RU2028607C1 - Method of hardening composition materials on the base of phenolformaldehyde binder - Google Patents

Abstract

FIELD: chemistry. SUBSTANCE: components of the material are heated from room temperature to 108-112 C at rate v₁= 0,8-1,2^°C/min of 0.8-1.2 C /min and held for 1.3-1.7 hours. Then the components are heated till reaching temperature of maximal hardening of samples at rate v₂= 1,3-1,7^°C/min of 1.3-1.7 C /min at permanent measurement of electric conductivity G and the loss tangent of a dielectric tgδ. Heating is stopped at temperature of maximal hardening of the sample when values G and G and tgδ are reached during some period of time. Characteristics of the material are the following: separation strength 34,46 kgs/сm³, separation module is 5323 kgs/сm³, strength at shifting along glue band is equal to 6,2 kgs/сm³, compressive strength is equal to 10,7 kgs/сm³, degree of hardening is equal to 96%, time of thermal treatment - 3 hours and 40 minutes. EFFECT: improved efficiency. 3 tbl

Description

 The invention relates to the production of polymer composite materials, and in particular to methods of curing composite materials based on phenol-formaldehyde binder LBS-4 (GOST 901-78).

Known is a method of curing composite materials mode based on a phenol-formaldehyde binder LBS-4 in particular, thermal processing of honeycomb panels based on glass preforms E-3-100 and binder LBS-4 (1), where heating to 80 ° ^C honeycombs produced during 2 hours, further heating to ^{160 °} C - maximum temperature curing produce a rate not exceeding 20 ^{° C} per hour and held at 160 ^{° C} for 1 hour and further cooled ^to 50 ° C in an oven; The disadvantage of this method is the long curing cycle.

Also known is the curing mode of fiberglass based on fiberglass KT-11-TOA and a binder LBS-4, cured by various methods in various modes. Since the cured pressing method (2) provides lift to ⁸⁰ ° C at a rate not exceeding ^{20 °} C / h at a pressure Rud = 0.5 MPa with further aging at 160 ^{° C} for at least 1 hour at Rud = 1-15 MPa, and cooled to 40-50 ^{° C} at a rate not exceeding ²⁰ ° C / h, above which the pressure is released.

The disadvantage of this method may be a low quality cured product: with a sharp temperature drop from 80 to ^{160 °} C may occur abrupt release of volatile accumulated in the cured material, which might cause the formation of pores and cavities, and in the presence of a constant pressure - strain and warpage, t .e. deterioration in the quality of cured KM.

The closest in technical essence is the vacuum molding method (3), according to which the workpiece is heated under vacuum at least 600 mm Hg. ^to 50 ° C for 1.5 hours to 60 ° ^C for 0.5 hours, to ⁹⁰ ° C at a rate not exceeding ^{20 °} C / h to ¹⁴⁰ ° C - maximum curing temperature with the same rate of 20 ° ^C / hours aging at 140 ^{° C} for at least 1 h with subsequent cooling in vacuo to ^about 50 C.

The disadvantage of this method is the long molding cycle, the complexity of the curing process. Thus, from the analysis of known technical solutions, the following disadvantages can be noted:
the lack of the same curing mode for the manufacture of various CMs based on LBS-4 (fiberglass and honeycomb materials);
lack of the same curing mode for the same KM-fiberglass based on KT-11-TOA fiberglass (press method and vacuum molding method);
the absence of the same mode using different fillers (fiberglass E-3-100 and KT-11-TOA) in the manufacture of various CM (honeycomb materials and fiberglass);
a long heat treatment cycle upon receipt of sotomaterials and a method of vacuum molding upon receipt of fiberglass (about 7 hours);
lack of a guarantee of obtaining high-quality products, especially with the press method of manufacturing fiberglass.

 The aim of the invention is to improve the quality of the curing of CM based on phenol-formaldehyde binder.

