WO2022269297A1

WO2022269297A1 - Biodegradable shaped articles

Info

Publication number: WO2022269297A1
Application number: PCT/HU2021/050042
Authority: WO
Inventors: Péter Tamás LAJTER; László JANOVÁK; László Bálint LÉVAI; József JÜLLICH
Original assignee: Lajter Peter Tamas; Janovak Laszlo
Priority date: 2021-06-22
Filing date: 2021-06-22
Publication date: 2022-12-29

Abstract

The present invention relates to a biodegradable shaped article with a hydrophobic surface, which shaped article has a hydrophilic backbone containing polyvinyl alcohol and its surface is covered with covalently bonded alkyl chains, which alkyl chains are formed by reacting the surface hydroxyl groups of polyvinyl alcohol with an alkyl monoaldehyde or a reactive alkylsilane. The invention also relates to the production of said shaped article.

Description

BIODEGRADABLE SHAPED ARTICLE

FIELD OF THE INVENTION

The present invention relates to a biodegradable shaped article with a hydrophobic surface, which has a hydrophilic backbone containing polyvinyl alcohol and its surface is covered with covalently bonded alkyl chains, which alkyl chains are formed by reacting the surface hydroxyl groups of the polyvinyl alcohol with an alkyl monoaldehyde or a reactive alkylsilane. The invention also relates to the production of said shaped articles.

TECHNICAL BACKGROUND

Proper disposal of the waste derived from disposable mass-produced articles that accumulates in our environment is a growing challenge year by year. One way to avoid further accumulation can be to make mass-produced articles from biodegradable plastics that become compost after use. However, biodegradable plastics typically have hydrophilic properties, i.e. they dissolute or at least swell in water, which prevents their use in wet environments, although a significant proportion of these disposable products are used in wet conditions, namely for storing, packaging and serving foods and beverages, or they are used as products in the food industry, in healthcare, in the cosmetics industry or in agriculture.

To solve the problem of water solubility, products made of biodegradable polymers are provided with a water-repellent coating. As the water-repellent coating, hydrophobic or moderately hydrophobic polymers or composites can be used, which have good film-forming properties, are compatible with the carrier polymer, i.e. the backbone of the product, and preferably are themselves biodegradable. Furthermore, substances harmful to health, such as small molecule plasticizers, monomers and the like used in the production of the polymer in the coating, must not migrate out of the coating in direct contact with the stored food or beverage.

Polyvinyl alcohol (hereinafter also referred to as PVA) is widely used as a hydrophilic biodegradable backbone or carrier because it is water-soluble, has good film-forming properties, is easy to handle, is completely transparent and colorless, and has favorable mechanical properties, its tensile strength is good and its properties can be varied within a wide range.

PVA is generally prepared by first polymerizing vinyl acetate and then hydrolyzing it to form PVA. The higher the degree of hydrolysis, the more moisture-resistant the product will be. PVA is difficult to process because its decomposition temperature is close to its melting range. Therefore, in many cases it is softened. In a bacterial environment, PVA degrades in 5-6 weeks. Its properties can be modified with other additives, for example starch or carboxymethyl cellulose (E466) is added to reduce its transparency. It can be converted to an opaque white color with titanium dioxide, the dispersibility of which can be promoted with soya lecithin, but the latter can turn the product off-white or cream-colored. PVA is compatible with water-soluble food dyes, which retain their color even after an acid treatment.

Its mechanical properties can be improved by crosslinking. Crosslinking is usually performed with glutaraldehyde followed by hydrogen chloride vapor treatment. The stiffness of PVA increases in proportion to the degree of crosslinking, so it is often softened with glycerine. The resulting crosslinked PVA, when dried at ambient pressure and room temperature, remains smooth, but when dried at higher temperatures, it can become creased and wrinkled. By crosslinking, the water solubility of PVA can be reduced or eliminated, however, even after the formation of the crosslink, it absorbs water and swells, thereby losing its strength and at the same time remaining biodegradable.

In addition to PVA, other biodegradable and biocompatible polymers are also known, such as polylactic acid (PLA) or polyhydroxyalkanoates (PHA), such as polyhydroxybutyrate. PHA increases the degradability, hydrolysis resistance, gas barrier properties of PLA, while PLA increases the transparency, solidity, impact strength of PHA and improves its processability (as it reduces its thermal sensitivity). As polyester polycaprolactone (PCL) or as aliphatic polyester poly(butylene adipate) and poly(butylene succinate) or, for example, poly(butylene succinate-co-adipate) (PBS A) and poly(butylene adipate-co-terephthalate) (PBAT) may also be mentioned. Polyethylene glycol (PEG) is mainly used as a plasticizer or copolymer in addition to other polymers such as PCL. Poly(ester amide) (PEA), cellulose acetate (CA) and starch (C6Hi₀O5)_n are also known. The latter is used in a form converted to thermoplastic starch (TPS), mostly in combination with PCL or PVA. Said biodegradable polymers can be divided into two groups in terms of their origin.

Examples of polymers derived from petrochemical products are polycaprolactone (PCL), poly(ester amide) (PEA), poly(butylene succinate-co-adipate) (PBS A) and poly(butylene adipate-co-terephthalate) (PBAT). The other production group is polymers produced from renewable resources. These can be polymers produced directly from biomass, such as starch and lignocellulose, or polymers produced by microorganisms of animal or plant origin, such as polyhydroxyalkalonate (PHA) and poly(hydroxybutyrate-co-valerate) (PHBV), or biotechnologically produced polymers, such as polylactic acid (PLA).

U.S. Patent No. 4,372,311 discloses disposable articles or substrates made from a water-soluble polymer, which has a surface coated with a degradable water-insoluble polymer. The product is preferably produced in the form of a film or sheet and used in healthcare products. PVA is mentioned as a water-soluble polymer, but no example is shown for it. The water-insoluble polymer used is a cyclic ester, poly(P-hydroxybutyrate) or dialkanoyl and other types of polymers, which is applied as a separate coating to the water- soluble polymer base.

In U.S. Patent Application No. US2012/0061883, a barrier coating is applied on preforms made of various plastic materials (PET, PP, PE, COC) by a dipping process, which barrier coating comprises at least one polyvinyl alcohol coating layer and on that, at least one polyvinyl acetal, such as polyvinyl butyral coating layer. Said layers are used in order to reduce the gas permeability. The preforms are blown into bottles.

Patent application W02004/016234 relates to capsule preparations containing cosmetic, dental or agrochemical agents, the inner surface of the capsule being coated with, inter alia, polyvinyl acetal or polyvinyl butyral and the outer surface with PVA. In Example 5, for example, a solution of polyvinyl alcohol is added to a suspension of melamine formaldehyde-based capsules prepared in situ , which is then acidified and formaldehyde is added to form polyvinyl acetal, which precipitates on the surface of said capsules.

