WO2020229406A1

WO2020229406A1 - Composition comprising polyninyl chloride (pvc) and organosilane-modified colloidal silica and associated method of preparation

Info

Publication number: WO2020229406A1
Application number: PCT/EP2020/063044
Authority: WO
Inventors: Asbjorn HOLT; Harald Jacobsen; Hans Lagnemo; Per Restorp; Anders Torncrona
Original assignee: Nouryon Chemicals International B.V.; Inovyn Europe Limited
Priority date: 2019-05-14
Filing date: 2020-05-11
Publication date: 2020-11-19

Abstract

The invention relates to a composition comprising PVC and colloidal silica particles, in which the colloidal silica particles are organosilane- modified. The invention also relates to a process for preparing such a composition in which PVC is formed by suspension or emulsion polymerisation, and adding orga nosilane-modified colloidal silica. The invention further relates to the use of orga nosilane-modified colloidal silica in improving the cleanability of PVC, improving the dirt pick-up resistance of PVC, increasing thermal stability of PVC and increasing weathering resistance of PVC.

Description

COMPOSITION COMPRISING POLYNINYL CHLORIDE (PVC) AND ORGANOSILANE-MODIFIED COLLOIDAL SILICA AND ASSOCIATED METHOD OF

PREPARATION

Technical Field

The present invention relates to a modified polyvinylchloride (PVC) having improved dirt pick-up resistance, improved cleanability, improved weathering resistance characteristics, and, in particular, improved thermal resistance. More specifically, the invention is directed to the use of colloidal silica and organosilane-modified colloidal silica for improving one or more of the dirt pick-up resistance, cleanability, weathering characteristics, and thermal stability of PVC.

Background Art

PVC is a widely used polymer, with applications in many fields, such as flooring, electric cable insulation, in buildings (e.g. uPVC windows), in tarpaulin sheet, in clothing and furniture, in sewage and water pipes, and in laboratory-ware (e.g. in containers, caps and flexible tubing).

PVC nanocomposites can be prepared in order to modify various properties of the polymer. For example, EP 2 428 531 describes the production of PVC modified with a nanomaterial source, which can be selected from silica, montmorillonite, organically modified montmorillonite, nano-metal, metal oxides, or inorganic or organic fibres.

WO 2015/007522 also describes the preparation of nanoparticle-modified polymers, such as PVC, in which the use of colloidal silica is exemplified.

CN102140217 describes PVC comprising an impact resistant modifier that comprises a silica/polyacrylate composite.

Colloidal silica can itself be modified with organic moieties, for example organosilanes, as described for example in W02004/035473, W02004/035474, which describe their use in paints and coatings applications. Similar uses are also mentioned in W02013/167501, and in Greenwood et al.; Pigment and Resin Technology, 40(5), 2011, 275-284. US

2010/0288963 discloses coatings with improved dirt resistance, comprising nano-silica particles having an aldehyde-containing oxysilane group.

Sun et al, Eur. Polymer. I; 42 (2006), 1643-1652 describes PVC composites comprising fumed silica, and also dimethyl dichloro silane-modified or g-methaylacryloxypropyl trimethoxy silane-modified fumed silica. The modified fumed silica reportedly imparts improved impact strength and tensile strength to the PVC, compared to fumed silica-free, while unmodified fumed silica-containing materials have reduced impact and tensile strength.

There remains a need for producing PVC having improved properties.

Summary of Invention

The invention is directed to a composition comprising polyvinyl chloride (PVC) and colloidal silica particles, the colloidal silica particles being modified with an organosilane.

The invention is also directed to a process for preparing such a composition, comprising producing a PVC dispersion from vinyl chloride monomer using suspension or emulsion polymerisation, and adding organosilane-modified colloidal silica.

The invention is further directed to the use of colloidal silica or organosilane-modified colloidal silica in any one or more of the following:

(i) improving the cleanability of PVC,

(ii) reducing dirt adherence to PVC;

(iii) increasing thermal stability of PVC;

(iv) improving weathering resistance of PVC. Brief Description of Drawings

Figure l is a bar chart comparing dirt pick-up and cleanability characteristics of unmodified and colloidal silica-modified PVC films that were exposed to iron oxide for 24h, where the colloidal silica content is 1 phr.

Figure 2 is a bar chart comparing dirt pick-up and cleanability characteristics of unmodified and colloidal silica-modified PVC films that were exposed to carbon black for 24h, where the colloidal silica content is 1 phr.

Figure 3 is a bar chart comparing dirt pick-up and cleanability characteristics of unmodified and colloidal silica-modified PVC films that were exposed to iron oxide for 24h, where the colloidal silica content is 5 phr.

Figure 4 is a bar chart comparing dirt pick-up and cleanability characteristics of unmodified and colloidal silica-modified PVC films that were exposed to carbon black for 24h, where the colloidal silica content is 5 phr.

Figure 5 is a bar chart comparing dirt pick-up and cleanability characteristics of modified colloidal silica-modified PVC films with PVC films modified with alternative, non- colloidal sources of silica.

Figure 6 is a bar chart comparing tensile strength at break of unmodified and colloidal silica-modified PVC films, where the colloidal silica content is 1 phr.

Figure 7 is a bar chart comparing tensile strength at break of unmodified and colloidal silica-modified PVC films, where the colloidal silica content is 5 phr.

Figure 8 is a bar chart comparing elongation at break of unmodified and colloidal silica- modified PVC films, where the colloidal silica content is 1 phr. Figure 9 is a bar chart comparing elongation at break of unmodified and colloidal silica- modified PVC films, where the colloidal silica content is 5 phr.

Figure 10 is a graph comparing changes in yellowing index with time for PVC/colloidal silica nanocomposite materials.

Figure 11 is a graph comparing changes in colour with time for PVC and PVC/colloidal silica nanocomposites.

Figure 12 is a graph comparing yellowing index with time for PVC and PVC/colloidal silica nanocomposites.

Figure 13 is a graph comparing viscosity properties of PVC and PVC/colloidal silica nanocomposite materials.

Figure 14 compares abrasion resistance of PVC and PVC/colloidal silica nanocomposite materials.

Description of Embodiments

The invention is directed to the use of colloidal silica for improving the properties of PVC. [PVC]

In the present invention, PVC refers to vinyl chloride polymers, and also copolymers.

In the present description, the terms "vinyl chloride polymer",“polyvinyl chloride”,

“PVC” or simply "polymer", mean a polymer containing at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight and particularly preferably at least 85% by weight of monomeric units derived from vinyl chloride

(monomer), i.e. both homopolymers of vinyl chloride (containing 100% by weight of monomers derived from vinyl chloride) and vinyl chloride copolymers with one or more ethylenically unsaturated monomers.

