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Title:
MULTI-REPELLENT WOOD VENEER AND PAPER SURFACE COATING
Document Type and Number:
WIPO Patent Application WO/2017/037289
Kind Code:
A2
Abstract:
The invention relates to a method for treatment of cellulose-based material comprising a coupling step and a hydrophobization step. The coupling step comprises the provision of a coupling solution comprising titanium (IV) isopropoxide (TTIP) or a basic solution of zinc oxide and the immersion of the cellulose-based material into the coupling solution. The following hydrophobization step comprises the provision of a hydrophobization solution comprising a hydrophobic compound and the immersion of the cellulose-based material in the hydrophobization solution, yielding a hydrophobic cellulose-based material, followed by drying of the hydrophobic cellulose-based material. According to a second aspect of the invention a cellulose-based material is provided characterized by its omniphobic properties, a cellulose-TTIP hybrid layer and/or Zn O hybrid layer.

Inventors:
BURGERT INGO (CH)
CABANE ETIENNE (CH)
GUO HUIZHANG (CH)
Application Number:
PCT/EP2016/070852
Publication Date:
March 09, 2017
Filing Date:
September 05, 2016
Export Citation:
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Assignee:
ETH ZÜRICH (CH)
EMPA EIDGENÖSSISCHE MATERIALPRÜFUNGS- UND FORSCHUNGSANSTALT (CH)
International Classes:
B27K3/20; B05D3/10; B05D5/08; B05D7/06; B27K3/22; B27K3/32; B27K3/34; B32B15/10; B32B21/14; C08J9/36; D06M13/252; D06M13/50; D06M13/513; D06M13/517; D21H21/16
Domestic Patent References:
WO2008055369A12008-05-15
WO2010042191A12010-04-15
WO2014149465A12014-09-25
WO2014012078A22014-01-16
WO2014012039A12014-01-16
Other References:
NEINHUIS, C.; BARTHLOTT, W, ANNALS OF BOTANY, vol. 79, 1997, pages 667 - 677
BONGIOVANNI, R. ET AL., PITTURE VERNICI, EUR. COAT., vol. 79, 2003, pages 25 - 30
WONG, T.-S. ET AL., NATURE, vol. 477, 2011, pages 443 - 447
CICELY ET AL., NANOTECHNOLOGY, 2014, pages 25
GLAVAN ET AL., ADV. FUNCT. MATER., vol. 24, 2014, pages 60 - 70
Attorney, Agent or Firm:
BOLSINGER, Dr. Jens (DE)
Download PDF:
Claims:
A method for treatment of cellulose-based material comprising

a) a coupling step comprising:

i. provision of a coupling solution comprising titanium(IV) isopropoxide (TTIP) or a basic solution of zinc oxide,

ii. immersion of said cellulose-based material into said coupling solution, iii. in case of the coupling solution comprising ZnO, a heat treatment step is performed at 40°C to 1 10°C, in particular 60°C to 1 10°C, more particular 80°C to 1 10°C and most particular 90°C to 100°C;

yielding a coupled cellulose-based material comprising a transparent hybrid layer; b) a hydrophobization step comprising:

i. provision of a hydrophobization solution comprising a hydrophobic compound, wherein said hydrophobic compound has a chemical affinity for complete wetting and adhesion of a lubricating fluid,

ii. immersion of said coupled cellulose-based material in said hydrophobization solution,

iii. drying of said hydrophobic cellulose-based material,

yielding a hydrophobic cellulose-based material comprising a transparent hydrophobic hybrid layer.

The method for treatment of cellulose-based material according to claim 1 , wherein the coupling solution comprises

• TTIP with a concentration from 1 wt% to 10 wt%, in particular 2 wt% to 8wt%, more particular 4 wt% to 6 wt%, and/or

• zinc oxide with a concentration of a saturated zinc oxide solution, in particular a ZnO concentration of 40mM to 60mM, more particular 45mM to 55mM, most particular 50mM.

The method for treatment of cellulose-based material according to any one of the preceding claims, wherein the coupling solution comprises:

- in the case of the coupling solution comprising ZnO, ammonium hydroxide, and/or

- in the case of the coupling solution comprising TTIP, an organic solvent, in particular an alcohol, more particular ethanol.

The method for treatment of cellulose-based material according to claim 3, wherein the coupling solution comprising TTIP comprises additionally Ce(NH4)2(N03)6. The method for treatment of cellulose-based material according to any one of the preceding claims, wherein

- the immersion time in the coupling step is between 10 minutes and 2 hours, in particular 30 minutes and 2 hours, more particular 1 hour and 1.5 hours,

- the heat treatment time in the coupling step is for a duration of 30 seconds to 5 minutes, in particular 1 minute to 4 minutes, more particular 2 minutes to 3 minutes.

