Growth substrate

Abstract

The present invention relates to a growth substrate formed of man-made vitreous fibres (MMVF) bonded with a binder, wherein the growth substrate comprises anionic wetting agent, wherein the growth substrate further comprises one or more salts each comprising a cation and an organic anion.

Description

[0001] GROWTH SUBSTRATE

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a growth substrate, the use of the growth substrate as a growth substrate for growing plants, or for propagating seeds, seedlings, or cuttings, a method of growing plants or propagating seeds, seedlings, or cuttings, a method of manufacturing the growth substrate, and a method of storing the growth substrate.

[0004] BACKGROUND

[0005] It has been known for many years to grow plants in growth substrates formed from man-made vitreous fibres (MMVF). MMVF products for this purpose, which are provided as a coherent plug, block or slab, generally include a binder, usually an organic binder, in order to provide structural integrity to the product. This allows the growth substrate product to retain its structure during water irrigation. However, MMVF products which are to be used as growth substrates must have a capacity to take up and hold water, which is routinely supplied by an irrigation system to the growth substrate product, and must also have re-wetting properties. Accordingly, it has been well known for many years to include a wetting agent in MMVF products which are to be used as growth substrates.

[0006] One class of wetting agents known for use in growth substrates are anionic wetting agents. For example, W02008 / 009467 discloses the use of an anionic wetting agent such as linear alkyl benzene sulphonate (LAS) in a growth substrate product. Alkyl ether sulphate (AES) wetting agents are also known for use in growth substrate products, as disclosed in WO2015 / 181323. EP1226749 also discloses the use of various surfactants including anionic surfactants as wetting agents in growth substrates. W02008 / 009467 and WO2015 / 181323 disclose that the growth substrate may contain other types of conventional additives in addition to binder and wetting agent, for instance salts such as ammonium sulphate. The inorganic salt ammonium sulphate is typically added as a latent acid catalyst for curing of the binder.Anionic wetting agents such as LAS and AES have been successfully used commercially in growth substrate products. However, growth substrates comprising anionic wetting agents may not exhibit satisfactory ageing properties. In particular, the hydrophilicity of the growth substrate may decrease after the growth substrate has been stored for a period of time, particularly when stored at higher relative humidities. This means that initial wetting of the growth substrate after storage may be more difficult and take longer.

[0007] There is therefore a need for growth substrates that comprise anionic wetting agents and that have improved ageing properties.

[0008] SUMMARY OF INVENTION

[0009] According to a first aspect of the invention, there is provided a growth substrate formed of man-made vitreous fibres bonded with a binder, wherein the growth substrate comprises anionic wetting agent, wherein the growth substrate further comprises one or more salts each comprising a cation and an organic anion.

[0010] The present invention is based on the surprising discovery that the presence of a salt comprising a cation and an organic anion in addition to the anionic wetting agent can improve the ageing properties of the growth substrate.

[0011] It is thought that the cations of the salt provide additional mobile charges which may improve mobility of the anionic wetting agent upon ageing of the growth substrate. In particular, the additional mobile charges may allow the anionic wetting agent to remain at the surface of the binder which may help prevent the decrease in the hydrophilicity of the growth substrate following storage. It has surprisingly been found that the addition of the salt is particularly effective at preserving the hydrophilicity of growth substrates that are stored at high relative humidities. It is thought that growth substrates stored at higher relative humidities contain more water which aids the mobility of the additional charges provided by the cations of the salt and thereby improves mobility of the wetting agent.The growth substrates of the invention may therefore maintain a higher hydrophilicity / wettability following storage than known growth substrates comprising anionic wetting agents, particularly when the growth substrates are stored at high relative humidities.

[0012] It has been found that inorganic salts (such as ammonium sulphate) are prone to crystallisation. Crystallisation is undesirable as it may lead to a heterogeneous coating of the binder on the fibres and affect the distribution of the anionic wetting agent. Furthermore, crystallisation of the salt may reduce the mobility of the ions which could impact their ability to maintain the mobility of the anionic wetting agent. In contrast, it has been found that the use of a salt comprising an organic anion can help prevent crystallisation of the salt and therefore provide the growth substrates with more consistent properties and performance.

[0013] According to a second aspect of the invention, there is provided the use of a growth substrate according to the first aspect of the invention as a growth substrate for growing plants, or for propagating seeds, seedlings, or cuttings.

[0014] According to a third aspect of the invention, there is provided a method of growing plants or propagating seeds, seedlings, or cuttings, the method comprising:

[0015] a) providing a growth substrate according to the first aspect of the invention;

[0016] b) positioning one or more plants, seeds, seedlings, or cuttings for growth in the growth substrate; and

[0017] c) irrigating the growth substrate.

[0018] According to a fourth aspect of the invention, there is provided a method of manufacturing the growth substrate according to the first aspect of the invention, comprising the steps of:

[0019] a) providing man-made vitreous fibres;

[0020] b) applying the binder to the man-made vitreous fibres;C) applying the anionic wetting agent to the man-made vitreous fibres; and

[0021] d) applying the one or more salts to the man-made vitreous fibres

[0022] e) collecting and consolidating the man-made vitreous fibres.

[0023] According to a fifth aspect of the invention, there is provided a method of storing the growth substrate according to the first aspect of the invention, wherein the growth substrate is stored at an elevated relative humidity.

[0024] As discussed above, it has been found that the salt added to the growth substrate of the invention may be particularly effective at preserving the hydrophilicity of growth substrates that are stored at high relative humidities. It may therefore be beneficial to store the growth substrates of the invention at an elevated relative humidity in order to maintain a high hydrophilicity.

[0025] DETAILED DESCRIPTION

[0026] The present invention relates to a growth substrate formed of man-made vitreous fibres (MMVF).

[0027] The growth substrate is in the form of a coherent mass. That is, the growth substrate is generally a coherent matrix of man-made vitreous fibres, which has been produced as such, but can also be formed by granulating a slab of mineral wool and consolidating the granulated material.

[0028] The MMVF can be any of the conventional types used for the formation of known MMVF growth substrates. For example, the MMVF may be glass wool, slag wool, or stone wool, preferably stone wool.

[0029] Stone wool generally has a content of iron oxide of at least 3% and a content of alkaline earth metals (calcium oxide and magnesium oxide) from 10 to 40%, along with the other usual oxide constituents of mineral wool. The other oxides usually present are silica; alumina; alkali metals (sodium oxide and potassium oxide)which are usually present in low amounts; and can also include titania and other minor oxides.

[0030] Fibre diameter is often in the range of 2 to 10 microns, in particular 3 to 8 microns, as conventional.

[0031] The growth substrate preferably comprises at least 90 wt. % man-made vitreous fibres by weight of the total solids content of the growth substrate. An advantage of having such an amount of fibres present in the growth substrate is that there are sufficient pores formed between the fibres to allow the growth substrate to hold water and nutrients for the plant, whilst maintaining the ability for roots of the plants to permeate the growth substrate. The remaining solid content is made up primarily of binder, wetting agent, and the one or more salts, as will be discussed in more detail below.

[0032] The growth substrate may have an average density of from 30 to 150 kg / m3, preferably 30 to 100 kg / m3, more preferably 40 to 90 kg / m3.

[0033] The growth substrate may have a volume in the range 3 to 86,400 cm3, preferably 5 to 30,000 cm3, more preferably 8 to 20,000 cm3.

[0034] The growth substrate may be in the form of a product conventionally known as a plug, or in the form of a product conventionally known as a block, or in the form of a product conventionally known as a slab.

[0035] The growth substrate may have dimensions conventional for the product type commonly known as a plug. Thus, the growth substrate may have a height from 20 to 35 mm, often 25 to 28 mm, and a length and width in the range 15 to 25 mm, often around 20 mm. In this case the growth substrate is often substantially cylindrical with the end surfaces of the cylinder forming the top and bottom surfaces of the growth substrate.

[0036] The volume of the growth substrate in the form of a plug is preferably not more than 150 cm3. In general, the volume of the growth substrate in the form of a plugis in the range 3 to 150 cm3and preferably not more than 100 cm3, more preferably not more than 80 cm3, more preferably not more than 75 cm3, most preferably not more than 70 cm3. The minimum distance between the top and bottom surfaces of a plug is preferably less than 60 mm, more preferably less than 50 mm and most preferably less than 40 mm.

[0037] Another embodiment of a plug has a height from 30 to 50 mm, often around 40 mm and a length and width in the range 20 to 40 mm, often around 30 mm. The growth substrate in this case is often of cuboid form. In this first case the volume of the growth substrate is often not more than 50 cm3, preferably not more than 40 cm3.

[0038] Alternatively, the growth substrate may be of the type of plug described as the first MMVF growth substrate in our publication WO2010 / 003677. In this case the volume of the growth substrate is most preferably in the range of from 10 to 40 cm3.

[0039] The growth substrate may have dimensions conventional for the product type commonly known as a block. Thus, the growth substrate may have a height from 4 to 20 cm, often 6 to 15 cm, and a length and width in the range 4 to 30 cm, often 10 to 20 cm. In this case the growth substrate is often substantially cuboidal. The volume of the growth substrate in the form of a block is preferably in the range 64 to 8000 cm3.

[0040] The growth substrate may have dimensions conventional for the product type commonly known as a slab. Thus, the growth substrate may have a height from 5 to 15 cm, often 7.5 to 12.5 cm, a width in the range of 5 to 30 cm, often 12 to 24 cm, and a length in the range 30 to 240 cm, often 40 to 200 cm. In this case the growth substrate is often substantially cuboidal. The volume of the growth substrate in the form of a slab is preferably in the range 750 to 86,400 cm3.

[0041] The height of the growth substrate is the vertical height of the growth substrate when positioned as intended to be used and is thus the distance between the topsurface and the bottom surface. The top surface is the surface that faces upwardly when the growth substrate is positioned as intended to be used and the bottom surface is the surface that faces downwardly (and on which the growth substrate rests) when the growth substrate is positioned as intended to be used.

[0042] In general, the growth substrate may be of any appropriate shape including cylindrical, cuboidal and cubic. Usually, the top and bottom surfaces are substantially planar.

[0043] The man-made vitreous fibres (MMVF) in the growth substrate of the invention are bonded with a binder. The binder is usually an organic binder, which is generally heat-curable. The growth substrate is therefore preferably a coherent matrix of MMVF connected by cured binder. The binder can be an organic hydrophobic binder, and in particular it can be a conventional heat-curable (thermosetting) hydrophobic binder of the type which has been used for many years in MMVF growth substrates (and other MMVF-based products). This has the advantage of convenience and economy. Thus, the binder may be a phenol formaldehyde (PF) resin or urea formaldehyde resin, preferably a phenol urea formaldehyde (PUF) resin.

[0044] Alternatively, the binder may be a sugar-based binder comprising a mixture of phenol urea formaldehyde (PUF) resin and dextrose. The dextrose can be present in an amount of up to 60 wt. % dextrose.

[0045] In a further embodiment, the sugar-based binder may be a formaldehyde-free binder, such as disclosed in WO 2012 / 028650. Prior to curing, such binders may comprise;

[0046] a) a sugar component,

[0047] b) a reaction product of a polycarboxylic acid component and an alkanolamine component, wherein the binder prior to curing contains at least 42% by weight of the sugar component based on the total weight (dry matter) of the binder components, preferably wherein the binder prior to curing contains 46 to64% by weight of the sugar component based on the total weight (dry matter) of the binder components.

[0048] The binder may alternatively be other known formaldehyde-free sugar-based binders, such as those disclosed in WO2013179323 and WO2016102444. For example, the binder may be formed of a formaldehyde-free aqueous binding composition comprising:

[0049] - at least one monosaccharide,

[0050] - ammonium sulfamate or alkali or alkaline earth metal sulfamate, - ammonium hydroxide, and / or an organic or inorganic ammonium salt.

[0051] Alternatively, the binder may be formed of an aqueous binder composition comprising:

[0052] - a component (i) in form of one or more carbohydrates;

[0053] - a component (ii) in form of one or more compounds selected from sulfamic acid, derivative of sulfamic acid or any salt thereof.

[0054] Formaldehyde-free binder compositions are particularly beneficial to plant growth, and especially plant propagation, as plants are sensitive to high concentrations of formaldehyde, which can have a detrimental effect on plant growth.

[0055] The binder may alternatively be a formaldehyde-free protein-based binder as described in WO2017 / 194722 or WO2022 / 175310. Such binders may be formed of a composition comprising:

[0056] - at least one phenol and / or quinone containing compound;

[0057] - at least one protein.

[0058] The binder may alternatively be a lignin or lignosulfonate binder as disclosed in WO2021197631 , WO2022 / 144110, WO2021 / 197661 , or W02020 / 070338. For example, the binder may be a cured aqueous binder composition, wherein the aqueous binder composition prior to curing comprises:

[0059] - a component (i) in the form of one or more oxidized lignins;

[0060] - a component (ii) in the form of one or more cross-linkers;a component (iii) in the form of one or more plasticizers.

[0061] Alternatively, the binder may be a cured aqueous binder composition, wherein the aqueous binder composition prior to curing comprises:

[0062] - a component (i) in form of one or more lignosulfonate lignins having a carboxylic acid group content of 0.03 to 1.4 mmol / g, based on the dry weight of the lignosulfonate lignins, and

[0063] - a component (ii) in form of one or more cross-linkers.

