WO2019220081A1

WO2019220081A1 - Surface modified layered double hydroxide

Info

Publication number: WO2019220081A1
Application number: PCT/GB2019/051295
Authority: WO
Inventors: Dermot O'hare; Chunping CHEN; Jean-Charles BUFFET
Original assignee: Scg Chemicals Co., Ltd.
Priority date: 2018-05-14
Filing date: 2019-05-10
Publication date: 2019-11-21

Abstract

39 ABSTRACT SURFACE MODIFIED LAYERED DOUBLE HYDROXIDE Processes for making surface-modified layered double hydroxides (LDHs) are disclosed, as well as surface-modified LDHs, and their uses in composite materials. The surface-modified LDHs of the invention are more hydrophobic than their unmodified analogues, which allows the surface- modified LDHs to be incorporated in a wide variety of materials, wherein the interesting functionality of LDHs may be exploited.

Description

SURFACE MODIFIED LAYERED DOUBLE HYDROXIDE

INTRODUCTION

[0001] The present invention relates to surface modified layered double hydroxides, as well as to processes for making the surface modified layered double hydroxides, and their uses in composite materials.

BACKGROUND OF THE INVENTION

[0002] Layered double hydroxides (LDHs) are a class of compounds which comprise two metal cations and have a layered structure. A review of LDHs is provided in Structure and Bonding; Vol 1 19, 2005 Layered Double Hydroxides ed. X Duan and D.G. Evans. The hydrotalcites, perhaps the most well-known examples of LDHs, have been studied for many years. LDHs can intercalate anions between the layers of the structure. WO 99/24139 discloses the use of LDHs to separate anions including aromatic and aliphatic anions.

[0003] Owing to the concentration of hydroxyl groups on their surface, conventionally-prepared LDHs are highly hydrophilic. As a consequence, conventionally-prepared LDHs often retain a considerable amount of water from the manufacturing process by which they were made.

[0004] The hydrophilicity of conventionally-prepared LDHs limits the extent to which they can be dispersed in organic solvents, thereby precluding their incorporation into a variety of materials wherein the interesting properties of LDH would be desirable. Attempts to address this by thermal treatment of the LDH to remove surface complexed water, results in the undesirable formation of highly aggregated,“stone-like”, non-porous bodies with low specific surface areas of typically 5 to 15 m²/g (as disclosed for example in Wang et al., Catai. Today, 201 1 , 164, 198).

[0005] A method of preparing LDHs with a specific surface area of at least 125 m²/g was reported (WO2015/144778), the method comprising slurrying a dispersion of a water-wet LDH in an aqueous-miscible organic (AMO) solvent, followed by recovery and drying of the so-called AMO- LDH. Nevertheless, such AMO-LDHs suffer from a high moisture uptake capacity compared with conventionally-prepared LDHs and as a result can be difficult to process and incorporate into composite materials.

[0006] The present invention was devised with the foregoing in mind. SUMMARY OF THE INVENTION

[0007] According to a first aspect of the present invention there is provided a process for forming a modified layered double hydroxide comprising the steps of:

a) providing a layered double hydroxide of formula (I):

[M^z+i_xM’^y+x(OH)₂]^a+(X'^1_)m · b ₂0 · c(L)

(I)

wherein

M is at least one charged metal cation;

M’ is at least one charged metal cation different from M;

z is 1 or 2;

y is 3 or 4;

0<x<0.9;

0<b£10;

0<c£10;

X is at least one anion;

n is the charge on anion(s) X;

a is equal to z(1-x)+xy-2;

m ³ a/rr, and

L is an organic solvent capable of hydrogen-bonding to water;

b) providing a modifier, wherein the modifier is an organosilane; and

c) mixing the layered double hydroxide of formula (I) provided in step a) with the modifier provided in step b);

wherein the mixing in step c) is conducted in the presence of less than or equal to 100% by weight of a solvent, relative to the total weight of the layered double hydroxide and the modifier.

[0008] According to a further aspect of the present invention there is provided a modified layered double hydroxide obtainable, obtained or directly obtained by a process defined herein.

[0009] According to a further aspect of the present invention there is provided a composite material comprising a modified layered double hydroxide as defined herein dispersed throughout a polymer. DETAILED DESCRIPTION OF THE INVENTION

Definitions

[0010] The term "(m-nC)" or "(m-nC) group" used alone or as a prefix, refers to any group having m to n carbon atoms.

[0011] The term“alkyl” as used herein includes reference to a straight or branched chain alkyl moieties, typically having 1 , 2, 3, 4, 5 or 6 carbon atoms. This term includes reference to groups such as methyl, ethyl, propyl (n-propyl or isopropyl), butyl (n-butyl, sec-butyl or tert-butyl), pentyl (including neopentyl), hexyl and the like. In particular, an alkyl may have 1 , 2, 3 or 4 carbon atoms.

[0012] The term“alkenyl” as used herein include reference to straight or branched chain alkenyl moieties, typically having 2, 3, 4, 5 or 6 carbon atoms. The term includes reference to alkenyl moieties containing 1 , 2 or 3 carbon-carbon double bonds (C=C). This term includes reference to groups such as ethenyl (vinyl), propenyl (allyl), butenyl, pentenyl and hexenyl, as well as both the cis and trans isomers thereof.

[0013] The term“alkynyl” as used herein include reference to straight or branched chain alkynyl moieties, typically having 2, 3, 4, 5 or 6 carbon atoms. The term includes reference to alkynyl moieties containing 1 , 2 or 3 carbon-carbon triple bonds (CºC). This term includes reference to groups such as ethynyl, propynyl, butynyl, pentynyl and hexynyl.

[0014] The term“alkoxy” as used herein include reference to -O-alkyl, wherein alkyl is straight or branched chain and comprises 1 , 2, 3, 4, 5 or 6 carbon atoms. In one class of embodiments, alkoxy has 1 , 2, 3 or 4 carbon atoms. This term includes reference to groups such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, tert-butoxy, pentoxy, hexoxy and the like.

[0015] The term“(m-cC)alkoxyl(m-nC)alkyl” means a (m-nC)alkoxyl group covalently attached to a (m-nC)alkylene group, both of which are defined herein.

[0016] The term "aryl" as used herein includes reference to an aromatic ring system comprising 6, 7, 8, 9 or 10 ring carbon atoms. Aryl is often phenyl but may be a polycyclic ring system, having two or more rings, at least one of which is aromatic. This term includes reference to groups such as phenyl, naphthyl and the like.

[0017] The term“aryl(m-nC)alkyl” means an aryl group covalently attached to a (m-nC)alkylene group, both of which are defined herein.

[0018] The term“carbocyclyl” as used herein includes reference to an alicyclic moiety having 3, 4, 5, 6, 7 or 8 carbon atoms. The group may be a bridged or polycyclic ring system. More often cycloalkyl groups are monocyclic. This term includes reference to groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, norbornyl, bicyclo[2.2.2]octyl and the like.

[0019] The term“carbocyclyl(m-nC)alkyl” means a carbocyclyl group covalently attached to a (m-nC)alkylene group, both of which are defined herein.

[0020] The term“heterocyclyl”,“heterocyclic” or“heterocycle” means a non-aromatic saturated or partially saturated monocyclic, fused, bridged, or spiro bicyclic heterocyclic ring system(s). Monocyclic heterocyclic rings contain from about 3 to 12 (suitably from 3 to 7) ring atoms, with from 1 to 5 (suitably 1 , 2 or 3) heteroatoms selected from nitrogen, oxygen or sulfur in the ring. Bicyclic heterocycles contain from 7 to 17 member atoms, suitably 7 to 12 member atoms, in the ring. Bicyclic heterocyclic(s) rings may be fused, spiro, or bridged ring systems. Examples of heterocyclic groups include cyclic ethers such as oxiranyl, oxetanyl, tetrahydrofuranyl, dioxanyl, and substituted cyclic ethers. Heterocycles containing nitrogen include, for example, azetidinyl, pyrrolidinyl, piperidinyl, piperazinyl, tetrahydrotriazinyl, tetrahydropyrazolyl, and the like. Typical sulfur containing heterocycles include tetrahydrothienyl, dihydro-1 , 3-dithiol, tetrahydro-2/-/- thiopyran, and hexahydrothiepine. Other heterocycles include dihydro-oxathiolyl, tetrahydro-oxazolyl, tetrahydro-oxadiazolyl, tetrahydrodioxazolyl, tetrahydro-oxathiazolyl, hexahydrotriazinyl, tetrahydro-oxazinyl, morpholinyl, thiomorpholinyl, tetrahydropyrimidinyl, dioxolinyl, octahydrobenzofuranyl, octahydrobenzimidazolyl, and octahydrobenzothiazolyl. For heterocycles containing sulfur, the oxidized sulfur heterocycles containing SO or SO2 groups are also included. Examples include the sulfoxide and sulfone forms of tetrahydrothienyl and thiomorpholinyl such as tetrahydrothiene 1 , 1 -dioxide and thiomorpholinyl 1 ,1 -dioxide. A suitable value for a heterocyclyl group which bears 1 or 2 oxo (=0) or thioxo (=S) substituents is, for example, 2-oxopyrrolidinyl, 2-thioxopyrrolidinyl, 2-oxoimidazolidinyl, 2-thioxoimidazolidinyl, 2-oxopiperidinyl, 2,5-dioxopyrrolidinyl, 2,5-dioxoimidazolidinyl or 2,6-dioxopiperidinyl. Particular heterocyclyl groups are saturated monocyclic 3 to 7 membered heterocyclyls containing 1 , 2 or 3 heteroatoms selected from nitrogen, oxygen or sulfur, for example azetidinyl, tetrahydrofuranyl, tetrahydropyranyl, pyrrolidinyl, morpholinyl, tetrahydrothienyl, tetrahydrothienyl 1 , 1 -dioxide, thiomorpholinyl, thiomorpholinyl 1 , 1 -dioxide, piperidinyl, homopiperidinyl, piperazinyl or homopiperazinyl. As the skilled person would appreciate, any heterocycle may be linked to another group via any suitable atom, such as via a carbon or nitrogen atom.

[0021] The term“heterocyclyl(m-nC)alkyl” means a heterocyclyl group covalently attached to a (m-nC)alkylene group, both of which are defined herein.

[0022] The term "heteroaryl" as used herein includes reference to an aromatic heterocyclic ring system having 5, 6, 7, 8, 9 or 10 ring atoms, at least one of which is selected from nitrogen, oxygen and sulphur. The group may be a polycyclic ring system, having two or more rings, at least one of which is aromatic, but is more often monocyclic. This term includes reference to groups such as pyrimidinyl, furanyl, benzo[b]thiophenyl, thiophenyl, pyrrolyl, imidazolyl, pyrrolidinyl, pyridinyl, benzo[b]furanyl, pyrazinyl, purinyl, indolyl, benzimidazolyl, quinolinyl, phenothiazinyl, triazinyl, phthalazinyl, 2H-chromenyl, oxazolyl, isoxazolyl, thiazolyl, isoindolyl, indazolyl, purinyl, isoquinolinyl, quinazolinyl, pteridinyl and the like.

