CA2389539A1

CA2389539A1 - Storage-stable prepregs on the basis of duroplastic, oleochemical matrices

Info

Publication number: CA2389539A1
Application number: CA002389539A
Authority: CA
Inventors: Michael Skwiercz; Ralf Bemmann; Horst Sulzbach
Original assignee: Cognis Deutschland GmbH and Co KG
Current assignee: Individual
Priority date: 1999-10-30
Filing date: 2000-10-21
Publication date: 2001-05-10
Also published as: JP2003514048A; AR026259A1; AU1853801A; EP1230294A1; WO2001032755A1; DE19952364A1

Abstract

The aim of the invention is to obtain prepregs on the basis of duroplastic, oleochemical matrices that can be stored at room temperature. To this end, a fiber material that preferably contains natural fibers is contacted with a matrix material at temperatures of 40 to 80 ~C in the presence of a suitable catalyst and the fiber material impregnated with the matrix is cooled to temperatures of 30 ~C and less. The matrix material is chosen from a fatty substance with at least 12 C atoms that contains epoxide and/or hydroxyl groups, a cross-linking agent and a catalyst, and the matrix material has a Brookfield viscosity of 600 to 1400 MPa at temperatures of 40 to 80 ~C.

Description

Storage-stable Prepregs on the Basis of Duroplastic, Oleochemical Matrices This invention relates to storage-stable prepregs, to a process for their production, to fibre composites produced from them and to the use of the fibre composites.
Fiber composites consist at least of fibers and a matrix material.
The function of the fibers is to strengthen the material. More particularly, the fibers absorb tensile forces acting on the material while the matrix fills voids between the fibers and coats the fibers. The matrix thus transmits the shear forces acting on the composite material. In addition, the matrix protects the coated fibers from outside influences such as, for example, the penetration of water or moisture, oxidative or photo-oxidative influences.
Known fiber composites include, for example, glass-fiber-, metal-fiber- or carbon-fiber-reinforced plastics. By virtue of their high strength, durability and reproducibility, composites such as these have hitherto been successfully used in many fields. However, in view of the need for sustainable development, products based on biomass and/or agricultural products as renewable raw materials have also been increasingly in demand for composite materials. In contrast to petrochemical and fossil raw materials, renewable raw materials are never exhausted and, through the cultivation of suitable plants, can be regenerated at any time by photosynthesis.
So-called prepreg technology is regularly used in the production of fibre/resin composites. A prepreg is a semifinished product preimpregnated with thermoplastic or thermoset material which is converted into the end product in another processing step. To produce prepregs, fibers are impregnated with a resin matrix in suitable installations.
The prepregs may then either be processed by curing to the desired end ' CA 02389539 2002-04-30 products immediately after their production or may be temporarily stored and then finished as required which is one of the advantages of this technology. Since the prepregs themselves are generally present in the form of mats, end products variable in shape, for example, can be obtained from them as required. Unfortunately, prepregs with thermoset matrixes are attended by the problem that, owing to the material properties of conventional thermosets, storage times are very short (a few weeks at most, sometimes only a few minutes) because the material cures quickly at normal temperature (21 °C). If thermoset-based prepregs are to be stored for prolonged periods, they usually have to be expensively deep-cooled (to -30°C).
Thermosets are known to be materials which are formed from oligomers by irreversible and crosslinkingvia covalent close bonds, optionally with addition of monomersor polymers.Thermosets in the context of present invention understoodto be both the the are raw materials before crosslinking (i.e. the impregnating resins) and the cured reaction products.
The problem addressed by the present invention was to produce prepregs based on thermoset matrixes which would avoid the above-mentioned disadvantages, particularly the short storage life at normal temperature. The prepregs would be produced from predominantly or completely renewable raw materials.
The problem stated above has been solved by the use of certain matrix materials based on oleochemical raw materials. In a first embodiment, the present invention relates to prepregs storable at room temperature containing a fibrous material and a thermoset matrix which contains (a) an epoxyfunctional and/or hydroxyfunctional fatty compound having at least 12 carbon atoms, (b) a crosslinking agent and (c) a catalyst.
The prepregs according to the invention may contain both synthetic fibers, such as glass fibers, carbon fibers, metal fibers and the like, and natural fibers. According to the invention, preferred prepregs are produced at least partly, but advantageously completely using natural fibers. The proportion of natural fibers is preferably 50% by weight or more, based on the weight of the fibers. Prepregs in which 100% by weight of the fibers consist of natural fibers as defined below are particularly preferred. These natural fibers may be used in the form of short fibers, yarns, rovings or preferably sheet-form textiles in the form of nonwovens, needle-punched nonwovens, random laid nonwovens, woven fabrics, laid fabrics or knitted fabrics. According to the invention, natural fibers are preferably selected from flax, hemp, straw, wood wool, sisal, jute, coconut, ramie, bamboo, bast, cellulose, cotton or wool fibers, animal hair or fibers based on chitin/chitosan and combinations thereof. Prepregs partly or completely containing flax fibers as the fibrous material are preferred for the purposes of the invention. The percentage by weight of fibrous material, based on the prepregs themselves, is between 10 and 70% by weight, preferably between 30 and 60% by weight and more particularly between 35 and 55%
by weight.
The fibers may be contacted with the matrix by any methods known to the expert in order to obtain the prepregs according to the invention.
The fibers are preferably dipped in the matrix but may also be sprayed with the matrix. The thermoset matrix itself consists predominantly and preferably entirely of oleochemical raw materials. These are mixtures of (a) reactive oxygen-containing fatty compounds with (b) crosslinking agents and (c) catalysts. The mixtures of components (a), (b) and (c) preferably have a Brookfield viscosity on application to the fibers of 600 to 1,400 mPas, preferably 800 to 1,200 mPas and more particularly 900 to 1,100 mPas, as measured with spindle 5 at 10 min-'. The viscosity values are all based on the application temperature. The matrix is applied to the fibers at temperatures of 40 to 80°C to give the prepregs according to the invention.
In one particularly advantageous embodiment, the matrixes selected have a Brookfield viscosity of 600 to 1,200 mPas at a temperature of 65°C.
This ensures that the matrixes do not yet cure completely, complete curing being known to be attributable to the complete reaction of components (a), (b) and (c) with one another. Instead, the prepregs obtained can still be molded as required which simplifies their subsequent processing. In addition, the prepregs do not cure as quickly in air at room temperature as known prepregs and thus show distinctly increased stability in storage.
The compounds of reaction component (a) are reactive oxygen-containing fatty compounds which may be characterized as follows, at least 12 carbon atoms having to be present in the molecule. The upper limit to the number of carbon atoms is preferably 56 and more particularly 36 carbon atoms. The compounds of reaction component (a) contain at least one reactive oxygen-containing group, either the epoxy group andlor the hydroxyl group, in the molecule which enables them to react with the crosslinking agents of group (b) to form solid agglomerates of relatively high molecular weight which, together with the fibers, provide the fiber composite with the required physical properties such as, for example, tensile strength and flexural strength.
One group of components (a) are epoxidized triglycerides obtained, for example, by reacting natural unsaturated fats and oils with formic acid and hydrogen peroxide. Examples of preferred starting materials are the natural fats and oils of rape, sunflowers, soya, flax, hemp, castor oil, coconuts, oil palms, oil palm kernels and olive trees which partly contain triglycerides of unsaturated fatty acids. The most important representatives of the epoxidized oils and fats are epoxidized soybean oil, epoxidized rapeseed oil and epoxidized linseed oil.
These epoxidized triglycerides may be converted into the corresponding hydroxyfunctional compounds by nucleophilic ring opening.
Nucleophiles are understood to include alcohols such as, for example, water, methanol, ethanol, ethylene glycol, glycerol and trimethylol propane;

