Polymeric film or coating comprising hemicellulose

Background to the invention

Most plastic materials for packaging are currently based on crude oil. Nevertheless, fossil sources on earth are limited. Burning them increases the greenhouse effect and, what is more, these materials are basically non-degradable. Sustainable development in the future requires a transition to the use of renewable raw materials.

In the case of many applications for food packaging, it is important to protect food against oxygen, because the oxidation of aromatic components caused by the access of oxygen deteriorates the quality and taste of the product. Protection can be provided by using a suitable barrier material that has low oxygen permeability. In addition, it is desirable that the material be flexible, mechanically robust, transparent and cheap.

EVOH (ethyl vinyl alcohol) and PVOH (polyvinyl alcohol) are examples of synthetic polymers exhibiting good barrier properties.

Recently, research has been carried out to obtain oxygen barriers based on renewable raw materials. Layers based on proteins or polysaccharides, such as starch or cellulose, have proven to be good oxygen barriers. The only disadvantage of these materials is their sensitivity to water. In the case when the relative humidity of the environment increases, the oxygen permeability also increases.

Hemicelluloses and polysaccharides are the result of biosynthesis in most plants, where they act as a matrix material present between cellulose microfibers, and a lignin-binding material and cellulose. Hemicelluloses were commercially used as sweeteners, thickeners and emulsifiers in food. Until now, the use of non-food-related hemicelluloses has been limited. For example, they have not been commercially used for the preparation of polymeric materials.

The properties of hemicellulose-based films have so far been very rarely studied. In general, hemicellulose exhibits poor film-forming properties, which results in the formation of fragmented and brittle films. However, the film-forming properties of hemicellulose change with the structure, which in turn depends on the natural source and extraction method. In order for it to become an appropriate barrier material, its film-forming properties must be improved.

WO 02/06411 discloses the use of heteroxylans for the preparation of a film forming composition containing a plant protection agent. The object of WO 02/06411 is to provide a composition useful for applying the composition

EP 1 606 339 for plants for grains or agricultural products. Thus, the heteroxylans were introduced with the intention of obtaining a film forming composition for applying a plant protection product.

The molecular weight of the heteroxylans used in WO 02/06411 ranged from 100,000 to 250,000 g / mol. The use of high molecular weight hemicellulose gives compositions with relatively high viscosities, which makes them difficult to handle in practice.

In US 6 004 616 a biodegradable film was obtained by subjecting the water-soluble hemicellulose to film formation. The cellulose used had an average molecular weight in the range from 50,000 to 1,000,000, preferably in the range of 100,000 to 400,000. Again, large molecular weights caused a high viscosity machining problem.

In addition, after drying, the thickness of the films described in US 6 004 616 is 0.1 mm. Thus, the films are relatively thick, which requires the consumption of large amounts of material in their production. Consequently, the cost of materials will be high.

Therefore, there is a need for biodegradable film forming compositions that will solve the aforementioned problems, and which exhibit the desired property of low oxygen permeability.

Summary of the invention

Accordingly, the present invention relates to elastic films or coatings based on hemicellulose with a molecular weight of 50,000 g / mol or less.

Another subject of the invention is a film-forming composition and films or coatings based on hemicellulose with a molecular weight of 50,000 g / mol or less, which are used as oxygen barriers.

These objects are obtained by mixing hemicellulose with a molecular weight of 50,000 g / mol or less, with at least one component selected from the group consisting of plasticizers, cellulose and an oligomer or polymer, and forming a film or coating therefrom. The polymer film or coating so formed is used as an oxygen barrier.

The use of hemicellulose with a molecular weight of 50,000 g / mol or less is convenient because it allows the use of more hemicellulose raw materials for the production of films or coatings. In addition, more extraction methods are available for molecules with lower molecular weights.

Another advantage of the present invention is the excellent properties of the films or coatings produced as oxygen barriers. The measured oxygen permeability was in the same range as for commercially available EVOH barriers and for starch films.

A further advantage of the present invention is that the mechanical properties of the films or coatings produced are controlled by adding various amounts or different types of plasticizers, cellulose or blending with other polymers or oligomers.

Another advantage is that the raw material in the present invention is renewable and is extracted from biomass.

Materials based on biosynthetic polymers have several advantages when it comes to environmental protection. After use, these materials do not contribute to increasing carbon dioxide emissions to

EP 1 606 339 of the atmosphere, in addition, most of them are biodegradable, so they can be removed by composting.

Detailed description of the invention

In the research work leading to the present invention, it was proved that coherent films based on hemicellulose, in particular on pentosan-rich polysaccharides, e.g. xylans, exhibit excellent oxygen barrier properties. It has surprisingly been found that hemicellulose with a molecular weight less than 50,000 g / mol can be used to produce films that are used as oxygen barriers.

