Starch hybrid copolymers

Abstract

The subject of the invention is a starch hybrid copolymer in the form of an aqueous dispersion or a water-redispersible powder obtainable by radically initiated polymerization and optionally subsequent drying in the presence of a starch in an aqueous medium of ethylenically unsaturated monomers, characterized in that the starch comprises an oxidized starch, and the ethylenically unsaturated monomers comprise one or more vinyl esters and ethylene wherein the total amount of vinyl esters and ethylene is > = 81% by weight, based on the total weight of the ethylenically unsaturated monomers, whereby no ethylenically unsaturated monomers bearing allyl, epoxy, silyl or N-hydroxymethyl groups are copolymerized.

Description

[0001] The present invention relates to starch hybrid copolymers based on oxidized starch, vinyl acetate and ethylene in the form of aqueous dispersions or water-redispersible powders, to a process for their production and to their use in adhesive or coating compositions, for example for flexible packaging, food containers, coffee capsules, straws, covering films, insecticide coatings or fishing nets, or in compositions for 3D printing.

[0002] For ecological reasons and to solve the problem of plastic waste, it is necessary to provide biodegradable polymers and at least partially replace petrochemical polymers by natural renewable raw materials such as starch. However, such replacement should preferably not impair the application properties of the applied product, in particular mechanical properties, such as elongation, tensile strength or impact strength. Moreover, the compatibility of natural renewable raw materials with other formulation ingredients of adhesives or coating compositions may be a problem. Such application and compatibility properties are usually not achieved only by physical blends of starch and petrochemical polymers. In addition, for starch hybrid copolymers, there may be problems in achieving the desired property distribution. Starch hybrid copolymers are based on polymers of ethylenically unsaturated monomers and starch, which can be connected to each other via, for example, chemical bonds, or bonded to each other in some other way.

[0003] A particular challenge stems from the fact that starch and petrochemical polymers have completely different chemical structures and properties. Therefore, partial substitution of petrochemical polymers with starch can lead to incompatibility and separation of the different substances, which significantly affects the performance characteristics of the applied product. Therefore, the starch must be present in a stable form alongside the petrochemical polymer. Since different petrochemical polymers have different performance characteristics, it is also impossible to transfer findings from one starch hybrid polymer to another based on a different petrochemical polymer. Petrochemical polymers vary greatly in their properties, for example, in their hydrophilicity or hydrophobicity, solubility or dispersibility, elastic or inelastic properties, and often in their thermal behavior, depending on their monomer composition. Furthermore, functional comonomer units, such as allyl, epoxy, silane, or N-methylol groups, carry a significant influence on the polymer properties, as such monomers, for example, are cross-linking and can react with starch, thereby stabilizing the starch hybrid copolymer.

[0004] Several methods for producing starch hybrid copolymers are known. For example, KR101473916B1 describes starch-based polymer particles with a core-shell structure. These particles are obtained by polymerizing hard and soft monomers in the presence of starch degradation products to form a core, onto which hard, soft, and silane monomers are polymerized as a shell. The soft monomers in KR101473916B1 are certain acrylic acid esters, which form homopolymers with glass transition temperatures ranging from 10°C to -80°C. In comparison, ethylene homopolymers have a glass transition temperature of -85°C.

[0005] The graft polymers of US4301017 are prepared by polymerizing a single or at least two vinyl monomers in the presence of derivatized starch, wherein the at least two vinyl monomers are acrylate monomers. WO15160794A1 describes bio-based nanoparticles of biopolymers and vinyl monomers. In WO11008272A1, hydrophobically modified starch is prepared by reacting a water-soluble polysaccharide with a hydrophilic monomer and a hydrophobic monomer, and then polymerizing with another monomer mixture. WO2015155159 teaches aqueous emulsion polymerization of 70 to 95% by weight of vinyl acetate and 5 to 25% by weight of (meth)acrylates and a limited amount of certain functional monomers (e.g., allyl- or glycidyl-acrylates) in the presence of starch. WO2022 / 218539 teaches starch hybrid copolymers with vinyl esters, ethylene, ethylenically unsaturated functional monomers with epoxy groups, silanes and / or N-methylol groups.

[0006] Starch has also been proposed as a protective colloid for polymers, for example in US Pat. No. 3,632,535. EP 1,082,370 B1 specifically describes styrene-acrylate polymers stabilized by starch. US Pat. No. 3,769,248 describes dispersions of vinyl acetate polymers stabilized with up to 4% by weight of starch as a protective colloid. US Pat. No. 4,532,295 teaches the emulsion polymerization of ethylenically unsaturated monomers in the presence of 1 to 5% by weight of cyanoalkyl starch, hydroxyalkyl starch, or carboxyalkyl starch as a protective colloid, based on the monomers. For US Pat. No. 4,532,295, it is necessary to omit the emulsifier during the polymerization. Protective colloids are known to have the function of stabilizing polymers. For example, aqueous dispersions of water-insoluble polymers can be stabilized by protective colloids. Water-insoluble polymers can also be converted into water-redispersible powders using protective colloids. In these cases, the water-insoluble polymer and the protective colloid starch take the form of separate polymers. Compositions in which starch and other polymers coexist are also referred to as physical mixtures or blends.

[0007] In this context, the object was to provide starch hybrid copolymers which exhibit advantageous biodegradability, in particular under home composting conditions, and preferably beneficial storage stability. Preferably, films made from starch hybrid copolymers exhibit advantageous mechanical properties, such as elongation.

