WO2010076587A1

WO2010076587A1 - Thermothickening sizing for antimigration.

Info

Publication number: WO2010076587A1
Application number: PCT/IB2008/003773
Authority: WO
Inventors: Patrick Moireau; Adina Cretu
Original assignee: Ocv Intellectual Capital, Llc
Priority date: 2008-12-30
Filing date: 2008-12-30
Publication date: 2010-07-08

Abstract

The present invention relates to the use of thermothickening polymers in sizing compositions for glass fibre materials in order to inhibit product migration, where the thermothickening polymer is a graft copolymer having a poly(meth)acrγlamide, poly(meth)acrylic acid or a poly((meth)acrylamide-co- (meth)acrylic acid) main chain and grafts pending on the main chain of at least one of the following types: polyoxyethylene, polyoxyethylene-co- polyoxypropylene, poly(N-isopropyKmettOacrγlamide), poly(dimethyl(meth)acrylamide), or poly(N-isopropyl(meth)acrγlamide-co- dimethyl(meth)acrylamide) copolymer. The invention relates to a method of coating glass fibres using sizing compositions containing such thermothickening polymers, specific aqueous sizing compositions themselves, coated glass fibres obtained by such a method of coating, and polymer composite materials obtained using such coated glass fibres.

Description

Thermothickening sizing for antimigration

Technical Field and Industrial Applicability of the Invention

The present invention relates to innovative polymer-containing sizing compositions used to coat glass fibres destined to be used as reinforcing agents in composite materials. The invention provides a method of coating glass fibres with the said sizings, a process for preparing glass fibres using this composition, and composites obtained from the said glass fibres. More particularly, the present invention relates to sizing compositions which contain so-called "thermothickening" or "heat sensitive" polymers.

Background of the Invention

Glass fibres are well known as reinforcements in composite materials, widely used for example in the aeronautics industry, marine or defence applications, building materials, wind blades, turbines, sport and leisure. In such composite materials, the glass fibres will be in contact with thermosetting or thermoplastic polymers and it is necessary to ensure compatibility with the organic matrix in which the glass fibres are dispersed.

It is known to manufacture glass fibres for reinforcement applications from streams of molten glass flowing out of the orifices of bushings. These fibres are drawn in the form of continuous filaments, then these filaments are assembled into strands, which are then collected.

Before they are assembled in the form of strands, organic coatings named "sizings" are usually deposited on the glass fibers in order to ensure optimal mechanical properties and compatibility with the organic matrix.

In general, a sizing is an aqueous dispersion, containing more than 80% water, of several components:

- one or several coupling agents, most commonly hydrolysable silanes, but titanates or zirconates can also be used; - one or several polymeric film formers, having the role of compatibilizer between the fibre and the matrix;

- a plasticizer / surfactant / dispersant system, in order to stabilize the emulsion and to improve the wettability and the impregnation of the glass fibres;

- one or several lubricants, having the role of diminishing the abrasion between filaments; and

- other possible additives, depending on the applications envisaged for the glass fibre-based material. Organic sizings have several roles:

- to ensure a correct fibre forming process and to protect the glass filaments during drawing and winding;

- to ensure the required mechanical properties (integrity, protection against abrasion, lubrication etc.) during processing, depending on the transformation process (weaving, rewinding, cutting, twisting etc.);

- to ensure good compatibility (wetting, impregnation, dispersion) and good bonding with the polymer matrix to be reinforced, in order to achieve the mechanical properties required by the application envisaged;

- to protect the glass fibres against chemical or environmental aggressions and to ensure satisfactory durability.

The deposition of organic sizings on glass fibers is generally made using a roll coater. The aqueous sizings have low viscosity (η<0,01 Pa.s) and during the process they are subjected to a very high shearing rate (about 10⁶S ¹).

Due to their low viscosity, sizing compositions do not show good behaviour on glass when the strand comes into contact with the various elements which are used to guide it to the winding-machine. A phenomenon of drying occurs, followed by a centrifugal projection of sizing under the effect of the drawing speed. Part of the sizing composition is also lost under the effect of the centrifugal force during the winding of the strand. The loss can be up to 50% according to the sizing composition. In addition, water is prejudicial to the mechanical properties of the final composite because it decreases adhesion between glass strands and the matrix to be reinforced. Water must consequently be eliminated, which is done traditionally by drying glass ravings in a large oven heated at a temperature of about 100⁰C to 150⁰C during 10 to 20 hours, depending on the weight of the roving and its initial water content.

Consequently, two major problems occur: on one hand, sizing projections occur due to the centrifugal forces during winding, leading to a decrease of size efficiency (size on fiber/total size consumed). On the other hand, sizing migration is observed during the drying of the ravings. This phenomenon leads to a loss of product, due to the fact that all ravings have to be stripped (3 - 5% of their weight), and a decrease of product quality. In effect, during drying, migration towards the inside and the outside of the ravings takes place, due to the fact that the components of the sizing are washed away by the water vapour as the temperature increases. The different components of the sizing have a strong tendency towards selective migration, depending on their affinity to water and their molecular weight. This generates a variation of the properties of the glass strand along the roving.

Furthermore, when the Loss On Ignition (LOI = the quantity of organic matter deposited on the glass fibre) along the roving is more than two times higher than the nominal value, the product is considered to have poor quality and it has to be removed. Depending on the type of winding and the application, the loss of product represents between 2 and 5% from the total weight of the roving (net loss). This operation called stripping is done manually and it generates an additional increase of the cost of the roving, as it requires a dedicated work force.