Hemicelluloses are substituted / branched polymers with molecular weights ranging from low to high. They contain a variety of sugar groups located in different parts and with various substituents. The pentosane-rich polysaccharides contain the predominant amount of pentose and make up the largest group of hemicelluloses.

As used herein, the term "pentosate-rich polysaccharide" refers to a polysaccharide with a pentosan content of at least 20% by weight, and a xylose content of at least 20% by weight; for example, a polysaccharide with a pentosan content of 40% to 80% by weight, and with a xylose content of 40% to 75% by weight.

Pentosate-rich polysaccharides, in particular xylans, are the most preferred compounds for use in the present invention, which is related to their lack of sensitivity to moisture. However, other types of hemicelluloses, e.g. glucomannan, galactoglucomannan or arabinogalactane, are also used according to the invention.

Hemicelluloses, in particular xylans that are used in the present invention, have a molecular weight of less than 50,000 g / mol. Preferably, the hemicellulose has a molecular weight greater than 8,000 g / mol. For example, hemicellulose has a molecular weight in the range of 8,000 - 50,000 g / mol, 8,000 - 48,000 g / mol or 8,000 - 45,000 g / mol.

Other examples of molecular weight hemicelluloses are 8,000 - 15,000 g / mol, 8,000 14,000 g / mol, 8,000 - 135,000 g / mol, 8,000 - 12,000 g / mol, or in particular 8,000 - 11,000 g /moth. The use of small molecular weights is beneficial because hemicellulose is used from many sources and the extraction procedure is simplified.

Other examples of molecular weight hemicelluloses are 15,000 - 50,000 g / mol, 20,000 50,000 g / mol, 15,000 - 48,000 g / mol, 20,000 - 48,000 g / mol, 15,000 - 45,000 g / mol, or in particular 20,000 - 45,000 g / mol or 20,000 - 40,000 g / mol. The use of slightly larger molecular weights facilitates the creation of a film. With even higher molecular weights, the high viscosity complicates the use of hemicellulose to produce a film or coating, and the extraction methods are severely limited.

Xylans occur in biomass such as wood, cereals, grass and herbs, and are considered the second most abundant biopolymer in the plant kingdom. In order to separate xylans from other components in various biomass sources, extraction with water and an aqueous base is used. Xylans are also commercially available from sources such as Sigma Chemical Company.

Xylans can be divided into sub-groups of heteroxylans and homoxylans. The chemical structure of homoxylans and heteroxylans differs from each other. The homoxylans have a backbone composed of xylose residues and substituents of glucuronic acid or 4-O-methyl glucuronic acid.

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Heteroxylans also have a backbone composed of xylose residues, but unlike homoxylans, they are notably substituted with not only the substituents of glucuronic acid or 4-O-methylglucuronic acid, but also the arabinose residues. The advantage of homoxylans over heteroxylans is that the homoxylans crystallize to a greater extent. Crystallinity both lowers gas permeability and moisture sensitivity.

An example of a homoxylan that is used in the present invention is glucuronoxylate.

Examples of heteroxylans that are used in the present invention are arabinoxylan, glucuronoarabinoxylate and arabinoglucuronoxylate.

For producing films or coatings in the present invention, xylans from any biomass or commercial source are used. To create a coherent film, the creation of a film is an essential condition of application.

The film-forming composition of hemicellulose, in particular xylans, is obtained by various methods. In one method, low molecular weight plasticizers are added. In a different method of preparing consistent films, very fine cellulose is added. In the third film preparation procedure, xylan is mixed with other oligomers or polymers. In another method, hemicelluloses with different molecular weights or structures are mixed to achieve better film-forming properties. It is also possible to use a combination of one or more of the above methods.

Films or coatings are prepared by making a cast from an aqueous solution or a suspension of a polysaccharide-rich pentosan. Although various solvents can be used in the present invention, water is the most preferred solvent.

The term "film" as used herein refers to a separate film that can be used, e.g., for packaging food or pharmaceuticals.

As used herein, the term "coating" refers to a coating that can be combined with, e.g., cardboard, to provide an oxygen barrier layer.

The film or coating according to the invention has a thickness of 100 microns or less. In particular, the film or coating has a thickness of 50 micrometers or less, or more particularly the film or coating has a thickness of 10 micrometers or less.

Surprisingly, it has been found that very thin films are obtained according to the present invention. For example, the film or coating has a thickness of 2 micrometers or 1 micrometer, still showing the desired properties.

As used herein, the term "plasticizer" refers to a low molecular weight substance that increases the elasticity of the material. Examples of plasticizers used are water, sugars such as glycerol, xylitol, sorbitol and maltitol, ethylene glycol, propylene glycol, butanediol, glycerin and urea.

