Method for treating reinforcing fibre and method for producing a reinforced composite article from the treated fibre

Abstract

The present invention relates to a reinforced composite material and a method for its production. The composite material comprises at least one cured resin having a reinforcing material. Preferably the reinforcing material is a plurality of glass fibres which are treated such that the properties of the interphase substantially surrounding each fibre are substantially equivalent to those of the bulk cured resin. The fibre treatment may be selected from the group consisting of a polymeric coating, a hydrophilic surface coating, a surface coating of a free radical inhibitor, or a reduction in the total surface area of the fibres. The reinforced composite material of the invention provides improved long-term mechanical properties compared to traditional glass fibre reinforced materials.

Claims

1. A molded composite material, comprising a cured reinforced composite material, wherein the cured reinforced composite material comprises at least one cured resin having: i) a polymer having a monomer content of between about 5 to 30% w/w; and ii) a plurality of reinforcing fibers coated with a coupling agent; wherein: a) the at least one cured resin adjacent to said reinforcing fibers defines an interphase; and, b) the coated plurality of reinforcing fibers are treated such that the properties of said interphase are substantially equivalent to those of the bulk cured resin.

2. The molded composite material of claim 1, wherein the polymer comprises between 5 to 50% w/w of the at least one cured resin.

3. The molded composite material of claim 1, wherein the at least one cured resin has flexural toughness greater than about 3 Joules when tested in a standard flexure test, the test piece having dimensions about 100 mm in length, 15 mm in width and 5 mm in thickness.

4. The molded composite material of claim 1, wherein the cured reinforced composite material has flexural toughness greater than 3 Joules for up to 5 years.

5. The molded composite material of claim 1, wherein the treatment is a polymeric coating and/or a hydrophilic surface coating applied to said coated plurality of reinforcing fibers.

6. The molded composite material of claim 5, wherein: i) the polymer of said polymeric coating is an unsaturated polyester resin having less than about 30% w/w monomer; or ii) the hydrophilic surface coating is prepared by reacting a vinyl functional silane with a polyol.

7. The molded composite material of claim 6, wherein the unsaturated polyester resin is provided by reacting a polyol with an acid; wherein: i) the polyol comprises propylene glycol, methyl propanediol, neopentyl glycol, or diethyleneglycol; ii) the acid comprises terephthalic acid, isophthalic acid, fumaric acid, or 1,4-cyclohexane diacid; and iii) the unsaturated polyester resin comprises a saturated to unsaturated acid ratio of between about 1.2:1 to 2:1.

8. The molded composite material of claim 1, wherein the coupling agent is a vinyl functional silane.

9. The molded composite material of claim 1, wherein the coupling agent is selected from the group consisting of methacryloxypropyltrimethoxysilane, vinylbenzylaminoethylaminopropyl-trimethoxysilane, and vinyl-tris(acetoxy) silane.

10. The molded composite material of claim 1, wherein the reinforcing fiber of the plurality of reinforcing fibers is a glass fiber.

11. The molded composite material of claim 10, wherein the glass fiber has a length of between about 100 and 1000 microns.

12. The molded composite material of claim 1, wherein the properties comprise: i) mechanical properties selected from the group consisting of strength, toughness, and brittleness, or a combination thereof; ii) physical or chemical properties selected from the group consisting of density, cross-link density, chemical resistance, molecular weight, and degree of crystallinity, or a combination thereof; or iii) or a combination of the mechanical, physical, or chemical properties.

13. The molded composite material of claim 1, wherein the cured composite material comprises one or more of the following: i) a flexural modulus of greater than about 3.5 GPa; ii) a flexural stress of greater than about 120 MPa; or iii) an elongation at break of greater than about 2%.

14. The molded composite material of claim 1, wherein the treatment: i) reduces catalyzation of resin polymerization polymerization in the interphase when compared to a fiber not treated; or ii) reduces embrittlement of said interphase when compared to a fiber not treated.