Janovak et al. described the modification of the surface of an amino-containing biopolymer (chitosan) with alkylaldehydes, which was used to control the pH-dependent properties of polyelectrolytes [European Journal of Pharmaceutical Sciences, 123, 79-88 (2018)].

However, to our knowledge, the hydrophobization of the surface of hydrophilic polymers by reacting with alkyl monoaldehydes or alkylsilanes to produce biodegradable products has not been described to date.

The aim of the present work was to create a hydrophobic surface layer with well- designable properties on PVA-containing hydrophilic plastics, wherein the product life of the article can be controlled by changing the properties of the surface layer, i.e. the biodegradation can be planned. This provides products for storage or packaging of liquids and wet goods that can be composted after use. In addition, the product (shaped article) of the present invention with the hydrophobic surface has other advantageous properties, which are described in the following description.

The modified polymer of the present invention is preferably used in all areas where liquid or solid foods are stored, packaged or served. It can also be used as a material for sanitary articles such as diapers, sanitary napkins, incontinence products, and in other fields such as the cosmetics industry or agriculture.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with the foregoing, the present invention relates to a biodegradable shaped article with a hydrophobic surface, which has a hydrophilic backbone containing polyvinyl alcohol and part or all of its surface is covered with covalently bonded alkyl chains, which alkyl chains are formed by reacting the surface hydroxyl groups of the polyvinyl alcohol with an alkyl monoaldehyde compound or a reactive alkylsilane compound.

In one embodiment, said alkyl monoaldehyde compound is butyraldehyde.

In another embodiment, said reactive alkylsilane compound is alkyl trichlorosilane.

In some embodiments, the hydrophilic backbone of the shaped article is formed from a composite comprising a polymer or polymers defined in any one of the following groups:

(i) polyvinyl alcohol;

(ii) a mixture of polyvinyl alcohol and one or more hydrophilic biodegradable polymers different from polyvinyl alcohol in any proportion;

(iii) a vinyl alcohol copolymer in which the other comonomer is styrene or an acrylate monomer or another vinyl monomer, or a mixture of said copolymer with one or more of the polymers of (i) or (ii) above; and

(iv) a backbone formed from one of the hydrophilic biodegradable polymers different from polyvinyl alcohol listed in (ii) above, or a mixture thereof in any proportion, which is coated with a polyvinyl alcohol-containing coating such as coated with a composite according to (i) or (ii) above.

In the above embodiments, the one or more hydrophilic biodegradable polymers different from polyvinyl alcohol are selected, for example, from the group consisting of starch, chitosan, cellulose and its derivatives, polyethylene glycol, gelatin, agar-agar, alginate, and polysaccharides.

In one embodiment, the copolymer is, for example, a copolymer consisting of vinyl alcohol and styrene or an acrylate (e.g., methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl acrylate-co-methyl methacrylate, acrylic polyurethane) or another vinyl monomer (polyvinyl acetate), wherein the ratio of monomers in the copolymer preferably ranges from 20 to 80%.

In some embodiments, the shaped article is crosslinked with dialdehyde.

In one embodiment, said dialdehyde is glutaraldehyde. In some embodiments, the shaped article comprises a plasticizer. In one embodiment, said plasticizer is glycerine.

In some embodiments, the shaped article comprises roughening particles.

In some embodiments, the roughening particles are inorganic particles selected from Si0₂, Ti0₂ and clay minerals, or organic particles selected from cellulose, alginate and chitosan, or a mixture thereof in any proportion.

The present invention relates to the preparation of the above-mentioned biodegradable, polyvinyl alcohol-containing shaped article with hydrophobic surface.

The process according to the invention comprises the following steps:

Step (a): the backbone of the shaped article is formed by one of the following alternative steps (al), (a2) or (a3):

Step (al): the powder or granules of a polymer according to any one of (i), (ii) or (iii) above, or a mixture of these powders or granules, is melted, a dialdehyde plasticizer is optionally added, a crosslinking agent is optionally added and roughening particles are optionally added to the resulting polymer melt, and then the mixture is pressed into a mould, Step (a2): an aqueous or alcoholic solution of the polymer or mixture of polymers according to any one of (i), (ii) or (iii) above is prepared by heating, then cooled down, and optionally a plasticizer, optionally a dialdehyde crosslinking agent and optionally roughening particles are added, then the mixture is poured on an even surface and the water is removed,

Step (a3): a backbone of shaped article is prepared from one or more biodegradable polymers different from polyvinyl alcohol by the process according to (al) or (a2) above, and in parallel, an aqueous or alcoholic solution of polyvinyl alcohol is prepared by heating, which optionally contains other biodegradable polymers, then cooled down, and optionally a plasticizer, optionally a dialdehyde crosslinking agent and optionally roughening particles are added to the polymer, and the resulting coating mixture is applied on said backbone of shaped article by a dipping or spraying process, then the water or alcohol used in the preparation of the solution is removed, to obtain a backbone of shaped article provided with a polyvinyl alcohol-containing coating;

Step (b): in case where a crosslinking agent is added in the preparation of the backbone of shaped article in the above-mentioned step (a), the crosslinking is carried out in an atmosphere saturated with hydrogen chloride vapor;

Step (c): the surface of the backbone of shaped article obtained in step (a) or (b) above is hydrophobized by one of the following alternative steps (cl) and (c2):

(cl) an alkylaldehyde reagent is applied in an aqueous or alcoholic solution to said surface by a dipping or spraying process, and it is reacted with the surface hydroxyl groups of the polyvinyl alcohol in the presence of hydrogen chloride vapor,

(c2) a reactive alkylsilane reagent is applied in an alcoholic or hexane solution to said surface by a dipping or spraying process, which reacts with the surface hydroxyl groups of the polyvinyl alcohol.

In one embodiment of the process according to the invention, a film-shaped shaped article is produced, which process comprises the following steps:

Step (a): an aqueous or alcoholic solution of polyvinyl alcohol is prepared, to which optionally a dialdehyde plasticizer, optionally a roughening particle and optionally a crosslinking agent is added, then the mixture is homogenized and poured onto an even surface;

Step (b): in case where said crosslinking agent is used, the crosslinking is carried out in an atmosphere saturated with acid vapor; and

Step (c): the surface of the obtained backbone of shaped article is hydrophobized by one of the following alternative steps (cl) and (c2):

(cl) an alkylaldehyde reagent is applied in an aqueous or alcoholic solution on the film obtained in step (a) or (b) by a dipping or spraying process, and it is reacted with the surface hydroxyl groups of the polyvinyl alcohol in an atmosphere saturated with hydrogen chloride vapor,

(c2) a reactive alkylsilane reagent is applied in an alcoholic or hexane solution on the film obtained in step (a) and (b) by a dipping or spraying process, and it is reacted with the surface hydroxyl groups of the polyvinyl alcohol.