The method for treatment of cellulose-based material according to any one of the preceding claims, wherein the hydrophobization solution comprises a hydrophobic compound selected from:

- long alkyl chain thiols,

- organic silanes,

- fatty acids,

- aromatic azide and

- fluorinated organic silane molecules.

The method for treatment of cellulose-based material according to any one of the preceding claims, wherein the hydrophobic compound in the hydrophobization solution is selected from:

- 1 H,1 H,2H,2H-Perfluorooctyltriethoxysilane;

- Trichloro (1 H,1 H,2H,2H-perfluorooctyl) silane,

- methyltrichlorosilane,

- decyltrichlorosilane,

- (3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl) trichlorosilane,

- stearic acid,

- 1-Dodecanethiol, and

- Trimethoxy(octyl)silane.

The method for treatment of cellulose-based material according to any one of the preceding claims, wherein:

- the immersion time in the surface hydrophobization step ranges from 0.5 hours to 24 hours, in particular 1 hour to 16 hours, more particular 2 hours to 12 hours, most particular 4 hours to 8 hours; and/or

- the drying of said hydrophobic cellulose-based material is performed at a temperature of 40°C to 80°C, in particular 50°C to 80°C, more particular 60°C to 75°C.

9. The method for treatment of cellulose-based material according to any one of claim 1 to 8, additionally comprises an omniphobization step comprising:

i. provision of a lubrication solution,

ii. immersion of said hydrophobic cellulose-based material into said lubrication solution,

iii. removal of excess lubrication solution,

yielding an omniphobic cellulose-based material.

10. The method for treatment of cellulose-based material according to claim 9, wherein the lubrication solution comprises a non-polar viscous liquid with a surface tension <40 mN/cm, in particular with a surface tension of 10 to 35 mN/cm, more particular 15 to 25 mN/cm, most particular 16 to 20 mN/cm.

1 1 . The method for treatment of cellulose-based material according to any one of claims 9 to 10, wherein the lubrication solution comprises:

i. fluorinated oils selected from DuPont Krytox GPL 100, 101 , 102, 103, 104, 105, 106 and 107; and/or

ii. crude oil or olive oil.

12. The method for treatment of cellulose-based material according to any one of claims 9 to 1 1 , wherein:

- the immersion time in the lubrication solution ranges from 5 to 30 minutes, in particular 10 to 20 minutes, more particular 15 minutes; and/or

- said removal of excess lubrication solution is achieved by removal of said cellulose-based-material from the lubrication solution and storage for a time of 10 minutes to 2 hours, in particular 30 minutes to 1 .5 hours, more particular 1 hour.

13. The method for treatment of cellulose-based material according to any one of the preceding claims, wherein the cellulose-based material is selected from wood, wood veneer, paper, cotton, nanocellulose paper or nanocellulose foam.

14. A cellulose-based material characterized by at least one of the following properties:

I. the advancing contact angles of water are at least 1 10°, in particular at least 120°, more particular at least 130° and the receding contact angles are at least 70°, in particular at least 80°, more particular at least 87°, and/or

II. the advancing contact angles for a liquid with a surface tension between 45 mN/s and 50 mM/s are at least 75°, in particular at least 80°, more particular at least 89° and the receding contact angles are at least 55° in particular at least 60°, more particular at least 62°, and/or

III. the advancing contact angles for a liquid with a surface tension between 25 mN/s and 30 mM/s are at least 50°, in particular at least 55° more particular at least 60° and the receding contact angles are at least 35°, in particular 40°, more particular 41 °, and/or

IV. a cellulose-TTIP hybrid layer, wherein TTIP derived from the coupling solution interacts with the OH and/or CO groups of cellulose and/or hemicellulose; and/or

V. a cellulose-ZnO hybrid layer, wherein ZnO derived from the coupling solution interacts with the OH and/or CO groups of cellulose and/or hemicellulose.

15. A cellulose-based material, particularly comprising the features of claim 14, obtainable by a process according to the method of any one of claims 1 to 13.

Description:
Multi-repellent wood veneer and paper surface coating

Field of the invention

The present invention relates to a method for treatment of cellulose-based materials that provides cellulose-based material with a multi-repellent surface. Background of the invention

In 1997, Neinhuis and Barthlott successfully explained the origin of "lotus effect" in nature, in which the self-cleaning properties of the plant surface were attributed to the micro- and nanometer epicuticular wax crystalloids (Neinhuis, C. & Barthlott, W; Annals of Botany, 79, 667-677, 1997). After decades of research based on the principle of "lotus effect" to prepare superhydrophobic surfaces, nowadays, researchers are facing the following challenges: the coating is whitish because of the light scattering effect of the rough nanostructure, which impedes the natural appearance of the substrate;

limited repellence to low surface tension liquids;

failure upon mechanical damage, and lack of self-healing properties.