Description

BEST MODE FOR CARRYING OUT THE INVENTION

(1) The present invention provides a method for producing a reinforced composite material and the composite body produced by the method. The method comprises the steps of combining at least one curable resin with a plurality of reinforcing fibres such that the fibres are substantially evenly dispersed throughout the resin, and curing the resin. Preferably the resin is a vinyl ester resin having about 40% of a reactive diluent, such as styrene monomer. However, other monomers may also be used, such as mono- and di- and tri-functional acrylates and methacrylates. Alternatively, the resin may be chosen from unsaturated polyester resins, epoxy vinyl ester resins, vinyl function resins, tough vinyl functional urethane resins, tough vinyl functional acrylic resins, and non-plasticised flexible polyester resins, and combinations thereof.

(2) In preferred embodiments, the fibres are glass fibres chosen from E-, S- and C-class glass having a length of between about 100 and 1000 microns. However, fibres having lengths greater then 1000 microns can also be used. Preferably any sizing agent is removed from the glass fibre prior to its treatment with the coupling agent(s). The preferred coupling agent is Dow Corning Z-6030. However, other coupling agents may be used such as Dow Corning Z-6032 and Z-6075.

(3) The, at least one curable resin may include a polymer, is chosen or modified with such a polymer to have predetermined properties chosen from one or more of improved tear resistance, strength, toughness, and resistance to embrittlement. Preferably the polymer-modified cured resin has a flexural toughness greater than 3 Joules for up to 5 years following production for a test piece having dimensions about 110 mm length, 15 mm width and 5 mm depth subjected to a standard flexure test.

(4) In preferred embodiments the polymer-modified curable resin is resistant to crack propagation. Such polymer-modified resins provide reduced embrittlement with age. Preferably the polymer is a monomer deficient (less than about 30% w/w monomer) low activity unsaturated polyester resin having only a relatively moderate amount of unsaturation. Examples of such polyesters are provided in the tables below. Desirably these polyesters are hydrophilic.

(5) Once the resin is cured to provide the reinforced composite material, the cured resin adjacent and substantially surrounding each of the glass reinforcing fibres defines an interphase, and the reinforcing fibres are treated prior to their addition to the curable resin such that the properties of the interphase are substantially equivalent to those of the bulk cured resin. In one embodiment, the treatment applied to the fibres is a polymeric coating. The polymer of the polymeric coating is preferably the low activity unsaturated polyester resin described above.

(6) As discussed above, without wishing to be bound by theory the applicant believes that a fibre treated with prior art coupling agents acts to catalyse resin polymerisation thereby forming an interphase having substantially different properties to the bulk cured resin. An interphase having highly cross-linked material will have properties vastly different to those of the bulk resin, thereby affecting the mechanical and physical properties of the final cured reinforced composite body. For example, an interphase having highly cross-linked material is inherently more brittle than the bulk resin. During fracture, a propagating crack will relatively easily rupture this brittle interphase and any crack-arresting properties of the resin in the interphase will substantially reduced. Further, as the skilled person will appreciate, the more fibre employed in the composite body the greater the total amount of brittle interphase will result, and the more brittle the composite body will become.

(7) By treating the coupled glass fibre to reduce catalysation of free radical polymerisation, the applicants have been able to reduce the effect of the coupled glass fibre on the interphase such that the interphase has similar properties to the bulk cured resin. In other embodiments, the surface of the glass fibre is treated with a coating of one or more free radical inhibitors, such as hydroquinone or acetyl acetone, hindered phenols and hindered amines. The coating of free radical inhibitor(s) is associated with the surface of the glass fibre such that catalysation of resin polymerisation in the interphase is reduced and the interphase has similar properties to the bulk cured resin.

(8) In a further embodiment, the treatment is a reduction in the total surface area of the fibres. For example, this may be achieved by substituting the glass fibre with a glass fibre having a relatively larger diameter. To explain, glass fibres typically used in glass fibre reinforced composites have diameters between about 5-12 microns. However, the applicants have discovered that use of glass fibres having diameters between about 15-24 microns provides significantly less embrittlement to the final properties of the reinforced composite body, since for a given weight of glass fibre the total surface area is inversely proportional to the increase in fibre diameter. Of course even larger diameter fibres can be used than 24 micron, however, there is a practical working limit of the fibre properties.