Examples of ethylenically unsaturated monomers copolymerizable with vinyl chloride include chlorinated monomers such as vinylidene chloride, fluorinated monomers such as vinylidene fluoride, monomers containing both chlorine and fluorine such as

chlorotrifluoroethylene, vinyl esters such as vinyl acetate, vinyl ethers such as vinyl methyl ether, dialkyl maleates such as dibutylmaleate, (meth) acrylic monomers such as n-butyl acrylate and methyl methacrylate, styrenic monomers such as styrene, and olefmic monomers such as ethylene, propylene and butadiene.

Several processes are known for the preparation of PVC. For example, PVC may be prepared by suspension polymerisation of vinyl chloride in a suspending liquid and in the presence of a suspending agent. This produces a slurry (or suspension) of PVC particles, typically of the order of 100 to 200 microns particle size. The resulting slurry of PVC is then dried, usually by centrifuging followed by fluid bed drying, to give a porous (i.e. sorbent) PVC. PVC produced by the suspension method is referred to as“S-PVC”. S- PVC can absorb plasticisers to give a dry blend.

PVC can also be produced by what are generally known as paste polymerisation processes. These are so-called because the resin formed, which may also be referred to as paste-PVC, is non-absorbent at ambient temperatures, so that when mixed with a plasticizer a paste (or plastisol) is formed. As well as the difference in porosity of the formed PVC compared to S-PVC, paste processes may also be characterised in that the polymerisation produces a latex of polymer particles of relatively small size compared to the S-PVC process, typically 0.2 to 5 microns. The latex can be dried, for example by spray-drying to produce PVC particles in the form of agglomerates. As well as being non-absorbent at ambient temperatures, the dried PVC polymer particles are compact and also much smaller than the dried particles produced by the suspension PVC processes.

An example of such a process is an emulsion polymerisation process. In such a process an emulsifier is used to produce small droplets of the monomer in a liquid phase. These polymerise to produce relatively small particles of PVC, known as“primary particles”, typically of the order of 0.2 to 1 micron particle size, in the form of a latex comprising said particles. The latex can then be spray-dried to produce PVC particles in the form of agglomerates, typically with a particle size of up to 63 microns. PVC polymer particles produced by such a process are much smaller than those produced by the suspension PVC processes, are compact and are non-absorbent at ambient temperatures. The PVC formed by emulsion polymerisation is a type of paste-PVC and may be referred to as such, but more specifically is usually referred to as“E-PVC”.

Other paste PVC processes include those known as mini-emulsion and micro-suspension, which polymerisations produce latexes of polymer particles typically of the order of about 0.2 to 5 microns particle size. These latexes can also be spray-dried to produce paste PVC particles.

Resin particles produced by paste polymerisation are generally used to make sheets and plastisols.

The modified PVC of the present invention can be prepared by incorporating a source of colloidal silica into a dispersion of the PVC polymer. Examples of suitable methods are described further below.

[Colloidal Silica]

In the discussion below, the terms“silica sol” and“colloidal silica” have the same meaning.

As used herein the term“colloidal silica” refers to a dispersion comprising 1 to 50wt% silica particles dispersed in an aqueous medium. The aqueous medium may comprise organic solvent, but where it does so it preferably comprises less than 10wt% organic solvent. If dissolved organic solvent is present, the aqueous medium more preferably contains no more than 5 wt% organic solvent. Typical organic solvents, when present, are water- miscible, for example being selected from one or more of C1-4 alkyl alcohols, C1-4 aldehydes, C1-4 ketones, C1-4 carboxylic acids and their C1-4 alkyl esters.

Aqueous silica sols can be basic, having a pH in the range of from 8.0 to 12.0, for example from 8.5 to 11.0. Other components of such sols include the presence of alkali metals, typically one or more of lithium, sodium and potassium. Typically sodium is the sole or predominant alkali metal. The alkali metals can be derived from soluble silicate solutions (e.g. water glass) that can be used to make the colloidal silica using conventional processes.

Examples of suitable aqueous alkali metal silicates or water glass that can be used to make aqueous silica sols include lithium, sodium and potassium silicates, preferably sodium silicate.

The silica particles are typically amorphous nanoparticles, and most typically have a particle diameter ranging from 2 to 150 nm as discussed further below.

It is preferred that the colloidal silica is made from particle growth from a soluble silicate or a polysilicic acid solution, and is not prepared by creating a dispersion from a solid form of silica nanoparticle. For example, in embodiments, the colloidal silica is not derived from solid forms of silica such as amorphous forms of fumed silica, silica fume and precipitated silica.

It is also preferred that the colloidal silica is not derived from crystalline forms of silica, such as micro-quartz or nano-quartz, which suffer the additional disadvantage of potential health risks.

Soluble silicate-derived colloidal silicas tend to have less aggregation of the silica particles compared to dispersions made from solid forms of silica. This is because, in general, solid forms of silica nanoparticle tend to be in the form of agglomerates of the primary nanoparticles, and it is not possible to disperse such silicas to create a colloidal silica comprising predominantly the discrete primary particles because larger agglomerates tend to remain. The silica particles in such colloidal silicas therefore tend to settle (precipitate) relatively rapidly. In contrast, colloidal silicas made from particle growth from a soluble silicate or a polysilicic acid solution do not include such large silica agglomerates. They are therefore stable and do not noticeably gel or precipitate for many months, typically for greater than 12 months.

In most preferred embodiments, the colloidal silica is made by converting soluble alkali metal silicate to polysilicic acid (with a pH typically in the range of from 1-3) by ion exchange or treatment with acid, and raising the pH to 7 or more, typically 8 to 12, for example 9 to 11, using a basic alkali metal salt such as alkali metal hydroxide or alkali metal silicate.

The content of alkali metals in the starting silica sol is typically in the range of from 0.1 to 5.0 wt%, expressed as alkali metal oxide. In embodiments, it is from 0.2 to 3.0 wt%.

The silica concentration in the colloidal silica is typically in the range of from 1 to 40wt%, for example from 2 to 35wt% or from 3 to 30wt%. As used here, silica concentrations are expressed as SiCk. A preferred minimum concentration is 5wt%, and most preferred ranges are therefore 5 to 50wt%, and more preferably 5 to 40wt%, for example 5 to 35wt% or 5 to 30wt%.

The colloidal silica particles typically have a surface area in the range of from 50 to 1000 m² g ¹, for example in the range of from 100 to 700 m² g ¹, such as in the range of from 140 to 550 m² g ¹. The surface area of colloidal silica particles in a silica sol can be calculated from NaOH titration following the method of Sears (Sears; Anal. Chem., 1956, 28(12), 1981-1983). The colloidal silica particles typically have an average particle diameter in the range of from 2 to 150 nm, for example from 2 to 100 nm or from about 3 to about 75 nm. In further embodiments, the particle diameter is in the range of from 4 to 50 nm.

