WO2010003171A1

WO2010003171A1 - Prepolymer composition

Info

Publication number: WO2010003171A1
Application number: PCT/AU2009/000824
Authority: WO
Inventors: Christopher Allan Lukey
Original assignee: University Of Wollongong
Priority date: 2008-07-09
Filing date: 2009-06-26
Publication date: 2010-01-14
Also published as: AU2009267786A1

Abstract

The present invention relates to a prepolymer composition comprising a polyester prepolymer, a vinyl-functional monomer having a vapour pressure which is less than styrene at 20° C and an accelerator. The prepolymer composition can be combined with a promoter which causes the prepolymer composition to cure. The cured composition forms a polymeric material which is capable of reinforcing surfaces, in particular the surfaces of mine tunnels including longwall coal mine roadways.

Description

PREPOLYMER COMPOSITION

TECHNICAL FIELD

The present invention relates to a prepolymer composition, a curable or cured composition or kit containing the prepolymer composition, processes for making the compositions and their use as polymeric materials for reinforcing surfaces, in particular the surfaces of longwall coal mine roadways.

BACKGROUND Currently skin reinforcement and confinement in longwall coal mine roadways is achieved using steel mesh. The current method of installation is slow and manual, and places mine personnel conducting the installation in a dangerous position under unsupported roof.

Ground support practices presently range from a single rib bolt per metre and no mesh to three or more rib bolts and complete ceiling to floor meshing, depending on the structural soundness of the rib coal and the degree of ground movement experienced. In most cases, however, skin reinforcement of the roof is full width and continuous. Roadway development practices range from cut-and-flit to bolting and meshing directly behind the continuous miner cutting head, depending on the stability of the strata. There is a need for a new system for skin reinforcement and confinement which may be rapidly and safely installed, preferably using an automated method. This would increase the rate of roadway advancement and remove personnel from the immediate face area.

In some mines, gas drainage is an issue. Other mines have problems with mine water at low pH. Any new material would preferably be able to be successfully applied, and provide the requisite level of long-term support under these widely varying conditions.

If a polymeric skin reinforcement material is to be successfully used in underground coal mines, it would preferably be capable of being spray-applied ahead of the bolters, and be sufficiently cured by the time the bolts were inserted.

SUMMARY

In a first aspect of the invention there is provided a prepolymer composition comprising: • a polyester prepolymer; • a vinyl-functional monomer having a vapour pressure which is less than styrene at 20⁰C; and

• an accelerator.

The polyester prepolymer is preferably a condensation product of: • a diacid and/or anhydride, preferably an alpha, beta-ethylenically unsaturated diacid and/or anhydride such as maleic anhydride and a non-polymerisable diacid and/or anhydride such as phthalic anhydride or adipic acid or both; and

• an organic diol, preferably a polyhydric alcohol which may be selected from the group consisting of 1 ,2-propanediol, 1,6-hexanediol, diethylene glycol, 1,3- propanediol, 2 -methyl- 1,3-propanediol, 1 ,4-butanediol, 1,5-pentanediol and 1,4- cyclohexanedimethanol and combinations thereof.

The vinyl-functional monomer may be an N-vinyl amide, preferably N- vinylpyrrolidinone (NVP).

The prepolymer composition, when combined with a promoter capable of causing said prepolymer composition to cure, may form a curable composition which is sprayable. The promoter is chosen so that the composition is capable of having a gel time at room temperature of less than about 1 minute.

In a second aspect of the invention there is provided a curable composition comprising: • the prepolymer composition as defined above; and

• a promoter capable of causing the prepolymer composition to cure.

The prepolymer or curable composition may additionally comprise one or more of a co-accelerator, filler, inhibitor or other additives such as antistatic agents or flame retardants. In a third aspect of the invention there is provided a process for making a prepolymer composition comprising combining:

• a polyester prepolymer;

• a low volatility vinyl-functional monomer; and

• an accelerator. The polyester prepolymer may be prepared by combining a diacid and/or anhydride with an organic diol.

In a fourth aspect of the invention there is provided a process for making a curable composition comprising combining:

• the prepolymer composition as defined above; and • a promoter capable of causing said prepolymer composition to cure.

The prepolymer composition may be made by the process defined above. In a fifth aspect of the invention there is provided a process for making a cured composition comprising curing the composition defined above.

In a sixth aspect of the invention there is provided a cured composition made by the process as defined above. In a seventh aspect of the invention there is provided a kit comprising:

• a first part comprising the prepolymer composition as defined above; and

• a second part comprising a promoter capable of causing said prepolymer composition of the first part to cure.

The cured composition as defined above may be used as a polymeric material for reinforcing a surface, in particular the surface of longwall coal mine roadways.

In an eighth aspect of the invention there is provided use of the prepolymer composition as defined above in the manufacture of a polymeric material such as a polymeric skin or liner.

In one embodiment, there is provided use of a polyester prepolymer, a vinyl- functional monomer having a vapour pressure which is less than styrene at 20⁰C and an accelerator in the manufacture of a polymeric material such as a polymeric skin or liner.

