Polymeric film or coating comprising hemicellulose

DESCRIPTION

FILM OR POLYMER COATING UNDERSTANDING HEMICELLULOSIS

Technical Field

The present invention relates to a film-forming composition and a polymeric film or coating comprising hemicellulose. It also relates to the use of said film or coating as an oxygen barrier. Still further, the invention relates to a method of producing a polymeric film or coating comprising hemicellulose, as well as a method of improving the film-forming properties of hemicellulose.

Background of the invention

Most plastic packaging materials are currently based on petroleum. However, fossil resources on earth are limited. Incineration results in an increase in the greenhouse effect and furthermore these materials are generally non-degradable. Sustained future development requires a conversion in the use of renewable natural materials.

In many food packaging applications it is important to protect food from oxygen as oxidation of aromatic compounds due to oxygen penetration reduces the quality and aroma of the product. This can be achieved using a material with barrier properties which has low oxygen permeability. Moreover, it is desirable that the material be flexible, mechanically resistant, transparent and inexpensive.

EVOH (ethylene vinyl alcohol) and PVOH (polyvinyl alcohol) are examples of synthetic polymers that exhibit good barrier properties.

Lately, research has been done to obtain oxygen barriers based on renewable natural materials. Protein and polysaccharide based films, such as starch and cellulose, have demonstrated good oxygen barrier properties. A disadvantage of these materials is their sensitivity to water. When the surrounding relative humidity is increased, the oxygen permeability also increases.

Hemicelluloses are polysaccharides that are biosynthesized in most plants, in which they act as a matrix material present between cellulose microfibers and as a bond between lignin and cellulose. Hemicelluloses have been used commercially in food products as sweetening, thickening and emulsifying agents. So far, non-food use of hemicelluloses has been quite limited. For example, they have not yet been used commercially for the preparation of polymeric materials.

The properties of hemicellulose-based films have so far been rarely studied. In general, hemicelluloses exhibit poor film-forming properties, resulting in fragmented or brittle films. However, its film-forming properties vary with the hemicellulose structure which in turn varies depending on its natural source and extraction method. To be suitable as a barrier material, the 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 protector. The purpose of WO 02/06411 is to provide a composition which is useful for applying a plant protector to seeds or agricultural products. Therefore, the purpose of incorporating heteroxylans is to obtain a film-forming composition for application of the plant protector.

The molecular weight of the heteroxylans used in WO 02/06411 ranges from 100,000 to 250,000 g / mol. The use of high molecular weight hemicelluloses produces compositions having relatively high viscosities, which makes practical handling of the compositions difficult.

In US Patent No. 6004616, a biodegradable film is obtained by subjecting water-soluble hemicellulose to film formation. The hemicellulose used has an average molecular weight ranging from 50,000 to 1,000,000, preferably from 100,000 to 400,000. Again, high molecular weights present problems due to high viscosity.

Furthermore, the thickness of the films described in US Patent No. 6004616 is 0.1 mm in the dry state. Therefore, the films are relatively thick, which requires the consumption of a lot of material for the manufacture of the films. As a consequence, the cost of materials will be very high.

Accordingly, there is a need for biodegradable film-forming compositions that overcome the aforementioned problems and have the desired property of having low oxygen permeability.

Summary of the invention

Accordingly, an object of the present invention is to provide flexible hemicellulose-based films or coatings having a molecular weight of 50,000 g / mol or less.

Another object is to provide a hemicellulose-based film or coating composition having a molecular weight of 50000 g / mol or less that can be used as an oxygen barrier.

These objectives are achieved by blending hemicellulose having 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. The polymeric film or coating thus formed may be used as an oxygen barrier.

The use of hemicellulose having a molecular weight of 50000 g / mol or less is advantageous as it allows the use of a greater number of natural hemicellulosic materials for the preparation of films or coatings. There are also more extraction methods available for extracting molecules having lower molecular weights.

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

Another advantage of the present invention is that the mechanical properties of the films or coatings produced can be controlled by adding various amounts or types of plasticizers, cellulose or by mixing with other polymers or oligomers.

Another advantage is that the natural material of the present invention is renewable and can be extracted from biomass.