The particle diameters can be calculated from the titrated surface area using a method described in "The Chemistry of Silica", by Iler, K. Ralph, page 465, John Wiley & Sons (1979). Based on the assumption that the silica particles have a density of 2.2 g cm ³, and that all particles are of the same size, have a smooth surface area and are spherical, then the particle diameter (PD) can be calculated from Equation 1 :

2727

^{P D} C¹™) = Surface Area (i,²g-¹) E^⁰" '

Other ways of measuring average particle diameters include ES-DMA (electro- spray differential mobility analysis), CLS (centrifugal liquid analysis), SEM (scanning electron microscopy) and TEM (transmission electron microscopy).

In embodiments, for unmodified colloidal silica, the S value is in the range of from 20 to 95 %, for example from 30 to 90%. The S-value is measured and calculated as described by Iler & Dalton (Iler & Dalton; J. Phys. Chem. 60(1956), 955-957). The S-value indicates the degree of aggregate or microgel formation and a lower S-value is indicative of a higher degree of aggregation.

The density of the silica sol is at least in part dependent on the silica content, and is typically in the range of from 1.01 to 1.45 g cm ³, and preferably of from 1.01 to 1.30 g cm ³. Density can be determined using ASTM D4052-18a.

The viscosity of the starting aqueous silica sol is typically less than 40 cP, for example less than 30 cP, and in particular less than 20 cP. In embodiments, it is less than 10 cP. These viscosities are measured at 20.0°C. Viscosities of silica sols, including those described herein, can be measured using a conventional rotational viscometer. A method that can be used is ASTM D4016-14. In aqueous systems, the colloidal silica particles can be dispersed in the presence of stabilising cations, which can be selected from alkali metals (e.g. K⁺, Na⁺, Li⁺), ammonium (NH₄ ⁺), organic cations, quaternary amino, tertiary amino, secondary amino, and primary amino, or mixtures thereof. Typically, they are selected from alkali metals and

ammonium.

Examples of sols that can be used as starting aqueous silica sols include silica sols marketed under the name Levasil™ or Bindzil™ from Nouryon.

[Organosilane-Modified Colloidal Silica]

The colloidal silica in embodiments can be functionalised with organosilane groups, which in embodiments are hydrophilic organosilane moieties.

Organosilane-functionalised colloidal silica can be made by conventional processes, as described for example in W02004/035473 or W02004/035474, and comprises colloidal silica particles modified with an organosilane moiety, which in embodiments is a hydrophilic organosilane moiety.

Typically, the organosilane-functionalised colloidal silica is formed from a reaction between one or more organosilane reactants, which can be expressed generally by the formula A4-_ySi-[R^m]_y, and one or more silanol groups on the silica surface, i.e. [SiCkl-OH groups. The result is a silica surface comprising one or more organosilane moieties attached to the surface.

In the organosilane reactant, each“A” is typically independently selected from Ci-₆ alkoxy, Ci-₆ haloalkoxy, hydroxy and halide. Other options are the use of siloxanes, e.g. of formula [R^m]bA3-bSi{-0-SiA2-_c[R^m]c}a-0-SiA3-b[R^m]b, where a is 0 or an integer of 1 or more, typically from 0 to 5; b is from 1 to 3; and c is from 1 to 2.

Other examples include disilazanes, of formula {[R^m]_bA3-_bSi}2-NH where b is from 1 to 3. Of the haloalkoxy groups, fluoro and chloro are preferred halo substituents. Alkoxy groups and halides are often preferred as the“A” species. Of the halides, chloride is a suitable choice. Of the alkoxy groups, C1-4 alkoxy groups, such as methoxy, ethoxy, propoxy or isopropoxy, are suitable choices. In embodiments, the organosilane reactant can undergo a prehydrolysis step, in which one or more“A” groups are converted to -OH, as described for example by Greenwood and Gevert, Pigment and Resin Technology, 2011, 40(5), pp 275-284.

The organosilane reactant can react with a surface silanol group to form from one to three Si-O-Si links between the silica surface and the organosilane silicon atom, i.e. { [S1O2]- 0-}_4-y-zSi[A]_z[R^m]_y where z is typically from 0 to 2, y is typically from 1 to 3, and 4-y-z is from 1 to 3, and usually in the range of from 1 to 2. A corresponding number of“A” groups are removed from the organosilane as a result. Remaining“A” groups can be converted to other groups as a result of reaction (e.g. hydrolysis) under the conditions experienced in the silanisation reaction. For example, if“A” is an alkoxy unit or a halide, it can convert to a hydroxy group.

It is also possible for at least a portion of the organosilane to be in a dimeric form or even oligomeric form before binding to the colloidal silica, i.e. where the two or more organosilane moieties are bound to each other through Si-O-Si bonds.

The chemically bound organosilane groups can be represented by the formula [{S1O2}- 0-]_4-y-z-Si[D]_z[R^m]_y. The group (SiCkj-O- represents an oxygen atom on the silica surface. The organosilane silicon atom has at least one, and optionally up to three such bonds to the silica surface, where 4-y-z is from 1 to 3, and usually in the range of from 1 to 2, i.e. 4-y-z is at least 1, and no more than 3. Group“D” is optionally present, and z is in the range of from 0 to 2. The organosilane silicon atom has from 1 to 3 [R^m] groups, i.e. y is from 1 to 3, typically from 1 to 2. Where there is more than 1 R^m group, they can be the same or different.

When z is not zero, the organosilane silicon contains unreacted“A” groups, and/or contains hydroxyl groups where the“A” group has been removed, for example through a hydrolysis reaction. Alternatively or additionally, an Si-O-Si link can be formed with the silicon atom of a neighbouring organosilane group. Thus, in the formula {[Si0₂]-0-}_4-y- _zSi[D]_z[R^m]_y, group“D” can (on each occurrence) be selected from the groups defined under“A” above, and also from hydroxy groups and -O- [SiR^m]’ groups where the

[SiR^m]’ group is a neighbouring organosilane group.

R^m is an organic moiety directly bound to a silicon atom by a direct Si-C bond. For convenience, the silane moiety attached to the silica surface can be represented by ºSiR^m, where ºSi represents the silicon atom of the silane moiety that is attached to the silica surface, and R^m can comprise from 1 to 16 carbon atoms, for example from 1 to 12 carbon atoms, or from 1 to 8 carbon atoms.

There can be more than one R^m group on each silane silicon atom (i.e. if y is greater than 1), in which case each R^m can be the same or different.

In other embodiments, the colloidal silica particles can be modified with two or more different organosilane moieties, for example there can be two different ºSiR^m groups, where two or more different organosilanes with different R^m groups are used to modify the colloidal silica.

