US20220002949A1

US20220002949A1 - Method for hydrophobizing a cellulose substrate by utilizing a fatty acid halide

Info

Publication number: US20220002949A1
Application number: US17/293,989
Authority: US
Inventors: Susanne Hansson; Raija Bådenlid; Carl-Magnus Brandén
Original assignee: Stora Enso Oyj
Current assignee: Stora Enso Oyj
Priority date: 2018-11-16
Filing date: 2019-11-15
Publication date: 2022-01-06
Also published as: WO2020100097A1; EP3880884A1; CN113227495A; EP3880886A4; US20220010493A1; JP2022507536A; EP3880884A4; WO2020100101A1; SE543029C2; JP2022507555A; SE1851430A1; EP3880886A1; KR20210100635A; CN113227494A; KR20210100636A

Abstract

The present invention relates to a method for hydrophobizing a cellulose substrate, which comprises a first side and a second side, which faces away from the first side, wherein the method comprising the steps of:—drying the cellulose substrate to a dry content above 80%, preferably above 85%;—providing a fatty acid halide in spray form; and—guiding said fatty acid halide in spray form to contact the first side of the cellulose substrate, and at least partially penetrate the cellulose substrate.

Description

FIELD OF INVENTION

Method for hydrophobizing a cellulose substrate, which substrate comprises a first side and an opposite second side.

BACKGROUND

There is a need to increase the hydrophobicity of materials based on cellulose in several fields, e.g. in the textile industry and the paper- and paperboard industry.
Paper- and paperboard are usually treated with sizing agents to enhance certain qualities, above all to increase the resistance to penetration of water and other liquids into the paper or paperboard. There are two types of sizing: internal and surface sizing. In internal sizing, chemicals are added to the pulp at the wet end, e.g. ASA, AKD or rosin size. Common surface sizing agents include e.g. starch or acrylic co-polymers.
U.S. 4,107,426 discloses a method for imparting water-repellent characteristics to a surface of a cellulose substrate. The process comprising the steps of exposing the surface to a vapour phase consisting essentially of aliphatic acid chloride.
A drawback with this method is that mainly the surface of a substrate that becomes hydrophobic and not the interior of the substrate. This causes problem with edge wicking, i.e. penetration of liquid into the edges of a substrate.
In WO2017002005, a method is described where a vaporized fatty acid halide is arranged to penetrate the cellulose substrate.
However, the equipment required to perform the method according to WO2017002005 occupies a lot of space and is therefore difficult to implement at an existing production site.
An object with the present invention is to provide an improved method for increasing the hydrophobicity of materials with a cellulose substrate that e.g. enhances the water repellency and resistance against edge wick penetration of a cellulose substrate.

SUMMARY OF THE INVENTION

The inventive method for hydrophobizing a cellulose substrate comprising the following steps:

- drying the cellulose substrate to a dry content above 80%, preferably above 85%;
- providing a fatty acid halide in spray form; and
- guiding said fatty acid halide to contact the first side of the cellulose substrate, and at least partially penetrate the cellulose substrate.

Treating a cellulose substrate according to the method of the present invention leads to an increase of the hydrophobicity of the material, not only at the surface but also at its core, and to enhanced water resistance thereof, as well as resistance against edge wick penetration of a cellulose substrate.
Several additional advantages are also achieved thanks to the method according to the invention. For example:

- the device for applying the sprayed fatty acid halide onto the substrate can be aimed in differently defined directions,
- the reagent (i.e. fatty acid halide) will have an even distribution over the surface even if the surface is rough,
- calibration of dosage enables for avoiding unwanted surplus of reagent on substrate,
- the amount of reagent can be easily controlled by adjusting the pressure or the number of spray units, and
- the nozzles/units do not require large space which facilitates installation at an existing on-line production site.