amines such as, for example, ethanolamine, diethanolamine, triethanolamine, ethylenediamine, dipropylenetriamine or hexamethylene diamine; or carboxylic acids, such as acetic acid, dimer fatty acid, malefic acid, phthalic acid, terephthalic acid or a mixture of mono- and/or 5 difunctional fatty acids containing 6 to 30 carbon atoms.
Nucleophiles for the ring opening of the epoxidized fatty compounds also include fatty alcohols. Suitable fatty alcohols are aliphatic, linear or branched primary alcohols containing 6 to 22 carbon atoms. Typical examples are caproic alcohol, caprylic alcohol, 2-ethylhexyl alcohol, capric alcohol, lauryl alcohol, isotridecyl alcohol, myristyl alcohol, cetyl alcohol, palmitoleyl alcohol, stearyl alcohol, isostearyl alcohol, oleyl alcohol, elaidyl alcohol, petroselinyl alcohol, arachyl alcohol, gadoleyl alcohol, behenyl alcohol, erucyl alcohol and brassidyl alcohol and the technical mixtures thereof obtained, for example, in the high-pressure hydrogenation of technical methyl esters based on fats and oils or aldehydes from Roelen's oxo synthesis and as monomer fraction in the dimerization of unsaturated fatty alcohols. Other suitable nucleophiles for reaction with epoxidized triglycerides are propenoic, butanoic, pentanoic, hexanoic, heptanoic, octanoic, nonanoic, decanoic, undecanoic, dodecanoic, tridecanoic, tetradecanoic, pentadecanoic, hexadecanoic, heptadecanoic, octadecanoic, nonadecanoic, eicosanoic, docosanoic, hexacosanoic and triacontanoic acid and mixtures thereof. However, crotonic acid, itaconic acid, malefic acid, fumaric acid and mixtures thereof are particularly preferred. Other functional groups capable of crosslinking, such as hydroxyl, mercapto, carboxyl, amino, anhydride groups, or even olefinic double bonds may be introduced into these triglycerides by methods known per se. According to the invention, however, the oxygen-containing derivatives are always preferred as component (a).
Besides the nucleophiles mentioned above, the epoxidized triglycerides may also be reacted with compounds corresponding to formula (I). Preferred compounds correspond to formula (I):
H2C=CR'-COOR2 (I) in which R' is a hydrogen atom or a methyl group and R2 is a hydrogen atom or an alkyl group containing 1 to 22 carbon atoms. The salts of these compounds are also suitable. Preferred compounds corresponding to general formula (I) are acrylic and methacrylic acid and esters thereof with fatty alcohols. Reactions products of linseed and/or soybean oil with acrylic andlor methacrylic acid are preferred.
Another group of suitable reaction components (a) is selected from reaction products of unsaturated fatty compounds, preferably fatty acids or fatty acid esters, with anhydrides, preferably malefic anhydride. Suitable unsaturated fatty acids are, for example, 10-undecanoic acid, lauroleic acid, myristoleic acid, palmitoleic acid, petroselic acid, petroselaidic acid, oleic acid, elaidic acid, ricinoleic acid, linoleic acid, linolaidic acid, gadoleic acid, arachidonic acid, erucic acid, brassidic acid and clupanodonic acid and mixtures thereof. Also suitable are polyunsaturated acids such as, for example, oleic acid, elaidic acid, ricinoleic acid, linoleic acid, linolenic acid, a-/~-elaeostearic acid, gadoleic acid, arachidonic acid and brassidic acid and the mixtures thereof obtained in particular in industrial-scale production. However, reaction products of triglycerides based on unsaturated fatty acids with the anhydrides are preferably used.