Biosynthesized polymer based materials have several environmental advantages. After use, these materials do not cause an increase in carbon dioxide in the atmosphere and additionally most of them are biodegradable and as such can be destroyed by composting.

Detailed Description of the Invention

In the research leading to the present invention it has been shown that coherent films based on hemicellulose, in particular pentosan-rich polysaccharides, eg xylans, exhibit excellent oxygen barrier properties. It has been surprisingly found that hemicelluloses having a molecular weight of less than 50,000 g / mol can be used for the purpose of preparing films that can be used as an oxygen barrier.

Hemicelluloses are low to high molecular weight substituted / branched polymers. They consist of different units of sugars arranged in different proportions and with different substituents. Pentosan-rich polysaccharides have a predominant pentose content and constitute the largest group within hemicelluloses.

As used herein, a pentosan-rich polysaccharide refers to a polysaccharide having a pentosan content of at least 20 wt% and a xylose content of at least 20 wt%; for example, the polysaccharide has a pentosan content of 40 to 80 wt% and a xylose content of 40 to 75 wt%.

Pentosan-rich polysaccharides, in particular xylanes, are the most preferred compounds for use in accordance with the present invention as they are not as sensitive to moisture. However, according to the invention, other types of hemicelluloses may be used, eg glucomannan, galactoglucomannan or arabinogalactane.

Hemicellulose, in particular xylans, for use according to the invention has a molecular weight of less than 50000 g / mol. Advantageously, hemicellulose has a higher molecular weight g / mol. For example,

8000 Hemicellulose may have a molecular weight in the range of 8000 - 50000 g / mol, 8000 - 48000 g / mol or 8000 - 45000 g / mol.

Other examples of hemicellulose molecular weights are 8000 - 15000 g / mol, 8000 - 14000 g / mol, 8000 - 13000 g / mol, 8000 - 12000 g / mol, or in particular 8000 - 11000 g / mol. The use of lower molecular weights is an advantage since hemicellulose from various sources can be used and the extraction process is simplified.

Another example of molecular weights of hemicelluloses are 15000 - 50000 g / mol, 20000 - 50000 g / mol, 15000 48000 g / mol, 20000 - 48000 g / mol, 15000 - 45000 g / mol, or in particular 20000 - 45000 g / mol or 20,000 - 40,000 g / mol. The use of slightly higher molecular weights facilitates film formation. If higher molecular weights are used, high viscosity can complicate the use of hemicellulose to produce a film or coating and extraction methods are considerably restricted.

Xylans are present in biomass such as wood, cereals, grass or herbs and are considered to be the second most abundant biopolymer in the plant kingdom. To separate xylans from other components into various biomass sources, extraction with water and an aqueous alkaline base may be used. Xylans are also commercially available from sources such as the Sigma Chemical Company.

Xylanes can be divided into subgroups of heteroxylans and homoxylans. The chemical structure of homoxylans and heteroxylans differs. Homoxylans have a xylose residue backbone and some substituents of glucuronic acids or 4-O-methyl glucuronic acids. Heteroxylans also have a xylose residue backbone but, in contrast to extensively substituted homoxylans, not only with glucuronic acid or 4-methyl glucuronic acid, but also with arabinose residues. An advantage of homoxylans compared to heteroxylans is that homoxylans crystallize to a greater extent. Crystallinity decreases both gas permeability and moisture sensitivity.

An example of a homoxylan which may be used in accordance with the present invention is glucuronoxylan.

Examples of heteroxylans which may be used in accordance with the present invention are arabinoxylan, glucuronoarabinoxylan and arabinoglucoronoxylan.

Xylanes isolated from any biomass or commercially available may be used to produce the films or coatings of the present invention. For a coherent film, film formation is a necessary requirement.

A hemicellulose film-forming composition, in particular xylans, can be achieved by various strategies. One way to do this is by adding low molecular weight plasticizers. Another way to prepare coherent films by adding finely divided cellulose.

A third process for obtaining films by blending xylan with other oligomers or polymers. An additional strategy for achieving better film forming properties is to mix hemicelluloses of different molecular weights or structures. It is also possible to use a combination of one or more of the above mentioned strategies.

The films or coatings may be prepared by molding an aqueous solution or dispersion of pentosan rich polysaccharide. Although other solvents may be used in the present invention, water is the most preferred solvent.

