WO2024101996A1

WO2024101996A1 - Starch-based tile adhesive

Info

Publication number: WO2024101996A1
Application number: PCT/NL2023/050595
Authority: WO
Inventors: Anna Maria Dijk-Van Delden; Anne Margriet Hofman - De Dreu; Remko Christiaan WELKER
Original assignee: Coöperatie Koninklijke Avebe U.A.
Priority date: 2022-11-11
Filing date: 2023-11-13
Publication date: 2024-05-16

Abstract

The invention provides a starch-based tile adhesive, said adhesive comprising a substituted starch and a filler, in which a limited amount of cement may be present, but which adhesive preferably does not comprise cement. The invention furthermore provides methods to provide the said tile adhesive, as well as methods for tiling using the said adhesive, and surfaces provided with tiles by use of the said adhesive.

Description

Title: Starch-based tile adhesive

The invention is in the field of tile adhesives.

Introduction

The current focus on sustainability and carbon footprint reduction has led the construction industry to investigate more sustainable alternatives to common construction materials. Dry mix tile adhesives for attachment of a tile to a surface such as a wall have traditionally been based on cement. Production of cement comes with high energy requirements and the associated high carbon footprint. Cement in itself cannot truly be recycled, that is, the adhesive power of cement cannot normally be reused, due to the fact that cement hardening is an irreversible chemical process.

Cement-based tile adhesives generally comprise about 25-40 wt.% of cement as an adhesive, 60-75 wt.% of sand as a filler, and about 0.15 - 0.50 wt.% of a cellulose derivative as a water retention aid. Typically cement type I (normal Portland cement) and type II are used in tile adhesives.

To prevent sagging of tiles during application, minor quantities (about 0.05 - 0.25 wt.%) of a starch ether can be added to a cement -based tile adhesive. The starch ether incorporates between the cement particles thereby providing yield stress to the tile adhesive. This provides the advantage that during placement of the tiles to the surface, the tiles remain in the placed location without sagging, until hardening of the cement. In such applications, the starch ether does not contribute to the adhesion of the tiles to the surface. In such applications, the weight ratio of cement to starch ether is often in the range of at least 100 or (much) higher.

Cement-based tile adhesives have several drawbacks. The pot life, also referred to as working time (the time for which the adhesive remains workable after mixing of the adhesive with water) is limited to 1 - 4 hours. After this time, the adhesive starts to set. The open time of cement -based tile adhesives is even shorter. The open time is the time between the application of a layer of tile adhesive to a surface and the start of the tiling. Cement-based tile adhesive must thus be used and applied relatively quickly. Moreover, tile adhesive that has been prepared in excess, remains after application and cannot be reused nor stored.

In addition, equipment used to contain the cement -based adhesive cannot be re-used after the cement-based adhesive has hardened. This is because the hardening is an irreversible process; equipment which was not cleaned in time must thus be discarded.

Cleaning of the equipment in itself, however, also represents difficulties. Cement particles are hard and heavy, so that cleaning water has a high chance of clogging sewage systems. In many instances, cleaning waste of cement-based tile adhesion equipment finds its way directly to the environment.

In general, due to fast and irreversible hardening and nonrecyclability of the material, and the fact that the tiler will always make excess material, the use of cement-based tile adhesives leads to a lot of waste.

Furthermore, cement-based tile adhesives generally have a pH of about 13. Skin contact with cement compositions of pH 13 can lead to dry skin and irritation, and inhalation of such compositions may lead to lung problems. This represents problems for construction workers, as it is difficult if not impossible to avoid all contact with the cement-based tile adhesive.

Moreover, cement contains Chromium 6 which is suspected to cause different health issues such as skin allergies, cancer and reduced fertility. Chromium 6 is rendered harmless in cement by the addition of reductors. Upon mixing with water, the reductors convert Chromium 6 into the harmless Chromium 3. However, the present reductors have a hmited shelf life which also limits the shelf life of cement.

Starch is a naturally occurring polymer of glucose. Starch occurs in the form of granules, which are particles of roughly 1 - 100 micrometers. Naturally occurring starch granules are generally called native starch.

Native starch comprises two types of glucose polymers: amylose and amylopectin. Amylose is a linear glucose polymer, and amylopectin is a branched glucose polymer. Regular native potato starch comprises approximately 20 - 25 wt.% amylose and 75-80 wt.% amylopectin.

Starch enriched in amylopectin is well-known. Such starch, generally called amylopectin starch, comprises at least 90 wt.%, preferably at least 95 wt.%, more preferably at least 98 wt.% amylopectin. Amylopectin starch may also be called “waxy starch”.

Starch granules comprise entangled amylopectin and amylose in crystalline and amorphous regions. Starch granules do not dissolve in water at room temperature. The glucose polymers can be released from the granule and individually dissolved by a process called gelatinization. Gelatinized starch is starch which has been subjected to the process of gelatinization: application of sufficient heat, preferably in combination with shear to the starch granules in water, which results in dissolution of the starch. The dissolved starch can subsequently be dried to provide a gelatinized starch powder (“pregelatinized starch”), which readily dissolves in water at room temperature.