Reaction products of epoxidized triglycerides with anhydrides are also suitable components (a) for the production of matrixes for storage-stable prepregs according to the invention. Preferred anhydrides are those obtained from cyclic polycarboxylic acids containing two free carboxylic acid groups, for example cyclohexane dicarboxylic anhydride, cyclohexene dicarboxylic anhydride, phthalic anhydride, trimellitic anhydride, hemimellitic anhydride, pyromellitic anhydride, 2,3-naphthalene anhydride, 1,2-cyclobutane dicarboxylic anhydride, 1,2-cyclopentane dicarboxylic anhydride, quinolinic anhydride, norbornene dicarboxylic anhydride, pinic anhydride, norpinic anhydride, truxilic anhydride, pinic anhydride, perylene-1,2-dicarboxylic anhydride, carboxylic anhydride, norcamphane dicarboxylic anhydride, isatoic anhydride, camphoric anhydride, naphthalene tetracarboxylic anhydride or mixtures of these anhydrides.
Particularly suitable anhydrides are malefic anhydride, phthalic anhydride and trimellitic anhydride and derivatives and mixtures of these anhydrides.
According to the invention, the crosslinking agent (b) is selected from organic compounds containing at least two reactive sites capable of reaction with the compounds (a) in the molecule. However, compounds containing three, four or even more reactive sites suitable for crosslinking in the molecule are also suitable. Component (b) is preferably selected from compounds corresponding to general formula (II):
HZC=CR3-(CHZ)~-X-A-X-(CH2)~-CR3=CH2 (I I ) in which A is a difunctional aliphatic radical containing 2 to 24 carbon atoms optionally interrupted by hetero atoms or an aromatic radical containing 6 to 10 carbon atoms and X is a CO, OCO or COO group, R3 is a hydrogen atom or a CH3 group and n is the number 0 or 1 to 3. Components (b) selected from the group consisting of diallyl phthalates, dipropylene glycol diacrylate or diethylene glycol diacrylate are particularly suitable. Reactive anhydrides, preferably malefic anhydride, are also suitable as component (b).
Catalysts (c) are added to the thermoset matrixes as initiators of the actual curing reaction. Preferred catalysts are organic peroxide compounds, such as tert. butyl perisononanoate (TBPIN) or tert. butyl perethyl hexanoate (TBPEH). Basic catalysts, preferably organic aliphatic or aromatic amine compounds, may also be used. Imidazoline derivatives, preferably 1-methyl imidazole, are particularly preferred.
Component (c) is present in the matrixes in quantities of 0.01 to 10%
by weight, preferably in quantities of 0.5 to 5% by weight and more particularly in quantities of 1.0 to 3% by weight. Components (a) and (b) make up the balance to 100% by weight of the matrix. Components (a) and (b) are preferably used in quantity ratios of (a) to (b) of 4:1 to 1:1.
Component (a) is preferably present in an excess over component (b) in the matrix. In this case, the quantity ratio of (a) to (b) is 80:20 to 60:40 and preferably 70:30.
Besides components (a) to (c), the matrixes may contain other auxiliaries and additives known per se to the expert for the production of prepregs, for example flame retardants, pigments, UV absorbers and organic and inorganic fillers.
In another embodiment, the present invention relates to a process for the production of a storage-stable prepreg in which (I) a fibrous material is contacted with a thermoset matrix material at temperatures of 40 to 80°C
in the presence of a catalyst and (II) the matrix-impregnated fibrous material is cooled to temperatures of 30°C or lower, the matrix material being selected from an epoxyfunctional and/or hydroxyfunctional fatty compound containing at least 12 carbon atoms, a crosslinking agent and a catalyst and the matrix material having a Brookfield viscosity of 600 to 1,400 mPas at the temperatures in step (I). The prepregs may be produced by any of the methods known to the expert, preferably continuous methods. Relevant particulars can be found, for example, in Schlichting et al., Verbundwerkstoffe, Lexika-Verlag, Grafenau, 1978, pages 208 to 211.
The prepregs thus obtained may be cured at temperatures of > 80°C
and preferably at temperatures of >100°C to form the required end products. A fiber composite according to the invention is preferably obtained by curing the prepregs according to the invention at 100 to 250°C.