(9) In this embodiment, whilst the glass surface still may catalyse resin polymerisation to produce a brittle interphase, the total amount of brittle interphase material is relatively reduced. In addition, to provide a final cured polymer composite with similar mechanical properties, the length of relatively larger diameter glass fibre used is preferably longer than that which would ordinarily be employed for the relatively smaller diameter fibre.

(10) As the skilled person would be aware, combinations of the above-described embodiments may also be employed where appropriate. For example, it would be possible to use glass fibres having a relatively larger diameter and coat the fibre with a free radical inhibitor, or coat the fibre with a polymer as described above.

(11) In further embodiments, the treatment comprises a two-step process whereby the glass fibre is firstly coated with a first agent and then a second agent is reacted with the first agent to provide a substantially hydrophilic surface-modified glass fibre. Preferably the first agent is a coupling agent having a first end adapted to bond to the fibre, and a second end adapted to bond either to the second agent or the resin when cured. In a preferred embodiment, the coupling agent is methacryloxypropyltrimethoxysilane (Dow Corning Z-6030). The second agent comprises the reaction product between the first agent and a tri-hydroxy compound such as trimetholylpropane. However, in alternative embodiments the hydroxy compound is a tetra-hydroxy compound such as pentaerythritol. The reaction of Z-6030 and trimetholylpropane is conducted in the presence of a tin catalyst, such as tri-butyl tin, under appropriate reaction conditions.

(12) The method of treating the glass fibre according to the previous embodiment further includes the step of mixing or compounding the coated reinforcing fibre with an emulsion. The emulsion preferably comprises: 16.6 parts water, 100 parts acetone and 200 parts polymer, wherein the polymer is preferably the hydrophilic low activity unsaturated polyester resin discussed above. The emulsion may also include a hydrophilic free radical inhibitor such as HQ.

EXAMPLES

(13) The present invention will now be described with reference to the following examples which should be considered in all respects as illustrative and non-restrictive.

(14) Treatment of a Glass Fibre with a Hydrophilic Surface Coating

(15) 1. E-glass fibres were cut to an average fibre length of 3400 micron and then milled to an average length of 700 micron. 2. The milled glass fibres were cleaned using boiling water, with a strong detergent and with powerful agitation. The detergent was then rinsed from the fibres. 3. 1% w/w of methacryloyloxypropyltrimethoxysilane (Dow Z-6030) was suspended in water at pH 4 and the fibres added to the suspension. The resulting mixture was stirred vigorously at room temperature for 60 minutes. 4. The liquid was then drained from the glass fibres, leaving them still wet with the mixture. 5. The Z-6030-treated fibres were then redispersed in water at a pH of 7. 6. Separately, a solution of Z-6030 was reacted with trimetholylpropane (TMP) in the presence of a tin catalyst (eg tributyl tin) for 15-20 minutes at 110-120 C. to form a Z-6030-TMP adduct having a viscosity of about 1200-1500 cP. Methanol is evolved during the reaction. 7. The Z-6030 treated fibres were then reacted with the Z-6030-TMP adduct to provide a hydrophilic treated fibre. This was achieved by dispersing the Z-6030 treated fibres in water and adding the Z-6030-TMP adduct to the water at a concentration of about 2-3 wt % of fibres. The mixture was stirred together for approximately 10 minutes. The fibres were then separated and then centrifuged to remove excess water. The wet fibres were then dried, initially at 30 C. for 3-4 hours, and then heated to between 110 and 125 C. for 5-7 minutes. 8. Separately, an emulsion of polymer was prepared having 200 parts polymers, 100 parts acetone and 16.6 parts water. Preferably the polymer is a hydrophilic resin such as an unsaturated polyester. 9. The hydrophilic treated fibres were then compounded with the emulsified resin until evenly distributed in the rations of about 93 w/w % fibres and 7 w/w % emulsion. 10. The compounded fibre-emulsion mixture was then added to the base resin at approximately 10-45% fibre-emulsion to 90-55% resin.