The present invention provides a tile adhesive in which the adhesion of the tile to the wall is achieved by a gelatinized substituted starch. This overcomes the above problems, and unexpectedly even provides better adhesive properties than traditional, cement-based tile adhesives. Detailed description

The invention provides a tile adhesive, comprising a substituted starch and a filler, wherein the weight ratio of cement to substituted starch is 0 - 2. Preferably, the invention provides a tile adhesive devoid of cement (weight ratio of cement to substituted starch of 0). The phrases “weight ratio” and “mass ratio” indicate the same concept, and can be used interch ange ably .

The present tile adhesive has the advantage that the binder is fully renewable. It can be used with much lesser environmental impact, due to decreased energy needs for production of the adhesive, and also due to the degradability of the adhesive. The present tile adhesive has a longer pot life and working time, which provides for a number of advantages. It allows for preparation of larger amounts in one time which can be stored and applied during an extended period of time. Excess material may be stored and reused. Also the open time is much longer which allows the tiler to work with less time constraints or to apply the adhesive to a larger surface area than with traditional cement -based tile adhesives. Furthermore, the adhesive can be formulated at any desired pH , leading to decreased risk by contact exposure. The present tile adhesive is more user friendly compared to traditional cement-based tile adhesives.

Equipment used for the application of tiles with the present adhesive need not be discarded, but can be cleaned with water. Any waste adhesive or cleaning waste is non-polluting. As a result, the tile adhesive of the invention reduces the amount of waste compared to traditional cementbased tile adhesives.

Thus, the pot life and open time of the present tile adhesive is much longer than for traditional cement-based adhesives, the adhesion strength is higher, and the present tile adhesive leads to reduced waste and is more user friendly. The present tile adhesive is an adhesive for attaching tiles to a surface. A tile is a construction material used for esthetic or practical purposes, which can be attached to a surface such as a wall or a floor in a process called tiling. In the present context, the tile adhesive is preferably an adhesive for indoor tiling. Further preferably, the tile adhesive is used in indoor dry rooms, or at least the dry part of an indoor room. A dry room is any room in which the quantity of water does not exceed regular living conditions. A dry room can be for example a living room, a hallway, or an office. A dry room is by definition distinct from a wet room: rooms (or a part thereof) in which water is abundantly present. A wet room colloquially comprises room types such as (part of ) a kitchen or (part of) a bathroom.

A tile is a generally known construction material. Any type of tile can be used for tiling using the present invention. A tile is, generally, a flat object, meaning the thickness (or for some forms of tile, the maximum thickness) is preferably less than 20%, more preferably less than 10 % of the longest straight-line diameter. A tile can be of any shape, although in most situations, a tile is square or rectangular. A tile can be made of any material. Preferably however, a tile for tiling using the present tile adhesive is a, stone, natural stone or ceramic tile.

A tile can have a porosity, expressed as water absorption, between 0.01 and 25 wt.%. In preferred embodiments, the tile can have a water absorption between 0.2 and 20 wt.%. In alternative preferred embodiments, the tile can have water absorption of equal or less than 0.5 wt.%. In another preferred embodiment, the tile can have a water absorption of 10 - 20 wt.%, preferably 12 - 18 wt.%. In further preferred embodiments, the water adsorption can be more than 15 wt.%.

Tiling is the process in which a tile is attached to a surface. In the process of tiling, generally known in the art, the tile adhesive is applied to the surface onto which tiles are to be placed, and/or onto a tile which is about to be attached to a surface, preferably in a more or less uniform layer. Subsequently, the tiles are placed on the surface with the layer of adhesive being placed between the tile and the surface. Then, the adhesive is allowed to harden (“dry”). Thereafter, the tiles are solidly attached; if the tile adhesive fulfills generally accepted adhesion requirements, the tile cannot be removed without significant force. In this invention, the term ’’hardening” is used for the process which results in solid attachment of the tile to the surface. Hardening of the tile adhesive can be achieved by chemical and/or physical processes.

The force required to remove a tile, and hence the adhesion strength, is the subject of various standards. In the European standard, EN 12004, the adhesion must be at least 1 N/mm² for the highest quality (C2) tile adhesive; for a lower quality (C 1) tile adhesive, the adhesion strength must be at least 0.5 N/mm². The standard is based on a particular type of tile: Winckelmans tiles, having a water absorption of less than 0.5 wt.%. The standard EN 12004, which is generally known, is used throughout the present document when referring to “adhesion strength”.

The present tile adhesive comprises a substituted starch. A substituted starch in the present context is defined as a starch bearing one or more substituents, in which each substituent is attached to the starch through one starch hydroxyl group on one starch glucose group through an ether, ester, or carbamate bond. A substituted starch is thus a starch which has been substituted on one starch glucose group through an ester, ether or carbamate bond to a group of atoms (the substituent), in which the group of atoms is not covalently bonded to a different starch glucose group. A substituted starch is a starch substituted with a group of atoms through an ether, ester or carbamate bond, in which the group of atoms is attached to the starch through covalent bonding to one starch glucose group. In the present context, starch substitution does not provide crosslinks, although a substituted starch, for some applications, may optionally be additionally crosslinked using crosslinking reagents such as defined elsewhere, in order to finetune the rheology of the tile adhesive. A substituted starch is the product of a reaction between starch and a monofunctional electrophilic reagent suitable for use in a nucleophilic substitution or addition reaction.

