Method for manufacturing of a hydrophobic cellulosic material Description The current invention relates to a process for manufacturing a hydrophobic cellulosic material by reacting a cellulosic material with an aliphatic carboxylic acid chloride in supercritical carbon dioxide.

Cellulosic materials based on cellulosic fibers, for example paper, are typically hydro- philic. Changing this towards hydrophobic is in several technical areas of interest. For example, aqueous printing inks are spreading over a cellulosic material due to its hy- drophilic surfaces. In case of a paper, a certain reduction of this hydrophilicity can improve printability, e.g. an accentuated contrast by increasing the ratio between a penetration of the ink into the paper and spreading over the paper surface. Another example is the soaking of a cellulosic material, if it gets in contact with water. This might only lead to reversible wetting, but in case of a paper surface, it might also lead to a damage by swelling, which is not completely reversed after drying. In case of a paper or a cardboard used for packaging, a certain water repellency is desirable and ideally, the mechanical properties are maintained to a certain degree in case of intense contact with water.

US 6342268 discloses a method for treating a solid material, which possesses reactive protogenic hydrophilic functions. A grafting reagent with a hydrophobic group, which is liquid under atmospheric pressure at a temperature of at least 200 °C and can react with the hydrophilic functions, is made part of a micro-dispersion. The micro-dispersion is produced on at least one part of the solid material. A gas stream, which is neutral to the grafting reaction of the grafting reagent, is applied at a temperature below the boiling point of the grafting reagent to carry out the grafting reaction by diffusion of the grafting reagent. In its examples, stearic acid chloride is often employed and either applied purely or as a pentane solution. In case of pentane or other solvents in its examples, evaporation of the solvent takes place prior to the grafting reaction.

US 2013/0236647 discloses a machine for treatment via chromatogenous grafting of a hydroxylated substrate and a process carried out by means of said machine. It refers to an equivalent of US 6342268, i.e. WO 99/08784 A for grafting by chromatogenic chemistry. It states that the reaction is made without a solvent, which contacts the substrate and the reagent and traps the released hydrochloric acid. The process for treatment by chromatogenous grafting of a substrate having a hydroxylated face comprises (a) the application on the hydroxylated face a grafting reagent, (b) development of the grafting reaction by a heating roller, (c) extraction of the emitted hydrochloric acid and (d) application of a hot air knife on the treated face of the substrate so as to evacuate the residual grafting agent. A proposed grafting reagent is a fatty acid chloride with stearic acid chloride being named. EP 2164647 A discloses a method for preparing a superhydrophobic surface on a solid substrate by adding a hydrophobic substance to a pressurized fluid, dissolving the hydrophobic substance in the pressurized fluid, causing the pressurized solution to flow in an expansion chamber with a lower pressure and depositing the formed particles of the hydrophobic substance on the substrate to obtain a superhydrophobic surface. The substrates is chosen for example from paper, plastics, glass, metal, wood, cellulose, silica, carbon tape, textile and paint. In its examples, supercritical carbon dioxide is employed to inter alia deposit alkylketenedimer on paper. There is still a need for further methods for hydrophobization of cellulosic materials, especially of paper. It exists already a first hurdle for contacting the hydrophilic surfaces of a cellulosic fiber with a predominantly hydrophobic agent. Furthermore in case of a reactive hydrophobization agent, e.g. which might forms at least partly covalent bonds with for example the hydroxyl groups of the surfaces of the cellulosic fibers, re- action in an acceptable time frame and / or in a sufficient overall yield is a second hurdle. Overall yield does primarily mean herein that the degree of reaction in view of the surfaces of the cellulosic fibers is high enough to provide a good repellency of water by the hydrophobized cellulosic material. Raising the temperature could be one technical measure to help overcoming one or both of the two hurdles, but cellulosic fibers are sensitive to an increased temperature especially if an acidic reaction product is present. Furthermore, a reactive hydrophobization agent is itself also prone to degrade at an elevated temperature.

It is an object of the present invention to provide a process for manufacturing a hydro- phobized cellulosic material, which possesses a high degree of hydrophobization. A high degree of hydrophobization is indicated by reduced water absorption in comparison to the untreated cellulosic material. It is further beneficial, if in addition also the mechanical stability of the cellulosic material in a wet stage is improved versus the untreated cellulosic material. In addition, it is desirable that the hydrophobization is achieved by the process with a low degree of degradation of other properties of the cellulosic material. For example, the mechanical stability of the single cellulosic fibers themselves or the mechanical stability of an assemblage of several cellulosic fibers should not or only to a low degree be reduced. For the process itself, it is desirable that few ingredients are employed and that these ingredients or by-products resulting from the process are easily removable after the process. A mild reaction temperature, e.g. one which is relatively close to room temperature, is desirable. In general, a simple conduction of the process is desirable.