[0023] The term“heteroaryl(m-nC)alkyl” means a heteroaryl group covalently attached to a (m- nC)alkylene group, both of which are defined herein.

[0024] The term "halogen" or“halo” as used herein includes reference to F, Cl, Br or I. In a particular, halogen may be F or Cl, of which Cl is more common.

[0025] The term“fluoroalkyl” is used herein to refer to an alkyl group in which one or more hydrogen atoms have been replaced by fluorine atoms. Examples of fluoroalkyl groups include -CHF₂, -CH₂CF₃, or perfluoroalkyl groups such as -CF₃ or -CF₂CF₃.

[0026] The term“substituted” as used herein in reference to a moiety means that one or more, especially up to 5, more especially 1 , 2 or 3, of the hydrogen atoms in said moiety are replaced independently of each other by the corresponding number of the described substituents. The term“optionally substituted” as used herein means substituted or unsubstituted.

[0027] It will, of course, be understood that substituents are only at positions where they are chemically possible, the person skilled in the art being able to decide (either experimentally or theoretically) without inappropriate effort whether a particular substitution is possible. For example, amino or hydroxy groups with free hydrogen may be unstable if bound to carbon atoms with unsaturated (e.g. olefinic) bonds. Additionally, it will of course be understood that the substituents described herein may themselves be substituted by any substituent, subject to the aforementioned restriction to appropriate substitutions as recognised by the skilled person.

[0028] As discussed hereinbefore, the present invention provides a process for forming a modified layered double hydroxide comprising the steps of:

a) providing a layered double hydroxide of formula (I):

[M^z+i_xM’^y+x(OH)₂]^a+(X'^1_)m · b ₂0 · c(L)

(I)

wherein

M is at least one charged metal cation;

M’ is at least one charged metal cation different from M;

z is 1 or 2;

y is 3 or 4;

0<x<0.9; 0<b£10;

0<c£10;

X is at least one anion;

n is the charge on anion(s) X;

a is equal to z(1-x)+xy-2;

m ³ a/rr, and

L is an organic solvent capable of hydrogen-bonding to water;

b) providing a modifier, wherein the modifier is an organosilane; and

[0029] Through extensive studies, the inventors have determined that the surface modification of conventionally-prepared LDHs is hindered by a number of factors. Principally, the presence of large amounts of water in the conventionally-prepared LDH significantly reduces the efficiency of the reaction between the surface modifying agent and the hydroxyl functional groups located on the surface of the LDH. In particular, rather than reacting with the available hydroxyl groups on the LDH, the surface modifying agent may react preferentially with the complexed water. Moreover, the presence of water is likely to give rise to an increased number of unwanted side- reactions, thus generating undesirable by-products which results in the generation of impure materials. Attempts to address this by thermal treatment of the conventionally-prepared LDH to remove complexed water results in the undesirable formation of highly aggregated,“stone-like”, non-porous bodies having low specific surface area of generally 5 to 15 m²/g, but even as low as 1 m²/g. The significantly reduced surface area translates to fewer available sites for surface modification, meaning that the ratio of LDH to surface modifying agent is undesirably low.

[0030] Previously, the inventors discovered a method of preparing LDHs with a specific surface area of at least 125 m²/g (WO2015/144778); the method comprising slurrying a dispersion of a water-wet LDH in an aqueous-miscible organic (AMO) solvent, followed by recovery and drying of the so-called AMO-LDH. Nevertheless, such AMO-LDHs suffer from a high moisture uptake capacity compared with conventionally-prepared LDHs and as a result can be difficult to process and incorporate into composite materials.

[0031] The inventors have now devised a means of successfully and flexibly modifying the surface properties of AMO-LDHs, thereby extending their interesting functionality to a wide array of applications. In particular, it has been discovered that the treatment of AMO-LDHs with organosilane modifiers by a mixing process carried out in the absence or near-absence of solvent, leads to a modified AMO-LDH having both good surface area and significantly reduced moisture uptake capacity. The process according to this invention also offers benefits in terms of scalability and environmental impact due to the avoidance of solvents.

[0032] The surface modified LDHs of the invention can be used in a variety of applications, wherein conventionally-prepared hydrophilic LDHs would be unsuitable.

[0033] In an embodiment, a layered double hydroxide of formula (I) is provided wherein when z is 2, M is Mg, Zn, Fe, Ca, Sn, Ni, Cu, Co, Mn or Cd or a mixture of two or more of these, or when z is 1 , M is Li. Suitably, z is 2 and M is Ca, Mg, Zn or Fe. More suitably, z is 2 and M is Ca, Mg or Zn.

[0034] In an embodiment, a layered double hydroxide of formula (I) is provided wherein when y is 3, M’ is Al, Ga, Y, In, Fe, Co, Ni, Mn, Cr, Ti, V, La or a mixture thereof, or when y is 4, M' is Sn, Ti or Zr or a mixture thereof. Suitably, y is 3. More suitably, y is 3 and M’ is Al. Suitably, M’ is Al.

[0035] In an embodiment, a layered double hydroxide of formula (I) is provided wherein x has a value according to the expression 0.18<x<0.9. Suitably, x has a value according to the expression 0.18<x<0.5. More suitably, x has a value according to the expression 0.18<x<0.4.

[0036] In an embodiment, a layered double hydroxide of formula (I) is provided which is a Zn/AI, Mg/AI, Zn,Mg/AI, Mg/AI,Sn, Mg/AI,Ti, Ni/Ti, Mg/Fe, Ca/AI, Ni/AI or Cu/AI layered double hydroxide.

[0037] The anion(s) X in the LDH may be any appropriate organic or inorganic anion, for example halide (e.g., chloride), inorganic oxyanions (e.g. X’_mO_n(OH)_p ^i?_; m = 1-5; n = 2-10; p = 0-4, q = 1-5; X = B, C, N, S, P: e.g. carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate, nitrate, phosphate, sulphate), anionic surfactants (such as sodium dodecyl sulfate, fatty acid salts or sodium stearate), anionic chromophores, and/or anionic UV absorbers, for example 4- hydroxy- 3- 10 methoxybenzoic acid, 2-hydroxy-4 methoxybenzophenone-5-sulfonic acid (HMBA), 4-hydroxy-3-methoxy-cinnamic acid, p-aminobenzoic acid and/or urocanic acid. In an embodiment, the anion X is an inorganic oxyanion selected from carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate, nitrate, sulphate or phosphate or a mixture of two or more thereof. More suitably, the anion X is an inorganic oxyanion selected from carbonate, bicarbonate, nitrate or nitrite. Most suitably, the anion X is carbonate.

[0038] In a particularly suitable embodiment a layered double hydroxide of formula (I) is provided wherein, M is Ca, Mg, Zn or Fe, M’ is Al, and X is carbonate, bicarbonate, nitrate or nitrite. Suitably, M is Ca, Mg or Zn, M’ is Al, and X is carbonate, bicarbonate, nitrate or nitrite. More suitably, M is Ca, Mg or Zn, M’ is Al, and X is carbonate. [0039] In an embodiment, a layered double hydroxide of formula (I) is provided wherein M is Mg, M’ is Al and X is carbonate.

[0040] In an embodiment, a layered double hydroxide of formula (I) is provided with the formula Mg_qAI-CC>3, wherein 1.8 £ q £ 5, and preferably wherein 1.8 £ q £ 3.5.

[0041] In an embodiment, a layered double hydroxide of formula (I) is provided wherein the layered double hydroxide of formula (I) is a Mg3AI-CC>3 layered double hydroxide.

[0042] In an embodiment, a layered double hydroxide of formula (I) is provided which is a Mg₄AI- CO₃ layered double hydroxide.

[0043] In an embodiment, a layered double hydroxide of formula (I) is provided which is a MgsAI- CO₃ layered double hydroxide.

[0044] In an embodiment, a layered double hydroxide of formula (I) is provided which is a Mg2ZnAI-CC>3 layered double hydroxide.

[0045] The organic solvent, L, present in formula (I) may have any suitable hydrogen bond donor and/or acceptor groups, so that it is capable of hydrogen-bonding to water. Hydrogen bond donor groups include R-OH, R-NH₂, R₂NH, whereas hydrogen bond acceptor groups include ROR, R₂C=0 RNO₂, R₂NO, R₃N, ROH, RCF₃. The term ‘AMO’ refers to aqueous-miscible organic solvents, such as ethanol, methanol and acetone. In the context of this application‘AMO’ is used to refer to solvents which are capable of hydrogen-bonding to water and as such, other organic solvents with limited aqueous miscibility (such as ethyl acetate) are also envisaged within the scope of an‘AMO’, for example when used in the term‘AMO-LDH’.

[0046] In an embodiment, L is selected from acetone, acetonitrile, dimethylformamide, dimethyl sulphoxide, dioxane, ethanol, methanol, n-propanol, isopropanol, tetrahydrofuran, ethyl acetate, n-butanol, sec-butanol, n-pentanol, n-hexanol, cyclohexanol, diethyl ether, diisopropyl ether, di n-butyl ether, methyl tert-butyl ether (MTBE), tert-amyl methyl ether, cyclopentyl methyl ether, cyclohexanone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl isoamyl ketone, methyl n-amyl ketone, furfural, methyl formate, methyl acetate, isopropyl acetate, n- propyl acetate, isobutyl acetate, n-butyl acetate, n-amyl acetate, n-hexyl acetate, methyl amyl acetate, methoxypropyl acetate, 2-ethoxyethyl acetate, nitromethane, and a mixture of two or more thereof.

[0047] Suitably, L is selected from acetone, ethanol, ethyl acetate, and a mixture of two or more thereof. In one embodiment L is ethanol.

[0048] In an embodiment, a layered double hydroxide of formula (I) is provided wherein M is Mg, M’ is Al, X is carbonate and the L is ethanol or acetone. [0049] In an embodiment, b has a value according to the expression 0<b£7.5. Suitably, b has a value according to the expression 0<b£5. More suitably, b has a value according to the expression 0<b£3. Even more suitably, b has a value according to the expression 0<b£1 (e.g. 0.2<b£0.95).

[0050] In an embodiment, c has a value according to the expression 0<c<7.5. Suitably, c has a value according to the expression 0<c<5. More suitably, c has a value according to the expression 0<c£1. Most suitably, c has a value according to the expression 0<c£0.5.

[0051] In an embodiment, the layered double hydroxide of formula (I) provided in step a) (also referred to as an AMO-LDH) has a BET (as determined by N₂ adsorption) specific surface area of at least 40 m²/g. Suitably, the AMO-LDH has a BET specific surface area of at least 70 m²/g. More suitably, the AMO-LDH has a BET specific surface area of greater than 125 m²/g. Even more suitably, the AMO-LDH has a BET specific surface area of at least 180 m²/g. Yet more suitably, the AMO-LDH has a specific BET surface area of at least 240 m²/g. Yet more suitably, the AMO-LDH has a BET specific surface area of at least 275 m²/g. Most suitably, the AMO-LDH has a BET specific surface area of at least 300 m²/g.