[0008] The present invention relates to starch hybrid copolymers in the form of aqueous dispersions or water-redispersible powders obtainable by free-radically initiated polymerization in an aqueous medium of ethylenically unsaturated monomers in the presence of starch and optionally subsequent drying, characterized in that

[0009] The starch comprises oxidized starch, and

[0010] The ethylenically unsaturated monomers include one or more vinyl esters and ethylene,

[0011] Wherein, based on the total weight of the ethylenically unsaturated monomers, the total amount of vinyl ester and ethylene is ≥ 81 wt %,

[0012] Thus, no ethylenically unsaturated monomers carrying allyl, epoxy, silane or N-methylol groups are copolymerized.

[0013] Examples of vinyl esters are vinyl esters of unbranched or branched alkylcarboxylic acids having 1 to 18 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinyl pivalate, and vinyl esters of α-branched monocarboxylic acids having 5 to 15 carbon atoms, such as VeoVa9. R or VeoVa10 R (Trade name for shells.) Vinyl acetate is preferred.

[0014] The starch hybrid copolymer is preferably 50 to 97 weight percent, more preferably 70 to 95 weight percent, and most preferably 80 to 90 weight percent based on vinyl esters, based on the total weight of ethylenically unsaturated monomers.

[0015] The starch hybrid copolymer is preferably 40-80% by weight, more preferably 45-75% by weight, most preferably 50-70% by weight based on the dry weight of the starch hybrid copolymer.

[0016] The starch hybrid copolymer is preferably 1-45 wt% based on the total weight of ethylenically unsaturated monomers, more preferably 3-30 wt%, even more preferably 5-25 wt%, most preferably 10-20 wt% based on ethylene.

[0017] The starch hybrid copolymer is preferably 1 to 45 wt%, more preferably 3 to 30 wt%, most preferably 5 to 20 wt% ethylene-based, based on the dry weight of the starch hybrid copolymer.

[0018] The total amount of vinyl ester and ethylene is preferably ≥ 85 wt%, more preferably ≥ 91 wt%, even more preferably ≥ 96 wt%, most preferably ≥ 99 wt%, based on the total weight of the ethylenically unsaturated monomers.

[0019] The total amount of vinyl ester and ethylene is preferably 40-95 wt%, more preferably 45-90 wt%, even more preferably 50-85 wt%, most preferably 60-80 wt%, based on the dry weight of the starch hybrid copolymer.

[0020] Most preferably, the ethylenically unsaturated monomers consist of vinyl esters and ethylene, in particular vinyl acetate and ethylene.

[0021] The starch hybrid copolymers may be based on one or more additional ethylenically unsaturated monomers, such as acrylic or methacrylic esters of branched or unbranched alcohols having 1 to 15 carbon atoms, dienes, propene, vinyl halides and vinyl aromatic compounds.

[0022] Examples of (meth)acrylates are acrylates or methacrylates of branched or unbranched alcohols having 1 to 15 carbon atoms. Preferred methacrylates or acrylic acid esters are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethylhexyl acrylate, and norbornyl acrylate. Particularly preferred are methyl acrylate, methyl methacrylate, n-butyl acrylate, 2-ethylhexyl acrylate, and norbornyl acrylate.

[0023] Examples of suitable dienes are 1,3-butadiene and isoprene. An example of a vinyl halide is vinyl chloride. The copolymerized vinyl aromatic compound may be, for example, styrene or vinyltoluene.

[0024] Preferred additional monomers are n-butyl acrylate, n-butyl methacrylate, tert-butyl acrylate and tert-butyl methacrylate.

[0025] Such additional ethylenically unsaturated monomers are copolymerized to an extent of preferably 0 to 19% by weight, more preferably 0.1 to 9% by weight, even more preferably 0.5 to 4% by weight, based on the total weight of the monomers.

[0026] Such additional ethylenically unsaturated monomers are copolymerized to an extent of preferably 0 to 10 wt%, more preferably 0 to 8 wt%, even more preferably 0.1 to 5 wt%, based on the total weight of the starch hybrid copolymer.

[0027] Most preferably, no further ethylenically unsaturated monomers are copolymerized, in particular no (meth)acrylates and / or no vinyl aromatic compounds.

[0028] The starch hybrid copolymer may optionally be further copolymerized with one or more auxiliary monomers. Based on the total weight of the monomers, preferably 0-19 wt. %, more preferably 0.01-10 wt. %, even more preferably 0.1-1 wt. % of the auxiliary monomers are copolymerized. Examples of auxiliary monomers are ethylenically unsaturated mono- and dicarboxylic acids, preferably acrylic acid, methacrylic acid, crotonic acid, fumaric acid, and maleic acid; ethylenically unsaturated anhydrides, preferably maleic anhydride; acrylamide; ethylenically unsaturated nitriles, preferably acrylonitrile; mono- and diesters of fumaric and maleic acids, such as diethyl and diisopropyl esters; and ethylenically unsaturated sulfonic acids and their salts, preferably vinylsulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid.

[0029] Preferred auxiliary monomers are ethylenically unsaturated mono- and dicarboxylic acids or their anhydrides, in particular ethylenically unsaturated sulfonic acids or their salts.

[0030] Most preferably, no auxiliary monomers are copolymerized.

[0031] For the preparation of starch hybrid copolymers, no ethylenically unsaturated monomers bearing allyl, epoxy, silane or N-methylol groups are copolymerized. Starch hybrid copolymers generally do not contain monomer units from monomers bearing allyl, epoxy, silane or N-methylol groups.

[0032] Examples of ethylenically unsaturated monomers having an allyl group are allyl esters of unsaturated carboxylic acids, such as allyl methacrylate or allyl acrylate.

