Emulsions from oxidation products of natural waxes with excellent barrier properties

Abstract

The present invention relates to emulsions from oxidation products of natural waxes having excellent barrier properties, to a method for producing such emulsions, and to cellulosic textile products or biopolymers coated with such emulsions from oxidation products of natural waxes. The present invention further relates to the use of such emulsions for coating substrates comprising cellulosic textiles or biopolymers.

Description

[Technical field]

[0001] The present invention relates to a natural wax-oxide emulsion for forming a water (vapor) barrier layer having excellent barrier properties, a method for producing said emulsion, and an article made of cellulose fibers or biopolymers coated with said emulsion. The present invention further relates to the use of said emulsion for coating a substrate comprising cellulose fibers or biopolymers. [Background technology]

[0002] A wide variety of packaging materials are required in the food and consumer goods industry, and for industrial products. Packaging of moisture-sensitive or water-containing goods must be protected from water penetration into the package. For this purpose, water-impermeable films or coated cellulosic substrates, such as coated paper or coated paperboard, are used.

[0003] Suitable coating materials for cellulosic substrates are thin impermeable polymer layers or water-repellent waxy coatings. Another factor here is the interaction of the coating with the object to be packaged. For food and beverage packaging, it is therefore preferable to use packaging materials that are free of substances of health concern, such as MOSH / MOAH, phthalates and other plasticizers from mineral oil fractions. Coatings of natural renewable waxes are therefore particularly suitable and have already been described many times in the literature.

[0004] For example, EP 3781485 describes a composition for impregnation of paper and paperboard containing vegetable waxes, such as sugarcane wax and / or rice bran wax. The composition is formed into pellets containing sugarcane wax and / or rice bran wax and can be applied as a barrier layer on a corresponding machine. Both sugarcane wax and rice bran wax, when applied alone to paper, initially adhere but delaminate from the paper substrate during prolonged contact with hot water. It has been observed that a waterproof layer consisting of a mixture of sugarcane wax and rice bran wax remains adherent and waterproof for a long time, even when in contact with hot water.

[0005] Heinrich et al. (2003) describe the water vapor barrier properties of beeswax, candelilla wax, rice wax and sunflower wax. Rice wax exhibits the highest water vapor permeability and the lowest barrier properties of all the waxes tested.

[0006] WO2006137274 describes a polymer composition containing rice bran wax suitable for forming a biodegradable thin layer barrier, and a laminate containing the same. The coating composition is anhydrous.

[0007] What the described natural wax-containing barrier coatings have in common is that they are applied from the melt and therefore require special equipment for the coating operation. Furthermore, the coatings require the input of thermal energy to convert the composition into the melt, which makes the application of the barrier layer energy intensive.

[0008] Patent document 3 (WO2007 / 061592) describes, inter alia, a composition for use in the manufacture of edible biodegradable containers comprising water, pregelatinized and natural starches, and a wax emulsion, the composition consisting essentially of food-grade materials.

[0009] The preferred wax emulsions are stable aqueous emulsions, usually consisting of carnauba wax, candelilla wax, rice bran wax, paraffin wax or another food grade wax. The wax used is bleached wax that has not been subjected to further oxidation, and the acid number of the bleached wax closely matches the acid number of the raw wax. The emulsions are produced using emulsifiers.

[0010] Preferred examples of wax emulsions known from WO2007 / 061592 as suitable for use in formulations are emulsified carnauba wax and emulsified candelilla wax. The emulsifiers mentioned are all emulsifiers approved for food use, in particular sorbitan monostearate, polysorbate 60, polysorbate 65, polysorbate 80, food-grade gums (e.g. arabinogalactan, carrageenan, furaceran, xanthan), stearyl monoglyceridyl citrate, succinstearin and hydroxylated lecithin. Wax emulsions are said to increase the water resistance of the composition, but do not help to form a barrier layer.

[0011] DE 102014001709 A discloses aqueous natural wax oxide emulsions with cationic emulsifiers, however, the document does not disclose aqueous natural wax oxide emulsions with anionic or nonionic emulsifiers.