For the preparation of superoleophobic surfaces, methods such as photolithography have been applied; however, they are cost intensive and not applicable to large scale applications. Alternatively, formulations comprising copolymers with specific properties can be prepared and applied to paper, textiles, leathers and wood as hydrophobic and oleophobic coating and finishing.

The addition of fluorinated acrylic monomers on the polymeric structure of wood coatings was reported, and it resulted in high hydrophobicity and oleophobicity of the coatings applied to wood panels (Bongiovanni, R. et al. Pitture Vernici, Eur. Coat. 79, 25-30; 2003).

WO 2008/055369 A1 disclosed a method to produce a hydrophobic or oleophobic finishing for coatings on all types of fibers or fabrics by dispersing particles comprising hydrophobic or oleophobic surface groups. Hydrophobic, oleophobic, and anti-icing coatings comprising a binder, particles with different size distribution and selected alkyl, haloalkyl or perfluoroalkyl chains were described in WO 2010/042191 A1.

However, these methods changed the natural appearance of the substrate materials and contained additional fungicide, acetone or petroleum, which are potentially harmful to humans and the environment.

In 201 1 , inspired by Nepenthes, pitcher plants, the research group headed by Aizenberg created omniphobic "slippery" surfaces (SLIPS) from low surface energy porous micro- structured solid substrates, such as Teflon membranes or arrays of nanoposts functionalized with polyfluoroalkylsilanes, by infusing them with a fluorinated lubricant (Wong, T.-S. et al. Nature; 477, 443-447; 201 1 ). Three factors were identified as crucial for the preparation of omniphobic coatings:

firstly, the lubricating liquid must have strong adhesion with the substrate;

- secondly, the material should be preferentially wetted by the lubricating liquid instead of the liquid to be repelled;

thirdly, the lubricating and impinging test liquids must be immiscible.

Based on these principles, Aizenberg and co-workers have prepared SLIPS-based antibiofilm surfaces which were stable under water, at extreme pH and salinity, or harsh UV conditions, as well as SLIPS-coated Aluminium surfaces with extreme anti-ice and anti-frost performance. They also pre-assembled colloids at the air/water interface and subsequently transferred them onto the desired substrates to form colloidal templating lubricant-infused structured surfaces.

Similar principles were used to design SLIPS functionalized cotton and polyester fabrics exhibiting decreased contact angle hysteresis and sliding angles, and omni-repellent properties against various fluids including polar and non-polar liquids (Cicely et al., Nanotechnology; 25, 2014). More recently "fluoroalkylated paper" that resisted wetting by low surface tension liquids (<15 mN m "1 ) by infusing the fluoroalkylated paper with perfluorinated oils has been reported (Glavan et al.; Adv. Fun . Mater. 24, 60-70, 2014), (WO 2014149465 A1 ).

In addition, WO 2014/012078 A2 disclosed a liquid repellent surface having selective wetting and transport properties, which comprise a liquid infused porous surface layer with patterned wettability. A multi-repellent material that included a reentrant curvature featured substrate and an immobilized layer of lubricating liquid wetting over the surface was described in WO 2014/012039 A1 .

Terms and definitions

In the context of the present specification, the term cellulose-based material refers to any material comprising cellulose and/or hemicellulose as an essential part. Examples for cellulose-based materials include wood, paper, cotton, nanocellulose paper and nanocellulose foam. About 35 to 50 wt. % of wood is cellulose and about 20 to 35 wt. % is hemicellulose. Paper contains about 70 to 90 wt. % cellulose and 5 to 15 wt. % hemicellulose. Cotton contains about 85 to 95 wt. % cellulose and 3 to 5 wt. % hemicellulose. Nanocellulose paper and foam contain 100 wt.% cellulose. In the context of the present specification the term percentage by weight (wt%) refers to the ratio of the mass of one substance to the mass of the total mixture multiplied by 100. Percentage by weight is calculated according to formula:

m tot J

with m s being the mass of one substance in a mixture and m to t the mass of the total mixture.

In the context of the present specification, the term multi-repellent surface refers to a surface that is hydrophobic and oleophobic. These surfaces have a resistance to wetting by polar and non-polar liquids including low surface tension liquids. The terms multi-repellent surface and omniphobic surfaces are used interchangeably in this description. Summary of the invention

The present invention was made in view of the prior art described above, and the problem underlying the present invention is to provide a method for treatment of cellulose-based materials that yields cellulose based-material with a multi-repellent surface. This problem is solved by the subject-matter of the independent claims.

