WO2015185885A1

WO2015185885A1 - Hydrophobic powder

Info

Publication number: WO2015185885A1
Application number: PCT/GB2015/000162
Authority: WO
Inventors: Christopher CHEESEMAN; Charikleia SPATHI
Original assignee: Imperial Innovations Limited
Priority date: 2014-06-05
Filing date: 2015-06-05
Publication date: 2015-12-10
Also published as: GB201410030D0; EP3152180A1

Abstract

The present application relates to a hydrophobic powder for use as a coating material or as an additive and methods of its production. The hydrophobic powder comprises particles of a core material derived from paper sludge ash and a surface functionalisation agent comprising an organic tail.

Description

HYDROPHOBIC POWDER

This invention relates to a hydrophobic powder for use as a coating material or as an additive and methods of its production, wherein the hydrophobic powder is formed from particles of a core material derived from paper sludge ash and an organic surface functionalisation agent. Background

The European pulp and paper industry produces 99.3 million tonnes of paper annually resulting in the generation of 1 1 million tonnes of waste. Approximately 7.7 million tonnes of this waste is generated during paper recycling which has a high sludge production rate. The waste sludge comes from a variety of processes and feedstocks and are generally composed of fibre, filler and other components which are unsuitable for the paper-making process (Monte et al., Waste Management, 29 (1), 293-308, 2009). The implementation of waste management legislation has led to a variety of adaptions in the pulp and paper industry. Considerable reductions in production residues have been made, but complete elimination of these waste streams is simply unfeasible. A range of recovery, recycling and reuse strategies have been implemented in order to reduce the percentage of waste being disposed of by landfilling. Some mills have incorporated energy recovery processes which combust dewatered waste paper sludge. This allows for electricity and heat production while also reducing waste volumes. The residual from the combustion process is known as Paper Sludge Ash (PSA).

Currently, approximately 125k tonnes per annum of PSA are produced in the United Kingdom. This figure is expected to rise to 300k tonnes per annum in the near future. The predicted increase is largely due the incorporation of co-combustion with biomass during the energy recovery process. Co-combusticn helps balance the relatively low calorific value of mechanically dewatered paper sludge (2.5-6 MJ/kg). Of the 125k tonnes per annum, 70% is being utilised in a small range of relatively low-value reuse applications. The remaining 30% goes to landfill disposal. In order to make better use of this PSA surplus and prevent as much going to landfill with the additional 175k tonnes per annum expected in coming years, it will be necessary to develop more high-value and beneficial end-uses. Viable reuse applications have worldwide implications too as pulp and paper production is due to result in increasing amounts of PSA. l In addition, in the field of civil engineering, there remains the need to develop means to prevent moisture damaging construction materials. When water percolates into

construction materials the water can cause corrosion and deformation. Such corrosion and deformation leads to the appearance of cracks and discolouration effects and spalling in materials such as concrete and, eventually, to a reduction of construction strength and integrity. Other internal objects in constructions, such as pipes and wires may also be damaged by moisture. Moisture may also cause biodegradation in wood and timber products and can also support algal and bacterial growth. It is clear that there is a significant issue around the production and wastage of PSA. In order to divert more of this material from landfill, the development of viable high-value reuse applications is critical. There also remains a need for further hydrophobic materials for use in the construction industry and for use in protecting and improving the durability of civil infrastructure.

Summary of invention

It has been determined that paper sludge ash can be treated through milling with a surface functionalising agent to form a hydrophobic powder. This hydrophobic property could be exploited for certain innovative high-value reuse applications such as in hydrophobic coatings and as an additive in construction materials, such as concrete, mortar or cement.

Accordingly, in a first aspect the invention provides a hydrophobic powder comprising: particles of a core material functionalised with a surface functionalisation agent, wherein the core material comprises paper sludge ash and the surface functionalisation agent comprises a functional group bound to the core material and an organic tail.

In a second aspect, the invention provides a hydrophobic powder comprising:

particles of a core material functionalised with a surface functionalisation agent;

wherein the surface functionalisation agent comprises a functional group bound to the core material and an organic tail; and the core material has a mineral composition comprising gehlenite, calcite and lime, optionally wherein the core material also comprises one or more of calcium silicate, mayenite and quartz and optionally wherein the core material has a composition, when expressed as oxides, comprising 30 to 70% calcium oxide, 15 to 35% silicon dioxide, 5 to 20% aluminium oxide and optionally comprising 0 to 5% magnesium oxide, 0 to 2% iron (III) oxide, 0 to 2% sulfur trioxide, 0 to 1 % titanium dioxide, 0 to 2% potassium oxide, 0 to 1% phosphorus (V) oxide, 0 to 1% sodium oxide and 0 to 1 % strontium oxide.

In a third aspect, the invention provides the hydrophobic powder as described herein, for use in coating a substrate.

In a fourth aspect, the invention provides the hydrophobic powder as described herein, for use as an additive for the production of materials for construction (for example, concrete, mortar or cement).

In a fifth aspect, the invention provides the hydrophobic powder as described herein, wherein the hydrophobic powder is made by a method comprising:

combining a core material and an amount of a surface functionalisation agent in a mill and milling the components to form the hydrophobic powder.

In a sixth aspect, the invention provides a method of manufacturing a hydrophobic powder as described herein, wherein the method comprises:

combining paper sludge ash and a surface functionalisation agent in a mill and milling the components to form the hydrophobic powder; and

wherein the surface functionalisation agent comprises a functional group capable of binding to the core material and an organic tail.

In a seventh aspect, the invention provides a coating material comprising a hydrophobic powder as described herein.

In an eighth aspect, the invention provides an additive for use in the production of construction materials comprising a hydrophobic powder as described herein.

In a ninth aspect, the invention provides a coated material comprising:

a substrate having a surface to be coated; and

a coating comprising a hydrophobic powder as described herein.

In a tenth aspect, the invention provides a method of preparing a coated material as described herein, wherein the method comprises:

coating the surface of a substrate with the hydrophobic powder as described herein so as to form a hydrophobic layer on the surface of the substrate. In an eleventh aspect, the invention provides a material comprising a hydrophobic powder as described herein as an additive.

Description of figures

Figure 1A shows an x-ray diffraction pattern of paper sludge ash supplied by Aylesford Newsprint in Kent.

Figure 1B shows an x-ray diffraction pattern of paper sludge ash supplied by UPM Shotton in Wales.

Figure 2 shows a liquid droplet on a solid surface, wherein Θ is the water contact angle balanced by ySL (the solid-liquid interfacial surface tension), yLV (liquid-vapour interfacial surface tension) and (ySV is the solid-vapour interfacial surface tension) at the three phase contact line.

Figure 3 shows the particle size distributions on a log scale for hydrophobic powder samples at different milling times (A: un-milled, B: 2-hour milled, C: 4-hour milled, D: 8- hour milled, E: 16-hour milled, F: Cumulative distribution curves for each milling time). Figure 4 is a graph showing how the water contact angle varies with the addition of greater wt% stearic acid to the hydrophobic powder.

Figure 5 shows FTIR spectra of hydrophobic powders prepared with different wt% stearic acid additions (A: paper sludge ash, B: hydrophobic powder with 1 wt% stearic acid, C: 4 wt% stearic acid, D: 8 wt% stearic acid)

Figure 6A shows a box plot graph of water contact angle results for hydrophobic powder samples prepared with various surface functionalisation agents.