[0033] Examples of ethylenically unsaturated monomers having epoxy groups are glycidyl acrylate and glycidyl methacrylate.

[0034] Examples of ethylenically unsaturated monomers bearing N-methylol groups are N-hydroxyalkyl-functional comonomers having a C1-C4 hydroxyalkyl group, more particularly an N-methylol group, such as N-methylolacrylamide (NMA), N-methylolamethacrylamide, N-methylolacrolein, C1-C4 alkyl ethers of N-methylolacrylamide, N-methylolamethacrylamide and N-methylolacrolein, such as their isobutoxy ethers, and C1-C4 alkyl esters of N-methylolacrylamide, N-methylolamethacrylamide and N-methylolacrolein. Particularly preferred are C1-C4 alkyl ethers of N-methylolacrylamide, N-methylolamethacrylamide, N-methylolacrolein and N-methylolacrolein, such as their isobutoxy ethers.

[0035] Ethylenically unsaturated monomers carrying silane groups include, for example, (meth)acryloxypropyltri(alkoxy)silane or (meth)acryloxypropyldialkoxymethylsilane, vinyltrialkoxysilane or vinylmethyldialkoxysilane, wherein the alkoxy groups included may be, for example, methoxy, ethoxy, propoxy, butoxy, acetoxy and ethoxypropylene glycol ether groups. Preferred ethylenically unsaturated silanes are vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane, vinyltris(1-methoxy)isopropoxysilane, vinyltributoxysilane, vinyltriacetoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, methacryloxymethyltrimethoxysilane, 3-methacryloxypropyltris(2-methoxyethoxy)silane, vinyltrichlorosilane, vinylmethyldichlorosilane, vinyltris(2-methoxyethoxy)silane, silane, triacetoxyvinylsilane, allylvinyltrimethoxysilane, allyltriacetoxysilane, vinyldimethylmethoxysilane, vinyldimethylethoxysilane, vinylmethyldiacetoxysilane, vinyldimethylacetoxysilane, vinylisobutyldimethoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinyltrihexyloxysilane, vinylmethoxydihexyloxysilane, vinyltrioctyloxysilane, vinyldimethoxyoctyloxysilane, vinylmethoxydioctyloxysilane, vinylmethoxydilauryloxysilane, and polyethylene glycol-modified silane. Particularly preferred ethylenically unsaturated silanes are vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyltri(1-methoxy)isopropoxysilane, methacryloxypropyltri(2-methoxyethoxy)silane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane and methacryloxymethyltrimethoxysilane.

[0036] The starch hybrid copolymer is based on preferably 45 to 95 wt %, more preferably 50 to 90 wt %, most preferably 55 to 85 wt % of ethylenically unsaturated monomers, based on the dry weight of the starch hybrid copolymer.

[0037] The fraction of ethylenically unsaturated monomers in the starch hybrid copolymer can be determined, for example, by NMR spectroscopy, preferably using calibration substances.

[0038] The selection of monomers and the weight fraction of comonomers is carried out here so that the glass transition temperature Tg of the starch hybrid copolymer is from -50°C to +120°C, preferably from -35°C to +45°C. Starch units generally do not exhibit a glass transition temperature. The glass transition temperature Tg of the polymer can be determined in a known manner by differential scanning calorimetry (DSC). Tg can also be approximately calculated in advance using the Fox equation. According to Fox TG, Bull.Am.Physics Soc.1,3, page 123 (1956): 1 / Tg=x1 / Tg1+x2 / Tg2+…+xn / Tgn, where xn is the mass fraction of monomer n (weight % / 100), and Tgn is the glass transition temperature of the homopolymer of monomer n in Kelvin. The Tg values ​​of homopolymers are listed in Polymer Handbook, 2 nd edition, J. Wiley & Sons, New York (1975).

[0039] The molecular weight of the oxidized starch is preferably 50,000-1,000,000 g / mol, more preferably 70,000-600,000 g / mol, and most preferably 100,0000-400,000 g / mol.

[0040] The oxidized starch has a carboxyl content expressed as sodium carboxylate of preferably 0.1 to 6.0% by weight, more preferably 3.0 to 5.0% by weight, based on the total weight of the oxidized starch.

[0041] The weight-average particle size Dw of the oxidized starch is preferably 100-5000 nm, more preferably 200-3000 nm, and most preferably 300-1000 nm. The parameters Dw and Dn and the particle size distribution are determined by laser diffraction and laser scattering of the starch hybrid copolymer, using an LS13320 instrument with a PVAC.RF780D optical model from Beckmann-Coulter, including a PIDS, after sufficient dilution of the aqueous polymer dispersion with completely demineralized water, in accordance with the instrument manufacturer's operating procedures.

[0042] The solubility of the oxidized starch at 60° C. is preferably 25-50 g / L water, more preferably 30-45 g / L water, and most preferably 33-39 g / L water.

[0043] The Brookfield viscosity of the aqueous solution of oxidized starch is preferably 2-1,500 mPas, more preferably 4-1,000 mPas, even more preferably 6-500 mPas, and most preferably 8-300 mPas (measured using a Brookfield viscometer at 60° C. and 20 rpm, with a solution solid content of 10%). Such a viscosity is particularly advantageous for achieving the objectives and advantageous effects of the present invention, in particular for obtaining a starch hybrid copolymer film having improved homogeneity and better mechanical properties.

