CN113181848A - Melamine resin microcapsule, preparation method thereof and composite material prepared from melamine resin microcapsule - Google Patents
Melamine resin microcapsule, preparation method thereof and composite material prepared from melamine resin microcapsule Download PDFInfo
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- 239000003094 microcapsule Substances 0.000 title claims abstract description 106
- 229920000877 Melamine resin Polymers 0.000 title claims abstract description 81
- 239000004640 Melamine resin Substances 0.000 title claims abstract description 61
- 239000002131 composite material Substances 0.000 title claims abstract description 34
- 238000002360 preparation method Methods 0.000 title claims abstract description 23
- 239000003822 epoxy resin Substances 0.000 claims abstract description 36
- 229920000647 polyepoxide Polymers 0.000 claims abstract description 36
- JDSHMPZPIAZGSV-UHFFFAOYSA-N melamine Chemical compound NC1=NC(N)=NC(N)=N1 JDSHMPZPIAZGSV-UHFFFAOYSA-N 0.000 claims abstract description 20
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonia chloride Chemical compound [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 claims abstract description 18
- 238000000034 method Methods 0.000 claims abstract description 15
- NWGKJDSIEKMTRX-AAZCQSIUSA-N Sorbitan monooleate Chemical compound CCCCCCCC\C=C/CCCCCCCC(=O)OC[C@@H](O)[C@H]1OC[C@H](O)[C@H]1O NWGKJDSIEKMTRX-AAZCQSIUSA-N 0.000 claims abstract description 12
- 235000010482 polyoxyethylene sorbitan monooleate Nutrition 0.000 claims abstract description 12
- 229920000053 polysorbate 80 Polymers 0.000 claims abstract description 12
- GSEJCLTVZPLZKY-UHFFFAOYSA-N Triethanolamine Chemical compound OCCN(CCO)CCO GSEJCLTVZPLZKY-UHFFFAOYSA-N 0.000 claims abstract description 9
- 235000019270 ammonium chloride Nutrition 0.000 claims abstract description 9
- WSFSSNUMVMOOMR-NJFSPNSNSA-N methanone Chemical compound O=[14CH2] WSFSSNUMVMOOMR-NJFSPNSNSA-N 0.000 claims abstract description 7
- 230000008569 process Effects 0.000 claims abstract description 6
- 238000003756 stirring Methods 0.000 claims description 28
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 24
- 238000010438 heat treatment Methods 0.000 claims description 20
- 239000000839 emulsion Substances 0.000 claims description 19
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 claims description 12
- 239000007864 aqueous solution Substances 0.000 claims description 10
- 239000008367 deionised water Substances 0.000 claims description 10
- 229910021641 deionized water Inorganic materials 0.000 claims description 10
- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 claims description 9
- 238000002156 mixing Methods 0.000 claims description 9
- 239000003795 chemical substances by application Substances 0.000 claims description 7
- 238000001035 drying Methods 0.000 claims description 6
- 238000001914 filtration Methods 0.000 claims description 6
- 239000008098 formaldehyde solution Substances 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 6
- 239000003208 petroleum Substances 0.000 claims description 6
- 238000005406 washing Methods 0.000 claims description 6
- 239000002994 raw material Substances 0.000 claims description 3
- 238000012695 Interfacial polymerization Methods 0.000 claims description 2
- 239000002775 capsule Substances 0.000 claims description 2
- 239000011248 coating agent Substances 0.000 claims description 2
- 238000000576 coating method Methods 0.000 claims description 2
- 230000000379 polymerizing effect Effects 0.000 claims description 2
- 238000013019 agitation Methods 0.000 claims 1
- 239000000463 material Substances 0.000 abstract description 14
- 238000011065 in-situ storage Methods 0.000 abstract description 3
- 238000006116 polymerization reaction Methods 0.000 abstract description 3
- 239000003921 oil Substances 0.000 description 46
- 239000002245 particle Substances 0.000 description 15
- 239000003995 emulsifying agent Substances 0.000 description 7
- 239000011162 core material Substances 0.000 description 6
- 239000004593 Epoxy Substances 0.000 description 5