Current organic polymer-based sizing compositions do not solve in a fully satisfactory way problems such as the above-cited problems of sizing projection under the effect of centrifugal forces, and sizing migration during drying. The present invention aims to provide solutions to the above-mentioned problems and in particular to suppress the migration, observed during drying, of products obtained by continuous winding (ravings, cakes, cops etc.). The invention is of particular interest in the manufacture of materials obtained using direct roving (weaving, winding) and those where fabrication of cakes is necessary in order to obtain the final products (cops, cakes for direct weaving, assembled ravings etc.). Both thermoplastic and thermosetting matrixes may be used.

Summary of the Invention

With the aim of solving the aforementioned problems, the present invention proposes the use of sizing compositions involving thermothickening polymers, also called "heat sensitive" polymers or "thermosensitive" polymers. Thermothickening polymers are already known per se. They are polymers which, at low concentrations, generally in aqueous solutions, show a very high increase of the viscosity when the temperature is increased, in contrast to conventional polymers, the viscosity of which continuously decreases with a rise in temperature. This phenomenon is generally due to the association of the grafts of these copolymers which leads to the formation of a physical network and, as a consequence, a decrease of their solubility at high temperatures. A "threshold temperature" is observed, corresponding to a transition point between a non-associated and an associated state. This threshold temperature can be modified and controlled depending on the copolymer's structure (for example, variation of the ratio between the main chain and the grafts), the solution pH or the presence of certain additives like surfactants. In a typical case, for example, a viscosity of several mPas at 2O⁰C is multiplied by a factor of about 10³ at 60 ⁰C.

Thermothickening copolymers of this type are already known and used in different applications (in particular in the oil industry and more particularly in the field of drilling fluids). Advantage is in particular taken there of the property of polyoxyalkylene or poly(N-isopropylacrylamide) chains or their copolymers, which are water-soluble at ambient temperature, of becoming hydrophobic at a temperature, referred to as the critical temperature, above 50⁰C.

Three families of thermothickening polymers are described in the literature:

1) cellulose derivatives - depending on the chemical nature of the pendant substituents, an association in the form of microdomains takes place upon heating, leading to gel formation. As examples of cellulose derivatives exhibiting thermothickening behaviour, there may be noted: methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose. Some of these products are commercialized by the Dow Chemical Company under the trade name METHOCEL® (with different grades, depending on the structure and molecular weight); 2) block copolymers, having one hydrophilic and one hydrophobic block.

Here, the hydrophobic portions can aggregate together to form micelles when the temperature reaches the critical solution temperature; the hydrophilic moieties link the micelles between them. By virtue of this, an increase in the temperature of the aqueous medium in which these thermosensitive polymers are dissolved can convert them from a liquid state to a viscous state forming a gel. Such polymers are well-known under the generic name of poloxamers. They are copolymers of propylene oxide and ethylene oxide blocks. They are commercialized by BASF under the trade name Poloxamer® or by ICI under the trade name Pluronic®. However, these thermosensitive polymers enable the formulation of aqueous solutions which have critical solution temperatures between 24° and 4O⁰C. Such formulations necessarily contain 15 to 50% of thermosensitive polymers in order to obtain a significant variation in the viscosity. Furthermore, despite the high percentage of thermosensitive polymers in these formulations, the variation in viscosity is less than a decade; 3) graft copolymers - these polymers are typically hydrophobically modified water soluble polymers. They are essentially water-soluble

(hydrophilic) polymers containing a small portion of hydrophobic groups usually in the form of side-chains or end groups. In aqueous media, the hydrophobic groups present in these polymers associate, thus creating the unusual and desired rheological properties. Typically these polymers consist of a water soluble polymer backbone modified with polymer grafts that exhibit a low critical solubility temperature (LCST). When subjected to temperature above this LCST the grafts associate and the resulting viscosity increases due to these physical crosslinks. The synthesis of these copolymers has been extensively described in the literature: EP 0,583,814, Polymer 35, 2624 (1994), Polymer 40,

4941 (1999), Polymer 46, 12190 (2005), Macromolecules 38, 8512 (2005),

Langmuir 23, 147 (2007). So far they are not commercially available. They can be obtained by three different methods:

- "grafting from" - polymerization of a water soluble monomer in the presence of a polymer capable of undergoing chain transfer reactions.

Examples include: a poloxamer POE-POP copolymer, or a polyvinyl alcohol, as thermosensitive main chain, on which are polymerized thermosensitive monomers such as: (meth)acrylic acid,

N-isopropyl(meth)acrylamide, dimethylacrylamide, dimethyl-aminopropyl-

(meth)acrylamide, in the form of homo- or copolymers;

- "grafting through" - copolymerization between a water soluble monomer and a thermosensitive macromonomer. Examples of water soluble monomers include: (meth)acrylic acid, (meth)acrylamide, or

2-acrylamido-2-2-methyl-propane sulfonic acid. Examples of thermosensitive macromonomers include: vinyl terminated polyoxyethylene, vinyl terminated poly(oxyethylene-oxypropylene) copolymer, or vinyl terminated poly(N-isopropyl(meth)acrylamide). - "grafting onto" - coupling reaction between a functionalized thermosensitive graft and the reactive groups of a main polymer chain. Examples of main polymer chains include: poly(meth)acrylic acid, poly(meth)acrylamide, poly(acrylamide-co-acrylic acid), polyvinyl alcohol, poly(2-acrylamido-2-2-methyl-propane sulfonic acid), poly(2-acrylamido- 2-2-methyl-propane sulfonic acid-co-acrylic acid), polyvinyl methyl ether-co- maleic anhydride), carboxymethylcellulose, triblock copolymer POE-POP-POE. Examples of functionalized thermosensitive grafts include: polyoxyethylene, poly(oxyethylene-co-oxy propylene), poly(N- isopropyl(meth)acrylamide), poly(dimethyl(meth)acrylamide), poly(N- isopropyKmethJacrylamide-co-dimethyKmethJacrylamide), poly(N- isopropyl(meth)acrylamide-co-butyl methacrylate), poly(N- isopropyl(meth)acrylamide-co-acrylic acid), poly(N- isopropyl(meth)acrylamide-co-2-acrylamido-2-2-methyl-propane sulfonic acid), polyCN-isopropyKmethJacrylamide-co-dimethylaminopropyl methacrylamide).