The object is achieved, according to the invention, by a process for manufacturing a hydrophobic cellulosic material, which comprises the steps of

(a) providing a cellulosic material, which is based on cellulosic fibers, wherein the fibers possess hydroxyl groups at their surface; (b) reacting the material from step (a) with a first aliphatic carboxylic acid chloride or a mixture, which comprises the first aliphatic carboxylic acid chloride, a second aliphatic carboxylic acid chloride, which is different to the first aliphatic carboxylic acid chloride, and optionally one or more further aliphatic carboxylic acid chloride, which is different to the first aliphatic carboxylic acid chloride and the second aliphatic carboxylic acid chloride, in supercritical carbon dioxide at an operating pressure above 7382 kPa and an operating temperature above 31.0 °C;

(c) separating the reacted material from step (b) from the reaction to obtain the hydrophobic cellulosic material.

At a pressure above 7382 kPa and a temperature above 31 .0 °C, carbon dioxide is present as a supercritical fluid. In this stage, there is neither a commonly liquid nor a gaseous phase of the carbon dioxide.

A cellulosic material, which is based on cellulosic fibers and wherein the fibers possess hydroxyl groups at their surface, is for example a cellulosic fiber such as a cotton fiber or a bacterial cellulosic fiber. In case of two or more fibers, a combination thereof is possible. It is also a pulp such as a mechanical pulp, a brown mechanical pulp, a chemo-thermo-mechanical pulp (CTMP), a semi-bleached pulp, a deinked pulp (DIP), a wood pulp or a combination thereof. A combination of a cellulosic fiber and a pulp is also possible. The cellulosic fibers can originate from a recycling process or represent fresh fibers. Preferably, the cellulosic material is in the form of a sheet of fibrous material, for example a paper or a cardboard, a plywood or a cotton fabric.

Paper or cardboard are both common expressions for a plane material produced basically from plant fibers with a grammage for example up to 600 g/m ² . The expression paper is used typically more for a grammage up to 225 g/m ² , whereas the expression cardboard is used typically more for a grammage above 150 g/m ² . The lower limit of the grammage is for example 5 g/m ² , in particular 20 g/m ² . Preferably, at least one of the two surfaces of the paper or the cardboard is uncoated, preferably both surfaces are uncoated. In case of a coating, a coating with a polymer containing hydroxyl groups is preferred. An example for a paper or a cardboard is a crude corrugated paper, a packaging paper, a sanitary paper, a tissue paper, a printing paper, a writing paper, a paper pulp or a combination thereof, especially in the form of a composite.

Preferred is a process, wherein the cellulosic material is a paper or a cardboard.

The cellulosic material can additionally contain a further ingredient, for example an in- organic pigment, a colourless organic pigment, fines such as for example a hemicellu- lose, a fluorescent whitener, a soluble dye, an insoluble dye for example in the form of a pigment, or a further chemical additive such as a retention aid, a fastener, a wet fixa- tive, a dry fixative, a defoamer, an impurity scavenger such as a cationic starch, or a sizing agent, in particular in an amount low enough that a sufficient amount of hydroxyl groups at the surface is left, for example at least 60% of the originally available ones in the unsized state. A mixture of further ingredients is also possible.

Preferably, the cellulosic material contains at least 60% by weight of cellulosic fibers based on the weight of the cellulosic material, especially at least 80% by weight, in particular at least 95% by weight and very particular at least 99% by weight. Preferred is a process, wherein the cellulosic material is a paper or a cardboard and contains at least 60% by weight of cellulosic fibers based on the weight of the cellulosic material.

Preferably, the initial water content of the provided cellulosic material is below 8% by weight based on the weight of the cellulosic material, especially below 6% by weight, in particular below 2% by weight, very particular below 1 % by weight and most particular below 0.5% by weight. The water content is defined by subtraction of the solids content of the cellulosic material measured as stated according to DIN EN ISO 3251 from the initial weight of the cellulosic material. In a practical manner, the determination is con- ducted at a test sample of the cellulosic material. For reduction of an originally high water content to the initial water content, i.e. the water content of the provided cellulosic material, a drying step can be conducted prior to providing the cellulosic material, for example by infra-red irradiation or by a gas flow. The initial water content can also or further be lowered prior to step (b) by a or a further drying step, for example by purg- ing with an inert gas and optionally interrupted by applying vacuum. An example is applying carbon dioxide at a drying pressure between 105 kPa and 500 kPa and at a temperature of 23 °C, followed by reducing the pressure until an atmospheric pressure is reached again. Preferred is a process, wherein the cellulosic material is a paper or a cardboard and contains at least 60% by weight of cellulosic fibers based on the weight of the cellulosic material and the water content of the cellulosic material is below 8% by weight based on the weight of the cellulosic material, especially below 6% by weight. Aliphatic carboxylic acid chlorides are partially commercially available. Especially aliphatic carboxylic acid chlorides, which are non-commercial or fragile might be prepared by transchlorination with a suitable reagent, for example with acetyl chloride or oxalyl chloride. A first aliphatic carboxylic acid chloride is for example an alkanoyl chloride, which does not contain an aromatic or heteroaromatic moiety, or an alkenoyl chloride, which does not contain an aromatic or heteroaromatic moiety. An alkanoyl chloride is for example hexanoyl chloride, octanoyl chloride, 2-ethylhexanoyl chloride, nonanoyl chloride, 2- methyloctanoyl chloride, decanoyl chloride, lauric acid chloride, tridecanoyl chloride, iso-tridecanoyl chloride, palmitic acid chloride, stearic acid chloride, icosanoyl chloride, docosanoyl chloride, tetracosanoyl chloride, hexacosanoyl chloride or triacontanoyl chloride. An alkenoyl chloride is for example hex-5-enoyl chloride, (E)-hex-2-enoyl chloride, sorbic acid chloride, oleic acid chloride, elaidic acid chloride, linoleic acid chloride, linolenic acid chloride, eleostearic acid chloride or erucic acid chloride.