- 239000000314 lubricant Substances 0.000 description 5
- 230000001050 lubricating effect Effects 0.000 description 5
- 239000010687 lubricating oil Substances 0.000 description 5
- 229920005989 resin Polymers 0.000 description 5
- 239000011347 resin Substances 0.000 description 5
- 229910000831 Steel Inorganic materials 0.000 description 4
- 239000002253 acid Substances 0.000 description 4
- 230000007547 defect Effects 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 239000011259 mixed solution Substances 0.000 description 4
- 239000007787 solid Substances 0.000 description 4
- 239000010959 steel Substances 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 238000004945 emulsification Methods 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 238000005461 lubrication Methods 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- 230000002035 prolonged effect Effects 0.000 description 2
- HECLRDQVFMWTQS-RGOKHQFPSA-N 1755-01-7 Chemical compound C1[C@H]2[C@@H]3CC=C[C@@H]3[C@@H]1C=C2 HECLRDQVFMWTQS-RGOKHQFPSA-N 0.000 description 1
- 229920001807 Urea-formaldehyde Polymers 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- PNPBGYBHLCEVMK-UHFFFAOYSA-N benzylidene(dichloro)ruthenium;tricyclohexylphosphanium Chemical compound Cl[Ru](Cl)=CC1=CC=CC=C1.C1CCCCC1[PH+](C1CCCCC1)C1CCCCC1.C1CCCCC1[PH+](C1CCCCC1)C1CCCCC1 PNPBGYBHLCEVMK-UHFFFAOYSA-N 0.000 description 1
- 239000002041 carbon nanotube Substances 0.000 description 1
- 229910021393 carbon nanotube Inorganic materials 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000001804 emulsifying effect Effects 0.000 description 1
- 238000005538 encapsulation Methods 0.000 description 1
- 229910021389 graphene Inorganic materials 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 239000011984 grubbs catalyst Substances 0.000 description 1
- 239000013003 healing agent Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000010907 mechanical stirring Methods 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- ODGAOXROABLFNM-UHFFFAOYSA-N polynoxylin Chemical compound O=C.NC(N)=O ODGAOXROABLFNM-UHFFFAOYSA-N 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
- B01J13/02—Making microcapsules or microballoons
- B01J13/06—Making microcapsules or microballoons by phase separation
- B01J13/14—Polymerisation; cross-linking
- B01J13/16—Interfacial polymerisation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
- B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Dispersion Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Oral & Maxillofacial Surgery (AREA)
- Thermal Sciences (AREA)
- Manufacturing Of Micro-Capsules (AREA)
Abstract
The invention discloses a melamine resin microcapsule, a preparation method thereof and a composite material prepared by the melamine resin microcapsule, wherein the melamine resin microcapsule is prepared by in-situ polymerization of 3-5 parts of formaldehyde, 5-10 parts of melamine, 0.1-0.5 part of triethanolamine, 0.1-1 part of tween 80, 0.2-1.5 parts of span 80, 6-20 parts of white oil and 0.5-1 part of ammonium chloride under specific process conditions, and the obtained microcapsule has high oil content, can meet the use requirement of a self-lubricating composite material, reduce the friction coefficient of an epoxy resin base material, remarkably improve the self-lubricating property of the material and effectively prolong the service life of the product.
Description
Technical Field
The invention belongs to the technical field of materials, and particularly relates to a melamine resin microcapsule, a preparation method thereof and a composite material prepared by the melamine resin microcapsule.
Background
The concept of microcapsules originates from the biochemical and pharmaceutical fields. In recent years, microcapsules having a lubricating function have received much attention in the field of composite materials. White et al in the united states first proposed the preparation of first generation microcapsules with urea-formaldehyde as the shell and dicyclopentadiene/Grubbs catalyst as the healing agent. Since then, microcapsules have rapidly developed in the field of composites.