[0064] The binder can be itself hydrophilic. A hydrophilic binder does not require the use of as much wetting agent as a hydrophobic binder. A wetting agent can nevertheless be used to increase the hydrophilicity of a hydrophilic binder in a similar manner to its action in combination with a hydrophobic binder. This means that the MMVF substrate will absorb a higher volume of water than if the wetting agent is not present. Any hydrophilic binder can be used, for example the binder disclosed in WO2012 / 028650.

[0065] The amount of the binder present in the growth substrate of the invention may be in the range of from 0.1 to 10 wt. % by weight of the total solids content of the growth substrate, preferably in the range of from 0.5 to 5.0 wt. %, more preferably in the range of from 1.5 to 5.0 wt. %.

[0066] The growth substrate of the invention further comprises anionic wetting agent. The growth substrate may comprise a single anionic wetting agent or a mixture of different anionic wetting agents.

[0067] Any suitable anionic wetting agents may be used in the growth substrates of the invention. Suitable anionic surfactants include salts (including, for example, sodium, potassium, ammonium and substituted ammonium salts such as mono-, di-and triethanolamine salts) of the anionic sulphate, sulphonate, carboxylate and sarcosinate surfactants. Other anionic surfactants include isethionates such as the acyl isethionates, N-acyl taurates, fatty acid amines of methyl tauride, alkylsuccinates and sulfosuccinates, mono esters of sulfosuccinates, di-esters of sulfosuccinates and N-acyl sarcosinates.

[0068] Further examples of suitable anionic wetting agents include salts of higher fatty acids, alkyl or aralkyl sulfates or sulfonates (in particular alkylbenzenesulfonates), fatty alcohol sulfates, and alkyl phosphates.

[0069] Preferably, the anionic wetting agent comprises at least one of an alkyl ether sulphate, an alkyl sulphate, and an alkyl benzene sulphonate. More preferably, the anionic wetting agent is selected from the group consisting of alkyl ether sulphates, alkyl sulphates, alkyl benzene sulphonates, and mixtures thereof.

[0070] The alkyl ether sulphate may be an alkali metal alkyl ether sulphate or an ammonium alkyl ether sulphate. Preferably, the alkyl ether sulphate is a sodium alkyl ether sulphate.

[0071] Preferably, the alkyl group in the alkyl ether sulphate has a chain length of 8 to 18 carbons, preferably 12 to 15 carbons, preferably 12 to 14 carbons. Such alkyl ether sulphates have a preferred size which means that they are less likely to be washed out of the growth substrate product.

[0072] Preferably the alkyl ether sulphate has an average degree of ethoxylation in the range 1 to 5, more preferably in the range 2 to 4. Use of such alkyl ether sulphates in growth substrate products show enhanced wetting properties. This is believed to be due to the larger surface tension lowering effect of such alkyl ether sulphates, which results in lower contact angles and therefore efficient and uniform spreading of water over the fibre surface (relative to more highly ethoxylated alkyl ether sulphates).

[0073] Preferably the alkyl ether sulphate has the formula:

[0074] R1O(CH2CH2O)nSO3Nawherein R1is a Cs- linear or branched, cyclic or non-cyclic alkyl group, preferably wherein R1is a C12-15 linear or branched, cyclic or non-cyclic alkyl group, more preferably wherein R1is a C12-14 linear or branched, cyclic or non-cyclic alkyl group; and wherein n is in the range 1 to 10, preferably wherein n is in the range 2 to 3. Such wetting agents display a large surface tension lowering effect, which results in low contact angles and therefore efficient and uniform spreading of water over the fibre surface.

[0075] A particularly preferred alkyl ether sulphate is sodium lauryl ether sulphate, preferably having an average degree of ethoxylation in the range 2 to 3. Such average degrees of ethoxylation are preferred as this equates to a low surface tension of sodium lauryl ether sulphate, which results in large surface tension lowering effect and therefore efficient and uniform spreading of water over the fibre surface.

[0076] The alkyl benzene sulphonate may be a linear or branched alkyl benzene sulphonate. The alkyl chain may have 5 to 20 carbon atoms. The sodium and potassium salts are preferred. This type of surfactant provides particularly beneficial water distribution properties for growth substrates of relatively large height and also provides excellent re-saturation properties and does not lead to foaming problems in the irrigation water.

[0077] Preferably the alkyl group in the alkyl benzene sulphonate has a chain length in the range 8 to 16, and more preferably at least 90% of the chains are in the range 10 to 13 and more preferably at least 90% (by weight) are in the range 10 to 12.

[0078] In one preferred embodiment of the invention, the anionic wetting agent is selected from branched alkylbenzene sulphonates. However, it is more preferred that the anionic wetting agent is selected from the group consisting of alkyl ether sulphates, alkyl sulphates, and mixtures thereof. In particular, the anionic wetting agent is preferably a mixture of alkyl ether sulphate and alkyl sulphate, such as sodium lauryl ether sulphate and sodium laureth sulfate.The total amount of anionic wetting agent present in the growth substrate of the invention may be in the range of from 0.01 to 5.0 wt. % by weight of the total solids content of the growth substrate, preferably in the range of from 0.01 to 3.0 wt. %, more preferably in the range of from 0.05 to 3.0 wt. %, more preferably in the range of from 0.05 to 1.0 wt. %, more preferably in the range of from 0.05 to 0.8 wt. %, more preferably in the range of from 0.05 to 0.5 wt. %, most preferably in the range of from 0.075 to 0.5 wt. %.

[0079] In addition to the binder and the anionic wetting agent, the growth substrate further comprises one or more salts each comprising a cation and an organic anion. In other words, the one or more salts are not anionic wetting agents and are present in the growth substrate in addition to the one or more anionic wetting agents that are present.

[0080] The one or more salts of the invention may comprise any suitable cations. If multiple salts are used, the cations of the salts may be the same or different.

[0081] It is preferred that the cations in the one or more salts of the invention are monovalent. As used herein, the term “monovalent” refers to a cation with a charge of + 1. It is thought that monovalent cations may help prevent crystallisation of the salt due to the weaker interactions between the ions compared to ions with higher valencies / charges. This may improve the mobility of the cations thereby further improving the mobility of the anionic wetting agent and preserving hydrophilicity of the growth substrate after storage.

[0082] Preferably, the cation of each of the one or more salts is independently selected from metal cations and ammonium. More preferably, the cation of each of the one or more salts is independently selected from monovalent metal cations, more preferably alkali metal cations, more preferably Li+, Na+, and K+, most preferably the cation is Na+. The preferred alkali metal cations are small and highly soluble which may improve mobility of the cations thereby further improving the mobility of the anionic wetting agent and preserving hydrophilicity of the growth substrate after storage.As used herein, the term “organic anion” refers to an anion comprising C-C and / or C-H covalent bonds, as would be understood by the skilled person.

[0083] The one or more salts of the invention may comprise any suitable organic anions. If multiple salts are used, the organic anions of the salts may be the same or different.

[0084] Examples of suitable organic anions include sulphonates, sulphates, carbonates, phosphates, and phosphonates. For example, the organic anion of each of the one or more salts may be independently selected from the group consisting of:

[0085] >

[0086]

[0087] wherein each R is independently an organic group.

[0088] It is preferred that the organic anions are stable, highly soluble, and have less tendency to crystallise in the growth substrate, from the perspective of increasing the mobility of the ions in the salts. This may further improve the mobility of the anionic wetting agent and preserve hydrophilicity of the growth substrate after storage, as discussed above. It is therefore preferred that the organic anion of each of the one or more salts is independently selected from the group consisting of:

[0089] c\zo o exzo ° z° °\ / ° R X o , R o , R o > and R X O-R, most preferably the organic anion is R X o > .

[0090] Each R may independently be any suitable organic group, such as an alkyl or aryl group. However, as discussed above, the one or more salts of the invention are not anionic wetting agents. The benefit of the one or more salts of the invention is that they may improve the mobility of the anionic wetting agent and thereby improve the ageing properties of the growth substrate, without adding additional anionic wetting agent which is not economical and could lead to wetting agentbeing leached from the growth substrates during irrigation causing foaming of the irrigation water. It is therefore preferred that the organic anions in the one or more salts of the invention are not surfactants. As such, it is preferred that each R is independently a small alkyl or aryl group.

[0091] For example, each R may be independently selected from the group consisting of:

[0092] (i) C1-C11 alkyl, preferably Ci-Cs alkyl, more preferably C1-C4 alkyl, more preferably methyl, ethyl, propyl, or butyl, more preferably methyl, ethyl, isopropyl, isobutyl, sec-butyl, or tert-butyl, most preferably methyl,

[0093] wherein the alkyl group is optionally substituted with one or more substituents independently selected from -OH and -0-(Ci-C3 alkyl), preferably -OH, -OMe, and -OEt; and

[0094] (ii) phenyl optionally substituted with C1-C4 alkyl, preferably phenyl optionally substituted with methyl, ethyl, propyl, or butyl, more preferably phenyl optionally substituted with methyl, ethyl, isopropyl, isobutyl, sec-butyl, or tert-butyl, most preferably phenyl optionally substituted with methyl,

[0095] wherein the alkyl group is optionally substituted with one or more substituents independently selected from -OH and -0-(Ci-C3 alkyl), preferably -OH, -OMe, and -OEt.

[0096] As used herein, the term “alkyl” refers to a linear, branched, or cyclic alkyl chain. As discussed above, smaller alkyl groups are preferred, such as methyl, ethyl, propyl, or butyl. For alkyl chains with more than 2 carbon atoms, it is preferred that the alkyl chain is branched rather than linear, which may help prevent crystallisation of the salt and thereby maintain mobility of the ions.

[0097] In a preferred aspect of the invention, each R is independently methyl or phenyl substituted with methyl. More preferably, the organic anion of each of the one or more salts is methanesulphonate or toluenesulphonate. More preferably, the oneor more salts comprise sodium methanesulphonate, sodium toluenesulphonate, or mixtures thereof.

[0098] In a more preferred aspect of the invention, R is methyl. More preferably, the organic anion is methanesulphonate. More preferably, the one or more salts comprise sodium methanesulphonate.

[0099] The one or more salts of the invention may be present in the growth substrate in any suitable amount. For example, the molar ratio of the one or more salts to anionic wetting agent may be in the range of from 0.1:1 to 10: 1. The molar ratio refers to the ratio of the number of moles of the one or more salts to the number of moles of anionic wetting agent. Increasing the amount of the one or more salts may increase the amount of soluble mobile cations thereby further improving the mobility of the anionic wetting agent. However, a large amount of the one or more salts may make the salts more prone to crystallisation and could negatively impact the strength of the binder. Preferably, the molar ratio of the one or more salts to the anionic wetting agent is therefore 0.5:1 to 9:1, more preferably in the range of from 1:1 to 8:1, more preferably in the range of from 3:1 to 7:1, most preferably in the range of from 4:1 to 6: 1.

[0100] The amount of the one or more salts may be in the range of from 0.01 to 5.0 wt.% by weight of the binder solids, more preferably in the range of from 0.10 to 4.0 wt. %, most preferably in the range of from 1.0 to 2.0 wt. %.

[0101] In addition to the anionic wetting agent, the growth substrates of the invention may comprise other known wetting agents such as cationic or non-ionic wetting agents.

[0102] The growth substrate of the invention may also contain other types of conventional additives in addition to the binder, wetting agent(s), and the one or more salts of the invention, for instance other salts such as ammonium sulphate and adhesion promoters such as silanes.Use of the growth substrate

[0103] The present invention also provides the use of a growth substrate according to the invention as a growth substrate for growing plants, or for propagating seeds, seedlings, or cuttings.

[0104] Method of growing plants or propagating seeds, seedlings, or cuttings

[0105] The present invention also provides a method of growing plants or propagating seeds, seedlings, or cuttings. The method comprises:

[0106] a) providing a growth substrate according to the invention;

[0107] b) positioning one or more plants, seeds, seedlings, or cuttings for growth in the growth substrate; and

[0108] c) irrigating the growth substrate.

[0109] Irrigation in step c) may occur by direct irrigation of the growth substrate, that is, water is supplied directly to the growth substrate, such as by a wetting line, tidal flooding, a dripper, sprinkler or other irrigation system.

[0110] Method of Manufacture

[0111] The present invention also provides a method of manufacturing the growth substrate of the invention. The method comprises the steps of:

[0112] a) providing man-made vitreous fibres;

[0113] b) applying the binder to the man-made vitreous fibres;

[0114] c) applying the anionic wetting agent to the man-made vitreous fibres;

[0115] d) applying the one or more salts to the man-made vitreous fibres; ande) collecting and consolidating the man-made vitreous fibres.

[0116] The man-made vitreous fibres (MMF) may be provided in step a) in any suitable manner. For example, the MMVF may be made by any of the methods known to those skilled in the art for the production of MMVF growth substrates. In general, a mineral charge is provided, which is melted in a furnace to form a mineral melt. The melt is then formed into fibres by means of rotational fiberisation such as internal centrifugal fiberisation e.g. using a spinning cup or external centrifuging e.g. using a cascade spinner, to form a cloud of fibres.

[0117] In step b), the binder is usually applied to the man-made vitreous fibres by spraying the man-made vitreous fibres with the binder composition. For example, the man-made vitreous fibres may be sprayed with a solution of the binder components in finely divided / atomised form.