It is to be understood that “spray form” means in the form of a plurality of liquid droplets or particles, and that the fatty acid halide in spray form may be delivered by means of a precision device for dispersion of freely flowing liquid fatty acid halide into said spray form. The droplets or particles may be in micro scale with sizes ranging from 1-900 μm in diameter.
According to another aspect of the invention, the sprayed fatty acid halide is guided to contact also the second side of the cellulose substrate, and at least partially penetrate the cellulose substrate. This may be accomplished by means of vacuum suction.
The cellulose substrate can be in the form of paper- or paperboard web, paperboard application, textiles made from cellulose fibres, or three-dimensional cellulose-based products e.g. produced by means of thermoforming. The paper- or paperboard web may be a single- or multilayer web.
According to another aspect of the invention, said guiding of the fatty acid halide is performed by vacuum sucking at the second side of the cellulose substrate, such that the fatty acid halide penetrates the cellulose substrate in a predetermined direction through the cellulose substrate. Such vacuum suction can be generated by means of a vacuum box, a rotating vacuum cylinder or any other suitable vacuum generating equipment. Thanks to the method according to the invention, the covalent degree can be more even throughout the thickness of the material compared to e.g. conventional roll coating of freely flowing reagents onto a running substrate.
The covalent degree is the ratio between the grafted fatty acids and the total fatty acids in the substrate, where the grafted corresponds to the reagent that has reacted and the total amount is this part together with the free fatty acids that only has been physically absorbed to the substrate.
According to another aspect of the invention, said guiding of the fatty acid halide is performed by vacuum sucking at the first side of the cellulose substrate, so that the fatty acid is guided along the surface of the first side of the cellulose substrate in a predetermined direction in such a way that the fatty acid is brought into contact with the cellulose substrate. In one example, “along the surface” means that the fatty acid is brought to move substantially parallel with the first side of the substrate for a controlled distance (depending on the substrate).
According to another aspect of the invention, the fatty acid halide is mixed with at least one solvent before it is sprayed onto the substrate. Preferably, said solvent is selected from the group comprising: acetone, ethyl acetate and methyl ethyl ketone. It is preferred that the solvent (or mixture of solvents) does not contain any OH-groups, and also that it is miscible with the fatty acid halide, which will help against clogging and promote the cleaning of the application system. The utilization of a solvent also makes it possible to minimize and control the amount of applied fatty acid halide in a better way.
The boiling point of the solvent shall preferably not be too high to ensure that there will be no residual solvent in the product, preferably it is below 200 degrees C., more preferably below 150 degrees C., and even more preferably below 100 degrees C. Acetone has a boiling point at 59 degrees C.; ethyl acetate has a boiling point at 77 degrees C. and methyl ethyl ketone has a boiling point at below 59 degrees C. Addition of a solvent to the fatty acid halide may lead to the advantage that the penetration of the reagent into the substrate is improved.
According to one aspect of the invention, the mixture of fatty acid halide and solvent comprises 0.1-20 wt %, preferably 0.1-10 wt %, more preferably 0.1-5 wt % solvent of the total weight of the mixture. If the solvent amount is too high, the reagent can be too diluted to form an even coverage and distribution upon application, and thereby increasing the need of increased application units. This can also result in a higher risk of residual solvent molecules in the final product. If the applied amount of reagent becomes too low, it can have a negative impact on the desirable material properties.
According to yet another aspect of the invention, the dry content of the cellulose substrate is above 80%, preferably above 85%, even more preferably above 90%. The higher dry content, the better will the result of the subsequent hydrophobation be. This is due to that the fatty acid halide has a high reactivity towards water. Therefore, presence of water can lead to the undesired formation of too high amounts of fatty acids that are not attached to the substrate.
According to yet another aspect of the invention, the fatty acid halide to be sprayed comprises an aliphatic chain length of between 10-22 carbon atoms. Said fatty acid is preferably selected from palmitoyl chloride (C16), stearoyl chloride (C18) or mixtures thereof.
According to yet another aspect of the invention, the method further comprises a step of heating the cellulose substrate, before and/or after adding the fatty acid halide.

FIGURES

In the following, the invention will be described further with reference to the drawings, wherein:

FIG. 1 shows a schematic view of the invention according to a first embodiment, where a fatty acid halide in spray form is applied onto a substrate;

FIG. 2 shows a schematic view of the invention according to a second embodiment, where a fatty acid halide in vaporized form is applied onto a substrate;

FIGS. 3a-b show schematic views of the invention according to a third and fourth embodiments, wherein both the first and second sides of a substrate are subjected to a fatty acid halide;

FIG. 4 shows a schematic view of the invention according to a fifth embodiment, where a fatty acid halide in vaporized form is applied onto a substrate; and

FIG. 5 illustrates in a schematic way hydrophobation of cellulose substrates, where such substrates are in the form of three-dimensional cellulose-based products.