Suitably, the plasticizer content is in the range of 1-60% on a dry basis, e.g. in the range of 20-50% on a dry basis.

Cellulose added to improve film-forming properties can be derived from any biomass such as cotton, wood and agricultural products, or from a commercial source, or can be produced by bacteria. Preferably the cellulose is very particulate.

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Correspondingly, the content of finely divided cellulose is in the range of 1-90% on a dry basis, e.g. in the range of 50-75% on a dry basis.

The polymer or oligomer added is of any type. For example, the polymer or oligomer added to form a coherent film is polyvinyl alcohol with different molecular weights. Suitably, the polymer or oligomer content is in the range of 1-90% on a dry basis, e.g. in the range of 20-75% on a dry basis.

The term "oxygen barrier" as used in this application means a material that has low oxygen permeability. The oxygen barrier is used to protect substances, e.g. food or drugs, from oxygen.

The polymer films or coatings of the present invention are used as oxygen barriers in food packaging or pharmaceutical packaging.

In addition, the films or coatings of the present invention are used as oxygen barrier layers e.g. on cartons or paper, optionally in combination with waterproof material.

Films or coatings of the present invention can be used for drug delivery systems, edible coatings, and other polymer-related applications.

Examples Example 1

This example illustrates the production of a xylan based film, where the film-forming properties have been improved using a low molecular weight plasticizer, xylitol. A series of films containing 20%, 27.5%, 35%, 42.5% and 50% added xylitol (in terms of dry mass) were tested. A mixture of xylitol and glucuronoxide from poplars with a total weight of 1 g was dissolved in 35 ml of water at 95 ° C for 15 minutes. The solution was then transferred to polystyrene petri dishes with a diameter of 14 cm. After drying at 23 ° C and 50% RH for two to three days, clear and more or less flexible films were obtained.

The molecular weight of the glucuronoxide was measured by size exclusion chromatography using 0.05 M LiBr in DMSO: water (90:10) as the mobile phase. The following set of PSS (Polymer Standard Service) columns was used: GRAM 30, 100, 3000 (8 x 300 mm) and a guard column (8 x 50 mm). The flow rate was 0.4 ml / min at 60 ° C, resulting in a pressure of 58 bar in the system. Samples were dissolved in the eluent, using a shaker, for 24 hours at room temperature, after which they were filtered using regenerated cellulose membranes (0.45 μm). A RI refractometric detector (Shodex RI-71), a detector with two-dimensional laser light scattering (Precision detectors PD 2000) and a viscometer detector (Viscotek H502) were used for the detection. Data were recorded and calculated using PSS software called WINGPC 6.0. The molar mass was calculated on the basis of viscosity and refractometric signal using a universal calibration using pullulan standards (PSS). The resulting molar mass was 15,000 g / mol.

The mechanical properties of the films were measured using a tensile testing machine (Lloyd L2000R) with a measuring head with a range of up to 100 N. The samples were cut into 1.5 cm wide strips.

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The thickness of the samples measured with a micrometer was 30-40 mm. The initial distance between the clamps was 20 mm, and the speed of the clamps was fixed at 5 mm / min (examples 1, 2 and 7) or 10 mm / min (example 4). At least five samples from each material were tested. A stress-strain curve was recorded for each sample and stress and strain at break were calculated.

The oxygen permeability of the films was measured using the Mocon Oxtran 2/20 instrumentation using a coulometric oxygen sensor. The surface of the sample was 5 cm²and the analysis was carried out at a relative humidity of 50% RH. Oxygen permeability was calculated based on the amount of oxygen permeating and the measured thickness of films, which is shown in units (cm³ μηι) / (πι² d kPa), where d = 24 h.

Crystallinity of fllm was investigated using a wide angle X-ray diffractometer (WAXS). The films were ground to a fine powder using liquid nitrogen, after which the samples were tested in a Siemens D5000 diffractometer. CuKa radiation was used with a wavelength of 1.54 A. The angle 2Θ varied between 5 ° and 30 °.

<td>Xylitol content %</td><td>Stress at interruption MPa</td><td>Deformation at interruption %</td><td>O2 permeability (cm³ | Im)^/(m² d ^kPand)</td>

<td>20</td><td>39.4</td><td>2.1</td><td>-</td>

<td>27.5</td><td>15.2</td><td>2.5</td><td>-</td>

<td>35</td><td>10.6</td><td>5.3</td><td>1.10</td>

<td>42.5</td><td>4.8</td><td>7.8</td><td>-</td>

<td>50</td><td>3.0</td><td>8.0</td><td>-</td>

The flexibility increased with the increasing amount of added plasticizer. All the films were semi-crystalline and the addition of xylitol only slightly affected the degree of crystallinity.