Preferably, the first aliphatic carboxylic acid chloride is a C6-C3o-alkanoyl chloride or a C6-C3o-alkenoyl chloride, especially a Cs-C22-alkanoyl chloride or a Cs-C22-alkenoyl chloride and very especially a Ci2-Cis-alkanoyl chloride or a Ci2-Cis-alkenoyl chloride. Preferably, the first aliphatic carboxylic acid chloride is linear and very preferably, the first aliphatic carboylic acid chloride is a compound of the formula I: H ₃ C[-CH2] _n -(C=0)- Cl (I) with n = 4 to 28, especially with n = 6 to 20 and very especially with n = 10 to 16. The first aliphatic carboxylic acid chloride is very preferably lauric acid chloride, palmitic acid chloride or stearic acid chloride.

Preferred is a process, wherein the first aliphatic carboxylic acid chloride is chosen from the group consisting of a C6-C3o-alkanoyl chloride and a C6-C3o-alkenoyl chloride.

Preferred is a process, wherein the first aliphatic carboxylic acid chloride is chosen from the group consisting of a Cs-C22-alkanoyl chloride and a Cs-C22-alkenoyl chloride.

Preferred is a process, wherein the first aliphatic carboxylic acid is lauric acid chloride, palmitic acid chloride or stearic acid chloride.

For the second aliphatic carboxylic acid chloride, the same preferences as listed for the first aliphatic carboxylic acid chloride apply and are independently chosen from the first aliphatic carboxylic acid chloride with the proviso that the second aliphatic carboxylic acid chloride is different to the first aliphatic carboxylic acid chloride. Preferably, the second aliphatic carboxylic acid chloride is defined by the same preference as the first aliphatic carboxylic acid chloride.

For the one or more further aliphatic carboxylic acid chloride, the same preferences as listed for the first aliphatic carboxylic acid chloride apply and are independently chosen from the first aliphatic carboxylic acid chloride and from the second aliphatic carboxylic acid chloride with the proviso that the one or more further aliphatic carboxylic acid chloride is different to the first aliphatic carboxylic acid chloride and the second aliphatic carboxylic acid chloride. Herein is understood that more further aliphatic carboxylic acid chloride means at least two further aliphatic carboxylic acid chlorides. These are different to each other. Preferred is a process, wherein the first aliphatic carboxylic acid chloride, the second aliphatic carboxylic acid chloride and the optional one or more further aliphatic carboxylic acid chloride are independently chosen from the group consisting of a C8-C22- alkanoyl chloride and a C8-C22-alkenoyl chloride.

The process can be conducted with the first aliphatic carboxylic acid chloride as the sole aliphatic carboxylic acid chloride, which is present at step (b). The process can also be conducted with a mixture, which comprises the first aliphatic carboxylic acid chloride, the second aliphatic carboxylic acid chloride and optionally one or more fur- ther aliphatic carboxylic acid chloride. Accordingly, the mixture is present at step (b) and the first aliphatic carboxylic acid chloride and the second aliphatic carboxylic acid chloride are both reacted. Optionally, the mixture comprises also one or more further aliphatic carboxylic acid chloride, which is also reacted. Preferred is a process, wherein at step (b) only the first aliphatic carboxylic acid chloride is present.

Preferred is a process for manufacturing a hydrophobic cellulosic material, which comprises the steps of

(a) providing a cellulosic material, which is based on cellulosic fibers, wherein the fibers possess hydroxyl groups at their surface;

(b) reacting the material from step (a) with a first aliphatic carboxylic acid chloride in supercritical carbon dioxide at an operating pressure above 7382 kPa and an operating temperature above 31.0 °C;

(c) separating the reacted material from step (b) from the reaction to obtain the hydrophobic cellulosic material.