' CA 02389539 2002-04-30 Particularly preferred curing temperatures are in the range from 120 to 180°C and more particularly in the range from 130 to 160°C. The cure time is generally short, amounting to only a few minutes at temperatures around 150°C.
The present intention also relates to fiber composites produced as described above and to their use for the production of structural components for vehicle and aircraft construction, the building industry, window manufacture, the furniture industry, the electronics industry, sports equipment, toys, machine construction, the packaging industry, agriculture or the safety sector.
Examples Example 1. Linseed oil acrylate (a) was mixed with dipropylene glycol diacrylate (b) as crosslinker in a ratio by weight of 70:30. The mixture had a Brookfield viscosity of 1,000 mPas at 65°C (spindle 5; 10 min-').
Quantities of 1 % by weight of TBPEH and TBPIN as radical initiators (c) were added to the mixture and the matrix was then applied to flax fibers at 65°C. The prepreg thus obtained was storable for 6 months at temperatures of <30°C. The prepreg was cured for 60 seconds at 150°C
and thus converted into a fiber composite workpiece.
Example 2. Soybean oil acrylate (a) was mixed with diallyl phthalate (b) in a ratio of 70:30 to form a matrix (Brookfield viscosity at 40°C 1,000 mPas, spindle 5; 10 min-'). Quantities of 1% by weight of TBPIN and TBPEH
were then added and the mixture was applied to flax fibers at 65°C. The prepreg thus obtained was storable for 6 months at temperatures of <30°C
and thereafter was readily converted into a workpiece by curing (150°C, seconds).