In another embodiment of the process according to the invention, a shaped article of any shape is produced, which process comprises the following steps:

Step (a): powder or granules of polyvinyl alcohol are melted at a temperature in the range of 120 °C to 180 °C, then a plasticizer is added to the resulting polymer melt, and the resulting melt is pressed into a mould of suitable size and shape;

Step (b): a reactive alkylsilane reagent is applied in alcoholic or hexane solution on the backbone of the shaped article by a dipping or spraying process, and it is reacted with the surface hydroxyl groups of the polyvinyl alcohol. Optionally, an additional layer is applied to the product obtained in steps (a) and (b) of the preceding paragraph by dipping or spraying to improve other properties of the shaped article (hardness, flexibility, mechanical properties, impact resistance). This lacquer layer may be an acrylic derivative, an acrylic polyurethane derivative, a vinyl derivative or copolymers thereof, as described above. In any of the above processes, the dialdehyde crosslinking agent optionally used is glutaraldehyde and the optionally used plasticizer is glycerine. Optionally, roughening particles are used. The roughening particles are selected from Si0₂, Ti0₂, clay minerals, cellulose, alginate and chitosan particles and mixtures thereof. DETAILED DESCRIPTION OF THE INVENTION

In the present invention, the surface of a product (shaped article) made of a polyvinyl alcohol (PVA) containing composite is modified with covalently bonded alkyl groups to form a uniform hydrophobic surface molecular layer covalently bonded to the hydrophilic polymer backbone. The hydrophobic surface makes the product suitable for storing or packaging liquids and wet goods. However, the surface modification according to the invention does not affect the internal structure of the backbone, thus the latter remains water-soluble. Thus, when the PVA-based plastic article becomes waste, its internal structure can be revealed, for example, by simple grinding, making it accessible to water, swelling, dissolving, and microbially degrading.

If the backbone is crosslinked, the crosslinked PVA retains its hydrophilic properties, i.e. it continues to absorb water, and consequently tends to swell, but this weakens its strength.

The hydrophilic backbone of the shaped article

The shaped article defines the shape of the product and provides the appropriate mechanical properties such as strength, rigidity or flexibility. The backbone is formed from a PVA-based polymer composite.

As used herein, the term composite refers to compositions formed by combining one or more polymers and polymerization and performance enhancing additives.

In one embodiment of the invention, the main component of the backbone composite is PVA, as described in (i) above for the backbone composites Commercial PVA products are generally prepared by hydrolysis of polyvinyl acetate.

The PVAs thus obtained are marketed with varying degrees of hydrolysis and contain a certain amount of acetate units.

There is no limitation on the vinyl acetate content of the PVA used in the present invention as long as its vinyl alcohol content is suitable for carrying out the present invention. The PVA we use typically contains 0-20% by weight, such as 8-14% by weight of vinyl acetate units. As used herein, this low vinyl acetate polymer is simply referred to as polyvinyl alcohol or PVA.

The PVA used in the following examples was obtained commercially.

PVA powder is produced by CTS Sri - Via Piave 20/22 - 36077 Altavilla Vicentina (VI). Product characteristics: ivory colored powder, viscosity: 4 ± 0.5 mPas (as 4% aqueous solution at 20 °C), density: 1.23 - 1.30 kg/L at 20 °C, pH about 5 (as a 4% aqueous solution at 20 °C), degree of hydrolysis 86-89, saponification number 140.

PVA granules are manufactured by SH Chemical Group Limited. Product characteristics: yellow or white granules, melting range 159-191 °C, glass transition temperature 30-62 °C, standard melt flow index (MFI) 14-20 g / 10 min, density 0.6-0.9 kg/L at 20 °C, pH 5-7, degree of hydrolysis 78.5-100.

In other embodiments, the backbone of the shaped article according to the present invention may be made of a composite comprising PVA and one or more other biodegradable polymers. Such are the composites given in (ii) above for the composites forming the material of the backbone. Examples of biodegradable polymers different from PVA are chitosan, cellulose and its derivatives, such as cellulose acetate, polyethylene glycol, gelatin, agar-agar, alginate, polysaccharides, polylactic acid, polyhydroxyalkanoates such as polyhydroxybutyrate, polyesters such as polycaprolactone, poly(butylene adipate) and poly(butylene succinate), polyethylene glycol, poly(ester amide) and starches and mixtures thereof, wherein the mixtures may be in any ratio, for example 20-80% for two components.

In this embodiment, the ratio of the PVA to the one or more other biodegradable polymers may be any ratio, as long as the present invention can be carried out with it. Said ratio is, for example, in the range from 0.1 to 20% by weight.

The backbone can also be made of a vinyl alcohol-containing copolymer or a combination of this copolymer with another biodegradable polymer or polymers.

Composites of this type are described in (iii) above. Said copolymer is, for example, a copolymer consisting of vinyl alcohol and styrene or an acrylate (for example methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl acrylate-co-methyl methacrylate, acrylic polyurethane) or another vinyl monomer (polyvinyl acetate), wherein the ratio of monomers in the copolymer preferably ranges from 20 to 80%. Furthermore, said copolymer may be of any type, for example a random, block or graft copolymer, provided that they are practicable in the present invention. Said copolymer can be formed by copolymerization of the corresponding monomers or by modification of a homopolymer and other known methods. These copolymers are, for example, copolymers of vinyl alcohol with styrene or an acrylate or another vinyl monomer.

In the case of the composites forming the backbone material, in the embodiment given in (iv) above, the backbone is made of a hydrophilic biodegradable polymer different from PVA or a mixture thereof, which is coated with a PVA-containing coating. As the hydrophilic biodegradable polymer different from PVA, the above-mentioned biodegradable polymers can also be used, namely chitosan, cellulose and its derivatives, polyethylene glycol, gelatin, agar-agar, alginate, polysaccharides, polylactic acid, polyhydroxyalkanoates such as polyhydroxybutyrate, polyesters such as polycaprolactone, poly(butylene adipate) and poly(butylene succinate), polyethylene glycol, poly(ester amide) and/or starches in any ratio with PVA, preferably 20-80%.

The coating according to the above-mentioned (iv) may consist only of a PVA homopolymer or of a PVA-containing polymer mixture referred to in the above-mentioned group (ii) of composites forming the backbone material. Thus, in this technical solution, a hydrophilic coating is applied to the hydrophilic backbone, wherein the surface of the coating is hydrophobized according to the technical solution of the present invention. In some embodiments, the backbone of the shaped article is crosslinked with, for example, 1 to 25% by weight of dialdehyde based on the weight of polyvinyl alcohol present. In one embodiment, said dialdehyde crosslinking agent is glutaraldehyde.

In some embodiments, the shaped article comprises a plasticizer in a concentration of 1 to 25% by weight based on the weight of the shaped article. In one embodiment, said plasticizer is glycerine.