In embodiments, R^m is a hydrophilic moiety. Where, for example, a PVC dispersion is employed as the source of PVC, the hydrophilic moiety enables the modified colloidal silica to be miscible with the aqueous phase. In addition, hydrophilic moieties are preferred, as they tend to impart better dirt pick-up resistance compared to hydrophobic moieties.

In embodiments, R^m comprises at least one group selected from hydroxyl, thiol, carboxyl, ester, epoxy, acyloxy, ketone, aldehyde, (meth)acryloxy, amino, amido, ureido, isocyanate or isocyanurate. In further embodiments, hydrophilic moieties comprise at least one heteroatom selected from O and N, and comprise no more than three consecutive alkylene (-CH2-) groups linked together. In embodiments, R^m comprises no aldehyde groups. R^m can comprise alkyl, alkenyl, epoxy alkyl, aryl, heteroaryl, Ci-₆ alkylaryl and Ci-₆ alkylheteroaryl groups, optionally substituted with one or more groups selected from ERⁿ.

In ERⁿ, E is either not present, or is a linking group selected from -0-, -S-,

-OC(O)-, -C(O)-, -C(0)0-, -C(0)0C(0)-, -N(R^P)-, -N(R^p)C(0)-,

-N(R^p)C(0)N(R^p)- and -C(0)N(R^p)- where R^p is H or Ci-₆ alkyl.

Rⁿ is linked to E, or directly to R^m if E is not present, and is selected from halogen

(typically F, Cl or Br), alkyl, alkenyl, aryl, heteroaryl, C1-3 alkylaryl and C1-3

alkylheteroaryl. Rⁿ can optionally be substituted with one or more groups selected from hydroxyl, halogen (typically F, Cl or Br), epoxy ,-OR^p or -N(R^P)2 where each R^p is as defined above. If E is present, Rⁿ can also be hydrogen.

In the above definitions, alkyl and alkenyl groups can be aliphatic, cyclic or can comprise both aliphatic and cyclic portions. Non-cyclic aliphatic groups or portions can be linear or branched. Where any group or substituent comprises halogen, the halogen is preferably selected from F, Cl and Br.

Some groups can undergo hydrolysis reactions in the colloidal silica medium, for example in sols having basic pH values. Thus, groups containing moieties such as halide, acyloxy, (meth)acryloxy and epoxy groups can hydrolyse to form corresponding carboxyl, hydroxyl or glycol moieties.

In embodiments, one or more R^m groups are Ci-₈ alkyl, Ci-₈ haloalkyl, Ci-₈ alkenyl or Ci-₈ haloalkenyl, typically Ci-₈ alkyl or Ci-₈ alkenyl, with an optional halide (e.g. chloride) substituent. Examples include methyl, ethyl, chloropropyl, isobutyl, cyclohexyl, octyl and phenyl. These Ci-₈ groups can, in embodiments, be Ci-₆ groups or, in further

embodiments, C_1-4 groups. Longer carbon chains tend to be less soluble in an aqueous system, which makes synthesis of the organosilane-modified colloidal silica more complex. In embodiments, R^m is a group comprising from 1 to 8 carbon atoms, e.g. a Ci-₈ alkyl group, and which additionally comprises an ERⁿ substituent where E is oxygen and Rⁿ is selected from optionally substituted Ci-₈-epoxyalkyl and Ci-₈ hydroxyalkyl or

dihydroxy alkyl. Alternatively, Rⁿ can be optionally substituted alkylisocyanurate.

Examples of such ERⁿ substituents include 3-glycidoxypropyl and 2,3- dihy droxypropoxypropyl .

In embodiments, R^m is a group comprising from 1 to 8 carbon atoms, e.g. a Ci-₈ alkyl group, and which additionally comprises an ERⁿ substituent where E is not present, and Rⁿ is epoxyalkyl, for example an epoxy cycloalkyl. An example of such an R^m group is beta- (3, 4-epoxy cy cl ohexyl)ethyl. The epoxy group can alternatively be two neighbouring hydroxyl groups, e.g. Rⁿ can be a dihydroxyalkyl such as a dihydroxy cycloalkyl, and R^m being (3,4-dihydroxycyclohexyl)ethyl.

There can be more than one different organosilane in the modified colloidal silica, for example where the organosilane-modified silica is produced by reacting a mixture of two or more organosilanes with colloidal silica, or by mixing two or more separately prepared organosilane-modified colloidal silicas.

In embodiments, the colloidal silica can be modified by more than one organosilane moiety. The additional organosilane moieties do not necessarily themselves have to be hydrophilic in nature. For example, they can be hydrophobic silanes, such as Ci-20 alkyl or alkenyl silane. However, the resulting modified colloidal silica should still be miscible with the aqueous phase.

Examples of organosilane reactants that can be used to make such functionalised colloidal silica include octyl triethoxysilane; methyl triethoxysilane; methyl trimethoxysilane; tris- [3-(trimethoxysilyl)propyl]isocyanurate; 3-mercaptopropyl trimethoxysilane; beta-(3, 4- epoxycyclohexyl)-ethyl trimethoxysilane; silanes containing an epoxy group (epoxy silane), glycidoxy and/or a glycidoxypropyl group such as 3-(glycidoxypropyl) trimethoxy silane (which can also be known as trimethoxy[3-(oxiranylmethoxy)propyl] silane), 3- glycidoxypropyl methyldi ethoxy silane, (3-glycidoxypropyl) tri ethoxy silane, (3- glycidoxypropyl) hexyltrimethoxy silane, beta-(3, 4-epoxy cy cl ohexyl)- ethyltri ethoxy silane; 3-methacryloxypropyl trimethoxy silane, 3-methacryloxypropyl triisopropoxysilane, 3-methacryloxypropyl triethoxysilane, octyltrimethoxy silane, ethyltrimethoxy silane, propyltri ethoxy silane, phenyltrimethoxy silane, 3- mercaptopropyltri ethoxy silane, cyclohexyltrimethoxy silane, cyclohexyltriethoxy silane, dimethyldimethoxy silane, 3- chi oropropyltri ethoxy silane, 3- methacryloxypropyltrimethoxy silane, i-butyltri ethoxy silane, trimethylethoxy silane, phenyldimethylethoxy silane, hexamethyldisiloxane, trimethyl silyl chloride,

ureidomethyltriethoxy silane, ureidoethyltri ethoxy silane, ureidopropyltri ethoxy silane, hexamethyldisilizane, and mixtures thereof. US4927749 discloses further suitable silanes which may be used to modify the colloidal silica.