The goal is that in the known method of curing composite materials based on phenol-formaldehyde binder LBS-4, which includes stepwise heating of the components of the material and maintaining at the temperature of maximum curing of the sample, while the components are heated from room temperature to T 108-112 ^about With v ₁ = 0.8-1.2 ^about C / min, maintained at T for τ = 1.3-1.7 hours, and then heated to the temperature of maximum curing of the samples with a speed of v ₂ = = 1.3-1 7 ^C / min, wherein during the heating conducting Continuous measurement of electric conductivity values G and the tangent of its dielectric loss tg δ, and heating at a maximum curing temperature of the sample is stopped when the constant values of G and tgδ time. Thus, the claimed method meets the criteria of the invention of "novelty."

 Monitoring the curing process of the composite material by electrophysical parameters is known. But in the technological process of obtaining CMs based on the phenol-formaldehyde binder LBS-4, the curing process is not monitored, and has not been described anywhere.

A known method of curing KM based on phenol-formaldehyde binder SF-010 under the control of the electrophysical method of analysis. However, this mode is common only for CMs based on binding agent SF-010 and cannot be applied to CMs based on LBS-4, because even for one class of binders there is no single regime for all, because Each binder has its own specific properties due to the chemical composition. Known method for determining the gelation temperature when curing composites in which according to the analysis of gas evolution during gelation binder LBS 4-defined step isothermal temperature T = 110 ° ^C. However, this method is not conducted specific curing time of the binder LBS-4 and CM at its basis.

 The authors propose to obtain KM based on the LBS-4 binder according to the curing mode of the binder itself, to obtain a visually uniform material during curing, which is not described anywhere for KM based on LBS-4, monitoring the state of the material according to the electrophysical analysis method; heating rate; the heating time at temperature T (temperature of the isothermal step) and during the regime to the maximum curing temperature is also determined by the homogeneity of the binder, which is also unknown, and the final curing time is determined by establishing constant values of G and tg δ, confirming the curing depth by analysis of the degree of curing KM according to the proposed regime.

 A new, never described, mode of curing the phenol-formaldehyde binder LBS-4 is proposed, as a result of which a visually homogeneous product on a binder LBS-4 is obtained and visually homogeneous without warping, delamination, with a stable degree of cure, with improved mechanical properties of fiberglass based on it.

 The use of the curing regime under non-destructive testing of CMs based on the phenol-formaldehyde binder LBS-4 will reduce the heat treatment cycle ≈2 times compared to the prototype, which can significantly reduce labor and energy costs in the manufacture of CMs based on it.

 Based on the foregoing, it is concluded that the decision statement meets the criterion of "substantial differences".

PRI me R 1. Binder LBS-4 (GOST 901-78) in an amount of 10 ml is poured into an electrophysical cell, which is a high glass tube, where plane-parallel copper electrodes are inserted in the form of spatulas with a measuring electrode area of 1 cm ² and a distance between electrodes 10 mm. The electrodes are connected to an E-7-8 type meter with an operating frequency of (1000 ± 10) Hz.

Electrophysical sample cell 4 is dipped LBS-suspended in the middle of a thermostated oven, heated by a heating system from room temperature up to T = 110 ^{° C} at a speed of v ₁ = 1.0 ° ^C / min, kept sample cell binding at T = 110 ± 2 ^{° C} for τ = 1,5 h, then heated to a maximum curing temperature ^about 160 C at a rate v ₂ = 1.5 ° ^C / min. Moreover, during heating, a constant measurement of the electrical conductivity of the LBS-4 binder sample and the dielectric loss tangent is carried out using an E-7-8 type meter to which the cell wires are connected. Heating at maximum curing temperature of 160 ± 2 ^{° C} is stopped when the constant values of G and the values of tgδ time. In parallel, 10 ml of LBS-4 binder is placed in a glass bottle to visually assess the state of the sample during heating and after curing. The resulting product is visually homogeneous (table 1 experiment 10).