[0012] Patent document 5 (US2007068642A1) discloses wax-containing emulsions for coating paper substrates or fruits. The waxes described are "palm wax" and "soy wax", which are partially and completely hydrogenated oils obtained by hydrogenation of triglycerides forming soybean oil and palm oil. In this way, palm or soy wax is obtained by reduction, which reduces the double bonds of the unsaturated fatty acids. Therefore, "palm and soy wax" are chemically completely different substances from natural wax oxides, which are produced from pure natural waxes, usually from monovalent esters of long-chain fatty acids. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] EP3781485 [Patent Document 2] WO2006137274 [Patent Document 3] WO2007 / 061592 [Patent Document 4] DE102014001709A [Patent Document 5] US2007068642A1 [Non-patent literature]

[0014] [Non-Patent Document 1] Heinrich et al., Powder Technology 357, 2019, 223-231 Summary of the Invention [Problem to be solved by the invention]

[0015] There is a need for a natural wax-containing coating that can be applied to polysaccharide substrates without heat input and that can form a barrier layer against water and water vapor. Moreover, such a natural wax-containing coating is also suitable for water (vapor) permeable polymer substrates and could potentially be used for water (vapor) permeable plastic films, such as biopolymer films, especially polylactic acid (PLA) films. The barrier layer should not require the addition of polymers or film formers, as far as possible, as they would adversely affect the barrier properties, should show good adhesion on the substrate, be applicable in thin layers, and be flexible enough not to become brittle or porous. [Means for solving the problem]

[0016] Surprisingly, it has been found that this object is achieved by an aqueous natural wax oxide emulsion comprising (a) at least one natural wax oxide having an acid number to OH number ratio of 1 or greater, and (b) at least one anionic or nonionic emulsifier.

[0017] Such emulsions are stable and therefore can be applied without difficulty to polysaccharide or biopolymer-containing substrates, preferably cellulosic substrates, forming a uniform layer that conforms and adheres to the substrate.

[0018] Emulsifiers refer to aids for the preparation and stabilization of emulsions, which serve to blend and stabilize two mutually immiscible liquids, such as oil and water, to obtain a finely divided mixture called an emulsion. The state is similar to mixing a solid insoluble substance with a liquid to produce a so-called suspension. This property is possessed by molecules with phase mediating properties, such as surfactants. Surfactants contain simultaneously hydrophobic and hydrophilic molecular parts and are therefore able to form micelles around finely divided droplets or particles (e.g. wax particles) and stabilize them in the dispersion medium (e.g. water) against aggregation and sedimentation. Here we distinguish between nonionic and ionic surfactants. The former contain partial charges, whereas in the case of ionic surfactants, the polar molecular part is represented by an ion. Thus, there are anionic, cationic and zwitterionic surfactants.

[0019] Suitable natural wax oxides can be emulsified in water by emulsifying with water and a specifically adapted emulsifier system with stirring at a temperature above the melting point of the wax, and then the emulsion thus formed can be cooled with stirring. The wax suspension thus made is referred to in industry as a "wax emulsion".

[0020] Here, nonionic or ionic emulsifier systems or a combination of the two can be used. Ionic emulsifiers can also be generated in the reaction mixture, for example by hydrolysis of wax or oil acids with alkaline medium or amines.

[0021] Suitable emulsifiers for the natural wax oxide emulsions are in particular anionic and nonionic emulsifiers, such as the emulsifiers Genapol® or Hostapur® from Clariant International.

[0022] The invention further provides methods for producing such emulsions and their use in producing coated polysaccharide- or biopolymer-containing substrates.

