness value L* of more than 75, preferably more than 80, based on the total of anhydrous starch and anhydrous plasticizer, and in the range of 39 to 47% by mass, in accordance with EN ISO 11664-4. Furthermore, it was also possible to achieve a b* (blue-yellow value) value in accordance with EN ISO 11664-4 of less than 22. This was achieved even with maize starch, which has a higher protein content than potato starch and is therefore more susceptible to discoloration when subjected to heat stress. Furthermore, these starch mixtures had a surprisingly low content of cyclic impurities such as tetrahydrofuran (THF). The THF content of the starch mixtures produced by the method of claim 12 of the present invention was generally less than 10 ppm, in particular less than 5 ppm, and particularly preferably less than 3 ppm.

[0051] The method of the present invention mainly (to the extent of more than 50% by mass), preferably 60% or more, provides access to starch mixtures consisting of renewable raw materials. The proportion of renewable raw materials can be determined by 14 method C in accordance with the DIN CERTCO standard or the Vincotte standard. Also, these starch mixtures can be biodegraded in a garden compost heap in accordance with the OK Compost HOME standard of the Vincotte certification system. Since the starch mixtures can be produced with few undispersed particles, they can be stretched to obtain films with a thickness of less than 20 μm, preferably less than 10 μm. Since the starch particles are uniformly dispersed in the polymer matrix, the films have very good mechanical properties, such as particularly high tensile strength and also high tear propagation resistance.

[0052] Preferred starch mixtures having the above properties have the following composition i) 53 to 61% by mass of polybutylene adipate-co-terephthalate (PBAT) and / or polybutylene sebacate-co-terephthalate (PBSeT) each containing 1,4-butanediol from renewable resources; ii) 39 to 47% by mass of thermoplastic starch It has.

[0053] In particular, it has the above-mentioned characteristic profile and the following composition i) 45.4 to 62.95% by mass of PBAT and / or PBSeT containing 1,4-butanediol from renewable resources; ii) 35 to 47% by mass of thermoplastic starch, iii) 2 to 7% by mass of polylactic acid; iv) 0.05 to 0.6% by mass of a copolymer based on styrene, acrylate and / or methacrylate having an epoxy group A starch mixture having is preferred.

Example

[0054] Starting materials: A1) ecoflex® F Blend C1200, an aliphatic aromatic polyester manufactured by BASF having an MVR of 3 to 5 at 190 °C / 2.16 kg B1) Natural corn starch, water content approximately 12% C1) Neosorb 70 / 70 - a sorbitol solution with a solid content of 70% and a sorbitol content of at least 50% from Roquette, which is very resistant to the influence of crystallization.

[0055] Description of the extruder used: E1) Co-rotating twin-screw extruder ZSK 40 MC manufactured by Coperion, diameter 40 mm, 14 electrically heatable and coolable barrel zones each with a length of 4D, L / D = 56, having a wet zone with a length of 20D, in which 3 kneading blocks are incorporated. Motor rated output 130 kW, specific torque 11.5 Nm / cm 3 .

[0056] Description of the blown film plant: Inflation plant: It consists of a single-screw extruder with a diameter of 30 mm and a length of 25D, and a spiral mandrel distributor with a diameter of 80 mm and a die gap of 0.8 mm. The blow-up ratio is usually 3.5, resulting in a bubble width of about 440 mm for the inflated film (laid-flat film).

[0057] Analysis: Measurement of moisture content: The residual moisture content of the granules was measured by the Karl Fischer method (Mettler-Toledo InMotion KF).

[0058] Melt volume rate: The melt volume rate was measured according to EN ISO 1133 at a specified temperature and a specified weight, and the unit was cm 3 / 10 min.

[0059] Average starch particle size: From the film produced in Example 2, a sample was obtained by cutting it parallel to the extrusion direction with a microtome at -80 °C. A 15×15 μm portion of this sample was observed with an atomic force microscope. The relatively hard TPS phase can be very easily distinguished from the relatively soft polymer phase, and the blend morphology and particle size of the starch particles dispersed in the polymer can be accurately determined. When the particle size was evaluated, the average particle size was 466 nm and the maximum particle size was only 1488 nm. This is evidence of a very fine dispersion of the starch particles in the polymer phase.

[0060] Measurement of THF: The measurement of THF 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 purpose, an appropriate amount of the sample was dissolved in dimethylethylacetamide, and THF-d8 was added as an internal standard. The sample enclosed in a glass headspace GC bottle was heated in the headspace oven of Agilent HS GC / MS at 85 °C for 30 minutes and then subjected to measurement. Helium was used as the carrier gas. The numerical values were calibrated externally based on the recovery rate of the internal standard substance (THF-d8) and the control of the matrix effect (Matrix Spike).

