RU2415891C2 - Binder, preparation method and prepreg - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: binder for preparing prepregs is a product of reacting polyamide acid and an epoxy-novolac oligomer with the following ratio of components in wt %: polyamide acid 1-20, epoxy-novolac oligomer - the rest. The invention also discloses a method of preparing the said binder and a prepreg from the said binder.

EFFECT: invention enables to obtain a product with homogeneous phase distribution of the polyimide component.

10 cl, 5 dwg, 2 tbl, 6 ex

Description

Technical field

The invention relates to the production of composite materials, in particular to binders and prepregs based on them, and can be used in the manufacture of high-strength structural materials in rocket and space technology, aviation, shipbuilding, mechanical engineering, electrical engineering, electronics, instrument making.

State of the art

As follows from the analysis of patent and scientific and technical literature, epoxynolac resins are often used as binders and adhesives in the production of composite materials (see, for example, RU 2326909). Their advantages include the fact that epoxynovolac resins do not have oxymethyl groups and cannot enter into a polycondensation reaction when heated to form high molecular weight phenolic resins; therefore, in the absence of moisture, they are stable during storage.

A feature of epoxynolac resins is a high cure rate, which reduces their residence time in a viscous flow state.

Recently, polyimide-based binders have become widespread (see US 5004575, RU 2279452). These binders are characterized by a uniform distribution of crystal structures, improved fluidity in the molten state and high performance characteristics of composite materials.

Epoxy and modified epoxy oligomers and polymers, including those modified with polyimide, have much higher performance characteristics.

A binder based on liquid phenolic novolac polymer and a cured product based on it are known, exhibiting excellent fluidity, moisture resistance and high heat resistance. The binder contains a liquid phenolic polymer and an imide compound with certain formulas, characterized by a viscosity of ≤1000 Poise at 50 ° C (see JP 2001214028).

A composition is also known that provides products with high heat resistance and mechanical characteristics (see JP 63086746). This composition was prepared by mixing the uncured novolac polymer (A) with the polyimide polymer (B) at a ratio of (A) / (B) as 97 / 3-70 / 30.

The disadvantages of the last two technical solutions include the impossibility of obtaining a cured product with a homogeneous phase distribution of the polyimide component, due to the fact that a polyimide having imide rings and a limited number of free functional groups capable of interacting with the novolac oligomer groups during the curing process is introduced into the composition.

Disclosure invention

The objective of the invention is to obtain compositions with a controlled distribution of the polyimide component in the cured composition, with the possibility of obtaining both homogeneous homogeneous compositions and the nanostructured phase of the second component in an epoxynol oligomer.

The problem is solved by a binder for the preparation of prepregs containing novolac-epoxy-polyimide block copolymer, in accordance with which it contains a block copolymer, which is the product of the interaction of polyamide acid with epoxy-novolac oligomer during curing in the following ratio of components, wt.%:

Polyamic acid 1-20 Epoxy novolac oligomer rest.

In preferred embodiments of the invention, it is desirable that the ratio is as follows, wt.%:

Polyamic acid 3-15 Epoxy novolac oligomer rest.

The best properties of the binder are achieved in the following ratio, wt.%:

Polyamic acid 5-10 Epoxy novolac oligomer rest.

In private embodiments of the invention, the problem is solved in that the cured binder is the product of the interaction of a polyamic acid obtained by the synthesis of resorcinol diamine and oxyphthalic dianhydride by low-temperature polycondensation in a solution of dimethylformamide and epoxynolac oligomer.

In other embodiments of the invention, the cured binder has a structure that is an epoxy homogeneous matrix with nano-inclusions of spindle-shaped polyimide chemically bonded to the epoxy matrix and is characterized by the structural formula

The problem is also solved by the method of manufacturing this binder, in accordance with which the epoxy-novolac oligomer is mixed with a mixture of polyamic acid and solvent, followed by removal of the solvent and curing.

In particular embodiments of the invention, solvent removal is carried out at 80-100 ° C.

To obtain a binder with a homogeneous structure, curing is carried out at 150-160 ° C.

To obtain a spindle-shaped polyimide binder with nanoinclusions, curing is carried out at 165-175 ° C.

The problem is also solved by the prepreg for the manufacture of composite materials, which is made of the above and contains components in the following ratio, wt.%:

Filler 60-65 Binder rest

The invention consists in the following.