A substituted starch can be obtained by reacting starch after activation, for example using a base catalyst, with reagents that are characterized by the presence of one electrophilic group suitable for nucleophilic displacement such an aldehyde, activated carboxylic acid (such as an acid anhydride, acyl chloride or vinyl ester), an epoxide group, or an alkyl halide. The reaction product is a starch ether, starch ester or starch carbamate (urethane).

The reagent used to obtain a substituted starch can also be a reagent for a nucleophilic addition reaction. Suitable reagents are characterized by an activated double bond. Such addition reactions are also known as Michael additions. Suitable reagents include acrylonitrile, (meth) acrylic acids, methyl (meth) acrylates, maleic acid, fumaric acid, and the like. The reaction product of such an addition reaction is a starch ether.

When starch in solution or starch granules are reacted with monofunctional electrophilic reagents in nucleophilic substitution or addition reactions as described above, the resulting starch is referred to as a substituted starch. Monofunctional reagents are reagents that are able to react once with a starch hydroxyl group.

Well known examples of a substituted starch suitable for use in the present invention are carboxymethylated starch, hydroxypropylated starch, hydroxyethylated starch, acetylated starch, succinated starch, a octenyl succinated starch, cationic starch, and starch phosphate, preferably carboxymethylated starch, hydroxypropylated starch, hydroxyethylated starch, acetylated starch, succinated starch, octenyl succinated starch and cationic starch.

The substituted starch preferably has a degree of substitution of at least 0.01 mol/mol, preferably at least 0.05 mol/mol. For carboxymethylated starch, hydroxybutylated starch, hydroxypropylated starch, hydroxyethylated starch, succinated starch and octenyl succinated starch, preferably carboxymethylated starch, hydroxypropylated starch, and hydroxyethylated starch, the degree of substitution is preferably at least 0.1 mol/mol.

For hydroxypropylated starch, the degree of substitution is preferably at least 0.1, more preferably at least 0.2, more preferably at least 0.3, most preferably 0.3 - 5.0, such as 0.3 - 4.5 mol/mol.

For carboxymethylated starch, the degree of substitution is preferably at least 0.1, more preferably at least 0.2, most preferably 0.2 - 3.0, such as 0.2 - 2.0, or 0.2 - 1.0 mol/mol.

For acetylated starch, the degree of substitution is preferably at least 0.05, such as 0.05 - 2.0, or 0.05 - 1.0 mol/mol.

The degree of substitution (“DS”) is the quantity of reagent bound to starch, expressed as mol bonded reagent per mol Anhydro Glucose Unit (AGU). The molecular weight of 1 mol AGU is 162 g/mol. As each AGU has three available hydroxyl groups, the maximum DS is three. The degree of substitution can be measured by methods know in the art for quantification of the degree of substitution.

The DS defined above can be calculated from the amount of substituents directly attached to an O-atom of the AGU; the term DS in the present context is used interchangeably with the concept of “molecular substitution” (“MS”). MS is calculated from the amount of substituents covalently bonded with to starch through any bond, directly attached to the O-atom of the AGU, or attached onto substituents already bonded with the AGU, as generally known in the art.

Well known examples of modified starches of which the degree of substitution is expressed as MS and which can have an MS larger than 3 are hydroxyalkylated starches or starches grafted with ethylenically unsaturated monomers. In case of such substituted starch types, DS in the present context should thus be read as MS.

The present tile adhesive further comprises a filler. A filler, in the present context, is a solid inert particulate material. The filler preferably has a particle size, expressed as D50, of at least 1 pm, preferably at least 5 pm, more preferably at least 10 pm. The particle size of the filler is at most 600 pm, preferably at most 500 pm, more preferably at most 300 pm, even more preferably at most 175 pm. The particle size distribution of fillers is generally determined by sieve fractionation. Alternatively, laser diffraction of suspensions or dry powder can be used to determine the particle size distribution. Particle size, as used herein, refers to the particle size determined by sieve fractionation.

Suitable fillers for use in the present tile adhesive are generally known fillers for use in cement-based tile adhesives. Examples include sand, clay, and calcium carbonate. It is an additional advantage of the present tile adhesive that further to the generally known filler types, also other filler types may be used, such as for example granular starch, ground waste concrete, ground waste plastic, ground organic fibres, ground inorganic fibres and saw dust.

In alternative embodiments, a tile adhesive without filler is contemplated and herein also disclosed. The sole presence of the substituted starch as a binder is sufficient for adhesion of a tile to a surface. In such embodiments, the tile adhesive comprises a substituted starch and further optional components, as defined elsewhere.

In the present tile adhesive, the weight ratio of cement to substituted starch is 0 - 2. Cement is a generally known construction material used for support and construction. Cement admixed with a fine filler is known as mortar; in combination with a rough filler, the mixture is known as concrete. Cement itself is generally an inorganic material, which hardens through an irreversible chemical reaction with water or carbon dioxide. Cement is generally a material comprising a mixture of silicates and oxides. In some embodiments, cement can be a material comprising calcium oxide.