The present invention provides a titanium isopropylate (TTIP) layer that penetrates into the cellulose-based material when it is immersed in TTIP solution to form a cellulose-TTIP hybrid layer. In an alternative approach, a ZnO layer penetrates the cellulose-based material by dipping it into the ZnO dissolved ammonia hydroxide solution followed by heat treatment. In both of these approaches, the present invention takes advantage of the coordination effect of TTIP or Zn[(OH) x (NH 3 ) y ] 2"x complexes, such as Zn(NH 3 ) 4 2+ , to OH or CO groups in cellulose and hemicellulose to form hybrid surfaces. Then, surface hydrophobization is carried out by modifying the as-prepared cellulose-based material with low-surface-energy materials. The low-surface-energy materials could be long alkyl chain thiols, organic silanes, fatty acids, aromatic azide or fluorinated organic silane molecules. Finally, the multi-repellent properties and the resistance to wetting by low surface tension liquids of the hydrophobic surfaces were further increased by infusing them with perfluorinated oils.

The invention disclosed here yields cellulose-based materials with a multi-repellent surface, wherein the surface coating is mechanically robust, self-healing and transparent, which will broaden the practical application of such products. This facile method can be used to modify any temperature sensitive- and non-conducting cellulose-based material.

According to a first aspect of the invention a method for treatment of cellulose-based material is provided comprising the following steps: a) A coupling step comprising:

i. The provision of a coupling solution comprising titanium(IV) isopropoxide (TTIP;

CAS No: 546-68-9) and alcohol or a basic solution of zinc oxide, and ii. the immersion of the cellulose-based material into the coupling solution, yielding a coupled cellulose-based material

b) .A hydrophobization step comprising:

i. The provision of a hydrophobization solution comprising a hydrophobic compound,

ii. the immersion of the coupled cellulose-based material in the hydrophobization solution, yielding a hydrophobic cellulose-based material, and

iii. drying of the hydrophobic cellulose-based material.

Detailed description of the invention

Wood is a versatile, strong and sustainable raw material. But its non-inert nature with a low dimensional stability and durability arising from water or moisture uptake strongly affects the reliability of wood in various applications. Moreover, the wood surface colour can be irreversibly changed by the uptake of liquids (e.g. red wine, oil, suncream). If a liquid repellent surface with low liquid-solid adhesion can be achieved, it should be possible to develop more inert wood materials for wider practical applications. The gist of this invention is to form a multi-repellent surface that repels polar liquids as well as low surface tension non polar liquids, that prevents the adsorption of liquid-borne contaminants and that reduces ice adhesion strength.

The novelty of this invention is that the coating is transparent, which is advantageous in preserving the natural appearance of wood materials, but is also desirable in processed cellulose-based goods such as paper or cotton fibres. The modified wood veneer retains its mechanical flexibility, and can be bent without destroying its omniphobic surface properties. The liquid repellent property of the coating stays intact even after cuts into the material, which indicates that the coating is self-healing and mechanically robust. The facile method can be further extended to modify any temperature sensitive- and non-conducting cellulose- based material, because of similar chemical functional groups.

According to the three criteria for designing the SLIPS proposed by Aizenberg, as explained above, the technical problem in creating an omniphobic surface of cellulose-based materials is that the surface is highly hydrophilic, consisting of a multitude of OH groups. This means that the chemical condition of the unmodified cellulose-based substrate is not suitable to immobilize perfluorinated oil films. In this invention, an inorganic coating was developed that acts as buffer layer, by the coordination effect of TTIP or Zn[(OH) x (NH 3 ) y ] 2"x , particular Zn(NH 3 ) 4 2+ , to OH and CO groups in cellulose and hemicellulose. Then, hydrophobization step was carried out to obtain a hydrophobic surface which has a chemical affinity for complete wetting and strong adhesion of lubricating fluid.

Common technologies used to achieve a porous surface with chemical affinity for liquids, facilitate a complete wetting by, and adhesion of, the lubricating fluid based on colloidal templating, chemical etching, roughening of the surface by nano/micro fibers or photolithography. However, these methods can hardly be applied to the rough and inhomogeneous wood surface and they are too cost intensive for large scale applications. In certain embodiments this invention takes advantage of the natural roughness (uneven topography with cut-open cells) and the chemical composition of wood to immobilize lubricant films onto wood veneers to form a multi-repellent wood surface.

The first aspect of the invention relates to a method for treatment of cellulose-based material comprising a coupling step and a hydrophobization step that are performed in this sequential order.

In the coupling step a coupling solution comprising titanium(IV) isopropoxide (TTIP) or a basic solution of zinc oxide is provided and the cellulose-based material is immersed in the coupling solution.