(16) Table 1 provides flexural strength data for cured clear casts of the commercially available Derakane epoxy vinyl ester resin 411-350 (Ashland Chemicals). These test panels were prepared according to the manufacturers specifications and the resulted in flexural modulus averages about 3.1 GPa, the flexural stress at yield averages about 120 MPa, and the elongation at break averages between about 5 to 6%.

(17) Table 2 shows similar test panels to those of Table 1 but having been thermally aged. Panels are thermally aged by heat treatment at 108 C. for two hours follows by controlled cooling to below 40 C. over about 2 hours. As can be seen, within experimental error, the flexural modulus and flexural stress are about the same post aging. However, the elongation at break has approximately halved, meaning that the panels have substantially embrittled with accelerated aging.

(18) TABLE-US-00001 TABLE 1 Flexural strength data for cured (un-aged) clear casts of Derakane 411-350 Epoxy Vinyl Ester Resin. Flexural Flexural Stress Elongation Modulus at Yield at Break Composite (GPa) (MPa) (%) Test Panel 1 2.98 112 4.9 Test Panel 2 3.12 119 5.7 Test Panel 3 3.11 123 5.6 Test Panel 4 3.28 132 6.0

(19) TABLE-US-00002 TABLE 2 Flexural strength data for aged clear casts of Derakane 411-350 Epoxy Vinyl Ester Resin. Flexural Flexural Stress Elongation Modulus at Yield at Break Composite (GPa) (MPa) (%) Test Panel 5 3.30 117 3.0 Test Panel 6 3.40 121 3.1 Test Panel 7 3.10 131 4.1 Test Panel 8 3.20 123 3.6 Test Panel 9 3.20 127 4.2

(20) Table 3 provides flexural strength data for aged cured clear casts of Derakane epoxy vinyl ester resin with various polymer additions (discussed below). As can be seen, the resulting flexural modulus averages about 3.3 GPa, the flexural stress at yield averages about 135 MPa, and the elongation at break averages between about 5 to 7%. Comparing the elongation data between Tables 2 and 3 it can be seen that the various polymer additions have substantially reduced aged embrittlement.

(21) TABLE-US-00003 TABLE 3 Flexural strength data for aged clear casts of Derakane 411-350 Epoxy Vinyl Ester Resin having 12-15 wt % of a polymer additive. Flexural Flexural Stress Elongation Modulus at Yield at Break Composite (GPa) (MPa) (%) Test Panel 10 + polymer 1 3.20 132 6.7 Test Panel 11 + polymer 2 3.20 131 4.9 Test Panel 12 + polymer 3 3.30 136 5.7 Test Panel 13 + polymer 4 3.50 140 6.0 Test Panel 14 + polymer 5 3.60 146 6.6

(22) The polymers provided in the tables are the condensation products of a polyol and a diacid. The polyol's and diacid's comprising each polymer are provided in Table 4. These polyesters are generally prepared by heating approximately equimolar amounts of diol and acid at temperatures in excess of about 200 C. for periods of about 4 to about 12 hours. Most of the unsaturation is present as fumarate diester groups. These polyesters have acid numbers in the range of from about 15 to about 25. (The acid number is the milligrams of potassium hydroxide needed to neutralize one gram of sample).

(23) A 3-liter, round-bottomed flask equipped with a paddle stirrer, thermometer, an inert gas inlet and outlet and an electric heating mantle. The esterification reactions were conducted in 2 stages. The first stage was reacting the saturated acids in excess glycol, and the second stage was carried out with the addition of the unsaturated acids and remaining glycols. The reactor vessel was weighed between the stages and glycols were added if needed to compensate for any losses. The mixture was heated to between 150 and 170 C. such that water was liberated and the condenser inlet temperature was greater than 95 C.

(24) During the next 2-3 hours the temperature of the mixture was raised to 240 C. The mixture was then cooled to 105 C. and blended with inhibited styrene. The final polyester resin contained 80 percent by weight of the unsaturated polyester and 20 percent styrene.