Figure 6B shows the effect of the surface functionalisation agent carbon chain length on the water contact angle of a hydrophobic powder.

Figure 7 shows a box plot graph of water contact angle results for hydrophobic powder samples prepared with different core materials.

Figure 8 shows the particle size distribution on log scale for a characteristic hydrophobic powder.

Figure 9 shows photographic images of mortar tiles (one the control, another coated with varnish and another with a varnish and hydrophobic powder coating). A is before the application of a powdered charcoal -water mixture and B is after application.

Figures 10A and 10B present data obtained from a sorptivity test of the hydrophobic coating on concrete blocks as water uptake over time. Detailed description of invention

Paper sludge ash (PSA) is the residual waste product formed by the combustion of the waste sludge produced by the paper recycling process. As used herein, the term paper sludge ash relates to a substance formed from combustion of paper sludge, generally at a minimum of 650-800°C. Paper sludge is a waste product comprising cellulose fibres, fillers such as calcium carbonate and china clays, such as kaolinite, and residual chemicals, such as ink, bound up with water. The combustion process is generally carried out using fluidised bed combustors and is regulated in Europe through the Waste

Incineration Directive (2000/76/EC). The directive specifies that paper plants must maintain incineration at 850°C for at least two seconds.

PSAs have been characterised with common features being noted. The chemical compositions of typical PSAs are reported in Table 1. Table 1 reports compositional data for PSAs produced by Aylesford Newsprint (ANP) in Kent, UK and UPM-Shotton in Wales, UK, along with three PSAs from the prior art (Segui et a., Applied Clay Science, 57, 79-85, 2012; Frias et al., Applied Clay Science, 42 (1-2), 189-193, 2008; and Vegas et a/., Construction and Building Materials, 23 (8), 2862-2868, 2009). The values reported in Table 1 were obtained by use of x-ray fluorescence spectroscopy (XRF) to analyse the elements present, with the results presented assuming elements are present as oxides. X-ray diffraction (XRD) analysis shows that PSA actually contained different, more complex, minerals/crystalline materials rather than just oxides. The mineralogical composition of ANP PSA and UPM PSA obtained through XRD can be found in Figures 1A and 1 B.

These studies showed that PSA is rich in calcium, silicon and aluminium. The major crystalline phases are gehlenite (Ca₂AI[AISi0₇]), lime (CaO) and calcite (Ca0₃). Also present can be mayenite (Ca₁₂AI₄0₃), quartz (Si0₂) and calcium silicate (Ca₂Si0₄). PSA particles have been characterised as being porous, heterogeneous and agglomerated, as a result of the combustion process (Mozafarri et al., Cement and Concrete Research, 28 (2), 144-152, 2009). PSA may also be a highly alkaline (pH >12), fine granular material with a moisture content less than 0.1 % w/w (Segui et al., Applied Clay Science, 57, 79- 85, 2012 and Mozafarri ef al., 2009). Table 1 :

Oxides Mean (wt%)

Segui er al. Frias et Vegas et Aylesford UPM

(201Z) PSA al. (2008) al. (2009) Newsprint Shotton PSA

PSA PSA PSA

Calcium oxide (CaO) 45.5 40.2 36.5 61.2 62.6

Silicon dioxide (Si0₂) 28.0 22.3 21.6 21.2 17.7

Aluminium oxide (Al₂0₃) 13.2 14.6 14.4 12.6 8.8

Magnesium oxide (MgO) 4.0 2.4 2.4 2.8 3.5

Iron (III) oxide (Fe₂0₃) 1.3 0.6 0.5 0.9 1.5

Sulfur trioxide (S0₃) 1.3 0.3 0.3 0.2 1.7

Titanium dioxide (Ti0₂) 0.7 0.3 0.3 0.3 0.7

Potassium oxide (K₂0) 0.7 0.4 0.4 0.4 1.2

Phosphorus (V) oxide (P₂0₅) 0.4 0.2 0.2 0.1 0.4

Sodium oxide (Na₂0) 0.4 0.1 0.1 not 0.5 detected

Strontium oxide (SrO) not not not 0.1 0.1 detected detected detected

Paper sludge ash can be characterised by its mineral composition, as a substance comprising gehlenite (Ca₂AI[AISi0₇]), calcite (Ca0₃) and lime (CaO) . Paper sludge ash can also comprise one or more of mayenite (Ca₁₂AI₄0₃), calcium silicate (Ca₂Si0₄), quartz (Si0₂) and optionally merwinite (Ca₃Mg(Si0₄)₂). Paper sludge ash may have a

composition, assuming the elements are present as oxides, comprising 30 to 70% calcium oxide, 15 to 35% silicon dioxide and 5 to 20% aluminium oxide. The composition may further comprise the following, also expresses as oxides, 0 to 5% magnesium oxide, 0 to 2% iron (III) oxide, 0 to 2% sulfur trioxide, 0 to 1% titanium dioxide, 0 to 2% potassium oxide, 0 to 1 % phosphorus (V) oxide, 0 to 1 % sodium oxide and 0 to 1 % strontium oxide.

A composition "expressed as oxides" or "assuming the elements are present as oxides" provides the elemental composition with the proportions of elements expressed on the assumption that the elements are present as oxides. The composition may actually comprise a more complex mineral/crystalline structure. The percentages given when a composition is "expressed as oxides" or "assuming the elements are present as oxides" are as a weight percentage (wt%) of the sample. Analysis of the PSA to determine the composition may be carried out by x-ray

fluorescence spectroscopy.

As used herein, a hydrophobic powder is a substance in particulate form that can repel water or a wetting liquid. A hydrophobic substance is one wherein the water contact angle is 90 to 180°. Optionally, a hydrophobic substance can be superhydrophobic. A

superhydrophobic substance is one where the water contact angle is 150° or greater.

The water contact angle can be seen in Figure 2. Figure 2 shows a liquid droplet on a solid surface showing a water contact angle Θ, balanced by interfacial tension forces at the three phase contact line. The three phase contact line must come to equilibrium. The balance of tension forces (ySL, ySV, yLV) fcr the three interfaces results in a water contact angle (Θ) forming at the droplet edge. The relationship between interfacial tension forces and the water contact angle is given by Young's equation: cos fl = ^YSV-^^SL (-1 < COS Q < 1, 0>> < Q < 180°)

Y

The water contact angle can be determined using a tensiometer.

As used herein, the term core material relates to the substance that acts as the nucleus or core of the hydrophobic powder to which the surface functionalisation agent (SFA) is bound. The core material can comprise paper sludge ash as described herein. Optionally the core material can consist essentially of paper sludge ash as described herein.

As used herein, a surface functionalisation agent is a substance that can be used to bind to the core material to functionalise one or more surfaces of the core material. The following discussion of the surface functionalisation agent applies to all aspects and embodiments of the invention as described herein, mutatis mutandis. The surface functionalisation agent comprises a functional group and organic tail. The surface functionalisation agent may have structure A-B-C, wherein A is a functional group, B is an optionally present linker and C is an organic tail, preferably comprising a hydrocarbon chain. Optionally, the surface functionalisation agent can have structure A-C, wherein A is a functional group and C is an organic tail, preferably a hydrocarbon chain. A surface functionalisation agent may be a fatty acid.