In embodiments, the organosilane or at least one organosilane comprises epoxy groups, for example as found in epoxyalkyl silanes or epoxyalkyloxyalkyl silanes. In embodiments, the organosilane can comprise a hydroxyl-substituent group, for example selected from hydroxyalkyl and hydroxyalkyloxyalkyl groups comprising one or more hydroxyl groups, e.g. 1 or 2 hydroxyl groups. Examples include organosilanes containing a glycidoxy, glycidoxypropyl, dihydropropoxy or dihydropropoxypropyl group. These can be derived from organosilane reactants such as (3 -glycidoxypropyl)trimethoxy silane, (3- glycidoxypropyl)tri ethoxy silane and (3 -glycidoxypropyl)methyldi ethoxy silane. In the compositions of the invention, epoxy groups can hydrolyse to form corresponding vicinal diol groups. Therefore, the invention also encompasses the diol equivalents of the above epoxy group-containing compounds.

The silane compounds can form stable covalent siloxane bonds (Si-O-Si) with the silanol groups. In addition, they can be linked to the silanol groups, e.g. by hydrogen bonds, on the surface of the colloidal silica particles. It is possible that not all silica particles become modified by organosilane. The proportion of colloidal silica particles that become functionalised with organosilane will depend on a variety of factors, for example the size of the silica particles and the available surface area, the relative amounts of organosilane reactant to colloidal silica used to functionalise the colloidal silica, the type of organosilane reactants used and the reaction conditions. The degree of modification (DM) of silica surface by organosilane can be expressed according to the following calculation (Equation 2), in terms of the number of silane molecules per square nanometre of silica surface:

Equation 2

wherein:

DM is the degree of surface modification in units of nm ²;

A is Avogadro’s constant;

N_organosiiane is the number of moles of organosilane reactant used;

S_siiica is the surface area of the silica in the colloidal silica, in m² g ¹; and

Msiiica is the mass of silica in the colloidal silica, in g.

DM can be at least 0.8 molecules of silane per nm², and is preferably in the range of from 0.5 to 4.0 molecules per nm². Preferred embodiments have DM in the range of from 0.5 to 3.0, for example from 0.8 to 2.2 molecules per nm².

In the above equation, the surface area of the silica is conveniently measured by Sears titration (Sears; Anal. Chem., 1956, 28(12), 1981-1983).

The colloidal silica used in the composition of the present invention is a stable colloid. By “stable” is meant that the organosilane-functionalised dispersed colloidal silica particles do not substantially gel or precipitate within a period of at least 2 months, and preferably at least 4 months, more preferably at least 5 months at room temperature (20°C).

Preferably, the relative increase in viscosity of the silane-functionalised colloidal silica dispersion between its preparation and up to two months after preparation is lower than 100%, more preferably lower than 50%, and most preferably lower than 20%. Preferably, the relative increase in viscosity of the silane-functionalised colloidal silica between its preparation and up to four months after preparation is lower than 200%, more preferably lower than 100%, and most preferably lower than 40%.

[PVC / Colloidal Silica Composite]

The modified PVC can be prepared by any suitable technique. For example, where the PVC is prepared by suspension polymerization, the modified PVC may be formed by polymerizing vinyl chloride monomer in a suspension polymerization process in the presence of a colloidal silica or an organosilane-modified colloidal silica.

The modified PVC is preferably prepared using procedures similar to those described in W02015/007522 and EP2438531, depending in particular on whether the PVC is a sorbent PVC or not.

[Preparation of Sorbent PVC/Colloidal Silica Composite]

Where the PVC is sorbent, and in particular is an S-PVC, the modified PVC is preferably formed by: a) providing a colloidal silica or an organosilane-modified colloidal silica, which comprises colloidal silica particles or organosilane-modified colloidal silica particles in a continuous liquid phase;

b) contacting the colloidal silica or organosilane-modified colloidal silica with sorbent polyvinyl chloride polymer; and

c) removing the continuous phase to form a mixture of the polymer and colloidal silica or organosilane-modified colloidal silica particles.

The continuous phase can be selected from paraffins, water and alcohols and miscible mixtures thereof. The colloidal silica or organomodified-colloidal silica can comprise 0.1 to 80wt% preferably 30 to 70wt% more preferably 20 to 60wt% of the mixture with the sorbent polyvinyl chloride polymer.

The colloidal silica or organosilane-modified colloidal silica can be added stepwise to the polymer, with removal of the continuous phase between additions. The mixture can be subjected to shearing such as calendaring or extrusion.

Typical particle sizes of the sorbent PVC can be in the range 20 to 1000 pm, preferably 50 to 500 pm, and more preferably 50 to 300pm. Particle sizes can be measured by wet sieving according to ISO 1624.

The porous structure can be measured as plasticizer absorption according to ISO 4608. The plasticizer absorption is preferably larger than 80 g/kg, preferably larger than 140 g/kg.

The liquid of the continuous phase should be capable of being sorbed by the polymer. The liquid may contain adjuvants such as cationic, non-ionic and anionic surfactants for example to stabilise the dispersion, to promote de-agglomeration or exfoliation of the (organosilane-modified) colloidal silica or to promote compatibility of the (organosilane- modified) colloidal silica and the polymer.

The (organosilane-modified) colloidal silica is contacted with and sorbed by the polymer, and the liquid continuous phase is then removed from the mixture. Typically the liquid is removed by heating or by reduction in pressure or both.

If the polymer is not very sorbent of the liquid phase, it may be necessary to perform several charging steps in which an amount of the (organosilane-modified) colloidal silica is sorbed onto the polymer and the liquid continuous phase removed. The total amount of colloidal silica material sorbed onto the polymer will depend on the materials involved and the desired properties but will typically be in the range 1 to lOphr for example 2 to 6phr. The dried mixture may be subjected to further conventional processing steps. For example, the mixture may be blended with other ingredients and subjected to shear, for example in a twin-screw extruder, a single-screw extruder, Brabender mixer, roll-mill or Gelimat-type thermokinetic mixer or by calendaring.

[Preparation of non-sorbent PVC/Colloidal Silica Composite]

Where the PVC is not sorbent, and in particular is a paste PVC, the modified PVC is preferably formed by paste polymerization comprising the steps of: a) forming an emulsion comprising vinyl chloride monomer, and optionally one or more comonomers, in an aqueous material

b) polymerising the emulsion to provide a latex comprising particles of polyvinyl chloride polymer,

c) adding a colloidal silica or an organosilane-modified colloidal silica to the latex, and d) spray-drying the latex.

As used herein, paste polymerisation is a polymerisation which produces a latex comprising particles of polymer, which latex when spray-dried produces PVC which is non-absorbent at ambient temperatures, so that when mixed with a plasticizer a paste (or plastisol) is formed.

As used herein, a "latex" is a dispersion of polymer particles in a liquid, said particles having a volume average particle size as measured by light scattering of from 0.01 to 8 microns, and more preferably from 0.2 to 5 microns.