DETAILED DESCRIPTION

The following detailed description illustrates examples of setups for performing the method according to the invention, which may serve to illustrate the principles of the inventive idea in a non-limiting way.
In FIGS. 1-4, a cellulose substrate 1, comprising a first side and a second side, is generally referred to as “1”. In these embodiments, the substrate is in the form of a cellulose-based web such as a paper- or paperboard web. The second side of said substrate 1 faces away from the first side. The cellulose substrate, e.g. a paper- or paperboard web 1, is dried in a drying step. The drying is performed by any conventional drying methods suitable for drying a cellulose substrate. A cellulose substrate of a paper- or paperboard web may for example be dried by drying cylinders. After the drying step, the cellulose substrate 1 has a dry content above 80%, preferably above 85% and most preferably above 90%. A higher dry content can give better results of the subsequent hydrophobation by obtaining a higher covalent degree.
The cellulose substrate 1 may thereafter be further dried and heated. The heating is preferably performed in a pre-treatment step by IR heating 2 as illustrated in FIGS. 1-3. The pre-treatment heating step has several advantages. It will minimize unwanted condensation of the gas upon contact with the substrate, and also lead to that the subsequent hydrophobizing agent will penetrate better through the substrate. Moreover, any remaining water residues can be further dried; the substrate 1 may possibly be dried even up to 95% dry content.
The first side of the dried and heated substrate 1 is then treated with a fatty acid halide, in spray form or in gas-phase, to hydrophobize the substrate, such that the substrate becomes hydrophobic. This is accomplished by means of a device 5 (also referred to as “spray device” 5) for dispersing liquid fatty acid halide into a spray 50, which spray may contact the substrate directly or become vaporized into gas phase where such gas contacts the substrate. Said spray device 5 may be in the form of a spray nozzle used for atomizing the liquid. “Spray atomization” here means the transformation of a liquid into a spray of fine particles by mixing the liquid with compressed air. A spray nozzle generates the atomized spray when being passed through an opening at high pressure and in a controlled manner. A higher pressure will create smaller liquid droplets and a finer spray. Different spray devices 5 are conceivable.
Another example is electrospraying whereby electrical forces are utilized on a liquid that flows from a nozzle, which can have various shapes and conformation, and thereafter fine, uniform and charged droplets are formed, due to that the electrical force exceeds the surface tension force. It can also be due to mechanical distortions. The general advantages of the electrospraying process are that it can be performed as one step at low cost, low energy input and with a good flexibility. Ambient temperatures and pressures also work.
Upon that said first side of the dried and heated substrate 1 has been treated with a fatty acid halide, the applied fatty acid halide will at least partially penetrate the cellulose of said substrate 1 and bind covalently to the cellulose therein, increasing the water repellency of the material. In order to enhance the penetration of the spray or gas through the substrate, the second side of the substrate can be subjected to a vacuum suction, simultaneously, during the hydrophobation of the substrate, such that the spray or gas is transported in a predetermined direction through the substrate. This enhances the hydrophobicity of the surface as well as the core of the substrate, so that the substrate will be more resistant against in-plane edge penetration.
The fatty acid halide is any halide that can be vaporized, however palmitoyl chloride, C16 has, in tests, shown to be particularly suitable. During tests a covalent degree of above 40% and even above 60% has been achieved, compared to conventional AKD sizing where no or just a small percentage of covalent binding can be obtained, which results in low retention, which thereby leads to e.g. migration problems, stains and machine stops etc.
Another advantage with use of spray for applying the fatty acid halide is that it is very position specific and hydrophobicity is only achieved where the spray can access the substrate. The reagent will react with the available hydroxyl groups forming HCl as a by-product. The reagent is also highly reactive towards water and the reaction requires dry substrates. Nevertheless, there will always be some presence of water whereupon the corresponding, less reactive, fatty acid also will be formed as an unbound molecule. It is therefore impossible to achieve 100% covalent degree. Yet other advantages associated with the use of a gas-phase reaction are that the gas can be penetrated and guided through the substrate more easily, the reaction can be faster and a lower amount of chemical reagents may be needed compared to application of the same reagent in a liquid state.
FIG. 1 illustrates an exemplary way of performing the method according to the invention. A dried and heated cellulose substrate 1 in the form of a paper- or paperboard is additionally heated and dried with IR heating from an IR heating box 2. The additional IR heating is optional.