Epoxy resin has the advantages of high adhesion, high and low temperature resistance, chemical corrosion resistance, low shrinkage, easiness in manufacturing and the like, but the application of the epoxy resin in many fields is limited due to the defect of poor friction and wear performance. Therefore, many researchers have conducted studies to improve tribological properties of epoxy-based composites. The improvement method is mainly to add solid lubricants or solid particles such as carbon nano tubes, graphite, graphene, alumina, silicon dioxide and the like into a resin substrate to improve the antifriction and wear resistance, but the friction coefficient of the solid lubricants is generally 50-100 times larger than that of liquid lubricants, and the defects of large dosage, difficult dispersion, high price and the like exist at the same time. The use of liquid lubricants to lubricate friction surfaces is another method for improving the tribological properties of epoxy resin materials, however, the molecular structure of the lubricant and the epoxy resin matrix is very different, which results in the lubricant having a microphase separated structure in the composite material and is not suitable for oil-sensitive materials or oil pollution-free operation conditions, so that the application of the liquid lubricants may be limited and the lubricating effect may be affected.
In view of this, the provision of the microcapsule-coated liquid lubricating oil greatly improves the existing state of the lubricating material in the polymer matrix material, so that the composite material shows the characteristic of boundary lubrication in the lubricating process, avoids various defects of an external lubricating system, and greatly enriches and widens the application field of the polymer-based composite material. For example, chinese patent CN 110628182 a discloses an epoxy resin cage material and a method for preparing the same, which is to add a liquid lubricant oil-containing microcapsule and a solid lubricant into the epoxy resin cage material and then improve the tribological properties of the epoxy resin cage material through the common lubrication action of the two. However, the existing preparation process of the oil-containing microcapsule generally has the problems of low stability, complex preparation process, difficult forming of the microcapsule structure and low encapsulation rate, and related preparation processes are yet to be further researched, developed and improved.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a melamine resin microcapsule, a preparation method thereof and a composite material prepared by the melamine resin microcapsule, wherein the preparation process of the microcapsule is simple, the obtained microcapsule has stable property and high preparation efficiency, the microcapsule has higher oil content, and the tribological property of the composite material can be improved after the microcapsule is applied to the preparation of an epoxy resin composite material, so that the self-lubricating effect is realized, and the service life of a product is prolonged.
The technical scheme of the invention is as follows: a preparation method of melamine resin microcapsules specifically comprises the following steps:
(1) preparing raw materials in parts by weight: comprises 3-5 parts of formaldehyde, 5-10 parts of melamine, 0.1-0.5 part of triethanolamine, 0.1-1 part of tween 80, 0.2-1.5 parts of span 80, 6-20 parts of white oil and 0.5-1 part of ammonium chloride;
(2) preparation of prepolymer aqueous solution: mixing a formaldehyde solution and melamine in corresponding parts by weight, mechanically stirring until the melamine is completely dissolved, adjusting the pH to be 8-9 by using triethanolamine, heating to 70-80 ℃, and then preserving heat for 60min to obtain a viscous and transparent melamine resin prepolymer;
(3) preparation of the emulsion: adding Tween 80 in a corresponding weight part into deionized water, mechanically stirring to obtain a water phase, adding span 80 in a corresponding weight part into white oil in a corresponding part, stirring to obtain an oil phase, mixing the oil phase and the water phase, and mechanically stirring to disperse the white oil to form an emulsion;
(4) preparing melamine resin microcapsules by an interfacial polymerization method: dropwise adding the melamine resin prepolymer prepared in the step (2) into the emulsion prepared in the step (3), adjusting the pH value to weak acidity by using ammonium chloride, raising the temperature to 75-85 ℃, preserving the temperature for 2-4 h, polymerizing the melamine resin prepolymer into a capsule wall, and coating white oil to form a melamine resin microcapsule;
(5) and (3) post-treatment: and (4) repeatedly washing the microcapsules obtained in the step (3) by using petroleum ether, filtering, and drying at 50-60 ℃.