The paste polymerisation is preferably an emulsion polymerisation where the latex preferably comprises particles of polymer of size from 0.2 to 3 microns, such as particles of polymer of size from 0.2 to 1 micron.

In this aspect the latex is mixed with the (organosilane-modified) colloidal silica. The (organosilane-modified) colloidal silica is preferably miscible with the liquid phase of the latex. Either or both liquid phases can contain dispersing or emulsifying agents. The mixture is then dried in a spray drier.

Vinyl chloride monomer may be used as the only monomer, in which case the polymer formed in step (b) is PVC homopolymer. Alternatively, one or more co-monomers may be included, such as vinyl acetate, in which case the polymer formed in step (b) is a PVC copolymer. (As used herein the term "polymer" encompasses both homopolymers and copolymers.)

The polymer formed in this aspect preferably has a glass transition temperature above 65°C. Preferably the glass transition temperature is above 66°C. such as at least 68°C, and most preferably at least 70°C, such as 70-85°C.

As used herein, the glass transition temperature should be measured on the polymer without addition of the colloidal silica. It may be determined by separating and spray drying a portion of the latex prior to addition of the source of the colloidal silica. The glass transition temperature should be determined by differential thermal analysis according to the method of ISO 1 1357-2, Plastics- Differential Scanning Calorimetry - Part 2:

Determination of glass transition temperature.

As is well known stabilisers and initiators and other materials may be present during the polymerisation. The emulsion of step (a) is generally an oil in water emulsion in which droplets of the monomer or monomers are dispersed in an aqueous continuous phase.

The (organosilane-modified) colloidal silica is added to the latex. A convenient way of achieving this is by adding the aqueous (organosilane-modified) colloidal silica to the liquid of the latex. The mixture can be stirred to achieve good incorporation.

Isolation of the solid composite PVC material is achieved by spray drying, for example using a disk or nozzle spray-dryer. The spray-dried particles may have a volume average particle size in the range 0.1 to 100 microns. Especially the spray-dried particles may have a volume average particle size in the range 1-63 microns, and preferably 5-40 microns. The spray-dried particles may have a volume average particle size of greater than 10 microns, such as greater than 15 microns. It has been found that the spray-drying of the particles leads to improved properties compared to other drying methods, such as those involving coagulation.

Typically the resulting particles will be processed for further use, for example by blending with stabilisers, processing agents and/or plasticisers and then subject to further transformation. Thus, for example, if it is desired to make sheets the material can be passed through a roll mill and then pressed. If it is desired to make a plastisol then the material can be blended with a plasticiser and optionally a stabiliser.

However prepared, typically, the amount of colloidal silica or organosilane-modified colloidal silica particles in the PVC (on a dry basis) is in the range of from 0.1 to 10 phr, where phr means“parts per hundred of resin”. Thus, 1 phr means 1 weight part of (modified) colloidal silica in 100 weight parts of PVC, based on dry weight (and giving a total of 101 parts of modified PVC), whilst 10 phr means 10 weight parts of (modified) colloidal silica to 100 weight parts of PVC based on dry weight (and giving a total of 110 parts of modified PVC). In embodiments, the amount is in the range of from 0.1 to 6 phr, for example 0.3 to 4 phr or 0.3 to 3 phr.

In terms of wt%, typically, the amount of colloidal silica or organosilane-modified colloidal silica particles in the PVC (on a dry basis) is in the range of from 0.1 to 9wt%. In embodiments, the amount is in the range of from 0.1 to 6wt%, for example 0.3 to 4wt% or 0.3 to 3wt%.

The PVC samples modified with colloidal silica or organosilane-modified colloidal silica particles, show improved dirt pick-up resistance and improved cleanability compared to (organosilane-modified) colloidal silica particle-free materials. This is the case for both hydrophilic dirt (e.g. inorganic oxide-based materials such as sand, brick dust, clays, and other silica materials), and also hydrophobic dirts (e.g. greases, oils, fats and other organic matter). These improved properties are exhibited without serious loss to other important characteristics, for example tensile strength or impact resistance. However, to ensure this remains the case, the relative ratio of colloidal silica to PVC should preferably be maintained within the limits set out above.

Examples

Example 1 - Comparative

A PVC film was prepared from a P1412-type E-PVC latex.

The latex was dried using a Niro™ rotary disk dryer with an outlet air temperature of 68°C. A plastisol was then formed by mixing 100 parts by weight of the dried PVC with 50 parts by weight Palatinol™ N diisononyl phthalate (DINP), 3 parts by weight Edenol™ D81 epoxidised soybean oil (ESO), 2.5 parts by weight Lankromark™ LZB567 Ba-Zn stabilizer and 5 parts by weight Kronos™ 2220 titanium dioxide. The plastisol mixture was stirred using a Hobart™ planetary mixer, and 1mm thick sheets were formed by allowing the plastisol to gel for 3 minutes at 190°C.

Example 2

A PVC dry nanocomposite was prepared in the same way as Example 1, except that a colloidal silica was added to the latex and stirred for 24 hours before being dried in the Niro™ rotary disk dryer. The plastisol was formed into a film in the same way as outlined in Example 1, using the components and amounts listed in Table 1.

The colloidal silica used was a Levasil™ unmodified colloidal silica (CS 15-150), having a silica content of 15wt% (as SiCE) and silica surface area of 500m²g ' (particle size 5 nm based on Equation 1). It was added to the latex in an amount of 1 part by weight (i.e.1 phr), based on dry silica content. Example 3

A PVC film was prepared as in Example 2, except that the colloidal silica used was a Levasil™ unmodified colloidal silica (C S30-236), having a silica content (as SiCE) of 30wt%, and a silica surface area of 360 m² g ¹ (particle size 7 nm based on Equation 1).

Example 4

A PVC film was prepared as in Example 2, except that a modified colloidal silica was used, which was produced by treating unmodified colloidal silica (Levasil™ CS 30-236) with (3-glycidyloxypropyl) tri ethoxy silane and also n-propyl tri ethoxy silane according to the general procedure described on page 8 of WO 2004/035473, which entails adding the appropriate amount of (3-glycidyloxypropyl) trimethoxy silane and n-propyl tri ethoxy silane directly to the unmodified colloidal silica, and stirring at room temperature for 2 hours.

The 1 phr loading of the modified colloidal silica is based on the weight of“bare” silica (expressed as SiCE), i.e. without silane, to the weight of PVC resin, on a dry basis.

The amount of organosilane reagents were chosen so as to provide a total degree of modification (DM) on the silica particle surface of 1.4 nm ².

In Table 1, the phr amount of this modified colloidal silica is based on the weight of“bare” silica (expressed as SiCE), i.e. without silane, to the weight of PVC resin, on a dry basis.