[0118] In step c), the anionic wetting agent is also generally applied by spraying the manmade vitreous fibres with the anionic wetting agent. For example, the man-made vitreous fibres may be sprayed with a solution or dispersion of the anionic wetting agent in finely divided / atomised form.

[0119] In step d), the one or more salts may also be applied to the man-made vitreous fibres by spraying the man-made vitreous fibres with the one or more salts. For example, the man-made vitreous fibres may be sprayed with a solution of the one or more salts in finely divided / atomised form.

[0120] The anionic wetting agent, the aqueous binder composition, and the one or more salts may be applied to the man-made vitreous fibres simultaneously or separately. Preferably, steps b) and c) occur simultaneously. The aqueous binder composition and the anionic wetting agent may be sprayed simultaneously from separate spraying devices. Alternatively, the aqueous binder composition and the anionic wetting agent may be mixed and sprayed from the same spraying device. An advantage of the aqueous binder composition and the anionic wetting agent being sprayed substantially simultaneously is that the man-made vitreous fibresreceive a consistent amount of both the aqueous binder composition and the anionic wetting agent.

[0121] More preferably, steps b), c), and d) occur simultaneously. The aqueous binder composition, the anionic wetting agent, and the one or more salts may be sprayed simultaneously from separate spraying devices. Alternatively, the aqueous binder composition, the anionic wetting agent, and the one or more salts may be mixed and sprayed from the same spraying device. An advantage of the aqueous binder composition, the anionic wetting agent, and the one or more salts being sprayed substantially simultaneously is that the man-made vitreous fibres receive a consistent amount of the components.

[0122] As discussed above, the binder is usually a curable binder. In which case, the method of manufacturing the growth substrate of the invention may further comprise the step of:

[0123] f) curing the binder.

[0124] Curing is normally conducted by passing the consolidated fibres from step d) through a curing oven. Curing is normally conducted at a temperature of around 200 °C or greater, often at least 220 °C, for instance in the range of from 220 to 290 °C, or in the range of from 220 to 275 °C. Examples of curing temperatures are 225, 240, and 250 °C.

[0125] Method of storing the growth substrate

[0126] The present invention also provides a method of storing the growth substrate of the invention, wherein the growth substrate is stored at an elevated relative humidity.

[0127] As discussed above, storing the growth substrates of the invention at an elevated relative humidity may be beneficial in terms of maintaining a high hydrophilicity of the growth substrates after storage.Preferably, the growth substrate is stored at a relative humidity of at least 30%, more preferably at least 40%, more preferably at least 50%, more preferably at least 75%.

[0128] The growth substrate may be stored for a period of at least a week, preferably at least two weeks, more preferably at least a month.

[0129] The growth substrate may be stored at a temperature of at least 20 °C, preferably at least 30 °C, more preferably at least 40 °C.

[0130] Further information relevant to the invention is provided below:

[0131]

[0132] Ageing Phenomena in Phenolic Resin Coatings

[0133] Abstract

[0134] Effects of physical and chemical ageing on the surface wettability of hydrophilic phenol-urea-formaldehyde (PUF) coatings were studied. All individual wetting agents (WAs) were thermally stable when exposed to common cure conditions and when subjected to accelerated ageing conditions of 70 °C and 75% RH. Ageing PUF coatings at 70 °C and 75% RH has shown that the surfaces undergo post-cure reactions, seen from both a change in surface chemistry and water contact angle value. PUF coatings containing anionic WZ4s which were stored at elevated temperatures showed a moderate increase in average water contact angle value. This change was attributed to chemical and physical changes in the PUF surface layers rather than degradation of the WZAs. The substrate on which the coatings were applied was found to influence the degree of ageing at 70 °C and 75% RH of the surface wettability. When PUF-WA coatings were applied on soda lime glass, only a limited decrease in hydrophilicity was observed due to leaching of sodium hydroxide from the glass substrate. The presence of mobile sodium ions ensures mobility of the WZAs upon ageing, allowing them to remain at the coating-air interface despite the surface rearrangements of PUF. However, ageing coatings at a lower relative humidity of 19% at the same temperature of 70 °C cannot prevent the loss of hydrophilicity, regardless of the substrate that is used. Addition of sodium methanesulphonate to the resin formulation reduces ageing even of coatings on glass substrates which are not prone to leaching of sodium hydroxide. These insights provide a basis to develop tools to extend the life and service time of hydrophilic phenolic resin coatings.Chapter 4

[0135] 4.1. Introduction

[0136] In an ideal world, a given coating lasts infinitely long without the loss of its properties. The gift and curse of reality is, however, that ideal cases are more often than not rarely true. Thus, functional coatings have a finite life and service time. A change in surface functionality is broadly referred to as ageing, and can be due to weathering from thermal, UV, moisture or chemical exposure, or because of wear and physical damage. Naturally, the effect of the exposure of a material to e.g. elevated temperatures depends on the chemistry of the material. Nevertheless, detailed studies have been done to try and establish descriptions on how weathering affects physical and chemical properties of coatings [1-4],

[0137] Physical ageing describes changes in material properties due to relaxation processes of a polymer or organic coating in its glassy state, in absence of a phase change or chemical reaction [5], Such changes are reversible, as opposed to those due to chemical ageing [6-8], Physical ageing phenomena in both thermoplastics and thermosets have been studied extensively over the years, with an increasing focus on organic coatings [6, 9-15], External factors like temperature and relative humidity (RH) are also known to affect physical ageing processes [7, 16], For instance, epoxy coatings held at 0% RH developed tensile stresses over time, whereas coatings stored at 52% and 97% RH showed compressive stresses building up

[0016] , For a carboxylic acid functional polyester / triglycidyl isocyanurate powder coating, Perera [7] found that the higher the RH, the higher the rate of initial physical ageing is, but the smaller the final effect is. Physical ageing as a consequence of relaxation of polymers has been observed for phenol-formaldehyde novolac cured epoxy resins, where the relaxation behaviour is dependent on the crosslink density

[0017] , As these cured resins were found to increasingly absorb water with increasing crosslink density, it can be argued that humidity will therefore also affect the relaxation times of these resins.

[0138] Chemical ageing relates to irreversible changes as a result of, for instance, post-cure reactions, accelerated under elevated thermal conditions, or UV radiation. As a result, chain scission and further crosslinking can occur, inevitably affecting the chemistry of the coating and its surface

[0011] , The occurrence of multiple ageing phenomena at the same time can make it complex to understand on account of all the ongoing processes and the multitude of factors that contribute to them. For thermosets, chemical ageing can lead to physical ageing, i.e., post-curing reactions can induce stress inside a coating

[0018] ,

[0139] The thermal stability and ageing of phenolic resin coatings and foams has been studied previously [19-24], Even at moderate conditions (20 °C and ambient relative humidity of 40%), phenolic resin coatings age slightly

[0022] , Most notably, there is evidence of post-cure reactions occurring, even in the glassy state [22, 23], and as a result the total surface energy of these coatings decreases

[0022] , which would make the surface more hydrophobic. Okhrimenko et al.

[0024] studied the hydrothermal (liquid water) andAgeing Phenomena in Phenolic Resin Coatings hygrothermal (water vapour) stability of cured PUF binders by accelerated ageing of stone wool fibres coated with PUF in a water bath at 80 °C for 3 h, or in a climate-controlled chamber at 70 °C and 91 % RH for 7 days. A strong influence of curing time on the hydrolytic stability of the linkages between formaldehyde and methylolated urea species was found. Furthermore, a decrease in the urea content was observed, indicating limited thermal stability relative to the phenolic moieties in the polymer network

[0024] , In case of hydrophilic phenolic resin coatings, there is an additional consideration a priori ageing, namely the relative thermal stability of the wetting agents (WAs) in the resin formulation. Common industrial curing procedures for phenolic resins are at temperatures above 180 °C

[0025] , Therefore, WAs have to be thermally stable so that they can withstand cure conditions

[0026] and enable hydrophilic surfaces. Most of the ageing phenomena of coatings as described above do not explicitly consider the substrate on which the coating is applied. Even before ageing, substrates can strongly influence the distribution of additives in a coating (see also the introduction of Chapter 3) [27, 28], Evanson and Urban

[0028] studied the influence of the surface energy of substrates on the mobility of surfactants in synthetic acrylic latex copolymers. For this, poly(tetrafluoroethylene) (PTFE) and glass-like substrates were used. It was found that the low surface energy of the PTFE substrates brought forth an enrichment of surfactants at the substrate-coating interface, while on the glass-like material almost no enrichment was observed at this interface. The authors postulate that the resin does not readily wet the PTFE substrate due to the low surface energy of the substrate, and hence surfactants are required to decrease the interfacial tension between the resin and PTFE

[0028] , Continued migration of surfactants in latexes over time is also known to occur, where the nature of the substrate also influences the degree of enrichment at the coating-substrate interface

[0029] ,

[0140] In most cases, the substrate is regarded as passive or inert: it has a certain surface energy which only affects the initial additive distribution during film formation. Yet, some substrates can be regarded as ‘active’ over time. When a coating is applied on a complex glass such as soda lime, aluminosilicate, or borosilicate glass, leachables from the glass network can end up in the coating. This contrasts with fused quartz glass, with the major difference between the two being the presence of network modifiers in case of the alkali silicates (Figure 1). Conversely, fused quartz glass is without such cations.

[0141] When a complex silicate is in contact with aqueous solutions, three processes can occur

[0030] : hydration, hydrolysis, and ion exchange and migration. Hydration refers to the case where water penetrates the glass as an intact species

[0030] , Hydrolysis, facilitated by hydration of the glass, occurs when water reacts with Si-0 bonds, thereby yielding hydroxyl groups. For ion exchange, cations present in the glassy network leach into the solution upon substitution for protons from the solvent (e.g., hydroxonium ions) [31-33], leading to what is also known as glass corrosion. Hydrolysis and ionChapter 4

[0142] exchange are both dependent on the composition of the glass and pH of the solution with which the glass is in contact. While corrosion of glass is commonly studied at acidic conditions (e.g., using hydrochloric or nitric acid) [34-36], in general glass corrosion through dissolution of the silicate network is more significant below a pH above 9, whilst alkali leaching occurs mostly below pH 9 [30, 37, 38],

[0143] Figure 1. Schematic representation of the surface of (a) a complex silicate and (b) fused quartz glass. Mono- and divalent cations (orange spheres) are present at interstitial sites where there are non-bridging oxygen atoms.

[0144] Abrajano et al. [39, 40] studied how humidity affects the corrosion of silicates. Boro-and aluminosilicates were aged under severe conditions: 202 °C and 95 - 100% RH. Still, it was found that there exists a critical relative humidity above which hydration and subsequent dealkalinisation of the surface effectively occurs. Comparing the hydration layer thickness of glasses of the same composition in contact with either saturated water vapour (relative humidity 100%) or liquid water showed that the hydration layer of the latter was almost 4 times higher than that of the former. Similar glasses exposed to 47 and 58 %RH did not show any appreciable difference in hydration rate or hydration layer

[0039] ,

[0145] The actual rate-limiting step and corresponding mechanism for leaching of cations as a result of ion exchange reactions has been a point of debate for some time [31 , 41 , 42], Leaching due to ion exchange between sodium ions and hydroxonium ions has been proposed to proceed according to:

[0146]

[0147] On the other hand, it has also been observed that when water molecules react with non-bridging oxygen atoms, sodium ions are no longer bound to the glassy network and leach to form an alkali depletion layer [30, 31 , 39, 43, 44] according to:Ageing Phenomena in Phenolic Resin Coatings ==SiO'Na++ H2O - ► zzzzzzSiOH + NaOH (2) The leaching of sodium ions in this case is accompanied by the release of hydroxyl ions. This has also been shown with relatively recent reactive molecular dynamics simulations [45, 46], where contact of a simulated glass with water results in a decrease in the concentration of non-bridging oxygen content and an increase in hydroxyl ion concentration within the surface layers of the substrate.

[0148] The ion exchange and subsequent migration as discussed above is only valid for complex silicates on account of the presence of network modifiers. In case of fused quartz glass, no ion exchange can occur because of a lack of alkali-ions. Hence, even when in contact with water for prolonged times at elevated temperatures, no leaching of sodium ions from fused quartz glass will be observed

[0047] ,

[0149] Although the fundamental question of the exact rate-limiting step of glass corrosion remains discussable, it is important to note that, whichever true, both scenarios lead to the loss of sodium ions from the glass. For applications such as hydrophilic stone wool for hydroponic purposes, this is an important consideration as here the phenolic resin coats fibres made from natural rocks such as volcanic basalt glass

[0048] , From a product performance point of view, it is crucial to understand the potential impact of leached ions on the wettability of the coating.

[0150] The ageing phenomena that might occur in hydrophilic phenolic resin coatings are studied in this Chapter. Both cure conditions and long hygrothermal exposure are used to gauge if significant changes occur to WAs and phenolic resin coatings. Additionally, the ageing study explicitly involves different glass substrates to determine the influence of leachables from the substrate on the possible ageing phenomena.