The present tile adhesive preferably does not comprise cement, in which case the weight ratio of cement to substituted starch is 0. Cement may however be present in the present tile adhesive. This may be advantageous in cases of consumer preference for the presence of at least some cement, to provide water or moisture resistance or where irreversible hardening would be required.

The present tile adhesive is however primarily a starch-based tile adhesive, and cement, if present, is considered an additive which may aid in binding, even if the substituted starch functions as the main or major binder. The weight ratio of cement to substituted starch is preferably 0 - 2.0, more preferably 0 - 1.5, more preferably 0 - 1.0, and even more preferably 0 - 0.5, more preferably 0 - 0.19, even more preferably 0 - 0.15, most preferably 0 - 0.1. Most preferably, the present tile adhesive does not comprise cement.

In some preferred embodiments, the substituted starch is also a crosslinked starch. That is, the starch used in the present tile adhesive can have been subjected to both a process of substitution, as described elsewhere, and to a process of crosslinking. Starch crosslinking is a process in which starch (in granular form or as a solution) is reacted with a bifunctional or polyfunctional electrophilic reagent suitable for a nucleophilic substitution or addition reaction. Such bifunctional or polyfunctional reagents are called crosslinkers. Crosslinkers are able to react at least twice with starch hydroxyl groups thereby crosslinking intra or intermolecularly amylose or amylopectin chains. In the context of the present invention, a crosslinked starch is distinct from a substituted starch. Crosslinking of the starch for use in the present invention may be performed before, during or after the substitution reaction. Methods to substitute and/or crosslink starch are well known to the person skilled in the art. Reference is made to O.B. Wurzburg, CRC Press, 1986, Modified Starches: Properties and Uses.

Well known types of crosslinked starch suitable for use in the present tile adhesive include epichlorohydrin crosslinked starch, trimetaphosphate- crosslinked starch, phosphoryl chloride crosslinked starch, and adipate crosslinked starch or starch crosslinked with di-or polyglycidylether, 1,2- dichloropropanol, dichloro acetic acid, a di- or polyepoxide crosslinker, a di or poly-isocyanate, or a di- or tricarboxylic acid, or mixtures thereof (e.g. a mixture of adipic acid with acetic anyhydride). Also, well-known crosslinkers include glyoxale, zirconium carbonate, borax, and compounds comprising multiple aldehyde or epoxy groups. The degree of crosslinking (“DC”) of a crosslinked starch is at least 0.0001 mol crosslinker/mol starch (“mol/mol”).

The substituted starch for use in the present tile adhesive can also be a degraded starch. A degraded starch is a starch in which the chains of the glucose polymers have been reduced in length, so as to attain a molecular weight which is lower than that of the initial starch. That is, the starch used in the present tile adhesive can have been subjected to both a process of substitution, as described elsewhere, and to a process of degradation. Starch degradation is well-known in the art. Reference is made to O.B. Wurzburg, CRC Press, 1986, Modified Starches: Properties and Uses. In preferred embodiments, the starch is a chemically degraded starch (preferably an acid-degraded starch), a physically degraded starch or an enzymatically degraded starch. All these types of degraded starch, and ways to obtain them, are generally known in the art.

In some embodiments, the starch can be a degraded, crosslinked and substituted starch.

In much preferred embodiments, the starch of the invention is a cold water soluble starch, i.e. a starch which has been pregelatinized. A pregelatinized starch is a starch which has been made cold water soluble by starch gelatinization. Starch originally exists as granules which only disperse in water but which do not dissolve in water. In order to become effective as adhesive, the starch should be gelatinized, that is, exist in solubilized form, at the moment of application. Starch gelatinization can be achieved by the generally known method of (jet) cooking, or using other methods well known in the art.

Preferably the starch of the invention has been pregelatinized to make it cold water soluble. Pregelatinization is the process of gelatinization of a starch suspension followed by drying into powder. Pre-gelatinization can be done prior, during or after substitution and/or crosslinking.

In case of pregelatinized starch, starch is gelatinized and then dried into starch powder or flakes. Pregelatinization may be achieved using techniques well known in the art including drum drying, spray drying, spray cooking and extrusion. Particular of interest is drum drying either a slurry of granular starch in water or a paste or solution of gelatinized starch. By drum drying a starch slurry, starch is simultaneously dissolved and dried on a heated drum by shear and temperature. By applying already gelatinized starch solution or paste on a rotating heated drum, a thin dry starch film is produced. Another particular relevant method to prepare cold water soluble substituted starch is starch extrusion. Extrusion may be employed to convert granular starch into pregelatinized starch as result heat and shear during extrusion. Extrusion also allows for simultaneous chemical and physical modification of granular starch into pregelatinized, cold water soluble substituted starch.

The pregelatinized starch may be grinded and sieved into a powder or flakes. The pregelatinized starch preferably has a particle size of less than 5 mm.

The substituted starch of the invention is preferably a pregelatinized starch. In further preferred embodiments, the substituted starch is a drumdried starch or an extruded starch. Further preferably, the substituted starch can be a pregelatinized and drumdried starch or a pregelatinized and extruded starch.