[0052] In an embodiment, the layered double hydroxide of formula (I) provided in step a) (also referred to as an AMO-LDH) has a BET (N₂) pore volume of at least 0.3 cm³/g. Suitably, the AMO-LDH has a BET pore volume of at least 0.4 cm³/g. More suitably, the AMO-LDH has a BET pore volume of at least 0.5 cm³/g. Yet more suitably, the AMO-LDH has a BET pore volume of at least 0.75 cm³/g. Most suitably, the AMO-LDH has a BET pore volume of at least 0.9 cm³/g.

[0053] In an embodiment, the layered double hydroxide of formula (I) provided in step a) (also referred to as an AMO-LDH) has a loose bulk density of less than 0.5 g/mL. Suitably, the AMO- LDH has a loose bulk density of less than 0.35 g/mL. More suitably, the AMO-LDH has a loose bulk density of less than 0.25 g/mL. In an embodiment, the AMO-LDH has a tap density of less than 0.5 g/mL. Tap densities are calculated by standard testing method (ASTM D7481-09) using a graduated cylinder. The powder was filled into a cylinder and a precise weight of sample (m) was measured. The volume was measured before (Vo) and after 1000 taps (V_t). The loose bulk and tap densities were calculated by: Loose bulk density = m/VO; Tap density = m/V_t . Suitably, the AMO-LDH has a tap density of less than 0.4 g/mL. More suitably, the AMO-LDH has a tap density of less than 0.35 g/mL. Yet more suitably, the AMO-LDH has a tap density of less than 0.27 g/mL.

[0054] In an embodiment, the layered double hydroxide of formula (I) provided in step a) is prepared by a process comprising the steps of

I. providing a water-washed, wet precipitate of formula (II) shown below, said

precipitate having been formed by contacting aqueous solutions containing cations of the metals M and M’, the anion(s) Xⁿ, and optionally an ammonia-releasing agent, and then ageing the reaction mixture:

[M ^z+ ₁ -_XM ^y+ _x(0 H ) ₂]^a+ (X⁰ ) _m £> H ₂0

(II) wherein M, M', z, y, x, m, b, n and X are as defined for formula (I);

II. contacting the water-washed, wet precipitate of step I) with a solvent L, as defined for formula (I).

[0055] The term“water-washed wet precipitate of formula (II)” used in step (I) will be understood to define a material having a composition defined by formula (II) which has been precipitated out of a solution of reactants and has subsequently been washed with water and then dried and/or filtered to the point that it is still damp. Crucially, the water-washed wet precipitate is not allowed to dry prior to it being contacted with the solvent according to step (II), since to do so results in the formation of highly agglomerated, stone-like particles of LDH, whose low surface area renders them inferior for surface modification using the types of modifiers described herein. The wet precipitate may have a moisture content of 15 to 60 % relative to the total weight of the wet precipitate.

[0056] It will be understood that the water-washed wet precipitate of step (I) may be pre-formed. Alternatively, the water-washed wet precipitate of step I) may be prepared as part of step (I), in which case step (I) comprises the following steps:

(i) precipitating a layered double hydroxide having the formula (II) from an aqueous solution containing cations of the metals M and M’, the anion(s) X^n_, and optionally an ammonia releasing agent;

(ii) ageing the layered double hydroxide precipitate obtained in step (i) in the reaction mixture of step (i);

(iii) collecting the aged precipitate resulting from step (ii), then washing it with water and optionally a‘solvent’ as defined hereinbefore for formula (I); and

(iv) drying and/or filtering the washed precipitate to the point that it is still damp.

[0057] The ammonia-releasing agent used in step (i) may increase the aspect ratio of the resulting LDH platelets. Suitable ammonia-releasing agents include hexamethylene tetraamine (HMT) and urea. Suitably, the ammonia-releasing agent is urea. The amount of ammonia releasing agent used in step i) may be such that the molar ratio of ammonia-releasing agent to metal cations (M + M’) is 0.5:1 to 10:1 (e.g. 1 :1 to 6:1 or 4:1 to 6:1). [0058] In an embodiment, in step (i), the precipitate is formed by contacting aqueous solutions containing cations of the metals M and M’, the anion X¹¹ , and optionally an ammonia-releasing agent, in the presence of a base being a source of OH (e.g. NaOH, NH₄OH, or a precursor for OH formation). Suitably the base is NaOH. In an embodiment, the quantity of base used is sufficient to control the pH of the solution above 6.5. Suitably, the quantity of base used is sufficient to control the pH of the solution at 6.5-13. More suitably, the quantity of base used is sufficient to control the pH of the solution at 7.5-13. Yet more suitably, the quantity of base used is sufficient to control the pH of the solution at 9-11.

[0059] In an embodiment, in step (ii), the layered double hydroxide precipitate obtained in step i) is aged in the reaction mixture of step (i) for a period of 5 minutes to 72 hours at a temperature of 15-180°C (e.g. 18-40°C).

[0060] Suitably, in step (ii), the layered double hydroxide precipitate obtained in step (i) is aged in the reaction mixture of step (i) for a period of 1 to 72 hours. More suitably, in step (ii), the layered double hydroxide precipitate obtained in step (i) is aged in the reaction mixture of step (i) for a period of 5 to 48 hours. Most suitably, in step (ii), the layered double hydroxide precipitate obtained in step (i) is aged in the reaction mixture of step (i) for a period of 12 to 36 hours.

[0061] Suitably, in step (ii), the layered double hydroxide precipitate obtained in step (i) is aged in the reaction mixture of step (i) at a temperature of 80-150°C. More suitably, in step (ii), the layered double hydroxide precipitate obtained in step (i) is aged in the reaction mixture of step (i) at a temperature of 90-140°C.

[0062] Step (ii) may be performed in an autoclave.

[0063] In an embodiment, in step (iii), the aged precipitate resulting from step (ii) is collected, then washed with water and optionally a solvent as defined hereinbefore for formula (I) until the filtrate has a pH in the range of 6.5-7.5. Suitably, step (iii) comprises washing the aged precipitate resulting from step (ii) with a mixture of water and solvent at a temperature of 15-100°C (e.g. 18-40°C). More suitably, the solvent is selected from ethyl acetate, ethanol and acetone. More suitably, the quantity of solvent in the washing mixture is 5-95% (v/v), preferably 30-70% (v/v).

[0064] In an embodiment, in step II) the water-washed wet precipitate is contacted with a solvent L by dispersing said precipitate in the solvent L to produce a slurry. In a further embodiment, the preparation process comprises a further step III) of maintaining the slurry resulting from step II). In an embodiment, the slurry produced in step II) and then maintained in step III) contains 1-100 g of water-washed wet precipitate per 1 L of solvent L. Suitably, the slurry produced in step II) and maintained in step III) contains 1 -75 g of wate r- washed wet precipitate per 1 L of solvent L. More suitably, the slurry produced in step II) and maintained in step III) contains 1 -50 g of water- washed wet precipitate per 1 L of solvent L. Most suitably, the slurry produced in step II) and maintained in step III) contains 1 -30 g of water- washed wet precipitate per 1 L of solvent L.

[0065] In step III), the slurry produced in step II) is maintained for a period of time. Suitably, the slurry is stirred during step III).

[0066] In an embodiment, in step III), the slurry is maintained for a period of 0.5 to 120 hours (e.g. 0.5 to 96 hours). Suitably, in step III), the slurry is maintained for a period of 0.5 to 72 hours. More suitably, in step III), the slurry is maintained for a period of 0.5 to 48 hours. Even more suitably, in step III), the slurry is maintained for a period of 0.5 to 24 hours. Yet more suitably, in step III), the slurry is maintained for a period of 0.5 to 24 hours. Most suitably, in step III), the slurry is maintained for a period of 1 to 8 hours. Alternatively, in step III), the slurry is maintained for a period of 16 to 20 hours).

[0067] The LDH resulting from step III) may be isolated by any suitable means, including filtering, filter pressing, spray drying, cycloning and centrifuging. The isolated AMO-LDH may then be dried to give a free-flowing powder. The drying may be performed under ambient conditions, in a vacuum, or by heating to a temperature below 60°C (e.g. 20 to 60°C). Suitably, the AMO-LDH resulting from step III) is isolated and then heated to a temperature of 10-40°C in a vacuum until a constant mass is reached. In an embodiment, the LDH may be dried by heating at 50°C -200°C, such as 100°C -200°C, for example 150°C -200°C.

[0068] In an embodiment, the layered double hydroxide provided in step a) (AMO-LDH) comprises less than 50% by weight of solvent L, relative to the weight of the layered double hydroxide. In an embodiment, the layered double hydroxide provided in step a) (AMO-LDH) comprises less than 25% by weight of solvent L, relative to the weight of the layered double hydroxide. In an embodiment, the layered double hydroxide provided in step a) (AMO-LDH) comprises less than 10% by weight of solvent L, relative to the weight of the layered double hydroxide. In an embodiment, the layered double hydroxide provided in step a) (AMO-LDH) is provided as a dry solid.

[0069] In an embodiment, the organosilane modifier used in step b) of the process may have a structure according to formula (II) shown below: ijj

wherein q is 1 , 2 or 3;

each Ri is independently hydrogen or an organofunctional group; each Y is independently absent, or is a straight or branched organic linker; and each R₂ is independently hydrogen, halo, hydroxy, carboxy, (1-4C)alkyl or a group -OR₃, wherein R₃ is selected from (1-6C)alkyl, aryl(1-6C)alkyl,

heteroaryl(1-6C)alkyl, cycloalkyl(1-6C)alkyl, heterocyclyl(1-6C)alkyl and (1- 6C) al koxy( 1 -4C) al kyl .

[0070] Suitably, at least one R₂ is not hydrogen or (1-4C)alkyl.

[0071] In an embodiment, q is 1.

[0072] Suitably, the organofunctional group is selected from acrylate, methacrylate, mercapto, aldehyde, amino, azido, carboxylate, phosphonate, sulfonate, epoxy, glycidyloxy, ester, halogen, hydroxyl, isocyanate, phosphine, phosphonate, alkenyl (e.g. vinyl), aryl (e.g. phenyl), cycloalkyl, heteroaryl and heterocyclyl (e.g. morpholinyl).

[0073] More suitably, the organofunctional group is selected from halo, epoxy, glycidyloxy, mercapto, alkenyl and aryl. Yet more suitably, the organofunctional group is selected from epoxy, glycidyloxy, mercapto, alkenyl and aryl.

[0074] Suitably, Y is a hydrocarbylene linker group containing 1 or more carbon atoms, wherein the linker optionally contains one or more atoms selected from O, N, S and Si within the linker, and wherein the linker is optionally substituted with one or more groups selected from hydroxyl, halo, haloalkyl, (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl, aryl(1-4C)alkyl, heteroaryl, heteroaryl (1-4C) alkyl, cycloalkyl, heterocyclyl, -Si(R₂)3 and NR_xR_y, wherein R₂ is as defined hereinbefore, and R_x and R_y are each independently hydrogen or (1-4C)alkyl.