The coupling step is yielding a coupled cellulose-based material comprising a transparent hybrid layer.

The titanium oxide layer derived from the TTIP treatment is a pure inorganic layer. It is generated by the hydrolysis of TTIP molecules initiated by the moisture in wood or the hydroxyl groups in wood. Moreover, because of the permeation of the TTIP and alcohol precursor solution into wood, the resulted Ti0 2 layer not only covers the wood surface but also covers the lumen surface inside wood.

In case of the coupling solution comprising ZnO, a heat treatment step is performed at 40°C to 1 10°C, in particular 60°C to 1 10°C, more particular 80°C to 1 10°C and most particular 90°C to 100°C for yielding a coupled cellulose-based material comprising a transparent hybrid layer.

The zinc amine complexes formed by dissolving ZnO powder into the ammonium solution will bind to the wood surface via coordination effects with the functional groups, such as hydroxyl and carbonyl groups. The zinc ammine complexes binding onto the wood surface will decompose into ZnO layer by the heat treatment. Thus, the wood surface is completely covered by a thin ZnO layer, which enables the binding of hydrophobic molecules.

This step creates a hybrid surface of the inorganic layer and the cellulose-based material by using the coordination effect of the inorganic coating with the OH and CO groups in cellulose and hemicellulose. The inorganic coating acts as a buffer layer between the cellulose-based material and the hydrophobic surface.

In some embodiments, a method for treatment of cellulose-based material is provided, comprising

a) a coupling step comprising:

i. provision of a coupling solution comprising titanium(IV) isopropoxide (TTIP) or a basic solution of zinc oxide,

ii. immersion of said cellulose-based material into said coupling solution, iii. in case of the coupling solution comprising ZnO, a heat treatment step is performed at 40°C to 1 10°C, in particular 60°C to 1 10°C, more particular 80°C to 1 10°C and most particular 90°C to 100°C;

yielding a coupled cellulose-based material comprising a transparent hybrid layer; b) a hydrophobization step comprising:

i. provision of a hydrophobization solution comprising a hydrophobic compound, wherein said hydrophobic compound has a chemical affinity for complete wetting and adhesion of a lubricating fluid,

ii. immersion of said coupled cellulose-based material in said hydrophobization solution,

iii. drying of said hydrophobic cellulose-based material,

yielding a hydrophobic cellulose-based material comprising a transparent hydrophobic hybrid layer.

In the hydrophobization step a hydrophobization solution comprising a hydrophobic compound is provided and the coupled cellulose-based material is immersed in the hydrophobization solution yielding a hydrophobic cellulose-based material followed by drying of the hydrophobic cellulose-based material.

The hydrophobic compound has a chemical affinity for complete wetting and adhesion of a lubricating fluid and is and is able to form a covalent bond or physical adsorption with the Ti0 2 or ZnO hybrid layer. The hydrophobization step is yielding a hydrophobic cellulose- based material comprising a transparent hydrophobic hybrid layer.

Thus, the hydrophobic compound is bound to the surface of Ti0 2 or ZnO layer by covalent bond attachment or physical adsorption. For example, a silane group will hydrolyse in the presence of a H 2 0 or OH group, and form a covalent Si-O- group bound to the surface, while stearic acid can bound to the surface by an ester like bond, it can also adsorb to the hydrophilic Ti0 2 or ZnO surface owing the affinity between the hydrophilic functional groups. This step introduces hydrophobic compounds to the surface, which has a chemical affinity for complete wetting and strong adhesion of the lubricating fluid.

In certain embodiments, the coupling solution comprises TTIP with a concentration from 1 wt% to 10 wt%, in particular 2 wt% to 8wt%, more particular 4 wt% to 6 wt%.

In certain embodiments, the coupling solution comprises zinc oxide with a concentration of a saturated zinc oxide solution, in particular a ZnO concentration of 40mM to 60mM, more particular 45mM to 55mM, most particular 50mM.

In certain embodiments, the coupling solution comprises ammonium hydroxide in the case of the coupling solution comprising ZnO.

In certain embodiments, the coupling solution comprises ZnO, ammonium hydroxide and water.

In certain embodiments, in the case of the coupling solution comprising ZnO, the coupling solution has a pH > 7, in particular pH 8-14, more particular pH 9-13, most particular pH 1 1- 12.

In certain embodiments, the coupling solution comprising TTIP comprises additionally Ce(NH 4 ) 2 (N0 3 )6- The cerium compound, preferably dissolved in alcohol, stabilize TTIP avoid a white precipitate during the production process.

