GB2310214A

GB2310214A - Toughened thermoset resin composition

Info

Publication number: GB2310214A
Application number: GB9602841A
Authority: GB
Inventors: Barry Woodfine
Original assignee: Kobe Steel Europe Ltd
Current assignee: Kobe Steel Europe Ltd
Priority date: 1996-02-13
Filing date: 1996-02-13
Publication date: 1997-08-20
Anticipated expiration: 2016-02-13
Also published as: GB9602841D0; GB2310214B

Description

TOUGHENED THERMOSET RESIN COMPOSITION This invention relates to a toughened thermoset resin composition.

Thermoset resins, such as epoxy resins or phenolic resins, are a useful class of materials and are utilised in a large number of areas. However, for many applications, unmodified epoxy resins lack toughness and it is common practice to add materials to the epoxy resin composition in order to improve the fracture toughness of the cured formulation. In applications demanding a high service temperature capability, the use of engineering thermoplastics as toughening agents is well known to those skilled in the art. Thermoplastics which are particularly favoured are poly(ether)sulphone [PES] and polyetherimide [PEl]. The use of PES as a toughening agent for epoxy resins is exemplified in volume 32 (1991) of the journal 'Polymer' on pages 2020-2032.

No toughening effects are to be expected from the use of polymethylmethacrylate [PMMA] as an additive in epoxy resin as cited in volume 34 (1993) of the journal 'Polymer' on page 2111. It would be expected therefore that the use of a combination of PES and PMMA would be less effective as a toughening agent than the use of PES alone and the use of this combination to produce an increase in fracture toughness of an epoxy matrix has not been reported. However, we have unexpectedly found that a combination of PES and PMMA or methyl methacrylate copolymers is effective as a toughening agent in thermoset resin compositions.

This invention thus relates to thermoset resin compositions containing mixtures of (i) poly(ether)sulphone [PES] and (ii) polymethylmethacrylate [PMMA] polymers or a copolymer containing at least 50% by weight of methyl methacrylate units as the toughening agents. Such resin compositions find application in many areas, including in the manufacture of fibre-reinforced composite structures.

The invention provides a thermoset resin, in particular an epoxy matrix, with increased levels of fracture toughness. The matrix is especially useful in fibrereinforced composite applications.

The thermoset resin is preferably an epoxy or phenolic resin.

The ratio by weight of (i) PES to (ii) PMMA or methyl methacrylate (MMA) copolymer is generally in the range of from 5:95 to 95:5, preferably from 25:75 to 75:25, and more preferably from 40:60 to 60:40. The total content of PES and PMMA or MMA copolymer in the composition is generally up to 40% by weight, preferably from 5 to 30% by weight, based on the weight of the thermoset resin.

The MMA copolymer contains at least 50% by weight of methyl methacrylate units, preferably at least 75%, and more preferably at least 90%. The other components in the copolymer may be any compatible monomer, such as those selected from alkyl acrylates and methacrylates, aromatic acrylates and methacrylates, functionally substituted acrylates and methacrylates (eg.

acrylonitrile) and vinyl compounds having alkyl, aromatic or functionalised substituents. Hereinafter, references to PMMA should be understood as also including such MMA copolymers.

Suitable PES polymers are commercially available, for example under the trade names Udel, Radel A, Victrex and Radel R. The PES is, for example, a bisphenol polysulphone (eg. bisphenol A polysulphone), a poly(arylene ether sulphone), a polyethersulphone or a polyphenylsuiphone. General formulae of some suitable polysulphones are as follows:

The increase in toughness of the epoxy matrix is achieved by addition of mixtures of PES and PMMA polymers as the toughening agents. It is essential that the combination of PES and PMMA is utilised. It is this combination which provides for improved levels of fracture toughness rather than the use of either PES or PMMA polymers individually. This synergistic action of the two polymers is advantageous and unexpected. The PES and PMMA polymers may be either homopolymers or copolymers.

The combination of PES and PMMA polymers as toughening additive in an epoxy composition provides for an unexpected and significant increase in fracture toughness of the cured matrix. This increase is greater than can be obtained by the use of PES or PMMA alone. The increase in toughness is also accompanied by no reduction in modulus of the cured matrix. The thermal capability of the cured composition is also substantially maintained as indicated by Tg data.