The choice of epoxynolac oligomer is due to its high physical and mechanical properties and heat resistance in products based on it. Also, when exposed to temperature, the epoxy-oligomer oligomer cures without the use of additional hardeners, which leads to a homogeneous structure without the inclusion of structural elements of a different nature. Storage of such an oligomer is also more preferable, since it is not reactive at low and room temperatures. However, one of the disadvantages of such an oligomer is its high viscosity, which requires the introduction of active diluents or solvents during its processing.

The introduction of polyamido acid into the composition leads to the formation of intermolecular interactions, which is confirmed by the data of IR spectroscopy on the functional groups of the polyamido acid and epoxynolac oligomer, however, intrachain crosslinking at room temperature does not occur, and the composition remains stable during storage.

Figure 1 shows the IR spectra of polyamido acids (1), epoxynolobol oligomer (2) and mixtures thereof (3).

In figure 2. a fragment of the IR spectrum of the mixture is presented in the region of 1800-1560 cm ^-1 when the sample is heated from room temperature to 200 ° C in increments of 20 ° C: 1) a cooled sample; 2) 20 °; 3) 100 ° C; 4) 120 ° C; 5) 200 ° C.

Figure 3 presents a fragment of the IR spectrum of the mixture in the range of 1050-880 cm ^-1 when the sample is heated from room temperature to 200 ° C in increments of 20 ° C: 1) a cooled sample; 2) 20 ° C; 3) 100 ° C; 4) 120 ° C; 5) 200 ° C.

Figure 4 presents the data of scanning microscopy of epoxynovolac-polyimide block copolymer, cured at a temperature of 150-160 ° C.

Figure 5 presents the data of scanning microscopy of epoxynovolac-polyimide block copolymer, cured at a temperature of 165-175 ° C.

Figure 1 shows that the spectrum of the mixture (curve 2) is not an additive sum of the spectra of polyamic acid and epoxynolac resin: there is a shift in the absorption bands relative to their position in individual substances and a change in the ratio of intensities.

During curing at a high reactivity of polyamido acid groups and at a high process speed at temperatures of 150-160 ° C, a large number of cross-links between the polymer and the oligomeric system can be formed, which can lead to the absence of phase separation and to obtain block copolymers of various structures.

According to the data of IR spectroscopy during curing, hydrolysis of the polyamido acid occurs with the formation of new functional groups that enter into a polycondensation reaction with the functional groups of the epoxy-oligomer oligomer to form a new block copolymer structure, FIGS. 2 and 3.

When the mixture is heated, the intensity value sharply decreases for the amide absorption band (Fig. 2), while the intensity of the symmetric C = O vibrations does not change at 1780 cm ^-1 , i.e. it can be assumed that the formation of the transition complex of the epoxy group and the N atom from the amide bond occurs, and the formation of imide rings may occur at higher temperatures and holding times.

At the same time, there is a decrease in the intensity of CO vibrations in epoxy groups (Fig. 3).

A decrease in the intensity of the absorption band of the amido group simultaneously with a decrease in the optical density of the absorption bands of epoxy groups clearly indicates that the polyamido acid acts as a hardener in this mixture, opening the epoxy ring and forming an intermolecular network.

The resulting morphological structure is characterized by a homogeneous distribution of polyamido acid fragments in the epoxynovolac composition with the formation of a new type of block copolymer characterized by increased strength and heat resistance, Fig. 4.

Such a distribution of polyamic acid in the epoxynolac oligomer occurs during the curing regime at temperatures of 150-160 ° C and long exposure for 5-6 hours. With an increase in the polyamido acid content in the epoxynol block copolymer, optimal concentrations are observed at which the process of yield loss (gelation) takes place over a period of time at which the composite material is formed with desired properties and morphological structure. When the content is below the optimum (1-2.5% wt.), An increase in gelation time is observed, the curing process is difficult and polyimide is released into a separate phase dispersed in the cured matrix of the epoxynolac oligomer.

With an increase in the concentration of polyamic acid above 10% of the mass. a significant decrease in gelation time is observed, the system loses fluidity in a short time due to the curing of the polyamido acid and epoxynolobol oligomer, and an excess of polyamido acid forms a separate phase. However, the formation of the nanoscale phase of the polyimide is diffusively difficult, and the resulting phase is larger.