[0023] The application of aqueous emulsions has the advantage that no heating is required for application and thinner, more flexible layers can be applied. The method is energetically advantageous compared to prior art coating methods, providing benefits in terms of resource utilization and facilitating paper recycling. The emulsion-applied layers have a very low water vapor permeability, which clearly reduces the water absorption of hydrophilic substrates. Furthermore, the layers are very homogeneous and non-porous, resulting in an excellent barrier effect. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 shows the Algro Finesse and Kohler Cobb values ​​of the coating substrates in the examples. [Diagram 2] FIG. 2 shows the water vapor transmission rate Q100 of each barrier layer in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The production of the natural wax oxides in the natural wax oxide-containing emulsion can be carried out, for example, using known oxidation methods, which not only oxidize the natural wax itself and increase the acid number of the natural wax oxide by at least 5 mg KOH / g, preferably at least 10 mg KOH / g, measured according to ISO 3681, compared to the starting material (generally natural wax or bleached natural wax), but also oxidize impurities in the wax and bleach the wax. These include oxidation with chromic acid, chromic sulfuric acid (chromium trioxide and sulfuric acid) and dichromate, thermal oxidation with oxygen, which can be carried out using a catalyst, electrochemical oxidation of all kinds, etc.

[0026] Suitable natural wax oxides are in particular those produced by oxidation of pure natural wax, by which is meant natural wax that is already in wax form as a raw material and does not require further chemical conversion in order to be considered a wax.

[0027] Preferred are natural waxes formed from monovalent esters of long-chain fatty acids. Particularly preferred are oxides of rice bran wax, oxides of corn wax, oxides of sugarcane wax, oxides of sunflower wax and oxides of carnauba wax. More preferred is oxides of rice bran wax.

[0028] The natural wax oxide preferably has an acid value of 1 to 140 mgKOH / g, preferably 15 to 140 mgKOH / g, more preferably 30 to 140 mgKOH / g, as measured according to ISO 2114. It is further preferable that the acid value is 15 to 110 mgKOH / g, or 30 to 110 mgKOH / g.

[0029] These acid number ranges are achieved by oxidation alone and do not require an additional esterification step. Such natural wax oxides are polar enough to be more easily emulsified in water, but not so polar that the barrier layer has defects in its microstructure that would adversely affect its barrier effectiveness.

[0030] In a preferred embodiment, the at least one natural wax oxide in the emulsion of the present invention has a saponification number, measured according to ISO 3681, of 30 to 200 mg KOH / g, preferably 50 to 180 mg KOH / g, more preferably 80 to 170 mg KOH / g, and even more preferably 80 to 140 mg KOH / g.

[0031] The at least one natural wax oxide in the emulsion of the present invention preferably has a hydroxyl number, measured according to DGF M-IV6, of less than 8 mg KOH / g, preferably less than 5 mg KOH / g, which indicates more homogeneous material properties and thus a more homogeneous barrier layer with fewer microstructural defects.

[0032] In a preferred embodiment, the natural wax oxide has an iodine color number, measured according to DIN 6162, of less than 20, preferably less than 15, and more preferably less than 10. A low iodine color number indicates that the wax is particularly light in color and therefore does not adversely affect the color of the substrate.

[0033] The at least one natural wax oxide in the emulsion of the present invention preferably has a dropping point, measured according to ISO 2176, between 65 and 110° C. This means that a coating with good thermal stability can be obtained without the need to expend a lot of energy to melt the natural wax in the preparation of the natural wax emulsion.

[0034] To facilitate application of the aqueous natural wax emulsion and to obtain a barrier layer that is as thin and uniform as possible, the natural wax oxide is present in the emulsion in the range of 5 to 50% by weight, preferably in the range of 10 to 45% by weight, more preferably in the range of 15 to 40% by weight, and most preferably in the range of 20 to 35% by weight, based on the total weight of the emulsion.

[0035] In a preferred embodiment, the at least one emulsifier is an anionic or nonionic emulsifier. Hydrophobic waxes can be emulsified particularly easily with anionic or nonionic emulsifiers.

[0036] Anionic emulsifiers have an ammonia odor, which may cause discomfort to users. This can be avoided by using nonionic emulsifiers, preferably surfactants. Anionic emulsifiers have a relatively high pH, ​​which may have a negative effect in some applications. Therefore, nonionic emulsifiers are preferred in some applications, for example, in pH-sensitive products or cosmetic applications.

[0037] The properties of a nonionic emulsifier can be described by the mass ratio of the polar and non-polar parts of the surfactant, defined by the HLB value ("hydrophilic-lipophilic balance", the ratio of the hydrophilic and lipophilic properties of the molecule). The level of this hydrophilic-lipophilic ratio can be determined by calculating the values ​​of different regions of the molecule, as explained by Griffin (see, for example, Journal of Society of Cosmetic Chemists, Vol. 5 (No. 4), pp. 249-256 (1954)).