It is desirable that the thermothickening polymers used in the present invention comply with several one or more, preferably several, and most preferably all of the following characteristics:

- a thermothickening character of the polymer which appears at concentrations lower than 2.5% w/w;

- a viscosity at ambient temperature (25°C) of the thermothickening sizing lower than 100 mPa.s, in order to allow the sizing to be deposited with a roll coater, the viscosity here being measured with a Brookfield viscosimeter;

- an association of the polymer that is observed in a temperature range of between 50⁰C and 80⁰C, in order to obtain the thickening of the sizing during the early period of the drying step, while the temperature begins to increase; it is preferable to avoid lower association temperatures, in order to have a wide enough working range during glass fibre forming;

- a preferred range of viscosity increase is from 10 to 10⁴ mPas, between 50⁰C and 80⁰C. A generally desirable association temperature of thermothickening polymers to be used in the present invention will preferably be situated between 50° and 70⁰C. Under such circumstances, increases in viscosity of the order of 10⁴ between room temperature (about 25°C) and a temperature of 80⁰C can be observed.

- preservation of the thermothickening character in acid media (pH from about 4 to about 5), since usually sizings have acidic pH;

- preservation of the thermothickening character in the presence of the components of a standard sizing.

It is further desirable that the thermothickening polymer to be used gives rise to emulsions that are statically and dynamically stable, since the shearing rate is about 10⁶ s ¹ during the deposition. It is desired that the thermothickening sizing preserve as much as possible the mechanical properties of the glass strand (tenacity, fuzz level) and show good compatibility with the polymer matrix (good impregnation, good mechanical properties of the composites). The use of certain types of thermothickening polymers showing some and preferably all of the above-referenced properties has been found by the present inventors to enable undesirable migration phenomena to be suppressed whilst maintaining the other properties required of a sizing composition.

After several fibre forming trials, the present inventors observed that thermothickening cellulose derivatives are not entirely satisfactory in suppressing migration, according to the purpose of the present invention. Tests using cellulose derivatives revealed product migration even prior to drying, visible upon winding of the ravings. Without wishing to be bound by any particular theory, it is postulated that the cellulose derivatives may act as a sponge and form aggregates which, under the effect of centrifugal forces which appear during winding, may as much encourage as prevent product migration from glass fibres.

It was also noticed by the inventors that sizings incorporating methyl cellulose are statically unstable. Thus, a macroscopic phase separation (formation of aggregates) was noticed 3 hours after the dissolution of the polysaccharide in the sizing formulation. At the same time, a dynamic instability was noticed under shearing at high temperatures, with the formation of aggregates while heating. This might cause an inhomogeneous deposition of the sizing on the glass fibre during the fibre forming and a less pronounced thermothickening effect.

Graft copolymers were subsequently synthesized and tested by the present inventors, and some types of thermothickening graft copolymer were surprisingly found to be rather effective in inhibiting product migration. More specifically, among the graft copolymers, certain specific types within the third, "grafting onto", group of graft copolymer thermothickening copolymers listed above, were found to be effective in inhibiting migration.

In particular, the present inventors have found, through experimental trials, that graft copolymers having a poly(meth)acrylamide, poly(meth)acrylic acid or a poly((meth)acrylamide-co-(meth)acrylic acid) main chain can be used, with grafts pending on the main chain of at least one of the following types: polyoxyethylene, polyoxyethylene-co-polyoxypropylene, poly(N- isopropyl(meth)acrylamide), poly(dimethyl(meth)acrylamide), or poly(N- isopropyKmethJacrylamide-co-dimethyKmethJacrylamide) copolymer. In the above description of polymer main chains and grafts,

"(meth)acrylic acid" refers to polymers derived from methacrylic acid units or acrylic acid units or both, and similarly "(meth)acrylamide" refers to polymers derived from methacrylamide units or acrylamide acid units or both.

Thus, the present invention is directed in one aspect to a method of coating glass fibres comprising the steps of: (a) extruding molten glass through an orifice to produce glass fibres; and

(b) after step (a), coating the glass fibres produced with a sizing composition containing a concentration by weight of at least 1.5% of thermothickening polymer in the sizing composition, where the thermothickening polymer is at least one graft copolymer having a poly(meth)acrylamide, poly(meth)acrylic acid or a poly((meth)acrylamide-co- (meth)acrylic acid) main chain and grafts pending on the main chain of at least one of the following types: polyoxγethylene, polyoxyethylene-co- polyoxypropylene, polyCN-isopropyKmethJacrylamide), poly(dimethyl(meth)acrylamide), or poly(N-isopropyl(meth)acrylamide-co- dimethyl(meth)acrylamide) copolymer.