In some embodiments, the shaped article comprises roughening grains in a concentration of 1 to 80% by weight based on the weight of the shaped article. The type and role of the roughening particles are returned to in the "Hydrophobic surface layer" section below.

Hydrophobic surface layer

The hydrophobic surface layer protects the hydrophilic backbone from moisture and other external influences, and by adjusting the properties of the surface layer, the degree of waterproofing property and lifetime can be controlled, thereby the product life of the article can be adjusted. In addition, the surface layer itself is biodegradable.

The hydrophobicity of the surface is determined by the coverage with alkyl chains. This can be controlled by changing the reaction parameters. Such parameters include, in particular, the concentration of the monoaldehyde or alkylsilane solution, the number of carbon atoms of the hydrophobizing molecules, the reaction time and the like. Thus, by varying these parameters, the water solubility of the originally water-soluble PVA-based backbone can be reduced or eliminated in a controlled manner.

In some embodiments of the invention, the hydrophobic layer covers the entire surface of the backbone of the shaped article, and in other embodiments, a portion of the surface.

The alkyl chain-coated surface is formed by reacting the hydroxyl groups on the surface sections of the polymer chains of PVA with alkyl monoaldehydes or alkylsilanes. Said polymer chains continue in an unmodified form below the surface, whereby the hydrophobic chain sections formed are chemically bonded to the unmodified PVA polymer chain sections below the surface. The latter are mixed at molecular level with the other subsurface polymer chains, and this mixture forms the material of the backbone of the shaped article. In the case of crosslinking, said polymer chains are chemically bonded to one another. Thus, in the technical solution according to the present invention, the hydrophobic surface is covalently bonded to the polymeric material of the backbone, which provides a much stronger bond than a polymer of similar chemical structure (i.e., PVA modified by an alkyl side chain) but produced in a separate step and applied onto the backbone by conventional coating techniques, because such a coating binds to the polymer carrier (polymer backbone) only by secondary forces (e.g., Van der Waals). The latter type of coatings is known in the art (see Technical background).

It follows from the above that the properties of the covalently bonded hydrophobic surface layer of the present invention can be better designed and reproduced more reliably.

A further advantage of hydrophobizing the surface of the product according to the present invention over the conventional coating methods mentioned above is that there is no problem of compatibility between the hydrophobic polymer coating and the hydrophilic polymeric carrier.

In addition, from the polymer coating applied in a separate step small molecules (such as plasticizers, monomers, catalysts, and the like) that are harmful to health and trapped between the polymer chains during the production of the polymer to be applied as coating can migrate to the surface over time. This phenomenon need not be taken into account in the technical solution according to the invention, since herein hydrophobic alkyl chains are bond to the hydrophilic polymer backbone.

When the PVA-containing surface of the shaped article is reacted with monoaldehydes, the alkylaldehyde is attached to two adjacent hydroxyl groups of the vinyl alcohol units of the PVA to form chain segments containing cyclic acetal units of the formula below:

wherein x is an integer from 1 to 6, preferably from 1 to 2. Thus, the alkylaldehyde used has 4 to 18, preferably 4 to 8, carbon atoms.

In another embodiment, the hydrophobic surface is formed by reacting alkylsilanes. In this case, the alkylsilane is attached to two adjacent hydroxyl groups of the vinyl alcohol units of PVA to form chain segments containing cyclic units of the formula below: wherein y is an integer from 1 to 6, preferably from 1 to 2. Thus, the alkylsilane used has 4 to 18, preferably 4 to 8, carbon atoms.

It is possible that the surface modification according to the present invention also produces units with a different chemical structure, which also contain alkyl side chains, and thus they also form part of the present invention. Therefore, the present invention is not limited to PVA-containing shaped articles having a surface coated with ring units of the above structural formula, but the present invention encompasses any biodegradable plastic product in which a PVA-containing backbone or carrier has a hydrophobic surface coated with alkyl side chains applied by reaction with an alkyl monoaldehyde or alkylsilane compound, and any process based on such type of surface modification.

The hydrophobicity of the surface of the product can be further increased by influencing the morphology of the surface, i.e. by increasing its roughness. By creating a suitable surface structure, a so-called superhydrophobic outer layer can be produced, wherein air is trapped between the surface structure elements in the micron or nanometer size range, thus only about 1-2% of the water droplets are in contact with the surface, therefore the water droplets are unable to make the surface wet, they roll down on it.

Some plants, such as the lotus leaf, have a superhydrophobic surface, but artificial water-repellent layers are also used in the industry, for example in so-called “Lotus-Effect” wall paints, which have very favorable self-cleaning properties. Mention may also be made of coatings to prevent corrosion and icing and deposition of scale and/or biofilm.

The surface of the product can be roughened by adding various organic or inorganic filler particles. The particles used can be inorganic or organic fillers. The amount of particles depends on, among other things, the size, surface properties and dispersibility. Examples of inorganic particles are silica, TiCE, various clay minerals (illite, montmorillonite, bentonite, hectorite, and the like), which have a particle size in the range of 10 nm to 500 nm. Examples of organic particles include fillers widely used in the polymer and food industries, such as cellulose, alginate, and chitosan, which have a particle size in the range of 1 micrometer to 50 micrometers.

The properties of the product can also be modified with additives. Its transparency can be reduced, for example, by mixing with starch or carboxymethyl cellulose (E466).

The product can be converted to an opaque white color with titanium dioxide. The dispersibility of the latter can be promoted, for example, with soya lecithin, but this can make the product off-white or cream-colored.

The product may be colored with water-soluble food dyes that are compatible.

The shaped article according to the invention may also comprise an additional layer in order to improve the other properties of the shaped article (hardness, flexibility, mechanical properties, impact resistance). This lacquer layer may be an acrylic derivative, an acrylic polyurethane derivative, a vinyl derivative or copolymers thereof, as described above.

The process according to the invention

Preparation of the hydrophilic shaped article

The backbone of the shaped article can be formed by pressing the above-described polymer composites or by pouring and drying an aqueous solution thereof.

In the case of a pressing process, the powder or granules of the polymer or polymers of the material of the backbone according to (i) to (iii) above are melted. The melting is performed, for example, by heating to 120-180 °C. Then additives, in particular a plasticizer and/or a crosslinking agent and/or roughening particles are optionally added to the resulting polymer melt, and the resulting composite is pressed into a mould.

In the case of a solvent process, an aqueous or alcoholic solution is prepared from the polymer or polymer mixture by heating. We allow it to cool, then optionally add additives, namely a plasticizer and/or a crosslinking agent and/or roughening particles, and pour the resulting mixture onto an even surface, then remove the water. The concentration of the PVA solution produced is selected depending on the wall thickness of the shape, film or coating to be formed. Generally, an aqueous solution having a concentration of 1 to 30% by weight is prepared. As the crosslinking agent, glutaraldehyde can be added in a concentration of 1 to 25% by weight based on the weight of the PVA.