In a ninth aspect of the invention there is provided a method for reinforcing a surface comprising:

• combining the prepolymer composition as defined above and a promoter to form a curable composition;

• applying the curable composition to a surface; and

• allowing the curable composition to cure on the surface to form a polymeric skin or liner.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be described, by way of an example only, with reference to the accompanying drawings wherein:

Fig. 1 is a graph showing variation in cure time with varying promoter concentration; Fig. 2 shows graphs showing the effects of promoter concentration on the mechanical properties of a cured polyester composition: a) tensile modulus; b) tensile strength; c) failure strain;

Fig. 3 is a graph showing flexure behaviour of a number of reinforced polyesters; and Fig. 4 is a graph showing the effect of hydroquinone inhibitor concentration on the gel time of Polyester 19 crosslinked with NVP. DETAILED DESCRIPTION

The present invention relates to a prepolymer composition which comprises a polyester prepolymer, a vinyl-functional monomer having a vapour pressure which is less than styrene at 20⁰C and an accelerator. The prepolymer composition is capable of curing when combined with a suitable promoter to form a polymeric material on a surface.

Polyester prepolymer

The polyester prepolymer may be a condensation product of at least one diacid and/or anhydride and at least one organic diol. The prepolymer comprises copolymerisable carbon-carbon double bonds which may be provided by either the diacid, anhydride and/or diol. Since the condensation of the diacid and/or anhydride with the diol results in an alternating copolymer prepolymer, it follows that the ratio between units derived from the diacid and/or anhydride and the diol is about 1 : 1. If the prepolymer has hydroxyl end groups, then the ratio will be slightly greater than 1 :1. If the prepolymer has carboxylic acid end groups, then ratio will be slightly less than 1 : 1.

The diacid and/or anhydride may be an aromatic or aliphatic diacid and/or anhydride. Examples include: aliphatic anhydrides such as maleic anhydride, succinic anhydride and glutaric anhydride; aromatic anhydrides such as phthalic anhydride and 1 ,8-naphthalic anhydride; cyclic anhydrides or diacids having 5 to 10 atoms in the ring (e.g. 5, 6, 7, 8, 9 or 10 atoms in the ring) such as cyclopentanedicarboxylic acid and cyclohexanedicarboxylic anhydride; aliphatic diacids (e.g. α,ω-diacids) where the two acid groups are joined by 1 to

10 carbon atoms 1 to 5 carbon atoms or 2 to 10 carbon atoms or 2 to 6 carbon atoms (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms) such as succinic acid, glutaric acid and adipic acid; and aromatic diacids such as phthalic acid, isophthalic acid and 1,8-naphthalenedioic acid.

In a preferred embodiment, the diacid and/or anhydride is a combination of an alpha, beta-ethylenically unsaturated diacid and/or anhydride and a non-polymerisable diacid and/or anhydride, preferably an alpha, beta-ethylenically unsaturated anhydride such as maleic anhydride and a non-polymerisable diacid and/or anhydride such as phthalic anhydride or adipic acid or both.

In the event that a mixture of acids and anhydrides is used, an acid and anhydride having a copolymerisable double bond may be present in the mixture at between about 25 to 75% on a molar basis; or about 25 to 50, 50 to 75, 30 to 70, 40 to 60 or 45 to 55%; or about 25, 30, 35, 40, 45, 50, 55, 60, 65, 70 or 75%.

The organic diol may be a saturated or unsaturated aliphatic diol which may be optionally interrupted by a cyclic group or an ether group. The diol may be an alkyl diol (e.g. an α,ω-diol) having 2 to 10 carbon atoms linking the two alcohol groups or 2 to 8, 2 to 6 or 2 to 4 carbon atoms. The carbon atoms linking the two alcohol groups may form a cyclic group such as a C^cyclic group for example a cyclopentane or cyclohexane ring. The diol may be an ether diol such as diethylene glycol or triethylene glycol. One or more diols (e.g. 2, 3 or 4) may be used. Suitable diols include 1,2- propanediol, 1,6-hexanediol, diethylene glycol, 1,3-propanediol, 2-methyl-l,3- propanediol, 1,4-cyclohexanedimethanol, 1 ,4-butanediol and 1,5-pentandiol or combinations thereof.

The polyester prepolymer is preferably a condensation product of maleic anhydride; phthalic anhydride or adipic acid or both, more preferably phthalic anhydride; and a polyhydric alcohol which may be selected from the group consisting of 1,2-propanediol, 1,6-hexanediol, diethylene glycol, 1,3-propanediol, 2-methyl- 1 ,3- propanediol, 1,4-butanediol, 1,5-pentanediol and 1,4-cyclohexanedimethanol and combinations thereof, more preferably 1,2-propane diol, 1,6-hexanediol or 1,4- butandiol. It will be understood that more than one polyester prepolymer may be present in the compositions of the invention. A preferred blend of prepolymers comprises condensation products of maleic anhydride, phthalic anhydride and 1,2-propanediol and maleic anhydride, phthatic anhydride and 1,6-hexanediol.

Monomer

The vinyl-functional monomer should be chosen so that the prepolymer may be safely used in a confined environment. It should also be such that the prepolymer is capable of rapid cure at ambient temperatures when combined with a promoter. This is achieved by use of a monomer have a vapour pressure which is less than styrene at 20⁰C. The vapour pressure is preferably less than about 2mmHg; less than about 1.5, 1,

0.5, 0.2 or 0.1 ; about 0.01 to 2, 0.01 to 1, 0.01 to 0.5, 0.01 to 0.1, 0.01 to 0.05, 0.05 to 2, 0.1 to 2, 0.5 to 2, 1 to 2, 0.1 to 1, 0.05 to 0.5 or 0.05 to 0.2, or about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1 , 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2mmHg at 2O⁰C. Suitable monomers include amides containing polymerisable double bonds. Examples include N-vinyl amides such as cyclic N-vinyl amides which may have 5 to 8 atoms in the ring. Preferably the monomer is N-vinylpyrrolidinone (NVP) which has a vapour pressure below about O.lmmHg at 24⁰C which is less than 1% that of styrene. Another advantage of using NVP is that it is reasonably priced and approximately three times more cost effective to use than styrene. For use in confined environments such as mining applications, it is preferable that the monomer is non-flammable, non- combustible, non-irritant and/or non-toxic. The monomer also functions to crosslink with the prepolymer under the influence of the accelerator and the promoter.