On the other hand, at a low rate of interaction of the polyamido acid and the oligomeric epoxynovolac system and a high cure rate at temperatures of 165-175 ° C, the resulting phase may have a weak chemical bond with the matrix. Under correctly selected process conditions, it is possible to obtain an optimal phase nanoscale structure with high adhesive strength to the cured matrix.

When the curing mode is carried out at temperatures of 165-175 ° C, not only the polyamide acid and epoxynolobol oligomer matching mechanism is realized, but also the polyimide formation mechanism during hydrolysis and cyclization of the polyamic acid and its isolation into a separate phase, forming nanoinclusions in the epoxynolobol oligomer matrix at optimal polyamide acid concentrations. In this case, a distribution is realized that leads to the formation of a snake-in-cell type nanostructure, which is characterized by an increased impact strength in the composite material and the ability to self-repair the structure under loads, Fig. 5.

With the introduction of polyamido acids in an amount of 1-2.5% of the mass. the formation of an interchain block copolymer does not occur, and a heterogeneous structure is formed with regions enriched in one of the components, polyimide. With a content of more than 10% of the mass. polyamido acids; the curing process of the epoxynovolac oligomer proceeds at high speeds and polyimide is also released into a separate phase, with sizes up to 10 microns.

With an optimal content of polyamic acid 5-10% of the mass. the epoxynovolac-polyimide imide block copolymer is cured and the polyimide is released into a separate nanostructured phase with an inclusion size of 100-500 nm.

The morphology of cured epoxynovolac-polyimide compositions changes significantly with increasing both the content of thermoplastic polyimide and curing temperature, forming systems in which particles of thermoplastic polyimide are dispersed in an epoxynovolac oligomer, and in the case of formation of nanophase, an increase in the strength of the system is achieved, since crack propagation is inhibited by dispersion spindle-shaped particles of polyimide. The phase enriched with thermoplastic polyimide can be continuous, with the formation of interpenetrating networks. The strength of such compositions increases to a large extent due to the occurrence of plastic deformations.

To achieve the greatest modifying effect, a strong adhesive interaction between the matrix and nanoinclusions of the polyimide phase is necessary. Obviously, the most durable interfacial interaction will be during the formation of chemical bonds between phases, i.e. the terminal functional thermoplastic polyimide nanoparticles are bonded to the resulting network of an epoxynolac oligomer or an epoxynolac polyimide block copolymer containing epoxy groups.

The resulting binder is used to prepare the prepreg, which is obtained by impregnating with the binder specially prepared unidirectional tapes and various fabrics of fibers, for example carbon, glass and basalt.

After impregnation, a sticky material is obtained, which allows forming multilayer structures of complex configuration with a given orientation of the fibers and the ability to carry specified loads.

After additional heat treatment - curing, composite products of any shape (hulls and parts of structures, machines, ships, etc.) are obtained from molded blanks.

The regulation of the composition and nanostructure of the fiber - binder interface allows one to obtain prepregs on the basis of which polymer composite materials with improved characteristics will be prepared.

The composition and nanostructure of the interface is determined by the properties of the binder and the conditions for the impregnation of fibers and fabrics and curing, in the conditions of which a given structure is formed, which is the subject of the invention.

The invention is as follows.

Compositions were prepared by simple mixing of the components while varying the content of polyamidocylates from 1 to 20% of the mass.

As the thermosetting matrix with good heat resistance, epoxynolac oligomers of the ENFB brand (TU 1-596-36-2005) D.E.N. ™ 438 ™ (Dow Chemical), UP-643 (2225-605-11131395-2003) were selected.

As a polyimide component for the epoxy-polyimide composition, a thermoplastic polyimide precursor was chosen - polyamide acid based on resorcinol diamine and oxidophthalic dianhydride synthesized by low-temperature polycondensation in a solution of dimethylformamide. The choice of dimethylformamide from a number of amide solvents is due to its low boiling point and good dissolving ability for epoxynolac oligomer.

In a glass with a pre-weighed epoxynovolac binder, a 15% solution of the prepolymer — polyamido acid — in dimethylformamide was added in a predetermined amount. Stirred on a mechanical stirrer for 1 hour. The filler was impregnated with a binder and the solvent was removed by exposure to air for 12 hours or by heating from 80 to 100 ° C in an oven.