Example 2

This example illustrates the production of a xylan-based film, where the film-forming properties have been improved using a low molecular weight plasticizer, sorbitol. The same procedure was used as in Example 1, except that sorbitol was used instead of xylitol as a plasticizer and a series of test samples included three different content of plasticizers, namely 20%, 35% and 50%.

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<td>Sorbitol content %</td><td>Stress at interruption MPa</td><td>Deformation at interruption %</td><td>O2 permeability (cm³ | Im)^/(m^{2 d kP}and)</td>

<td>20</td><td>35.4</td><td>2.0</td><td>-</td>

<td>35</td><td>13.5</td><td>5.8</td><td>0.21</td>

<td>50</td><td>3.9</td><td>10.4</td><td>-</td>

The flexibility of the films increased with the increasing amount of sorbitol. The addition of sorbitol had only a small effect on the relative crystallinity of the films.

Example 3

This example illustrates the production of films made of xylan and polyvinyl alcohol. The same procedure was used as in Example 1, but 0.75 g of polyvinyl alcohol (molecular weight 20,000) was mixed with 0.25 g of xylan. Flexible films were obtained. The measured oxygen permeability through the films was 0.18 (cm³ Am) / (m² d kPa).

Example 4

This example illustrates the production of films made of xylan and finely divided cellulose. 0.37 g of glucuronoxide was dissolved in 20 ml of water at 95 ° C for 15 minutes, after which it was added to 1.13 g of bacterial cellulose homogenized in 120 ml of water. The mixture was left for 30 minutes. The resultant gel was transferred to a polystyrene petri dish with a diameter of 14 cm, then dried at 50 ° C for 48 hours. After drying a flexible film was obtained. The film produced in this way showed a strain at 102.8 MPa, strain at break 3.1% and oxygen permeability 0.225 (cm) / (md kPa).

Example 5

This example illustrates the production of a xylan-based film, where xylan is obtained from agricultural products such as oat husks, barley husks, flax. 1 g of arabinoxylan was dissolved in 35 ml of water at 95 ° C for 15 minutes. The solution was then poured into a polystyrene Petri dish with a diameter of 14 cm. After drying at 23 ° C and 50% RH for two to three days, flexible films were obtained.

In this case, water is a preferred plasticizer. The possibility of obtaining films of arabinoxylan without adding any other plasticizers than water is an extremely beneficial and unexpected form of the present invention.

The film thickness measured with a micrometer was 30 - 40 μητ

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The molar mass of the arabinoxylan was determined by size exclusion chromatography as described in example 1. The molar mass obtained was 34,000 g / mol.

The oxygen permeability of the films was measured with the Mocon Oxtran 2/20 instrumentation using a cosmometric oxygen sensor. The surface of the sample was 5 cm²and the analysis was carried out at a relative humidity of 50% RH. The oxygen permeability, calculated on the basis of the amount of oxygen permeated and the measured thickness of films, was 0.19 (cm / cm) / (md kPa), where d = 24 h.

Example 6

This example illustrates the production of a xylan-based coating. A mixture of 0.105 g of sorbitol and 0.195 g of glucuronoxylate from poplars was dissolved in 30 ml of water at 95 ° C for 15 minutes. The solution was then applied to a plastic film in a polystyrene Petri dish with a diameter of 14 cm. After drying at 23 ° C and 50% RH for two to three days, a xylene coating was obtained on the plastic film.

The molar mass of glucuronoxylate was determined by size exclusion chromatography as described in example 1. The molar mass obtained was 15,000 g / mol.

The thickness of the coating was obtained by subtracting the thickness of the plastic film from the thickness of the film with the xylan coating measured by the micrometer. The resulting coating thickness was 1 micrometer.

Example 7

This example illustrates the production of a film based on glucomannan, where the film-forming properties have been improved by using sorbitol as a low molecular weight plasticizer. Films without sorbitol and films containing 20% ​​added sorbitol (in terms of dry mass) were studied. A mixture of sorbitol and glucomannan with a total weight of 0.2 g was dissolved in 20 ml of water at 95 ° C for 15 minutes. The solution was then transferred to a polystyrene Petri dish with a diameter of 9 cm. After drying at 23 ° C and 50% RH for two to three days, clear and more or less flexible films were obtained.

The mechanical properties of films were tested as in example 1. The thickness of the samples measured with a micrometer was 60 - 70 μητ

<td>Sorbitol content%</td><td>Stress at break MPa</td><td>Deformation at break %</td>

<td>0</td><td>20.3</td><td>2.7</td>

<td>20</td><td>7.2</td><td>6.8</td>

Flexibility increased with the addition of plasticizer.

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