In the preparation process of the microcapsule, the key step of the success of the preparation of the microcapsule is to emulsify the white oil to form stable emulsion. The HLB values required by different core materials emulsified into stable emulsion are different, and the optimal HLB value for emulsifying the white oil can be achieved by adjusting the adding parts of the Tween 80 and the span 80 so as to obtain the stable emulsion and facilitate the subsequent preparation and forming of the microcapsules.
Further, the rotation speed of mechanical stirring in the step (2) and the step (3) is 300-1000 rpm.
The melamine resin microcapsule prepared by the in-situ polymerization method has the wall material of melamine resin polymerized by formaldehyde and melamine, and the core material of white oil. Further, the mass percentage of the white oil in the microcapsules is 60-85%, and the average diameter of the microcapsules is 20-60 mu m; the wall thickness of the microcapsule is 0.7-1.5 mu m.
When the melamine resin microcapsule/epoxy resin composite material prepared from the melamine resin microcapsules is used, the melamine resin microcapsules, the epoxy resin and the curing agent are uniformly mixed according to a certain proportion, then the mixture is placed into a mold, the mold is heated to 70-90 ℃, and the temperature is kept for 3-8 hours, so that the melamine resin microcapsule/epoxy resin composite material can be obtained.
Furthermore, the melamine resin microcapsule accounts for 3-15% by mass, and the curing agent accounts for 2-10% by mass.
1. According to the invention, an oil-in-water emulsification method is adopted, and the proportion and emulsification process of the emulsifier Tween 80 and span 80 are adjusted, so that the optimal HLB value suitable for white oil emulsification can be reached after the water phase and the oil phase are mixed, the emulsion state is stable, the rapid molding of the melamine resin microcapsules is facilitated, and the preparation speed is improved;
2. according to the invention, an in-situ polymerization method is adopted, a shell is formed on the surface of a stable emulsion, and the melamine resin microcapsule is obtained by adjusting the raw material ratio and the process parameters, wherein the melamine resin microcapsule has an oil content of 60-85% and meets the requirements of a self-lubricating composite material;
3. the microcapsule prepared by the method disclosed by the application is added into epoxy resin to prepare the epoxy resin composite material, so that the epoxy resin composite material has a self-lubricating function under the abrasion condition, the friction coefficient is reduced, and the service life of a product can be prolonged.
Drawings
FIG. 1 is a schematic structural view of a melamine resin microcapsule;
fig. 2 is an SEM image of the melamine resin microcapsules prepared in example 1.
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings, but not limited thereto, and any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be covered by the protection scope of the present invention.
Example 1:
(1) dissolving 5 parts of melamine in 3 parts of formaldehyde solution with the mass concentration of 37%, adding deionized water, mechanically stirring at the speed of 400 r/min until the melamine is completely dissolved, adjusting the pH value to 9 by using 0.1 part of triethanolamine, heating to 80 ℃, and preserving heat for 1 hour to form melamine resin prepolymer aqueous solution;
(2) adding 0.28 part of emulsifier Tween 80 into 100 mL of deionized water, mechanically stirring at 400 r/min to obtain a water phase, adding 0.22 part of span 80 into 10 parts of white oil, stirring for 30 minutes to obtain an oil phase, mixing the oil phase and the water phase, and stirring for 30 minutes to disperse the white oil to form a stably-dispersed emulsion;
(3) dropwise adding the melamine resin prepolymer aqueous solution into the emulsion at a slow speed, adding ammonium chloride, adjusting the pH value of the mixed solution to weak acid, heating to 80 ℃, heating for 30-60 min, and preserving heat for 2-4 h.