The substituted starch for use in the present invention can be of any origin. Preferably, the substituted starch is a substituted tuber starch, a substituted root starch, a substituted nut starch, a substituted cereal starch or a substituted legume starch. More preferably, the substituted starch can be a substituted potato starch, a substituted sweet potato starch, a substituted tapioca starch, a substituted corn starch, a substituted wheat starch or a substituted pea starch.

The quantities of substituted starch as binder and filler in the present tile adhesive are not particularly limited. Generally, the tile adhesive comprises a quantity of substituted starch, expressed relative to the dry weight of the tile adhesive, of 2 - 99 wt.%, preferably 2.5 - 75 wt.%, more preferably 5 - 50 wt.%. Further generally, the tile adhesive comprises a quantity of filler, expressed relative to the dry weight of the tile adhesive, of 1 - 98 wt.%, preferably 25 - 97.5 wt.%, more preferably 50 - 95 wt.%.

In the present tile adhesive, the mass ratio filler I substituted starch is preferably 0.25 - 40, more preferably 0.3 - 25, even more preferably 1.0 - 20.

The mass ratio filler I total binder is larger than 0.5, preferably larger than 1.0. The “total binder” quantity refers to the total of the quantity of substituted starch and any further binding materials, if present. Further binding materials in this context may be for example cement, redispersible powder, synthetic polymers or gums.

The weight ratio cement I substituted starch is equal or less than 2, preferably equal or less than 1.8, more preferably equal or less than 1.5, most preferably in the range of 0 - 1. In another preferred embodiment the tile adhesive of the invention does not comprise any cement.

The present tile adhesive may be provided in the form of a dry mix suitable for mixing with water, or in the form of an aqueous tile adhesive composition wherein the substituted starch is present in gelatinized form, which aqueous tile adhesive composition has a viscosity of 300 - 700 Pa.s, as measured with a Brookfield Helipath, using spindle T-E measured at 4 rpm and 23°C.

The dry mix is a preferred form for marketing the present tile adhesive. In case the tile adhesive is a dry mix, the substituted starch preferably is a pregelatinized substituted starch. This facilitates mixing the dry mix with water under end-use conditions so as to obtain a tile adhesive comprising a dissolved substituted starch. The dry ingredients are as defined above, and include at least a substituted starch and a filler. Alternatively, the present tile adhesive may also be provided in the form of an aqueous mixture., In case of an aqueous mixture, the substituted starch may also be a granular substituted starch. Before mixing the granular substituted starch with the other ingredients and end-use of the composition for tiling, the substituted starch must be subjected to a step of gelatinization. After gelatinization, the gelatinized starch solution is added to the other ingredients, or vice versa. The added ingredients include at least a filler.

The aqueous tile adhesive composition is the form in which the present tile adhesive will be used for tiling. It can be prepared immediately prior to tiling by mixing with water, but it can also be prepared industrially on large scale, to be marketed in suitable containers to the end consumer. In the aqueous tile adhesive composition, the substituted starch is present as a gelatinized substituted starch. Preferably, the viscosity of the aqueous tile adhesive composition is 300 - 700 Pa.s, as measured with a Brookfield Helipath, using spindle T-E measured at 4 rpm and 23°C. This viscosity is advantageous, because at this viscosity, dripping and sagging of the adhesive is minimized, while application is still relatively easy.

The tile adhesive may further optionally comprise various additional ingredients. Suitable ingredients include as non-limiting examples redispersabible polymer powder, hydrated lime, gypsum anhydrate, water retention agents such as cellulose ethers ((HP/HE)-methylcellulose) or guar gum and its derivatives. Other ingredients that may optionally be included are calcium formate, glass spheres, cellulose fibers , polypropylene Fibers, polyethylenetherephtelate fibres, polyvinylalcohol, thickeners, accelerators, retarders, superplasticizer, waterrepelent agents, hydrophobic agents, airentrainers, de-foamers, pigments, gelatin, proteine, urea formaldehyde resin, melamine formaldehyde resin, synthetic polymer dispersions,. Optionally, the tile adhesive may comprise an additive to improve the water resistance of the finished tile adhesive. Such additives can be hydrophobic agents, network -builders or hardeners.

A hydrophobic agent imparts hydrophobicity to the tile adhesive. A hydrophobic agent can be based on an additive or emulsion comprising fatty acids, or a type of oil, paraffin, or wax. Other suitable hydrophobic agents are water based silane, siloxane and silicone resin additives. Again other types are based on synthetic polymer dispersions.

Network -builders may improve the water resistance of the tile adhesive by creating a starch network during or after application of the tile adhesive. Suitable network -builders effect a crosslinking reaction of the starch hydroxyl groups during or after tiling with the present adhesive. Suitable network -builders in the present context can be crosslinkers known for starch crosslinking as discussed elsewhere, which allow for a crosslinking reaction under the conditions at which the tile adhesive is applied (that is, ambient temperature in aqueous environment). One suitable network-builder is glyoxal. Other suitable starch network-builders are zirconium carbonate, borax, and compounds comprising multiple aldehyde or epoxy groups.