Similarly to this example of carrying out the optimum curing regime of the LBS-4 binder, a series of experiments was carried out to conduct the curing of the LBS-4 binder to develop conditions that did not visually cause material swelling at the shortest curing cycle (time), namely: the optimum temperature rise rate v ₁ , the temperature of the isotherm T, the exposure time on it and the heating rate v ₂ to the temperature of maximum cure.

As can be seen from the data in Table 1, a homogeneous material is obtained at the minimum boundary values of the heating rates v ₁ and v ₂ (table 1, experiment 7).

v ₁ = 0.8 ^about C / min, v ₂ = 1.3 ^about C / min
and at maximum boundary values of heating rates
v ₁ and v ₂ (table 1, experiment 11)
v ₁ = 1.2 ^about C / min v ₂ = 1.7 ^about C / min
A decrease or increase in heating rates from optimal by 0.5 ^° C / min (experiment 12.5 for v ₁ ) (experiment 9.15 for v ₂ ) causes swelling of the material.

Thus, the boundaries of the first heating rate v ₁ = 0.8-1.2 ^about C / min and the second v ₂ = 1.3-1.7 ^about C / min are set. Changing the temperature T from the optimum to ± 2 ° ^C / min (Run 7-11) does not alter the quality of the material - the product is homogeneous curing; increasing the temperature deviation ± 5 ^{° C} (experiment 6,16,13) causes swelling and the formation of air inclusions in the material. Thus, the limiting temperature limits of the isotherm T are (108-112) ^о С.

From a comparative analysis with an analogue and prototype, it is seen that heating is carried out with varying rates of rise to predetermined temperatures without holding at these temperatures, this mode of curing the binder even at a slow heating rate v ₁ to any temperature T, for example 100-110 ^о С a further increase in speed v ₂ (as can be seen from table 1, experiment 1-2) causes the formation of caps of the binder bubbles. When the exposure time is 0.5 h and other conditions being equal (experiment 3, table 1), the expansion becomes more uniform and decreases with increasing exposure time to 1 hour (experiment 4, table), the material becomes slightly expanded with increasing exposure time up to 1.5 hours (experiment 5, table 1), which leads to the decision on the need for a stepwise regime with isothermal exposure to T isotherms. A change in the exposure time at the temperature of the isotherm T by ± 0.2 h does not affect the quality of the cured product (experiment 7.11), with a change in the exposure time by ± 0.5 h (experiment 8.14), the material swells. Thus, the boundaries of the exposure time to T isotherms can take 1.3-1.7 hours

Optimal conditions for conducting mode (Run 8) have been chosen for convenience of reference with the experiment: heating at a speed of v ₁ = 1.0 ^{° C} / min to T = ^{110 °} C, holding at T = 110 ± 2 ^{° C} for τ = 1.5 h, further heating v ₂ = 1.5 ^о С / min to Т = 160 ^о С with exposure at 160 ± 2 ^о С to constant values of G and tan δ. In this optimized mode, stepwise heating of the components of the composite material based on LBS-4 is carried out.

PRI me R 2. The object of the study was the factory run on the basis of phenol-formaldehyde resin LBS-4 and filler made of silica finished fiberglass KT-11-TOA. From this prepreg, a CTKT-B fiberglass panel is made of six layers of prepreg laid in one direction (base to base), size 220x280 mm. The brass electrodes of the measuring cell are installed between the 1st and 2nd and 5-6th layers of the prepreg and connected to the meter E-7-8. A temperature sensor is installed near the electrodes. Temperature control in the sample is carried out using a KSP-4 recording and recording device; control of electrophysical parameters is performed on E-7-8. The panel is cured by vacuum molding using a bag of balloon fabric "500" according to the established mode. To do this, the prepreg panel blank is placed in a furnace, heat treated using a heating system that allows you to raise the temperature at a given speed and create isothermal heat treatment conditions in the furnace. Then prepreg panel tested by heating from room temperature to a temperature T = 110 ^{° C} at a speed of v ₁ = 1.0 ° ^C / min, maintained at T = 110 ± 2 ^{° C} for τ = 1,5 hours, after which heated to a maximum curing temperature ^about 160 samples at a rate of ₂ v = 1.5 ° ^C / min, wherein heating is carried out during continuous measurement of conductivity values G and the tangent of its dielectric loss tg δ, and heating at a maximum curing temperature of 160 ± 2 ^o C the sample is stopped after 1 h when a constant value of G and tanδ in time. The total heat treatment time was 3 h 40 min. Then, the preform is cooled under vacuum to 50 ° ^C. After curing, the plastic samples obtained were examined for determination of the degree of cure by alcohol Soxhlet extraction and the mechanical properties. The data are shown in table.2 in comparison with the basic mechanical characteristics of the prototype.