The polymer backbone may also be formed from one or more biodegradable polymers different from polyvinyl alcohol. In this case, a polyvinyl alcohol-containing coating is applied to the backbone. The coating solution is prepared and applied in a similar manner to the solvent process outlined above, i.e., to an aqueous or alcoholic solution of the water- soluble PVA and additional polymer(s) at a concentration of 1 to 30% by weight, optionally a plasticizer, a crosslinking agent, and optionally roughening particles are optionally added, and the resulting coating mixture is applied to the backbone by a dipping or spraying process. By this, we obtain the backbone of the shaped article with a polyvinyl alcohol-containing coating.

As the crosslinking agent in any of the above processes, a dialdehyde crosslinking agent such as glutaraldehyde may be used in a concentration of 1 to 25% by weight based on the weight of the polyvinyl alcohol. As the plasticizer, for example, glycerine can be used in a concentration of 1 to 25% by weight based on the weight of the shaped article. The roughening particles can be used in a concentration of 1 to 80% by weight, based on the weight of the shaped article.

In addition to the above, other additives such as the above-mentioned opacifying or bleaching additives, or coloring agents may be added.

If a crosslinking agent is added in the process, the finished shaped article is crosslinked by treatment in an atmosphere saturated with hydrogen chloride vapor.

Formation of the hydrophobic surface

The surface of the backbone of the shaped article produced in an appropriate shape and size is hydrophobized by reaction with alkylaldehyde or reactive alkylsilane. During this, the backbone is immersed in a solution of an alkylaldehyde or alkylsilane compound for a period of time.

With this process, the hydrophobic surface can be easily formed, which is of particular importance here because of the production of disposable mass-produced articles.

As the alkylaldehyde, alkylaldehydes having 4 to 18 carbon atoms, preferably 4 to 8 carbon atoms, can be used in an aqueous or alcoholic solution of 0.1 to 15% by weight, preferably 0.2 to 8% by weight, which is applied to the shaped article by dipping or spraying, and then in the presence of hydrogen chloride vapor, it is reacted with the surface hydroxyl groups of the polyvinyl alcohol.

As the alkylsilane, a reactive alkylsilane reagent having 4 to 18 carbon atoms, preferably 4 to 8 carbon atoms, such as an alkyl trichlorosilane is used in an alcoholic or hexane solution of 0.1 to 15% by weight, preferably 0.2 to 5% by weight, and this is applied to the shaped article, wherein it reacts with the surface hydroxyl groups of the polyvinyl alcohol. The reaction is usually carried out at an elevated temperature, for example at 50 °C to 80 °C for 2-120 minutes.

In case of both reagents, the alkyl groups attached to the surface of the PVA make the surface more hydrophobic.

After the hydrophobization reaction, the excess reagent is washed from the resulting product with the same pure solvent used to prepare the solution.

One embodiment of the invention relates to the production of a PVA film with a hydrophobic surface. An advantageous feature of PVA, in addition to those described above in the Technical background, is that it can be poured on a Teflon or glass sheet on its own and forms an easy-to-handle plastic-like film that can be easily removed from the surface after drying.

In this process, first an aqueous PVA solution of 1 to 30% by weight is prepared by mixing polyvinyl alcohol powder in cold water and boiling it.

A plasticizer is added to the cooled solution and homogenized. Glycerine is generally used as the plasticizer, but any conventional plasticizer is suitable. The amount of plasticizer added is typically 1 to 25% by weight based on the amount of PVA.

If we want to produce a crosslinked film, a dialdehyde crosslinking agent is added to the solution and homogenized again. Preferably, 1 to 25% by weight of glutaraldehyde, based on the weight of the PVA, is used.

In the case of a roughened surface, the next step is to mix roughening particles to the polymer solution in a concentration of 1 to 80% by weight based on the weight of PVA. The amount of particles added depends on the particle size, surface properties and dispersibility.

If air bubbles have entered the mixture during homogenization, the resulting mixture is placed in a vacuum chamber to remove them.

The bubble-free PVA-based solution is poured onto a hydrophobic low-energy surface, such as an even surface coated with Teflon or silicone, and warm air is blown onto it to remove residual water.

For crosslinking, the film is placed in a chamber filled with hydrogen chloride vapor. Upon action of the hydrogen chloride, the glutardi aldehyde crosslinks the PVA content of the sample.

The resulting PVA film is then immersed in an aqueous or alcoholic solution of 0.1 to 15% by weight, preferably 0.2 to 8% by weight, of an alkylaldehyde having 4 to 8 carbon atoms, or said solution is applied to the surface by spraying. The PVA film containing said solution on its surface is placed in a chamber saturated with hydrogen chloride vapor, wherein the reaction between the hydroxyl groups of the PVA and the aldehyde takes place. The excess of the unreacted aldehyde compound is washed off with pure water or alcohol. Finally, the finished film is peeled off the even surface.

Another embodiment of the invention relates to the production of a shaped article with a hydrophobic surface of any shape. In this process, PVA powder or granules are heated in a heated container or extruder above the melting range, i.e., 120-180 °C, and then a plasticizer, such as glycerine, is added to the resulting polymer melt. The amount of plasticizer added is typically 1 to 25% by weight based on the total amount of polymer.

The resulting polymer melt is pressed into a mould of suitable size and shape, wherein it takes the shape of the mould.

The resulting PVA-based composite thin layer is immersed in an alcoholic or hexane solution of 0.01-15% by weight, preferably 0.1-5% by weight, of an activated alkylsilane having 4 to 7 carbon atoms, or said solution is applied to the surface by spraying.

The excess of the unreacted silane compound is washed off the surface of the product with pure alcohol or hexane. For example, the disposable biodegradable cup shown in Figure 1 was prepared by the latter process.

DESCRIPTION OF THE FIGURES

Figure l is a schematic view of a cup with a hydrophobized surface prepared according to Example 9, and of the structure of its sidewall, with droplet photographs and contact angle values.

Figure 2 shows the effect of soaking time on the contact angle values of a PVA sample treated with a hexane solution of butyl trichlorosilane.

Figure 3 shows the effect of soaking time on the contact angle values of a PVA sample treated with a hexane solution of octyl trichlorosilane.

Figure 4 shows the wetting properties of PVA powder treated with butyl trichlorosilane (B-PVA) or octyl trichlorosilane (O-PVA) in water.

Figure 5 is a photograph of the disk-shaped PVA samples used for dissolution tests.

Figure 6 shows a photograph of PVA samples before (top row) and after (bottom row) dissolution tests.

Figure 7 shows photographs taken during dissolution of PVA samples.

Figure 8 shows the gravimetrically determined dissolution kinetics of the initial PVA.

The present invention is illustrated by the following examples, but they are not intended to limit the scope of the invention. The scope of the invention is defined by the claims.