The vinyl-functional monomer may be present in the prepolymer composition is an amount of about 20 to about 50% by weight; about 20 to 40, 20 to 30, 30 to 50, 40 to 50 or 30 to 40%; or about 20, 25, 30, 31, 32, 33, 34, 35, 40, 45 or 50% by weight.

Accelerator

The accelerator may be a transition metal salt such as a cobalt, iron, copper, manganese, tin or vanadium salt, for example a cobalt (II) salt. Suitable accelerators include transition metal salts of an organic acid such as transition metal salts of a carboxylic acid. Examples include cobalt naphthenate, cobalt octanoate, cobalt 2- ethylhexanoate, cobalt hexanoate, iron naphthenate, copper naphthenate, manganese octanoate, tin octanoate, vanadyl acetyl octanoate and vanadium acetyl acetonate, preferably cobalt naphthenate. In an alternative embodiment, a co-accelerator such as a tertiary amine as described hereinafter may be used with or replace the accelerator. The accelerator may be present in the prepolymer composition at a level of between about 0.1 and about 3% by weight; about 0.1 to 2, 0.1 to 1, 0.1 to 0.5, 0.1 to 0.2, 0.2 to 1, 0.5 to 1, 0.5 to 3, 1 to 3, 2 to 3, 0.5 to 2, 1 to 2 or 0.3 to 0.8%; or about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5 or 3% by weight.

Curable composition

The invention also provides a curable composition comprising the prepolymer composition defined above and a promoter capable of causing the prepolymer composition to cure. The curable composition will spontaneously cure once formed due to crosslinking of the prepolymer with the monomer under the influence of the promoter and accelerator.

The prepolymer composition preferably is capable of formulation into a sprayable curable composition. Suitable curable compositions have a short gel time of under about 1 minute, preferably under 45 seconds, under 30 seconds, 10 to 60 seconds, 10 to

45 seconds, 10 to 30 seconds, 10 to 20 seconds, 20 to 45 seconds, 30 to 45 seconds or 15 to 30 seconds or about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 or 60 seconds.

The term "gel time" as used herein refers to the time following mixing of the prepolymer with the promoter until the resulting mixture has gelled as estimated visually. In the present specification the phrase "gel time" or "initial cure" "at room temperature" indicates that the composition is initially mixed at room temperature (e.g. at about 20 to 25⁰C; or 20, 21, 22, 23, 24 or 25⁰C) and that no external heating or cooling is applied thereafter until the composition gels. It will be understood that the actual temperature of the curing mixture will vary due to heat evolved during the curing process.

The requirement for a short gel time is particularly important when the composition is for reinforcing surfaces in confined environments such as the ceiling, walls and/or floor of a tunnel. Thus rapid cure is required firstly in order to ensure that the formulation does not flow away from its initial location prior to gelation, secondly to enable the cured composition to be bolted in place without excessive delay, and thirdly to minimise the time required to reinforce the tunnel so as to achieve a safe working environment for workers in the tunnel.

The cured composition may be bolted in place when used to reinforce mining tunnels. Bolts are typically made of mild steel. They may be up to 1.8m long and are typically about 2.5cm diameter. They may be ribbed for most of their length and may have a screw thread on the bottom end. The bolts may be self-drilling bolts. Self- drilling bolts commonly have a hardened steel drill tip and are hollow (and therefore wider than other types of bolts) to allow the chemical anchor resin through to the annulus between the hole and the bolt. Thus commonly in use of such bolts, a chemical anchor resin flows up through the hollow core and into the annular space between the hole and the bolt, thereby anchoring the bolt when set. The chemical anchor resin may be the same as the curable composition described herein, or may be a different curable resin. The requirement for sprayability of the composition may be met when both the prepolymer composition and the promoter used to cure the prepolymer composition are liquids. They should each have a viscosity such that when combined the resulting composition has a viscosity such that it is sprayable. The viscosity of the prepolymer composition and the promoter may be the same or different. They may each independently be between about 200 and 1000 cP; about 200 to 700, 200 to 500, 400 to

1000, 500 to 1000, 300 to 600 or 400 to 50OcP; or about 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 or lOOOcP. These values are as measured at 25⁰C using a Brookfield viscometer. Suitable conditions for the Brookfield viscometer are spindle LVl at 6rpm. The viscosity may be varied as required by addition of a suitable diluent, for example the vinyl-functional monomer, in small quantities. Promoter

Suitable promoters include organic peroxides. Examples include the following:

1. Diacyl peroxides such as benzoyl peroxide, dilauryoyl peroxide, acetyl peroxide, caprylyl peroxide, p-chlorobenzoyl peroxide, decanoyl peroxide, 2,4- dichlorobenzoyl peroxide, pelargonoyl peroxide or propionyl peroxide;

2. Ketone peroxides usually transition such as monomeric or dimeric methyl ethyl ketone peroxide (MEKP), acetyl acetone peroxide or cyclohexanone peroxide;