[0038] The Griffin method was developed mainly for nonionic surfactants. The HLB value is calculated by the following formula: HLB = 10 x Mh / M, where Mh is the molecular weight of the hydrophilic part of the molecule and M is the molecular weight of the whole molecule, on a scale of 0 to 20. An HLB value of 0 indicates a completely lipophilic molecule, and an HLB value of 20 indicates a completely hydrophilic molecule.

[0039] Surfactants with low HLB value have good fat dissolving properties, while high HLB value has good wetting of hydrophilic surfaces. Based on different HLB values, it is possible to form stable emulsions of O / W to W / O systems.

[0040] Oil-in-water emulsifiers (O / W emulsifiers) are understood to mean emulsifiers having a sufficiently high HLB value to give oil-in-water emulsions. The HLB value of such emulsifiers is usually greater than 8 and often ranges from 8 to 18. The nonionic emulsifiers stabilize the natural wax oxide-in-water emulsions of the invention and preferably have an HLB value of 11 to 19. The use of such nonionic emulsifiers makes it possible to particularly effectively stabilize the natural wax oxide emulsions. The HLB value is more preferably 13 to 18.

[0041] The nonionic emulsifiers preferably have an EO value of greater than 10 and up to 80 (the number of ethylene oxide units attached to a functional group).

[0042] The nonionic emulsifiers are preferably fatty alcohol polyglycol ethers, alcohol ethoxylates, such as fatty alcohol ethoxylates, and tributylphenol ethoxylates.

[0043] In another embodiment, the emulsifiers stabilizing the aqueous natural wax oxide emulsions are anionic emulsifier systems, because such systems are surprisingly very good at stabilizing the emulsion and forming a barrier layer, flexibility and stability, which has very good water stability and water vapor barrier action, which means that these emulsifiers are particularly suitable for applications where high water stability is required, such as wood care products.

[0044] The anion of the anionic emulsifier system can be obtained by adding a water-soluble or water-dispersible alkali metal hydroxide and / or basic ammonium compound to an organic acid having a linear aliphatic hydrocarbyl group having 12 to 24 carbon atoms. The anion is supplied as an alkali metal salt, preferably the sodium and / or potassium salt, or similar ammonium or substituted ammonium salt of a similar organic acid.

[0045] The term "ammonium salt" refers to the neutralization product obtained by the reaction of a surfactant acid with ammonia or an amine in an aqueous medium. The amine may be a volatile base such as, for example, morpholine, methylaminopropanol, diethylaminoethanol (DEAE), or a non-volatile base such as, for example, α,ω- and α,γ-substituted diamines such as, for example, monoethanolamine, triethanolamine, isopropanolamine, ethylenediamine, propylene-1,2-diamine, propylene-1,3-diamine, butylene-1,4-diamine, etc. DEAE, due to its basic properties, can form salts similar to organic acids.

[0046] The polar organic group of the salt or acid may be a carboxylate, sulfate or sulfonate ion, and the anion-providing compound may have two or more such polar groups.

[0047] Suitable organic acids providing the anion are, for example, natural and synthetic aliphatic carboxylic acids having 12 to 24 carbon atoms, such as myristic acid, palmitic acid, stearic acid, oleic acid and behenic acid, in particular those soaps obtained by cleavage of triglyceride oils, such as tallow fatty acid, which is a mixture of fatty acids consisting mainly of palmitic acid, stearic acid and oleic acid. The anion is preferably one in which an alkyl or alkenyl group having 16 to 24 carbon atoms is present.

[0048] Preferably, an oleic acid / ammonium hydroxide / KOH emulsifier system is used.

[0049] The amount of emulsifier used affects the stability of the suspension and the distribution and size of the wax particles. It has been found that a particularly thin and homogeneous barrier layer can be formed when the emulsifier is present in the emulsion in an amount ranging from 1 to 20% by weight, preferably from 2 to 15% by weight, based on the total weight of the emulsion.