[0075] More suitably, Y is a hydrocarbylene linker group containing 1-10 carbon atoms, wherein the linker optionally contains one or more atoms selected from O, N and S within the linker, and wherein the linker is optionally substituted with one or more groups selected from hydroxyl, halo, haloalkyl, (1-6C)alkyl, (2-6C)alkenyl, (1-6C)alkoxy, aryl, aryl(1-4C)alkyl, heteroaryl, heteroaryl(1- 4C)alkyl and NR_xR_y, wherein R_x and R_y are each independently hydrogen or (1-4C)alkyl. Alternatively, Y is absent.

[0076] In an embodiment, the organosilane modifier is selected from the group consisting of 3- aminopropyltriethoxysilane, (3-glycidyloxypropyl)triethoxysilane, (3-glycidyloxypropyl)- trimethoxysilane (3-mercaptopropyl)-triethoxysilane, triethoxyvinylsilane, triethoxyphenylsilane, trimethoxy(octadecyl)silane, vinyl-tris(2-methoxy-ethoxy)silane, g-methacryloxy- propyltrimethoxysilane, g-aminopropyl-trimethoxysilane, b(3,4-epxycryclohexyl)- ethyltrimethoxysilane, g-mercaptopropyltrimethoxysilane, (3-aminopropyl)triethoxysilane, N-(3- triethoxysilylpropyl)ethylenediamine, 3-aminopropyl-methyl-diethoxysilane, vinyltrimethoxy- silane, chlorotrimethylsilane, tert-butyldimethylsilyl chloride, trichlorovinylsilane, methyltrichlorosilane, 3-chloropropyl trimethoxysilane, chloromethyltrimethylsilane, diethoxy- dimethylsilane, propyltrimethoxysilane, triethoxyoctylsilane, trichloro(octadecyl)silane and y- piperazinylpropylmethyldimethoxysilane

[0077] Suitably, the organosilane modifier is selected from the group consisting of 3- aminopropyltriethoxysilane, (3-glycidyloxypropyl)triethoxysilane, (3-glycidyloxypropyl)- trimethoxysilane, (3-mercaptopropyl)triethoxy-silane, triethoxyvinylsilane, trimethoxy- methylsilane, triethoxyoctylsilane, trichloro(octadecyl)-silane and triethoxyphenylsilane.

[0078] In an embodiment, the organosilane modifier provided in step b) is provided as a neat organosilane. The neat organosilane may be a liquid or a low melting point solid. Optionally, when the organosilane is a low melting point solid, step b) includes the steps of melting the organosilane to provide a liquid organosilane modifier.

[0079] Step c) comprises mixing the layered double hydroxide of formula (I) provided in step a) with the modifier provided in step b), wherein the mixing in step c) is conducted in the presence of less than or equal to 100% by weight of a solvent, relative to the total weight of the layered double hydroxide and the modifier. For the avoidance of doubt, and purely as an example, if 1 g of AMO-LDH is mixed with 0.5 g of modifier, then 100% by weight of a solvent would be 1.5 g of solvent. Step c) may be conducted in air or under an inert atmosphere (e.g. under a N₂ blanket). In an embodiment, step c) is conducted under an inert atmosphere.

[0080] In an embodiment, the mixing in step c) is conducted in the presence of less than 100% by weight of a solvent relative to the total weight of the layered double hydroxide and the modifier.

[0081] In an embodiment, the mixing in step c) is conducted in the presence of less than or equal to 50% by weight of a solvent relative to the total weight of the layered double hydroxide and the modifier.

[0082] In an embodiment, the mixing in step c) is conducted in the presence of less than 10% by weight of a solvent relative to the total weight of the layered double hydroxide and the modifier.

[0083] The solvent which may be present in step c), may be the same solvent as the solvent Y present in the AMO-LDH provided in step a), or it may be a different solvent.

[0084] In an embodiment, the mixing in step c) is conducted with substantially no solvent, or no solvent present.

[0085] In an embodiment, the mixing in step c) is conducted using more than 5% by weight modifier, relative to the weight of layered double hydroxide. [0086] In an embodiment, the mixing in step c) is conducted using more than 10% by weight modifier, relative to the weight of layered double hydroxide.

[0087] In an embodiment, the mixing in step c) is conducted using more than 20% by weight modifier, relative to the weight of layered double hydroxide.

[0088] The mixing in step c) can be carried out by a variety of means. The mixing may be achieved by manual (e.g. grinding in a pestle and mortar) or automated means (such as a vortex mixer or fluidised bed mixer). In an embodiment, the mixing in step c) is carried out by means of vapour treatment, a dry mixer, a vortex mixer, or by milling the layered double hydroxide in the presence of the modifier. In an embodiment, the mixing in step c) is carried out by means of a vortex mixer. The mixing in step c) may be carried out in an open vessel (such as a pestle and mortar, or an open batch mixer), or in a closed vessel (such as a sealed tube in a vortex mixer). In an embodiment, the mixing in step c) is carried out in an open vessel. In an embodiment, the mixing in step c) is carried out in a closed vessel.

[0089] The modified AMO-LDH product resulting from step c) may be subjected to a further drying step. In an embodiment, the process for forming a modified layered double hydroxide comprises a further step of:

d) thermally treating the modified layered double hydroxide resulting from step c) at a temperature of 15-200 °C.

[0090] In an embodiment, in step d) the thermal treatment is carried out at 100-200 °C.

[0091] In an embodiment, in step d) the thermal treatment is carried out under vacuum at a temperature of 15-200 °C.

[0092] In an embodiment, in step d) the thermal treatment is carried out under vacuum at a temperature of 15-60 °C.

[0093] In an embodiment, in step d) the thermal treatment is carried out for 2-24 hours.

[0094] In an embodiment, in step d) the thermal treatment is carried out for 10-16 hours.

Modified LDHs of the invention

[0095] In another aspect, the present invention provides a modified layered double hydroxide obtainable, obtained or directly obtained by a process defined herein.

[0096] In an embodiment, a modified layered double hydroxide obtained by a process according to the present invention has a BET surface area (as determined by N₂ adsorption) of at least 40 m²/g. Suitably, the modified layered double hydroxide has a BET surface area of at least 60 m²/g. More suitably, the modified layered double hydroxide has a BET surface area of at least 80 m²/g. Even more suitably, the modified layered double hydroxide has a BET surface area of at least 100 m²/g.

[0097] In an embodiment, a modified layered double hydroxide obtained by a process according to the present invention has a BET (N₂) pore volume of at least 0.3 cm³/g. Suitably, the modified layered double hydroxide has a BET pore volume of at least 0.4 cm³/g. More suitably, the modified layered double hydroxide has a BET pore volume of at least 0.5 cm³/g. Yet more suitably, the modified layered double hydroxide has a BET pore volume of at least 0.75 cm³/g. Most suitably, the modified layered double hydroxide has a BET pore volume of at least 0.9 cm³/g.

[0098] In an embodiment, a modified layered double hydroxide obtained by a process according to the present invention has a loose bulk density of less than 0.5 g/ml_. Suitably, the modified layered double hydroxide has a loose bulk density of less than 0.35 g/ml_. More suitably, the modified layered double hydroxide has a loose bulk density of less than 0.25 g/ml_. In an embodiment, the modified layered double hydroxide has a tap density of less than 0.5 g/ml_. Tap densities are calculated by standard testing method (ASTM D7481-09) using a graduated cylinder. The powder was filled into a cylinder and a precise weight of sample (m) was measured. The volume was measured before (Vo) and after 1000 taps (V_t). The loose bulk and tap densities were calculated by: Loose bulk density = m/VO; Tap density = m/V_t . Suitably, the modified layered double hydroxide has a tap density of less than 0.4 g/mL. More suitably, the modified layered double hydroxide has a tap density of less than 0.35 g/mL.

[0099] In an embodiment, a modified layered double hydroxide obtained by a process according to the present invention has a moisture uptake level of less than 20 wt% of dry LDH, when measured at RH99 at 20 °C for 90 hours. Suitably, the modified layered double hydroxide has a moisture uptake level of less than 15 wt% of dry LDH, when measured at RH99 at 20 °C for 90 hours. More suitably, the modified layered double hydroxide has a moisture uptake level of less than 10 wt% of dry LDH, when measured at RH99 at 20 °C for 90 hours.

[00100] In an embodiment, a modified layered double hydroxide obtained by a process according to the present invention has a contact angle greater than or equal to 60°. Reference made herein to contact angles will be understood by one of ordinary skill in the art to refer to the contact angle of water. Suitably, the modified layered double hydroxide has a contact angle greater than or equal to 80°.

[00101] In an embodiment, a modified layered double hydroxide obtained by a process according to the present invention has a BET surface area of at least 40 m²/g and a moisture uptake level of less than 20 wt% of dry LDH, when measured at RH99 at 20 °C for 90 hours. In an embodiment, a modified layered double hydroxide obtained by a process according to the present invention has a BET surface area of at least 60 m²/g and a moisture uptake level of less than 20 wt% of dry LDH, when measured at RH99 at 20 °C for 90 hours. In an embodiment, a modified layered double hydroxide obtained by a process according to the present invention has a BET surface area of at least 80 m²/g and a moisture uptake level of less than 20 wt% of dry LDH, when measured at RH99 at 20 °C for 90 hours.

[00102] In an embodiment, a modified layered double hydroxide obtained by a process according to the present invention has a BET surface area of at least 40 m²/g and a contact angle of greater than or equal to 60°. In an embodiment, a modified layered double hydroxide obtained by a process according to the present invention has a BET surface area of at least 60 m²/g and a contact angle of greater than or equal to 60°. In an embodiment, a modified layered double hydroxide obtained by a process according to the present invention has a BET surface area of at least 80 m²/g and a contact angle of greater than or equal to 60°. In an embodiment, a modified layered double hydroxide obtained by a process according to the present invention has a BET surface area of at least 100 m²/g and a contact angle of greater than or equal to 60°. In an embodiment, a modified layered double hydroxide obtained by a process according to the present invention has a BET surface area of at least 100 m²/g and a contact angle of greater than or equal to 80°.

Applications of the LDHs

[00103] As described hereinbefore, the present invention also provides a composite material comprising a modified layered double hydroxide as defined herein dispersed throughout a polymer.

[00104] LDHs have a variety of interesting properties that make them attractive materials for use as fillers in polymeric composites. However, given that conventionally-prepared LDHs are only dispersible in aqueous solvents, the preparation of polymer-LDH composite materials using polymers that are soluble in organic solvents has been restricted.

[00105] Owing to their increased hydrophobicity, the modified LDHs of the invention have increased dispersibility in a range of organic solvents. This allows the preparation of a homogenous mixture of modified LDH, polymer and solvent, which can be processed into a LDH- polymer composite material, wherein the modified LDH is uniformly dispersed throughout the polymeric matrix.

[00106] In an embodiment, the polymer is selected from polypropylene, polyethylene, polyvinyl chloride, polyvinylidene chloride, polylactic acid, polyvinyl acetate, ethylene vinyl alcohol, ethylene vinyl acetate, acrylonitrile butadiene styrene, polymethyl methacrylate, polycarbonate, polyamide, an elastomer, or mixtures of two or more of the aforementioned.