3. Peroxy esters such as t-butyl peroxybenzoate, t-butyl peroxyacetate, t-butyl peroxy(2-ethylhexanoate), t-butyl peroxyisobutyrate, t-butyl peroxyisopropylcarbonate, t-Butyl peroxypivalate, 2,5-dimethylhexyl-2,5-di(peroxybenzoate), 2,5-dimethylhexyl- 2,5-di(peroxy(2-ethylhexanoate)), di-t-butyl diperoxyphthalate or 1, 1,3,3- tetramethylbutyl peroxy-2-ethylhexanoate;

4. Alkyl peroxides such as di-t-butyl peroxide, dicumyl peroxide, n-butyl-4,4- bis(t-butyl peroxy)valerate, 2,5-dimethyl-2,5-bis(t-butyl peroxy)hexane, 2,5-dimethyl- 2,5-bis(t-butyl peroxy)hexyne-3, 1 ,1 -di-t-butyl peroxyl cyclohexane or 1,1 -di-t-butyl peroxyl-3,5,5-trimethylcyclohexane; and

5. Hydroperoxides such as cumene hydroperoxide, t-butyl hydroperoxide or 2,5 -d imethy lhexane-2, 5 -d ihydroperoxide .

The ketone peroxides of group 2 generally require the use of a transition metal salt as accelerator with a tertiary amine as an optional co-accelerator. Groups 1, 3, 4 and 5 may be used with a tertiary amine accelerator such as dimethylaniline or dimethyltoluidine either in the absence or presence of a transition metal salt.

Preferably the promoter is a ketone peroxide such as MEKP.

The promoter may be provided neat or in solution. The solvent for the solution may be an inert solvent. Suitable solvents include mineral oil, dibutyl phthalate, benzene, high boiling organic solvents and mineral spirits.

The inventors have found that the gel time initially decreases rapidly with increasing promoter concentration, however above a certain promoter concentration no further benefit (in terms of cure acceleration) is obtained. This threshold concentration is typically about 3% by weight of the prepolymer composition as shown in Fig. 1. The promoter is generally present (or will be added to the prepolymer composition) in a ratio of between about 2 and about 4% w/w of the prepolymer composition; about 2 to 3, 3 to 4 or 2.5 to 3.5%; or about 2, 2.5, 3, 3.5 or 4%. Higher promoter levels may be used in order to achieve desirable physical properties. Fig. 2 illustrates the change in physical properties including tensile modulus, tensile strength and elongation at break as the concentration of promoter is varied. It should be noted that the experimental results shown in Figs. 1 and 2 were, for convenience, obtained using slower curing systems, however these results serve to illustrate typical trends.

Co-accelerator The prepolymer or curable composition may additionally comprise a co- accelerator. The co-accelerator may be used instead of the accelerator as described above. The co-accelerator may be a tertiary amine such as a tertiary aromatic amine, for example, a dialkylaniline derivative. The alkyl groups of the dialkylaniline derivative may be C^alkyl groups such as methyl, ethyl or propyl groups. Suitable co- accelerators include N,N-dimethyltoluidine (DMT) or N,N-dimethylaniline or derivatives thereof.

The co-accelerator, if used may be present in a ratio of about 10 to about 100% to that of the accelerator by weight; about 10 to 50, 10 to 20, 20 to 100, 50 to 100, 20 to 80, 20 to 50 or 50 to 70%; or about 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100% by weight.

Filler

The prepolymer or curable composition may additionally comprise a filler such as a fibrous filler, for example a reinforcing filler. Examples of suitable fillers include short glass fibres which may have a mean fibre length of less than about 10cm; less than about 5, 2 or lcm; about 0.1 to 10, 0.1 to 5, 0.1 to 2, 0.1 to 1, 0.1 to 0.5, 0.5 to 10, 1 to

10, 2 to 10, 5 to 10, 0.5 to 5, 0.5 to 2 or 1 to 5cm; or about 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6,

0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 6, 7, 8, 9 or 10cm.

The filler may be pretreated so as to improve its adhesion to the polymeric material when formed. Suitable pretreatments include treatment with silane coupling agents for example vinylfunctional silanes such as methacryloyloxypropyltrimethoxysilane.

The filler may be present in the curable composition at about 5 to about 50% by weight or volume; about 5 to 20, 5 to 10, 10 to 50, 20 to 50, 10 to 30, 20 to 40 or 15 to 25%; or about 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50% by weight or by volume.

The filler may also be present in the prepolymer composition prior to formation of the curable composition in approximately the same amount as in the curable composition, i.e. about 5 to about 50% by weight or by volume. Inhibitor

An inhibitor can be used in the prepolymer or curable composition to ensure that the gel time is short. Suitable inhibitors include quinones such as hydroquinone or naphthoquinone which serve the additional function of enhancing storage or stability.

Additives

It will be appreciated that the prepolymer, curable or cured composition may include polymeric additives. Examples include antistatic agents, flame retardants or both.

One major application of the compositions of the present invention is for use in mine tunnels. Static electricity is generated underground by the movement of dry air over susceptible surfaces, and by other mechanisms. This poses a danger as it is a potential spark source which can lead to a fire. Steel mesh, which is presently used as a reinforcement material, is able to conduct static electricity away to be earthed through the rock bolts, thereby reducing the risk due to static electricity. Most polymers (including polyesters) are intrinsically electrically insulating, and so static electricity can build up on polymer surfaces. Therefore, if it is desired to replace steel mesh with a polymer-based alternative, some degree of electrical conductivity in the polymer may be desirable.