As used herein, the term film refers to a separate sheet which may be used, eg, for food or medicine packaging.

As used herein, the term coating refers to a cover that can be integrated into, eg, a cardboard, to provide an oxygen barrier layer.

The film or coating according to the invention may have a thickness of 100 micrometers or less. In particular, the film or coating may have a thickness of 50 micrometers or less or, more specifically, the film or coating may have a thickness of 10 micrometers or less.

It has been surprisingly found that according to the present invention very thin films can be made. For example, the film or coating may have a thickness of 2 micrometers or 1 micrometer and still still have the desired properties.

The term plasticizer as used herein refers to a low molecular weight substance that increases the flexibility of the material. Examples of piastisers that may be used are water, sugars such as glycerol, xylitol, sorbitol and malitol, ethylene glycol, propylene glycol, butanediol, glycerin and urea.

Suitably the plasticizer content ranges from 1-60% dry weight, eg from 20-50% dry weight.

Cellulose added to improve film-forming properties may come from any biomass, such as cotton, wood and agricultural or commercial waste, or may be produced by bacteria. Preferably, the cellulose is finely divided. Suitably the finely divided cellulose content

g.

50-75% ranges from 1-90% dry weight, dry weight.

The added polymer or oligomer may be of any type. For example, the polymer or oligomer added to obtain a coherent film is polyvinyl alcohol of various molecular weights. Suitably the polymer or oligomer content ranges from 1-90% dry weight, eg from 20-75% dry weight.

By the term oxygen barrier used throughout this application is meant a material having low oxygen permeability. The oxygen barrier may be used to protect a substance, eg food or medicine, from exposure to oxygen.

Polymeric films or coatings according to the present invention may be used as an oxygen barrier in food packaging or drug packaging.

Additionally, the films or coatings of the present invention may be used as an oxygen barrier layer on, eg, cardboard or paper, possibly in combination with a water resistant material.

The films or coatings of the present invention may also be used for the delivery of drugs, edible films and other polymeric applications.

Examples

Example 1

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

The molar mass of glucuronoxylan was calculated using LiBr molecular exclusion chromatography.

<td>0.05M</td><td>in</td><td>DMSO: water</td><td> (90:10</td><td> )</td><td>how</td><td>The</td><td>mobile phase. Was</td>

<td>used</td><td>O</td><td colspan="2">following group of</td><td colspan="2">columns</td><td>PSS</td><td>(Polymer Standard</td>

<td>Service):</td><td colspan="2">GRAM 30, 100,</td><td> 3000</td><td> (8</td><td>x 300</td><td>mm)</td><td>and a pre-column</td>

<td>(8x50</td><td>mm)</td><td>. 0 flow rate</td><td>it was 0,</td><td> 4</td><td>mL / min</td><td>, a</td><td>60 ° C resulting</td>

at a system pressure of 58 bar. Samples were dissolved in the eluent on a shaker for 24 hours at room temperature and filtered using regenerated cellulose membranes (0.45 pm). For detection, an IR detector (Shodex RI-71), a two-angle laser radiation diffusion detector (Precision PD 2000 detectors) and a viscometer (Viscotek H502) were used. Data were collected and calculated using the software.

PSS WINGPC 6.0. Molecular mass data were calculated from viscosity and IR signals by universal calibration using pullulan standards (PSS). The molecular weight obtained was 15000 g / mol.

The mechanical properties of the films were measured using a tensile testing machine (Lloyd L2000R) with a 100 N cell capacity. Samples were cut into dog bone-shaped strips 1.5 cm long. The thickness of the samples, measured with a micrometer, was 30-40 pm. The initial distance between the jaws was 20 mm and the jaw separation speed was constant at 5 mm / min (Examples 1, 2 and 7) or 10 mm / min (Example 4). At least five replicates of each material were tested. For each sample the yield strength curve was recorded and the tensile strength and the tensile strength were calculated.

Oxygen permeability of the films was measured with a Mocon oxtran 2/20 equipment using a colorimetric oxygen sensor. The sample area was 5 cm² and the analysis was performed with 50% RH. Oxygen permeability was calculated from oxygen transmission and measured film thickness and is presented in units of (cm³ pm) / (m² d kPa), where d = 24 h.