[0050] The present invention further provides a method for producing an aqueous natural wax oxide emulsion, comprising the steps of: (a) providing a natural wax oxide and an anionic or nonionic emulsifier; and (b) emulsifying the natural wax oxide with the emulsifier in water at a temperature above the melting point of the natural wax oxide, wherein the natural wax oxide has an acid number to OH number ratio of at least 1. The natural wax oxide can be produced by the oxidation method described above.

[0051] The present invention further provides the use of the aqueous natural wax oxide emulsion of the present invention for coating a polysaccharide- or biopolymer-containing substrate, preferably a cellulosic substrate, with a water vapor barrier layer.Furthermore, water vapor barrier layers of water-permeable polymer substrates, such as biopolymer substrates, in particular substrates made of polylactic acid (PLA), are suitable.

[0052] Thus, the present invention further provides a polysaccharide- or biopolymer-containing substrate comprising a water vapor barrier layer produced from the aqueous natural wax oxide emulsion of the present invention.

[0053] The polysaccharide- or biopolymer-containing substrate is preferably a cellulosic substrate, more preferably paper or paperboard. These coated polysaccharide- or biopolymer-containing substrates can be used in any type of package or shell, such as tobacco products, outer packaging for tobacco products, paper cups, frozen goods packaging, packaging for bread, sausage and cheese, and plants, as well as cardboard boxes, outer packaging for electronic goods, etc.

[0054] The present invention further provides a method for preparing a polysaccharide- or biopolymer-containing substrate, the method comprising the steps of: a) coating the polysaccharide- or biopolymer-containing substrate with an aqueous natural wax oxide emulsion of the present invention; and b) drying the coated substrate to form a barrier layer. EXAMPLES

[0055] [Table 1]

[0056] Example implementation: Table 2 shows the waxes and wax oxides used.

[0057] [Table 2]

[0058] Preparation of corn wax oxide 1-3 Since corn wax oxide is not commercially available, the experimental conditions for the preparation of corn wax oxide are detailed below.

[0059] A 3 L reaction vessel equipped with a stirrer, temperature sensor, dropping funnel and reflux condenser was first charged with the amount of chromium trioxide in sulfuric acid (concentration: 100 g CrO3 / L) shown in Table 4 and heated to 100°C. Untreated molten natural wax (90°C) was then added in portions. The reaction mixture was brought to a temperature of 110°C and stirred with a precision glass stirrer at about 200 rpm for 4 hours. Heating and stirring were stopped and the aqueous phase was separated as soon as the phases separated. This procedure was carried out twice to produce Corn Wax Oxide 1 and 2, and five times to produce Corn Wax Oxide 3, using the amounts shown in Table 3.

[0060] [Table 3]

[0061] The organic phase was washed with solutions of oxalic and sulfuric acid in water, then in water to remove chromium residues, drained into a warm centrifuge tube and centrifuged.

[0062] [Table 4]

[0063] A) Preparation of Water-Based Wax Emulsion A1) The preparation of the blends F1, F2, F9, and F10 in Table 5 and the preparation of the blends F12, F13, F14, and F15 in Table 6 are as follows. Each wax and each emulsifier was thoroughly melted at 125°C and stirred to homogenize. Boiling distilled water was added to the 125°C wax melt and further stirred. The resulting emulsion was cooled (approximately 3K / min) with strong stirring.

[0064] A2) The preparation of formula F4 in Table 5 is as follows: The wax is fully melted at 125°C, and then DEAE is slowly added dropwise. The melt is stirred for 2 minutes. Boiling distilled water is added to the wax melt at 125°C and further stirred. The resulting emulsion is cooled (approximately 3K / min) with vigorous stirring.

[0065] A3) The preparation of formulations F3, F5 and F6 in Table 5 and F16 and F17 in Table 6 is as follows: The respective wax, oleic acid, ammonia solution and KOH were mixed with 50% of the required amount of distilled water. The mixture was heated to 135°C in a pressure reactor and the remaining distilled water was added to the mixture at about 125°C. The mixture was stirred for 15 minutes at 135°C. The resulting emulsion was cooled to 30°C with stirring (about 3K / min).