EXAMPLES

Example 1

Preparation of a PVA film with hydrophobic surface by aldehyde reaction

Polyvinyl alcohol powder is mixed in cold water and heated to the boiling point with constant stirring. The resulting PVA solution is allowed to cool to room temperature, thus an aqueous PVA solution with a concentration of 1 to 30% by weight is prepared. Glycerine plasticizer is added and the resulting mixture is homogenized with stirring. The amount of glycerine is typically 1 to 25% by weight based on the weight of the PVA.

If air bubbles have entered the sample during stirring, the resulting mixture is placed in a vacuum chamber to remove them.

The bubble-free PVA-based solution is poured onto a low-energy hydrophobic surface, such as an even surface coated with Teflon or silicone, and warm air is blown onto it until the residual water is removed.

The resulting PVA-based composite thin layer is immersed in an aqueous or alcoholic solution of 0.1 to 15% by weight, preferably 0.2 to 8% by weight, of a C4-C8 alkylaldehyde (e.g. butyraldehyde), or said solution is applied to the surface by a spraying process.

The film containing aldehyde on its surface is placed in a chamber saturated with hydrogen chloride vapor, wherein the reaction between the hydroxyl groups of the PVA and the aldehyde takes place, and the hydrophobic surface is formed.

The excess of the unreacted aldehyde is washed off the surface of the product with pure water or alcohol.

Example la

Preparation of a PVA film with hydrophobic surface by aldehyde reaction

Polyvinyl alcohol powder is mixed in cold water and heated to the boiling point with constant stirring. The resulting PVA solution is allowed to cool to room temperature, thus an aqueous PVA solution with a concentration of 15% by weight is prepared. Glycerine plasticizer is added and the resulting mixture is homogenized with stirring. The amount of glycerine is typically 15% by weight based on the weight of the PVA.

The bubble-free PVA-based solution is poured onto an even surface coated with Teflon, and warm air is blown onto it until the residual water is removed.

The resulting PVA-based composite thin layer is immersed in an aqueous solution of 7% by weight of butyraldehyde.

Example 2

Preparation of a PVA film with a rough hydrophobic surface by aldehyde reaction

In the next step, inorganic particles in the range of 10 nm to 500 nm (e.g. S1O2, T1O2, clay mineral) or organic particles in the range of 1 micrometer to 50 micrometers (e.g. cellulose, microcrystalline cellulose, alginate, chitosan) are mixed with the polymer solution at a concentration of 1 to 80% by weight based on the weight of the PVA.

The resulting PVA-based composite thin layer is immersed in an aqueous or alcoholic solution of 0.1 to 15% by weight, preferably 0.2 to 8% by weight, of a C4-C8 alkylaldehyde (e.g. butyraldehyde), or said solution is applied to the surface by spraying technique.

Example 3

Preparation of a crosslinked PVA film with hydrophobic surface by aldehyde reaction

Then 1 to 25% by weight of glutaraldehyde crosslinking agent, based on the weight of the PVA, is added to the solution and homogenized again.

For crosslinking, the dried film is placed in a chamber filled with hydrogen chloride vapor.

The excess of the unreacted aldehyde is washed off the surface of the product with pure water or alcohol. Example 3a

Preparation of a crosslinked PYA film with hydrophobic surface by aldehyde reaction

Then 1 to 25% by weight of glutaraldehyde crosslinking agent and 1 to 10% by weight of citric acid, based on the weight of the PVA, are added to the solution and homogenized again.

The crosslinking takes place during the drying process due to the glutaraldehyde and citric acid in the PVA.

Example 4

Preparation of a crosslinked PVA film with a rough hydrophobic surface by aldehyde reaction

In the next step, inorganic particles in the range of 10 nm to 500 nm (e.g. Si0₂, Ti0₂, clay mineral) or organic particles in the range of 1 micrometer to 50 micrometers (e.g. cellulose, microcrystalline cellulose, alginate, chitosan) are mixed with the polymer solution at a concentration of 1 to 80% by weight based on the weight of the PVA.

Example 5

Preparation of a PVA film with hydrophobic surface by silanization

The resulting PVA-based composite thin layer is immersed in an alcoholic or hexane solution of 0.01 to 15% by weight (preferably 0.2 to 5% by weight) of a reactive C4-C8 alkylsilane (e.g. butyl trichlorosilane), or said solution is applied to the surface by spraying technique. The reaction is carried out at a temperature of 50-80 °C for 2-120 minutes.

The excess of the unreacted silane compound is washed off the surface of the product in pure alcohol or hexane.

Example 6

Preparation of a PYA film with a rough hydrophobic surface by silanization

The bubble-free PVA-based solution is poured onto a hydrophobic low-energy surface, such as an even surface coated with Teflon or silicone, and warm air is blown onto it until the residual water is removed.

Example 6a

Preparation of a PVA film with a rough hydrophobic surface by silanization Polyvinyl alcohol powder is mixed in cold water and heated to the boiling point with constant stirring. The resulting PVA solution is allowed to cool to room temperature, thus an aqueous PVA solution with a concentration of 20% by weight is prepared. Glycerine plasticizer is added and the resulting mixture is homogenized with stirring. The amount of glycerine is typically 20% by weight based on the weight of the PVA.

In the next step, S1O2 particles in the range of 10 nm to 500 nm are mixed with the polymer solution at a concentration of 60% by weight based on the weight of the PVA.

If air bubbles have entered the sample during stirring, the resulting mixture is placed in a vacuum chamber to remove them. The bubble-free PVA-based solution is poured onto an even surface coated with silicone, and warm air is blown onto it until the residual water is removed.

To the resulting PVA-based composite thin layer, a hexane solution of 10% by weight of butyl trichlorosilane is applied to the surface by spraying technique. The reaction is carried out at a temperature of 70 °C for 60 minutes. The excess of the unreacted silane compound is washed off the surface of the product in pure alcohol or hexane.

Example 7

Preparation of a PVA shaped article with hydrophobic surface by aldehyde reaction and injection molding PVA powder or granules are heated to 120-180 °C in a heated container or extruder, and then a glycerine plasticizer is added to the resulting polymer melt. The amount of glycerine is typically 1 to 25% by weight based on the weight of the PVA.

The resulting polymer melt is pressed into a mould of suitable size and shape.

The film containing aldehyde on its surface is placed in a chamber saturated with hydrogen chloride vapor, wherein the reaction between the hydroxyl groups of the PVA and the aldehyde takes place, and the hydrophobic surface is formed. The excess of the unreacted aldehyde is washed off the surface of the product with pure water or alcohol. Example 8

Preparation of a PYA shaped article with a rough hydrophobic surface by aldehyde reaction and injection molding

PVA powder or granules are heated to 120-180 °C in a heated container or extruder, and then a glycerine plasticizer is added to the resulting polymer melt. The amount of glycerine is typically 1 to 25% by weight based on the weight of the PVA.

The resulting polymer melt is pressed into a mould of suitable size and shape.