Example 5

A PVC film was prepared as in Example 4, except that the modified colloidal silica used was prepared by modification of Levasil™ CS 15-150 with (3- glycidyloxypropyl)trimethoxysilane and n-propyl triethoxysilane.

The amount of organosilane reagents were chosen so as to provide a total degree of modification (DM) on the silica particle surface of 1.4 nm ². Example 6

This was prepared in exactly the same way as Example 2, except that the colloidal silica loading in the PVC was 5 phr.

Example 7

This was prepared in exactly the same way as Example 3, except that the colloidal silica loading in the PVC was 5 phr.

Example 8

This was prepared in exactly the same way as Example 4, except that the colloidal silica loading in the PVC was 5 phr.

Example 9

This was prepared in exactly the same way as Example 5, except that the colloidal silica loading in the PVC was 5 phr.

Example 10 - Comparative

A PVC film was made in the same way as Example 1, except that in the plastisol no titanium dioxide was added, and the Edenol™ D81 epoxidised soybean oil was replaced with the same weight of Lankroflex™ E 2307 epoxidised soybean oil.

Example 11

A PVC film was made in the same way as Example 10, except that the same modified colloidal silica as used in Example 4 was added such that the amount of silica on a dry basis was 1 phr. Example 12

A PVC film was made in the same way as Example 11, except that the same modified colloidal silica as used in Example 5 was added, such that the amount of silica on a dry basis was 1 phr.

Example 13

A PVC film was made in the same way as Example 11, except that a solid and amorphous form of silica, Sidistar™ T120U, was added to the E-PVC latex instead of a colloidal silica, such that the amount of silica on a dry basis was 1 phr.

Example 14

A PVC film was made in the same way as Example 11, except that a solid and amorphous source of fumed silica, Aerosil™ 200, was added to the E-PVC latex instead of a colloidal silica, such that the amount of silica on a dry basis was 1 phr.

Example 15 - Comparative

A PVC film was made in the same way as Example 10, except that the plastisol was made using 100 parts by weight of PVC, 60 parts by weight of Platinol™ N DINP, 2.5 parts by weight Lankromark™ LZB 567 stabilizer, 3 parts by weight Lankroflex™ E 2307 epoxidised soybean oil, and 5 parts by weight Kronos™ titanium dioxide. 1.2mm films were prepared.

Example 16

A PVC film was made in the same way as Example 15, except that 2 phr of the colloidal silica used in Example 4 were added to the E-PVC latex. Example 17

A PVC film was made in the same way as Example 16, except that 5 phr of the colloidal silica used in Example 4 were added to the E-PVC latex.

Example 18 - Comparative

A PVC film was made in the same way as Comparative Example 1, except that no

Kronos™ 2220 titania was added.

Examples 19 to 22

PVC films were made in the same way as Examples 2 to 5 respectively, except that no

Kronos™ 2220 titania was added.

[Dirt Pick-Up Resistance and Cleanability]

Films of Examples 1 to 9 were exposed to a hydrophobic material (carbon black) or to a hydrophilic material (iron (III) oxide) contaminant, according to the following procedure: i) circles of 2cm diameter were marked on a series of samples to be tested, along with reference samples.

ii) 1ml of either a 2wt% dispersion of carbon black or a 2wt% dispersion of iron (III) oxide was added using a pipette. Reference samples were not treated.

iii) All samples were placed in a heating chamber at 50°C, and removed after 24 hours. iv) The contaminated samples were washed gently under running water using a piece of paper and then dried.

v) The extent of adherence of the dirt on both the contaminated and reference samples was measured by colourimetry using a Konica Minolta CM-600d

spectrophotometer according to Equation 3 :

AE^* = VAL*² + Aa*² + Ab*² Equation 3 where DE* (change in emissivity) represents the differences in the L*, a* and b* values before and after ageing (L* denotes colour lightness, a* denotes hue on a red-green axis and b* denotes hue on a yellow-blue axis, according to the CIELAB colour scale).

Figure 1 shows the results for PVC containing no colloidal silica (Example 1) or 1 phr colloidal silica or organosilane-modified colloidal silica (Examples 2 to 5), when exposed to iron oxide, to simulate the effect of hydrophilic dirts.

In terms of both dirt pick-up (adherence), and in terms of cleanability, i.e. after being flushed with soap and water, the colloidal silica-containing PVC films are clearly superior to the colloidal silica-free material.

Figure 2 shows similar results, except that the contaminant used was carbon black, to simulate hydrophobic dirts.

Some improvement in dirt pick-up (adherence) is observed with colloidal silica incorporation, and cleanability is substantially improved.

Figures 3 and 4 show similar results to Figures 1 and 2, except that the colloidal silica loading is 5 phr (i.e. Examples 6 to 9). In these examples, reduced adherence of both hydrophilic and hydrophobic dirt is apparent. In terms of cleanability, improvement is seen in all samples in relation to hydrophobic dirt, whereas there is no overall trend in terms of cleanability with regard to hydrophilic dirt.

Examples 10 to 14 were exposed to hydrophilic dirt (iron oxide) in the same way as Examples 1 to 9, except that exposure was for 8 days, before being evaluated for dirt pick up resistance and cleanability in the same way. Results are shown in Figure 5.

The organomodified colloidal silica-modified samples exhibit the best performance in terms of both dirt pick-up resistance and cleanability. The two different non-colloidal silicas showed different performance. Both were significantly worse than the modified colloidal silica samples. Example 13 was also worse than the silica-free reference.

Figure 1 shows that the performance of organo-modified and unmodified colloidal silica to iron oxide dirt were approximately the same. Figure 5 shows a significant deterioration of performance when solid forms of silica are used in place of colloidal silica, highlighting that colloidal sources of silica offer improved performance.

[Tensile Measurements]

Tensile measurements on the films were carried out according to ISO 527.

Figures 6 and 7 show the tensile strength of the PVC films for Examples 1 to 9, with Figure 6 showing 1 phr silica-loaded samples, and Figure 7 showing 5 phr silica-loaded samples. For the 1 phr samples, the tensile strength at break is essentially unaffected compared to silica-free material. For 5 phr, there is a small reduction compared to the silica-free material.

Figures 8 and 9 show elongation at break properties for Examples 1 to 9, where Figure 8 compares PVCs comprising 1 phr silica, and Figure 9 compares PVCs comprising 5 phr silica. Similar trends are observed, i.e. almost no change for the 1 phr samples, and a small reduction for the 5 phr samples compared to the silica-free comparative example.