Liquid fatty acid halide is stored in a separate tank 3 wherefrom it is ejected through a device 5 for dispersing the liquid into a spray 50. Such spray device 5 can for instance be in the form of a spray nozzle used for atomizing the liquid, i.e. breaking up the fluid into droplets 50. In the present example, the droplets are sprayed by means of the device 5 onto a first side 1 a of the underlying, running substrate 1. Said first side laside of the substrate 1 is at the same time in contact with a downstream rotating cylinder 6, for instance a heated cylinder that heats the droplets into gas whereby the atomized fatty acid molecules react more efficiently with the cellulose of the substrate. It is conceivable to arrange multiple spraying units positioned after each other in sequences in connection to the running substrate, where each such unit can comprise one or a plurality of spraying nozzles. This would enable for application of fatty acid in consecutive steps, whereby smaller doses can be applied several times instead of one unit applying the whole amount at one occasion. Such procedure may in some cases improve the penetration of the reagent in the thickness of the cellulose web.
It is also conceivable that a rotating vacuum cylinder with holes (not shown) is arranged in connection with a second side 1 b of the substrate and downstream of the spray device 5, arranged to vacuum sucking fatty acid halide in a predetermined direction through the cellulose substrate 1. Thereby, the cellulose substrate 1 can be hydrophobized through the complete thickness of the substrate.
Another arrangement for applying the fatty acid halide is that the substrate 1 is arranged to enter between two nip rolls (not shown), preferably where at least one of the rolls is a heated nip roll, and that the fatty acid halide spray is directed into the nip roll junction whereby the spray droplets are converted into gaseous phase by means of the heated roll/s. In this arrangement, the spray may also be directed to contact the heated nip roll immediately upstream of the nip roll junction, whereby the fatty acid halide is vaporised by the heat of the roll and directly thereafter, i.e. within seconds or milliseconds, applied onto the substrate.
Yet another arrangement for applying the fatty acid halide is that the fatty acid halide is sprayed directly onto a heating roll arranged to immediately, i.e. within seconds or milliseconds, transfer said fatty acid halide onto a running substrate. Upon contacting the substrate, the heat from the roll will transform the fatty acid halide into gas phase meaning that the vaporization occurs simultaneously with that the fatty acid halide is brought into contact with the substrate. In such embodiment, the heated roll provides several functions: the function of bringing the fatty acid halide into contact with the substrate, the function of vaporizing the fatty acid halide into gas phase and the function of promoting the chemical reaction to covalent bind the fatty acid halide to the substrate. Vaporization of the fatty acid halide can be arranged to occur before the heated roll contacts the substrate, or simultaneously with that the heated roll contacts the substrate depending on where on the heated roll the spray is applied. E.g. if the spray is directed so that the fatty acid halide hits the heated roll a small distance prior to that said roll contacts the substrate the vaporization will take place before contact, whereas in case the spray is directed so that the fatty acid halide hits the heated roll at the nip between the roll and the substrate the vaporization will take place simultaneous to contact.
If not all the spray is vaporized, it will still be distributed in a uniform matter on the roll and then be taken up by the board in droplet form.
Moreover, the HCl by-product and possibly unreacted e.g. palmitoyl chloride and/or unbound C16 can be removed and collected for handling.
In FIG. 2, a second embodiment according to the present invention is schematically shown. Herein, a dried and heated cellulose substrate 1 in the form of a paper- or paperboard is optionally further heated and dried with IR heating from an IR heating box 2, as also previously described in connection with FIG. 1.
Liquid fatty acid halide is stored in a separate tank 3 wherefrom it is transferred e.g. via a tube 4 (or other transferring means) to a device 5 for dispersing the liquid into a spray 50. Such device 5 can for instance be in the form of a spray nozzle used for atomizing the liquid, i.e. breaking up the fluid into droplets 50. In the present example, the droplets are sprayed via the device 5 into a heating chamber 7 such as a pressurized heating tank 7. The spray droplets are heated inside said tank 7 to vaporize into gas-phase, and said gas 70 is thereafter ejected or deposited through a gas spreading device 71 onto the first surface of said substrate 1. Said first side of the substrate is at the same time in contact with a rotating cylinder 6. Yet another rotating cylinder of vacuum type may be arranged at the second side 1 b of the substrate for sucking the gas in a predetermined direction through the cellulose substrate 1. Thereby, the cellulose substrate 1 can be hydrophobized through the complete thickness of the substrate. Any HCl by-product and possibly unreacted e.g. palmitoyl chloride and/or unbound C16 can be removed and collected for handling.
For both exemplified methods shown in FIGS. 1-2, it is possible to firstly treat the first side of the substrate and subsequently treat the second side of the substrate with an additional unit facing the second side of the substrate. Such treatment of both sides ensures that the whole core of substrate will be modified. The usage of two or more spray units can be placed in such way that the minimum amount of space is needed and fitted to the existing equipment. By utilizing a plurality of units, it can also be possible to run the machine at an increased speed.