In case of a mixture, the first aliphatic carboxylic acid chloride is defined as the aliphatic carboxylic acid chloride with the highest content in percentage by weight based on the total weight of all aliphatic carboxylic acid chlorides, which are present at step (b). The second aliphatic carboxylic acid chloride is defined as the aliphatic carboxylic acid chloride with the second highest content in percentage by weight based on the total weight of all aliphatic carboxylic acid chlorides. In case that two or more aliphatic carboxylic acid chlorides are present in the same percentage, the aliphatic carboxylic acid chlo- ride with the higher number of carbon atoms is defined as the first aliphatic carboxylic acid chloride. If no differentiation is possible then the first carboxylic acid chloride is the one with the most saturated bonds, followed by the one with the most carbon atoms in a main chain. The second aliphatic carboxylic acid chloride is defined in analogy versus an optionally present further aliphatic carboxylic acid chloride.

Preferred is a process, wherein at step (b), the mixture is present and the second aliphatic carboxylic acid chloride is also reacted. Preferred is a process for manufacturing a hydrophobic cellulosic material, which comprises the steps of

(a) providing a cellulosic material, which is based on cellulosic fibers, wherein the fibers possess hydroxyl groups at their surface;

(b) reacting the material from step (a) with a mixture, which comprises a first aliphatic carboxylic acid chloride, a second aliphatic carboxylic acid chloride, which is different to the first aliphatic carboxylic acid chloride, and optionally one or more further aliphatic carboxylic acid chloride, which is different to the first aliphatic carboxylic acid chloride and the second aliphatic carboxylic acid chlo- ride, in supercritical carbon dioxide at an operating pressure above 7382 kPa and an operating temperature above 31.0 °C;

(c) separating the reacted material from step (b) from the reaction to obtain the hydrophobic cellulosic material. Preferably, the weight ratio of the first aliphatic carboxylic acid chloride to the second aliphatic carboxylic acid chloride is between 1 and 4. The latter boundary represents accordingly 4 parts of the first aliphatic carboxylic acid chloride and 1 part of the second aliphatic carboxylic acid chloride. The weight ratio is especially between 1 and 2. Preferred is a process, wherein the content of the first aliphatic carboxylic acid chloride in the mixture is more than 40% by weight based on the weight of the mixture.

Preferred is a process, wherein the content of the second aliphatic carboxylic acid chloride in the mixture is more than 20% by weight based on the weight of the mixture.

Preferred is a process, wherein the sum of the content of the first aliphatic carboxylic acid chloride, the content of the second aliphatic carboxylic acid chloride and the content of the optional one or more further aliphatic carboxylic acid chloride is more than 20% by weight based on the weight of the mixture.

Preferred is a process, wherein the sum of the content of the first aliphatic carboxylic acid chloride, the content of the second aliphatic carboxylic acid chloride and the content of the optional one or more further aliphatic carboxylic acid chloride is more than 90% by weight based on the weight of the mixture.

Preferred is a process for manufacturing a hydrophobic cellulosic material, which comprises the steps of

(a) providing a cellulosic material, which is based on cellulosic fibers, wherein the fibers possess hydroxyl groups at their surface;

(b) reacting the material from step (a) with a first aliphatic carboxylic acid chloride or a mixture, which consists of the first aliphatic carboxylic acid chloride, a second aliphatic carboxylic acid chloride, which is different to the first aliphatic car- boxylic acid chloride, and optionally one or more further aliphatic carboxylic acid chloride, which is different to the first aliphatic carboxylic acid chloride and the second aliphatic carboxylic acid chloride, in supercritical carbon dioxide at an operating pressure above 7382 kPa and an operating temperature above 31.0 °C;

(c) separating the reacted material from step (b) from the reaction to obtain the hydrophobic cellulosic material.

Preferred is a process for manufacturing a hydrophobic cellulosic material, which com- prises the steps of

(a) providing a cellulosic material, which is based on cellulosic fibers, wherein the fibers possess hydroxyl groups at their surface;

(b) reacting the material from step (a) with a first aliphatic carboxylic acid chloride or a mixture, which consists of the first aliphatic carboxylic acid chloride, a sec- ond aliphatic carboxylic acid chloride, which is different to the first aliphatic carboxylic acid chloride, and one or more further aliphatic carboxylic acid chloride, which is different to the first aliphatic carboxylic acid chloride and the second aliphatic carboxylic acid chloride, in supercritical carbon dioxide at an operating pressure above 7382 kPa and an operating temperature above 31.0 °C;

(c) separating the reacted material from step (b) from the reaction to obtain the hydrophobic cellulosic material.

Preferred is a process for manufacturing a hydrophobic cellulosic material, which comprises the steps of

(a) providing a cellulosic material, which is based on cellulosic fibers, wherein the fibers possess hydroxyl groups at their surface;

(b) reacting the material from step (a) with a mixture, which consists of a first aliphatic carboxylic acid chloride, a second aliphatic carboxylic acid chloride, which is different to the first aliphatic carboxylic acid chloride, and optionally one or more further aliphatic carboxylic acid chloride, which is different to the first aliphatic carboxylic acid chloride and the second aliphatic carboxylic acid chloride, in supercritical carbon dioxide at an operating pressure above 7382 kPa and an operating temperature above 31.0 °C;

(c) separating the reacted material from step (b) from the reaction to obtain the hydrophobic cellulosic material.