Hardeners may alternatively be added to induce the formation of a network during or after tiling. To this end proteins such as gelatin may be added, or a network-forming resin such as an urea formaldehyde resin or a melamine formaldehyde resin. A further suitable hardener is water glass.

The tile adhesive may comprise a synthetic binder such as an acrylic resin. Preferably, the present tile adhesive does not comprise more than 15 wt.%, relative to dry matter of the total composition, of synthetic binders. In much preferred embodiments, the present adhesive does not comprise synthetic binders. The invention furthermore provides a method for preparing a tile adhesive as defined above, comprising, in any order, the steps of providing a solution of a substituted starch in water, and homogenization of dry ingredients in water at a water/total dry ingredients mass ratio of 0.1 - 5. End use of the present tile adhesive is based on the aqueous tile adhesive composition, in which the substituted starch is present in a dissolved form as a gelatinized substituted starch.

In either option, the dry ingredients are mixed with water at a water/total dry ingredients mass ratio of 0.1 - 5, preferably 0.2 - 4, more preferably, 0.3 - 3. This mass ratio ensures that the mixture obtained after homogenization has an appropriate viscosity. The dry ingredients are as defined above, and include at least a substituted starch and a filler.

The preferred viscosity for end-use of the present tile adhesive is 300 - 700 Pa.s, as measured with a Brookfield Helipath, using spindle T-E measured at 4 rpm and 23°C.

In some embodiments, the tile adhesive can be fully starch-based. In such embodiments, the tile adhesive comprises a gelatinized substituted starch as binder and a granular starch as filler, preferably a pregelatinized substituted starch as binder and a granular starch as filler. The fully starch-based tile adhesive can be admixed with cold water to provide an aqueous tile adhesive composition, which can be used as detailed elsewhere. The use of granular potato starch as filler provides the advantage that the tile adhesive is fully renewable and 100 % starch-based.

The invention furthermore provides a method for providing a surface with one or more tiles, comprising the steps of a) providing an aqueous tile adhesive composition comprising a gelatinized substituted starch as defined elsewhere, which aqueous tile adhesive composition has a viscosity of 300 - 700 Pa.s, and which aqueous tile adhesive composition is optionally provided by homogenizing a dry mix for a tile adhesive as defined elsewhere with water; b) providing a surface which is to be provided with one or more tiles or at least one tile which is to be tiled onto a surface at least partially with the aqueous tile adhesive composition; c) attaching one or more tiles onto the surface; d) allowing the aqueous tile adhesive composition to dry.

In the present method for providing a surface with one or more tiles, steps b) - d) represent steps in line with common general knowledge in the field of tiling. Step a) represents the provision of the aqueous tile adhesive composition for use in tiling, which may be provided as is (such as an aqueous composition from a suitable container), or which may be provided by homogenization of a dry mix with water.

The invention furthermore provides a surface comprising one or more tiles, wherein said tiles are attached to the surface using a tile adhesive as defined above. Said surface comprising one or more tiles comprises 3 layers: a base surface layer, an intermediate layer and a tile layer, wherein the base layer is a surface capable of being provided with tiles, the intermediate layer comprises the dried tile adhesive, and the tile layer comprises tiles, as defined elsewhere.

The base surface layer is the surface layer onto which the tiles are adhered using the tile adhesive. The base surface layer can be made from different types of materials such as concrete, bricks, wood, mortar or plaster. The tile adhesive is suitable to fix tiles to any base surface layer, but in particular is suitable to adhere tiles to concrete or wood base surface layers. The intermediate surface comprises the dried tile adhesive, and as such comprises a gelatinized substituted starch and a filler, as well as any optional further ingredients, defined elsewhere.

Examples

The tile adhesives described below are prepared by dry mixing of the solid ingredients. Cold water soluble starches have been used for the preparation of the aqueous tile adhesives. Tap water (20 °C) has been used. All solid materials have been used as commercially dry.

Preparation of tile adhesive

The mixing procedure is based on EN- 120004. In short:

• Dry blend all the compounds in a plastic bag, close the bag and shake well.

• Fill mixing bowl with required amount of water.

• Attach the paddle to the mixer.

• Add the dry blend to the water and place the bowl into the mixer and start the mixer after 30 seconds (t=0)

• The mixer follows the following mixing protocol: a. Minute 0 to A: the mortar is mixed with the mixer at 140 rpm. b. Minute A to lA: rest; lower the bowl in the mixer and scrape the paddle; take the bowl out of the mixer and scrape inner side of the bowl. c. Minute 1A to 2 A: the mortar is mixed again at 140 rpm d. Minute 2 A to 5: rest; when the viscosity is high, again scrape down the paddle and bowl. e. Minute 5 to 5A: final mixing with the mixer at 140 rpm. • Take the bowl out of the mixer and scrape down the paddle and bowl.