(4) And repeatedly washing the microcapsules by using petroleum ether, filtering, and drying at 50 ℃ to obtain the microcapsules with the particle size of about 40-60 mu m.
In this example, the composition of the finished microcapsule is as follows: the wall material is melamine resin polymerized by melamine and formaldehyde, the core material is white oil, the wall thickness of the microcapsule is about 1 μm, and the mass of the white oil in the microcapsule accounts for about 65% of the mass of the microcapsule. The obtained microcapsule has smooth surface, average particle size of about 52 μm and narrow particle size distribution range, and the morphology and particle size range of the microcapsule are favorable for dispersing in epoxy resin.
Adding 3 wt.% of microcapsule into epoxy resin, uniformly stirring the resin and a curing agent, pouring into a mold, heating to 80 ℃, preserving heat for 5 hours, and curing to obtain the melamine resin microcapsule/epoxy resin composite material.
And measuring the friction coefficient of the surface of the composite material by using a friction wear testing machine, wherein the friction couple is a steel ball with the diameter of 5 mm during measurement, the load is 20N, the rotating speed is 0.1 m/s, the rotating radius is 4 mm, and finally the measured friction coefficient is 0.073. Under the same experimental conditions, the coefficient of friction of the neat epoxy was 0.225. Therefore, compared with pure epoxy resin without melamine resin microcapsules, the self-lubricating property of the composite material added with 3% of oil-containing microcapsules is remarkably improved (the friction coefficient is reduced by 67%).
Example 2
(1) Dissolving 6 parts of melamine in 3.6 parts of formaldehyde solution with the mass concentration of 37%, adding deionized water, mechanically stirring at the speed of 600 r/min until the melamine is completely dissolved, adjusting the pH value to 9 by using 0.2 part of triethanolamine, heating to 70 ℃, and preserving heat for 1 hour to form melamine resin prepolymer aqueous solution;
(2) adding 0.56 part of emulsifier Tween 80 into 100 mL of deionized water to obtain a water phase, mechanically stirring at 600 r/min, adding 0.44 part of emulsifier span 80 into 20 parts of white oil, continuously stirring to obtain an oil phase, mixing the water phase and the oil phase, and stirring for 30 minutes to disperse the white oil to form a stably-dispersed emulsion;
(3) dropwise adding a melamine resin prepolymer aqueous solution into the emulsion at a slow speed, adding ammonium chloride, adjusting the pH value of the mixed solution to weak acid, heating to 80 ℃, heating for 30-60 min, and keeping the temperature for 2-4 h;
(4) and repeatedly washing the microcapsules by using petroleum ether, filtering, and drying at 50 ℃ to obtain the microcapsules with the particle size of about 30-40 microns.
In this example, the composition of the finished microcapsule is as follows: the wall material is melamine resin polymerized by melamine and formaldehyde, the core material is white oil, the wall thickness of the microcapsule is about 1.2 mu m, and the mass of the white oil in the microcapsule accounts for about 83 percent of the mass of the microcapsule. The obtained microcapsule has smooth surface, average particle size of about 35 μm, narrow particle size distribution range, and good dispersibility in epoxy resin.
Adding 9 wt.% of microcapsule into epoxy resin, uniformly stirring the resin and a curing agent, pouring into a mold, heating to 80 ℃, preserving heat for 5 hours, and curing to form the melamine resin microcapsule/epoxy resin composite material.
And measuring the friction coefficient of the surface of the composite material by using a friction wear testing machine, wherein the friction couple is a steel ball with the diameter of 5 mm during measurement, the load is 20N, the rotating speed is 0.1 m/s, the rotating radius is 4 mm, and finally the measured friction coefficient is 0.085. Under the same experimental conditions, the coefficient of friction of the neat epoxy was 0.225. Therefore, compared with pure epoxy resin without oil-containing microcapsules, the self-lubricating property of the epoxy resin composite material with 9% by weight of melamine resin microcapsules is remarkably improved (the friction coefficient is reduced by 60%).