Preferred is a process for manufacturing a hydrophobic cellulosic material, which comprises the steps of

(a) providing a cellulosic material, which is based on cellulosic fibers, wherein the fibers possess hydroxyl groups at their surface;

(b) reacting the material from step (a) with a mixture, which consists of a first aliphatic carboxylic acid chloride, a second aliphatic carboxylic acid chloride, which is different to the first aliphatic carboxylic acid chloride, and one or more further aliphatic carboxylic acid chloride, which is different to the first aliphatic carboxylic acid chloride and the second aliphatic carboxylic acid chloride, in supercritical carbon dioxide at an operating pressure above 7382 kPa and an op- erating temperature above 31.0 °C;

(c) separating the reacted material from step (b) from the reaction to obtain the hydrophobic cellulosic material.

The process is preferably conducted in a reaction vessel with an inner containment. The reaction vessel is for example an autoclave, which is suited for the high pressure and the temperature and which is resistant to hydrogen chloride and preferably also to hydrochloric acid. The latter one might be formed by traces of humidity from hydrogen chloride. The reaction vessel possesses preferably a pressure control and a temperature control. The latter one can be achieved by a heating and cooling jacket, whereas the pressure control can be achieved by an inlet valve and an outlet valve. Both valves are mounted on the top of the autoclave. Pressure is externally increased by addition of carbon dioxide and reduced by opening of the outlet valve. An increase of the temperature leads to an internal increase of the pressure until the pressure control reacts sufficiently. During the step (b), the reaction vessel is preferably closed with the exception of a pressure increase by addition of carbon dioxide or a pressure reduction by release of mainly carbon dioxide via the outlet valve.

Preferably, during step (b), the cellulosic material is mounted in a gadget, which leaves a distance between the bottom of the inner containment and the provided cellulosic material. The distance is chosen large enough to avoid contamination of the hydro- phobized cellulosic material with residuals at step (c). The gadget is for example a wired cage. In case the cellulosic material is in the form of a sheet of fibrous material, the sheet can be placed in the inner containment as without being coiled or in the form of a roll.

Preferred is a process, wherein the step (b) takes place in a reaction vessel with an inner containment.

Since recirculation occurs during the process, a homogenous distribution of the aliphat- ic carboxylic acid chlorides is enabled during step (b). Furthermore, in contrast to the chromatogenic grafting, the process avoids that for each individual aliphatic carboxylic acid chloride an own optimum of temperature applies. This is especially relevant in case of a mixture of aliphatic carboxylic acid chlorides. The process avoids also that parts of the aliphatic carboxylic acid chloride are lost by diffusion from the overall amount of aliphatic carboxylic acid chloride. Since stirring at step (b) supports a homogenous distribution of the aliphatic carboxylic acid chlorides, stirring is preferred at step (b), in particular at step (b) and at step (c). The stirring is preferably by a mechanical stirrer, for example a magnetic stirrer.

Preferred is a process, wherein the step (b) takes place in the inner containment of the reaction vessel, wherein the operating pressure varies by less than 15% over the diameters of the inner containment at a certain point in time and the operating temperature varies by less than 15% over the diameters of the inner containment at the certain point in time. In particular, the variations of the operating pressure and the operating temperature are both less than 5%, in particular less than 2%.

Preferred is a process, wherein at step (b), the provided cellulosic material is completely immersed in carbon dioxide and the first aliphatic carboxylic acid chloride or the mixture at the operating pressure and at the operating temperature. Preferred is a process, wherein at step (b), a stirring is applied.

It is possible by a specific regulation of the pressure and the temperature that the carbon dioxide transforms from gaseous carbon dioxide directly into superfluidic carbon dioxide without traversing a situation, in which liquid carbon dioxide exists. The benefit thereof is the avoidance of a liquid phase of carbon dioxide.

Preferred is a process, wherein at the step (b), in the presence of the provided cellulosic material and the first aliphatic carboxylic acid chloride or the mixture, firstly, an initial pressure is applied at an initial temperature, secondly the temperature is raised to the operating temperature, wherein the initial pressure is maintained by regulation or only increased by the raising of the temperature but remains in both cases below 7382 kPa, and thirdly, the pressure is raised to the operating pressure, and

when the initial temperature is between -10 °C and less than 0 °C, the initial pressure is between 101 kPa and 2000 kPa,

when the initial temperature is between 0 °C and less than 10 °C, the initial pressure is between 101 kPa and 3000 kPa,

when the initial temperature is between 10 °C and less than 20 °C, the initial pressure is between 101 kPa and 4000 kPa,

when the initial temperature is between 20 °C and less than 26°C, the initial pressure is between 101 kPa and 5000 kPa,

when the initial temperature is between 26°C and 30°C, the initial pressure is between 101 kPa and 6000 kPa.