[0044] The gelatinization temperature of the oxidized starch is preferably between 45°C and 90°C, more preferably between 50°C and 85°C, and most preferably between 53°C and 75°C. The gelatinization temperature is a well-established parameter in starch technology. Starch gelatinization is a process in which the intermolecular bonds of starch molecules break down in the presence of heat and water, ultimately dissolving the starch in water. The temperature at which gelatinization begins is characteristic of the starch material. The proposed gelatinization temperature also contributes to better achieving the objectives of the present invention, particularly obtaining stable aqueous dispersions or avoiding gelatinization.

[0045] The starch hybrid copolymer is preferably based on 5 to 59 wt%, more preferably 10 to 50 wt%, most preferably 15 to 45 wt% oxidized starch, based on the dry weight of the starch hybrid copolymer.The starch content of the starch hybrid copolymer can generally be determined by NMR spectroscopy.

[0046] Typical sources for preparing oxidized starch can be derived, for example, from tubers or roots, such as potatoes, arrowroot (arrowroot flour), cassava (tapioca flour), or sweet potatoes (sweet potatoes); cereal seeds, such as wheat, corn, rye, rice, barley, millet, oats, triticale, or sorghum; fruits, such as bananas, chestnuts, acorns, peas, beans, or other legumes, or pith, such as sago. The oxidized starch is preferably derived from tubers or roots, such as, more particularly, potatoes or cassava (tapioca flour), or cereals, such as, more particularly, wheat or corn. The oxidized starch can also be obtained from waste, such as potato residues or potato peels.

[0047] Oxidized starch can be produced using conventional methods for this purpose. Starch can be oxidized by typical oxidizing agents, such as persulfates, peroxides, permanganates, perborates, or preferably hypochlorites, particularly sodium hypochlorite. The oxidation reaction can be achieved in a variety of ways, but is generally carried out simply by slurrying the raw starch in an aqueous solution and oxidizing it in this medium with an oxidizing agent. The oxidation reaction is generally carried out under alkaline conditions. The extent to which the starch can be oxidized can vary widely in a conventional manner and will depend in part on the nature of the oxidizing agent utilized and the conditions under which the reaction is completed. Sodium hypochlorite-oxidized starch has been found to be particularly useful in the present invention.

[0048] Oxidized starch is also commercially available, for example from the company Samyang under the trade name Sunsize C3011 or from the company Deasang.

[0049] The fraction of oxidized starch is preferably ≥ 50 wt%, more preferably ≥ 90 wt%, even more preferably ≥ 95 wt%, each based on the total weight including starch.Most preferably, the starch present is exclusively oxidized starch.

[0050] In addition to oxidized starch, one or more additional starch types may also be applied. This additional starch is different from oxidized starch and does not contain oxidized starch. This additional starch may, for example, be native, degraded, or chemically modified. Native starch typically contains amylose and / or amylopectin as main components. Native starch is typically not degraded and is not chemically modified and is not oxidized. Degraded starch typically has a lower average molecular weight than native starch. Starch degradation can occur, for example, enzymatically or by exposure to acid or alkali, more particularly by hydrolysis. This typically also results in an increase in the level of oligosaccharides or dextrins. Typically, by chemical modification, chemical groups are attached to the starch by covalent addition. For example, for chemical modification, native or degraded starch can be used. Therefore, chemical modification is typically different from degradation. Examples of chemical modification are esterification or etherification, such as carboxymethylation or nonionic, anionic or cationic modification. Examples of chemically modified starches are carboxymethyl-, methyl-, hydroxyethyl-, or hydroxypropyl-starch, starch ethers, or starch phosphates.

[0051] The starch hybrid copolymer is preferably not based on such additional starch.

[0052] The starch hybrid copolymer may optionally be protective colloid-stabilized or preferably emulsifier-stabilized. In a preferred embodiment, the starch hybrid copolymer is not protective colloid-stabilized.

[0053] Examples of protective colloids are polyvinyl alcohol, polyvinyl acetal, polyvinyl pyrrolidone, copolymers of (meth)acrylates with carboxyl-functional comonomer units, poly(meth)acrylamides, polyvinylsulfonic acid and copolymers thereof, melamine-formaldehydesulfonates, naphthalene-formaldehydesulfonates, styrene-maleic acid copolymers and vinyl ether-maleic acid copolymers. Preferred protective colloids are partially hydrolyzed polyvinyl alcohols, preferably with a degree of hydrolysis of 80 to 95 mol %, more particularly 85 to 92 mol %. Polyvinyl alcohol is preferably dissolved in a 4% strength aqueous solution. The viscosity is 1 to 30 mPas, more particularly 3 to 15 mPas (20 ° C The protective colloid can be obtained by methods known to those skilled in the art.

[0054] The protective colloid fraction is preferably 0-30 wt%, more preferably 0.1-25 wt%, even more preferably 0.5-20 wt%, based on the total weight of the starch hybrid copolymer.

[0055] Most preferably, the starch hybrid copolymer is not protective colloid-stabilized.

[0056] Starch hybrid copolymers are preferably not stabilized with starch. The starch contained in starch hybrid copolymers generally does not act as a protective colloid. In starch-stabilized polymers, the starch and polymer generally exist only in the form of aggregates and / or blends. In starch-stabilized polymers, the starch is substantially not attached to the polymer. Therefore, starch hybrid copolymers are generally not starch-stabilized polymers.

[0057] Anionic, cationic or nonionic emulsifiers may be included. Anionic emulsifiers are preferred, and nonionic emulsifiers are particularly preferred.