The functional group is a moiety that can bind to another substance (for example, the core material). The functional group can, for example and without limitation, be any of a carboxylic acid, a sulfonic acid or a succinic anhydride. The functional group can bind to the core material via various interactions such as electrostatic, covalent and/or Van der Waals interactions. The organic tail comprises a linear or branched aliphatic group, which may be optionally substituted and/or interrupted with one or more of silicon, oxygen, nitrogen, sulfur, phosphorus or boron. The organic tail may also be substituted and/or interrupted with one or more carbocyclic or heterocyclic groups. In some embodiments, an organic tail may be a hydrocarbon chain or a carbocyclic group with a hydrocarbon chain attached thereto. Preferably, an organic tail is a hydrocarbon chain.

"Aliphatic" as used herein may be a straight or branched chain aliphatic which is completely saturated or contains one or more units of unsaturation. Thus, aliphatic may be alkyl, alkenyl or alkynyl. The aliphatic group may contain at least 5 carbon atoms, at least 6 carbon atoms, preferably at least 10 carbon atoms, at least 12 carbon atoms, for example, 13, 14, 15, 6, 17, 18 or more carbon atoms. The aliphatic group may contain up to 30 carbon atoms or up to 25 carbon atoms. A hydrocarbon chain is a chain of carbon atoms that are covalently attached to one another and are substituted with hydrogen atoms. The hydrocarbon chain can be linear or branched, saturated (for example, an alkyl chain) or unsaturated (for example, an alkenyl or alkynyl chain). In some embodiments, the hydrocarbon chain is linear. In some embodiments, the hydrocarbon chain is saturated (for example, an alkyl chain). The hydrocarbon chain may contain at least 10 carbon atoms, preferably at least 12 carbon atoms, for example, 13, 14, 15, 16, 17, 18 or more carbon atoms. The hydrocarbon chain may contain up to 30 carbon atoms or up to 25 carbon atoms. Preferably, the hydrocarbon chain contains from 12 and 30 carbon atoms, from 16 and 25 carbon atoms or from 18 and 22 carbon atoms.

The term alkyl as used herein refers to a straight or branched chain alkyl group. The term alkenyl as used herein refers to an alkyl chain containing at least one C=C double bond. The term alkynyl as used herein refers to an alkyl chain containing at least one C≡C triple bond.

The term carbocyclic group as used herein refers to a saturated or partially unsaturated mono-, bi- or tri-cyclic group having 3 to 14, preferably 3 to 8 and more preferably 3 to 6, ring carbon atoms or a mono-, bi- or tri-cyclic aromatic ring having 6 to 14, preferably 6 to 0, carbon atoms. A carbocyclic group is optionally a cycloalkyl, which as used herein refers to a fully saturated cyclic alkyl group, or an aryl. Optionally, a cycloalkyl group is a C₃-C₆ cycloalkyl group and optionally, an aryl is phenyl or napthyl. Bi- or tri-cyclic groups may contain fused aromatic, saturated and/or partially unsaturated rings. The term heterocyclic group as used herein refers to a saturated or partially unsaturated mono-, bi- or tri-cyclic group having 3 to 14, preferably 3 to 10, ring atoms or a mono-, bi- or tri-cyclic aromatic ring having 6 to 14, preferably 6 to 10, ring atoms and having, in addition to carbon ring atoms, one or more ring heteroatoms selected from oxygen, nitrogen, phosphorus and sulfur. A heterocycle is cycloheteroaliphatic, preferably a heterocycloalkyl, which as used herein refers to a saturated heterocyclic group, or a heteroaryl, which refers to a monocyclic or bicyclic aromatic ring system. A heterocycle preferably has 3 to 7 ring atoms or if aromatic, 5 to 10 ring atoms and may contain fused aromatic, saturated and/or partially unsaturated rings. Preferably a heterocycle is piperidine, morpholine, piperazine, pyrrolidine, pyridine or imidazole.

As used herein, a carboxylic acid is a group of structure -C(0)OH or salts or derivatives thereof. A sulfonic acid is a group of structure -S(0)₂OH or salts or derivatives thereof. A succinic anhydride group is a dihydro-2,5-furandione moiety or derivatives thereof.

Preferably, a succinic anhydride may bind to the hydrocarbon group at either the 3- or the 4-position of the furan ring.

A linker is a moiety capably of bonding to at least two other moieties. A linker may be selected from, without limitation, alkyl, alkenyl, alkynyl, carbocyclyl, heterocyclyl, carbonyl, sulfonyl, sulfoether, oxy, amino, amido, imino.

As used herein, a fatty acid is a carboxylic acid with a hydrocarbon chain. Optionally, a fatty acid has the structure R-C(0)OH or salts or derivatives thereof, wherein R is an organic tail as described herein, preferably R is a hydrocarbon chain. A fatty acid may, for example, be a C₁₄.₂2 fatty acid, preferably saturated, preferably stearic acid.

A hydrophobic powder as described herein may be used as a coating to coat a substrate tc form a coated material. The hydrophobic powder may coat the surface of the substrate tc form a hydrophobic layer. The hydrophobic powder may also be used in conjunction with a binder. The binder may be applied to the surface of the substrate in combination with the hydrophobic powder or it may be applied to the surface of the substrate before application of the hydrophobic powder. As used herein, a substrate is material to which other substance can be applied. Other substances (for example, a hydrophobic powder, a hydrophobic coating or a binding agent) can be applied to the surface of the substrate. Optionally, the substrate is a material requiring the application of a hydrophobic coating, such as concrete, paper, wood, cardboard, ceramics and metals (for example, steel).

As used herein, a binder is a substance that can be used as an adherent to attach a hydrophobic powder to a substrate. A binder may comprise one or more polymers or solvents. A binder may comprise a gluing agent or a varnish.

A hydrophobic powder as described herein may be used as an additive for the production of construction materials. An additive is a substance that is added to a construction material to increase its hydrophobicity. An additive may be added during formation of the construction material. The hydrophobic powder additive may be dispersed within the construction material. The construction material may be, for example, concrete, mortar or cement. The additive may be added to the construction material during the formation of the construction material. For example, the additive may be added as a powder to a precursor to be used for the production of concrete, mortar or cement.

As used herein, mean particle size refers to the mean value for particle diameter when a distribution of particle sizes is obtained by measuring the particle sizes in a sample.

Particle size can be measured by laser diffraction as in the examples.