In certain embodiments, in the case of the coupling solution comprising TTIP the coupling solution comprises an organic solvent, in particular an alcohol, more particular ethanol, methanol or isopropanol.

In certain embodiments, wherein the immersion time in the coupling step is between 10 minutes and 2 hours, in particular 30 minutes and 2 hours, more particular 1 hour and 1.5 hours.

In certain embodiments, the coupling step further comprises a heat treatment step at 40°C to 1 10°C, in particular 60°C to 1 10°C, more particular 80°C to 1 10°C and most particular 90°C to 100°C, for a duration of 30 seconds to 5 minutes, in particular 1 minute to 4 minutes, more particular 2 minutes to 3 minutes.

In certain embodiments, the heat treatment step in the coupling step is followed by a washing step in ethanol.

In certain embodiments, the hydrophobization solution comprises an organic solvent, selected from nonpolar solvents, such as hexane, or polar solvents such as ethanol and methanol. In certain embodiments, the hydrophobization solution comprises a hydrophobic compound selected from long alkyl chain thiols, organic silanes, fatty acids, aromatic azide or fluorinated organic silane molecules.

In certain embodiments, the hydrophobic compound in the hydrophobization solution is selected from:

- 1 H,1 H,2H,2H-Perfluorooctyltriethoxysilane (CAS: 51851 -37-7);

- Trichloro (1 H,1 H,2H,2H-perfluorooctyl) silane (CAS: 78560-45-9),

- methyltrichlorosilane (CH 3 SiCI 3 ; CAS: 75-79-6),

- decyltrichlorosilane (CH 3 (CH 2 ) 9 SiCI 3 , CAS: 13829-21 -5),

- (3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl) trichlorosilane (CF 3 (CF 2 ) 5 CH2CH 2 SiCI 3 , CAS: 17527-29-6),

- stearic acid (CAS: 57-1 1-4),

- 1-Dodecanethiol (CAS: 1 12-55-0), and

- Trimethoxy(octyl)silane (CAS: 3069-40-7).

In certain embodiments, the immersion time in the surface hydrophobization step ranges from 0.5 hours to 24 hours, in particular 1 hour to 16 hours, more particular 2 hours to 12 hours, most particular 4 hours to 8 hours

In certain embodiments, the hydrophobic cellulose-based material is dried at a temperature of 40°C to 80°C, in particular 50°C to 80°C, more particular 60°C to 75°C.

In certain embodiments, the duration of drying may be prolonged depending on the size of the wood material. A non-limiting example is wood material of the dimensions radial (R) x tangential (T) x longitudinal (L) dimensions: 5x25x40 mm requiring a heat treatment of at least 5 minutes at 60°C, preferably 60°C for 2 hours. Wood material of smaller or larger dimension might require proportionally shorter or longer, respectively and/or lower temperatures. In general requires wood material of larger dimensions longer drying duration than wood material of smaller dimensions.

In certain embodiments, the method for treatment of cellulose based-material additionally comprises an omniphobization step. In this step a lubrication solution is provided and the hydrophobic cellulose-based material is immersed in the lubrication solution and excess lubrication solution is removed, yielding an omniphobic cellulose-based material.

This step adds a layer of lubricant to the surface that is essential for the self-healing properties of the surface. In certain embodiments, the lubrication solution comprises a non-polar viscous liquid with a surface tension < 40 mN/cm, in particular with a surface tension of 10 to 35 mN/cm, more particular 15 to 25 mN/cm, most particular 16 to 20 mN/cm.

In certain embodiments, the non-polar viscous liquid is an oil.

In certain embodiments, the lubrication solution comprises fluorinated oils with a surface tension <40 mN/cm, in particular with a surface tension of 10 to 35 mN/cm, more particular 15 to 25 mN/cm, most particular 16 to 20 mN/cm.

In certain embodiments, the lubrication solution comprises fluorinated oils selected from DuPont Krytox GPL 100, 101 , 102, 103, 104, 105, 106, 107, or any other oil with lower surface tension than the liquid to be repelled, such as crude oil or olive oil.

In certain embodiments, the immersion time in the lubrication solution ranges from 5 to 30 minutes, in particular 10 to 20 minutes, more particular 15 minutes

In certain embodiments, the removal of excess lubrication solution is achieved by removal of said cellulose-based-material from the lubrication solution and storage for a time of 10 minutes to 2 hours, in particular 30 minutes to 1.5 hours, more particular 1 hour.

In certain embodiments, the cellulose-based material is selected from wood, wood veneer, paper or cotton, nanocellulose paper and nanocellulose foam.