Film crystallinity was investigated using wide-angle X-ray diffraction (WAXS). The films were sprayed to a fine powder using liquid nitrogen and the samples were analyzed with a Siemens D5000 diffractometer. CuKa radiation with a wavelength of 1.54 Â was used. 2Θ ranged from 5 ° to 30 °.

<td>Content in xylitol (%)</td><td>Tension in break (MPa)</td><td>Deformation in break (%)</td><td>Permeability O2 (cm³ pm) / (m²d kPa)</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>

Flexibility increased with increasing amount of plasticizer added. All films were semi-crystalline and the degree of crystallinity was little affected by the addition of xylitol.

Example 2

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

<td>Content in sorbitol (%)</td><td>Tension in break (MPa)</td><td>Deformation in break (%)</td><td>Permeability O₂ (cm³ pm) / (m²d kPa)</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 with xylan and polyvinyl alcohol. The same procedure as in Example 1 was used, but 0.75 g of polyvinyl alcohol (molecular weight 20,000) was mixed with 0.25 g of xylan. Flexible films were formed. The measured oxygen permeability of the films was 0.18 (cm³ pm) / (m² d kPa).

Example 4

This example illustrates the production of films made with xylan and finely divided cellulose. 0.37 g of solubilized glucuronoxylan in 20 ml of water at 95 ° C for 15 minutes was added to 1.13 g of homogenized bacterial cellulose in 120 ml of water. The mixture was allowed to interact for 30 minutes. The resulting gel was poured into 14 cm diameter polystyrene petri dishes and dried at 50 ° C for 48 hours. After drying, a flexible film was obtained. Films produced according to this method exhibit a rupture stress of 102.8 MPa, a rupture strain of 3.1% and an oxygen permeability of 0.225 (cm -1).³ pm) / (m² d kPa).

Example 5

This example illustrates the production of a xylan-based film, where xylan is obtained from an agricultural residue such as oak spelled, barley bark or flax. 1 g of arabinoxylan was solubilized in 35 mL of water at 95 ° C for 15 minutes. The solution was then poured into 14 cm diameter polystyrene petri dishes. After drying at 23 ° C and 50% RH for two or three days, flexible films were obtained.

In this case, the preferred plasticizer is water. The possibility of obtaining arabinoxylan films without the addition of any plasticizer other than water is very advantageous and a surprising aspect of the present invention.

The thickness of the films, measured with a micrometer, was 30-40 pm.

The molar mass of arabinoxylan was measured using molecular exclusion chromatography as described in Example 1. The molecular weight obtained was 34,000 g / mol.

Oxygen permeability of the films was measured with a Mocon oxtran 2/20 equipment using a colorimetric oxygen sensor. The sample area was 5 cm² and the analysis was performed with 50% RH. The oxygen permeability calculated from the oxygen transmission and the measured film thickness was 0.19 (cm³ pm) / (m² d kPa), where d = 24 h.

Example 6

This example illustrates the production of a xylan based coating. A mixture of 0.105 g sorbitol and 0.195 g beech glucuronoxylan was solubilized in 30 ml water at 95 ° C for 15 minutes. The solution was then poured onto a plastic film in polystyrene petri dishes with a diameter of 14 cm. After drying at 23 ° C and 50% RH for two or three days, a xylan coating on plastic film was obtained.

The molar mass of glucuronoxylan was measured using molecular exclusion chromatography as described in Example 1. The molecular weight obtained was 15000 g / mol.

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

Example 7

This example illustrates the production of a glucomannan-based film, wherein the film-forming properties were improved using sorbitol as a low molecular weight plasticizer. Films without sorbitol and with 20% sorbitol (dry weight) were investigated. A total weight of 0.2 g of sorbitol and glucomannan was solubilized in 20 ml of water at 95 ° C for 15 minutes. The solution was then poured into 9 cm diameter polystyrene petri dishes. After drying at 23 ° C and 50% RH for two or three days, clear and more or less flexible flexible films were obtained.

The mechanical properties of the films were measured as described in Example 1. The thickness of the samples, measured with a micrometer, was 60-70 pm.

<td>Content in</td><td>Tension in</td><td>Deformation in</td>

<td>sorbitol (%)</td><td>break (MPa)</td><td>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.

Lisbon, October 09, 2008