A mill is a machine designed to break a granular material into smaller pieces by mechanical grinding forces, such as impact and friction, in a process called milling. Milling may be carried out without the addition of any fluids, known as dry milling. Optionally, a mill is a ball mill. A ball mill is a type of mill: a rotating cylinder partially filled with balls, usually ceramic (for example, alumina), stone or metal, that grinds material to the necessary fineness by friction and impact with the tumbling balls. In the present invention, milling is the process step used to promote reaction of the surface functionalisation agent with the core material. In a first aspect, the invention provides a hydrophobic powder comprising:

particles of a core material functionalised with a surface functionalisation agent, wherein the core material comprises paper sludge ash and the surface functionalisation agent comprises a functional group bound to the core material and an organic tail. The core material may have a mineral composition comprising gehlenite, calcite and lime, optionally wherein the mineral composition also comprises one or more of calcium silicate, mayenite and quartz. The core material may have a composition when expressed as oxides comprising 30 to 70% calcium oxide, 15 to 35% silicon dioxide, 5 to 20% and aluminium oxide. Preferably the composition of the core material, expressed as oxides, further comprises 0 to 5% magnesium oxide, 0 to 2% iron (III) oxide, 0 to 2% sulfur trioxide, 0 to 1% titanium dioxide, 0 to 2% potassium oxide, 0 to 1% phosphorus (V) oxide, 0 to 1 % sodium oxide and 0 to 1% strontium oxide. The core material may comprise 35 to 65% (preferably 55 to 65%) calcium oxide, 5 to 30% (preferably 15 to 25%) silicon dioxide and/or 5 to 15% aluminium oxide. In some embodiments, at least 0.05%

magnesium oxide is present. In some embodiments, the core material may comprise at least 2% (preferably at least 2.5%) magnesium oxide. In some embodiments, the core material may comprise at least 0.05% (preferably at least 0.5%) iron (III) oxide, at least 0.05% (preferably at least 0.1%) sulfur trioxide, at least 0.05% (preferably at least 0.1%) titanium dioxide, at least 0.05% (preferably at least 0.2%) potassium oxide and/or at least 0.05% phosphorus (V) oxide. In some embodiments, the core material may comprise at least 0.05% sodium oxide and/or at least 0.05% strontium oxide.

In a second aspect, the invention provides a hydrophobic powder comprising:

wherein the surface functionalisation agent comprises a functional group bound to the core material and an organic tail; and the core material has a mineral composition comprising gehlenite, calcite and lime, optionally wherein the core material also comprises one or more of calcium silicate, mayenite and quartz. Optionally the core material may have a composition, when expressed as oxides, comprising 30 to 70% calcium oxide, 15 to 35% silicon dioxide and 5 to 20% aluminium oxide. Preferably the composition of the core material, expressed as oxides, further comprises 0 to 5% magnesium oxide, 0 to 2% iron (III) oxide, 0 to 2% sulfur trioxide, 0 to 1% titanium dioxide, 0 to 2% potassium oxide, 0 to 1 % phosphorus (V) oxide, 0 to 1 % sodium oxide and 0 to 1% strontium oxide. The core material may comprise 35 to 65% (preferably 55 to 65%) calcium oxide, 15 to 30% (preferably 15 to 25%) silicon dioxide and/or 5 to 15% aluminium oxide. Iri some embodiments, at least 0.05% magnesium oxide is present. In some embodiments, the core material may comprise at least 2% (preferably at least 2.5%) magnesium oxide. In some embodiments, the core material may comprise at least 0.05% (preferably at least 0.5%) iron (III) oxide, at least 0.05% (preferably at least 0.1%) sulfur trioxide, at least 0.05% (preferably at least 0.1%) titanium dioxide, at least 0.05% (preferably at least 0.2%) potassium oxide and/or at least 0.05% phosphorus (V) oxide. In some embodiments, the core material may comprise at least 0.05% sodium oxide and/or at least 0.05% strontium oxide. In any of the embodiments of the invention described herein, the core material may consist essentially of the components described herein assumed as oxides.

In any embodiment of the first or second aspect of the invention, the surface

functionalisation agent of the hydrophobic powder as described herein may be present in an amount of at least 1 wt% based on the weight of the core material, preferably at least 2 wt% based on the weight of the core material. In some embodiments, the surface functionalisation agent of the hydrophobic powder as described herein may be present in an amount of up to 10 wt% based on the weight of the core material , preferably up to 8 wt% based on the weight of the core material, preferably up to 6 wt% based on the weight of the core material. In some embodiments, the surface functionalisation agent of the hydrophobic powder as described herein may be present in an amount of from 1 to 8 wt% based on the weight of the core material, preferably from 2 to 6 wt% based on the weight of the core material, preferably from 3 to 5 wt% based on the weight of the core material and preferably about 4 wt% based on the weight of the core material.

The organic tail of the surface functionalisation agent as described herein may comprise a hydrocarbon chain, optionally wherein the hydrocarbon chain contains at least 10 carbon atoms. In some embodiments, the hydrocarbon chain contains at least 14 carbon atoms, preferably wherein the hydrocarbon chain contains at least 18 carbon atoms. The hydrocarbon chain may contain from 10 to 30 carbon atoms, preferably from 14 to 25 carbon atoms, and more preferably from 16 to 25 carbon atoms.

The functional group of the surface functionalisation agent as described herein may comprise a carboxylic acid, a sulfonic acid or succinic anhydride.

The surface functionalisation agent as described herein may be a fatty acid, for example stearic acid. The particles of the core material functionalised with a .surface functionalisation agent of the hydrophobic powder as described herein may have a mean particle size of from 1 to 10 micrometres, optionally from 2 to 8 micrometres and optionally from 4 to 6

micrometres. In a third aspect, the invention provides a hydrophobic powder as described herein, for use in coating a substrate, optionally wherein the hydrophobic powder is used in conjunction with a binder. In a fourth aspect, the invention provides a hydrophobic powder as described herein, for use as an additive for the production of materials for construction (for example, concrete, mortar or cement).

In a fifth aspect, the invention provides a hydrophobic powder as described herein, wherein the hydrophobic powder is made by a method comprising:

In a sixth aspect, the invention provides a method of manufacturing a hydrophobic powder, wherein the method comprises:

In some embodiments of the fifth aspect of the invention, the surface functionalisation agent may be present in an amount of at least 1 wt% based on the weight of the core material, preferably at least 2 wt% based or the weight of the core material. In some embodiments, the surface functionalisation agent may be present in an amount of up to 10 wt% based on the weight of the core material, preferably up to 8 wt% based on the weight of the core material, preferably up to 5 wt% based on the weight of the core material. In some embodiments, the surface functionalisation agent may be present in an amount of from 1 to 8 wt% based on the weight of the core material, preferably from 2 to 6 wt% based on the weight of the core material, preferably from 3 to 5 wt% based on the weight of the core material and preferably about and preferably about 4 wt% based on the weight of the core material. The organic tail of the surface functionalisation agent may comprise a hydrocarbon chain, optionally wherein the hydrocarbon chain contains at least 10 carbon atoms, preferably wherein the hydrocarbon chain contains at east 14 carbon atoms and preferably wherein the hydrocarbon chain contains at least 18 carbon atoms. The functional group of the surface functionalisation agent may comprise a carboxylic acid, a sulfonic acid or succinic anhydride. The surface functionalisation agent may be a fatty acid, optionally the surface

functionalisation agent may be stearic acid.

The particles of the core material functionalised with a surface functionalisation agent of the hydrophobic powder as described herein may have a mean particle size of from 1 to 10 micrometres, optionally from 2 to 8 micrometres and optionally from 4 to 6

micrometres.

The paper sludge ash may be manufactured by combustion of paper sludge. Accordingly, the method may comprise the step of obtain ng paper sludge as a waste product of paper recyling and combusting paper sludge to produce paper sludge ash prior to combining with a surface functionalisation agent in a mill.

In a seventh aspect, the invention provides a coating material comprising a hydrophobic powder as described herein, optionally also comprising a binder.