According to a second aspect of the invention a cellulose-based material characterized by at least one of the following properties:

I. The advancing contact angles of water are at least 1 10°, in particular at least 120°, more particular at least 130° and the receding contact angles are at least 70°, in particular at least 80°, more particular at least 87°, and/or

II. the advancing contact angles for a liquid with a surface tension between 45 mN/s and 50 mM/s are at least 75°, in particular at least 80°, more particular at least 89° and the receding contact angles are at least 55° in particular at least 60°, more particular at least

62°, and/or

III. the advancing contact angles for a liquid with a surface tension between 25 mN/s and 30 mM/s are at least 50°, in particular at least 55° more particular at least 60° and the receding contact angles are at least 35°, in particular 40°, more particular 41 °, and/or IV. a cellulose-TTIP hybrid layer, wherein TTIP derived from the coupling solution interacts with the OH and/or CO groups of cellulose and/or hemicellulose; and/or

V. a cellulose-ZnO hybrid layer, wherein ZnO derived from the coupling solution interacts with the OH and/or CO groups of cellulose and/or hemicellulose. Properties I. to III. refer to the omniphobic properties against high surface tension and low surface tension liquids of the wood material.

In some embodiments the contact angle of a water drop on the surface of the wood material is measured. The term contact angle refers to the angle formed by the intersection of the liquid-solid interface and the liquid-vapor interface. In case the liquid used is water a contact angle smaller than 90° indicates a hydrophilic surface, a contact angle between 90° and 150° indicates a hydrophobic surface and contact angles above 150° indicate a superhydrophobic surface. In other words the higher the contact angle between a solid surface and a water droplet is the less hydrophilic and the more hydrophobic the solid surface is. A more adequate characterization of the wettability properties of surface can be obtained by measuring dynamic contact angles. The contact angle measured by expanding the liquid is referred to as the advancing contact angle and the contact angle formed by contracting the liquid is referred to as the receding contact angle. Subtraction of the receding contact angle from the advancing contact angle yields the contact angle hysteresis. Known methods to measure contact angle include direct measurement by goniometers.

According to a third aspect of the invention a cellulose-based material comprising the features according to the second aspect of the invention, obtainable by a process according to the method of the first aspect of the invention is provided.

Wherever alternatives for single separable features such as, for example, a treatment duration or temperature, a solution component or immersion duration are laid out herein as "embodiments", it is to be understood that such alternatives may be combined freely to form discrete embodiments of the invention disclosed herein.

The invention is further illustrated by the following examples and figures, from which further embodiments and advantages can be drawn. These examples are meant to illustrate the invention but not to limit its scope.

Short description of the figures

Fig. 1 shows a schematic illustration of the structure of the omniphobic coating on a wood surface

Fig. 2 shows time-sequence images of a drop of water (a), hexadecane (b) and olive oil (c) rolling down from the Krytox 100 infused spruce veneer after modification with TTIP and 1 H,1 H,2H,2H-Perfluorooctyltriethoxysilane. The tilt angle is about 15°. It reveals that the as-prepared wood veneer not only repels high surface tension water but also low surface tension organic solvent

Fig.3 shows Snapshots from the measurement of advancing and receding contact angles of water, ethylene glycol and hexadcane droplets on the ZnO nanorods arrays modified wood surface after infused with lubricant (a), advancing (■) and receding (· ) contact angle as well as contact angle hysteresis of water, ethane glycol and hexadecane on the lubricant infused hierarchical wood surface as a function of the surface tension of the tested liquid, (b) The inset displays the rolling off of a droplet of olive oil which is highlighted in red cycles.

The rolling off distance of a droplet of water (■), ethylene glycol ( · ) and hexadecane (A) from the lubricant infused hierarchical wood surface with a title angle of about 16.8 degree as a function of time. The quality of water, ethane glycol and hexadecane droplet is 27.9, 42.8 and 17.2 mg, respectively (c). Compared to water and ethane glycol, the hexadecane droplet has the smallest receding and advancing contact angles, as well as the smallest contact angle hysteresis (-19.22°). It is different from the conventionally known Cassie-Baxter type nonwetting surface. The rolling off speed increased as the contact angle hysteresis decreased. In spite of that the water droplet has the largest contact angle, it displayed the lowest rolling off speed.

shows a transparent Ti0 2 Gel generated by adding Ce(NH 4 )2(N0 3 )6 into the ethanol TTI P solution, a) is the UV-Vis spectra of the free standing Ti0 2 gel. It indicates that the Ti0 2 gel is transparent to visible light, but absorbs almost all of the UV light compare to glass. The insert in a) displays that the logo of EMPA could be clearly see though the light yellow Ti0 2 xerogel. b) is the x-ray diffraction patterns of spruce wood and the Ti0 2 xerogel coated spruce. It demonstrated that the Ti0 2 xerogel on wood surface is amorphous. The intensity of the diffraction peaks of the crystalized cellulose in wood is suppressed because of the coating on the surface.