Example 3
(1) Dissolving 6 parts of melamine in 3.6 parts of formaldehyde solution with the mass concentration of 37%, adding deionized water, mechanically stirring at the speed of 400 r/min until the melamine is completely dissolved, adjusting the pH value to 9 by using 0.2 part of triethanolamine, heating to 70 ℃, and preserving heat for 1 hour to form melamine resin prepolymer aqueous solution;
(2) adding 0.42 part of emulsifier Tween 80 into 100 mL of deionized water to obtain a water phase, mechanically stirring at 400 r/min, adding 0.33 part of span 80 into 15 parts of white oil, stirring to obtain an oil phase, mixing the water phase with an oil tank, and stirring for 30 minutes to disperse the white oil to form a stably-dispersed emulsion;
(3) dropwise adding the melamine resin prepolymer aqueous solution into the emulsion at a slow speed, adding ammonium chloride, adjusting the pH value of the mixed solution to weak acid, heating to 80 ℃, heating for 30-60 min, and preserving heat for 2-4 h.
(4) And repeatedly washing the microcapsules by using petroleum ether, filtering, and drying at 50 ℃ to obtain the microcapsules with the particle size of about 40-60 mu m.
In this example, the composition of the finished microcapsule is as follows: the wall material is melamine resin polymerized by melamine and formaldehyde, the core material is white oil, the wall thickness of the microcapsule is about 0.9 μm, and the mass of the white oil in the microcapsule accounts for about 75% of the mass of the microcapsule. The obtained microcapsule has smooth surface, average particle size of about 50 μm, narrow particle size distribution range, and good dispersibility in epoxy resin.
Adding 6 wt.% of microcapsule into epoxy resin, uniformly stirring the resin and a curing agent, pouring into a mould, heating to 80 ℃, preserving heat for 5 hours, and curing to form the melamine resin microcapsule/epoxy resin composite material.
The friction coefficient of the surface of the composite material is measured by using a friction wear testing machine, the friction couple is a steel ball with the diameter of 5 mm during measurement, the load is 20N, the rotating speed is 0.1 m/s, the rotating radius is 4 mm, and finally the measured friction coefficient is 0.075. Under the same experimental conditions, the coefficient of friction of the neat epoxy was 0.225. Therefore, compared with pure epoxy resin without the oil-containing microcapsule, the composite material with the oil-containing microcapsule added in the mass fraction of 6% has good self-lubricating performance (the friction coefficient is reduced by 67%).
Comparative example
(1) Dissolving 5 parts of melamine in 3 parts of formaldehyde solution with the mass concentration of 37%, adding deionized water, mechanically stirring at 500 r/min until the melamine is completely dissolved, adjusting the pH value to 9 by using 0.1 part of triethanolamine, heating to 70 ℃, and preserving heat for 1 hour to form melamine resin prepolymer aqueous solution;
(2) adding 1.5 parts of emulsifier Tween 80 into 100 mL of deionized water, mechanically stirring at 500 r/min to obtain a water phase, adding 1.8 parts of span 80 into 10 parts of white oil, stirring to obtain an oil phase, mixing the water phase and the oil phase, and stirring for 30 minutes to disperse the white oil to form a stably-dispersed emulsion;
(3) dropwise adding the melamine resin prepolymer aqueous solution into the emulsion at a slow speed, adding ammonium chloride, adjusting the pH value of the mixed solution to weak acid, heating to 80 ℃, heating for 30-60 min, and preserving heat for 2-4 h.
(4) And repeatedly washing the microcapsules by using petroleum ether, filtering, and drying at 50 ℃ to obtain the microcapsules with the particle size of about 35-55 microns.