The enhanced performance obtained results in a lower overall loading of toughening agent in the epoxy composition being required to achieve the same toughness criterion. The lower level of thermoplastic in the epoxy composition leads to a lower formulation viscosity. Further benefits in areas such as ease of processing arise from the lower resin viscosity.

The invention is illustrated by the following Examples.

Abbreviations. DGEBA is diglycidylether of Bisphenol-A (Epon 828 (Shell) and MY750 (Ciba-Geigy) were used in these Examples). IPD is isophoronediamine and DDS is diaminodiphenylsulphone. PES and PMMA are defined earlier, and were obtained from Aldrich Chemical Company. The PES and PMMA were dissolved in dichloromethane solvent to assist incorporation into the epoxy resin.

Test methods. Flexural strength and modulus were determined according to ASTM D790M. Toughness measurements (Kic and Gic) were determined according to the ESIS protocol of March 1990 (based on ASTM E399). The glass transition temperature (Tg) is the tanb peak determined using a Polymer Laboratories DMTA operating at 10Hz and using a linear temperature gradient of 4 C/minute.

Comparative Examples 1-3 and Example 4. The relative proportions of ingredients for these examples are given in the Table. The following procedure was adopted for production of the cured samples. The DGEBA was heated to 70 100"C, and the thermoplastic solution added (examples 2-4). The solvent was evaporated from the mixture with any residual solvent being removed under vacuum. The mixture was then cooled to 50"C and IPD added. The mixture was made homogeneous, de-aerated and transferred to a hot mould. A cure schedule of heating at 160 C for 30 minutes was used. The cured sheets were cut to size for testing and the results obtained are recorded in the Table.

Comparative Example 5 and Example 6. The relative proportions of ingredients for these examples are given in the Table. The following procedure was adopted for production of the cured samples. The DGEBA was heated to 70 100"C, and the thermoplastic solution added (example 6). The solvent was evaporated from the mixture with any residual solvent being removed under vacuum. The mixture was then heated to 1300C and DDS added. The mixture was made homogeneous, de-aerated and transferred to a hot mould. A cure schedule of heating at 1300C for 120 minutes followed by 200"C for 180 miutes was used. The cured sheets were cut to size for testing and the results obtained are recorded in the Table.

Table.

Example. 1 2 3 4 5 6 DGEBA 100 100 100 100 100 100 IPD 23 23 23 23 - DDS - - - - 36 36 PES - 15 - 7.5 - 7.5 PMMA - - 15 7.5 - 7.5 Properties.

Tg/ C 165 148 167 159 224 219 KIC/MPa#m 0.70 0.82 0.78 1.55 0.72 0.97 GIC/KJ.m-2 0.13 0.20 0.18 0.67 0.15 0.28 Flexural 3.2 2.9 3.1 3.1 3.0 2.9 modulus/GPa Flexural 167 92 125 57 123 120 strength/MPa

Claims

CLAIMS:

1. A thermoset resin composition containing (i) a poly(ether)sulphone COPES) and (ii) polymethylmethacrylate (PMMA) or a copolymer containing at least 50% by weight of methyl methacrylate units.

2. A thermoset resin composition according to claim 1, in which the thermoset resin is an epoxy or phenolic resin.

3. A thermoset resin composition according to claim 1 or 2, in which the PES is a bisphenol polysulphone, a poly(arylene ether sulphone), a polyethersulphone or a polyphenylsulphone.

4. A thermoset resin composition according to any of claims 1 to 3, in which the ratio by weight of (i) to (ii) is in the range of from 5:95 to 95:5.

5. A thermoset resin composition according to claim 4, in which the ratio by weight of (i) to (ii) is in the range of from 25:75 to 75:25.

6. A thermoset resin composition according to any of claims 1 to 5, in which the total content of (i) and (ii) is up to 40% by weight, based on the weight of the thermoset resin.

7. A thermoset resin composition according to claim 6, in which the total content of (i) and (ii) is from 5 to 30% by weight, based on the weight of the thermoset resin.

8. Use of (i) PES and (ii) PMMA or a copolymer containing at least 50% by weight of methyl methacrylate units in combination for toughening a thermoset resin composition.