[0151] 4.2. Experimental

[0152] Materials

[0153] Methyl red (MR; ACS grade), triethylamine (TEA; >99.5%), urea (U; > 99%), and phenol (P; > 99%) were obtained from Sigma-Aldrich. Formaldehyde (F) 37 wt% solution in water (including 10-15% methanol stabiliser) and sodium methanesulphonate (NaMeS; > 98%) were purchased from ThermoScientific. Ethoxylated fatty acid (EFA), branched alkylbenzenesulphonate (BAS; active substance (a.s.) 25 wt% in water), and alkyl ethoxylated sulphate (AES; active substance 27 wt% in water) were kindly supplied by ROCKWOOL A / S. Before use phenol was stored at room temperature under Ar atmosphere and with P2O5in a desiccator. All other chemicals were used as received.Chapter 4

[0154] Silicon wafers (Si-W) were single sided polished and purchased from Siegert Wafers. Soda lime glass (SL) microscopy slides were obtained from Merck (Epredia™ Superfrost™) and the fused quartz (QZ) substrates were purchased from ThermoScientific. Stone melt wafers (SMW) were kindly supplied by ROCKWOOL A / S, and mechanically polished and cut into 1 x 1 cm substrates.

[0155] Resin Synthesis and Binder Preparation

[0156] PUF-TEA and PF-TEA were synthesised as described in Chapter 3, and will henceforth be called PUF and PF. Commercial PUF-KOH resin was used to prepare coatings with and without wetting agents.

[0157] PUF resin with dye (PUF-MR) was prepared by addition of methyl red (MR; 16 mg / 25 g resin) and using a vortex mixer until the dye was dissolved. PUF-MR coatings were applied on both soda lime glass and fused quartz glass. Coatings of PUF, PUF-AES, and PUF-BAS were applied on soda lime glass, fused quartz glass, Si wafers, and stone melt wafers. EFAwas not considered for these experiments, on account of its demixing upon curing.

[0158] PUF-WA-NaMeS coatings were prepared by addition of a molar excess of NaMeS relative to AES and BAS (nNaMeS= 5 • nWA). For PUF-AES, this amounted to 0.0176 g NaMeS / g PUF and for PUF-BAS, this amounted to 0.0191 g NaMeS / g PUF.

[0159] Silicon wafers were cut to a similar size as the soda lime glass microscopy slides. Prior to coating application, the fused quartz and silicon wafers were stored in isopropyl alcohol at room temperature for at least 1 day. Substrates were cleaned by wiping with lint-free paper and subsequently blowing the surface with air. To enable facile dip coating of the stone melt wafers, they were first adhered to piece of Si wafer using PUF resin which was subsequently cured for 20 minutes. Then, the surface of the stone melt wafers were cleaned with acetone and ethanol, consecutively, before dip coating. After dip coating using a withdrawal speed of 100 mm / min, all coatings were cured in a semiclosed chamber at 150 °C for 20 minutes under an N2flow of approximately 150 L / h at 1 bar.

[0160] Thermal Studies of Wetting Agents

[0161] Hygrothermal ageing of wetting agents was performed by placing vials with approximately 4 g of WA in a desiccator with a saturated NaCl solution in an oven at 70 °C. Samples were aged for up to 28 days, after which they were dried in a desiccator with P2O5for 3 days. The WA structure after ageing was studied with ATR-FTIR and1H-NMR. To determine the CMC of the aged wetting agents, after drying, they were redissolved in MilliQ water to restore the original active substance.

[0162] For experiments where WAs were exposed to temperatures commonly used for curing phenolic resins, 8 mL of WAwas added to a 200 mL flask. Samples were then placed inAgeing Phenomena in Phenolic Resin Coatings an oven at 200 °C for 10 and 30 minutes. Finally, wetting agent structure and performance was studied with ATR-FTIR and1H-NMR, and SFT measurements, respectively. In case of BAS and AES, some samples were frozen in liquid nitrogen and subsequently dried using a Christ Alpha 1 -4 LDplus at approximately -50 °C and 0.15 mbar for at least 48 hours.

[0163] Hygrothermal Ageing of PUF Coatings

[0164] For all ageing procedures, coatings were stored in a desiccator containing a saturated NaCl or LiCl solution, providing an environment with a theoretical relative humidity of approximately 75% and 11 % RH, respectively

[0049] , Relative humidity and temperature of samples was recorded over the course of the experiment with an Ebro EBI 20-TH1 logger (see Figure 18). The accuracy of the loggers was ± 0.8 °C and ± 3% RH.

[0165] Before the start of the hygrothermal ageing experiments of PUF coatings, the WCA of coatings without WAs was determined from two measurements on two different spots per coating. For PUF-BAS and PUF-AES coatings, 1 measurement per coating was performed. The average of all measurements was used as the average WCA value before ageing, i.e., day 0. After performing the reference WCA measurements, coatings were aged at 75% RH and room temperature or 70 °C. Coatings were taken out of the desiccator after a set amount of time, and subsequently 7 - 9 WCA measurements were performed to determine the average WCA value and standard deviation after ageing. The measurements performed on individual coatings were used to determine the change in hydrophilicity (AWCA) of each specific coating as a result of the ageing (i.e., on individual basis):

[0166] AWCA = WCA),=i- WCA)(l, (4.1)

[0167] where WCA^0indicates the WCA value of coating n before ageing (t = 0), and WCA„=1the WCA value of that same coating n after ageing for i days (t = i).

[0168] For the ageing of PUF-MR coatings two desiccators were used, with a saturated NaCl solution to keep the inside at 75% RH. One of these desiccators was placed in an oven at 70 °C whilst the other was kept at 20 °C ± 0.5 °C (room temperature). For ageing of PUF(-WA) coatings on different glass substrates, only ageing at 70 °C was done, either exposing samples to 75% RH or 20% RH.

[0169] Salt-Doped Coating Preparation

[0170] Salt-doped PUF(-WA) coatings were prepared by addition of 0.0248 g K2SO4 / g PUF resin and stirring the solutions until the salt was completely dissolved. The resin was applied by means of dipcoating on glass substrate and cured in either an oven or semiclosed chambers as described in Chapter 2.Chapter 4

[0171] For each coating, several droplets of water (each approximately 2 pL) were placed on the surface and evaporated in air under ambient conditions. This way, both the crystals that dissolved and were redistributed by the presence and evaporation of water, as well as the crystals in surface layers, could be monitored over the course of the experiment.

[0172] Thermogravimetric Analyses

[0173] Thermogravimetric analyses (TGA) were performed on a TA Instruments Discovery TGA 550. PUF resins were measured under N2, and WAs were measured under both N2and air. In case of BAS and AES, samples were first held at 120 °C for 60 minutes to evaporate water. The first mass recorded after this isotherm was set to 100% of the sample weight. Subsequently, sample mass changes were recorded when heating at a rate of 10 °C / min to 700 °C.

[0174] UV-Vis Spectrophotometry

[0175] UV-Vis measurements on liquid samples were performed on a Shimadzu UV 2700 spectrophotometer. For the PUF-MR coatings, UV-Vis measurements were done on a Perkin Elmer Lambda 750 UV / Vis / NIR spectrophotometer. Depending on the coating substrate, either soda lime or quartz glass was used as the baseline.

[0176] Water Contact Angle Measurements

[0177] Water contact angle (WCA) measurements were performed as described in Chapter 2. The reported results are, in general, the average of at least three measurements per coating, on at least two coatings per formulation, includingthe standard deviation. Due to the small size, typically only two measurements per coating on the stone melt wafers was performed.

[0178] X-Ray Photoelectron Spectroscopy

[0179] Coating and substrate composition was determined with X-ray photoelectron spectroscopy (XPS), for which the measurements were largely performed as described in Chapter 2. For measurements on uncoated soda lime glass, quartz glass and stone melt wafers, the average number of survey and detailed scans was set to 50, and a pass energy of 50 eV and a step size of 0.1 eV (0.5 eV for the survey scans) was used. Binding energy spectra were recorded with the ThermoFisher Scientific Avantage software and subsequently analysed with CasaXPS. A Shirley background and relative sensitivity factors for each element (RSFcis = 1, RSFois = 2.881, RSFN ls= 1.676, RSFAl2p= 0.56, RSFCa 2p= 5.970, RSFMg 1s= 14.941, RSFNa 1s= 10.588, RSFsi 2p= 0.9, RSFK2p= 4.671, RSFFe 2p= 14.35) were used to obtain relative atomic percentages. Reported values areAgeing Phenomena in Phenolic Resin Coatings the average of at least two measurements, each performed on a different location of the sample. Reported errors are the corresponding standard deviation based on at least two measurements.

[0180] Dynamic Vapour Sorption

[0181] Mass changes of PUF and PF powders exposed to different relative humidity values at 25 °C were measured on a Surface Measurement Systems DVS Revolution II. Prior to each measurement, samples were stored in a desiccator with P2O5. Measurements consisted of a drying step at 0% RH for at least 60 minutes, after which the relative humidity was increased to 75%. Measurements were stopped when the change in mass was more or less negligible (i.e., when mass changes were smaller than 0.001%). Free standing PF films were prepared by adding a small quantity of resin to an aluminium cup, and subsequently curing the resin in the semi-closed chamber at 150 °C for 20 minutes under N2. The hardened resin could easily be separated from the cup afterwards, and was cut to size (approximately 5 mm diameter). The resulting films were then used for the determination of the water diffusion coefficient.

[0182] Crank and Park

[0050] derived, for a plane sheet, that the ratio of sorption for a single side at time t to sorption at equilibrium is1

[0183]

[0184] where Mtis the amount of vapour adsorbed at time t, Mmthe amount of vapour adsorbed at equilibrium, D the diffusion coefficient, d the film thickness and t the time. Using Equation 4.2, the diffusion coefficient can be determined when considering the slope of the plot of — versus — , taking into account that for the Payne cell setup a

[0185]

[0186] humidity gradient was used (meaning that the experiment was single-sided, e.g., only sorption from one face of the film):

[0187]

[0188] 1ln the book ‘Diffusion in Polymers’

[0050] , ‘it’ has been misplaced in the printed equation in Chapter 5: The Glassy State and Slow Process Anomalies. The correct equation is given in Chapter 1 : Methods of Measurement as equation 36, as well as in

[0051] .Chapter 4

[0189] Typically, the fit for the slope is only considered valid for the first stage of diffusion, up to Mt = 0.5

[0051] , Reported results were obtained over the range 0.1 < Mt < 0.4, with

[0190]

[0191] R2=(L990.

[0192] The flux of vapour J through a film can be defined with Fick’s law of diffusion

[0052]

[0193] 1 dm ,AJ = - • — , (4.4) A dt

[0194] where A is the area of the film and

[0195]

[0196] the mass change over time, which can be determined from sorption data as measured with DVS.

[0197] The flux through a film can also be defined when there is a pressure difference Ap across the film

[0050] , which in turn is related to the relative humidity:

[0198] _ PAp _ P (p0RH75— pgRHg) _ P ■ p0RH75

[0199]

[0200] J~ ~d~ ~ d ■ 100 “ d ■ 100 ’ with P the permeability, p0the pressure at 100 % RH, RH75the relative humidity of 75% and d the film thickness.

[0201] Hence, relating Equations 4.5 and 4.6, the permeability can be calculated by

[0202] d ■ 100 1 dm

[0203] P = - . (4.6) p0RH75A dt

[0204] Last, the permeability and the diffusion coefficient are linked via the solubility by the relation

[0050]

[0205] P

[0206] (4.7)S= D

[0207] Surface Tension Measurements

[0208] Surface tension (SFT) measurements were performed according to the method in Chapter 3, and results supplemented by the calculation of the adsorbed amount:

[0209]

[0210] where R is the gas constant, T the temperature of the solution, y the surface tension and c the concentration of WA.Ageing Phenomena in Phenolic Resin Coatings 4.3. Results and Discussion

[0211] Hygrothermal Stability of Wetting Agents

[0212] Thermal stability of WAs was evaluated by TGA in both air and N2, and additional experiments were done by keeping samples of WA at temperatures similar to common cure temperatures of phenolic resins (200 °C). A detailed description of the results can be found in the Appendix of this Chapter, but the most important observation was that there was no convincing indication of degradation occurring for WAs exposed to temperatures below 200 °C.

[0213] To study long-term stability of WAs, samples were hygrothermally aged by exposing them to 70 °C and 75% relative humidity for up to 28 days. Physical changes occurred to some of the WAs over the course of the ageing procedure (Figure 2). Most notably, AES and BAS became more solid-like upon ageing due to the loss of water. After 1 day of ageing, AES in fact had already become a gel, after which it turned into a white paste. Eventually, after 28 days a gel had once again formed. The morphology of AES with varying degrees of ethoxylation is known to undergo several changes depending on the relative amount of water [53-55], Similar observations have been made for BAS, of which the phase behaviour is affected by both the counterion and amount of water

[0056] ,

[0214] Figure 2. Visible physical changes of WAs after exposure to 70 °C and 75% RH. After 28 days of ageing, addition of water to BAS and AES resulted in a physical state similar to that of unaged WA.

[0215] Examination of the ATR-FTIR and1H-NMR spectra of the WAs shows no significant discernible differences (Figure 3). However, intermittent analyses indicated variations in samples of AES aged for 14 and 28 days (Figure 22). Since no chemical changes were seen in the corresponding1H-NMR spectra, these differences are likely a result of the variations in the structural ordering of AES [57, 58],

[0216] EFA, comprised of ethoxylated linoleic acid, turned to a darker orange colour upon ageing. It has been reported_previously that heating oleic acid will result in the darkening of the oleic acid

[5962] , This is a result of oxidation which is enhanced by the presence of minor constituents (e.g., C46H76O13and C24H41O7)

[0061] ,Ageing Phenomena in Phenolic Resin Coatings

[0217] Figure 3. ATR-FTIR and1H-NMR spectra of (a) AES, (b) BAS, and (c) EFA before and after ageing at 75% RH and 70 °C for 28 days.