shows a transparent Ti0 2 Xerogel on wood surface, a) and b) show the microstructure of the cut opened wood cell structure; c) shows the Ti0 2 xerogel coating on the tangential section of the wood surface; d) shows the Ti0 2 xerogel coating on wood surface observed from cross section, from which the thickness of the coating could be measured.

shows Ti0 2 Xerogel inside wood (on wood lumen surface), a) is the schematic illustration of the SEM sample preparation by cutting into the wood, b) show the back scattering electron image of Ti0 2 xerogel coating on the lumen surface of the cells inside wood. The distribution of the Ti0 2 xerogel can be distinguished based on the contrast. The exhibition of Ti0 2 inside wood was further check by Energy Dispersive X-ray Spectrum (EDX) as shown in c).

Spectra A and B are acquired from the regions marked in b). It indicates that Ti0 2 xerogel is mainly coating on the lumen surface, d) the cross section of the same sample, from which the coating on the lumen surface of the wood cells inside the wood could be seen.

Examples

The process of wood surface modification according to the invention comprises the following steps:

I) Wood-TTIP hybrid surface

1 ) Wood veneer was immersed in a titanium alkoxide [titanium(IV) isopropoxide (TTIP)] - ethanol solution for a certain period of time, in particular 2 hours at room temperature. The treated wood veneer was washed in fresh ethanol, and then a wood-TTIP hybrid surface was obtained. The concentration of TTIP in ethanol solution should range from 1 wt% to 10 wt%; the immersion time should range from 10 min to 2 h.

Alternatively, Ce(NH 2 ) 2 (N0 3 ) 6 can be added to the solution (e.g. isopropanol/ethanol) in a concentration of 0.1 mM to 10mM before the wood samples were immersed. The addition of Ce(NH 2 )2(N0 3 ) 6 can avoid a white powder on the surface of the products. Thus, a Ti0 2 _Ce0 2 hydrid layer is provided. However, the amount of Ce0 2 is very small.

II) ZnO layer covered wood surface

1 ) Excess ZnO powder was added to ammonium hydroxide solution to obtain a saturated ZnO dissolved solution with the assistance of magnetic stirring.

2) Dipping the wood veneer into the ZnO dissolved solution described in step 1 ) for a certain period of time, in particular, 5 min at room temperature, before heat treatment Heat treatment temperature should be in the range of 40°C to 1 10 °C; the heat treatment time should be in the range of 30 seconds to 5 min.

III) Fluorosilanization

1 ) Immersing the wood veneer obtained from process I) or II) into the organic solvent containing hydrophobic compounds. The organic solvent could be hexane, ethanol or methanol, and the fluorinated organic silanes could be an hydrophobic compound selected from 1 H,1 H,2H,2H-Perfluorooctyltriethoxysilane (CAS: 51851-37-7);

Trichloro (1 H,1 H,2H,2H-perfluorooctyl) silane (CAS: 78560-45-9), decyltrichlorosilane

(CH 3 (CH 2 ) 9S1CI3 , CAS: 13829-21-5), and (3,3,4,4,5,5,6,6,7,7,8,8,8- tridecafluorooctyl) trichlorosilane CAS: 17527-29-6) ; the immersing time could range from 0.5 h to 24 h; the fluorinated organic silanes dissolved in organic solvent could be also dropped onto the wood veneer surface, and then dried in air.

2) Removal of the wood veneer from the organic solution and drying in an oven. In this step, wood veneer can be dried at a temperature ranging from 40°C to 80°C.

IV) Lubrication

The hydrophobic wood veneer obtained in step III) is infused with lubricants by adding the lubricant liquid to the substrate followed by dipping into the lubricant liquid for 5 to 30 minutes followed by storage for half hour to remove the excess lubricants. The lubricants could be fluorinated oils such as DuPont Krytox GPL 100, 101 , 102, 103, 104, 105, 106, 107..

V) The procedures demonstrated in Step I) to Step IV) can not only be used for wood surface modification but can also be applied to modify cellulose paper with the exact same method.

Compared with existing technologies, the advantages of this invention include the following points:

1 ) The wood surface covering process as described is facile, mild and economic. Almost all of the procedures can be finished in a short time at room temperature;

2) The modified wood surface can repel a wider variety of liquids compared to traditional superhydrophobic surfaces;

3) The coating is transparent, which preserves the natural appearance of wood after modification;

4) The coating is robust to mechanical damage as observed by a knife scratch test;

5) The presented method can be extended to prepare multi-repellent nanocellulose papers;

6) The presented method can be easily scaled-up for large scale surface modification;