Anti-static additives for polymers generally fall into two categories. The first category is ionic organic compounds that migrate to the surface of the polymer and reduce static by attracting atmospheric water which condenses on the surface. These compounds eventually wash off and are replaced by more of the additive migrating to the surface. Ultimately, however, the reservoir of additive in the bulk of the polymer is exhausted and the anti-static activity ceases. An additional problem with this type of agent in the underground environment is that static electricity is typically generated by the passage of ventilation air that contains very little moisture, so the anti-static action may never "switch on". The second category of anti-static agents is the so-called "permanent anti-stats".

These additives are generally metals or semiconductors, and operate by providing electrical connectivity. In order to be effective, however, they generally need to be added in relatively high amounts.

One possibility for suppressing static electricity in the present compositions of the invention is to apply an anti-static powder to the surface as the polyester is curing, thereby confining all of the anti-static activity to the surface. In this way much less of - li the anti-static material would be required. A second option is to incorporate an additive that migrates to the surface during cure (known as "self-stratifying" additives).

In underground coal mines there is always a risk of fire. Coal itself is combustible, and often flammable methane gas is associated with the coal. A major advantage of steel mesh over many polymeric alternatives is that it is non-combustible.

If an alternative to steel mesh is to be used, it is preferable that it be less combustible than the coal to which it is attached.

There are several approaches to the endowment of polymeric materials with flame retardancy. One approach is to make the polymer from flame-retardant monomers, thus making the resultant polymer inherently flame-retardant. Halogen- functional monomers (those containing chlorine or bromine) are mostly used in this context. An alternative, and possibly more cost-effective, approach is to use flame- retardant additives, of which there are 3 types:

• substances that disrupt free radical propagation in the flame; • substances that decompose when heated to produce a flame-suppressant gas such as CO₂; and

• substances that char and swell when heated and thereby remove the seat of the flame from the fuel source.

Additives in the third category are known as "intumescent" flame retardants. Typically two or more types are used in conjunction to produce an effective flame-retardant system.

Suitable additives include mixtures of silica gel and potassium carbonate, which enhance char formation. Such mixtures have been used to provide effective flame retardancy to a range of polymers (both inherently char-forming and non-char-forming) at total additive levels up to 10%. Silica gel and potassium carbonate are both inexpensive and readily available. An advantage of this system for use underground is that CO formation during combustion was not significantly increased by the presence of the additives.

Thus the prepolymer composition, the curable composition and the cured composition described herein may all comprise either an antistatic agent or a flame retardant or both. The antistatic agent, if present, may be distributed in the cured composition either throughout the cured composition or on the surface thereof. Thus the process for making prepolymer or curable composition may comprise the additional step of mixing an effective amount of an antistatic agent or of a flame retardant or both with the composition once formed, or with one or more of the components prior to mixing them to form said composition. Alternatively or additionally, the process for forming the cured composition may comprise applying (e.g. spraying) an antistatic agent onto the surface of the curable composition after it has been located in the desired location and before it has gelled, or before the surface of the curable composition has become tack-free. In this context, "tack-free" refers to a state in which the antistatic agent fails to adhere to the surface. In one embodiment, one or both of the monomer and the polyester prepolymer are at least partially halogenated (e.g. chlorinated or brominated). This may serve to provide intrinsic flame retardancy to the compositions incorporating them without the need for separate added flame retardants. Thus the monomer may be at least partially halogenated, or the diacid, anhydride or diol (or more than one, optionally all, of these) used in making the prepolymer may be at least partially halogenated. Suitable prepolymers may be made using (or may have monomer units derived from) halogenated anhydrides such as dibromophthalic anhydride, dichlorophthalic anhydride etc.

Suitable antistatic agents that may be added to the compositions of the present invention, include carbon black, fullerenes, carbon nanotubes, graphene, tetrapod zinc oxide, electrolytic nickel powder, intrinsically-conducting polymers such as BTATZ (bis(aminotetrazolyl)tetrazine), polyacetylene and polyparaphenylene sulphide.

Suitable flame retardants that may be added to the compositions of the present invention, include combinations of silica gel and a metal carbonate such as potassium carbonate. Metal hydroxides, for example aluminium hydroxide, magnesium hydroxide etc. may also be used.

Processes

The invention also provides a process for making the prepolymer composition. This process comprises combining the components of the prepolymer composition, i.e. the polyester prepolymer, the vinyl-functional monomer, the accelerator and the inhibitor if present. These may be combined in any desired order, as no chemical reaction is desired at this stage. Thus the components may all be added and then combined, or the prepolymer may be combined with the monomer and the inhibitor if present and the resulting mixture mixed with the accelerator, or some other order may be used. If a co-accelerator, filler, and/or other additives are included, they may be combined at any stage of the process for making the prepolymer composition. The components of the prepolymer composition may be combined using any suitable known apparatus such as a batch reactor. The invention also provides a process for making the curable composition. This process comprises combining the prepolymer composition with a promoter capable of causing the prepolymer composition to cure. If a co-accelerator, filler, inhibitor and/or other additives are included, they may be combined at any stage of the process for making the curable composition. In one embodiment, the process involves combining the filler with the prepolymer composition or with the promoter or with the combined prepolymer composition and promoter. In one example of the process, the promoter is combined with the prepolymer composition which is then combined with the filler to produce the curable composition which is then sprayed onto the desired surface (e.g. the wall, ceiling and/or floor of a mine tunnel) where it cures in situ. In another embodiment of the process the filler is located on the desired surface, for example as a bed of filler. Separately the promoter is combined with the prepolymer composition, which is then sprayed onto the filler. The prepolymer composition then combines with the filler by penetrating into and/or through the filler to form the curable composition where it cures in situ.