[0066] A4) The preparation of F7 is as follows: The wax and E5 emulsifier were thoroughly melted at 125°C and then stirred to homogeneity. While stirring, the KOH / ethylene glycol mixture was added dropwise and mixed for an additional 2 minutes. The hot wax mixture was added to boiling distilled water and stirred. The resulting emulsion was cooled (approximately 3K / min) with vigorous stirring.

[0067] [Table 5]

[0068] [Table 6]

[0069] In Tables 5 and 6, the inventive formulations F1-F6 and F12-17 all form stable emulsions. Comparative Example F10 contains 20% wax but does not form a stable emulsion. Comparative Example F9 contains 10% wax and forms a stable emulsion, but the low wax content is detrimental to coating quality and drying time.

[0070] B) Preparation of a paper substrate coated with a wax emulsion The wax emulsion shown in Table 7 was coated with a 50 μm coating bar, and a test piece of 12.5 cm x 12.5 cm was cut out and stored at a constant temperature of 23° C. and a relative humidity of 30% for 24 hours. The test piece was weighed (Tara1) and fixed in a Cobb aluminum cup.

[0071] Next, 100 ml of distilled water was added to the sample over 60 seconds and then removed. The remaining water was removed with blotting paper and absorbent rollers and the sample was reweighed (Tara2). The Cobb value was calculated using the following formula: Cobb value 60s = (Tara2 - Tara1) x 115.48658

[0072] The values ​​were measured three times and the median values ​​are shown in Table 7.

[0073] [Table 7]

[0074] All of the examples F1 to F6 and F12 to F17 according to the present invention have a significantly reduced water absorption rate and Cobb values ​​compared to the uncoated papers, examples F7 and F9. 60 This was reflected in a decline in

[0075] c) Preparation of coated carrier films to measure the barrier effect of wax coatings using water vapor transmission rate Wax or wax-oxide emulsions or dispersions were coated as a thin film on cellophane. For coating, a semi-automatic Sumet Messtechnik CUF5 coating system was used to process sheet-like substrates with a maximum area of ​​DIN A3 format (420 x 297 mm). The wet coating was 50 μm. The coating speed was 30 mm / s. The drying temperature was between 70 °C and 90 °C, the drying time was 1-5 min.

[0076] To eliminate the effect of the substrate, all barrier layers were coated on cellophane, which is known to be water vapor permeable. The water vapor transmission rate Q of cellophane film is 1084 g / (m 2 The water vapor barrier was measured for its water vapor transmission rate Q at 23°C according to DIN 53122-1 and for the humidity gradient at a relative humidity of 85% on one side of the barrier layer and 0% on the other side. The measured Q value (unit: g / (m 2 *d)) represents how many grams of water per day penetrate an area of ​​1 square meter.

[0077] However, this value is highly dependent on the thickness of the wax layer. The thicker the wax layer, the lower the value. Therefore, to be able to compare different materials of different thicknesses, we normalized the value to a layer thickness of 100 μm (Q100[g*100μm / (m 2 *d)]) which can be calculated using the following formula:

[0078]

number

[0079] In this manner, the water vapor transmission rate of each barrier layer for the measured values ​​in Table 8 can be calculated using the following formula:

[0080]

number

[0081] The layer thickness of the barrier layer was measured microscopically on microtome sections of the coated substrate to determine the water vapor permeability Q100 normalized to the layer thickness.

[0082]

number

[0083] The water vapor transmission rate of Lupolen is used as the reference value, and its Q100 value is set to 1.

[0084] Additionally, the water vapor permeability of the crude RBW thin films that were not coated onto the cellophane substrate was measured.

[0085] The measured values ​​in Table 8 are the average values ​​of four measurements.

[0086] [Table 8]

[0087] All of the inventive examples exhibit significantly improved water vapor permeability compared to uncoated cellophane films, which is reflected in lower Q100 values ​​that are in the same range as the Q100 value of the Lupolen 100 reference film, which represents a standard polyethylene-based barrier material.

[0088] Rice bran wax has good barrier properties but is not emulsifiable. Coating from the melt requires a higher energy input and results in a thicker layer compared to aqueous emulsions, which negatively impacts material consumption. Furthermore, the thicker layer has a negative impact on the adhesion and flexibility of the barrier layer.