Example 3. 60% by weight of an epoxidized linseed oil (a), 39% by weight of a mixture of hexahydrophthalic anhydride and trimellitic anhydride (b) and 1 % by weight of 1-methyl imidazole as catalyst (c) were mixed and contacted with flax fibers at 65°C. The mixture had a Brookfield viscosity at 5 65°C of 2,000 mPas. The prepreg was then cooled to 20°C and was stable in storage. It was cured at 180°C (cure time ca. 1 minute) to form a stable fiber composite.

Claims

1. ~A prepreg storable at room temperature containing a fibrous material and a thermoset matrix, the thermoset matrix containing at least (a) an epoxyfunctional and/or hydroxyfunctional fatty compound having at least 12 carbon atoms, (b) a crosslinking agent and (c) a catalyst, characterized in that the thermoset matrix material has a Brookfield viscosity at 60°C of 600 to 1,400 mPas.

2. A prepreg as claimed in claim 1, characterized in that the fibrous material is partly or completely selected from natural fibers.

3. A prepreg as claimed in claim 1 or 2, characterized in that the fibrous material makes up from 10 to 70% by weight, preferably from 30 to 60% by weight and more particularly from 35 to 55% by weight of the prepreg.

4. A prepreg as claimed in claims 1 to 3, characterized in that the fibrous material is partly or completely selected from the group consisting of flax, hemp, straw, wood wool, sisal, jute, coconut, ramie, bamboo, bast, cellulose, cotton or wool fibers, animal hair or fibers based on chitin/chitosan and combinations thereof.

5. A prepreg as claimed in claims 1 to 4, characterized in that flax fibers are selected as the fibrous material.

6. A prepreg as claimed in claims 1 to 5, characterized in that component (a) of the matrix material is selected from the group of epoxidized triglycerides of unsaturated fatty acids and mixtures thereof.

7. A prepreg as claimed in claims 1 to 6, characterized in that component (a) is selected from the group consisting of epoxidized linseed oil, hemp oil, coconut oil, palm oil, palm kernel oil, rapeseed oil, castor oil, soybean oil and sunflower oil.

8. A prepreg as claimed in claims 1 to 7, characterized in that component (a) is selected from reaction products of epoxidized triglycerides with compounds corresponding to general formula (I):

H2C=CR1-COOR2~ (I) in which R1 is a hydrogen atom or a methyl group and R2 is a hydrogen atom or an alkyl group containing 1 to 22 carbon atoms, and salts of these compounds.

9. A prepreg as claimed in claims 1 to 8, characterized in that component (a) is selected from reaction products of epoxidized triglycerides with acrylic acid and/or methacrylic acid.

10. A prepreg as claimed in claims 1 to 9, characterized in that component (a) is selected from reaction products of epoxidized triglycerides with crotonic acid, itaconic acid, maleic acid, fumaric acid or mixtures thereof.

11. A prepreg as claimed in claims 1 to 10, characterized in that component (a) is selected from reaction products of unsaturated fatty acids and/or triglycerides with anhydrides.

12. A prepreg as claimed in claims 1 to 11, characterized in that component (a) is selected from reaction products of epoxidized triglycerides with anhydrides.

13. A prepreg as claimed in claims 1 to 12, characterized in that component (a) is selected from reaction products of epoxidized triglycerides with maleic anhydride, phthalic anhydride, trimellitic anhydride or mixtures thereof.

14. A prepreg as claimed in claims 1 to 13, characterized in that component (b) is selected from compounds corresponding to general formula (II):

H2C=CR3-(CH2)n -X-A-X-(CH2)n-CR3=CH2~~(II) in which A is a difunctional aliphatic radical containing 2 to 24 carbon atoms optionally interrupted by hetero atoms or an aromatic radical containing 6 to carbon atoms and X is a CO, OCO or COO group, R3 is a hydrogen atom or a CH3 group and n is the number 0 or 1 to 3.

15. A prepreg as claimed in claims 1 to 14, characterized in that component (b) is selected from diallyl phthalates, dipropylene glycol diacrylate or diethylene glycol diacrylate.

16. A prepreg as claimed in claims 1 to 15, characterized in that the ratio by weight of (a) to (b) in the matrix is 4:1 to 1:1.

17. A prepreg as claimed in claims 1 to 16, characterized in that component (c) is selected from the group of organic peroxide compounds.

18. A prepreg as claimed in claims 1 to 17, characterized in that component (c) is selected from the group of organic aliphatic or aromatic amine bases.

19. A prepreg as claimed in claims 1 to 18, characterized in that the thermoset matrix material has a Brookfield viscosity at 40 to 80°C of 600 to 1,400 mPas, preferably 800 to 1,200 mPas and more particularly 900 to 1,100 mPas.

20. A process for the production of a storage-stable prepreg in which a fibrous material is contacted with a thermoset matrix material at temperatures of 40 to 80°C in the presence of a catalyst and the matrix-impregnated fibrous material is cooled to temperatures of 30°C or lower, characterized in that the matrix material is selected from an epoxyfunctional and/or hydroxyfunctional. fatty compound (a) containing at least 12 carbon atoms, a crosslinking agent (b) and a catalyst (c) and the matrix material has a Brookfield viscosity of 600 to 1,400 mPas at the temperatures in step (I).

21. A process as claimed in claim 20, characterized in that it is carried out continuously.

22. A process for the production of fiber composites, characterized in that the prepreg claimed in claims 1 to 16 is cured at temperatures of 100 to 250°C.

23. A fiber composite produced by the process claimed in claim 22.

24. The use of the fiber composites claimed in claim 23 for the production of structural components for vehicle and aircraft construction, the building industry, window manufacture, the furniture industry, the electronics industry, sports equipment, toys, machine construction, the packaging industry, agriculture or the safety sector.