From the table. 2 it can be seen that, according to the main mechanical indicators, τ _sr , τ _{of the} degree of curing and the heat treatment time, the proposed regime significantly exceeds the known quality: thus, the compressive strength of fiberglass increases by 4.3 times; accordingly, the bending strength of 5.4 times, the degree of cure by 4%, and the acceleration of the process by 2 times compared with the prototype.

PRI me R 3. The proposed mode was also tested during heat treatment of blanks honeycomb panels based on fiberglass E-3-100 and a binder LBS-4. For this, two industrial blanks of honeycomb panels prepared according to (1) were investigated according to the known (1) and proposed modes. In the case of the proposed mode, the curing process was carried out under the control of the dielectric analysis method, for which an electrophysical cell in the form of a clamping clothespin with a measuring electrode diameter of 4 mm was fixed on the cell wall, consisting of 2 sheets of E-3-100 fiberglass (5 mm in size) impregnated LBS-binder 4, and then the cell was heated from room temperature according to the proposed mode at a speed of v ₁ = 1.0 ° ^C / min up to T = 100 ^{° C} with exposure at 110 ± 2 ^{° C} for τ = 1,5 hours, further heating at a speed of v ₂ = 1.5 ° ^C / min to ^{160 °} C in Derzhko at 160 ± 2 ^{° C} until constant values of G and tgδ.

The total heat treatment time was 3 h 40 min. Then cooling was performed ^to 50 ° C in an oven.

For comparison performed curing the second workpiece honeycomb panels according to mode (1) heating from room temperature to 80 ° ^C for 2 hours, raising to a temperature of ^{160 °} C at a rate not exceeding ^{20 °} C / min and held at 160 ^{° C} for 1 h. The total heat treatment time was 7 hours. then the produced honeycomb panels cooling ^to 50 ° C in an oven, the samples were cured according to the known and proposed regimens were tested for mechanical properties, which are listed in Table 3. As can be seen from Table 3, the data of mechanical tests of samples of cellular material based on the LBS-4 binder and E-3-100 fiberglass, obtained according to the well-known mode for honeycomb panels (1) and optimized mode, show a 10-15% better result in the case of use of the proposed regime. This shows the advantage of the new technology over the existing one not only in reducing the curing cycle by 2.0 times, but also in the quality of the obtained cellular materials.

Claims (1)

METHOD FOR CURING COMPOSITE MATERIALS BASED ON Phenolformaldehyde Binder LBS-4 by stepwise heating of the components of the material and holding at the temperature of maximum curing of the sample, characterized in that, in order to improve the quality of the material, the components are heated from room temperature to 108 - 112 ^o С with speed V ₁ = 0.8 - 1.2 deg./min, withstand 1.3 - 1.7 hours, then heated to a temperature of maximum curing of the samples with a speed of V ₂ = 1.3 - 1.7 deg. / Min with constant measurement of electrical conductivity G and tangent SFA dielectric loss tgδ, and heating at a maximum curing temperature of the sample is stopped upon reaching constant values of G and tgδ time.

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