[Thermal Stability]

Thermal stability studies were carried out by exposing PVC films of Examples 18 to 22 to a temperature of 190°C for various amounts of time, and subsequently measuring the yellowness index (measured according to ASTM D1925 using a Konica Minolta CM-600d spectrophotometer). Results are shown in Figure 10. Improved thermal stability of the PVC is exhibited when colloidal silica and modified colloidal silica are incorporated, based on reduced increase in yellowness index with duration of heat treatment. The yellowness index is a measure of degradation of the PVC, and increases dramatically after 20 minutes of heat treatment where no colloidal silica is present. Conversely, in the colloidal silica-containing nanocomposite materials, degradation is more gradual. Particular improvements are also observed with the modified colloidal silica-containing materials compared to the unmodified colloidal silica-containing materials. Example 21, for example, using modified CS30-236 colloidal silica shows significant improvements over Example 20, using the unmodified C S30-236 colloidal silica, whilst Example 22 using modified CS 15-150 colloidal silica shows significant improvements over Example 19, using the unmodified CS15-150 colloidal silica, thus demonstrating the improved thermal stability of the modified colloidal silica materials.

[Accelerated Weathering Tests]

These were carried out on Examples 15 to 17 according to ISO 4892-2, using an Atlas™ Weather-o-meter Ci4000. Colour change according to Equation 3 was determined by colourimetry, and yellowing was also measured in both cases using a Konica Minolta CM- 3600d spectrophotometer.

Colourimetry results for Examples 15 to 17 are shown in Figure 11. The colloidal silica- containing samples show improved colour hold, i.e. the colour being maintained for about 50% longer compared to the silica-free material. Figure 12 shows a similar trend in terms of the yellowness index, i.e. resistance to weathering, of the samples.

[Viscosity Measurements]

The Brookfield viscosity of the PVC latex and colloidal silica-modified latexes of

Examples 1 to 5 were measured after 24 hours at various shear rates. Results are shown in Figure 13. At low shear rate, the colloidal silica-containing dispersions showed higher viscosity, although the differences over silica-free latex diminished at higher shear rates. This demonstrates that the colloidal silica does not have a significant negative impact on the rheology of the PVC, indicating their suitability for use in making PVC sheet, for example.

[Taber Abrasion Tests]

Examples 1 to 5 were tested according to ISO 9352. Results are shown in Figure 14, highlighting little difference between the unmodified and colloidal silica-containing PVC. This also suggests that the colloidal silica-containing PVC does not have any significant negative impact on the abrasion resistance of the PVC.

Claims

1. A composition comprising polyvinyl chloride, PVC, and colloidal silica particles, the colloidal silica particles being modified with an organosilane.

2. A composition as claimed in claim 1, in which the composition is a dispersion or suspension of PVC in an aqueous phase that also comprises the organosilane-modified colloidal silica particles, or is in the form of a sheet, a plastisol, dry granules, dry powder or extrudates.

3. A composition as claimed in claim 1 or claim 2, obtainable by combining an organosilane-modified colloidal silica with an aqueous emulsion of PVC, and spray drying.

4. A composition as claimed in any one of claims 1 to 3, wherein the organosilane moiety bound to the surface of the colloidal silica is represented by the formula ºSi(R^m)_y, where

ºSi represents the silicon atom of the organosilane moiety, which is bound to the silica surface;

y is an integer in the range of from 1 to 3;

R^m is selected from alkyl, alkenyl, epoxy alkyl, aryl, heteroaryl, Ci-₆ alkylaryl and Ci-₆ alkylheteroaryl groups, optionally substituted with one or more groups selected from ERⁿ; E is either not present, or is a linking group selected from -0-, -S-,

-OC(O)-, -C(O)-, -C(0)0-, -C(0)0C(0)-, -N(R^p)-, -N(R^p)C(0)-,

-N(R^p)C(0)N(R^p)- and -C(0)N(R^p)- where R^p is H or Ci-₆ alkyl;

Rⁿ is linked to E, or directly to R^m if E is not present, and is selected from halogen (typically F, Cl or Br), alkyl, alkenyl, aryl, heteroaryl, C_1-3 alkylaryl and C_1-3

alkylheteroaryl, in which any Rⁿ group can optionally be substituted with one or more groups selected from hydroxyl, halogen, epoxy ,-OR^p or -N(R^P)2 where each R^p is as defined above;

and, if E is present, Rⁿ can also be hydrogen.

5. A composition as claimed in claim 4, in which the or at least one R^m group comprises at least one group selected from hydroxyl, thiol, carboxyl, ester, epoxy, acyloxy, ketone, aldehyde, (meth)acryloxy, amino, amido, ureido, isocyanate or isocyanurate.

6. A composition as claimed in claim 4 or claim 5, in which the or at least one R^m group comprises at least one heteroatom selected from O and N, and comprises no more than three consecutive alkylene (-CH2-) groups linked together.

7. A composition as claimed in any one of claims 1 to 6 wherein the colloidal silica used in the organosilane-modified colloidal silica is made by particle growth from a soluble silicate or a polysilicic acid solution.

8. A composition as claimed in any one claims 1 to 7, in which the colloidal silica used in the organosilane-modified colloidal silica has one or more of the following properties:

- the colloidal silica particles have a surface area in the range of from 50 to 1000 m² g ¹;

- the colloidal silica particles have a particle diameter, determined by Sear’s titration, in the range of from 2 to 150 nm;

- the colloidal silica particles are modified with two organosilane groups, one being hydrophilic and one being hydrophobic.

9. A composition as claimed in any one of claims 1 to 8, in which the content of organosilane-modified colloidal silica particles in the PVC is in the range of from 0.1 to 10 parts by weight of the modified colloidal silica to 100 parts by weight of the PVC on a dry basis, the silica being expressed as SiCk.

10. A process for preparing a composition as claimed in any one of claims 1 to 9, comprising producing a PVC dispersion from vinyl chloride monomer using suspension or emulsion polymerisation, and adding organosilane-modified colloidal silica.

11. A process as claimed in claim 10, in which either (i) the PVC is produced by suspension polymerisation to form a sorbent PVC, which is dried and contacted with organosilane-modified colloidal silica; which is optionally dried, for example by heating and/or by pressure reduction; or

(ii) the PVC is produced by emulsion polymerisation to form an aqueous PVC latex comprising non-sorbent PVC, and the latex is contacted with organosilane- modified colloidal silica, the resulting mixture optionally being dried, for example by spray drying, and mixed with a plasticiser to form a plastisol.

12. A process according to claim 10 or claim 11, in which the composition is a dispersion or suspension of PVC in an aqueous phase that also comprises the organosilane- modified colloidal silica particles, or is in the form of a sheet, a plastisol, dry granules, dry powder, or extrudates.

13. Use of colloidal silica for increasing the thermal stability of PVC.

14. Use of colloidal silica as claimed in claim 13, in which the colloidal silica is an organosilane-modified colloidal silica.

15. Use of colloidal silica as claimed in claim 13 or claim 14 wherein the colloidal silica is made by particle growth from a soluble silicate or a polysilicic acid solution.