[00107] In an embodiment, the polymer is a biopolymer.

[00108] The following numbered statements 1-48 are not claims, but instead describe various aspects and embodiments of the invention:

1. A process for forming a modified layered double hydroxide comprising the steps of: a) providing a layered double hydroxide of formula (I):

[M^z+i_xM’^y+x(OH)₂]^a+(X'^1-)m · b ₂0 · c(L)

(I)

wherein

M is at least one charged metal cation;

M’ is at least one charged metal cation different from M;

z is 1 or 2;

y is 3 or 4;

0<x<0.9;

0<b£10;

0<c£10;

X is at least one anion;

n is the charge on anion(s) X;

a is equal to z(1-x)+xy-2;

m ³ a/rr, and

L is an organic solvent capable of hydrogen-bonding to water;

b) providing a modifier, wherein the modifier is an organosilane; and

2. The process according to statement 1 , wherein when z is 2, M is Mg, Zn, Fe, Ca, Sn, Ni, Cu, Co, Mn or Cd or a mixture of two or more of these, or when z is 1 , M is Li.

3. The process according to statement 1 or 2, wherein when y is 3, M’ is Al, Ga, Y, In, Fe, Co, Ni, Mn, Cr, Ti, V, La or a mixture thereof, or when y is 4, M¹ is Sn, Ti or Zr or a mixture thereof. The process according to statement 1 or 2, wherein M’ is Al.

The process according to any one of statements 1 to 4, wherein the layered double hydroxide is a Zn/AI, Mg/AI, Mg,Zn/AI, Mg/AI,Sn, Mg/AI,Ti, Ca/AI, Ni/Ti or Cu/AI layered double hydroxide.

The process according to any one of statements 1 to 5, wherein X is an anion selected from at least one of halide, inorganic oxyanion, or an organic anion (e.g. an anionic surfactant, an anionic chromophore or an anionic UV absorber).

The process according to statement 6, wherein the inorganic oxyanion is carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate, nitrate, sulphate or phosphate or a mixture of two or more thereof.

The process of any one of statements 1 to 7, wherein the layered double hydroxide of formula (I) is prepared by a process comprising the steps of

I. providing a water-washed, wet precipitate of formula (II) shown below, said precipitate having been formed by contacting aqueous solutions containing cations of the metals M and M’, the anion(s) X¹¹ , and optionally an ammonia-releasing agent, and then ageing the reaction mixture:

[M ^z+ 1 _xM ^,y+ _x(0 H ) ₂]^a+ (X^n~) m · £>H₂0

(II) wherein M, M', z, y, x, m , b and X are as defined for formula (I);

II. contacting the water-washed, wet precipitate of step I with a solvent L as defined for formula (I). The process according to any one of statements 1 to 8, wherein the layered double hydroxide provided in step a) comprises less than 50% by weight of a solvent, relative to the weight of the layered double hydroxide.

The process according to any one of statements 1 to 8, wherein the layered double hydroxide provided in step a) is provided as a dry solid.

The process according to any one of statements 1 to 10, wherein in step b) the modifier is provided as a neat organosilane.

The process according to any one of statements 1 to 1 1 , wherein more than 5% by weight modifier, relative to the weight of layered double hydroxide, is mixed with the layered double hydroxide in step c).

The process according to any one of statements 1 to 1 1 , wherein more than 10% by weight modifier, relative to the weight of layered double hydroxide, is mixed with the layered double hydroxide in step c). The process according to any one of statements 1 to 13, wherein the layered double hydroxide provided in step a) has a BET specific surface area of greater than 125 m²/g. The process according to any one of statements 1 to 14, wherein in step b) the organosilane modifier has a structure according to formula (III) shown below:

wherein

q is 1 , 2 or 3;

each Ri is independently hydrogen or an organofunctional group;

each Y is independently absent, or is a straight or branched organic linker; and each R₂ is independently hydrogen, halo, hydroxy, carboxy, (1-4C)alkyl or a group -OR₃, wherein R₃ is selected from (1-6C)alkyl, aryl(1-6C)alkyl, heteroaryl(1- 6C)alkyl, cycloalkyl(1-6C)alkyl, heterocyclyl(1-6C)alkyl and (1-6C)alkoxy(1- 4C) alkyl. The process according to statement 15, wherein the organofunctional group is selected from acrylate, methacrylate, mercapto, aldehyde, amino, azido, carboxylate, phosphonate, sulfonate, epoxy, glycidyloxy, ester, halogen, hydroxyl, isocyanate, phosphine, phosphonate, alkenyl, aryl, cycloalkyl, heteroaryl and heterocyclyl.

The process according to any one of statements 1 to 16, wherein the organosilane modifier is selected from the group consisting of 3-aminopropyltriethoxysilane, (3- glycidyloxypropyl)triethoxysilane, (3-mercaptopropyl)triethoxysilane, triethoxyvinyl- silane, triethoxyphenylsilane, trimethoxy(octadecyl)silane, vinyl-tris(2-methoxy- ethoxy)silane, g-methacryloxypropyltrimethoxysilane, g-aminopropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl)ethyltrimethoxysilane, g-glycidoxypropyltrimethoxysilane, g- mercaptopropyltrimethoxysilane, (3-aminopropyl)triethoxysilane, N-(3-triethoxysilyl- propyl)ethylenediamine, 3-aminopropyl-methyl-diethoxysilane, vinyltrimethoxysilane, chlorotrimethylsilane, tert-butyldimethylsilyl chloride, trichlorovinylsilane, methyl- trichlorosilane, 3-chloropropyl trimethoxysilane, chloromethyltrimethylsilane, diethoxy- dimethylsilane, propyltrimethoxysilane, triethoxyoctylsilane, trichloro(octadecyl)silane and g-piperazinylpropylmethyldimethoxysilane.

The process according to any one of statements 1 to 17, wherein the mixing in step c) is conducted in the presence of less than or equal to 50% by weight of a solvent relative to the total weight of the layered double hydroxide and the modifier. The process according to any one of statements 1 to 17, wherein the mixing in step c) is conducted in the presence of less than 10% by weight of a solvent relative to the total weight of the layered double hydroxide and the modifier.

The process according to any one of statements 1 to 17, wherein the mixing in step c) is conducted with no solvent present.

The process according to any one of statements 1 to 20, wherein in step c) the mixing is carried out by means of vapour treatment, a dry mixer, a vortex mixer, or by milling the layered double hydroxide in the presence of the modifier.

The process according to any one of statements 1 to 21 , wherein step c) is conducted under an inert atmosphere.

The process according to any one of statements 1 to 22, comprising a further step of: d) thermally treating the modified layered double hydroxide resulting from step c) at a temperature of 15-200 °C.

The process according to statement 23, wherein in step d) the thermal treatment is carried out at 100-200 °C.

The process according to statement 23, wherein in step d) the thermal treatment is carried out under vacuum at a temperature of 15-60 °C.

The process according to any one of statements 23 to 25, wherein in step d) the thermal treatment is carried out for 2-24 hours.

A modified layered double hydroxide obtainable by a process according to any one of statements 1 to 26.

The modified layered double hydroxide of statement 27, wherein the modified layered double hydroxide has a BET surface area (as determined by N₂ adsorption) of at least 40 m²/g.

The modified layered double hydroxide of statement 27, wherein the modified layered double hydroxide has a BET surface area (as determined by N₂ adsorption) of at least 60 m²/g.

The modified layered double hydroxide of statement 27, wherein the modified layered double hydroxide has a BET surface area (as determined by N₂ adsorption) of at least 80 m²/g.

The modified layered double hydroxide of statement 27, wherein the modified layered double hydroxide has a BET surface area (as determined by N₂ adsorption) of at least 100 m²/g.

The modified layered double hydroxide of any one of statements 27 to 31 , wherein the modified layered double hydroxide has a BET (N₂) pore volume of at least 0.3 cm³/g. The modified layered double hydroxide of statement 32, wherein the modified layered double hydroxide has a BET (N₂) pore volume of at least 0.4 cm³/g. The modified layered double hydroxide of statement 32, wherein the modified layered double hydroxide has a BET (N₂) pore volume of at least 0.5 cm³/g.

The modified layered double hydroxide of statement 32, wherein the modified layered double hydroxide has a BET (N₂) pore volume of at least 0.75 cm³/g.

The modified layered double hydroxide of statement 32, wherein the modified layered double hydroxide has a BET (N₂) pore volume of at least 0.9 cm³/g.

The modified layered double hydroxide of any one of statements 27 to 36, wherein the modified layered double hydroxide has a loose bulk density of less than 0.5 g/ml_.

The modified layered double hydroxide of statement 37, wherein the modified layered double hydroxide has a loose bulk density of less than 0.35 g/ml_.

The modified layered double hydroxide of statement 37, wherein the modified layered double hydroxide has a loose bulk density of less than 0.25 g/ml_.

The modified layered double hydroxide of any one of statements 27 to 39, wherein the modified layered double hydroxide has a tap density of less than 0.5 g/ml_.

The modified layered double hydroxide of statement 40, wherein the modified layered double hydroxide has a tap density of less than 0.4 g/ml_.

The modified layered double hydroxide of statement 40, wherein the modified layered double hydroxide has a tap density of less than 0.35 g/ml_.

The modified layered double hydroxide of any one of statements 27 to 42, wherein the modified layered double hydroxide has a moisture uptake level of less than 20 wt% of dry LDH, when measured at RH99 at 20 °C for 90 hours.

The modified layered double hydroxide of statement 43, wherein the modified layered double hydroxide has a moisture uptake level of less than 15 wt% of dry LDH, when measured at RH99 at 20 °C for 90 hours.

The modified layered double hydroxide of statement 43, wherein the modified layered double hydroxide has a moisture uptake level of less than 10 wt% of dry LDH, when measured at RH99 at 20 °C for 90 hours.

The modified layered double hydroxide of any one of statements 27 to 45, wherein the modified layered double hydroxide has a water contact angle greater than or equal to 60°. The modified layered double hydroxide of statement 46, wherein the modified layered double hydroxide has a water contact angle greater than or equal to 80.

A composite material comprising a modified layered double hydroxide according to any one of statements 27 to 47, dispersed throughout a polymer. EXAMPLES

[00109] Embodiments of the invention will now be described, for the purpose of illustration only, with reference to the accompanying figures, in which

Fig. 1 (a) shows the XRD patterns of Examples 2.1 and 2.2 overlaid with AMO-LDH (AMO-LDH- 2); and (b) shows the TGA weight loss curves for Examples 2.1 and 2.2 compared to AMO-LDH.

Fig. 2 (a) shows the BET surface area of AMO-LDH (AMO-LDH-2) and Example 2.1 ; and (b) shows the Oil absorption number (OAN) of AMO-LDH (AMO-LDH-2) and Example 2.1.

Fig. 3 shows the percentage water uptake of Examples 2.1 and 2.2 and AMO-LDH (AMO-LDH- 2) at various time points during exposure to RH99 at 20°C.