[0061] Measurement of lightness value L* and b* value: The measurement was carried out in accordance with EN ISO 11664-4 (CIE 15:2004). The average value was calculated from four measurements of granular particles (size 3 - 8 mm) in a layer with a thickness of 2 cm to ensure the formation of an opaque layer. During the four measurements, the container was rotated 90° each time. Datacolor 650 was used for the measurement. The measurement was performed with a spherical shape, d / 8°, including the specular component (SCI), and the standard light source D65 combined with the CIE 1963 10° standard observer.

[0062] Examples of the present invention: Examples 1 - 7 (Extruder E1, Embodiment B).

[0063] For the addition of all starting materials, a weight measurement system was used. Natural starch B was added in powder form to zone 1 of the extruder. Using a gravity-controlled gear pump, plasticizer C was added, for example, to the center of zone 2. Granular starting material A was added to zone 6 of the extruder using a side feeder (ZSB). Between the plasticizer addition point position in zone 2 and the polymer addition position in zone 6, not only conveying elements but also 1 to 5 mixing elements (neutral kneading blocks and / or toothed reverse conveying mixing elements) were installed. Excess moisture was removed in zone 13 through a 40-mm horizontal devolatilization unit, and the product was extruded into a string shape using a die plate, cooled in a water bath, and granulated.

[0064] Thereafter, the polymer granules were dried at 70 °C to the residual moisture level described in the table.

[0065] Example 8 (Extruder E1, Embodiment A): For the addition of all starting materials, a weight measurement system was used. Natural starch B and starting material A were added to zone 1 of the extruder using two separate weight measurement systems. Plasticizer C was added in a liquid state to approximately the center of zone 2 using a weight-controlled gear pump. Only screw elements for conveying were used in zones 1 to 6. Excess moisture was removed in zone 13 through a 40-mm horizontal devolatilization system, and the product was extruded into a string shape using a die plate, cooled in a water bath, and granulated.

[0066] Thereafter, the polymer granules were dried at 70 °C to the residual moisture level described in the table.

[0067] [Table 1]

[0068] * WC = Water cooling, not controllable ** The distance from the addition of the plasticizer (in whole or in part) to the start of the starch melting / plasticizing zone, expressed as a multiple of the diameter D of the extruder.

[0069]

Table 2

[0070] * Limit the minimum film thickness of the film plant B2 at 30 / min to 9 μm to achieve the maximum take-off speed. Depending on the quality of the starch mixture, it is also possible to produce thinner films. ** 1: A small number of small undispersed particles, no holes; 2: A small number of undispersed particles, some slightly larger particles, no holes; 3: More undispersed particles, sometimes medium to large-sized undispersed particles, sometimes with holes; 4: A large number of medium-sized and some large-sized undispersed particles, holes occur regularly, the film can run slightly; 5: A large number of medium-sized and some large-sized undispersed particles, holes occur frequently, the film cannot run stably for a long time; 6: A large number of medium to large-sized undispersed particles, holes occur continuously, the film collapses continuously *** A mixture of 60 kg / h of A1, 33.7 kg / h of B1, and 14.0 kg / h of C1 was produced by an extruder E1 by a method based on the extruder configuration of Example 1 of EP 2467418A1. At a rotational speed of 350 rpm, the melt temperature at the die outlet was 248 °C. The obtained blown film had a considerably larger number of starch aggregates and constantly occurring holes compared to Example 5, so it could not be stretched to a thickness of less than about 25 μm. Furthermore, the product showed a yellowish discoloration. The lightness value L* of the granules was as low as 72.96, and the b* value was 24.29. That is, the granules were considerably darker and had a higher yellow value than the granules of the present invention in Example 5.

[0071]

Table 3

[0072]

Table 4

[0073] * WC = water cooling, uncontrollable The distance from the addition of (all or part of) the plasticizer to the start of the melting zone / plasticizing zone of the starch was defined as a multiple of the diameter D of the extruder.

[0074]

Table 5

[0075] * 1: A small number of small undispersed particles, no holes. 2: A small number of undispersed particles, some slightly larger particles, no holes. 3: More undispersed particles, sometimes medium to large-sized undispersed particles, sometimes with holes. 4: A large number of medium-sized and some large-sized undispersed particles, holes occurring regularly, the film can run slightly. 5: A large number of medium-sized and some large-sized undispersed particles, holes occurring frequently, the film cannot run stably for a long time. 6: A large number of medium to large-sized undispersed particles, holes occurring continuously, the film collapses continuously.

