Curable compositions containing benzoxazine epoxy blend and use thereof

Abstract

A curable resin composition capable of providing good OHC performance at elevated temperatures when used in polymer matrix composites. This resin composition includes, as major components, one or more multifunctional benzoxazine compounds and cycloaliphatic epoxy resin.

Claims

1. A curable resin composition comprising: (A) a cycloaliphatic epoxy resin containing two or more epoxide groups; and (B) a tri-functional benzoxazine compound represented by the following structure: ##STR00009## where R.sub.1, R.sub.2 and R.sub.3 are independently selected from alkyl, cycloalkyl, and aryl, wherein the cycloalkyl and aryl groups are optionally substituted, and where substituted, one or more substituent groups may be present on each cycloalkyl and aryl group; and R.sub.4 is selected from hydrogen, halogen, alkyl and alkenyl.

2. The curable resin composition of claim 1 further comprising: (C) a phenol compound as a catalyst.

3. The curable resin composition of claim 1 further comprising: (D) a di-functional benzoxazine compound.

4. The curable resin composition of claim 3, wherein the benzoxazine compounds (B) and (D) constitute for more than 50% by weight based on the total weight of the composition.

5. The curable resin composition of claim 1, wherein the tri-functional benzoxazine compound (B) is: ##STR00010##

6. The curable resin composition of claim 1, wherein the tri-functional benzoxazine compound (B) is: ##STR00011##

7. The curable resin composition of claim 1, wherein the tri-functional benzoxazine compound (B) is: ##STR00012##

8. The curable resin composition of claim 1, wherein the cycloaliphatic epoxy resin is 3,4-epoxycyclohexyl-3,4-epoxycyclohexane carboxylate, represented by the following structure: ##STR00013##

9. The curable resin composition of claim 3, wherein the di-functional benzoxazine compound (D) is represented by the following structure: ##STR00014## where: Z.sup.1 is selected from a direct bond, C(R.sup.3)(R.sup.4), C(R.sup.3)(aryl), C(O), S, O, S(O), S(O).sub.2, a divalent heterocycle and [C(R.sup.3)(R.sup.4)].sub.xarylene-[C(R.sup.5)(R.sup.6)].sub.y, or the two benzyl rings of the benzoxazine moieties may be fused; and R.sup.1 and R.sup.2 are independently selected from alkyl, cycloalkyl, and aryl, wherein the cycloalkyl and aryl groups are optionally substituted by a substituent selected from: C.sub.1-8 alkyl, halogen and amine groups, and where substituted, one or more substituent groups may be present on each cycloalkyl and aryl group; R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are independently selected from H, C.sub.1-8 alkyl, and halogenated alkyl; and x and y are independently 0 or 1.

10. The curable resin composition of claim 2, wherein the phenol compound (C) is thiodiphenol (TDP).

11. A composite material comprising reinforcement fibers impregnated or infused with the curable composition of claim 1.

12. The composite material of claim 11, wherein the reinforcement fibers are selected from carbon fibers, glass fibers, and aramid fibers.

13. A prepreg comprising reinforcement fibers impregnated or infused with the curable composition of claim 1, wherein reinforcement fibers are in the form of unidirectional fibers or a fabric.

14. A cured composite part produced from a method comprising: (i) impregnating or infusing reinforcement fibers with the curable composition of claim 1; and (ii) curing the resin-impregnated or resin-infused fibers.

Description

EXAMPLES

Example 1

(1) Eight different resin blends were prepared according to the formulations shown in Table 1. All values are in weight percentage unless stated otherwise.

(2) TABLE-US-00001 TABLE 1 RD2011-029 m-Bis- Araldite? Pa-Type Tris m-Tris- p-Tris- Reagents Bis-BOX BOX CY-179 BOX BOX BOX BOX TDP Formulation 1 68 23 9 Formulation 4 70 30 Formulation 5 48.11 23.25 19.55 9.1 Formulation 6 47.52 22.96 20.54 8.98 Formulation 9 35 30 35 Formulation 10 48 23 20 9 Formulation 11 0 23 68 9 Formulation 12 48.11 58 23 10 9

(3) RD2011-29 (Bisphenol A benzoxazine) and Araldite CY179 (cycloaliphatic epoxy) were supplied by Huntsman Advanced Materials. TDP refers to thiodiphenol.

(4) Pa-Type BOX was a monofunctional benzoxazine supplied by Shikoku Chemical Corporation and is represented by the following structure:

(5) ##STR00007##

(6) Tris BOX refers to the aniline tris benzoxazine compound (1) described above and was synthesized according the following reaction:

(7) ##STR00008##

(8) 150 g (0.49 mol) of 1,1,1-tris(4-hydroxyphenyl)ethane and 93 g (3.1 mol) para-formaldehyde were thoroughly mixed in a 2 L glass reactor equipped with a mechanical stirrer at room temperature. Then 143.6 g (1.54 mol) of aniline was added at room temperature to avoid foaming. The reaction mixture was stirred with the slow addition of aniline at room temperature. After the internal reaction temperature cools to 60? C., the reactor was then submerged in an oil-bath preheated at 80? C. The resulting reaction mixture was a viscous semi-solid. The oil bath was heated to 110? C. for 30 minutes. The oil bath was then heated to 130? C., when the internal temperature was above 110? C. the reaction timer was set for 30 minutes. After 30 minutes, the molten reaction mixture was poured into an aluminum dish using a spatula to distribute the resin evenly over the pan and allowed to cool to room temperature. The resulting gold crystalline product was then ground into a powder. The powder was washed twice in 2 L of a 1 N NaOH solution at 70? C. and in 2 L of water at the same temperature as many times as needed to obtain a neutral pH. The product was dried in a vacuum oven for a week at 45? C.