It will be appreciated that once the promoter is combined with the prepolymer composition, the curable composition cures rapidly without further stimulus. It is therefore desirable to apply the curable composition to the surface as rapidly as possible. It is also preferable to combine the prepolymer composition with the promoter as rapidly as possible. These objectives may be met using any suitable apparatus such as automated systems, for example spray heads which combine the two parts and spray them onto a desired location. Other mixing/dispensing devices may also be used to combine and apply the curable composition.

Cured Composition

The cured composition may be used as a polymeric material for reinforcing a surface. The surface may be a floor, a wall or a ceiling. It may be in a confined space such as a mine or in a house or a in a dwelling or in some other location.

The cured composition may be used for the purpose of reinforcing, protecting or substantially preventing matter from detatching from the surface so as to avoid danger to humans and/or animals. The cured composition may at least partially adhere to the surface. It is preferably applied to the surface by spraying. In mining applications, the at least partially cured composition may additionally be bolted to the surface. The spacings between the bolts spacing are commonly specified by geotechnical engineers based on strata stability and may vary considerably based on local conditions. As the cured composition of the present invention is impermeable to liquid water, there is the potential for water to build up behind the composition as water seeps through the wall and/or ceiling of the mine tunnel. This water build-up may be alleviated by perforating the cured composition at regular intervals in order to allow the water to penetrate the composition. Thus the process may additionally comprise the step of perforating the cured composition following application to the surface of the mine tunnel.

Properties

The mechanical properties of the polymeric material of the present invention are similar to or superior to the steel mesh which is presently used to reinforce the surfaces of tunnels in mines.

The typical mechanical and physical properties of the polymer material of the present invention are as follows:

Applications The compositions of the present invention have use in many applications. These include, but are not limited to, the following:

1. Reinforcement in confined applications.

As discussed above, the composition of the present invention is capable of forming a polymeric skin and/or liner which may be used to reinforce the surface in hard rock mines, readings in longwall mines and provide stabilisation of road and corridor excavators. They can also provide bord and pillar coal mine strata support, and temporary arrest of fretting and spall ing of longwall faces in mines. 2. Lining for an aged reinforced concrete water supply and/or drainage conduit.

The composition may be used to waterproof water vessels such as tanks, pipes and underground concrete sewers. These structures frequently develop cracks as they age, due to deterioration or embrittlement of the construction materials or to movement in substrates. Coating these structures with a polymeric material described herein can provide a waterproofing treatment which is capable of absorbing minor movements in the substrate without failure.

3. Residential and Commercial Buildings

Sprayed onto surfaces such as floors, ceilings or walls, the composition may be used as a building material. This may find application for example in Japan. Typhoons and torrential rainstorms repeatedly hit Japan every year. Residences commonly need to be reinforced against storms using designs that ensure the strength and waterproofing of buildings. In addition, as a precaution against ignition and spread of fires, which is of great importance in neighbourhoods with houses arranged close together. Fireproof materials such as those of the present invention are also desirable so as to achieve fire- retardant performance. The compositions may also be used to cover dangerous and difficult to remove building products for example to remediate old asbestos containing buildings.

Issues of importance in the Japanese housing market include:

• formaldehyde concentration;

• toluene and xylene concentration;

• floor sound insulation performance; • air sealing performance;

• thermal insulation performance;

• earthquake resistance for the plan.

The present invention may assist in addressing at least some of these issues.

4. Unsupported Rock failures in undergrounds mining

Tenaciously adhering, deformable polymeric materials such as those of the present invention have an ability to substantially mitigate damage often seen to result when catastrophic unsupported rock failure occurs. Shotcrete support, while demonstrating significant capacity to restrain rock heave and fragment ejection, has been noted to suffer generally greater layer damage and potential breakup than any of the spray-on polymeric materials. Rockbolts and bolt-and-mesh support media provided least effective support restraint in terms of reducing fragment ejection, restriction of the extent of the damage zone formed and prevention of damage to support materials.

S. Spray on Truck bed liners These are generally comprised of a variety of materials such as polyethylene, polypropylene or polyvinylchloride. These liners are generally vacuum formed to fit a particular configuration of a vehicle bed and then stored in inventory. Once a molded liner is purchased, it is dropped into the vehicle bed and may be attached to the bed to act as a protective liner. The disadvantages of a molded liner are numerous. Molded drop-in-place liners may require drilling or bolting to the vehicle body, which exposes the vehicle bed to rust and corrosion. Further, molded vehicle bed liners may warp, crack, tear or vibrate loose. Additionally, no matter how closely the bed liner models that of the vehicle to be lined, the molded liner will leave gaps between the liner and the vehicle bed. The gaps may become filled with dirt, moisture or other materials that create the environment for accelerated corrosion of the vehicle bed beneath the liner. Also, worn out portions of molded liners cannot readily be replaced or repaired. Thus, the entire molded liner must be replaced after a portion of the liner is worn through, regardless of the condition of the remainder of the liner. A spray on polymeric material such as provided by the present invention may be readily applied to line any truck bed without the need to be customer manufactured.

EXAMPLES

Polyester Prepolymer Synthesis

In a typical polyesterification synthesis, the reactants are introduced into a flask (usually with a slight stoichiometric excess of diol) equipped with a stirrer, condenser and a source of nitrogen gas (to avoid oxidation during the synthesis). The contents are slowly heated with stirring until a homogeneous mixture is achieved, and then the mixture is heated at up to 23O⁰C for about 24h. The final stage of the synthesis involves removal of the last traces of water by azeotropic distillation with xylene, followed by xylene removal before decanting the finished polyester.