• When necessary, carefully cut through the mortar with the silicone spatula to get rid of air cavities in the mortar and flatten the surface of the mortar with the top of the silicone spatula

Viscosity measurement

The viscosity is determined by Brookfield Helipath, using spindle T-E at 4 rpm and 23°C. The viscosity measurement is started 7 minutes after start of adhesive preparation. Measuring points are taken with an interval of 1 secon. After 18 seconds of stabilization, the average of 10 data points (10 seconds) is reported as the viscosity. The water/powder ratio (w/p ratio) is chosen in such a way that the Brookfield viscosity of the tile adhesive is between 300 and 700 Pa.s,

Adhesion strength and open time

The adhesion strength and open time is determined according to EN 12004, using Winckelmans tiles but also using MOSA tiles. For adhesion strength Winckelmans tiles are used. Winckelmans tiles have (very) low porosity (water adsorption < 0.5 % by mass), whereas MOSA tiles used for open time have high porosity (water adsorption about 15 ± 3%). Using both high and low porosity tiles, the general applicability of the present tile adhesive is supported. Unless otherwise mentioned, adhesion was determined on a concrete surface. In short:

10 minutes after the start of the preparation, a layer of tile adhesive is applied onto a surface • Place Winckelmans tiles into the adhesive layer 5 minutes after applying the adhesive layer. These tiles are used for adhesion strength.

• Place MOSA tiles into the adhesive layer 5, 30 or 60 minutes after applying the adhesive layer. These tiles are used for open time.

Starches used in the present examples include the following.

AS and DC are expressed as the amount of reagent added to starch during reaction as mol reagent per mol AGU. A conventional reference cement -based tile adhesive was prepared according to the following recipe:

¹ Quartz sand; D50 of 144 gm

² HPMC defined by viscosity (2% solution, 20°C): 25,000 - 35,000 mPa-s

Example 1: starch types for use as tile adhesive

Starch-based tile adhesives were prepared using the following recipe:

¹ Quartz sand; D50 of 144 gm

Starch is added as commercially dry material. The moisture content depends on the starch type: Dextrins (11 wt% moisture), Maltodextrin (7 wt.%), Extruded starch (13 wt.%), Drumdried starch (6 wt.%).

Adhesion strength was determined following EN 12004 for all types of starch. The results are provided in Table 1:

¹ w/p = water/powder ratio.

In table 1, it is shown that starches 1 - 7 show insufficient adhesion to Winckelmans. Starches 8 - 18 all show the required adhesion to Winckelmans, easily fulfilling C2 requirements.

From this, it can be inferred that substituted starches provide for sufficient adhesion under EN 12004. It can also be inferred that many starch types even perform better than the reference (cement -based) tile adhesive, even in the absence of cement. Further modification of the starch, such as crosslinking, does not prevent adhesion of a substituted starch. Crosslinked starch may thus be used in situations where this could lead to optimized rheology. Example 2: fillers to be combined with starches in a tile adhesive

Using starch 9, the tolerability of the tile adhesive for the presence of different fillers was evaluated using the recipe of Example 1. Alternative fillers used were Durcal 40 (a calcium carbonate with a D50 of 40 pm), or native potato starch. It is to be noted that the native potato starch was present in the tile adhesive in granular form. The tile adhesive as used in the adhesion tests in Experiment 2-2 thus comprised a gelatinized substituted starch as binder and a granular starch as filler.

The results are shown in table 2:

The results show that alternative fillers can be used while still fulfilling C2 requirements under EN 12004.

Example 3: tolerance in the ratio substituted starch/filler

Different ratios between the substituted starch and the filler were evaluated, using starches 9 and 13 as exemplary starches and using quartz sand as the filler. The results are shown in table 3.

The results show that at 1 % of starch 9 the adhesion becomes insufficient, while as of 2.5 % until 100 % of starch 9 the adhesion fulfills the requirements C2. Similar behavior is observed for starch 13. An increase in starch content (and thus a decrease in sand content) results in the need for a higher w/p ratio. Notably, a filler is not strictly required in order to fulfil the adhesion requirements.

Table 3:

Example 4: open time

A starch-based tile adhesive based on starch 9 in the recipe of Example 1 was compared to the cement based reference adhesive, using MOSA tiles. The filler in both adhesives was sand (Dorentrup 12 A). The results are shown in Table 4:

Table 4 shows that both the reference (experiment 4-2) and the starch 9 formulation (experiment 4-5) fulfill the requirements of an adhesive strength of at least 0.5 N/mm² after an open time of 30 minutes. However, the starch 9 formulation (experiment 4-6) still easily fulfills this requirement even after 60 minutes whereas the cementitious reference does not (experiment 4-3). Therefore, the open time of the present (starch-based) tile adhesive is longer than the open time of the cement-based reference, which allows the tiler to work with less time constraints and to apply the adhesive to a larger surface area than with traditional cement-based tile adhesives., and which thus avoids waste generation to a significant degree.

Example 5: adhesion to an alternative surface material

Various starch-based tile adhesives according to the recipe of Example 1 were tested for their adhesive strength to wood (multiplex), and compared to the cement -based reference, using the procedure set forth in EN 12004.