Fig. 4 (a) shows solid state ²⁹Si NMR spectra for Examples 2.1 and 2.2; and (b) shows solid state ²⁷Al NMR spectra for AMO-LDH (AMO-LDH-2) and Example 2.1.

Fig. 5 shows XRD patterns of unmodified AMO-LDH (AMO-LDH-2) and Example 3.1 TEVS- modified AMO-LDHs prepared with 0.1 (P0.1), 0.6 (P0.6), 1.2 (P1.2) and 1.8 (P1.8) ml TEVS per gram AMO-LDH.

Fig. 6 shows FT-IR spectra of unmodified AMO-LDH (AMO-LDH-2) and Example 3.1 TEVS- modified AMO-LDHs prepared with 0.1 (P0.1), 0.6 (P0.6), 1.2 (P1.2) and 1.8 (P1.8) ml TEVS per gram AMO-LDH.

Fig. 7 shows TGA curves of unmodified AMO-LDH (AMO-LDH-2) and Example 3.1 TEVS- modified AMO-LDHs prepared with 0.1 (P0.1), 0.6 (P0.6), 1.2 (P1.2) and 1.8 (P1.8) ml TEVS per gram AMO-LDH.

Fig. 8 shows the percentage water uptake at various time points on exposure to RH99 at 20°C of unmodified 150°C-dried AMO-LDH (AMO-LDH-2) and Example 3.1 TEVS-modified AMO- LDHs prepared with 0.1 (P0.1), 0.6 (P0.6), 1.2 (P1.2) and 1.8 (P1.8) ml TEVS per gram AMO- LDH.

Fig. 9 (a) shows TGA curves of unmodified AMO-LDH (AMO-LDH-2) and Example 3.2 TEVS- modified AMO-LDHs prepared with 0.1 (CO.1), 0.6 (C0.6), 1.2 (C1.2) and 1.8 (C1.8) ml TEVS per gram AMO-LDH; and (b) shows the percentage water uptake at various time points on exposure to RH99 at 20°C of unmodified 150°C-dried AMO-LDH (AMO-LDH-2) and Example 3.2 TEVS- modified AMO-LDHs prepared with 0.1 (CO.1), 0.6 (C0.6), 1.2 (C1.2) and 1.8 (C1.8) ml TEVS per gram AMO-LDH.

Fig. 10 (a) shows Oil absorption number (OAN) and (b) shows a plot of OAN versus BET surface area of unmodified AMO-LDH (AMO-LDH-2) and Example 3 TEVS-modified AMO-LDHs prepared with 0.1 , 0.6, 1.2 and 1.8 ml TEVS per gram AMO-LDH for both wet-cake (C) and dry- powder (P) methods.

Fig. 1 1 (a) shows the XRD patterns of Examples 4A-4D overlaid with AMO-LDH (AMO-LDH-2); and (b) shows the FT-IR spectra of Examples 4A-4D.

Fig. 12 (a) shows the measured contact angles of unmodified LDH (AMO-LDH-2) and Examples 4A-4D. The error bars represent the deviation over 3 repeat measurements per sample; and (b) shows a plot of average contact angle and Si/AI molar ratio for Examples 4A-4D.

Fig. 13 shows the BET surface area of unmodified LDH (AMO-LDH-2) and Examples 4A, 4B and 4D.

Fig. 14 (a) shows the XRD patterns of Examples 5A-5C overlaid with AMO-LDH (AMO-LDH-2); and (b) shows the FT-IR spectra of Examples 5A-5C.

Fig. 15 shows the measured contact angles of unmodified LDH (AMO-LDH-2) and Examples 5A- 5C. The error bars represent the deviation over 3 repeat measurements per sample

Fig. 16 shows the BET surface area of unmodified LDH (AMO-LDH-2) and Examples 5A-5C.

Fig. 17 (a) shows the XRD patterns of Examples 6A and 6B overlaid with AMO-LDH (AMO-LDH-

1); and (b) shows the Si/AI molar ratio for Examples 6A and 6B.

Fig. 18 (a) shows the XRD patterns of Examples 7A and 7B overlaid with AMO-LDH (AMO-LDH-

2); (b) shows the Si/AI molar ratio for Examples 7A and 7B; and (c) shows the BET surface areas of unmodified LDH (AMO-LDH-2) and Examples 7A and 7B.

Fig. 19 (a) shows the XRD patterns of Examples 8A and 8B overlaid with AMO-LDH (AMO-LDH- 2); (b) shows the Si/AI molar ratio for Examples 8A and 8B; and (c) shows the BET surface areas of unmodified LDH (AMO-LDH-2) and Examples 8A and 8B.

Fig. 20 shows in situ FT-IR spectra recorded after modification of AMO-LDH-2 with TEVS according to Example 9.

Fig. 21 shows in situ FT-IR spectra recorded after modification of AMO-LDH-2 with TEOS according to Example 9.

Fig. 22 shows in situ FT-IR spectra recorded after modification of AMO-LDH-2 with TMGPS according to Example 9.

Fig. 23 (a) shows the XRD patterns of Example 10 overlaid with AMO-LDH (AMO-LDH-2); and (b) shows the FT-IR spectra of Example 10.

Fig. 24 shows the measured contact angles of unmodified LDH (AMO-LDH-2) and Example 10. The error bars represent the deviation over 3 repeat measurements per sample. Fig. 25 shows a plot of measured contact angles and Si/AI molar ratios for comparative examples 11.1 to 11.6.

EXAMPLES

[00110] Unless otherwise indicated, all reagents were purchased commercially and used as supplied.

[00111] Where AMO-LDH samples were modified by grinding with an organosilane modifier, the grinding was conducted manually in a pestle and mortar.

[00112] Where AMO-LDH samples were modified by mixing with an organosilane modifier in a Vortex Mixer, the sample and modifier were placed in a reaction tube, the tube was sealed and mixing was carried out using an Advanced Vortex Mixer (Fisherbrand™ ZX3 Vortex Mixer) at a speed of approximately 2800 rpm.

Example 1 - Preparation of AMO-LDHs (Mg₃AI-C0₃)

AMO-LDH-1

[00113] Mg(N0₃)₂-6H₂0 (9.60 g, 37.4 mmol) and AI(N0₃)₃-9H₂0 (4.68 g, 12.5 mmol) were dissolved in 50 mL of distilled water (Solution A). A second solution was made containing Na₂C0₃ (2.65 g, 25.0 mmol) and NaOH (4 g, 100 mmol) dissolved in 200 mL distilled water (Solution B). Solution A was added quickly to Solution B and stirred for 30 minutes. The LDH was washed twice with water and once with acetone by centrifuge-washing cycles. Six centrifuge tubes were used at 9000 rpm for five minutes. The resulting LDH slurry was dispersed in 200 mL acetone for 17 hours. The LDH slurry was then filtered, washed with 100 mL acetone and dispersed in 100 mL acetone for one hour. This procedure was repeated three times. The resulting LDH was dried overnight in a vacuum oven.

AMO-LDH-2

[00114] Mg(N0₃)₂-6H₂0 (9.60 g, 37.4 mmol) and AI(N0₃)₃-9H₂0 (4.68 g, 12.5 mmol) were dissolved in 50 mL of de-carbonated water (Solution A). A second solution contained Na₂C0₃ (2.65 g, 25.0 mmol) in 50 mL of deionised water (Solution B). Solution A was added drop-wise (58 mL/min) to Solution B. The system was kept at constant pH 10 by using 4 M NaOH and aged for 16 hours at room temperature. The slurry was then filtered and the filter cake was washed with de-carbonated water until the pH of the washings was close to 7. The cake was then washed with ethanol (1000 mL). The wet solid was re-dispersed in ethanol (600 mL) and slurried for 1 hour. The slurry was filtered, rinsed with ethanol (400 ml_), and dried in a vacuum oven for 24 hours.

Example 2 - Synthesis of orqanosilane-modified AMO-LDHs

2.1 - Method A - TEVS

[00115] 1.0 g of dried powder AMO-LDH (prepared according to AMO-LDH-2 protocol) was ground with 1.8 ml_ of triethoxyvinylsilane (TEVS) (8.5 mmol/g LDH) for 15 minutes at room temperature. The solid was then dried at 150 °C for 6 h under N₂ before being isolated in near quantitative yields.

2.2 - Method B - TEVS

[00116] 1.0 g of dried powder AMO-LDH (prepared according to AMO-LDH-2 protocol) was ground with 1.8 mL of triethoxyvinylsilane (8.5 mmol/g LDH) for 15 minutes at room temperature. The solid was then dried under vacuum (40 mbar) at room temperature before being isolated in near quantitative yields.

[00117] The XRPD patterns in Figure 1a for Examples 2.1 and 2.2 show that after surface modification of the AMO-LDHs, no impurity phases were observed.

[00118] The TGA curves in Figure 1 b show that the AMO-LDHs modified with organosilane exhibited much lower water content (2.6 wt% for Ex. 2.1 and 12.7 wt% for Ex. 2.2) compared to unmodified AMO-LDH (17.3 wt%) when measured at 200°C.

[00119] The BET surface area after organosilane modification is reduced compared to unmodified AMO-LDH, presumably due to interconnection of particles via silane linkages - see Figure 2a. Similarly, as shown in Figure 2b, the oil absorption number (OAN) is reduced post modification, presumably as a result of the lower surface area.

[00120] Figure 3 demonstrates that the organosilane modifications significantly reduce the moisture uptake compared to unmodified AMO-LDH. Example 2.1 took up more water than Example 2.2, as it had a lower water content to start with (2.6 wt% c.f. 12.7 wt%).

[00121] Figure 4 shows the solid-state NMR spectra for the ²⁹Si (Fig. 4a) and ²⁷Al (Fig. 4b) nuclei. Figure 4a indicates that silane has been grafted onto the AMO-LDH via T3, T2 and T 1 silicone bonding. Figure 4b shows that after silane modification, some octahedral Al has migrated out to form tetrahedral Al, probably in the form of Si-O-AI. Example 3 - Synthesis of modified AMO-LDHs - effect of orqanosilane loading

3.1 Dry powder method

[00122] 1.0 g of dried powder AMO-LDH (prepared according to AMO-LDH-2 protocol) was ground with triethoxyvinylsilane (TEVS) (see table below for different loadings) for 15 minutes at room temperature. The solid was then dried at 150 °C for 6 h under N₂ before being isolated in near quantitative yields.

[00123] The XRPD patterns in Figure 5 show that after surface modification of the AMO-LDH, with various loadings of TEVS, no impurity phases were observed.

[00124] The FT-IR spectra for the isolated solids in Figure 6 show that as the TEVS loading increases, the vibrations, due to TEVS-modification (such as -CH=CH2, =C-H, Si-C) of the AMO- LDH, become stronger.

[00125] The TGA curves in Figure 7 demonstrate the modified samples have reduced moisture content (<2 wt% at 200 °C) compared to unmodified AMO-LDH which has also been dried at 150 °C for 6 h under N₂ (4 wt% at 200 °C).