FIGS. 3a-b show a third and fourth embodiment, respectively, wherein both the first and second side of a substrate 1 are subjected to hydrophobization/hydrophobation by means of application of a fatty acid halide in spray form.
Referring to FIG. 3a , the substrate 1 is firstly subjected to pre-treatment 2 in the form of heating, e.g. IR heating. A device 5 for dispersing liquid into spray is positioned downstream of the pre-treatment 2 at the second side 1 b of the substrate, adjacent to a rotating cylinder 6 and arranged to direct a spray 50 of fatty acid halide onto the surface of the cylinder 6 which, upon rotating further, will deliver the fatty acid halide onto the surface of the second side 1 b of the substrate 1. The rotating cylinder 6 may be heated, also to such extent that the sprayed droplet transform into gas before touching the substrate. A vacuum box 8 is arranged at the first side la of the substrate 1 to draw the reagent into the cellulose structure. According to the herein described third embodiment, the substrate 1 is further hydrophobized in a subsequent downstream step, wherein fatty acid halide 50′ is applied also onto the first side 1 a of the substrate 1. Accordingly, as seen in FIG. 3a , a second device 5′ for dispersing liquid into spray 50′ is positioned adjacent to a second rotating cylinder 6′, said device 5′ being arranged to direct a spray 50′ of fatty acid halide onto the surface of the cylinder 6′ which, upon rotating further, will deliver the fatty acid halide onto the surface of the first side 1 a of the substrate 1. The rotating cylinder 6′ may be heated. A vacuum box 8′ is arranged in close proximity of the rotating cylinder, at the second side 1 b of the substrate, to guide the reagent to at least partially penetrate the substrate 1. The skilled person understands that the equipment ( e.g. spray device 5, 5′; vacuum box 8, 8′; cylinder 6, 6′ etc) are interchangeable and that it is possible to firstly treat the first side 1 a of the substrate 1 and thereafter the second side 1 b.
A fourth embodiment according to the invention is seen in FIG. 3b , serving the same purpose as in FIG. 3a , namely to treat both sides of a substrate 1 to increase the hydrophobicity thereof. In a similar manner as described for FIG. 3a , the substrate 1 is guided through two subsequent hydrophobation steps wherein fatty acid halide is applied firstly onto the second side 1 b of the substrate, and secondly onto the first side 1 a thereof. In the first step, a spray device 5 is positioned adjacent to a second side 1 b of the running substrate 1 and is arranged to direct a spray 50 of fatty acid halide directly onto said surface 1 b. A vacuum box 8 is arranged at the first side 1 a of the substrate, opposing the spray device 5, said vacuum box 8 being arranged to draw the fatty acid halide to at least partially penetrate the substrate by means of vacuum suction. A downstream rotating cylinder 6 may be provided, preferably a heated cylinder, to promote the binding of reagent to the cellulose substrate 1. A corresponding, second hydrophobation step is arranged downstream of the first cylinder 6, whereby fatty acid halide is applied also onto the first side 1 a of the substrate in a corresponding manner as described for the first hydrophobation step.
The fatty acid halide in the fourth embodiment can be converted from spray form to gaseous form before being guided to contact the substrate 1.
In FIG. 4, a fifth embodiment according to the present invention is shown. A pre-treatment step for heating the substrate is illustrated, where such heating may be performed by means of e.g. IR-heating. Furthermore, said guiding of fatty acid halide is herein performed by vacuum sucking 8 at the first side 1 a of the cellulose substrate, so that the fatty acid is guided along the surface of the first side 1 a of the cellulose substrate 1 in a predetermined direction in such a way that the fatty acid is brought into contact with the cellulose substrate 1. The fatty acid is thereby brought to move substantially parallel with the first side of the substrate.
FIG. 5 illustrates in a schematic way the method according to the invention where the substrate 10 is a three-dimensional cellulose based product. Herein, a conveyor belt 9 is transferring a plurality of three-dimensional cellulose products 10 through a unit 11 arranged to hydrophobize said products by means of the method of claim 1. Said three-dimensional products 11 may be e.g. pre-produced paper trays, mugs or containers, or other types of 3D-shaped objects made from cellulose. After having passed through the unit 11 wherein vaporized fatty acid halide is brought to contact the cellulose substrate, and at least partially penetrated its thickness, the exiting product 10′ has acquired hydrophobic properties.
To characterize the success of the reaction, contact angle measurement was utilized to qualitatively analyze how much the cellulose substrate has been hydrophobized by the method. An un-treated cellulose substrate had before a contact angle around 40° and after treatment of the inventive method a contact angle of 110-130° on both the first side and the second side of the substrate, despite only one surface was in direct contact with the reagent. Contact angles greater than 90° (high contact angle) generally means that wetting of the surface is unfavourable, so the fluid will minimize contact with the surface and form a compact liquid droplet.
In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. For example, the method according to the invention may be used as a complement to other methods of application of fatty acid halide onto a substrate. However, it should be apparent that such other modifications and variations may be affected without departing from the spirit and scope of the invention.