[0058] Examples of anionic emulsifiers are alkyl sulfates, alkyl sulfonates or alkyl carboxylates having a chain length of 8 to 18 carbon atoms, alkyl or alkylaryl ether sulfates, sulfonates or carboxylates having 8 to 18 carbon atoms and up to 40 ethylene oxide or propylene oxide units in the hydrophobic group, alkyl or alkylaryl sulfonates having 8 to 18 carbon atoms, full and monoesters of sulfosuccinic acid with monohydric alcohols or alkylphenols, or phosphates, ether phosphates, phosphonates and ether phosphonates, and combinations thereof.

[0059] Examples of nonionic emulsifiers are alkylpolyglycol ethers or alkylarylpolyglycol ethers having 8 to 40 ethylene oxide units or ethylene oxide / propylene oxide block copolymers or generally EO-PO copolymers having 2 to 40 EO and / or PO units, and also alkylpolyglycosides having 1 to 20 carbon atoms and etheralkylpolyglycosides having 2 to 40 EO and / or PO units, or combinations thereof.

[0060] The emulsifier fraction is preferably 0-10 wt%, more preferably 0.1-5 wt%, most preferably 0.5-3 wt%, based on the total weight of the starch hybrid copolymer.

[0061] The starch hybrid copolymer in the form of an aqueous dispersion preferably has a solids content of 10-80%, more preferably 30-70%, even more preferably 40-60%.

[0062] The Brookfield viscosity of the aqueous dispersion of the starch hybrid copolymer is preferably 50 to 50,000 mPas, more preferably 100 to 25,000 mPas, even more preferably 600 to 10,000 mPas (measured with a Brookfield viscometer at 23° C. and 20 rpm, with a solids content of 50%).

[0063] The aqueous dispersion of the starch hybrid copolymer preferably has a lower viscosity than a blend of only the corresponding amount of starch and the corresponding copolymer.

[0064] The weight average particle size Dw of the starch hybrid copolymer is preferably 100-10,000 nm, more preferably 200-8,000 nm, most preferably 300-6,000 nm. Dw is determined as described for oxidized starch.

[0065] In the starch hybrid copolymer, the oxidized starch is preferably linked to the polymer of ethylenically unsaturated monomers via a covalent bond. The linking can be carried out, for example, by grafting as part of a free radical-initiated polymerization or by a condensation reaction. A measure of the grafting density of the starch hybrid copolymer is the grafting rate. The grafting rate of the starch hybrid copolymer is preferably 40-85%, more preferably 40-80%, and most preferably 40-75%. The grafting rate is determined by the following method. A dry film of the starch hybrid copolymer is continuously extracted with toluene in a Soxhlet extractor. The insoluble portion of the film remaining in the extraction sleeve is the grafted portion of the starch hybrid copolymer. The insoluble portion is dried to obtain fraction 1. The portion swollen in the solvent is also dried to obtain fraction 2. The ratio of the weight of fraction 2 to the weight of fraction 1 gives the grafting rate.

[0066] The starch hybrid copolymer preferably does not have a core-shell structure. The monomers are preferably copolymerized statistically. The oxidized starch is preferably added statistically to the starch hybrid copolymer.

[0067] Another subject of the present invention is a process for preparing starch hybrid copolymers in the form of aqueous dispersions or water-redispersible powders, comprising free-radically initiated polymerization (more particularly emulsion polymerization) in an aqueous medium of ethylenically unsaturated monomers in the presence of starch, and optionally subsequent drying, characterized in that

[0068] The starch comprises oxidized starch, and

[0069] The ethylenically unsaturated monomers include one or more vinyl esters and ethylene,

[0070] Wherein, based on the total weight of the ethylenically unsaturated monomers, the total amount of vinyl ester and ethylene is ≥ 81 wt %,

[0071] Thus, no ethylenically unsaturated monomers carrying allyl, epoxy, silane or N-methylol groups are copolymerized.

[0072] The polymerization temperature is preferably from 40 to 120° C., more preferably from 50 to 95° C. In the case of copolymerization of gaseous comonomers such as ethylene, 1,3-butadiene or vinyl chloride, it is also possible to operate at superatmospheric pressure, generally between 5 and 100 bar.

[0073] The pH before and / or during polymerization is preferably between 3 and 10, more preferably between 3 and <5. The pH can be controlled in conventional ways, for example by adding conventional acids, bases, or preferably buffers. Examples of pH regulators are NH4OH, NaOH, sodium bicarbonate, sodium carbonate, or mixtures thereof. Such measures also contribute to better achieving the objectives of the present invention, in particular obtaining stable aqueous dispersions or avoiding gelation.

[0074] Suitable free radical initiators are common oil-soluble or water-soluble initiators. Examples of oil-soluble initiators are oil-soluble peroxides, such as tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxypivalate, tert-butyl peroxyneodecanoate, dibenzoyl peroxide, tert-amyl peroxypivalate, di(2-ethylhexyl) peroxydicarbonate, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, di(4-tert-butylcyclohexyl) peroxydicarbonate, dilauroyl peroxide, cumyl hydroperoxide or oil-soluble azo initiators, such as azobisisobutyronitrile or dimethyl 2,2'-azobis(2-methylpropionate). Examples of water-soluble initiators are peroxodisulfates, such as potassium peroxodisulfate, hydrogen peroxide, water-soluble hydroperoxides such as tert-butyl hydroperoxide, manganese(III) salts or cerium(IV) salts. In each case, the amount of initiator used is generally 0.005-3.0 wt %, preferably 0.01-1.5 wt %, based on the total weight of the ethylenically unsaturated monomers. Preferably, a redox initiator is used. The redox initiator used is a combination of the initiator and a reducing agent. Examples of suitable reducing agents are sodium sulfite, iron (II) salts, sodium hydroxymethanesulfinate, particularly ascorbic acid and isoascorbic acid or their salts, preferably alkali metal salts. Preferred redox initiators are cerium (IV) salts, such as ammonium cerium (IV) nitrate, manganese (III) salts or peroxodisulfates, particularly hydrogen peroxide or water-soluble hydroperoxides, such as tert-butyl hydroperoxide. When a reducing agent is used, the amount of the reducing agent is preferably 0.01-0.5 wt %, based on the total weight of the ethylenically unsaturated monomers.