The results are shown in table 5:

Table 5 and the previous examples show that the starch-based tile adhesive can be used on different surfaces, including wood and concrete. Moreover, the experiment shows that a substituted starch is required for adhesion of a tile to a wooden surface as the unsubstituted starch 7 (drum dried potato starch) did not provide any adhesion strength. Example 6: hybrid tile adhesives

The tolerance of the present starch-based tile adhesive for the presence of cement, was evaluated. This was done by evaluating mixtures of the reference tile adhesive and the present formulations, in various proportions. The evaluated compositions are shown below:

This translates to adhesion tests on the following compositions, with the results as shown in table 6 (quantities in wt.% as is):

PARAMETERS

The results in Table 6 show that mixtures comprising a substituted starch, a filler as well as cement do not always provide sufficient adhesion strength. However, presence of cement is tolerated, albeit at the cost of adhesion strength. It follows that cement may be present, but preferably in relatively low quantities, as compared to the substituted starch.

Example 7: tolerance for other ingredients The tolerance of the present starch-based tile adhesive for the presence of other components was evaluated. This was done by addition of additives which are common in cement -based tile adhesive, as well as another additive. The type of components, and the results, are shown in table 7:

Table 7 demonstrates that addition of typical cementitious tile adhesive components like redispersible powders (“RD P”, Vinnapas 5010 N) or nanoclay (Cloisite 116) do not affect the adhesion negatively. Neither does an atypical cementitious tile adhesive component like Gelatin 250 Bloom.

Claims

1. A tile adhesive, comprising a substituted starch and a filler, wherein the weight ratio of cement to substituted starch is 0 - 2.

2. A tile adhesive according to claim 1, wherein the filler comprises sand, clay, calcium carbonate, granular starch, ground waste concrete, ground waste plastic, ground organic material, ground inorganic material and/or saw dust.

3. A tile adhesive according to claim 1 or 2, wherein the filler has a particle size, expressed as D50, of at least 1, preferably at least 5 pm, and wherein the particle size preferably is at most 500 pm, preferably at most 300 pm, more preferably at most 175 pm.

4. A tile adhesive according to any of claims 1 - 3, wherein the substituted starch is a carboxymethylated starch, a hydroxybutylated starch, a hydroxypropylated starch, a hydroxyethylated starch, an acetylated starch, an octenyl succinated starch, a cationic starch, or any combination thereof, and wherein preferably, the degree of substitution of the said starch is at least 0.01 mol/mol.

5. A tile adhesive according to claim 4, wherein the substituted starch is also a crosslinked starch, preferably an epichlorohydrin crosslinked starch, a trimetaphosphate-crosslinked starch, a phosphoryl chloride crosslinked starch, an adipate crosslinked starch, and/or wherein the substituted starch is also a degraded starch, preferably an acid-degraded starch, an physically degraded starch or an enzymatically degraded starch.

6. A tile adhesive according to any of claims 1 - 5, wherein the substituted starch is a pregelatinized starch.

7. A tile adhesive according to any of claims 1 - 6, wherein the substituted starch is a substituted tuber starch, a substituted root starch, a substituted nut starch, a substituted cereal starch, or a substituted legume starch, and wherein the substituted starch is preferably a substituted potato starch, a substituted sweet potato starch, a substituted tapioca starch, a substituted corn starch, a substituted wheat starch or a substituted pea starch.

8. A tile adhesive according to any of claims 1 - 7, wherein the quantity of substituted starch is 2 - 99.9 wt.% and wherein the quantity of filler is 0.1 - 98 wt.%, said quantities being expressed relative to the dry weight of the tile adhesive.

9. A tile adhesive according to any of claims 1 - 8, wherein the mass ratio filler I substituted starch is 0.25 - 40, preferably 0.3 - 25, more preferably 1.0 - 20.

10. A tile adhesive according to any of claims 1 - 9, wherein the mass ratio filler I total binder is larger than 0.5, preferably larger than 1.0.

11. A tile adhesive according to any of claims 1 - 10, wherein the tile adhesive does not comprise cement.

12. A tile adhesive according to any of claims 1 - 11, wherein the tile adhesive is a dry mix suitable for mixing with water, wherein the substituted starch is a pregelatinized starch, or wherein the tile adhesive is an aqueous tile adhesive composition wherein the substituted starch is a gelatinized substituted starch, which aqueous tile adhesive composition has a viscosity of 300 - 700 Pa.s measured with a Brookfield Helipath, using spindle T-E measured at 4 rpm and 23°C.

13. A method for preparing a tile adhesive according to any of claims 1 - 12, comprising, in any order, the steps of providing a solution of a substituted starch in water, and homogenization of at least one dry ingredient in water at a water/total dry ingredients mass ratio of 0.1 - 5.

14. A method for providing a surface with one or more tiles, comprising the steps of a) providing an aqueous tile adhesive composition comprising a gelatinized substituted starch as defined in claim 12, which aqueous tile adhesive composition is optionally provided by homogenizing the dry mix for a tile adhesive as defined in claim 12 with water; b) providing a surface which is to be provided with one or more tiles, or at least one tile which is to be tiled onto a surface, at least partially with the aqueous tile adhesive composition; c) attaching the one or more tiles onto the surface ; d) allowing the aqueous tile adhesive composition to dry.

15. A surface comprising one or more tiles, wherein said tiles are attached to the surface using a tile adhesive as defined in any of claims 1 -