[0218] Depending on the type of minor constituent, the colour stability of oleic acid is already severely affected for concentrations of as low as < 1.0%

[0060] . The ATR-FTIR spectra of EFA in Figure 3c show the emergence of a peak 1648 cm'1upon ageing. On one hand, this could correspond to the C=C stretch of conjugated double bonds, which would make sense given the colour change and oxidation of EFA. On the other hand, an increase in the signal at 3462 cm'1is observed, which together with the increase at 1648 cm'1suggests the presence of water. Drying aged EFA samples in a desiccator with P2O5shows that the removal of water results in a decrease in both signals. The reverse was also observed; an increase in sample mass was detected only for EFA upon ageing, implying the uptake of moisture (Figure 23). Conversely, a mass loss for BAS and AES was measured due to the evaporation of water from their solutions. Last, it should be noted that the1H-NMR spectra of aged EFA also shows the presence of water through the broad signal observed at 2.6 ppm. Overall, although physical changes of EFA were noticeable, the chemical changes were minor.

[0219] Despite there being differences between the CMC of the unaged and aged WAs, and hence some variation in their efficiency, the effectiveness as evaluated by the surface pressure was more or less the same (Figure 4 and Table 4.1). The strongest change for the anionic WAs was for their maximum adsorbed amount at the water-air interface, where typically an increase was seen. All in all, the WAs used in this study are quite stable at the chosen accelerated ageing conditions.

[0220] Figure 4. Surface tension as a function of the WA concentration before (filled symbols) and after (open symbols) ageing the WAs at 70 °C and 75% RH for 28 days. Lines represent linear fits which were used to determine the critical micelle concentration.Chapter 4

[0221] Table 4.1. CMC, surface pressure at the CMC, and the adsorbed amount of wetting agents at 20 °C before and after ageing the wetting agents at 70 °C and 75% RH.

[0222]

[0223] Hygrothermal Ageing of Phenolic Resin Coatings

[0224] With the obtained understanding of the stability of the WAs under hygrothermal conditions, the foundation for subsequent ageing experiment has been laid. Therefore, the extent of ageing of phenolic resin coatings was studied next.

[0225] Thermogravimetric measurements of cured PUF-KOH, PUF, and PF resins are shown in Figure 5. PUF-KOH and PUF which were cured at 200 °C show a similar degradation profile, which matches with data from literature [24, 63], However, for the PUF powder cured at 150 °C a slightly stronger mass loss up to 350 °C was seen. Because the final mass change at 600 °C is similar independent of the cure temperature (Tc), the initial difference in mass loss is likely the result of post-curing reactions through which for instance formaldehyde and water are liberated.

[0226] Figure 5. Mass change of PUF-KOH, PUF, and PF powders as function of temperature (purge gas is mentioned in legend). Resins were cured at either 150 °C or 200 °C (TG).Ageing Phenomena in Phenolic Resin Coatings Although TGA reveals a decent thermal stability of the resins at moderate temperatures, it does not give insight into the stability against ageing per se. Therefore, PUF-KOH coatings with and without WAs were stored at elevated temperature (70 °C) and relative humidity (75% RH) over the course of 28 days, during which their surface wettability was monitored (Figure 6). Notably, PUF-KOH coatings became more hydrophobic after 14 days of ageing, indicating a possible post-cure reaction. While it is assumed that after curing the PUF matrix is more or less vitrified, post-cure effects are believed to be facilitated by the elevated relative humidity and the associated plasticisation of the surface layers. The resulting maturing of the network and surface presumably leads to an evolved state of cure where most of the dimethylene ether bridges have been converted to methylene ether linkages, increasing the water contact angle values of these coatings. These phenomena will be addressed in more detail in later sections.

[0227] Figure 6. Water contact angle values of PUF-KOH(-WA) coatings before and after storage at 70 °C and 75% RH. For PUF-KOH-EFA, coatings measured after 7 and 14 days showed immediate wetting, hence the contact angle was set to 0. Differently than for Chapter 2, 0.37 wt% of coupling agent 3 -amino propylsilanetriol (APS; 40 wt% in water, kindly provided by Grodan) was added to the binder formulations to avoid delamination.

[0228] PUF-KOH-BAS coatings showed a gradual increase for prolonged ageing times, although for samples aged between 1 and 7 days, the average contact angle value was somewhat lower than typically expected. It is likely that this is not because of the ageing procedure, but rather variations from the samples as a result of fluctuations in crystal number density and distribution, in turn also surface wettability. For PUF-KOH-AES, there appears to be an increase in the hydrophobicity with increasing ageing time,Chapter 4

[0229] which levelled off after 2 days. Regarding coatings of PUF-KOH-EFA, large variations in wettability were observed already before ageing. Compared with PUF-EFA counterparts (see e.g. Chapter 3), the differences in surface wettability obtained here were significantly larger. Most probably, the presence of crystals in PUF-KOH coatings and the immiscibility of EFA with the resin during the cure strongly influences the distribution of EFA on the surface, leading to vastly heterogeneous coatings.

[0230] Surface changes of PUF-KOH(-WA) coatings were also monitored with optical microscopy (CM). More specifically, the stability of crystals on the surface and in surface layers was assessed for coatings exposed to elevated temperatures and relative humidity for up to 117 days. Salt-doped TEA-containing PUF coatings were also included in this ageing study, on account of a higher affinity of water vapour to PUF compared to PUF-KOH, as measured with dynamic vapour sorption (DVS; see also Figure 24). Whilst changes in crystal morphology and wetting agent distribution were observed after direct contact with liquid water and subsequently drying the coating surfaces, changes in crystal morphology and number density due to moisture uptake might also affect surface characteristics of the phenolic resin coatings.

[0231] Over the course of 117 days, none of the samples showed signs of physical ageing (Figure 7 and Figures 25 and 26). This is not necessarily surprising given that the deliquescence point of K2SO4is known to be > 95% RH [49, 64, 65], However, even in presence of WAs, the K2SO4crystals both on top of the coatings and buried in the surface layers were remarkably stable. While organic compounds such as surfactants can reduce the deliquescence point of salts [66, 67], this effect is typically only moderate. Hence, humidity-induced physical ageing will most likely not manifest itself through changes in the K2SO4crystals, even in the long-term.

[0232] The next step therefore was to omit these crystals and study the ageing of phenolic resin coatings without crystal-induced roughness and crystal-affected distribution of wetting agents. To this end, PUF(-WA) coatings were prepared and stored at elevated relative humidity of 75%, either at room temperature or at 70 °C. Prior to ageing it was found that the average WCA value of PUF coatings prepared for the ageing experiments was lower than could reasonably expected based on previous results (see Chapter 2 and Chapter 3), with an increased standard deviation. This had been the case for multiple batches within the span of several weeks, where no obvious differences in carrying out the synthesis and coating procedure were made. It is thought that the external conditions during curing, such as relative humidity, play an effect in resulting surface properties. PUF-WA coatings on the other hand were relatively consistent with earlier results (for instance, as described in Chapter 3), indicating that the WAs thoroughly mask the inherent surface wettability of the phenolic resin coating.

[0233] Acknowledging this different surface wettability of PUF coatings at the start of the experiment, it was interesting to see that already after 1 day for both ageing temperatures the WCA values increased (Figure 8). Moreover, the standard deviationAgeing Phenomena in Phenolic Resin Coatings decreased. In partthisis because of an increasedamountof datapointsforthe average (9 versus 2), however, the overall changes point toward some relaxation or rearrangement effect that occurs in the surface layers. Specifically, the decrease in wettability and increase in reproducibility for PUF coatings aged at 20 °C seem to indicate a physical ageing effect rather than a chemical one, enabled by the constant exposure to elevated relative humidity.

[0234] Figure 7. Optical micrographs of (a) PUF-KOH, (b) PUF-KOH-EFA, and (c,d) PUF before and after storage at 75% RH and 70 °C for 117 days. Scale bar: 125 pm.Chapter 4

[0235] For example, it has been reported that absorption of water into films of poly(lactic acid) increases the segmental mobility by disruption of the network (e.g., increasing the free volume) and hence facilitating rearrangements

[0068] , Water absorption and plasticisation of PUF and PF has been observed both in this work (Chapters 2 and 3) and in literature

[0069] , and could therefore also aid the relaxation of the PUF surface layers.

[0236] Figure 8. Average WCA values of PUF(-WA) coatings before and after storage at 75% RH, either at room temperature (closed symbols) or at 70 °C (semi-closed symbols).

[0237] The consequences of plasticisation do not rule out chemical ageing from occurring, however. Table 4.2 shows the surface composition of the PUF coatings after hygrothermal ageing for 1 and 77 days obtained from XPS analyses. The changes in surface chemical composition for coatings held at elevated temperature are reminiscent of the changes seen between coatings cured at 150 °C versus 200°C (Chapter 2). Indeed, the CO / CC ratio decreases upon ageing at high temperatures and the PUF surfaces become more hydrophobic. Changes in the CO / CC ratio are inherently linked to changes in the N:C and O:C ratios, and as such it follows that these decrease upon ageing, too. No noteworthy changes in surface chemical composition can be discerned for PUF coatings stored at room temperature, in line with the largely unaffected WCA values.Ageing Phenomena in Phenolic Resin Coatings PUF-AES coatings which were stored at 70 °C were always measured first after taking them out of the desiccator. As a result, it can be seen that even at 75% RH a response of AES towards humidity can be observed. This response to humidity has already been discussed in Chapter 3, and is believed to be due to aggregation of the WA at the coating surface. The decrease in hydrophilicity seen for PUF-AES coatings exposed to elevated temperatures is observed to varying degrees, and seems to be somewhat inconsistent.

[0238] Table 4.2. Surface composition of PUF and PUF-AES surfaces as determined with XPS after hygrothermal ageing for 1 and 77 days. Standard deviations which were insignificant are omitted.

[0239]

[0240] The surface composition of PUF-AES coatings was also measured with XPS (Table 4.2), however, the detection of wetting agent in the surface layers through the sulphur content was proven to be unreliable. As BAS and AES only have one sulphur atom per molecule which chemically distinguishes them from the bulk, the S : C atomic ratio is rather low. Interestingly, a strong difference was again observed for the N : C atomic ratio, indicatingthat possible rearrangements of urea moieties in the surface layers has a more pronounced effect on the changes in hydrophilicity than the WAs themselves. A similar decrease in CO / CC ratio is seen for PUF-AES and PUF. This substantiates the hypothesis that changes in wettability are not due to chemical ageing of the WAs, but rather a result of chemical and physical ageing processes of the PUF surface.

[0241] For PUF-BAS coatings, there appears to be an effect of thermal exposure for a longer period (> 50 days) on the overall wettability (Figure 8). While initially this increase might be slightly surprising on account of the thermal stability of BAS, especially compared to EFA and AES, based on the results of previous ageing experiments the observed changes indicate no chemical change from a WA point of view but rather a physical ageing by depletion from the coating-air interface. Such a depletion could be enabled by the water plasticisation effects of the surface layers of the PUF coating, resulting in the migration of WAs deeper into the surface layers (see also Chapters 2 and 3).

[0242] Finally, the wettability of PUF-EFA coatings was relatively unaffected by the ageing procedure. In general, WCA values between 0 (indicating virtually immediate and complete wetting) and 20 degrees were commonly observed for these coatings (Figure 8). Overall good hygrothermalstabilitywas already evident from the ageing studiesChapter 4

[0243] performed on pure EFA, which is also observed here. It is possible that the underlying PUF surface has changed, but that these changes are masked by the phase separated WA.

[0244] Calculating the difference in WCA values (AWCA; see also Equation 4.1) of the aged samples and the same but unaged samples (measured before the start of the experiment) shows in more detail a clear effect of ageing at elevated temperature. Some interesting features can be observed when comparing the AWCA values of coatings aged at 20 °C (Figure 9a,c,e) with those of coatings aged at 70 °C (Figure 9b,d,f).

[0245] Figure 9. The difference (A) in WCA values between aged and unaged PUF(-WA) coatings, for coatings exposed to either (a,c,e) 20 °C or (b,d,f) 70°C. Lines between datapoints have been added to guide the eye.

[0246] Although datapoints are connected with a line to guide the eye, it appears that PUF and PUF-BAS coatings change similarly over time. Despite the absolute values still being relatively different, the trend is comparable. This could imply that the change in WCA observed for BAS is indeed related more to the ageing of the PUF matrix, rather than of the WA itself. In general, all PUF samples kept at 70 °C show an increased WCAAgeing Phenomena in Phenolic Resin Coatings compared to unaged coatings, although it somewhat varies when this increase sets in exactly. This is most likely due to post-curing effect which is facilitated by the plasticisation as a result of the high relative humidity. The difference between unaged coatings and those aged at 20 °C is definitely smaller and can be seen to be slightly more constant than for the coatings aged at 70 °C.