In the graft copolymers used in the present invention, the value of molecular weight of the main chain may appropriately be situated between 40,000 and 1,200,000 g/mole, preferably between 50,000 and 700,000 g/mole. The molecular weight of the grafts may appropriately be situated between

1,000 and 25,000 g/mole, preferably between 6,000 and 12,000 g/mole. The percentage of the grafts relatively to the main chain may appropriately be situated between 10% and 50% w/w, preferably between 15% and 30% w/w.

In the case of poly((meth)acrylamide-co-(meth)acrylic acid) main chains, the ratio between (meth)acrylamide and (meth)acrylic acid moieties may appropriately be between 50/50 and 90/10 mole/mole, preferably between 60/40 and 80/20 mole/mole.

The graft polymers used in the present invention are appropriately used at a concentration of 1.5% to 5% of the total weight of the sizing, preferably between 1.5% and 3.5 % by mass of thermothickening polymer with respect to 100 % of overall aqueous sizing composition. More preferably, the thermothickening graft copolymers used in the present invention are present in the aqueous sizing composition at a concentration of between 2.0 % and 3.0% by mass of thermothickening polymer with respect to 100 % of overall aqueous sizing composition, and, in a currently preferred embodiment, around 2.5% by mass of thermothickening polymer is present with respect to 100 % of overall aqueous sizing composition.

The present invention thus provides a method to reduce sizing migration during the drying of the ravings. Reducing sizing migration according to the present invention is obtained by using a sizing composition for the glass fibres that contains an appropriate type of thermothickening polymer as described above.

Another object of the present invention is to provide a glass fibre coated with the sizing composition previously described. The invention is also directed to a sizing composition per se comprising: (a) one or more appropriate thermothickening polymers as described above; (b) at least one coupling agent of the type silane, titanate and/or zirconate; (c) at least one film former polymeric material, distinct from the said thermothickening polymer(s); and (d) optional further additives comprising one or more components selected from one or more of the following groups: plasticizers, surfactants, dispersants and lubricants.

Yet another object of the present invention is to provide a composite material obtained from an organic and/or inorganic matrix reinforced with the glass fibres obtained according to the invention. The invention further relates to the use of thermothickening polymers as described above in sizing compositions for glass fibre materials in order to inhibit product migration.

Detailed Description and Preferred Embodiments of the Invention The sizing compositions to be used in the present invention will advantageously include the following components:

- 1.5 to 5% by mass of at least one thermothickening polymer;

- 0.15 to 4% by mass of coupling agents, such as hydrolysable silanes, or titanates or zirconates; - 2 to 8% by mass of film former polymeric materials, distinct from the thermothickening polymer;

- 0.1 to 8% by mass of at least one component chosen from the class of plasticizers, surfactants and dispersants; and - 0.1 to 4% by mass of lubricants.

The amount of water in the sizing compositions will preferably be at least 80% by weight of the total weight of the sizing composition.

As previously described, the term "thermothickening copolymer" (also described as "heat-sensitive copolymer") refers to a polymer with a viscosity in an aqueous medium which increases with temperature beyond a temperature threshold, in contrast to conventional polymers, the viscosity of which continuously decreases with a rise in temperature. In effect, certain water- soluble polymers have the property that their chains locally combine together beyond a certain temperature threshold. This results in the formation of a physical network with a high molar mass and thus an increase in viscosity, thus creating the heat-thickening property. In the present invention advantage is taken of this property in order to formulate sizings which will have increased viscosity beyond a certain temperature, around 80⁰C. Thus, while heating, in the early period of the drying step, the viscosity of the sizing will strongly increase, due to the thermothickening effect. This will prevent the low molecular weight components of the sizing from migrating from the interior towards the exterior of the roving.

[Examples of thermothickening polymers that have been identified through the research of the present inventors to be effective in this context include the following graft (co)polymers: polymers containing a poly(meth)acrylamide, poly(meth)acrylic acid or a poly((meth)acrylamide-co- (meth)acrylic acid) main chain and grafts such as polyoxyethylene, polyoxyethylene-co-polyoxypropylene, poly(N-isopropyl(meth)acrylamide), poly(dimethyl(meth)acrylamide), or poly(N-isopropyl(meth)acrylamide-co- dimethyl(meth)acrylamide) copolymer. The function of a silane or analogous coupling agent in a sizing composition is to enhance the adhesion of the film forming polymers to the glass fibres and the matrix to be reinforced and to reduce the level of fuzz, or broken fibre filaments, during subsequent processing. [Examples of silane coupling agents which may be used in the present size composition may be characterized by the functional groups amino, epoxy, vinyl, methacryloxy, azido, ureido, and isocyanato. Suitable silane coupling agents for use in the size include, but are not limited to, γ^aminopropyltriethoxysilane, β-aminoethyl-^ aminopropyl-trimethoxysilane, ^methacryloxypropyltrimethoxysilane, γ^glycidoxypropyltrimethoxysilane, methyl-trichlorosilane, methyl-trimethoxysilane, γ-mercaptopropyl-trimethoxy-silane, bis-(3-[triethoxysilyl]propyl)tetrasulfane, γ-chloropropyl-trimethoxy-silane, vinyl- triethoxy-silane, vinyl-tris-(2-methoxyethoxy)silane, vinylmethyldimethoxysilane, vinyl-triacetoxy silane, octyltriethoxysilane, methyltriethoxysilane, and methyltrimethoxysilane. Such silane coupling agents are available from various commercial suppliers.