After removal of the solvent, curing was carried out according to a given mode in a vacuum drying oven ШСВ-65 IZ.

Table 1 shows the properties of the binder, depending on the content in the composition of polyamic acid.

Table 2 shows the properties obtained from these compositions of the binder prepreg.

Table 1 No. p / p The content of polyamido acids in the composition,% wt. Solution color The content of the main substance,% of the mass. Gel time
niya at 13 5 ° C, with The degree of crosslinking at 150-160 ° C / 165-175 ° C Morphological structure of 150-160 ° C /
165-175 ° C one 1.00 brown 50.1 315 98.6 / 98.8 Has inclusions 3-5 microns /
Has inclusions up to 10 microns 2 2.5 brown 50,2 422 98.1 / 98.5 Has inclusions up to 10 microns / Has inclusions up to 5 microns 3 5 brown 50,0 301 98.7 / 98.5 Homogeneous homogeneous / Has inclusions of 100-300 nm four 10 brown 50.1 300 98.6 / 98.7 Homogeneous homogeneous / Has inclusions of 100-300 nm 5 fifteen brown 50.2 241 98.4 / 98.3 Has inclusions up to 3 microns / Has inclusions up to 10 microns 6 twenty brown 50,2 145 98.4 / 98.2 Has inclusions 3-5 microns / Has inclusions up to 10 microns

table 2 The composition of the binder according to table 1 The composition of the prepreg,% of the mass. Prepreg Properties Filler Communication-
that is The content of the binder after impregnation,% of the mass. Gelation time at 135 ° С, s The degree of crosslinking at 150-160 ° C / 165-175 ° C one 60 carbon fiber 40 40.5 301 99.2 / 99.5 2 60 Fiberglass 40 40,2 398 99.5 / 99.6 3 60 carbon fiber 40 41.0 269 99.2 / 99.5 four 60 carbon fabric 40 39.8 264 99.1 / 99.7 5 60 Basalt fabric 40 40,2 200 99.2 / 99.0 6 60 carbon fabric 40 39.8 132 98.9 / 99.1 one 65 Fiberglass 35 35,2 305 99.2 / 99.5 2 65 carbon fiber 35 34.2 401 99.4 / 99.5 3 65 Basalt fabric 35 34.6 272 99.5 / 99.3 four 65 Fiberglass 35 35,4 270 99.2 / 99.4 5 65 carbon fiber 35 35.1 207 99.1 / 99.4 6 65 carbon fabric 35 34.7 136 99.0 / 99.2

Claims (10)

1. Binder for the preparation of prepregs containing novolac oligomer, characterized in that it additionally contains polyamic acid in the following ratio of components, wt.%:
Polyamic acid 1-20 Epoxy novolac oligomer Rest
and is a product of the interaction of the aforementioned polyamic acid and epoxy oligomer in the curing process. 2. The binder according to claim 1, characterized in that it contains components in the following ratio, wt.%:
Polyamic acid 3-15 Epoxy novolac oligomer Rest 3. The binder according to claim 1, characterized in that it contains components in the following ratio, wt.%:
Polyamic acid 5-10 Epoxy novolac oligomer Rest 4. The binder according to claim 1, characterized in that it is a product of the interaction of polyamic acid obtained by the synthesis of resorcinol diamine and oxyphthalic dianhydride by low-temperature polycondensation in a solution of dimethylformamide. 5. The binder according to claim 3, characterized in that it has a structure that is an epoxy homogeneous matrix with nano-inclusions of spindle-shaped polyimide chemically bonded to the epoxy matrix. 6. A method of manufacturing a binder in accordance with claim 1, characterized in that the epoxy-novolac oligomer is mixed with a mixture of polyamic acid and solvent, followed by solvent removal and curing. 7. The method according to claim 6, characterized in that the removal of solvent is carried out at 80-100 ° C. 8. The method according to claim 6, characterized in that the curing is carried out at 150-160 ° C. 9. The method according to claim 6, characterized in that the curing is carried out at 165-175 ° C. 10. A prepreg containing a binder and a filler, characterized in that it is made of a binder in accordance with any one of claims 1 to 5 of the formula and contains components in the following ratio, wt.%:
Filler 60-65 Binder Rest

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