In an eighth aspect, the invention provides an additive for use in the production of construction materials comprising a hydrophobic powder as described herein. In a ninth aspect, the invention provides a coated material comprising:

a substrate having a surface to be coated; and

a coating comprising a hydrophobic powder as described herein. In some embodiments, the coated material also comprises a binder. In a tenth aspect, the invention a method of preparing a coated material as described herein, wherein the method comprises:

coating the surface of a substrate with the hydrophobic powder as described herein so as to form a hydrophobic layer on the surface of the substrate. In some embodiments, the method also comprises applying a binder to the surface of the substrate either in combination with the hydrophobic powder or before application of the hydrophobic powder.

In an eleventh aspect, the invention provides a material comprising a hydrophobic powder as described herein as an additive. In some embodiments, the material may be a construction material such as concrete, cement or mortar. Embodiments described herein in relation to the first aspect of the invention apply mutatis mutandis to the second to eleventh aspects of the invention.

Examples

The PSA used throughout these examples v/as supplied by Aylesford Newsprint (ANP). Aylesford Newsprint is located on a 100-acre site in Kent, United Kingdom. The plant produces 400,000 tonnes of 100% recycled newsprint from 500,000 tonnes of waste paper fibre per year. The PSA is a grey ash with relatively fine grains. The chemical and mineralogical properties of the ANP PSA are shown in Table 1 and Figure 1.

Scanning electron microscopy (SEM) analysis of the ANP PSA was used to characterise the ash particles. They were found to be highly porous and heterogeneous, comprising of relatively loose agglomerations of smaller individual particles. This was as a result of the combustion process.

The hydrophobic powder is produced during a dry ball milling run using a percentage weight addition of stearic acid to the PSA. Dry ball milling of PSA was carried out in order to mechanically fracture the ash material between large ball media. It will act to reduce the particle size distribution of PSA while mixing and reacting the core material with the SFA being used.

The milling apparatus used was a 3L ceramic container (Pascall Engineering Co. Ltd.) loaded with 2.5kg of high density alumina 19mm milling media. The milling media were roughly spherical. The container was then loaded with 0.5kg of core material in order to achieve a milling media.core material ratio of 5:1 , plus a percentage weight addition of SFA. The mill container was rotated at a rate of 45 rpm for a set unit of time. Once the dry milling run was completed, the prepared powder was separated from the milling media using a coarse sieve.

Water contact angle (WCA) analysis was carried out as a method to quantify the hydrophobicity of powder samples. Water contact angle analysis was executed using a KRUSS Easy Drop tensiometer via sessile drop method. It was complimented with Drop Shape Analysis software to facilitate contact angle determination. The tensiometer is an instrument fitted with a light source and a camera to generate a digital image of a water droplet on a sample surface. It can visually capture the interfaces between solid surface, water droplet and air. A 5mm drop of distilled water was carefully placed on the surface of small pressed disks of powder sample in order to assess the contact angle formed. The software is used to determine the contact angle between the water droplet and the sample disk. This can be done through a variety of mathematical models. The Tangent-2 model was used in these examples. The sample disks were prepared by placing approximately 1g of sample powder into a 19.76mm diameter cylindrical die before pressing at a 4kN load using a mechanical press yielding sample disks that had been pressed to 13.05MPa.

Particle size analysis was carried out in order to investigate the effect that milling time had on the particle size distribution of the prepared PSA powder. This analysis was executed by laser diffraction using a Coulter LS100 particle size analyser in the range of 0.4 to 900μιτι. The analyser used tap water as the dispersant media. The hydrophobic powders samples were lightly mixed in a pestle and mortar with Teepol detergent to disperse them in the analyser. The Teepol acted as a surfactant which helped to wet the material. The mixing took place for 1 minute and all samples were wet at the end of this mixing period. Once the powders had been dispersed in the surfactant, they were suitable for introduction to the analyser. Samples remained fully dispersed throughout the procedure.

The particle size analyser ran each sample three times to establish a mean particle size distribution. This also helped ensure the material remained fully dispersed over time through visual assessment of particle size distributions over time and confirming no re- agglomeration of particles occurred.

X-ray diffraction (XRD) analysis was carried out using a Philips PW 830 diffractometer system with 40mA and 40kV, Cu radiation.

For x-ray fluorescence (XRF) analysis, the samples were completely dried prior to measurement. The analysis was done in accordance with Section 5 in the British

Standard EN 196-2, 2013.

FTIR analysis was executed using a Thermo Scientific Nicolet 6700 spectrometer with OMNIC Spectra software. The samples were prepared by incorporation into Potassium Bromide (KBr) disks. Sample powders were mixed at 1-2% with KBr salt and added to a 10mm die for pressing. A small mechanical press was used to press the sample at 10,000kg. The resultant disks were relatively translucent and suitable for analysis. Reference is now made to the following examples, which illustrate the invention in a non- limiting fashion.

Example 1: Effect of milling time on hydrophobic powders Powder samples were prepared at different milling times in order to note any effect that milling time has on hydrophobicity and other characteristics. The samples and milling times are recorded in Table 2. All other process parameters remained constant throughout.

Table 2:

Sample Core Material SFA wt. Addition Milling Time (hours)

1 PSA Stearic Acid 1 0·

2 PSA Stearic Acid 1 2

3 PSA Stearic Acid 1 4

4 PSA Stearic Acid 1 8

5 PSA Stearic Acid 1 16

*The 0 hour milled sample was simply hand stirred to mix the stearic acid addition into the

PSA material. Results of WCA analysis carried out on hydrophobic powder samples prepared with different milling times are presented in Table 3. Without milling, the produced sample disk simply absorbed the water droplet. The optimal milling time of 8 hours produced a sample powder with a WCA of 1 5°. Table 3:

Milling Time WCA Std. Dev.

0 n/a n/a

2 71.6 3.5

4 120.2 S.1

8 144.5 3.6

16 138.4 2.5 The particle size distributions for the various milling time samples are presented on log scale in Figure 3. Particle size decreases with an increase in milling time. The optimally hydrophobic sample (B: 8 hour milled) shows a much finer particle size distribution than that of the as-received PSA (A: PSA As-Received). There is also a marked change in the shape of the distributions with longer milling durations. A skewed peak of larger particle size (A: PSA As Received) is transformed to a more bimodal distribution (B,C,D) before final transformation to a single peak of smaller particle size (D: 16 hour milled). The cumulative distribution curves (F: Cumulative Distributions) show how the milling time reduces particle size.

The mean particle size and volume diameter values are reported in Table 4. The average particle size changes dramatically from the as-received PSA (Mean: 130pm, Median: Ι ΟΟ.δμιη) to the 8-hour milled sample (Mean: 5.5pm, Median: 3.6μηι). The biggest particle size reduction takes place over the first 2 hours of milling. One can also note that the 16- hour milling process produces a slightly larger particle size distribution than the 8-hour milling time from Table 4, but with a single peak from Figure 3.