[00126] Figure 8 demonstrates that the TEVS modifications significantly reduced the moisture uptake propensity compared to unmodified AMO-LDH, even when a 0.1 ml/g of LDH loading of TEVS was used. Once the loading of TEVS was 0.6 ml/g of LDH or higher, then the moisture uptake did not exceed 15-20 wt% even after 90 hours at RH99.

3.2 Wet cake method

[00127] 1.0 g of 27 wt% wet cake AMO-LDH (27 wt% solid; prepared according to AMO-LDH-2 protocol) was ground with triethoxyvinylsilane (TEVS) (see table below for different loadings) for 15 minutes at room temperature. The solid was then dried at 150 °C for 6 h under N₂ before being isolated in near quantitative yields.

[00128] The TGA curves in Figure 9(a) demonstrate the modified samples have reduced moisture content (<2 wt% at 200 °C) compared to unmodified AMO-LDH which has also been dried at 150 °C for 6 h under N₂ (4 wt% at 200 °C).

[00129] Figure 9(b) demonstrates that the TEVS modifications significantly reduced the moisture uptake propensity compared to unmodified AMO-LDH, even when a 0.1 ml/g of LDH loading of TEVS was used. Once the loading of TEVS was 0.6 ml/g of LDH or higher, then the moisture uptake did not exceed 15-20 wt% even after 90 hours at RH99.

[00130] Figure 10(a) shows that modified samples have lower OAN values compared to unmodified AMO-LDH.

[00131] Figure 10(b) illustrates how OAN and BET surface area decrease proportionally as loading of TEVS increases for both dry powder and wet slurry methods.

Example 4 - Synthesis of modified AMO-LDHs - effect of solvent level (Vortex mixing)

[00132] 1.0 g of dried powder AMO-LDH (prepared according to AMO-LDH-2 protocol) was mixed with 0.35 g of triethoxyvinylsilane (TEVS) (35% w/w; 1.8 mmol/g LDH) and ethanol (none (0% w/w) - 4A; 0.85 ml (50% w/w) - 4B; 1.71 ml (100% w/w) - 4C; or 3.41 ml (200% w/w) - 4D)* using a Vortex Mixer for 15 minutes at room temperature. The solid was then dried at 150 ^°C for 6 h under N₂ before being isolated.

*weight of solvent relative to the total weight of LDH+TEVS

[00133] The XRPD patterns in Figure 1 1a show that after surface modification of the AMO-LDH, with various levels of solvent present, no impurity phases were observed.

[00134] The FT-IR spectra in Figure 1 1 b show for Examples 4A-4D peaks at around 750 and 920-1090 cm^-1 which correspond to the vibrations of -Si-C- and -Si-O-M(Si)- from TEVS, and peaks at 1348 and 1531 cm^-1 are due to vibration of C0₃ ² from LDH. It is worth noting that the vibration of water from LDH become very weak after the organosilane modifications, indicating reduced water content in the silane-modified samples. Examples 4C and 4D, prepared in the presence of more ethanol, show weaker vibrations from silane compared with 4A and 4B.

[00135] Figure 12a shows the contact angles of Examples 4A-4D alongside unmodified AMO- LDH (AMO-LDH-2). Organosilane modification of the AMO-LDH with TEVS in a Vortex Mixer results in the LDHs demonstrating larger contact angles. Examples 4A (no ethanol) and 4B (50% w/w ethanol) had the highest contact angles (85-90°) and as the amount of ethanol increased further the contact angle decreased to -75° for Example 4C (100% w/w ethanol) and -40° for Example 4D (200% w/w ethanol). Figure 12b plots the contact angles for Examples 4A-4D with the respective Si/AI molar ratios. The Si content and Al content of samples was determined by inductively coupled plasma mass spectrometry (ICP-MS). Samples for ICP-MS (Perkin Elmer Elan 6100DRC) analysis were prepared by digestion in high purity HNO₃ solution (2 h reflux), and dilution with 18.2 megohms Dl water, calibrated using external calibration analysis (a series of standards of known Al concentrations were prepared and measured externally to the samples to produce a linear calibration). Figure 12b indicates that increased Si/AI molar ratio, which is indicative of greater incorporation of organosilane modifier into the AMO-LDH, correlates well with higher contact angle, which is indicative of increased hydrophobicity of the organosilane- modified AMO-LDH.

[00136] As shown in Figure 13, after silane modification of AMO-LDH-2 the BET surface area decreased to 100-120 m²/g. With increasing the amount of ethanol from 0% w/w to 200 %w/w during the mixing process, the surface area slightly increased.

Example 5 - Synthesis of modified AMO-LDHs - effect of solvent level (grinding)

[00137] 1.0 g of dried powder AMO-LDH (prepared according to AMO-LDH-2 protocol) was ground with 0.35 g of triethoxyvinylsilane (TEVS) (35% w/w; 1.8 mmol/g LDH) and ethanol (none (0% w/w) - 5A; 0.85 ml (50% w/w) - 5B; or 1.71 ml (100% w/w) - 5C)* in a pestle and mortar for 15 minutes at room temperature. The solid was then dried at 150 ^°C for 6 h under N₂ before being isolated.

*weight of solvent relative to the total weight of LDH+TEVS

[00138] The XRPD patterns in Figure 14a show that after surface modification of the AMO-LDH, with various levels of solvent present, no impurity phases were observed.

[00139] The FT-IR spectra in Figure 14b show for Examples 5A-5C peaks at around 750 and 920-1090 cm^-1 which correspond to the vibrations of -Si-C- and -Si-O-M(Si)- from TEVS, and peaks at 1348 and 1531 cm^-1 are due to vibration of C0₃ ² from LDH.

[00140] Figure 15 shows the contact angles of Examples 5A-5C alongside unmodified AMO- LDH (AMO-LDH-2). Organosilane modification of the AMO-LDH with TEVS via a grinding process results in the LDHs demonstrating larger contact angles.

[00141] As shown in Figure 16, after silane modification of AMO-LDH-2 the BET surface area decreased to approximately 120 m²/g for all 3 samples prepared. Example 6 - Synthesis of modified AMO-LDHs - solvent effect on TEVS modification of AMO-LDH-1

[00142] 1.0 g of AMO-LDH (prepared according to AMO-LDH-1 protocol) was mixed with 0.35 g of triethoxyvinylsilane (TEVS) (35% w/w; 1.8 mmol/g LDH) and ethanol (none (0% w/w) - 6A; or 3.41 mL (200% w/w) - 6B)* using a Vortex Mixer for 15 minutes at room temperature. The solid was then dried at 150 ^°C for 6 h under N₂ before being isolated.

*weight of solvent relative to the total weight of LDH+TEVS

[00143] The XRPD patterns in Figure 17a show that after surface modification of the AMO-LDH, no impurity phases were observed.

[00144] Figure 17b shows the Si/AI molar ratios of Examples 6A and 6B. The results indicate that 6A (non-solvent system) contains a much higher amount of the organosilane modifier at the same modifier loading, compared with 6B, which had 200% w/w ethanol present during the mixing process.

Example 7 - Synthesis of modified AMO-LDHs - solvent effect on TEAPS modification

[00145] 1.0 g of AMO-LDH (prepared according to AMO-LDH-2 protocol) was mixed with 0.35 g of 3-aminopropyltriethoxysilane (TEAPS) (35% w/w; 1.6 mmol/g LDH) and ethanol (none (0% w/w) - 7A; or 3.41 mL (200% w/w) - 7B)* using a Vortex Mixer for 15 minutes at room temperature. The solid was then dried at 150 ^°C for 6 h under N₂ before being isolated.

*weight of solvent relative to the total weight of LDH+TEAPS

[00146] The XRPD patterns in Figure 18a show that after surface modification of the AMO-LDH, no impurity phases were observed.

[00147] Figure 18b shows the Si/AI molar ratios of Examples 7 A and 7B. The results indicate that 7 A (non-solvent system) contains a higher amount of the organosilane modifier at the same modifier loading, compared with 7B, which had 200% w/w ethanol present during the mixing process.

[00148] Figure 18c shows the BET surface areas of unmodified AMO-LDH-2 and Examples 7 A and 7B. The surface areas of both 7 A and 7B were significantly reduced by surface modification, with the modified AMO-LDH prepared by solvent-free modification (7 A) having a lower surface area than the equivalent AMO-LDH modified in the presence of 200% w/w ethanol (7B). These results are in line with the Si/AI ratios, indicating that more modifier was incorporated into 7 A than 7B. Example 8 - Synthesis of modified AMO-LDHs - solvent effect on TMGPS modification

[00149] 1.0 g of AMO-LDH (prepared according to AMO-LDH-2 protocol) was mixed with 0.35 g of (3-glycidyloxypropyl)trimethoxysilane (TMGPS) (35% w/w; 1.5 mmol/g LDH) and ethanol (none (0% w/w) - 8A; or 3.41 ml_ (200% w/w) - 8B)* using a Vortex Mixer for 15 minutes at room temperature. The solid was then dried at 150 ^°C for 6 h under N₂ before being isolated.

*weight of solvent relative to the total weight of LDH+TMGPS

[00150] The XRPD patterns in Figure 19a show that after surface modification of the AMO-LDH, no impurity phases were observed.

[00151] Figure 19b shows the Si/AI molar ratios of Examples 8A and 8B. The results indicate that 8A (non-solvent system) contains a much higher amount of the organosilane modifier at the same modifier loading, compared with 8B, which had 200% w/w ethanol present during the mixing process.

[00152] Figure 19c shows the BET surface areas of unmodified AMO-LDH-2 and Examples 8A and 8B. The surface areas of both 8A and 8B were significantly reduced by surface modification, with the modified AMO-LDH prepared by solvent-free modification (8A) having a lower surface area than the equivalent AMO-LDH modified in the presence of 200% w/w ethanol (8B).

Example 9 - Synthesis of modified AMO-LDHs - FT-IR reaction monitoring

[00153] 100 mg of dried powder AMO-LDH (prepared according to AMO-LDH-2 protocol) was ground with 20 mg of modifier (either TEVS, triethoxy(octyl)silane (TEOS) or 3- Glycidyloxypropyl)-trimethoxysilane (TMGPS)) for 2 minutes at room temperature. The samples were then monitored by in situ FT-IR recorded every 5 minutes.

[00154] Figure 20 shows the FT-IR spectra for the TEVS sample; the ethoxy groups in the range of 1090-1200 cm^-1 are decreasing with increasing time. After one hour, the vibrations of ethoxy groups completely disappeared. While the functional groups of TEVS such as -CH=CH2, =C-H, -Si-C- remained in the sample. The results confirmed that silane has been grafted on LDH surface by reacting hydroxyl group of LDH with ethoxy groups of silane and reaction time is estimated at 60 minutes.

[00155] Figures 21 and 22 show the FT-IR spectra for the TEOS and TMGPS samples respectively; the vibrations of ethoxy groups in the range of 1090-1200 cm^-1 decreased with increasing time. The vibrations of Si-O-Metal/Si-O-Si at around 1000 cm ¹ increased with increasing time. The results confirmed that silane has been grafted on LDH surface by reacting hydroxyl group of LDH with ethoxy groups of silane. Example 10 - Synthesis of modified AMO-LDHs - pre-modification thermal treatment

[00156] 1.0 g of AMO-LDH (prepared according to AMO-LDH-2 protocol) was thermally treated at 150 °C for 6 h and was then ground with 0.35 g of TEVS (35 wt% of LDH) for 15 minutes at room temperature. The solid was then dried at 150 °C for 6 h under N₂ before being isolated.