The resulting PVA-based composite thin layer is immersed in an aqueous or alcoholic solution of 0.1 to 15% by weight, preferably 0.2 to 8% by weight, of a C4-C8 alkylaldehyde (e.g. butyraldehyde), or said solution is applied to the surface by spraying technique. The film containing aldehyde on its surface is placed in a chamber saturated with hydrogen chloride vapor, wherein the reaction between the hydroxyl groups of the PVA and the aldehyde takes place, and the hydrophobic surface is formed.

The excess of the unreacted aldehyde is washed off the surface of the product with pure water or alcohol. Example 9

Preparation of a PVA shaped article with hydrophobic surface by silanization and injection molding

The resulting polymer melt is pressed into a mould of suitable size and shape.

The resulting PVA-based composite thin layer is immersed in an alcoholic or hexane solution of 0.01 to 15% by weight, preferably 0.1 to 8% by weight, of a reactive C4-C8 alkylsilane, or said solution is applied to the surface by spraying technique. The reaction is carried out at a temperature of 50-80 °C for 2-120 minutes.

The excess of the unreacted silane compound is washed off the surface of the product in pure alcohol or hexane. Figure l is a schematic view of a cup with a hydrophobized surface prepared according to Example 9, and of the structure of its sidewall. The droplet photographs shown in the figure represent the wetting properties of each structural component, namely the water contact angle is <5° on the hydrophilic backbone, while the water contact angle is >90° on the hydrophobized product, and the water contact angle is about 150° on the roughened surface.

Example 10

Preparation of a PYA shaped article with a rough hydrophobic surface by silanization and injection molding PVA powder or granules are heated to 120-180 °C in a heated container or extruder, and then a glycerine plasticizer is added to the resulting polymer melt. The amount of glycerine is typically 1 to 25% by weight based on the weight of the PVA.

The resulting polymer melt is pressed into a mould of suitable size and shape.

Example 11 Preparation of a crosslinked PVA shaped article with a rough hydrophobic surface by silanization and injection molding

PVA powder or granules are heated to 120-180 °C in a heated container or extruder, and then a glycerine plasticizer, glutaraldehyde and citric acid are added to the resulting polymer melt. The amount of glycerine and glutaraldehyde is typically 1 to 25% by weight, and the amount of citric acid is 1 to 10% by weight based on the weight of the PVA.

The resulting polymer melt is pressed into a mould of suitable size and shape.

The crosslinking takes place during or after the injection molding process due to the glutaraldehyde and citric acid in the PVA.

The resulting PVA-based composite thin layer is immersed in an alcoholic or hexane solution of 0.01 to 15% by weight, preferably 0.1 to 8% by weight, of an activated C4-C8 alkylsilane, or said solution is applied to the surface by spraying technique.

Example 12

Preparation of a PVA-based cup with hydrophobic surface by injection molding

We follow the procedure of any one of Examples 7 to 10 above, wherein the PVA powder is melted at 180 °C and the melt is pressed into a cup-shaped mould.

Wetting tests

Contact angle measurements were performed to determine the wetting properties of the solid surfaces. In the process, water droplets with a certain volume (typically 10 pL) were placed on the surface of the samples, which droplet fitted to the solid surface at a given angle depending on the wetting properties of the surface. The contact angle is related to the interfacial tension between the drop and the test surface as follows. The value of the contact angle, also known as the wetting angle (0_W, contact angle), is defined by the Young equation with the following relation:

(YSV YSL )

COS 0 =

YLV wherein ysv is the solid-vapor, J_SL is the solid-liquid and J _V is the liquid-vapor interfacial tension values.

The effect of surface treatment with butyl trichlorosilane or octyl trichlorosilane on the wetting properties of the initial PVA is shown below. It can be seen in Figure 1 that as a result of the treatment (soaking) time, the characteristic contact angle (<5°) of the initial PVA increases significantly, and in case of butyl trichlorosilane it reaches about 130° and in case of the octyl trichlorosilane it reaches 120°.

Figures 2 and 3 show the contact angles of PVA samples hydrophobized with a hexane solution containing 1% butyl trichlorosilane or 1% octyl trichlorosilane, respectively, as a function of reaction time. The figures show the effect of soaking time on the contact angle values of the treated PVA samples.

The photos shown in Figure 4 also show that, after surface treatment with butyl trichlorosilane and octyl trichlorosilane, the initial water-soluble PVA (first photo from the left) was no longer water-dispersible (photos in the middle and on the right).

Degradation tests

The dissolution kinetics of the PVA-based samples were examined on discs with a diameter of about 5.4 cm (m=4.570±0.046 g) (Figure 5). Dissolution was determined gravimetrically: the discs were cut into four equal portions (Figure 6), their initial weights were determined (Table 1), and each quarter was placed in 75 ml of 22.5 °C tap water and the system was mildly stirred (250 rpm). As a function of the dissolution time, the systems were photographed (Figure 7), and at given time intervals 1-1 samples were taken out, dried and weighed (Table 1). From the obtained data, the solubility and dissolution kinetics of the sample can be calculated.

Table 1 and Figure 8 show the dissolution kinetics of the initial PVA sample (without the hydrophobic surface layer). Based on the results, it can be seen that, due to its hydrophilic properties, the PVA sample was completely dissolved in tap water in 75 minutes under the applied test conditions. The above test was also performed on the hydrophobized samples and the amount of time required for complete dissolution for each sample was determined. Our summary results are shown in Table 2. Based on the results, it can be concluded that the solubility properties of the samples in tap water can be significantly varied with the synthesis conditions: the initial hydrophilic PVA has a dissolution time of 1.25 hours, which can be extended to up to 80-100 days by crosslinking, controlling the surface morphology (roughness) and the hydrophobic surface layer (quality and quantity of the aldehyde and silane molecules used).

Based on the methods found in the literature, we also determined how PVA samples degrade in soil [Adriana de Campos et al. , Braz. Arch. Biol. Technol. 54 (2011) 1367-1378 and Xiao-feng Chen et al. , Journal of Nanomaterials 810464 (2015)]. In the experiments, PVA pieces of unit size (see Figure 2) were placed in commercially available potting soil to a depth of 10 cm, but before that, tap water was mixed to the soil, as much as could be adsorbed (about 60%). Thereafter, the moisture content thus generated was kept constant. The soil was not sterilized prior to testing so that the microorganisms in it causing biodegradation were not killed. Here, PVA degradation was also determined gravimetrically: at given time intervals 1-1 PVA samples were taken out, carefully cleaned, dried and weighed. From the obtained data, the degradation of the sample can be calculated. Table 2 shows the times required for complete degradation of the samples. Based on the results, it can be concluded here as well that the biodegradation properties of the samples measured in wet soil can be significantly changed with the synthesis conditions: the initial hydrophilic PVA is typically characterized by a degradation time of about two months, which can be extended to up to 8-10 years by crosslinking, controlling the surface morphology (roughness) and the hydrophobic surface layer (quality and quantity of aldehyde and silane molecules used).