[0247] Influence of Substrate on Ageing of PUF Coatings

[0248] The possible influence of the type of substrate on the surface characteristics of PUF(-WA) coatings was monitored first by using two different glasses: fused quartz glass and soda lime glass. Possible changes in the acidity of the coating matrix were monitored using the pH-sensitive methyl red (MR) dye, although this does not directly provide information regarding changes in surface properties (Figure 10a). The selection of a suitable dye was based on its availability, solubility in the resin formulation, and its sensitivity or colour range. In accordance with literature [70, 71] the absorption spectrum of MR in solution is dependent on the pH, with absorbance peaks visible at 522 nm (acidic media) or 432 nm (basic media). For the transition region between pH 4.4-6.2, contributions from both peaks can be seen.

[0249] Figure 10. Absorption spectra of (a) MR in water at varying pH and (b) PUF-MR coatings exposed to either an acidic or basic medium.

[0250] Incorporating MR into the PUF resin yielded coatings which were responsive to their environment, as also reported by Villegas and Pascual

[0070] for silica coatings doped with this chromophore. Exposure to a basic or acidic environment yielded a change in coating colour (Figure 10b). This responsiveness was seen for both direct immersion in a medium and after exposure to basic or acidic vapour (ammonia and acetic acid,Chapter 4

[0251] respectively). Additionally, the inclusion of MR also allowed to further corroborate a crucial step during the cure process of PUF resin: acidification. Just after dip coating, applied PUF layers were yellow. Over the course of the hardening process, evaporation of TEA shifted the pH towards acidic values, evidenced by a purple colour of the coatings. After the complete cure time, slight basification had evidently occurred as the coatings were orange, indicative of a pH value in the transition region.

[0252] Although there is some discrepancy between the location of the peak maximum for the given data of methyl red in solution and in coatings, the relationship of peak location with pH still holds true and shows the viability for using the MR dye in PUF coatings. Next, coatings of PUF-MR on soda lime and fused quartz glass were prepared and aged for 45 days at 75% RH, either at 20 °C or at 70 °C. Prior to this, the UV-Vis absorption spectra of coatings was measured, where no obvious differences between coatings on fused quartz and on soda lime glass could be discerned (Figure 11). Main features that were seen for coatings on both glasses were the presence of an absorption peak at 420 nm and one at 530 nm, indicating an intermittent pH of the matrix between 4.4 and 6.2. Naturally, because the peak at 420 nm has a larger intensity than the one at 530 nm, the matrix pH is estimated to be more on the basic side of this pH range. The small difference in how pronounced the peak at 530 nm is (also observed when comparing Figure 10b with Figure 11) is likely due to coating-to-coating variations. Especially in the transition region, slight changes in pH can elicit strong changes in the absorption spectrum (also seen for pH = 5.4 and pH = 5.9 in Figure 10a).

[0253] Interestingly, it appears that there is an influence of the substrate on the pH upon ageing. For PUF-MR on soda lime glass, the peak at 530 nm disappears, whilst for PUF-MR on fused quartz glass only a slight decrease in intensity is observed. This modest decrease is likely an effect of post-curing and evaporation of residual TEA, which will be discussed more in the next section.

[0254] Figure 11. Normalised absorption spectra of PUF-MR coatings on (a) soda lime (SL) or (b) fused quartz glass (QZ) before and after ageing at 75 %RH at either room temperature or 70 °C for 45 days.Ageing Phenomena in Phenolic Resin Coatings Comparing PUF-MR held at 75% RH at RT on both substrates, it can also be seen that there is a slight decrease in peak intensity at 530 nm for the coating applied on soda lime glass. Possibly, the coating and curing procedure already induces leaching of Na+and OH' ions, resulting in the eventual alkalinisation. Only at elevated temperatures, however, this continuous leaching and diffusion is sufficient to induce further changes. The leaching and migration of sodium ions from the glass substrate could possibly also be facilitated by water vapour during the ageing process. As such, a note regarding the permeability of PUF coatings to water vapour is implemented in the Appendix.

[0255] Influence of Substrate on Ageing Process

[0256] To test if the observed changes in the pH of the polymer matrix influence the surface properties, coatings of PUF-WA were applied on four different substrates: soda lime glass, fused quartz glass, silicon wafers and stone melt wafers. By comparing soda lime with fused quartz glass and silicon wafers, the influence of ion leaching on the ageing process of PUF(-WA) coatings can be determined. Soda lime has hitherto been used as a model glass substrate to approximate the chemistry of stone wool fibres. Here, to extend the research, wafers made from a stone melt have been used as substrate which is chemically closer to stone wool substrates. The approximate composition of the different glassy substrates was determined with XPS. Despite cleaning, all samples showed the presence of an adventitious carbon layer (5.4 ± 2.0 at%). This layer, however, did not appear to affect the ratio of network modifiers and network formers relative to Si (Table 4.3; carbon not shown).

[0257] Table 4.3. Average composition of soda lime (SL) glass, stone melt wafers (SMF) and quartz glass (QZ) as determined with XPS. Composition was normalised to Si. Standard deviations which were insignificant are omitted.

[0258] "

[0259]

[0260] Only a trace amount of sodium was detected for the fused quartz substrates. The composition of soda lime glass and the stone melt wafers was quite different from one another. Quite distinct are the elevated calcium and aluminium content of the SMWs compared to soda lime glass, in line with typical stone wool substrates[48, 72], It is well-documented that the composition of a glass affects corrosion and leaching [32,Chapter 4

[0261] 37, 73-76], On that basis, a different ageing behaviour between coatings on SMWs and SL substrates is to be expected.

[0262] Reference contact angle measurements were performed before storing coatings of PUF-WA in a desiccator with a saturated NaCl solution (providing an environment of 75 % RH) at 70 °C. After 45 days, coating surfaces were probed with water droplets again to determine possible changes in the surface wettability.

[0263] As shown in Figure 12a, all PUF coatings free of WAs on SL, QZ and Si-W show a similar increase in water contact angle value upon ageing. Comparing the surface composition of the unaged and unaged PUFcoatings on soda lime, itwould seem that a decrease in both the nitrogen and oxygen content contributed to the observed ageing (Table 4.4). Consequentially, the CO / CC ratio is lower than for unaged PUF coatings. In fact, the O:C and CO / CC ratios match well with those reported in Chapter 2 for coatings cured at 200 °C and 150 °C.

[0264] Table 4.4. Average composition as determined with XPS of PUF coatings on SL, QZ, and SMW substrates, before and after ageing at 70 °C and 75% RH for 45 days. The full width at half -maximum (FWHM) of the O 1 s binding energy spectra has only been determined for PUF coatings without WAs. Standard deviations which were insignificant are omitted.

[0265] "

[0266]

[0267] A notable difference is the average full width at half-maximum (FWHM) of all the O 1s binding energy spectra, which for coatings on SL and QZ were rather inconsistent after ageing. Thus, contributions from oxidation to surface changes cannot be completely excluded for these coatings. The coatings on the stone melt wafers conversely do not show a drastic change in FWHM upon ageing. However, should oxidation occur for allAgeing Phenomena in Phenolic Resin Coatings coatings, there is no obvious explanation for why coatings on SMW would be exempt from oxidation.

[0268] Interpretation of the O:C ratio (and thus inherently also the N:O ratio) and CO / CC ratio for PUF-AES and PUF-BAS is challenging, as the changing presence of WAs at the coating-air interface introduces an extra factor affecting these ratios. In part because of this, there does not appear to be a discernible trend regarding the CO / CC ratio and substrates for the PUF-WA coatings.

[0269] The difference in surface chemistry between PUF on SLand on SMW was also reflected in the surface wettability. As shown in Figure 12a, the unaged PUF-SMW coatings are more hydrophobic than the usual PUF coatings, with an average water contact angle value of 80.8° ± 2.8°. Not only does this yield a vastly different starting point for the ageing of these coatings, but the end point is also significantly different. After 45 days, coatings appeared to increase even further in their hydrophobicity up to a water contact angle value of 96.3° ± 1.4°. However, it was found that the origin of this large initial WCA value was the size of the substrates (see also Figure 28 and corresponding considerations in the Appendix). The smaller substrate size results in a larger edge-to-area ratio of the applied coatings, which in turn is presumed to strongly affect evaporation of TEA, formaldehyde and H2O, and hence affects curing and the WCA value.

[0270] Figure 12. Average WCA values before and after ageing of (a) PUF, (b) PUF-AES and (c) PUF-BAS coatings on soda lime glass, fused quartz glass, Si wafers, and stone melt wafers at 75% RH and 70 °C for 45 days.Chapter 4

[0271] For coatings with AES and BAS, only limited ageing was observed for the coatings applied on soda lime glass (Figure 12b,c). For the aged PUF-AES and PUF-BAS coatings on fused quartz and silicon wafers, the average water contact angle value was similar to that of unaged PUF. Although for PUF-AES and PUF-BAS coatings on SMWs the presence of WAs somewhat masked the effects induced by the smaller substrate size, upon ageing the wettability decreased even more relative to coatings on QZ and Si-W.

[0272] In light of the previously established hygrothermal stability of the WAs as well as these results, degradation of the WAs upon ageing again appears unlikely. Although mobility of these anionic WAs was not readily observed (see Chapter 3), the coating surface appears to become significantly less enriched with WAs after ageing on fused quartz glass, silicon wafers, and stone melt wafers. Presumably, the PUF matrix plays an important role in this process, as it is seen to change in surface chemistry and wettability.

[0273] One possibility is that the surface plasticisation by water allows for sufficient mobility of the WA through the surface layers, away from the coating-air interface. In case of coatings on soda lime glass, however, the leaching of NaOH introduces additional charges into the coating, which fixate the wetting agents at the surface. Another possibility is that the introduction of mobile charges from the soda lime glass leads to enhanced mobility of the wetting agents in the surface layers. Without such charges, wetting agents become fixated in deeper surface layers upon ageing. This fixation occurs through the presence of quaternary ammonium ions (e.g., TEA+or hexamethylenetetramine*), which can still be present in the cured matrix (Figure 13).

[0274] Figure 13. Schematic representation of hypotheses of the ageing mechanism on (a) soda lime glass, where ageing is inhibited due to the leaching of mobile charges from the substrate, and (b) fused quartz or silicon wafers, where ageing is observed due to the lack of wetting agent immobilisation due to the absence of leached, mobile charges from the substrate.Ageing Phenomena in Phenolic Resin Coatings To corroborate these hypotheses, the sodium content of coatings on different substrates was determined. The initial and final WCA value and Na:C ratio of the coatings are presented in Table 4.5, and detailed Na 1s binding energy spectra can be found in Figure 29. For coatings on soda lime, the Na content mostly remained similar or increased slightly after ageing. For PUF-AES and PUF-BAS, it was assumed that the initial Na:C ratio of the coatings on QZ substrates was similar to coatings on SL substrates. This is indirectly verified by the fact that initial WCA values of coatings on both types of substrates are similar. Based on this assumption, the decrease in sodium content for coatings on QZ after ageing is striking. Given the absence of sodium ions in PUF layers on fused quartz (Figure 29), this implies that there are still some WAs in the surface layers, although the amount is not sufficient to yield an appreciable decrease in WCA.

[0275] Table 4.5. Average WCA values and sodium content of PUF(-WA) coatings on different substrates before (WCAo) and after ageing for 45 days at 70 °C and 75% RH (WCA43). Standard deviations which were insignificant are omitted.

[0276]

[0277] Although the SMW substrates are rich in network modifiers (Table 4.3), no inhibition of the deterioration of hydrophilicity was observed. With no increase in the sodium content after the ageing procedure for the PUF coatings without WAs, and only a decrease in sodium content for the PUF-WA coatings, it would appear that leaching of ions from the SMW is not prone to happen. One factor contributing to this is likely the relatively large content of divalent cations in the SMWs such as Ca2+. Smets etal.

[0032] found that the addition of CaO, ZnO, or MgO to a sodium silicate glass increases its corrosion resistance, meaning that this leads to a decreased leaching of Na+ions with increasing divalent cation content. Moreover, significant leaching of the divalent cations was not observed, unless the glass composition yielded a more open glass structure

[0032] ,

[0278] It can rightfully be argued that the observed increase in Na:C ratio for the PUF coatings on SL glass is minimal, leading to the question whether leaching of sodium ions truly isChapter 4

[0279] correlated to the observed inhibited ageing of PUF-WA coatings on soda lime glass. However, combined with the observations made in the previous section with the PUF-MR coatings, it seems reasonable that there is an important contribution of sodium ions to the ageing (or lack thereof) of PUF-WA coatings. Additionally, results of a similar ageing experiment where the relative humidity was not constant at 75% over the course of the ageing period can be found in the Appendix. In general, the same trends were observed but at times in a more exaggerated manner (e.g., larger measured Na concentrations).

[0280] Overall, for PUF coatings stored at 75% RH and 70 °C, it was found that:

[0281] • PUF coatings on soda lime glass become more basic upon ageing compared to PUF coatings on fused quartz glass.

[0282] • The basicity increase observed for PUF coatings on soda lime glass are likely a result of leaching of NaOH.

[0283] • In all cases, the Na:C ratio of coatings on soda lime glass increases or at the very least remains stable.

[0284] • For PUF-WA coatings on fused quartz glass, the sodium content is found to decrease.

[0285] • PUF coatings with WAs on soda lime glass age significantly less than similar coatings on fused quartz glass in terms of their hydrophilicity.

[0286] Thus, these results would support the hypothesis that mobile charges, like Na+, sufficiently mobilise anionic WAs, thereby allowing them to remain at the coating-air interface to lower the surface energy of the coating.