Claims

1. A method for hydrophobizing a cellulose substrate, which comprises a first side and a second side facing away from the first side, wherein the method comprises the steps of:

drying the cellulose substrate to a dry content above 80%;

providing a fatty acid halide in spray form; and

guiding said fatty acid halide to contact the first side of the cellulose substrate, and at least partially penetrate the cellulose substrate.

2. The method according to claim 1, further comprising the step of:

guiding said fatty acid halide to contact the second side of the cellulose substrate, and at least partially penetrate the cellulose substrate.

3. The method according to claim 1, wherein said guiding of the fatty acid halide is performed by vacuum sucking at the second side of the cellulose substrate, such that the fatty acid penetrates the cellulose substrate in a predetermined direction through the cellulose substrate.

4. The method according to claim 1, wherein said guiding of the fatty acid halide is performed by vacuum sucking at the first side of the cellulose substrate, such that the fatty acid is guided along a surface of the first side of the cellulose substrate in a predetermined direction whereby the fatty acid is brought into contact with the cellulose substrate.

5. The method according to claim 1, wherein the dry content of the cellulose substrate is above 90%.

6. The method according to claim 1, wherein the fatty acid comprises an aliphatic chain length of between 10-22 carbon atoms.

7. The method according to claim 1, wherein the fatty acid comprises palmitoyl chloride, C16, stearoyl chloride, C18, or mixtures thereof.

8. The method according to claim 1, wherein the fatty acid to be sprayed is mixed with at least one solvent or a mixture of solvents, wherein the at least one solvent or a mixture of solvents is selected from a group consisting of: acetone, ethyl acetate, and methyl ethyl ketone.

9. The method according to claim 8, wherein the mixture of fatty acid halide and the at least one solvent or a mixture of solvents comprises 0.1-20 wt % solvent.

10. The method according to claim 1, wherein the cellulose substrate is a paper- or paperboard web.

11. The method according to claim 10, wherein the web is a single- or multilayer web.

12. The method according to claim 1, wherein the cellulose substrate is a three-dimensional cellulose-based product.

13. The method according to claim 1, further comprising a step of:

heating the substrate before, or after, or before and after adding the fatty acid halide.

14. The method according to claim 12, wherein the substrate heating step is performed by IR heating.

15. The method according to claim 3, wherein the vacuum sucking is performed by a vacuum box.

16. The method according to claim 3, wherein the vacuum sucking is performed by a rotating vacuum cylinder.

17. A cellulose-based product having been treated by the method according to claim 1.

18. The method according to claim 1, wherein the dry content of the cellulose substrate is above 85%.

19. The method according to claim 8, wherein the mixture of fatty acid halide and the at least one solvent or a mixture of solvents comprises between 0.1-10 wt % solvent.

20. The method according to claim 8, wherein the mixture of fatty acid halide and the at least one solvent or a mixture of solvents comprises between 0.1-5 wt % solvent.