A typical general-purpose laminating polyester resin consists of a mixture of phthalic anhydride and maleic anhydride as the diacid component. Maleic anhydride is unsaturated and provides the double bonds for crosslinking of the resin. The diol component is commonly 1,2-propanediol. The polyester made from these raw materials, when cured with styrene, is hard, glassy and inflexible, reflecting the properties of the starting materials. To introduce greater flexibility to the polyester, the saturated diacid component, the diol component, or both may be replaced with more flexible monomers.

Nine polyester prepolymers were synthesised using the above general procedure. The table below shows the diacid and diol components. In all cases, the unsaturated diacid was maleic anhydride, and was present at 50 mol% of the stated diacid component.

Raw Materials for In-house Polyester Prepolymers

Cure and Mechanical Properties of Polyester Prepolymers Crosslinked with Styrene

The mechanical properties of the polyester prepolymers were measured when crosslinked with styrene. In a typical experiment, 2Og polyester prepolymer was mixed with 1Og styrene and stirred with heating until a clear viscous liquid resulted. The mixture was cooled and 0.15g (0.5%) cobalt naphthenate accelerator stirred in, resulting in a magenta liquid. To this was added 0.6g (2%) MEKP promoter with vigorous stirring, and this mixture was poured into a dogbone mould. Typical gel times of 1 hour were recorded. In some cases a few drops of dimethyl toluidine (DMT) co-accelerator were added, giving gel times of about 1 min, but this had no effect on the measured mechanical properties. After cure, the solid sample was removed from the mould and subjected to tensile testing to determine the tensile modulus (Youngs modulus, a measure of stiffness), tensile strength and failure strain (elongation at break). Six of the seven cured polyesters, and including two blends, were tested and the tensile test results are shown in the table below. Pro erties of Pol esters Crosslinked with St rene

* For blends involving 2 polyesters, a 50/50 mixture (by mass) was used

It can be seen from the Table that the blend of Polyesters 1 and 2 gave the strongest product, with a failure strain of about 8%. A modulus of 1-2GPa is typical of glassy polymers, and it can be seen that those polyesters with the higher moduli also exhibited lower failure strain, which is also typical behaviour. Polyester 2 gave the highest failure strain with reasonable strength and stiffness, whereas Polyester 8 was rubbery at room temperature. Of the polyesters tested so far, Polyesters 2, 19 and 20 appear to be exhibiting the most promising mechanical properties. Reinforcement, most likely with short glass fibre, should significantly increase the stiffness and strength without unduly reducing the failure strain.

Replacement of Styrene with Potential Low-odour Alternative Monomers

Styrene is a flammable, high-odour irritant with a significant vapour pressure at room temperature, so is unsuitable for use in spray applications underground. It was appropriate, therefore, to investigate potential low-odour, low-irritant, low vapour pressure monomers as alternatives to styrene. The table below shows the range of alternative monomers investigated to date, and the mechanical properties of Polyester 1 crosslinked with these monomers. All samples were produced using 2Og Polyester 1 and 1Og monomer, with 0.5% cobalt naphthenate and 2% MEKP. DMT was not used. Gel times ranged from 15 minutes (NVP) to overnight (BuAc and HEA).

* contained 0.5% DMT and 30ppm hydroquinone

** contained 30ppm hydroquinone but no DMT (with DMT the mixture gelled before MEKP was added)

According to the above table, of the monomers investigated NVP appears to be the most promising candidate. The mechanical properties do not appear to be significantly compromised in relation to the styrene-containing equivalent, and the cure time is shorter than for styrene. NVP has a significantly lower vapour pressure than styrene at room temperature (<0.1 mmHg at 24°C compared with 4.3 mmHg at 15°C for styrene), has a very slight sweetish odour, and is not considered to be flammable or combustible.

The mechanical properties of a number of polyesters crosslinked with NVP are shown in the table below. Gel times ranged from 1 to 15 minutes. The blend of Polyesters 1 and 2 again gave a product with the highest tensile strength, with a slightly lower modulus than with styrene, and which failed at 5% elongation. Properties of Polyesters Crosslinked with NVP

Of the formulations thus far investigated, Polyester 27 crosslinked with NVP and the blend of Polyester 1 and 2 crosslinked with NVP appear to be the most promising.

DMT was used as a co-accelerator in the experiment involving Polyester 3 in the above table. The same polymer system reinforced with 17.6 vol% glass fibre had approximately the same gel time and showed a fully-cured flexural strength of 47.3MPa.

Flexure Behaviour of Reinforced Polyesters

Fig. 3 shows the flexure behaviour of a number of commercial and in-house polyesters reinforced to 20vol% with chopped strand mat. The polyester compositions are described earlier. A wide range of flexural strengths and flexibilities were observed, depending on the polyester composition and the crosslinking monomer used. It is therefore clear that the properties of the cured composition may be readily tailored to the desired application.

Effect of Hydroquinone Inhibitor on Gel Time As an example of cure time control, the effect of hydroquinone inhibitor concentration on the gel time of Polyester 19 crosslinked with NVP is shown in Fig. 4. For the example shown, cobalt naphthenate was used as the catalyst, present at 0.5 weight %, and MEKP was used as the promotor at 2 wt%. Where used, dimethyl toluidine (DMT) co-catalyst was added at 0.25 wt%.

Hydroquinone is added primarily to enhance storage stability, however other quinone-type stabilisers, such as naphthoquinone, can also be used for this purpose. Such inhibitors also have an effect of the gel time as shown in the figure. It can be seen that, in the presence of DMT, with up to 50ppm added hydroquinone the gel time remains under 1 minute. With the addition of lOOppm hydroquinone, a cure time of -15 minutes was found when DMT was not used.