[00157] XRPD patterns in Figure 23(a) show no impurity phase was observed after surface modification with TEVS.

[00158] FT-IR spectrum of Example 10 in Figure 23(b) shows vibrations from both AMO-LDH and TEVS. The peaks at around 750 and 920-1090 cm^-1 are corresponding to the vibrations of - Si-C- and -Si-O-M(Si)- from TEVS, respectively. The peaks at 1348 and 1531 cm^-1 are due to vibration of C0₃ ² from LDH. It is worth noting that the vibration of water from LDH became very weak after silane modification, indicating that much less water in the silane modified sample.

[00159] Figure 24 shows the contact angles of Example 10 alongside unmodified AMO-LDH (AMO-LDH-2). Organosilane modification of the AMO-LDH results in the LDH demonstrating a larger contact angle.

Example 11 - Comparative Examples

Water-washed LDH formation

[00160] A mixed metal solution was prepared from 9.6 g of Mg(NC>₃)₂-6H₂0 (37.4 mmol), 4.7 g of AI(N0₃)₃-9H₂0 (12.5 mmol) in 50 mL of de-carbonated water (Solution A). A second solution contained 2.65 g of Na₂CO₃ (25.0 mmol) in 50 mL of deionised water (Solution B). The solution A was added drop-wise (58 mL/min) to the Solution B. The system was kept at constant pH 10 by using 4 M NaOH and aged for 16 hours at room temperature. The slurry was then filtered and the filter cake was washed with de-carbonated water until the pH was close to 7. The water- washed Mg3AI-CC>3 LDH was dispersed in water to give a 29% w/v slurry.

TEVS modification

Example 11.1

[00161] Water washed Mg3AI-CC>3 LDH slurry (29% w/v in water, equal to 1 g of dry LDH) was dispersed into 100 mL of ethanol purged with N₂. Triethoxyvinylsilane (TEVS) (2.8 mmol/g LDH) was injected dropwise into the suspension followed by reflux at 80 °C for 18 h. The solid was collected by filtration and washed with ethanol (300 mL) followed by drying for 16 h.

Example 11.3

[00162] The water-washed Mg3AI-CC>3 LDH slurry was dried in vacuum overnight and then thermally treated at 180 °C for 6 h, prior to being dispersed into 100 mL of ethanol purged with N2. Triethoxyvinylsilane (TEVS) (2.8 mmol/g LDH) was injected dropwise into the suspension followed by reflux at 80 °C for 18 h. The solid was collected by filtration and washed with ethanol (300 ml_) followed by drying for 16 h.

Example 11.5

[00163] Water washed Mg3AI-CC>3 LDH slurry (29% w/v in water, equal to 1 g of dry LDH) was dispersed into 100 mL of water purged with N2. Triethoxyvinylsilane (TEVS) (2.8 mmol/g LDH) was injected dropwise into the suspension followed by reflux at 80 °C for 18 h. The solid was collected by filtration and washed with ethanol (300 mL) followed by drying for 16 h.

Example 11.6

[00164] Water washed Mg3AI-CC>3 LDH slurry (29% w/v in water, equal to 1 g of dry LDH) was dispersed into 1 : 1 ethanol:water (100 mL) purged with N2. Triethoxyvinylsilane (TEVS) (2.8 mmol/g LDH) was injected dropwise into the suspension followed by reflux at 80 °C for 18 h. The solid was collected by filtration and washed with ethanol (300 mL) followed by drying for 16 h.

Ethanol-treated LDH formation

[00165] A mixed metal solution was prepared from 9.6 g of Mg(NC>₃)₂-6H₂0 (37.4 mmol), 4.7 g of AI(N0₃)₃-9H₂0 (12.5 mmol) in 50 mL of de-carbonated water (Solution A). A second solution containing 2.65 g of Na2CC>3 (25.0 mmol) in 50 mL of deionised water (Solution B). The solution A was added drop-wise (58 mL/min) to the Solution B. The system was kept at constant pH 10 by using 4 M NaOH and aged for 16 hours at room temperature. The slurry was then filtered and the filter cake was washed with de-carbonated water until the pH was close to 7 and followed by washing with ethanol. It was then re-dispersed in ethanol and slurried for 1 hour. The slurry was filtered and rinsed with ethanol. The ethanol-treated Mg3AI-CC>3 LDH was dispersed in ethanol to give a 29% w/v slurry.

TEVS modification

Example 11.2

[00166] Ethanol-treated AMO Mg₃AI-C0₃ LDH slurry (29% w/v in ethanol, equal to 1 g of dry LDH) was dispersed into 100 mL of ethanol purged with N2. Triethoxyvinylsilane (TEVS) (2.8 mmol/g LDH) was injected dropwise into the suspension followed by reflux at 80 °C for 18 h. The solid was collected by filtration and washed with ethanol (300 mL) followed by drying for 16 h. Example 11.4

[00167] Ethanol-treated AMO Mg₃AI-C0₃ LDH slurry was dried in vacuum overnight and then thermally treated at 180 °C for 6 h, prior to being dispersed into 100 mL of ethanol purged with N2. Triethoxyvinylsilane (TEVS) (2.8 mmol/g LDH) was injected dropwise into the suspension followed by reflux at 80 °C for 18 h. The solid was collected by filtration and washed with ethanol (300 mL) followed by drying for 16 h.

[00168] Figure 25 shows the contact angles and Si/AI molar ratios for Examples 1 1.1 to 1 1.6.

Claims

[M^z+i_xM’^y+x(OH)₂]^a+(X'^1_)m · b ₂0 · c(L)

(I)

wherein

M is at least one charged metal cation;

M’ is at least one charged metal cation different from M;

z is 1 or 2;

y is 3 or 4;

0<x<0.9;

0<b£10;

0<c£10;

X is at least one anion;

n is the charge on anion(s) X;

a is equal to z(1-x)+xy-2;

m ³ a/rr, and

L is an organic solvent capable of hydrogen-bonding to water;

b) providing a modifier, wherein the modifier is an organosilane; and

2. The process according to claim 1 , wherein when z is 2, M is Mg, Zn, Fe, Ca, Sn, Ni, Cu, Co, Mn or Cd or a mixture of two or more of these, or when z is 1 , M is Li,

and

when y is 3, M’ is Al, Ga, Y, In, Fe, Co, Ni, Mn, Cr, Ti, V, La or a mixture thereof, or when y is 4, M¹ is Sn, Ti or Zr or a mixture thereof.

3. The process according to claim 1 or 2, wherein the layered double hydroxide is a Zn/AI, Mg/AI, Mg, Zn/AI, Mg/AI,Sn, Mg/AI,Ti, Ca/AI, Ni/Ti or Cu/AI layered double hydroxide, and X is an inorganic oxyanion selected from carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate, nitrate, sulphate or phosphate or a mixture of two or more thereof.

4. The process of any one of claims 1 to 3, wherein the layered double hydroxide of formula (I) is prepared by a process comprising the steps of

[M ^z+ 1 _xM ^,y+ _x(0 H ) ₂]^a+ (X^n~) m · £>H₂0

(I I) wherein M, M', z, y, x, m , b and X are as defined for formula (I);

II. contacting the water-washed, wet precipitate of step I with a solvent L as defined for formula (I).

5. The process according to any one of claims 1 to 4, wherein either or both of the following statements A) and B) applies:

A) the layered double hydroxide provided in step a) comprises less than 50% by weight of a solvent, relative to the weight of the layered double hydroxide;

B) in step b) the modifier is provided as a neat organosilane.

6. The process according to any one of claims 1 to 5, wherein more than 10% by weight modifier, relative to the weight of layered double hydroxide, is mixed with the layered double hydroxide in step c).

7. The process according to any one of claims 1 to 6, wherein the layered double hydroxide provided in step a) has a BET specific surface area of greater than 125 m²/g.

8. The process according to any one of claims 1 to 7, wherein in step b) the organosilane modifier has a structure according to formula (III) shown below:

wherein

q is 1 , 2 or 3;

each Ri is independently hydrogen or an organofunctional group;

each Y is independently absent, or is a straight or branched organic linker; and each R₂ is independently hydrogen, halo, hydroxy, carboxy, (1-4C)alkyl or a group -OR₃, wherein R₃ is selected from (1-6C)alkyl, aryl(1-6C)alkyl, heteroaryl(1- 6C)alkyl, cycloalkyl(1-6C)alkyl, heterocyclyl(1-6C)alkyl and (1-6C)alkoxy(1- 4C) alkyl.

9. The process according to any one of claims 1 to 8, wherein the organosilane modifier is selected from the group consisting of 3-aminopropyltriethoxysilane, (3- glycidyloxypropyl)triethoxysilane, (3-mercaptopropyl)triethoxysilane, triethoxyvinyl- silane, triethoxyphenylsilane, trimethoxy(octadecyl)silane, vinyl-tris(2-methoxy- ethoxy)silane, g-methacryloxypropyltrimethoxysilane, g-aminopropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl)ethyltrimethoxysilane, g-glycidoxypropyltrimethoxysilane, g- mercaptopropyltrimethoxysilane, (3-aminopropyl)triethoxysilane, N-(3-triethoxysilyl- propyl)ethylenediamine, 3-aminopropyl-methyl-diethoxysilane, vinyltrimethoxysilane, chlorotrimethylsilane, tert-butyldimethylsilyl chloride, trichlorovinylsilane, methyl- trichlorosilane, 3-chloropropyl trimethoxysilane, chloromethyltrimethylsilane, diethoxy- dimethylsilane, propyltrimethoxysilane, triethoxyoctylsilane, trichloro(octadecyl)silane and g-piperazinylpropylmethyldimethoxysilane.

10. The process according to any one of claims 1 to 9, wherein the mixing in step c) is conducted in the presence of less than 10% by weight of a solvent relative to the total weight of the layered double hydroxide and the modifier;

or

wherein the mixing in step c) is conducted with no solvent present.

11. The process according to any one of claims 1 to 10, wherein either or both of the following statements A) and B) applies:

A) in step c) the mixing is carried out by means of vapour treatment, a dry mixer, a vortex mixer, or by milling the layered double hydroxide in the presence of the modifier;

B) step c) is conducted under an inert atmosphere.

12. The process according to any one of claims 1 to 1 1 , comprising a further step of: d. thermally treating the modified layered double hydroxide resulting from step c) at a temperature of 15-200 °C.

13. The process according to claim 12, wherein in step d) the thermal treatment is carried out at 100-200 °C;

or

in step d) the thermal treatment is carried out under vacuum at a temperature of 15-60 °C.

14. A modified layer double hydroxide obtainable by a process according to any one of claims 1 to 13.

15. A composite material comprising a modified layer double hydroxide according to claim 14, dispersed throughout a polymer.