Alkoxysilanes of this type are hydrolysed in aqueous solution, in the presence of an acid like acetic acid, lactic acid or citric acid. The silane coupling agents may be used in partially or fully hydrolysed/polymerized form. Hydrolysis / polymerization may appropriately be carried out in situ in the preparation of sizing compositions in the present invention.

Examples of titanate coupling agents include, but are not limited to, neopentyl(diallyl)oxitri(dioctyl)phospato titanate, neopentyl(diallyl)oxitri(N- ethylenediamino)ethyl titanate, or bis [2-[(2-aminoethyl)amino]ethanolato]- [2-[(2-aminoethyl)amino]ethanolato]-propane-2-olato-titanate.

Examples of zirconate coupling agents includes, but are not limited to, neopentyl(diallyl)oxitri(dioctyl)phospato zirconate or neopentyl(diallyl)oxitri(N- ethylenediamino)ethyl zirconate. The amount of coupling agent will preferably be within the range of 0.15 % to 4 % by mass of coupling agent with respect to 100% by mass of all the components of the aqueous sizing composition including the water.

In the sizing compositions used in the present invention, polymer materials, distinct from the thermothickening polymer(s), may be used as film- forming materials. The choice of appropriate film-forming polymers generally depends on the chemical nature of the matrix to be reinforced.

The film former polymer plays several roles: it protects the filaments of the glass fibres against abrasion during the fibre drawing, on one hand, and on the other hand it protects the glass fibres against chemical and environmental aggressions. It insures the integrity of the glass strand and it increases the compatibility between the sizing and the matrix to be reinforced.

The film forming polymer can be chosen from one of the following examples (not limited): polyvinyl acetates (homopolymers or copolymers, for example copolymers of vinylacetate and ethylene), polyesters, polyethers, epoxy resins, polyacrylates (homo and copolymers) or polyurethanes. Polyvinyl acetates, epoxy resins with molecular weight lower than 1,000 g/mole or polyethylene glycols with molecular weight higher than 20,000 g/mole are preferred. The film forming polymer is introduced in the sizing composition generally as an emulsion.

Preferably, the amount of film forming polymer is situated between 2 to 8% by mass of the total formulation.

The sizing composition used in the present invention may contain one or more surfactants, dispersants and plasticizers with the role to enable the formation of an homogenous emulsion and to allow the dispersion of different components of the sizing, to avoid liquid - liquid phase separation phenomena and to ensure an effective and rapid wetting during the forming step and impregnation of the glass fibres by the matrix to be reinforced, during composite manufacturing. Plasticizers, surfactants and dispersants often play several roles as they posses several chemical functions, so their classification in one or another category is difficult to assess.

EΞxample of plasticizers, surfactants and dispersants used in the present invention include, but are not limited to:

• organic components, notably: o aliphatic or aromatic, possibly halogenated, polyalkoxylated derivatives, such as ethoxylated/propoxylated alkylphenols, preferably having 1 to 30 ethylene oxide groups and 0 to 15 propyleneoxide groups, ethoxylated/propoxylated bisphenols, preferably having 1 to 40 ethylene oxide groups and 0 to 20 propyleneoxide groups, ethoxylated/propoxylated fatty alcohols or esters, preferably having 8 to 20 carbon atoms in the alkyl chain, 2 to 50 ethylene oxide groups and 0 to 20 propyleneoxide groups. These polyalkoxylated derivatives may be block or random copolymers; o amine derivatives, possibly alkoxylated amines, amine oxides, alkylamides; o succinate derivatives, such as potassium or ammonium succinate; o phosphate derivatives, such as sodium, potassium or ammonium alkylphosphate.

• inorganic derivatives, such as silica derivatives; such components may be used alone or in combination with one of the organic components previously cited.

Preferably, the amount of plasticizers, surfactants and dispersants is situated between 0.1 to 8% by mass of the total formulation.

The sizing composition used in the present invention may contain one or more lubricants to facilitate manufacturing. Any conventional lubricant may be incorporated into the size composition. Non-exclusive examples of lubricants suitable for use in the size composition include, but are not limited to, ethoxylated or non-ethoxylated esters of fatty acids, such as decyl laurate, isopropyl palmitate, cetyl palmitate, isopropyl stearate, butyl stearate, isobutyl stearate, trimethylol propane trioctanoate, trimethylol propane tridecanoate, alkylphenol derivatives, such as ethoxylated octylphenol, alkoxylated or non- alkoxylated fatty alcohols, such as polyethylene glycol laurate or stearate, having methyl chain ends, and preferably having less than 10 oxyethylene groups, a mixture based on mineral oil, alkylamine, a polyethylene wax, polyalkylamines, polyalkylamides. Preferably, the lubricant is included at a concentration between 0.1 and

4% of the total mass of sizing formulation.

The sizing composition of the present invention may optionally contain conventional additives such as anti-static agents, thermal stabilizers, biocides, anti-foaming agents, anti-oxidants, wetting agents, pH control agents, such as acetic acid, citric acid, and/or any other conventional additives up to 5% of the total mass of the sizing.

The balance of the size composition is composed of water. The quantity of water to be introduced in the sizing formulation is preferably calculated to obtain a dry matter content of the final sizing between 3 to 15%, more preferably between 5 to 10%.

The preparation of the sizing composition appropriately includes the following steps consisting in: a) hydrolyzing the coupling agent(s), b) mixing the coupling agent(s), the film forming component, the component chosen in the group of plasticizers, surfactant and dispersing agents, possibly the additives, and water, c) adding the thermothickening polymers, in a solid form or in water solution, preferably under stirring.