Table 4:

Milling Time Mean Particle Size (μιτι) dio dgo

0 130 295.7 100.8 7.9

2 14.4 36.3 9 1.4

4 9 77 A S.8 1.7

8 5.5 13.4 3.6 0.9

16 6.4 15.4 4 1

XRD was also undertaken to assess the effect of milling on the mineralogical profile of PSA. It was determined that dry milling for 8 hours has no significant effect on the mineralogical composition of PSA. Example 2: Effect of surface functionalisation agent addition on hydrophobic powders

A number of samples were prepared in order to investigate any effect that different percentage weight additions of stearic acid as the SFA has on the hydrophobicity or other characteristics. The samples and stearic acid additions are reported in Table 5. All other process parameters remained constant throughout. Table 5:

Sample Core Material SFA wt.% Addition Milling Time (hours)

1 PSA Stearic Acid 1 8

2 PSA Stearic Acid 2 8

3 PSA Stearic Acid 4 8

4 PSA Stearic Acid 8 8 Results for the WCA analysis carried out on 8 hour milled hydrophobic powder samples prepared with different additions of stearic acid are presented in Figure 4 and Table 6. It is clear from Figure 4 that there is an increase in hydrophobicity with the addition of stearic acid up to 4 wt%. This optimal hydrophobic powder is considered superhydrophobic with a WCA greater than 150°.

Table 6 reports the mean WCA values used in the above figure, where it can be noted that a 4 wt% addition of stearic acid yields a superhydrophobic powder with a WCA of over 153°. We can also note from these results that the addition of SFA above 4 wt% does not increase hydrophobicity.

Table 6:

Stearic Acid wt.% WCA Std. Dev.

1 14U 3-

2 145.0 5.0

4 153.2 33

8 152.9 3.2

FTIR spectra for hydrophobic powder samples comprising PSA prepared with different additions of stearic acid including as-received PSA are presented in Figure 5. Spectrum A shows the standard absorption pattern for as-received PSA. The presence of absorption bands between 2960 and 2850cm^"1 is distinctive of symmetric and anti-symmetric C-H stretching vibrations of the hydrocarbon moiety. This indicates the presence of un-burnt hydrocarbons. These absorption bands become increasingly large with greater additions of stearic acid. This is due to the large hydrocarbon tail of stearic acid (SAM tail group).

The fingerprint region of the FTIR spectra (below 1500cm^"1) does not change considerably between the samples. The most important peaks, which are only present in some of these spectra, are at 1707cm^"1 and 1588cm^"1. Spectra C and especially spectra D contain the absorption band at 1588cm^"1. This band is indicative of anti-symmetrical carboxylate ion (- C0₂ ^") stretching. In fact, it is particularly distinctive of calcium carboxylic. This implies binding of stearic acid molecules to the substrate surface through reaction with calcium ions to form calcium stearate. The absorption band at 1707cm^"1 on spectra D indicates the presence of free saturated carboxylic acids ( 725-1700cm^"1). It can be concluded that for the 8wt% addition of stearic acid, surface calcium ions have become the limiting agent for full reaction to calcium stearate monolayers. Example 3: Effect of alternative surface functionalization agents on hydrophobic powders

The potential of SFAs other than stearic acid to produce hydrophobic powders was investigated. Samples were characterised tc assess any effect of SFA carbon chain length on hydrophobicity. A list of samples processed during the experiment is shown in Table 7.

Table 7:

I Core C-Chaln wt.% Milling Time

Material Length Addition (hours)

1 PSA Capric Add 10 4* 8

2 PSA Myristic Acid 14 4* 8

3 PSA Stearic Acid 18 4 8

4 PSA Behenic Acid 22 4* 8

* These alternative SFAs were not sourced at the same percentage purity as the stearic acid due to availability. Different mass additions for each SFA were used to comply with an equivalent mass addition of 4wt% stearic acid at 95% purity. Results for WCA analysis carried out on hydrophobic powder samples prepared with alternative SFAs are presented in Figures 6A and 6B.

Figure 6A presents the WCA data in box plot format for each of the carboxylic acids used. The box plot is composed of minimum, 1st quartile, median, 3rd quartile and maximum WCA values. Figure 6B is a line graph representing the same data, but in terms of carbon chain length and the effect it has on hydrophobicity. There is a positive relationship between carbon chain length and WCA from 10 to 18 carbons. However, the

hydrophobicity does not increase from 18 to 22 carbon chain length.

Table 8 reports the mean WCA values for each SFA and respective carbon chain length. The optimal SFA tested was the stearic acid, with behenic acid also producing superhydrophobic powders.

Table 8:

SFA WCA Std.Dev.

CapricAdd (IOC) 121.6 2.3

Myristlc Acid (14C) 142.0 5.0

Stearic Add (18C) 153.2 3.3

Behenic Acid (22C) 150.5 1.5

Example 4: Assessment of alternative core materials

The ability of alternative core materials to form hydrophobic powders under the standard preparation method was investigated. The list is not extensive but was based on availability and chemistry represented within paper sludge ash. For example, precipitated calcium carbonate was representative of the calcite in PSA. The table of samples processed during the experiment is shown in Table 9. All other process parameters remained constant between samples. Table 9:

Sample Core Material SFA wt.% Addition Milling Time (hours)

1 AN SA Stearic Add 4 8

2 Calcium Carbonate Stearic Acid 4 8

3 Hydrated Lime Stearic Acid 4 8

4 Silica Fume Stearic Acid 4 8

Results on the WCA analysis carried out or hydrophobic powder samples prepared with alternative core materials and milled for 8 hours with a 4wt.% stearic acid addition are presented in Figure 7. The box plot is composed of minimum, 1st quartile, median, 3rd quartile and maximum WCA values. There is significant variation in hydrophobicity of hydrophobic powder samples produced using different core materials under this general ball milling method. Silica fume (Si0₂) remained very hydrophilic and disk samples quickly absorbed the water. Table 10 reports the mean WCA values for the different core materials used. The calcium carbonate sample performed the best out of the alternative materials in terms of hydrophobicity. However, it still had a lower WCA than the PSA hydrophobic powder sample. These materials are not as effective as PSA. Table 10:

Core Material WCA Std. Dev.

PSA 153.2 3.3

Calcium Carbonate 139.6 1.3

Hydrated Lime 88.3 5.2

Silica Fume n/a n/a

Example 5: Characterisation of a characteristic hydrophobic powder As established from the results above, the hydrophobic powder was produced via the dry milling preparation method using ANP PSA as the core material, milled for 8 hours with an addition of 4 wt% stearic acid as the SFA. The WCA was found to be 53.22°, with a standard deviation of 3.3°. Particle size analysis results for this hydrophobic powder are reported in this section. Figure 8 presents the particel size distribution on a log scale and Table 1 1 reports the mean particle size and volume diameter values.

Table 1 1 :

Sample Mean Particle Size (μτη) dio dso doo

Optimum G.1 15.1 3.9 1

This characteristic hydrophobic powder has been milled for 8 hours and shows a similar distribution to the 1wt% stearic acid sample. However, the mean particle size and volume diameter values are slightly larger and the distribution shape seems more distinctly bimodal. This increased bimodality could be as a result of less agglomerate breakdown during milling or from a greater tendency to re-agglomerate due to the higher stearic acid addition. Example 6: Preparation of a hydrophobic coating

The hydrophobic powder was tested as a hydrophobic coating on mortar tiles. Mortar tiles were prepared as substrate for coating application and characterisation. The mortar mix was prepared with sandxement.water proportions of 3:1 :0.7 which formed a relatively dry paste. Tiles were created by placing mortar mixture into the 110mm x 55mm mould of a Nanetti MIGNON SS DGT hydraulic press. Pressing was carried out at a load of 40kN for 10 seconds (6.6MPa). Thickness of tiles varied but was not of substantial importance. The tiles were allowed to cure overnight before any coating was applied. The resultant tiles were hard but quite porous.