(9) m-Tris-BOX refers to the m-tris benzoxazine compound (3) discussed above and was synthesized according to the method disclosed in U.S. patent application Ser. No. 14/980,407, filed on Dec. 28, 2015 and assigned to Cytec Industries Inc.

(10) p-Tris-BOX refers to the p-tris benzoxazine compound (2) discussed above and was synthesized according to the method disclosed in U.S. patent application Ser. No. 14/562,799, filed on Dec. 8, 2014 and assigned to Cytec Industries Inc.

(11) Resin films were formed from the resin formulations disclosed on Table 1. Each resin film had a film weight of about 39 gsm. Prepregs were made by impregnating unidirectional IM7 carbon fibers in web form with the resin films using a hot-melt lamination method. The target fabric areal weight (FAW) for the carbon fibers was 145 gsm and 35% resin content per prepreg. With the use of hot-melt prepregging equipment, two resin films were applied to a unidirectional carbon fiber web on both the top and bottom simultaneously, and impregnation was done with the aid of a hot plate heated to temperature between 160? F. and 230? F. Composite laminate was made by laying up 24 prepreg plies according to orientation [+45/90/?45/0]3s to create a composite panel. During composite panel fabrication, debulking was also carried out every 4.sup.th ply, for 3 minutes under vacuum. Subsequently, the composite panel was vacuum bagged and cured in an autoclave at 8.16 bars for 2 h at 180? C. and then an additional 2 h at 200? C.

(12) The cured composite panels were tested to determine open hole compression (OHC) and open hole tension (OHT) performance using ASTM test methods D6484 and D766 respectively.

(13) To obtain data for OHC, 12?1.5 inch test specimens of cured composite panels were made. A 0.25 inch hole was drilled in the center of each test specimen. Specimens were conditioned by immersing specimens in a water bath set at 71? C. for 2 weeks.

(14) The OHC results are shown in Table 2.

(15) TABLE-US-00002 TABLE 2 Open Hole Compression (OHC) Test Values (MPa) Dry Wet* Wet* Wet* (23? C.) (82? C.) (121? C.) (149? C.) Formulation 1 349.6 322 301.3 240.6 Formulation 4 357.2 342.7 251.7 128.9 Formulation 5 368.2 328.9 306.1 269.6 Formulation 6 340.6 321.3 310.3 264.1 Formulation 9 348.2 318.5 290.3 190.3 Formulation 10 363.4 340 325 289.7 Formulation 11 355.8 340 313 289.6 Formulation 12 367 329 311.7 293 *conditioned: 2-week water soak

(16) The resin formulations that contained both the Araldite CY-179 cycloaliphatic epoxy and tri-functional benzoxazines (Formulations 5, 6, 10-12) yielded the best wet OHC performance at higher temperatures, 121? C. and 149? C. These high values in wet OHC at 121? C. and 149? C. were also accompanied by an increase in dry and wet T.sub.g as compared to other resin formulations, see Table 3.

(17) TABLE-US-00003 TABLE 3 Composite T.sub.g (? C.) as determined by DMTA Resin Formulation 1 4 5 6 9 10 11 12 Dry Tg (E) 208.5 168.7 228.7 231.1 181.4 229 235 251 onset Wet Tg (E) 169.9 148.6 181.1 180.8 150.1 182 183 189 onset

(18) T.sub.g was measured by Dynamic Mechanical Thermal Analysis (DMTA). It was observed that the tri-functional benzoxazines lowered the T.sub.g of the benzoxazine composites that contained no cycloaliphatic epoxy (Formulation 9). Again, the increase in T.sub.g was achieved with having both the cycloaliphatic epoxy and tri-functional benzoxazines in the resin system.

(19) The open hole tension (OHT) values for composite panels based on Formulations 1, 4, 5, 6, and 9 were measured and are reported in Table 4.

(20) TABLE-US-00004 TABLE 4 Open Hole Tension (OHT) Test Values (MPa) Condition Resin 23? C. ?59? C. Formulation 1 483.3 473.7 Formulation 4 628.1 628.1 Formulation 5 549.5 530.2 Formulation 6 582.6 557.1 Formulation 9 612.3 625.4

(21) Composite panels based on Formulations 4, 5, 6, 9 had tension values greater than the composite panel based on Formulation 1. More importantly, the combination of tri-functional benzoxazine and epoxy (Formulations 5 and 6) did not cause a decrease in the OHT strength, instead an increase was obtained. This is unexpected because an increase in compressive strength is typically accompanied by a loss in tensile strength. This was not the case with the use of Formulations 5 and 6.