[0076]

Table 6

[0077] Example 9: Using the same parameters as in Example 5, a mixture was made from 54.8% of a partially bio-based bio-PBAT (the same as A1 but containing 100% bio-based bio-BDO produced by fermentation instead of fossil BDO), 5% of Natureworks' polylactic acid 4043D, 0.2% of Joncryl ADR 4468, 33.7% of B1, and 14.0% of C1. The polylactic acid and Joncryl were added together with the bio-PBAT. The MVR after drying was 2.8 (190 °C / 5 kg), the lightness value L* was 83.64, and b* was 17.8. This mixed substance could be processed easily with the same parameters as in Example 5, and a 10-μm-thick film substantially free of undispersed particles could be obtained, which had sufficiently good mechanical properties (especially the tear propagation behavior perpendicular to the machine direction) as a fresh produce bag and had a bio-based 14 C content that was approximately 60% higher than in Example 5.

Claims

**Claim 1** A method for producing a starch mixture by a one-step method using a twin-screw extruder, comprising: i) a step of passing starch together with a plasticizer through a wet section having a length of 8D to 30D of the extruder while mixing at a temperature of less than 85°C, where D is defined as the screw diameter of the screw cylinder, and the wet section is defined as starting at a position on the screw of the extruder where all or part of the total amount of starch and plasticizer meet each other and ending at the position of the extruder where the starch gelatinizes; ii) a step of gradually adjusting the temperature of the extruder to above 130°C in a plasticizing section having a length of 10D to 50D, where the starch is thermoplastically plasticized and dispersed in a starch-immiscible polymer, and a water content of less than 5% based on the starch mixture is established before the material exits the extruder; and a production method of adding a starch-immiscible polymer in a molten state or a granular state at an arbitrary position of the extruder to produce a mixture of all the components present as a result. **Claim 2** A method for producing a starch mixture using two twin-screw extruders arranged in series, comprising: i) a step of passing starch together with a plasticizer through a wet section having a length of 8D to 80D of the extruder while mixing at a temperature of less than 85°C, where D is defined as the screw diameter of the screw cylinder, and the wet section is defined as starting at a position on the screw of the extruder where all or part of the total amount of starch and plasticizer meet each other and ending at the position of the extruder where the starch gelatinizes; ii) a step of gradually adjusting the temperature of the extruder to above 130°C in a plasticizing section having a length of 10D to 50D, where the starch is thermoplastically plasticized and dispersed in a starch-immiscible polymer, and a water content of less than 5% based on the starch mixture is established before the material exits the extruder; and a production method of adding a starch-immiscible polymer in a molten state or a granular state at an arbitrary position of the extruder to produce a mixture of all the components present as a result. **Claim 3** The production method according to claim 1 or 2, wherein the length of the wet section is at least 12D. **Claim 4** The production method according to any one of claims 1 to 3, wherein the temperature of the wet section is maintained at less than 60°C. **Claim 5** The production method according to any one of claims 1 to 4, wherein the starch-immiscible polymer is added in a solid state before the start of the wet section. **Claim 6** The method of manufacture according to any one of claims 1 to 4, wherein the wet zone includes an additional mixing screw element together with the conveying element, and the starch immiscible polymer is added only downstream of the additional mixing screw element in the wet zone.

7. The method of manufacture according to claim 6, wherein the starch immiscible polymer is added in a solid state.

8. The method of manufacture according to claim 6 or 7, wherein the starch immiscible polymer is added before the dispersed phase.

9. The method of manufacture according to any one of claims 1 to 8, wherein the minimum length of the extruder is 44D.

10. The method of manufacture according to any one of claims 1 to 9, wherein the plasticizer is selected from water, glycerol, sorbitol, oligomerized glycerol, and any mixture of these compounds.

11. The method of manufacture according to claim 10, wherein the plasticizer includes an aqueous solution of sorbitol having a water content of 5 to 80%.

12. The method of manufacture according to claim 11, wherein the aqueous solution of sorbitol is produced by hydrogenation of an incompletely depolymerized starch solution containing at least 5% by significant proportion of a compound having a higher molecular weight than sorbitol based on the anhydrous mixture.

13. The method of manufacture according to any one of claims 1, 2, and 12, wherein the starch immiscible polymer includes an aliphatic or aliphatic aromatic polyester containing 1,4 - butanediol as a diol component and is biodegradable in accordance with EN 13432.

14. A starch mixture containing a starch immiscible polymer, wherein the content of thermoplastic starch is 39 to 47% by mass based on the total of anhydrous starch and anhydrous plasticizer, and the lightness value L* in accordance with EN ISO 11664 - 4 / CIE 15:2004 is greater than 75.

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

16. The starch mixture according to claim 14 or 15, wherein the starch used includes corn starch, wheat starch, or pea starch.

17. The starch mixture according to claim 16, wherein the starch used includes corn starch.

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