The present invention has also the aim to obtain glass strands covered with the above mentioned composition of sizing. In the present invention, by "glass strand", one should understand basic glass fibre resulting from the gathering under the sizing applicator of a multitude of filaments, and the derivative products of these fibres, in particular the assemblies of these strands in ravings. Such assemblies can be obtained by reeling up simultaneously several basic glass fibre rollings, then by gathering them in strands which are wound on a support in rotation. It can be also "direct" rovings of title (or linear density) equivalent to multiend ravings, obtained by the gathering of filaments directly under the sizing applicator, and wound on a rotating support. As mentioned previously, the aqueous composition of sizing is applied to the filaments before their gathering into strands. Water is usually removed by drying the strands after their gathering in the form of rovings under defined conditions of temperature and duration in order to make it possible to achieve a water content lower than 0.25%, preferably lower than 0.1%. Generally, drying is carried out at a temperature which varies from 100 to 150⁰C for 10 to 20 hours according to the type of roving and the initial water content.

The glass fibres obtained according to the present invention can be drawn with glass of any kind, for example E, C, R, AR and Advantex (boron free glass). E and AR glasses are preferred. The diameter of glass filaments constituting the fibre can vary for example from 5 to 30 μm. In the same manner, the linear density of the fibre can vary widely, from 11 to 4800 tex according to the applications envisaged.

In general, the quantity of sizing accounts for 0.2 to 5% in weight of the final glass fibre, preferably 0.35 to 3%. Another object of the present invention is a composite material associating at least an organic and/or inorganic matrix and the glass fibres covered with the sizing composition previously described. The organic matrix can be made up of one or more thermoplastic or thermoset polymers. Examples include, but are not limited to, polyesters, polyamide, polypropylene, and epoxy resins. The inorganic matrix can be for example cement, gypsum or organic/inorganic blends.

The percentage of glass within a composite material generally lies between 5 and 60% in weight. The examples given hereafter illustrate the invention without however limiting it.

Examples

The following sections describe the general methods used to prepare sizing compositions, as well as the materials used in the following experimental examples as well as the test methods used to evaluate the results.

Sizing composition: Example general procedure for sizing fabrication

The following indicates a general procedure for sizing fabrication: Operation 1: Silane hydrolysis

The silane coupling agent is hydrolyzed in a minimum of 10 times its volume of deionised water, at a pH generally comprised between 3.5 and 5 (acidic pH is needed for the hydrolysis of methoxy or ethoxy groups into hydroxyl groups; acidic pH is obtained by using acetic acid, lactic acid or citric acid). The hydrolysis reaction is performed at room temperature for about 20 minutes.

Operation 2: Mixture of silanes if necessary. Homogenization for 5 minutes under stirring.

Operation 3: Adding film formers, which may be diluted if they are very viscous.

Stirring till complete dissolution and homogenization - 5 to 15 minutes. Operation 4: Adding additives - lubricants, surfactants, plasticizers, catalysts, with stirring until complete homogenization is achieved.

Operation 5: Adding the necessary quantity of water in order to obtain the desired dry matter content. Operation 6: Slowly adding the thermothickening polymers (in solid form in the case of methyl cellulose, as water solution in the case of graft copolymers). Stirring for several hours until complete dissolution is achieved.

Sizing components used in Examples

- film forming agents

^■ EPIREZ® 3510 W60 supplied by HEXION: aqueous emulsion of bisphenol A epoxy resin ; molecular weight < 700 g/mole ; dry matter content: 62 %

^■ NEOXIL® 962D supplied by DSM: aqueous emulsion of low molecular weight epoxy ester resin (EEW 470-550 g/eq) ; dry matter content: 40 %

- coupling agents

- SILQUEST^® A-174 supplied by GE SIUCONES: gamma- methacryloxy propy ltri methoxysi lane

^■ SILQUEST^® A-1387 supplied by GE SILICONES: polysilazane (50 % w/w in methanol)

- dispersants. lubricants and plasticizers

^■ SETILON® KN supplied by COGNIS: C₈-C₂₂ ethoxylated fatty alcohols ; dry matter content: 57 %

^■ TEXLUBE® NI/CS2 supplied by ACHITEX: mixture of ethoxylated fatty alcohols and glycerol esters; dry matter content: 100 %

- thermothickening polymers

^■ METHOCEL® A4C - supplied by DOW CHEMICAL ; methyl cellulose, methoxyl degree of substitution: 1.8 ; viscosity at 2% in water: 507 cPs ^■ METHOCEL® A4M - supplied by DOW CHEMICAL ; methyl cellulose, methoxyl degree of substitution: 1.8 ; viscosity at 2% in water: 4857 cPs

^■ poly(acrylamide-co-acrylic acid)-g-poly(N-isopropyl acrylamide-co- dimethyl acrylamide) synthesized prior to use according to the reference Langmuir 23, 147 (2007) ; molecular weight of the main chain poly(acrylamide-co-acrylic acid): 1,070,000 g/mole; ratio acrylamide/acrylic acid: 80/20; molecular weight of poly(N-isopropyl acrylamide-co-dimethyl acrylamide)grafts: 6,000; ratio between main chain and grafts: 75/25.

Measurement of viscosity

Viscosity was measured by means of a BROOKFIELD LVF viscosimeter equipped with a LV type mobile under the following conditions: the mobile is plunged in 500 g of the sizing composition contained in a cylindrical beaker 9 cm in diameter, and turned at the suitable speed (for example a mobile n°2 turning to 60 rpm for a viscosity up to 500 mPa.s) for 1 minute. Viscosity is measured at 25°C temperature and it is expressed in mPa.s. The measured value does not correspond to the absolute value of viscosity; the measured values can be compared between them.