In the comparative example, because the proportion of the emulsifier Tween 80 and span 80 is not added according to the established requirement, the yield of the microcapsule is 20 percent under the proportion; the composition of the finished microcapsule product is as follows: the wall material is melamine resin polymerized by melamine and formaldehyde, the core material is white oil, the wall thickness of the microcapsule is about 0.9 μm, and the mass of the white oil in the microcapsule accounts for about 53 percent of the mass of the microcapsule. The obtained microcapsule has smooth surface, average particle size of about 43 μm and narrow particle size distribution range, and the morphology and particle size range of the microcapsule are favorable for dispersing in epoxy resin.
Adding 6 wt.% of microcapsule into epoxy resin, uniformly stirring the resin and a curing agent, pouring into a mold, heating to 80 ℃, preserving heat for 5 hours, and curing to obtain the melamine resin microcapsule/epoxy resin composite material.
And measuring the friction coefficient of the surface of the composite material by using a friction wear testing machine, wherein the friction couple is a steel ball with the diameter of 5 mm during measurement, the load is 20N, the rotating speed is 0.1 m/s, the rotating radius is 4 mm, and finally the measured friction coefficient is 0.18. Under the same experimental conditions, the coefficient of friction of the neat epoxy was 0.225. Therefore, compared with pure epoxy resin, the self-lubricating performance of the epoxy resin composite material added with the melamine resin microcapsule with the mass fraction of 6% is not remarkably improved (the friction coefficient is reduced by 20%).
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (5)
1. A preparation method of melamine resin microcapsules is characterized by comprising the following steps:
(1) preparing raw materials in parts by weight: comprises 3-5 parts of formaldehyde, 5-10 parts of melamine, 0.1-0.5 part of triethanolamine, 0.1-1 part of tween 80, 0.2-1.5 parts of span 80, 6-20 parts of white oil and 0.5-1 part of ammonium chloride;
(2) preparation of prepolymer aqueous solution: mixing a formaldehyde solution and melamine in corresponding parts by weight, mechanically stirring until the melamine is completely dissolved, adjusting the pH to be 8-9 by using triethanolamine, heating to 70-80 ℃, and then preserving heat for 60min to obtain a viscous and transparent melamine resin prepolymer;
(3) preparation of the emulsion: adding Tween 80 in a corresponding weight part into deionized water, mechanically stirring to obtain a water phase, adding span 80 in a corresponding weight part into white oil in a corresponding part, stirring to obtain an oil phase, mixing the oil phase and the water phase, and mechanically stirring to disperse the white oil to form an emulsion;
(4) preparing melamine resin microcapsules by an interfacial polymerization method: dropwise adding the melamine resin prepolymer prepared in the step (2) into the emulsion prepared in the step (3), adjusting the pH value to weak acidity by using ammonium chloride, raising the temperature to 75-85 ℃, preserving the temperature for 2-4 h, polymerizing the melamine resin prepolymer into a capsule wall, and coating white oil to form a melamine resin microcapsule;
(5) and (3) post-treatment: and (4) repeatedly washing the microcapsules obtained in the step (3) by using petroleum ether, filtering, and drying at 50-60 ℃.
2. The process for producing melamine resin microcapsules according to claim 1, wherein the rotation speed of the mechanical agitation in the step (2) and the step (3) is 300 to 1000 rpm.
3. The melamine resin microcapsule prepared by the preparation method of the melamine resin microcapsule according to any one of claims 1 to 2, wherein the mass percentage of the white oil in the microcapsule is 60-85%, and the average diameter of the microcapsule is 20-60 μm; the wall thickness of the microcapsule is 0.7-1.5 mu m.
4. The melamine resin microcapsule/epoxy resin composite material prepared from the melamine resin microcapsules according to claim 3, wherein the composite material is prepared by uniformly mixing the epoxy resin, the melamine resin microcapsules with the mass fraction of 3-15% and the curing agent with the mass fraction of 2-10%, and then placing the mixture into a mold for heating and curing.
5. The melamine resin microcapsule/epoxy resin composite material as claimed in claim 4, wherein the temperature for heating and curing is 70-90 ℃ and the holding time is 3-8 h.
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