Table 1: Weights of the PVA samples measured initially and after dissolution and the percentage values determined therefrom, as a function of dissolution time

Weight Residual

Sample Dissolution Initial weight remaining after weight number time (min) (g) dissolution (g) (%)

1 10 1.146 0.9037 78.85

2 20 1.1635 0.6660 57.24

3 30 1.1007 0.4152 37.72

4 45 1.0796 0.0893 8.27

5 60 1.0604 0.0131 1.23

6 75 1.141 0 0 7 90 1.1492 0 0

Table 2: Weights of the PVA samples measured initially and after dissolution and the percentage values determined therefrom, as a function of dissolution time

Claims

1. Biodegradable shaped article with hydrophobic surface, which shaped article has a hydrophilic backbone containing polyvinyl alcohol and a part of its surface or the whole surface is covered with covalently bonded alkyl chains, wherein said alkyl chains are formed by reacting the surface hydroxyl groups of polyvinyl alcohol with an alkyl monoaldehyde compound or a reactive alkylsilane compound.

2. The shaped article according to claim 1, wherein said alkyl monoaldehyde is butyric aldehyde.

3. The shaped article according to claim 1, wherein said reactive alkylsilane is butyl trichlorosilane.

4. The shaped article according to any of claims 1 to 3, wherein the hydrophilic backbone is formed from a composite consisting of a polymer or polymers defined in any one of the following groups:

(i) polyvinyl alcohol;

(ii) a mixture of polyvinyl alcohol and one or more biodegradable polymers different from polyvinyl alcohol;

(iii) a vinyl alcohol copolymer, wherein the other comonomer is styrene or an acrylate monomer or another vinyl monomer, or a mixture of said copolymer with the polymer of group (i) above or the polymers of group (ii) above; and

(iv) a backbone formed from a biodegradable polymer or a mixture of biodegradable polymers different from polyvinyl alcohol, in any proportion, wherein the backbone is provided with a coating containing polyvinyl alcohol.

5. The shaped article according to claim 4, wherein the one or more biodegradable polymers different from polyvinyl alcohol are selected from the group consisting of starch, chitosan, cellulose and its derivatives, polyethylene glycol, gelatine, agar-agar, alginate and polysaccharides.

6. The shaped article according to any of claims 1 to 5, which is optionally crosslinked with a dialdehyde, wherein the dialdehyde is for example glutaric aldehyde, and/or wherein the shaped article optionally contains a plasticizer, wherein the plasticizer is for example glycerine, and/or wherein the shaped article optionally contains roughening particles, wherein the roughening particles are selected for example from Si0₂, Ti0₂, clay minerals, cellulose, alginate and chitosan.

7. Process for the preparation of the polyvinyl alcohol-containing biodegradable shaped article with hydrophobic surface, according to any of claims 1 to 6, which process comprises the following steps:

Step (a): the backbone of the shaped article is formed, wherein

(al) powder or granules of a polymer or polymers defined in any one of the groups according to claim 4 is melted, to the resulting polymer melt a plasticizer and/or a dialdehyde crosslinking agent and/or roughening particles are optionally added, and the mixture is pressed into a mould; or

(a2) an aqueous or alcoholic solution of a polymer or a polymer mixture defined in any one of the groups according to claim 4 is prepared by heating, then cooled down and a plasticizer and/or a crosslinking agent and/or roughening particles are optionally added, then this mixture is poured on an even surface and the water or alcohol is removed, or

(a3) a backbone of shaped article is prepared from one or more biodegradable polymers different from polyvinyl alcohol by the process according to point (al) or (a2) above, in parallel, an aqueous or alcoholic solution of polyvinyl alcohol with a concentration of 1-30 % by weight is prepared by heating, then cooled down and optionally a plasticizer and/or a dialdehyde crosslinking agent and/or roughening particles are added, and the resulting coating mixture is applied on said backbone of shaped article by a dipping or spraying process and the water or alcohol used in the preparation of the solution is removed, to obtain a backbone of shaped article coated with polyvinyl alcohol;

Step (b): in case where a crosslinking agent is added in the preparation of the backbone of the shaped article, the crosslinking is carried out in an atmosphere saturated with hydrogen chloride vapour;

Step (c): the surface of the backbone of shaped article obtained in step (a) or (b) above is hydrophobized, wherein

(cl) an alkylaldehyde reagent is applied in aqueous or alcoholic solution on said surface by a dipping or spraying process, then it is reacted with the surface hydroxyl groups of the polyvinyl alcohol in the presence of hydrogen chloride vapour, or

(c2) a reactive alkylsilane reagent is applied in alcoholic or hexane solution on said surface by a dipping or spraying process, then it is reacted with the surface hydroxyl groups of the polyvinyl alcohol.

8. The process according to claim 7, wherein the optionally added dialdehyde crosslinking agent is glutaric aldehyde, the optionally added plasticizer is glycerine and the optionally added roughening particles are selected from particles of Si0₂, Ti0₂, clay minerals, cellulose, alginate and chitosan and their mixtures of any proportion.

9. The process according to claim 7 or 8 for the preparation of polyvinyl alcohol-containing biodegradable shaped article with hydrophobic surface, wherein the shaped article is a film, which process comprises the following steps:

Step (a): an aqueous or alcoholic polyvinyl alcohol solution is prepared, a plasticizer and/or roughening particles and/or a dialdehyde crosslinking agent is optionally added, then the mixture is homogenized and poured onto an even surface;

Step (b): in case where a dialdehyde crosslinking agent is added, the crosslinking is carried out in an atmosphere saturated with acid vapour; and

Step (c): the obtained backbone of shaped article is hydrophobized, wherein (cl) an alkylaldehyde reagent is applied in aqueous or alcoholic solution on the film obtained in step (a) or (b) by a dipping or spraying process, then it is reacted with the surface hydroxyl groups of the polyvinyl alcohol in an atmosphere saturated with hydrogen chloride vapour, or

(c2) a reactive alkylsilane reagent is applied in alcoholic or hexane solution on the film obtained in step (a) or (b) by a dipping or spraying process, then it is reacted with the surface hydroxyl groups of the polyvinyl alcohol.

10. The process according to claim 7 for the preparation of the polyvinyl alcohol-containing biodegradable shaped article with hydrophobic surface, which process comprises the following steps:

Step (a): powder or granules of polyvinyl alcohol is melted, to the resulting polymer melt a plasticizer and/or roughening particles are optionally added, then the resulting mixture is pressed into a mould of suitable size and shape to obtain the backbone of the shaped article; and

Step (b): a reactive alkylsilane reagent is applied in alcoholic or hexane solution on the backbone of the shaped article obtained in step (a) by a dipping or spraying process, then it is reacted with the surface hydroxyl groups of the polyvinyl alcohol.