The preparation method for the hydrophobic powder coating involved the application of a layer of binder solution with to the tile surface using a brush. This layer was allowed to partially cure until the binder solution develooed a tacky consistency. The binders tested included Super Glue Gel solution and an outdoor varnish. The hydrophobic powder micro- particulate powder was placed in a pan before being patted by a dry firm paintbrush to collect the powder amongst the bristles. This brush was then repeatedly patted on the binder surface to deposit the hydrophobic powder and stick the particulates into the binder. The process was repeated rapidly until the entire tile surface was covered in a loose excess of hydrophobic powder.

After the tiles were allowed to cure overnight, the excess hydrophobic powder was removed with compressed air. This was done no powder could be observably removed when a finger was rubbed on the surface.

Examples 7 to 9 outlines the analyses that were conducted in order to characterise the prepared coatings. Analyses were performed on tiles with just the binder (glue or varnish) and tiles with the binder and the hydrophobic powder as well as running analyses on the untreated tile (control).

Example 7: Water contact angle (WCA) analysis of hydrophobic coating

WCA analysis was conducted in much the same way as was explained above. However, instead of using pressed disks, the sample tiles were simply placed on the tensiometer platform to assess the coating WCA. Both varnish and super glue sample sets were tested. Only the coating with the optimal WCA would be further characterised in the test methods outlined below. Table 12 presents the WCA analysis data obtained for the tile samples. It is clear that there are considerable differences between the samples. Although the control tiles with the binder solutions were non-porous and water resistant, they were still hydrophilic with substantially lower WCAs than when the hydrophobic powder was added overtop.

Table 12

Sample WCA Std. Dev.

Control n/a n/a

Varnish Control 75.8 3.4

Varnish * PSA 144./ 7i>

Control 2 n/a n/a

Glue Control 69.9 23.

Glue + PSA 116.9 5.5

Both hydrophobic powder-incorporating coatings are considered hydrophobic (>90° WCA) but the varnish and hydrophobic powder coating has a substantially higher WCA than the glue and hydrophobic powder coating (145° versus 117°). It is almost superhydrophobic. The varnish and hydrophobic powder coating was selected as optimal and was further characterised

Example 8: Visual assessment of stain resistance of hydrophobic coating

A simple experiment was designed to visually assess the coatings performance in terms of stain resistance and self-cleaning. The test was prepared with the optimal coated tile and control tiles placed at a 12° angle, using a prop on a lab bench. 4ml of a ground charcoal and tap water suspension was applied to each tile by means of a pipette to represent soiled/contaminated water. Photographs were taken before and after to visually compare any differences in resistance to staining/contamination amongst the tile samples. Figure 9 shows the before and after photographic images obtained from the visual assessment of stain resistance experiment for the varnish and hydrophobic powder coating. There is a distinct difference between the control, varnish control and the varnish and hydrophobic powder coating tile samples. The uncoated mortar tile control was both hydrophilic and porous. It absorbed the water and immediately became soiled with charcoal. The sample coated with the varnish binder solution was hydrophilic but non-porous. The charcoal suspension was not absorbed but wetted the surface and tended to drip. Given time, the water would have evaporated, leaving a soiled surface. The fully coated tile of varnish and hydrophobic powder was very hydrophobic. The charcoal -water mixture droplets did not wet the surface and rolled quickly off the tile surface. The coating remained stain-free.

Example 9: Measuring the sorptivity of the Hydrophobic Coating

Sorptivity measures the water absorption of a material due to capillary rise. Quantification of this property can be quite important for certain industrial applications, such as offshore structure integrity. Noting the ability of the developed coating to reduce sorptivity in cement would be crucial in determining commercial applications.

Sorptivity testing was carried out using cylindrical cement blocks in order to assess the relative performance of the binder and hydrophobic powder coating against the two controls. As the binder solutions used had water-resistance properties, it would be interesting to note if the addition of the hydrophobic powder micro-particulates reduces sample water absorption further.

The sorptivity test was carried out via the method outlined below:

• Cylindrical cement samples were produced by setting Cem-1 52.5N at 0.38

waterxement in plastic containers with internal diameter and height of 48mm.

• The samples were de-moulded after 24 hours and allowed to cure for another 24 hours before weighing.

• The cement samples were then dried in an oven at 100°C overnight and weighed the following day. This ensured they had dried to equilibrium, i.e. less than 0.2% weight difference after oven-dried.

• At equilibrium, samples were sealed in zip-lock bag and allowed to cool overnight.

• Coatings were applied where appropriate to one circular surface and allowed to cure for 24 hours in a zip-lock bag.

• The sides of the cement blocks were sealed with waterproof tape. This prevented water absorption to the sample block, except through the surface of interest. Three samples were prepared: a control, a binder control (just binder) and a block with binder and hydrophobic powder. • The blocks were supported on plastic props in water baths to ensure the surface of interest was as fully exposed to water as possible.

• Samples were weighed before being placed into the water bath. Once placed in the water bath, they were weighed each hour for six hours. Finally, a final weight was taken at 24 hours. Any excess water on blocks was removed before weighing using a damp cloth.

The cumulative volume of water per unit area (/) absorbed by each block was measured over time (t^{1 2}) in minutes. The sorptivity was given by the slope of the initial straight line from the graph produced, before water uptake began to level-off. This relationship is given by the following formula:

i = St^1/2 units: g/mm²/minV²

Figures 10A and 10B present the data obtained from the sorptivity test. Two separate graphs were produced as there is a great difference in sorptivity from the control cement block sample to the coated samples. This is not surprising as the varnish interlayer used for the varnish control and the varnish and hydrophobic powder coating has water resistant properties. It can be seen that the sorptivity of the control sample tapers off after six hours and this is the point to where the sorptivity results were taken (using

trendline/slope).

On comparing the water absorption curves represented in Figure 10B, there is a lower sorptivity with the addition of the hydrophob c powder to the varnish interlayer. Table 13 displays the sorptivity results derived from the slope of the water absorption curves in Figures 10A and 10B.

Table 13

Sample Sorptivlty (g/mm²/min^1/2) R²

Control 0.0004 05988

Varnish Control 0.00001 0.9979

Vamlsh+PSA 0.000007 0 698

The control and coated samples can be easily compared. A sorptivity of

0.000007g/mm²/min^{1 2} was obtained by the hydrophobic powder coating versus 0.00001 g/mm²/min^1/2 for the varnish control. Embodiments of the invention have been described by way of example only. It will be appreciated that variations of the described embodiments may be made which are still within the scope of the invention.

Claims

Claims:

1. A hydrophobic powder comprising:

particles of a core material functional sed with a surface functionalisation agent, wherein the core material comprises paper sludge ash and the surface

functionalisation agent comprises a functional group bound to the core material and an organic tail.