Claims

1. (a) at least one natural wax oxide having an acid number to OH number ratio of 1 or greater; and (b) at least one anionic or nonionic emulsifier; 1. An aqueous natural wax oxide emulsion for forming a water and / or water vapor barrier layer on a polysaccharide- or biopolymer-containing substrate comprising:

2. 2. The aqueous natural wax oxide emulsion of claim 1, wherein said natural wax oxide is selected from the group consisting of rice bran wax oxide, corn wax oxide, sugar cane wax oxide, sunflower wax oxide and carnauba wax oxide.

3. 2. The aqueous natural wax oxide emulsion of claim 1, wherein the natural wax oxide has an acid number, measured according to ISO 2114, of 1 to 140 mg KOH / g.

4. 2. The aqueous natural wax oxide emulsion of claim 1, wherein the natural wax oxide has a hydroxyl number, measured according to DGF M-IV6, of less than 8 mg KOH / g.

5. 2. The aqueous natural wax oxide emulsion of claim 1, wherein the natural wax oxide has an iodine color value, measured according to DIN 6162, of less than 20.

6. 2. The aqueous natural wax oxide emulsion of claim 1, wherein the natural wax oxide has a dropping point, measured according to ISO 2176, of 65 to 110°C.

7. 2. The aqueous natural wax oxide emulsion of claim 1, wherein the natural wax oxide is present in the emulsion in the range of 5 to 50 weight percent, based on the total weight of the emulsion.

8. 2. The aqueous natural wax oxide emulsion of claim 1, wherein said nonionic emulsifier has an HLB value of 11-19.

9. 2. The aqueous natural wax oxide emulsion of claim 1, wherein the at least one nonionic emulsifier is selected from the group consisting of fatty alcohol polyglycol ethers, alcohol ethoxylates and tributylphenol ethoxylates.

10. 2. The aqueous natural wax oxide emulsion of claim 1, wherein said emulsifier is an anionic emulsifier system.

11. 2. The aqueous natural wax oxide emulsion of claim 1, wherein the emulsifier is present in the emulsion in the range of 1 to 20% by weight, based on the total weight of the emulsion.

12. (a) providing an oxidized natural wax and an anionic or nonionic emulsifier; (b) emulsifying the natural wax oxide in water at a temperature above the melting point of the natural wax oxide with an emulsifier; Here, the ratio of the acid value to the OH value of the natural wax oxide is 1 or more.

2. A method for producing the aqueous natural wax oxide emulsion of claim 1.

13. 13. The method for producing an aqueous natural wax oxide emulsion according to claim 12, characterized in that the natural wax oxide can be produced by an oxidation method selected from the group consisting of chromic acid oxidation, chromium sulfate oxidation (chromium trioxide and sulfuric acid), dichromate oxidation, oxidation with atmospheric oxygen and electrochemical oxidation.

14. 10. Use of the aqueous natural wax oxide emulsion of claim 1 for coating a polysaccharide-containing substrate with a water and / or water vapor barrier layer.

15. 10. A polysaccharide- or biopolymer-containing substrate comprising a water and / or water vapor barrier layer formed from the aqueous natural wax oxide emulsion of claim 1.

16. 16. The polysaccharide- or biopolymer-containing substrate of claim 15, wherein the polysaccharide- or biopolymer-containing substrate is a cellulosic substrate.

17. a) coating the aqueous natural wax oxide emulsion of claim 1 onto a polysaccharide-containing or biopolymer-containing substrate; b) drying the coated substrate to form a barrier layer; 17. A method for producing the polysaccharide- or biopolymer-containing substrate of claim 15 or 16, comprising:

18. 2. The aqueous natural wax oxide emulsion of claim 1, wherein said natural wax oxide is selected from rice bran wax oxide and corn wax oxide.

19. 2. The aqueous natural wax oxide emulsion of claim 1, wherein said emulsifier is an oleic acid / ammonia hydroxide / KOH emulsifier system and / or a diethylaminoethanol emulsifier system.

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