[0075] Redox initiators, in particular the preferred reducing agents and / or redox initiators mentioned above, are particularly useful for solving the objects and achieving the beneficial effects of the present invention, such as biodegradability.

[0076] The reaction mixture can be stabilized, for example, by means of protective colloids and / or preferably emulsifiers, preferably as described above.

[0077] The polymerization can be carried out with all or individual components of the reaction mixture included in the initial charge, or with some of the components included in the initial charge and subsequently metered, or by a metering process without an initial charge. The procedure is preferably such that at least a portion, preferably the entire amount, of the starch, in particular the oxidized starch, is included in the initial charge, in particular in water. The ethylenically unsaturated monomers and initiator are included completely or preferably partially in the initial charge, and, where appropriate, the remainder of the ethylenically unsaturated monomers and initiator is metered in. In the case of a batch process, the monomers and starch and a portion of the initiator are included in the initial charge in water, and the remainder of the initiator is metered in or added in pulses.

[0078] Emulsifiers and / or protective colloids, if applied, are preferably applied in the initial charge.

[0079] Most preferably, starch, particularly oxidized starch, and optionally an emulsifier and / or protective colloid, and optionally one or more additives, are first dispersed or dissolved in water and then combined with the ethylenically unsaturated monomer and initiator as described above. The starch, particularly oxidized starch, and optionally an emulsifier and / or protective colloid, and optionally one or more additives, are preferably mixed in water at a temperature of 55 to 95°C. The resulting solution can be applied directly to the process or pre-cooled to a suitable temperature, such as room temperature. The starch, particularly oxidized starch, is thereby preferably gelled or emulsified. Such measures also contribute to better achieving the objectives of the present invention, particularly obtaining a stable aqueous dispersion or avoiding gelling.

[0080] After the polymerization is completed, the pH is preferably adjusted to 3 to 10, more preferably to 4 to 9, even more preferably to >5 to 8, and most preferably to 7 to 8. The above describes exemplary measures for adjusting the pH. Such measures also contribute to better achieving the objectives of the present invention, in particular, obtaining a stable aqueous dispersion or avoiding gelation.

[0081] After the polymerization is complete, one or more additives, such as defoamers, can be added to the resulting polymer dispersion. Examples of defoamers are oil-based defoamers, water-based defoamers, in particular silicone-based defoamers, EO / PO-based defoamers, alkyl polyacrylates, or mixtures thereof. Preferably, the additive, in particular the defoamer, is present in an amount of up to 3% by weight, in particular 0.1-1.5% by weight, based on the starch hybrid copolymer.

[0082] After the polymerization is complete, residual monomers can be removed by post-polymerization using known methods. Volatile residual monomers and other volatile components can also be removed by distillation or stripping, preferably under reduced pressure.

[0083] Aqueous dispersions of starch hybrid copolymers can be converted into starch hybrid copolymers in the form of water-redispersible powders by drying. For this purpose, the aqueous dispersion is usually admixed with a drying aid, preferably in an amount of 0.5 to 30% by weight, more particularly 5 to 20% by weight, based on the solids content of the aqueous dispersion. The total amount of drying aid and, if applicable, protective colloid before the drying operation is preferably 1 to 30% by weight, based on the solids content of the aqueous dispersion. Examples of drying aids are the aforementioned protective colloids.

[0084] The aqueous dispersion can be dried, for example, by fluidized bed drying, freeze drying or preferably spray drying. Spray drying can be carried out in conventional spray drying units, wherein the atomization can be carried out using a single, two or more fluid nozzles or using a rotating disk. Depending on the unit, the Tg of the starch hybrid copolymer and the desired drying level, the outlet temperature selected is generally in the range of 45° C. to 120° C., preferably 60° C. to 90° C. The viscosity of the feed for atomization is adjusted to a value of <500 mPas (Brookfield viscosity at 20 rpm and 23° C.), preferably <250 mPas, via the solids content. The solids content of the dispersion for atomization is preferably 30-75% by weight, more preferably 50-60% by weight.

[0085] In many cases, amounts of up to 1.5% by weight of defoamer, based on the starch hybrid copolymer, have proven useful. The defoamer is preferably added during atomization.

[0086] In order to extend the shelf life by improving adhesion stability, particularly in the case of starch hybrid copolymer powder with low glass transition temperature, the obtained powder can be equipped with, for example, one or more anti-blocking agents (anti-caking agents). Anti-blocking agent is preferably not added to the aqueous starch hybrid copolymer dispersion, i.e., preferably not before drying, but preferably during or after drying, more specifically during drying, added to the spray drying unit. Based on the gross weight of the polymer component, preferred powder includes anti-blocking agent, more particularly 1-30 weight %. The example of anti-blocking agent is Ca and / or Mg carbonate, talc, gypsum, silicon dioxide, kaolin such as metakaolin, silicate, preferably with a particle size in the range of 10nm to 10 μm.