The process has the advantage that a solvent in addition to carbon dioxide is not oblig- atory. The solvent is being defined herein as a solubilising substance, which is in the liquid state at 23°C and at 101 .013 kPa, and which is different to the first aliphatic carboxylic acid chloride, the second aliphatic carboxylic acid chloride, the optional one or more further aliphatic carboxylic acid chloride and water. Furthermore, a weight percentage for the solubilising substance equals in case of two or more solubilising substances the sum of all weight percentages of all solubilising substances, which individually fulfill the definition of the solubilising substance.

Preferred is a process, wherein at step (b), a solubilising substance, which is in the liquid state at 23°C and at 101 .013 kPa, and which is different to the first aliphatic carboxylic acid chloride, the second aliphatic carboxylic acid chloride, the optional one or more further aliphatic carboxylic acid chloride and water, is present in less than 20% by weight based on the higher one out of the weight of the first aliphatic carboxylic acid chloride and the sum of the weight of the first aliphatic carboxylic acid chloride, the second aliphatic carboxylic acid chloride and the optional one or more further aliphatic carboxylic acid chloride. In particular, the solubilising substance is present in an amount of less than 10% by weight, especially less than 5% by weight and very especially less than 1 % by weight based on the higher one out of the weight of the first aliphatic carboxylic acid chloride and the sum of the weight of the first aliphatic carboxylic acid chloride, the second aliphatic carboxylic acid chloride and the optional one or more further aliphatic carboxylic acid chloride.

Very particular, the solubilising substance is present in an amount of less than 10% by weight, especially less than 5% by weight and very especially less than 1 % by weight based on the weight of the first aliphatic carboxylic acid chloride.

Often in a reaction with a carboxylic acid chloride, a base is used. A base is for example a suitable basic neutralization agent, which is non-nucleophilic to avoid an alternative reaction with the carboxylic acid chloride. Typically, a base is an organic basic agent. Suitable organic agents are for example monocyclic or polycyclic compounds, which possess at least one nitrogen atom, which is basic. Basic means that this compound in its non-protonated form leads to a pH value above 7 once it is added to an aqueous solution at a temperature of 25°C at a concentration of 0.1 mol of basic nitrogen atoms per liter. Preferred is a process, wherein the content of a monocyclic or polycyclic compound, which possesses at least one basic nitrogen atom, is below 15% by weight based on the sum of the weight of the first aliphatic carboxylic acid chloride, the optional second aliphatic carboxylic acid chloride, and the optional one or more further aliphatic carboxylic acid chloride, in particular below 5% by weight, very particular below 1 % by weight, especially essentially free of a monocyclic or polycyclic compound, which possesses at least one basic nitrogen atom, and very especially free of a monocyclic or polycyclic compound, which possesses at least one basic nitrogen atom. Preferred is a process, wherein the content of an organic basic agent is below 15% by weight based on the sum of the weight of the first aliphatic carboxylic acid chloride, the optional second aliphatic carboxylic acid chloride, and the optional one or more further aliphatic carboxylic acid chloride, in particular below 5% by weight, very particular be- low 1 % by weight, especially essentially free of an organic basic agent and very especially free of an organic basic agent.

Preferred is a process, wherein the content of a base is below 15% by weight based on the sum of the weight of the first aliphatic carboxylic acid chloride, the optional second aliphatic carboxylic acid chloride, and the optional one or more further aliphatic carboxylic acid chloride, in particular below 5% by weight, very particular below 1 % by weight, especially essentially free of a base and very especially free of a base.

The operating pressure is preferably above 7382 kPa and below 25000 kPa, in particu- lar above 7382 kPa and below 20000 kPa. Surprisingly, a higher temperature does not lead necessarily to a higher degree of hydrophobization. The operating temperature is above 31.0 °C and below 100 °C, in particular above 31 .0°C and below 85°C, especially above 31 .0°C and below 55 °C, very especially above 31.0 °C and below 45 °C. Preferably, the operating temperature is above 32.0°C, in particular above 33.0°C, and the operating pressure is above 7400 kPa, in particular above 7500 kPa.

Preferred is a process, wherein the operating pressure is above 7382 kPa and below 25000 kPa and the operating temperature is above 31 .0 °C and below 100 °C. Preferred is a process, wherein the operating pressure is above 7382 kPa and below 25000 kPa and the operating temperature is above 31 .0 °C and below 55 °C.

Preferred is a process, wherein the operating pressure is above 7400 kPa and the operating temperature is above 32.0 °C.

Preferred is a process, wherein the operating pressure is above 7400 kPa and below 25000 kPa and the operating temperature is above 32.0 °C and below 100 °C.