Evaluation of coated glass fibres

1 - loss on ignition (LOI)

LOI values are measured according to the standard ISO 1887 and are expressed in %.

2 - quantity of fuzz

The quantity of fuzz makes it possible to appreciate the abrasive resistance of a glass fibre. It is measured by weighing the quantity of matter which is detached from the fibre after passing this one on a series from 4 or 6 ceramics cylindrical guide-eyes laid out so that the angle of deviation of the glass on the level of each guide-eye is equal to 90°. The quantity of fuzz is given in mg for 1 kg of tested fibre.

3 - tenacity of the glass fibre Tenacity is evaluated by measurement of the breaking load in traction under the conditions defined by the standard ISO 3341. It is expressed in N/tex.

4 - migration

Migration is evaluated by the ratio R of the maximum content of sizing measured on the fibre in the roving to the nominal value of sizing. A ratio R is preferred to be less than or equal to 2. Rovings were inspected both prior to and after drying to observe possible migration.

Formulation Examples The following formulation examples show illustrative examples of the preparation of sizing compositions using thermothickening polymers applicable in the present invention. The present invention is not limited to the use of the specific components shown in the following examples.

Comparative [Example 1: Thermothickening sizing composition containing methyl cellulose

- Solution 1: 5.5 g (0.55%) of silane A174 were hydrolyzed in 500 g deionised water under stirring for 30 minutes. The pH of the solution was adjusted to 4.5 with 0.5 ml acetic acid. - Solution 2: 1.9 g (0.19%) of silane A1387 were hydrolyzed in 100 g deionised water under stirring for 30 minutes. The pH of the solution was adjusted to 4.5 with 0.5 ml acetic acid.

- Solution 3: 40.15 g (4.015%) Epirez® 3510W60 were dissolved in 100 g deionised water under stirring for 15 minutes, then 25.3 g (2.53%) Neoxil® 962D were added to the solution, which was kept under stirring for 15 minutes.

- Solution 4: 1.3 g (0.13%) of Setilon® KN were dissolved in 50 g deionised water at a temperature of 70°C, under stirring for 30 minutes. 3.2 g (0.32%) of Texlube® NI/SC2 were added to the solution and stirring was continued for 5 more minutes.

- At the end, the four solutions were mixed together and 172 g deionised water were added in order to obtain a dry matter content of around 7.5% (weight of total organic solid content relative to total weight of the sizing, including water).

- In order to obtain a thermothickening sizing based on methylcellulose, 10 g of Methocel® A4C were dissolved in 990 g sizing prepared as described above and the solution was kept under vigorous stirring for 6 hours.

Sizing compositions were applied to E glass fibers using a roll coater. The glass filaments have a diameter of 13 μm and a title of 300 tex. They were assembled in ravings which were dried at 12O⁰C for 15 hours.

Comparative Example 2

Sizing compositions containing methylcellulose were prepared as shown in Table 1.

The composition of the sizing compositions are given in following Table 1, the amount by weight of each component being indicated as a percentage with respect to 100% by overall weight of the sizing composition. The properties of the glass fibers obtained are also given in Table 1.

Comparative Example 3: Thermothickening sizing composition containing graft copolymer poly(acrylamide-co-acrylic acidVo-PoMN-isopropyl acrylamide-co- dimethyl acrylamide) - Solution 1: 43.56 g (0.55%) of silane A174 were hydrolyzed in 2000 g deionised water under stirring for 30 minutes. The pH of the solution was adjusted to 4.5 with 1.6 ml acetic acid.

- Solution 2: 15.05 g (0.19%) of silane A1387 were hydrolysed in 1000 g deionised water under stirring for 30 minutes. The pH of the solution was adjusted to 4.5 with 4 ml acetic acid.

- Solution 3: 318 g (4.015%) Epirez® 3510W60 were dissolved in 1150 g deionised water for 15 minutes, then 200.38 g (2.53%) of Neoxil® 962D were added to the solution, which was kept under stirring for 15 minutes.

- Solution 4: 10.3 g (0.13%) of Setilon® KN were dissolved in 756 g deionised water at a temperature of 70⁰C, under stirring for 30 minutes. 25.34 g (0.32%) of Texlube® NI/SC2 were added to the solution and stirring was continued for 5 more minutes. - At the end, the four solutions were mixed together and 396 g deionised water were added in order to obtain a dry matter content of around 7.5% by mass.

- In order to obtain a thermothickening sizing based on graft copolymers, 2080 g thermothickening copolymer solution of the graft copolymer poly(acrylamide-co-acrylic acid)-g-poly(N-isopropyl acrylamide-co-dimethyl acrylamide), at a concentration of 4% by mass, were added to the sizing prepared as described above, and the final sizing solution was kept under stirring for 6 hours.

The final concentration of thermothickening polymer in the sizing composition was 1% by mass.

Examples 1 and 2: Comparative Examples 4 and 5

Different sizing compositions containing graft copolymer were prepared as shown in Table 1. Sizing compositions were applied to the E glass fibers using a roll coater.

The glass filaments have a diameter of 13 μm and a title of 300 tex

(Comparative Example 3, Example 1, Comparative Example 4) or a diameter of

19 μm and a title of 600 tex (Example 2 and Comparative Example 5). They were assembled in ravings which were dried at 120⁰C for 15 hours.

The properties of sizing compositions and of the glass fibers obtained are given in Table 1.

Comparative Example 4 and 5 are free of thermothickening polymers.