[0087] The starch hybrid copolymers are generally suitable as binders for coating compositions or adhesive bonding compositions, in particular for paints, fibers, textiles, leather, paper or carpets. Particularly preferred uses of the starch hybrid copolymers are as binders for bonding fiber materials, more particularly for the production of textiles (e.g. nonwovens, woven and knitted fabrics, leather and rugs or carpets), or as binders for architectural coatings, more particularly aqueous emulsion paints or powder paints.

[0088] Preferred is the use of the starch hybrid copolymer in an adhesive or coating composition for the preparation of flexible packaging, food containers, coffee capsules, straws, covering films, insecticide coatings or fishing nets, or in a composition for 3D printing.

[0089] Furthermore, starch hybrid copolymers are also suitable for chemical products in the construction industry. They can be used alone or in combination with conventional polymer dispersions or dispersion powders, optionally in combination with hydraulic binders such as cement (Portland cement, aluminate cement, pozzolana cement, blast furnace cement, magnesia cement, or phosphate cement), gypsum, and water glass, to produce leveling compositions, construction adhesives, renders, filling compounds, joint mortars, grouts, integrated exterior coating systems, or paints such as powder paints. Among construction adhesives, tile adhesives or adhesives for exterior insulation systems are preferred applications. Leveling compositions are also preferred; preferred leveling compositions are self-leveling floor filling compounds and screeds.

[0090] The starch hybrid copolymers of the present invention advantageously enable the use of renewable raw material starch in polymer applications. Thus, the starch hybrid copolymers show excellent biodegradability, even under home composting conditions. The starch hybrid copolymers of the present invention in the form of aqueous dispersions, water-redispersible powders or corresponding aqueous dispersions are advantageously stable in storage, do not show a tendency to separate or gel, and can approach a homogeneous composition, preferably even in the case of aqueous dispersions with starch hybrid copolymers having a high solids content. The starch hybrid copolymers of the present invention are also preferably compatible with other formulation ingredients, such as petrochemical polymers or biopolymers. Surprisingly, the aqueous dispersions of the starch hybrid copolymers of the present invention are even more stable and provide better film-forming and mechanical properties than corresponding dispersions of copolymers stabilized by starch as a protective colloid or containing starch added after polymerization.

[0091] Additionally, aqueous dispersions of starch hybrid copolymers can have a low viscosity, which facilitates their processing in application formulations and enables the handling of dispersions with a higher solids content.

[0092] Films from the starch hybrid copolymers of the invention are advantageously homogeneous and exhibit even advantageous mechanical properties, in particular advantageous elongation or flexibility, impact strength.

[0093] The following examples are provided to further illustrate the present invention.

[0094] Example 1:

[0095] Starch hybrid copolymer with 20% oxidized starch:

[0096] Under stirring, the following materials were added to a laboratory autoclave (5 L):

[0097] 1545g deionized water,

[0098] 4.36g citric acid,

[0099] 0.764g sodium citrate,

[0100] 16.4 g sodium vinyl sulfonate (25%) and

[0101] 493 g of oxidized starch "SUN-SIZE" (trade name of Samyang Corporation; Mw ˜700,000 g / mol).

[0102] The pH was adjusted to 4.0, and 1.20 g of ammonium iron(II) sulfate was added. The autoclave was then evacuated and filled with nitrogen. 1397 g of vinyl acetate was added, the reactor was heated to 40°C, and 300 g of ethylene was injected. A 3% aqueous solution of tert-butyl hydroperoxide (TBHP) was then started at a rate of 45.3 g / h, and a 5.7% aqueous solution of sodium isoascorbate was started at a rate of 45.0 g / h. After the reaction began, the initiator rate decreased, as evident from the increase in internal temperature (TBHP 16.6 g / h, sodium isoascorbate 16.4 g / h). From the start of the reaction, the internal temperature increased from 55°C to 60°C at a rate of 0.25°C / min. Sixty minutes after the start of the reaction, 246 g of vinyl acetate was metered at a rate of 123 g / h. After the monomer feed was complete, the initiator feed was continued for an additional 60 minutes. The batch was then cooled to 30°C and the pressure was let down. 0.854 g Silfoam SE2 (silicone-based defoamer emulsion) was added, followed by postpolymerization with 11.5 g TBHP (10%) and 22.6 g sodium isoascorbate (6.25%). The batch was adjusted to a pH of 6.0 with ammonia (12.5%) and preserved with hydrogen peroxide (10%).

[0103] The properties of the aqueous dispersion are listed in Table 1 below.

[0104] Comparative Example 2:

[0105] Blend of vinyl acetate-ethylene copolymer dispersion with 20% oxidized starch:

[0106] A vinyl acetate-ethylene copolymer dispersion (85% by weight of vinyl acetate, 15% by weight of ethylene) was mixed with 20% of oxidized starch "SUN-SIZE" (trade name of Samyang; Mw ˜700,000 g / mol).

[0107] The properties of the aqueous dispersion are listed in Table 1 below.

[0108] Comparative Example 3:

[0109] Starch hybrid copolymer with 20% native starch:

[0110] Comparative Example 3 was carried out in the same manner as Example 1, with the only difference being that the oxidized starch SUN-SIZE was replaced by the natural starch CornStarch produced by Samyang Company.

[0111] The properties of the aqueous dispersion are listed in Table 1 below.

[0112] Table 1: Characterization of the dispersions of the invention and (comparative) examples 1 to 3:

[0113]

[0114] Determination of biodegradability:

[0115] The starch hybrid copolymers from the (comparative) examples were each applied to cellulose powder and tested for anaerobic biodegradability according to ISO 14855-1 and the EL724 method at 58±2° C. for 45 days. The biodegradability was calculated relative to the cellulose.

[0116] The test results are given in Table 2 below.