Mechanical Strength and Flexure Behaviour

Steel mesh is constructed using drawn low carbon steel wire welded in a square mesh pattern. Roof mesh is typically 4% steel by volume, thus a very rough estimate of the tensile properties of mesh in the direction of the wire can be made based upon measured properties of the wire. Typical tensile 5 properties of steel wire and mesh, and the reinforced polymer of the present invention are shown below. It can be seen that, with the exception of failure strain, the reinforced polymer possesses tensile properties similar or superior to steel mesh.

Typical Tensile Properties of Steel Wire, Mesh and Polymeric Material of the resent invention reinforced with filler

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims

Claims:

1. A prepolymer composition comprising:

• a polyester prepolymer;

• a vinyl-functional monomer having a vapour pressure which is less than styrene at 20⁰C; and

• an accelerator.

2. The prepolymer composition of claim 1 wherein the vinyl-functional monomer is an N-vinyl amide.

3. The prepolymer composition of claim 2 wherein the N-vinyl amide is N- vinylpyrrolidinone.

4. The prepolymer composition of any one of claims 1 to 3 wherein the accelerator is a transition metal salt of an organic acid.

5. The prepolymer composition of claim 4 wherein the transition metal salt of an organic acid is cobalt naphthenate.

6. The prepolymer composition of any one of claims 1 to 5 further comprising a co-accelerator.

7. The prepolymer composition of claim 6 wherein the co-accelerator is a tertiary amine.

8. The prepolymer composition of claim 7 wherein the tertiary amine is N,N-dimethyltoluidine or N,N-dimethylaniline.

9. The prepolymer composition of any one of claims 1 to 8 wherein the polyester prepolymer is a condensation product of:

• a diacid and/or anhydride; and

• an organic diol.

10. The prepolymer of claim 9 wherein the diacid and/or anhydride is an alpha, beta-ethylenically unsaturated diacid and/or anhydride and the organic diol is a polyhydric alcohol.

1 1. The prepolymer of claim 10 wherein the alpha, beta-ethylenically unsaturated diacid and/or anhydride is maleic anhydride, the non-polymerisable diacid and/or anhydride is phthalic anhydride or adipic acid or both and the polyhydric alcohol is selected from the group consisting of 1,2-propanediol, 1 ,6-hexanediol, diethylene glycol, 1,3-propanediol, 2-methyl-l,3-propanediol, 1,4-butanediol, 1,5-pentanediol and 1,4-cyclohexanedimethanol and combinations thereof.

12. The prepolymer of any one of claims 9 to 1 1, wherein two or more polyester prepolymers are present.

13. A curable composition comprising:

• the prepolymer composition of any one of claims 1 to 12; and

• a promoter capable of causing said prepolymer composition to cure.

14. The curable composition of claim 13 wherein the promoter is an organic peroxide.

15. The curable composition of claim 14 wherein the organic peroxide comprises methyl ethyl ketone peroxide.

16. The curable composition of claim 14 or claim 15 wherein the promoter is present in a ratio of between about 2 and about 4% w/w of the prepolymer composition.

17. The curable composition of any one of claims 13 to 16 additionally comprising a filler.

18. The curable composition of claim 17 wherein the filler is a fibrous filler.

19. The curable composition of claim 18 wherein the fibrous filler is short glass fibres.

20. The curable composition of claim 18 or claim 19 wherein the fibrous filler has a mean fibre length of less than about 10cm.

21. The curable composition of any one of claims 13 to 20 wherein said curable composition has a gel time at room temperature of under about 1 minute.

22. The curable composition of any one of claims 13 to 21 wherein said curable composition is sprayable.

23. A process for making a prepolymer composition comprising combining:

• the polyester prepolymer of any one of claims 1 to 12;

• a low volatility vinyl-functional monomer; and • an accelerator.

24. A process according to claim 23, wherein the polyester prepolymer is prepared by combining a diacid and/or anhydride with an organic diol.

25. A process for making a curable composition, comprising combining:

• the prepolymer composition of any one of claims 1 to 12; and • a promoter capable of causing said prepolymer composition to cure.

26. The process of claim 25 comprising combining a filler with the prepolymer composition or with the promoter or with the combined prepolymer composition and promoter.

27. A process for making a cured composition comprising curing the composition of any one of claims 13 to 22.

28. A cured composition made by the process of claim 27.

29. The cured composition of claim 28 which has one or more of the following properties:

Tensile Modulus (GPa) : 0.2 - 1 Tensile Strength (MPa) : 4 - 90 Elongation at Break (%) : 2.5-10

Flexural Modulus (GPa) : 3 or less Flexural Strength (MPa) : 4 - 1 10 Impact Strength (MPa) : 0.3 or less Vickers Hardness : 20 60

30. A kit comprising:

• a first part comprising the prepolymer composition of any one of claims 1 to 12; and

31. Use of the prepolymer composition of any one of claims 1 to 12 in the manufacture of a polymeric material.

32. Use of a polyester prepolymer, a vinyl-functional monomer having a vapour pressure which is less than styrene at 20⁰C and an accelerator in the manufacture of a polymeric material.

33. Use of claim 31 or 32 wherein the polymeric material is a polymeric skin or liner.

34. A method for reinforcing a surface comprising:

• combining the prepolymer composition of any one of claims 1 to 12 and a promoter to form a curable composition;

• applying the curable composition to a surface; and

35. The method of claim 34 wherein the surface is a floor, wall or ceiling of a mine tunnel.