Glass fibers according to Comparative Example 3, Example 1 and Comparative Example 4, were used to obtain unidirectional composite plates with parallel fibers under the conditions of the standard ISO 9291 by using the following resins:

- epoxy resin made of 100 parts by weight epoxy resin LY 564 (marketed by HUNSTMAN) and 96 parts by weight of hardener ARALDITE® XB 3486 (marketed by HUNTSMAN).

- polyester resin made of 100 parts by weight unsaturated isophtalic polyester resin SYNOUTE® 1717N1 (marketed by DSM) and 1.5 parts by weight of methylisobutylketone peroxide (TRIGONOX® HM marketed by AKZO NOBEL) The plates were treated under the following conditions:

Temperature (⁰C) Time (hours)

Epoxy resin 80 8 Polyester resin 60 16

Test samples are cut in the plates which are treated during 72 hours

(epoxy resin) or 24 hours (polyester resin) in boiling water. Mechanical properties are measured according to the standard ISO 14125 on the test samples before and after the ageing treatment: 3 points bending flexural strength in the longitudinal and transverse direction. The value in longitudinal direction enables the calculation of the value of the flexural strength at 100% glass content. The results of the measurements are given in Table 2.

Table 1

Table 2: Mechanical properties of composites

Claims

1. Method of coating glass fibres comprising the steps of:

(a) extruding molten glass through an orifice to produce glass fibres; and (b) after step (a), coating the glass fibres produced with a sizing composition containing at least 1.5% by weight of thermothickening polymer, where the thermothickening polymer is at least one graft copolymer having a poly(meth)acrylamide_/ poly(meth)acrylic acid or a poly((meth)acrylamide-co-

(meth)acrylic acid) main chain and grafts pending on the main chain of at least one of the following types: polyoxyethylene, polyoxyethylene-co- polyoxypropylene, poly(N-isopropyl(meth)acrylamide), poly(dimethyl(meth)acrylamide), or poly(N-isopropyl(meth)acrylamide-co- dimethyl(meth)acrylamide) copolymer.

2. Method of coating glass fibres according to claim 1, wherein the said sizing composition also comprises:

- at least one coupling agent selected from the group consisting of: hydrolysable silanes, titanates or zirconates; and

- at least one film former polymeric material, distinct from the said thermothickening polymer(s), where the film former polymeric material is selected from the group consisting of: polyvinyl acetates, polyesters, polyethers, epoxy resins, polyacrylates, and polyurethanes.

3. Method of coating glass fibres according to claim 1 or 2, wherein the said sizing composition comprises:

- at least 80% by mass of water;

- at least 1.5 % by mass and at most 5 % by mass of the said thermothickening polymer(s);

- at least 2 % by mass and at most 8 % by mass of at least one film former polymeric material, distinct from the said thermothickening polymer(s); - at least 0.15 % by mass and at most 4 % by mass of at least one coupling agent selected from the group consisting of: hydrolysable silanes, titanates or zirconates;

- at least 0.1 % by mass and at most 8 % by mass of at least one component chosen from the classes of plasticizers, surfactants and dispersants;

- at least 0.1 % by mass and at most 4 % by mass of at least one lubricant.

4. Method of coating glass fibres according to either of claims 2 or 3, wherein the said film former polymeric material, distinct from the said thermothickening polymer(s) is selected from the group consisting of: polyvinyl acetates; epoxy resins with molecular weight lower than 1,000 g/mole; or polyethylene glycols with molecular weight higher than 20,000 g/mole.

5. Coated glass fibres as produced by the method of any of claims 1 to 4.

6. Aqueous sizing composition comprising:

(a) one or more thermothickening polymers at a concentration of at least 1.5% by weight of thermothickening polymer in the overall aqueous sizing composition, where the thermothickening polymer is at least one graft copolymer having a poly(meth)acrylamide, poly(meth)acrylic acid or a poly((meth)acrylamide-co-(meth)acrylic acid) main chain and grafts pending on the main chain of at least one of the following types: polyoxyethylene, polyoxyethylene-co-polyoxypropylene, poly(N-isopropyl(meth)acrylamide), poly(dimethyl(meth)acrylamide), or poly(N-isopropyl(meth)acrylamide-co- dimethyl(meth)acrylamide) copolymer;

(b) at least one coupling agent of the type silane, titanate and/or zirconate;

(c) at least one film former polymeric material, distinct from the said thermothickening polymer(s) and selected from the group consisting of: polyvinyl acetates; epoxy resins with molecular weight lower than 1,000 g/mole; or polyethylene glycols with molecular weight higher than 20,000 g/mole; and

(d) optional further additives comprising one or more components selected from one or more of the following groups: plasticizers, surfactants, dispersants and lubricants.

7. Polymer composite material comprising:

(a) a polymer matrix comprising a thermoplastic or thermosetting polymer; and

(b) glass fibres coated with a sizing composition according to claim 6.

8. Use of a thermothickening polymer at a concentration of thermothickening polymer of at least 1.5% by weight in sizing compositions for glass fibre materials in order to inhibit product migration, where the thermothickening polymer is a graft copolymer having a poly(meth)acrylamide, poly(meth)acrylic acid or a poly((meth)acrylamide-co-(meth)acrylic acid) main chain and grafts pending on the main chain of at least one of the following types: polyoxyethylene, polyoxyethylene-co-polyoxypropylene, poly(N- isopropyl(meth)acrylamide), poly(dimethyl(meth)acrylamide), or poly(N- isopropyl(meth)acrylamide-co-dimethyl(meth)acrylamide) copolymer.