[0287] The effect of relative humidity was also investigated by ageing coatings at 70 °C and 19% RH (Figure 14). It should be noted that a saturated LiCl solution was used to control the RH, but that the theoretical value of 11%

[0049] was not attained, but rather an average value of 19.3 ± 0.8 % RH. Of note is that in case of low RH, a strong increase in WCA value is seen for all coatings, regardless of the substrate. This would imply that relative humidity has a strong effect on changes in hydrophilicity. If it is assumed that the content of leached sodium is similar for coatings on SL exposed to 19% and 75% RH, then the requirement for limited ageing would be not only to allow for mobilisation of anionic WAs through charges, but also through sufficient water in the surface layers. PUF coatings without WAs all show in increased WCA value reminiscent to those in Figure 12a, indicating that the lower relative humidity was still sufficient to facilitate post-curing at elevated temperatures. In case of PUF-WA coatings (Figure 14b-c), the combination of a denser surface layer and lower relative humidity does not allow for as much mobility of the WAs compared to the cases similar to PUF-WA coatings at 75% RH (Figure 12b-c).Ageing Phenomena in Phenolic Resin Coatings

[0288] Figure 14. Average WCA values before and after ageing of (a) PUF, (b) PUF-AES and (c) PUF-BAS coatings on soda lime (SL) glass, fused quartz (QZ) glass, and Si wafers (Si-W) at 70 °C and 19% RH for 45 days.

[0289] To some degree, such a response to varying RH was previously observed in Chapter 3, Figure 3.10a. Exposing PUF-AES coatings to 90% RH for only 1 h already yielded an increase in hydrophilicity, which was largely reversible when subsequently exposing the coatings to 10% RH for 1 h. This points towards a possible humidity-induced mobility of these WAs, resulting in reorientation at the surface, or surface enrichment. Similarly, the changes in Figure 12b could be due to the insufficient mobility as a result of the low humidity conditions.

[0290] Investigating Inhibited Ageing on Inert Substrates

[0291] Based on the hypothesis that the leached mobile charges facilitates mobilisation of WAs at the coating-air interface, the sodium content in the coating was increased by addition of the sodium salt of methane sulphonate (NaMeS). This should then introduce mobile charges to the coating so that even on inert substrates such as fused quartz glass, WAs remain mobile and at the coating-air interface (Figure 15). AnChapter 4

[0292] alternative route would be to use a silicate glass with increased Na2O content, although it is assumed for applications slightly changingthe resin formulation is more feasible. An excess of NaMeS (nNaMeS= 5 • nWA)wasadded to the PUF resin formulations. Increasingthe salt concentration even further yielded macroscopically visible crystals after curing, and additionally a drastic decrease in water contact angle for PUF coatings without any wetting agents. However, even at the used amount of NaMeS, the water contact angle of PUF coatings was found to be lowered to approximately 57.6° ± 4.8° (Figure 16a). Still, as it was thought that this would not interfere with the hydrophilicity of the coatings when WAs were added, this concentration of NaMeS was used for subsequent experiments.

[0293] Figure 15. Schematic representation of method and hypothesis to immobilise wetting agents in coatings applied on (a) soda lime glass and (b) fused quartz glass and silicon wafers by addition of the sodium salt of methane sulphonate (NaMeS) to the resin.

[0294] Interestingly, the presence of NaMeS in fact did interfere with the hydrophilicity of PUF-WA coatings, as seen by a lower average WCA to the salt-free counterparts (Figure 16a). Presumably the change in WCA values for the PUF(-WA) coatings with NaMeS can be tuned by decreasing the amount of NaMeS added to the formulations, so that the hydrophilicity of the coatings matches better with the salt-free counterparts. A similar increase in hydrophilicity was also observed for coatings of PUF-AES with varying concentrations of Na2SO4(Figure 31). An important distinction between what is essentially doping the coatings with NaMeS and with Na2SO4is that the latter results in a hazy coating due to formation of crystals upon curing, whereas for the former such crystals are not observed. In both cases however the result is that the water-wettability of the PUF-WA coatings is enhanced. Although synergistic phenomena in mixtures of surfactants are reported in literature [77, 78], NaMeS would not likely be classified as a surfactant. Therefore, it is more probable that the resulting increase in hydrophilicity is a result of the formation of ion pairs between anionic wetting agents and excess Na+, thereby screening charges between anionic WAs andAgeing Phenomena in Phenolic Resin Coatings lowering the CMC and SFT [79-81], This would then also affect the distribution of WAs within the coating upon curing, and hence lead to an enhanced hydrophilicity. Additional support for this was found from the non-surface activity of NaMeS in water, for which a water-air interfacial tension of 71.3 ± 0.2 mN / m was measured at a concentration similar to that used in the resin formulation. In case of the decrease in WCA value of PUF-NaMeS coatings, it is proposed that the large salt concentration influences the cure process slightly, leading to a somewhat different surface chemistry than usual.

[0295] Figure 16. Average WCA values of coatings of (a) PUF(-WA)-NaMeS on soda lime (SL) glass, and of (b) PUF-NaMeS, (c) PUF-AES-NaMeS, and (d) PUF-BAS-NaMeS on soda lime (SL) glass, fused quartz (QZ) glass and silicon wafers (Si-W) before and after ageing at 75% RH and 70 °C for 45 days. Datapoints after 2 s for PUF-AES-NaMeS on SL in (c) have been set to 0 to indicate the virtually complete wetting.

[0296] The average WCA value of PUF-NaMeS coatings was seen to increase upon ageing the surfaces, regardless of the substrate (Figure 16b). Although the added salt can influence the initial hydrophilicity of the PUF coatings, it does not seem to affect any subsequent chemical and / or physical ageing of the PUF surface.Chapter 4

[0297] PUF-AES and PUF-BAS surfaces on soda lime glass show a similar response after ageing when doped with NaMeS (Figure 16c-d). Interestingly, the hydrophilicity of these coatings increases after the hygrothermal treatment for 45 days. For PUF-AES, addition of NaMeS yields a surface for which virtually immediate wetting occurs, and coatings appeared somewhat hazy, indicative of phase separation and therefore enrichment of AES at the coating - air interface. For PUF-BAS the decrease in WCA value is noticeable, yet less severe. When coated on QZ and Si-W substrates, PUF-AES and PUF-BAS with NaMeS begin to exhibit appreciable differences after ageing. Most distinctly, the average WCA for PUF-BAS-NaMeS coatings on QZ and Si-W increases by approximately 10-15°. Conversely, for PUF-AES-NaMeS an increase of only 8° is observed, indicating a slower ageing process. In absolute values, the increase in WCA values observed for the PUF-WA-NaMeS coatings is still less than for PUF-WA coatings (Table 4.6), although it should be noted that the initial WCA was already different. This would imply a difference in concentration of WAs at the coating - air interface. Despite this, it appears that the distribution of BAS in PUF surface layers is still more susceptible to changes in the matrix than AES, even in presence of NaMeS.

[0298] Table 4.6. Average CA values and sodium content of PUF-(-WA)NaMeS coatings on different substrates before (WCAo)and after ageingfor 45 days at 70 °C and 75% RH (WCA43). Standard deviations which were insignificant are omitted.

[0299]

[0300] NaMeS-containing coatings were also aged at 19% RH, where from the WCA values it is clear that in this case, the presence of mobile charges could not prevent the loss of hydrophilicity (Figure 17). Together with the results of PUF-WA coatings aged at similar conditions (Figure 14), it is evident that relative humidity has a strong influence on the ageing of surface hydrophilicity of PUF-WA coatings. This is also emphasised by the fact that the final WCA of PUF-WA-NaMeS coatings are similar to that of their salt-free counterparts, despite the initial WCA values being lower.Ageing Phenomena in Phenolic Resin Coatings

[0301] Figure 17. Average WCA values of coatings of (a) PUF-NaMeS, (b) PUF-AES-NaMeS, and (c) PUF-BAS-NaMeS on soda lime glass, fused quartz glass and silicon wafers before and after ageing at 19% RH and 70 °C for 45 days.

[0302] 4.4. Conclusions

[0303] The effect of different ageing conditions on the stability and performance of three different WAs and two different types of phenolic resins was studied. Hygrothermal ageing of PUF coatings with and without WAs has shown two interesting phenomena. First, PUF surfaces undergo post-cure reactions, likely facilitated by the combination of elevated relative humidity and temperature. This results in an increase in water contact angle value over time, yielding less hydrophilic coatings. In case of PUF coatings with WAs, only coatings with anionic WAs stored at elevated temperatures showed a moderate increase in average water contact angle value. Chemical analyses of the coating surfaces show a surface chemistry akin to that of a post-cured, WA-free PUF coating. Some evidence of physical ageing through relaxation facilitated by moisture-induced plasticisation was also observed. In light of the stability of the WAs, it is therefore believed that WAs do not degrade during the accelerated ageingChapter 4

[0304] procedure, but rather physically deplete from the coating - air interface due to the chemical and physical changes in the PUF surface layers.

[0305] The substrate on which the coatings were applied had a distinct influence on the change in hydrophilicity upon ageing samples at 70 °C and 75% RH. Only coatings of PUF with WA applied on soda lime glass showed a limited decrease in hydrophilicity, whereas the WCA of PUF-WA coatings on fused quartz glass, stone melt wafers, and silicon wafers became reminiscent of that of WA-free PUF surfaces. This was attributed to the leaching of sodium hydroxide, only occurring for the soda lime glass. The influx of positive sodium ions ensures mobility of the wetting agents upon ageing. However, when coatings are aged at a lower relative humidity of 19%, an increase in WCA was observed regardless of the substrate used.

[0306] Addition of NaMeS to PUF-AES resins leads to coatings which either show an increased hydrophilicity after ageing at 70 °C and 75% RH, or a limited decrease of hydrophilicity. PUF-BAS doped with NaMeS under similar conditions does not readily show such inhibition of ageing, possibly due to a stronger affinity with the PUF matrix due to its aromaticity. When PUF-WA-NaMeS coatings were aged at 19% RH and 70 °C, the WCA value of the coatings decreased to a similar value as that of coatings without NaMeS. Ageing of the PUF-WA coatings therefore appeared quite sensitive to the relative humidity in which samples were stored. These insights could provide tools, i.e., addition of a sodium salt or storage at elevated relative humidity, to improve the preserve the hydrophilicity of phenolic resin coatings with wetting agents over time.

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[0401] Appendix

[0402] Figure 18. Relative humidity and temperature within the desiccator with saturated NaCl solution and samples of EFA, AES and BAS. Sudden drops and subsequent increases in the relative humidity are due to opening and closing of the desiccator to take samples. An increased relative humidity for the first 5 days is likely due to the evaporation of water from BAS and AES.

[0403] Thermal Stability of Wetting Agents

[0404] The thermal stability of the wetting agents was initially determined at conditions not necessarily close to cure conditions by thermogravimetric measurements (Figure 19). For the anionic WAs, water was evaporated before the temperature ramp by keeping samples at 120 °C for 60 min. The mass at the end of this isothermal step was set to 100%.

[0405] While AES and EFA appear to be at the cusp of degradation at temperatures of 200 °C, BAS remains stable until 400 °C. The degradation profiles for AES are similar to thatChapter 4

[0406] reported in literature for SDS

[0082] , An oxygen-rich environment accelerates the decomposition of EFA and BAS, although significant degradation still occurs at temperatures higher than for AES.

[0407] Figure 19. Mass change of WAs as function of temperature. Measurements were performed under inert N2 and air atmosphere. Due to machine limitations, the temperature range was not the same for all samples. Chemical changes of the WAs due to thermal exposure are not readily expected based on TGA, but to verify and substantiate these results WAs were subjected to 200 °C, which is a common cure condition for phenolic resins. Typical cure times are approximately 10 minutes, but an extension of this time was chosen whenever possible to test the stability of wetting agents in a more extreme case. For AES, this did not appear to be possible, as longer exposure times resulted in clear degradation of the sample (Figure 20). This is corroborated by the results of the TGA, where 200 °C is the onset of a steep mass decrease within a relatively small temperature window. AES was therefore aged for a shorter time period, and additionally at a lower temperature of 150 °C.

[0408] Although EFA also shows signs of degradation starting from 200 °C (Figure 19), this degradation is more gradual over a broader temperature range. In case of EFA, both an as-received sample was used, and one to which water was added. This was done to study the possibility of hydrolysis occurring under the above-mentioned ageing conditions.

[0409] Chemical differences of WAs were monitored after the thermal exposure (Figure 21). An overview of the most important signals in the ATR-FTIR spectra are given in Tables A4.1-3. The peak assignment for WA signals in the1H-NMR spectra can be found in Chapter 3.Ageing Phenomena in Phenolic Resin Coatings

[0410] Figure 20. Physical changes of WAs after exposure to 200 °C for 10 or 30 minutes in air.