Preferred is a process, wherein the operating pressure is above 7400 kPa and below 25000 kPa and the operating temperature is above 32.0 °C and below 55 °C

The concentration of the aliphatic carboxylic acid chlorides is defined in the superfluidic stage by the amount of the aliphatic carboxylic acid chlorides divided by the reaction volume. For example, the reaction volume is in case of a reaction vessel with an inner containment the free, i.e. not occupied by equipment, volume of the inner containment. Preferably, the concentration of the first aliphatic carboxylic acid chloride or in case of a mixture the sum of the first aliphatic carboxylic acid chloride, the second aliphatic carboxylic acid chloride and the optional one or more further aliphatic carboxylic acid chloride is between 1 g/L and 45 g/L, in particular between 2 g/L and 35 g/L, especially between 3 g/L and 26 g/L and very especially between 10 g/L and 20 g/L.

The weight ratio between the weight of the provided cellulosic material and the weight of the first aliphatic carboxylic acid chloride or the weight of all aliphatic carboxylic acid chlorides in case of a mixture varies preferably between 0.05 to 25. The latter boundary represents accordingly 25 parts of the provided cellulosic material and 1 part of the aliphatic carboxylic acid chlorides. The weight ratio is in particular between 0.1 to 25, especially between 0.3 to 20 and very especially 0.4 to 10.

Separating the reacted material at the step (c) from the step (b) can easily be conduct- ed for example by first reducing the pressure, for example via the outlet valve of the autoclave, and secondly lowering the temperature. Hydrogen chloride is concomitantly removed together with exhausting carbon dioxide.

A further embodiment of the invention is a hydrophobic cellulosic material, which is obtained by the process as described above. The preferences for the process as described above lead to preferred hydrophobic cellulosic materials, which are obtained through the processes.

The obtained hydrophobized cellulosic material is in case of a paper or a cardboard especially useful for manufacturing of a corrugated cardboard. An article with desired water-repellent properties is for example a box for fruits or vegetables.

The invention is illustrated by the non-limiting examples below. Experimental part

Unless the context suggests otherwise, percentages are always by weight.

Solids contents are measured according to DIN EN ISO 3 251 (determination of non- volatile matter of paints and varnishes as well as binders for paints and varnishes) by the infrared-heated balance Mettler Toledo HR 83. The average of two measurements is taken.

Cellulosic material:

Pa paper The used paper is a brown unsized testliner from Thurpapier (a Model AG company, Weinfelden, Switzerland) with a base weight of 130 g/m ² and a Cobb6o value of 156 g/m ² . The initial water content of the applied paper sample is around 4-5% as defined by subtraction of the solids content of a test paper sample measured as stated accord- ing to DIN EN ISO 3251 from the initial weight of the test paper sample.

Hydrophobizing agents:

SA stearic acid

SACI stearic acid chloride (octadecanoyl chloride)

LACI lauric acid chloride (dodecanoyl chloride)

TACI tallow acid chloride

The used stearic acid [CAS No. 57-1 1-4] is an analytical standard grade from Fluka Inc.

The used stearic acid chloride contains essentially 92% stearic acid chloride and 8% palmitic acid chloride.

The used lauric acid chloride [CAS No. 1 12-16-3] is a commercial grade from Alrich Inc.

The used tallow acid chloride contains essentially 50% stearic acid chloride and 50% palmitic chloride.

Other used materials are commercially available for example from Aldrich Inc. Example Pa-1 : untreated paper

As a reference for the treated paper samples, untreated paper is used.

General treatment procedure:

An autoclave with a laboratory scale (300 ml.) vessel made of acid resistant stainless steel, which allows for temperature settings up to 350°C and a maximum pressure of 325 bar, is used. In- and out-flow of gasses, liquids and supercritical fluids through a three way valve is controlled by an external pressure and metering system. Temperature is measured directly inside the autoclave with a pt100 sensor and controlled by a thermo fluid in a double wall jacket.

The hydrophobization agent in a defined amount of 5 g (unless stated otherwise) is dosed into the autoclave using a spatula in case of a solid or a pipette in case of a liquid. A magnetic stirrer is positioned on the bottom of the autoclave. An untreated paper sample with a weight of around 1 g is uprightly fixed in a wire cage as sample holder, which is mounted in the autoclave. Subsequently, the autoclave is closed and flushed three times with CO2 gas at 2 bar to remove moisture and inert gas. The CO2 pressure is increased to an initial pressure of 50 bar (unless stated otherwise) at 23 °C and the temperature is increased to the desired operating temperature of 40°C (unless stated otherwise). The pressure increases only slightly due to the reaction time of the pressure regulation, but remains always below 73 bar (unless the initial pressure is already higher than 73 bar). Subsequently the magnetic stirrer is switched on and the pressure is increased to the operating pressure of 150 bar. During the rise of the pressure to the operating pressure at 73 bar, CO2 condenses into a supercritical fluid, dissolving or at least partly dissolving the hydrophobization agent and submersing the paper sample completely. Pressure and temperature are kept constant for 10 min before relieving the pressure at the operating temperature of 40 °C (unless stated otherwise) through the exit connection of the 3-way valve. During reduction of the pressure to 1 bar, initially supercritical CO2 leaves the autoclave and finally, gaseous CO2 is released. The temperature is cooled to 23 °C. Most of the residual hydrophobization agent is finally deposited as a residue at the bottom of the autoclave. The paper sample is subsequently removed from the autoclave. Example Pa-2:

Stearic acid is used as hydrophobization agent.