[0117] Table 2: Biodegradability test results:

[0118]

[0119] Compared to the blend of Comparative Example 2, the starch hybrid copolymer of Example 1 exhibited significantly higher biodegradability, and a relative degradation rate of about 70.1% was achieved in 45 days, as shown in Table 2.

[0120] Compared with the starch hybrid copolymer with native starch shown in Comparative Example 3, the starch hybrid copolymer of the present invention of Example 1 also provides better biodegradability.

[0121] The starch hybrid copolymer dispersion of Example 1 also exhibits favorable storage stability, forms a uniform film, such as elongation, and the obtained film has beneficial mechanical properties.

[0122] Furthermore, the aqueous dispersions of the starch hybrid copolymers of Example 1 exhibit lower viscosities compared to the dispersions of the comparative examples, which facilitates their processing in application formulations and enables the handling of dispersions with higher solids contents.

Claims

1. A starch hybrid copolymer in the form of an aqueous dispersion or water-redispersible powder, obtainable by free-radically initiated polymerization in an aqueous medium of ethylenically unsaturated monomers in the presence of starch and optionally subsequent drying, characterized in that The starch includes oxidized starch, and The ethylenically unsaturated monomers include one or more vinyl esters and ethylene, The total amount of vinyl ester and ethylene is ≥ 81 wt %, based on the total weight of the ethylenically unsaturated monomers, and no ethylenically unsaturated monomers having allyl groups, epoxy groups, silane groups or N-methylol groups are copolymerized.

2. The starch hybrid copolymer in the form of an aqueous dispersion or a water-redispersible powder according to claim 1, characterized in that The starch hybrid copolymer is based on 40 to 80 weight percent vinyl ester, based on the dry weight of the starch hybrid copolymer.

3. The starch hybrid copolymer in the form of an aqueous dispersion or a water-redispersible powder according to claim 1 or 2, characterized in that The starch hybrid copolymer is based on 1 to 45 weight percent ethylene, based on the dry weight of the starch hybrid copolymer.

4. The starch hybrid copolymer in the form of an aqueous dispersion or a water-redispersible powder according to any one of claims 1 to 3, characterized in that The total amount of vinyl ester and ethylene is ≥ 91 wt%, based on the total weight of the ethylenically unsaturated monomers.

5. The starch hybrid copolymer in the form of an aqueous dispersion or a water-redispersible powder according to any one of claims 1 to 4, characterized in that The total amount of vinyl ester and ethylene is 41 to 95 wt % based on the dry weight of the starch hybrid copolymer.

6. The starch hybrid copolymer according to any one of claims 1 to 5 in the form of an aqueous dispersion or a water-redispersible powder, characterized in that The ethylenically unsaturated monomers consist of one or more vinyl esters and ethylene.

7. The starch hybrid copolymer in the form of an aqueous dispersion or a water-redispersible powder according to any one of claims 1 to 6, characterized in that The oxidized starch has a carboxyl content expressed as sodium carboxylate of 0.1 to 6.0 wt % based on the total weight of the oxidized starch.

8. The starch hybrid copolymer in the form of an aqueous dispersion or a water-redispersible powder according to any one of claims 1 to 7, characterized in that The Brookfield viscosity of the aqueous solution of the oxidized starch is 2-1,500 mPas (measured using a Brookfield viscometer at 60° C. and 20 rpm, with a solid content of 10%).

9. The starch hybrid copolymer in the form of an aqueous dispersion or a water-redispersible powder according to any one of claims 1 to 8, characterized in that The starch hybrid copolymer is based on 5 to 59 wt% of oxidized starch, based on the dry weight of the starch hybrid copolymer.

10. The starch hybrid copolymer in the form of an aqueous dispersion or a water-redispersible powder according to any one of claims 1 to 9, characterized in that The fraction of oxidized starch is ≥ 50 wt. %, based on the total weight of the starches included overall.

11. The starch hybrid copolymer in the form of an aqueous dispersion or a water-redispersible powder according to any one of claims 1 to 10, characterized in that The Brookfield viscosity of the aqueous dispersion of the starch hybrid copolymer is 50 to 50,000 mPas (measured with a Brookfield viscometer at 23° C. and 20 rpm, with a solid content of 50%).

12. A process for preparing starch hybrid copolymers in the form of aqueous dispersions or water-redispersible powders, comprising free-radically initiated polymerization in an aqueous medium of ethylenically unsaturated monomers in the presence of starch and optionally subsequent drying, characterized in that The starch includes oxidized starch, and The ethylenically unsaturated monomers include one or more vinyl esters and ethylene, The total amount of vinyl ester and ethylene is ≥81% by weight, based on the total weight of the ethylenically unsaturated monomers, and no ethylenically unsaturated monomers carrying allyl groups, epoxy groups, silane groups or N-methylol groups are copolymerized.

13. The method for preparing a starch hybrid copolymer in the form of an aqueous dispersion or a water-redispersible powder according to claim 12, characterized in that The pH before and / or during the polymerization is 3 to ≤5, and after completion of the polymerization, the pH is adjusted to >5 to 10.

14. Use of the starch hybrid copolymer according to any one of claims 1 to 11 in the form of an aqueous dispersion or water-redispersible powder in adhesives or in coating compositions or in chemical products for the construction industry.

15. Use of the starch hybrid copolymer in the form of an aqueous dispersion or water-redispersible powder according to any one of claims 1 to 11 in an adhesive or coating composition for preparing flexible packaging, food containers, coffee capsules, straws, covering films, insecticide coatings or fishing nets, or in a composition for 3D printing.

Images