[0411] Both AES samples which were unaged and freeze-dried, and those exposed to 200 °C for 10 min showed a more detailed ATR-FTIR spectrum than the reference samples. In part, this is due to the absence of water from these samples. Furthermore, for dodecyl sulphate (SDS) in water, which is relatively similar to AES, the concentration and temperature will change the conformation and packing density of SDS, which is seen from differences in FTIR spectra [57, 83, 84], The corresponding1H-NMR spectra show only small differences relative to pristine AES, apart from the two signals between 4.0 4.2 ppm. These signals are attributed to the carbon adjacent to the sulphate headgroup, for which the decrease in integral would imply the occurrence of hydrolysis. Thermal decomposition of SLES and SDS can lead to the formation of dodecane, dodecane ethers, dodecanol, and mixtures thereof [85, 86], Based on the FTIR and1H-NMR spectra of AES held at 200 °C for 10 min, the formation of dodecanol cannot be excluded; the FTIR spectrum shows the presence of hydroxyl moieties and1H-NMR is not necessarily reliable to detect alcohol functionalities, especially since D2O was used as a solvent. AES exposed to 200 °C for 30 min, which turned black after the exposure period, shows signs of the presence of hydroxyl groups through the broad and sharp peakat 4 ppm in its1H-NMR spectrum. On the other hand, the FTIR spectrum does not readily indicate their presence. Yet, the decrease in intensity of the peaks associated with the sulphate headgroup (e.g., 1224 cm'1) would seem to corroborate the decomposition of AES into for instance dodecanol.

[0412] BAS and EFA remained unchanged after being exposed to 200 °C for 10 min (Figure 21 b,c). The appearance of a broader signal between 2.5 3.5 ppm is attributed to water presence in the CDCl3solvent, and therefore not indicative of possible hydrolysis having occurred during the thermal exposure. Although the appearance of EFA appears to be slightly darker in colour, chemical consequences of such a darkening (e.g., oxidation; see also the discussion in the main text) were not observed.

[0413] In most cases, no convincing effect of the thermal stability study on the chemistry of WAs was observed, despite the discoloration.

[0414] Figure 21. ATR-FTIR and1H-NMR spectra of (a) AES, (b) BAS, and (c) EFA before and after exposure to 200 C.Ageing Phenomena in Phenolic Resin Coatings Table A4.1. Peak assignment for the ATR-FTIR spectra of EFA, based on

[0087] .

[0415]

[0416] Table A4.2. Peak assignment for the ATR-FTIR spectra of AES, based on [57, 87].

[0417]

[0418] Table A4.3. Peak assignment for the ATR-FTIR spectra of BAS, based on [87-89].

[0419]

[0420] Chapter 4

[0421] Figure 22. ATR-FTIR spectra of freeze-dried and aged AES. Ageing conditions were 75% RH and 70 °C. Figure 23. Mass change of wetting agents upon ageing by exposure to 70 °C and 75% RH for up to 28 days. BAS and AES decrease in mass on account of the evaporation of water. Only EFA absorbs water vapour.

[0422]

[0423] Figure 25 Optical micrographs of (a) PUF-EFA, (b) PUF-AES, and (c) PUF-BAS before and after storage at 75% RH and 70 °C for 117 days. Scale bar: 125 pm.

[0424] Figure 26. Optical micrographs of (a) PUF-KOH, (b) PUF-KOH-AES, and (c) PUF-KOH-BAS before and after storage at 75% RH and 70 °C for 117 days. Scale bar for (a): 50 pm. Scale bar for (b-c): 125 pm.Ageing Phenomena in Phenolic Resin Coatings A Note on the Possibility of Leaching During Ageing

[0425] As mentioned in the main text, it could not be determined if the typical increase in sodium content for coatings on soda lime glass is a result of initial ion exchange and migration during dip-coating and curing, or also the result of continuous leaching due to the elevated relative humidity conditions. The former is to be reasonably expected on account of the relatively high water content of the resin (approximately 66 wt%) and the rapid acidification of the resin upon curing. The latter is dependent on the waterbarrier properties of the applied PUF layer and the corrosion resistance of the glass substrate.

[0426] The diffusion of water vapour can be measured using dynamic vapour sorption (DVS), employing a Payne cell. Here, a free-standing film is clamped in between a headspace filled with drying agent and a lid with a hole in the middle. Exposing the outside of the cell and film to elevated relative humidity, and tracking the resulting mass changes, allows for the calculation of the diffusion coefficient.

[0427] Mass changes of PF and PUF powders and films were measured at 75% RH by dynamic vapour sorption (DVS; Figure 27). For PUF powders, the average mass change recorded was found to be 8.4% ± 0.8% and for PF the average mass change amounted to 4.2% ± 0.1% (Table A4.5). Especially PUF appeared to show a stronger affinity towards water vapour, likely on account of the more polar matrix due to the presence of urea moieties. Although the mass change for the PF and PUF films is similar, it is interesting to observe a quite low diffusion coefficient and permeability of PUF films compared to the PF films. This can be attributed to the polar nature of the bulk of the PUF film, which increases the interaction of water vapour with the film. The increased interactions with the material relative to PF films then would lead to an overall slower diffusion process. It should be noted that the determined permeability values for both PUF and PF are larger than what has been reported for Bakelite (0.6 — — ) in bar-m2-min literature

[0050] , However, processing and synthesis parameters influence the material properties of the final cured phenolic resin (see also Chapter 2), so a direct comparison is challenging to make.

[0428] Table A4.5. Mass change of PUF and PF powders and films upon exposure to 75% RH, and determined diffusion coefficient D, permeability P, and solubility S of water vapour through a P(U)F film.

[0429]

[0430] Chapter 4

[0431] As a final note, the silica gel with dye which was used in the headspace of the Payne cell was in all cases colourless, a direct result of the absorption of moisture. On the whole, there are indications of the possibility of moisture playing a role in the ion exchange and migration at the coating-substrate interface.

[0432] Figure 27. Mass change of PUF and PF powders when exposed to 75% relative humidity, as measured with DVS. Measurements were carried out at 25 °C.

[0433] Effect of substrate size on wettability

[0434] The most notable difference between the substrates is the size: stone melt wafers are pre-cut into 1 x 1 cm2pieces, whilst the total coated area of soda lime substrates is typically 2 x5-6 cm2.

[0435] When curing coatings on soda lime substrates of reduced size, often an increased average contact angle value was found compared to the normal-sized soda lime (Figure 28). Hence, it appears that the substrate size has a profound influence on the curing process. It is thought there are two possible factors contributing to this decreasing wettability with decreasing substrate size. First, smaller substrates have a lower total dipping time and as such experience draining forces for a smaller time relative to larger substrates. This way, coatings with a different thickness gradient are produced (5.2 pm ± 0.6 pm for coatings on stone melt wafers; 4.9 pm ± 1.5 pm for coatings on normal-sized soda lime). Second, the edge-to-area ratio is significantly different for the two samples. For coatings on SMWs, edge effects such as enhanced evaporation of solventAgeing Phenomena in Phenolic Resin Coatings and TEA could be more dominant, leading to a more advanced state of cure than could be seen for coatings on SL.

[0436] Figure 28. Average water contact angle value over time of (a) PUF, (b) PUF-AES, (c) PUF-BAS and (d) PUF-EFA coatings on stone melt wafers (SMW; 1 x 1 cm), soda lime (SL; 2.5 x 5 cm) and cut soda lime (SL Small; 1 x 1 cm) substrates.

[0437] Figure 29. Na 1s binding energy spectra of PUF coatings on (a) SL, (b) QZ, and (c) SMW before and after ageing for 45 days at 70 °C and 75% RH.

[0438] Ageing of PUF coatings on different substrates with uncontrolled RH

[0439] As described in the main text, an initial ageing experiment of PUF(-WA) coatings was performed where the relative humidity was not consistently 75%. Unfortunately, the humidity and temperature logger inside the desiccator was also not recording, so the exact relative humidity profile over time is unknown. Yet rather than dismissing this experiment, it is worthwhile to examine the results of this ageing procedure still.

[0440] Figure 30 shows the initial and final average water contact angle values of PUF(-WA) coatings on soda lime, quartz and Si wafers. In general, the results are in line with those discussed in the main text: WA-free coatings all show an increase in WCA, and only coatings of PUF-WA show a lesser increase in WCA when applied on soda lime substrates. There are also some key differences, however. First, the increase in WCA seen for PUF coatings is drastically larger compared to that presented in the main text. The same holds true for PUF-AES and PUF-BAS coatings on soda lime. Additionally, the sodium content is also quite different before and after ageing (Table A4.6).Ageing Phenomena in Phenolic Resin Coatings

[0441] Figure 30. Average WCA values of PUF(-WA) coatings before and after ageing for 45 days at 70 °C. Starting relative humidity was 75%, and 28% at the end.

[0442] Table A4.6. Average WCA values and Na : C ratios of PUF(-WA) coatings on different substrates before and after ageing for 45 days at 70 °C. Starting relative humidity was 75%, and 28% at the end.

[0443]

[0444] Figure 31. Average WCA values of PUF-AES coatings doped with Na2SO4. The arrow indicates the concentration at which there is approximately a 5 x molar excess of Na2SOi relative to AES.

Claims

66CLAIMS1. A growth substrate formed of man-made vitreous fibres bonded with a binder, wherein the growth substrate comprises anionic wetting agent, wherein the growth substrate further comprises one or more salts each comprising a cation and an organic anion.

2. The growth substrate according to claim 1 , wherein the cation of each of the one or more salts is monovalent.

3. The growth substrate according to claim 1 or 2, wherein the cation of each of the one or more salts is independently selected from metal cations and ammonium, preferably monovalent metal cations, more preferably alkali metal cations, more preferably Li+, Na+, and K+, most preferably the cation is Na+.

4. The growth substrate according to any preceding claim, wherein the organic anion of each of the one or more salts is independently selected from the group consisting of:wherein each R is independently an organic group, preferably the organic anion of each of the one or more salts is independently selected from the group consisting of:O\ z° 9 °S z°“ °X z°“ °\ zO X > X > X > R o , R O , R o and R O-R, most preferably the organic anion is R O .

5. The growth substrate according to claim 4, wherein each R is independently selected from the group consisting of:(i) C1-C11 alkyl, preferably Ci-Cs alkyl, more preferably C1-C4 alkyl, more preferably methyl, ethyl, propyl, or butyl, more preferably methyl, ethyl, isopropyl, isobutyl, sec-butyl, or tert-butyl, most preferably methyl,67wherein the alkyl group is optionally substituted with one or more substituents independently selected from -OH and -O-(Ci-C3 alkyl), preferably -OH, -OMe, and -OEt; and(ii) phenyl optionally substituted with C1-C4 alkyl, preferably phenyl optionally substituted with methyl, ethyl, propyl, or butyl, more preferably phenyl optionally substituted with methyl, ethyl, isopropyl, isobutyl, sec-butyl, or tert-butyl, most preferably phenyl optionally substituted with methyl,wherein the alkyl group is optionally substituted with one or more substituents independently selected from -OH and -O-(Ci-C3 alkyl), preferably -OH, -OMe, and -OEt.

6. The growth substrate according to claim 4 or 5, wherein R is methyl.

7. The growth substrate according to any preceding claim, wherein the one or more salts comprise sodium methanesulphonate.

8. The growth substrate according to any preceding claim, wherein the molar ratio of the one or more salts to the anionic wetting agent is in the range of from 0.1:1 to 10:1, preferably in the range of from 0.5:1 to 9:1, more preferably in the range of from 1:1 to 8:1, more preferably in the range of from 3:1 to 7:1, most preferably in the range of from 4:1 to 6:1.

9. The growth substrate according to any preceding claim, wherein the anionic wetting agent comprises at least one of an alkyl ether sulphate, an alkyl sulphate, and an alkyl benzene sulphonate, preferably at least one of an alkyl ether sulphate and an alkyl sulphate.

10. The growth substrate according to any preceding claim, wherein the total amount of anionic wetting agent is in the range of from 0.01 to 3.0 wt. % by weight of the total solids content of the growth substrate, preferably in the range of from 0.05 to 3.0 wt. %, more preferably in the range of from 0.05 to 1.0 wt. %, more preferably in the range of from 0.05 to 0.8 wt. %, more preferably in the range of from 0.05 to 0.5 wt. %, most preferably in the range of from 0.075 to 0.5 wt. %.6811. The growth substrate according to any preceding claim, wherein the total amount of anionic wetting agent is in the range of from 0.01 to 3.0 wt. % by weight of the total solids content of the growth substrate, and wherein the molar ratio of the one or more salts to the anionic wetting agent is in the range of from 0.1:1 to 10:1.

12. The growth substrate according to any preceding claim, wherein the binder is a phenol formaldehyde resin ora urea formaldehyde resin, preferably a phenol urea formaldehyde resin.

13. Use of a growth substrate according to any preceding claim as a growth substrate for growing plants, or for propagating seeds, seedlings, or cuttings.

14. A method of growing plants or propagating seeds, seedlings, or cuttings, the method comprising:a) providing a growth substrate according to any of claims 1 to 12;b) positioning one or more plants, seeds, seedlings, or cuttings for growth in the growth substrate; andc) irrigating the growth substrate.

15. A method of manufacturing the growth substrate according to any of claims 1 to 12, comprising the steps of:a) providing man-made vitreous fibres;b) applying the binder to the man-made vitreous fibres;c) applying the anionic wetting agent to the man-made vitreous fibres;d) applying the one or more salts to the man-made vitreous fibres; ande) collecting and consolidating the man-made vitreous fibres.6916. A method of storing the growth substrate according to any of claims 1 to 12, wherein the growth substrate is stored at a relative humidity of at least 30%, more preferably at least 40%, more preferably at least 50%, more preferably at least 75%.

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