Example Pa-3:

Laurie acid chloride is used as hydrophobization agent.

Example Pa-4:

Tallow acid chloride is used as hydrophobization agent. Example Pa-5:

Stearic acid chloride is used as hydrophobization agent. Example Pa-6:

Tallow acid chloride is used as hydrophobization agent, but different to the general treatment procedure, the amount of the hydrophobization agent is 1 .5 g and the initial pressure is changed to 100 bar.

Example Pa-7:

Tallow acid chloride is used as hydrophobization agent, but different to the general treatment procedure, the operating temperature is changed to 60 °C.

Example Pa-8:

Tallow acid chloride is used as hydrophobization agent, but different to the general treatment procedure, the operating temperature is changed to 80 °C.

Example Pa-9:

Tallow acid chloride is used as hydrophobization agent, but different to the general treatment procedure, the amount of the hydrophobization agent is 1 .5 g. Example Pa-10:

Tallow acid chloride is used as hydrophobization agent, but different to the general treatment procedure, the amount of the hydrophobization agent is 7.5 g and the operating temperature is changed to 80 °C.

Example Pa-1 1 :

Tallow acid chloride is used as hydrophobization agent, but different to the general treatment procedure, the amount of the hydrophobization agent is 10 g and the operating temperature is changed to 80 °C.

Table 1-A provides an overview of the parameters of the examples Pa-1 to Pa-1 1.

Footnotes: a) comparative

b) according to the invention

c) the concentration is calculated from the volume of the autoclave (V _au to- ciave = 0.3 L) and the amount of the hydrophobization agent mhydrophob-agent according to c = m _hyC iro hob -agent / V _a utoclave

d) 1 bar is 100 kPa

Physical properties of the processed papers

Several physical properties of the paper samples from examples Pa-1 to Pa-1 1 are determined.

All paper samples are stored for 24 h under standard conditions (23°C, 50% relative humidity) as defined by DIN EN 20187 before determination of physical properties. The Cobb values Cobb6o (60 s) and Cobbsoo (300 s) are determined according to DIN EN 20 535 (determination of water absorptiveness - Cobb method), however with a smaller wetting diameter of 4 cm due to the size of the paper samples. The results of this method are found to be consistent with the standardized Cobb values when refer- ence samples are compared with known water absorption values. The Cobb values indicate the amount of water, which is absorbed in a certain time period, i.e. 60 s or 300 s. The lower a value of a sample, the higher is its hydrophobicity. For better comparability, all values are normalized to the value of the untreated paper sample. The contact angle of the sample is an angle that quantifies the wettability of the solid surface by water as a liquid according to Young's equation. It is determined from a microscopic picture by drop shape analysis of a sessile drop of deionized water on the surface. A high contact anlge indicates less tendency of a liquid, i.e. herein water, to spread on the cellulosic material's surface. The higher the contact angle of a sample versus water, the higher is the sample's hydrophobicity.

The wet tensile strength is measured in analogy to EN ISO 1924 05/2009 using a Zwick Roell TYP BX 2.5 / TS1 S-006 with software TextXpert 2 after submersing the paper sample (1 .5 cm x 5 cm) for 30 min in water. For better comparability, all values are normalized to the value of the untreated paper sample. The higher the percentage above 100, the higher is the mechanical strength in comparison to the chosen reference.

Table 2-A shows physical properties of the hydrophobized papers.

Table 2-A

Footnotes: a) comparative

b) according to the invention

c) not determined d) absolute Cobb6o is 156 g/m ²

e) absolute Cobbsoo is 243 g/m ²

The measured physical properties of the paper samples of examples Pa-1 to Pa-1 1 show

(a) that the paper sample of example Pa-5 with stearic acid chloride performs better than the paper sample of example Pa-2 with stearic acid;

(b) that the paper sample of example Pa-4 with a mixture of equally distributed parts of stearic acid chloride and parts of palmitic acid chloride performs better than the paper sample of example Pa-5 with predominantly stearic acid chloride;

(c) that the paper sample of example Pa-4 with an operation temperature of 40 °C performs better than the paper sample of example Pa-7 with an operating temperature of 60 °C or the paper sample of example Pa-8 with an operating temperature of 80 °C.