(25) TABLE-US-00004 TABLE 4 Polyesters used to modify the Derakane base resin in Tables 3 and 5. ratio of saturated to Polymer polyol diacid unsaturated acids Polymer propylene glycol terephthalic acid 2 3:2 1 4 moles, MP-diol moles, isophthalic 1.5 moles acid 1 mole, fumaric acid 2 moles Polymer diethylene glycol terephthalic acid 3:2. Also, a 0.5M 2 5.5 moles 3 moles, fumaric excess glycol was acid 2 moles maintained at the commencement of the second stage Polymer diethylene glycol 1,4-cyclohexane 4:3 3 6 moles, MP-diol diacid, fumaric 1.5 moles acid Polymers Nuplex 316/ 4 and 7 Terephth 50/50 blend Polymer neopentyl glycol 1,4-cyclohexane 3:2 5 6.25 moles, diacid 4.5 moles, propylene glycol fumaric acid 2 moles 3 moles Polymer diethylene glycol 1,4-cyclohexane 3:2 6 diacid 3 moles, fumaric acid 2 moles Polymer neopentyl glycol 1,4-cyclohexane 4:3 8 6.25 moles, diacid 4 moles, propylene glycol fumaric acid 1 mole 3 moles

(26) Table 5 provides flexural strength data for Derakane epoxy vinyl ester resin having the stated ratios of resin to glass fibre (in brackets) wherein the glass fibre is treated only with the Z-6030 coupling agent.

(27) TABLE-US-00005 TABLE 5 Flexural strength data for aged Z-6030 treated glass fibres in Derakane 411-350 epoxy-vinyl ester resin. Flexural Flexural Stress Elongation Modulus at Yield at Break Composite (GPa) (MPa) (%) Test Panel 15 (2.3:1) 6.20 124 0.87 Test Panel 16 (2:1) 6.70 129 0.70 Test Panel 17 (1.9:1) 7.50 135 0.63 Test Panel 18 (1.7:1) 8.10 142 0.60 Test Panel 19 (1.6:1) 9.00 149 0.58

(28) Table 6 shows flexural strength data for aged test panels of Derakane epoxy vinyl ester resin having about 12-15 weight % of a polymer additive as described above and 45-50 weight % of a treated glass fibre according to the present invention.

(29) TABLE-US-00006 TABLE 6 Flexural strength data for aged Derakane 411-350 epoxy vinyl ester resin having 12-15 wt % of a polymer additive and 47 wt % of treated glass fibre Flexural Flexural Stress Elongation Modulus at Yield at Break Composite (GPa) (MPa) (%) Test Panel 20 + polymer 5 6.10 136 2.6 Test Panel 21 + polymer 6 6.20 133 2.2 Test Panel 22 + polymer 6 5.90 129 2.9 Test Panel 23 + polymer 7 6.00 134 3.1 Test Panel 24 + polymer 8 6.20 135 3.4
according to the present invention, wherein the treatment comprises the hydrophilic surface coating and the emulsified polymer.

(30) In the comparison of the flexural data provided in Table 5 and Table 6, it can be seen that the test panels 20-24 according to the present invention have significantly improved the elongation at break for aged panels, providing a reduction in aged embrittlement.

(31) Table 7 provides flexural strength data for aged test panels of Derakane epoxy vinyl ester resin having the stated ratios of resin to glass fibre (in brackets) wherein the glass fibre is treated with a monomer deficient resin. Test panel 25 is uncoated and panels 26 to 28 are coated. Panels having the coated glass fibre show significantly improved toughness.

(32) TABLE-US-00007 TABLE 7 Flexural strength data for aged test panels of Derakane 411-350 epoxy vinyl ester resin having a polymer treated glass wherein the polymer is a monomer deficient resin. Flexural Flexural Stress Elongation Modulus at Yield at Break Composite (GPa) (MPa) (%) Test Panel 25 (2.3:1) 6.20 124 0.87 Test Panel 26 (5:1) 3.80 120 4.0 Test Panel 27 (5:1) 3.50 115 4.0 Test Panel 28 (5:1) 3.60 118 4.0

INDUSTRIAL APPLICABILITY

(33) The present invention is useful in a wide variety of industries, including: construction, automotive, aerospace, marine and for corrosion resistant products. The reinforced composite material of the invention provides improved long-term mechanical properties compared to traditional glass fibre reinforced materials.

(34) Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.