2. The hydrophobic powder of claim 1 , wherein the core material has a mineral

composition comprising gehlenite, calcite and lime, optionally wherein the mineral composition also comprises one or more of mayenite, calcium silicate and quartz.

3. The hydrophobic powder of claims 1 or 2, wherein the core material has a

composition when expressed as oxides comprising 30 to 70 wt% calcium oxide, 15 to 35 wt% silicon dioxide, 5 to 20 wt% aluminium oxide.

4. A hydrophobic powder comprising:

particles of a core material functionalised with a surface functionalisation agent; wherein the surface functionalisation agent comprises a functional group bound to the core material and an organic tail; and the core material has a mineral composition comprising gehlenite, calcite and lime, optionally wherein the core material also comprises one or more of calcium silicate, mayenite and quartz and optionally wherein the core material has a composition, when expressed as oxides, comprising 30 to 70 wt% calcium oxide, 15 to 35 wt% silicon dioxide, 5 to 20 wt% aluminium oxide.

5. The hydrophobic powder of any preceding claim, wherein the composition of the core material, expressed as oxides, further comprises any one, more than one or all of 0 to 5 wt% magnesium oxide, 0 to 2 wt% iron (III) oxide, 0 to 2 wt% sulfur trioxide, 0 to 1 wt% titanium dioxide, 0 to 2 wt% potassium oxide, 0 to 1 wt% phosphorus (V) oxide, 0 to 1wt% sodium oxide and 0 to 1 wt% strontium oxide.

6. The hydrophobic powder of any preceding claim, wherein the core material further comprises any one, more than one or all of features:

a. 35 to 65 wt% (preferably 55 to 65 wt%) calcium oxide;

b. 15 to 30 wt% (preferably 15 to 25 wt%) silicon dioxide;

c. 5 to 15 wt% aluminium oxide; d. at least 0.05 wt% magnesium oxide, preferably at least 2 wt% (preferably at least 2.5 wt%) magnesium oxide;

e. at least 0.05 wt% (preferably at least 0.5 wt%) iron (III) oxide;

f. at least 0.05 wt% (preferably at least 0.1 wt%) sulfur trioxide;

g. at least 0.05 wt% (preferably at least 0.1 wt%) titanium dioxide;

h. at least 0.05w t%(preferably at least 0.2 wt%) potassium oxide; and/or i. at least 0.05 wt% phosphorus (V) oxide.

7. The hydrophobic powder of any of claims 1 to 6, wherein the surface

functionalisation agent is present in an amount of at least 1 wt% based on the weight of the core material, preferably at least 2 wt% based on the weight of the core material.

8. The hydrophobic powder of any of claims 1 to 7, wherein the surface

functionalisation agent is present in an amount of up to 8 wt% based on the weight of the core material, preferably up to 6 wt% based on the weight of the core material.

9. The hydrophobic powder of any of claims 1 to 8, wherein the surface

functionalisation agent is present in an amount of from 1 to 8 wt% based on the weight of the core material, preferably from 2 to 6 wt% based on the weight of the core material and preferably about 4 wt% based on the weight of the core material.

10. The hydrophobic powder of any preceding claim, wherein the organic tail of the surface functionalisation agent comprises a hydrocarbon chain, optionally wherein the hydrocarbon chain contains at least 10 carbon atoms.

11. The hydrophobic powder of claim 10, wherein the hydrocarbon chain contains at least 14 carbon atoms, preferably wherein the hydrocarbon chain contains at least 8 carbon atoms.

12. The hydrophobic powder of claim 10, wherein the hydrocarbon chain contains from 10 to 30 carbon atoms, preferably from 14 to 25 carbon atoms, and more preferably from 16 to 25 carbon atoms.

13. The hydrophobic powder of any preceding claim, wherein the functional group of the surface functionalisation agent comprises a carboxylic acid, a sulfonic acid or succinic anhydride.

14. The hydrophobic powder of any preceding claim, wherein the surface

functionalisation agent is a fatty acid, optionally wherein the surface

functionalisation agent is stearic acid.

15. The hydrophobic powder of any preceding claim, wherein the particles of the core material functionalised with a surface functionalisation agent have a mean particle size of 1 to 10 micrometres.

16. The hydrophobic powder of any preceding claim, for use in coating a substrate, optionally wherein the hydrophobic powder is used in conjunction with a binder.

17. The hydrophobic powder of claims 1 to 15, for use as an additive for the

production of materials for construction (for example, concrete, mortar or cement).

18. The hydrophobic powder of any preceding claim, wherein the hydrophobic powder is made by a method comprising:

19. A method of manufacturing a hydrophobic powder as defined in any of claims 1 to 18, wherein the method comprises:

20. The method of claim 19, wherein the surface functionalisation agent is present in an amount of at least 1 wt% based on the weight of the core material, preferably at least 2 wt% based on the weight of the core material.

21. The method of any of claims 19 to 2C, wherein the surface functionalisation agent is present in an amount of up to 8 wt% based on the weight of the core material, preferably up to 6 wt% based on the weight of the core material.

22. The method of any of claims 19 to 21 , wherein the surface functionalisation agent is present in an amount of from 1 to 8 wt% based on the weight of the core material, preferably from 2 to 6 wt% based on the weight of the core material and preferably about 4 wt% based on the weight of the core material.

23. The method of any of claim 19 to 22, wherein the organic tail of the surface

functionalisation agent comprises a hydrocarbon chain, optionally wherein the hydrocarbon chain contains at least 10 carbon atoms, preferably wherein the hydrocarbon chain contains at least 14 carbon atoms and preferably wherein the hydrocarbon chain contains at least 18 carbon atoms.

24. The method of any of claims 19 to 23, wherein the functional group of the surface functionalisation agent comprises a carboxylic acid, a sulfonic acid or succinic anhydride.

25. The method of any of claims 19 to 24, wherein the surface functionalisation agent is a fatty acid, optionally wherein the surface functionalisation agent is stearic acid.

26. The method of any of claims 19 to 25 wherein the particle of the core material functionalised with a surface functionalisation agent have a mean particle size of 1 to 10 micrometres.

27. The method of any of claims 19 to 26, wherein the paper sludge ash is

manufactured by combustion of paper sludge.

28. The method of any of claims 19 to 27, wherein the method comprises the step of obtaining paper sludge as a waste product of paper recyling and combusting paper sludge to produce paper sludge ash prior to combining with a surface

functionalisation agent in a mill.

29. A coating material comprising the hydrophobic powder of any of claims 1 to 18, optionally also comprising a binder.

30. An additive for use in the production of construction materials comprising the hydrophobic powder of any of claims 1 to 18.

31. A coated material comprising:

a substrate having a surface to be coated; and

a coating comprising the hydrophobic powder of any of claims 1 to 18.

32. The coated material of claim 31 , also comprising a binder.

33. A method of preparing the coated material of claim 31 or 32, wherein the method comprises coating the surface of a substrate with the hydrophobic powder according to any of claims 1 to 18 so as to form a hydrophobic layer on the surface of the substrate.

34. The method of claim 33, also comprising applying a binder to the surface of the substrate either in combination with the hydrophobic powder or before application of the hydrophobic powder.

35. A material comprising the hydrophobic powder of any of claims 1 to 18 as an

additive.

36. The material of claim 35, wherein the material is a construction material such as concrete, cement or mortar.