WO2015074348A1 - 环氧微胶囊的制备方法 - Google Patents

环氧微胶囊的制备方法 Download PDF

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WO2015074348A1
WO2015074348A1 PCT/CN2014/071991 CN2014071991W WO2015074348A1 WO 2015074348 A1 WO2015074348 A1 WO 2015074348A1 CN 2014071991 W CN2014071991 W CN 2014071991W WO 2015074348 A1 WO2015074348 A1 WO 2015074348A1
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epoxy
preparing
melamine resin
emulsifier
microcapsule according
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PCT/CN2014/071991
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English (en)
French (fr)
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朱光明
吕乐阳
汤皎宁
邢峰
董必钦
王险峰
韩宁旭
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深圳大学
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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
    • B01J13/18—In situ polymerisation with all reactants being present in the same phase
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B20/00—Use of materials as fillers for mortars, concrete or artificial stone according to more than one of groups C04B14/00 - C04B18/00 and characterised by shape or grain distribution; Treatment of materials according to more than one of the groups C04B14/00 - C04B18/00 specially adapted to enhance their filling properties in mortars, concrete or artificial stone; Expanding or defibrillating materials
    • C04B20/10—Coating or impregnating
    • C04B20/1018—Coating or impregnating with organic materials
    • C04B20/1029—Macromolecular compounds
    • C04B20/1037—Macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B40/00—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability
    • C04B40/06—Inhibiting the setting, e.g. mortars of the deferred action type containing water in breakable containers ; Inhibiting the action of active ingredients
    • C04B40/0633—Chemical separation of ingredients, e.g. slowly soluble activator

Definitions

  • the invention relates to the field of self-repairing concrete, in particular to a preparation method of microcapsule repairing agent in microcapsule self-repairing concrete.
  • the self-repairing concrete pre-embeds the repairing agent in the concrete.
  • the repairing agent is released and the crack is repaired by itself.
  • a preferred method of embedding a repairing agent in concrete is to microencapsulate it, and add it together with the coarse and fine aggregates during cement pulping. After pouring, the microcapsules are buried in the concrete member and become a latent type. Repair agent.
  • Epoxy resin has good adhesion to concrete, and has low shrinkage and stable performance when cured. Long storage period has become the most commonly used concrete organic restorative agent. However, it is not easy to microencapsulate epoxy resin. This is mainly because the epoxy resin is relatively viscous, the polarity of the molecule is large, the reactivity is high, and it is not easy to be emulsified. It is easy to react with the precursor of the wall material during the formation of the microcapsule. , leading to demulsification and lower coating efficiency.
  • microcapsules have been widely used in many fields such as food, medicine, cosmetics, textiles, feed, electronic ink, phase change energy storage, etc.
  • the technology is mature and the preparation methods are numerous, but the mature method for preparing epoxy resin microcapsules Not much.
  • epoxy microcapsules using urea-formaldehyde resin as the wall material are generally used in the prior art, and are generally prepared by in-situ polymerization.
  • the in-situ polymerization mechanism of urea-formaldehyde resin is complicated, and the morphology of urea-formaldehyde/epoxy microcapsules is difficult to control, and has not yet been commercialized.
  • the melamine resin is also an amino resin, but the melamine resin is more likely to form a wall material.
  • urea aldehyde is often modified by adding an appropriate amount of melamine to obtain microcapsules of urea-formamide composite wall material, which greatly improves the coating efficiency. This is because melamine reacts more readily with formaldehyde than urea to form a bulk-structured polymer that accelerates the deposition of the polymer at the O/W interface to form the wall of the capsule.
  • microcapsules using pure melamine resin as the wall material have been widely used in pressure-sensitive copying paper (the core material is a dye), and red phosphorus microcapsules coated with melamine resin are also often used as a flame retardant.
  • the concrete itself is a porous structure, the microcapsule repair agent is too small to carry a low load, the capsule wall is not easily broken, and the repair efficiency is low. It is generally desirable that the microcapsules used for self-healing concrete have a particle size of 50 microns or more. Microcapsules with pure melamine resin as the wall material usually have a small particle size of about 5 microns, which is not suitable for self-repairing concrete.
  • the invention aims to provide a preparation method of an epoxy microcapsule capable of preparing a melamine resin having a large particle diameter as a wall material, and the microcapsule which uses a melamine resin as a wall material in the prior art generally has a small particle size.
  • the invention is achieved by the method of preparing an epoxy microcapsule having a larger particle diameter using a melamine resin as a wall material by an in-situ polymerization method, and the preparation method of the epoxy microcapsule comprises the steps of:
  • an epoxy resin to an aqueous solution of an emulsifier to obtain an epoxy emulsion, the emulsifier comprising polyvinyl alcohol;
  • the pH of the epoxy emulsion is adjusted to 4.5 to 5.5, and then the melamine resin prepolymer is added dropwise, and the melamine resin obtained by in-situ polymerization is used as a wall material epoxy microcapsule.
  • the invention provides a method for preparing epoxy microcapsules having a larger particle diameter using a melamine resin as a wall material by an in-situ polymerization method, and the obtained microcapsules can be applied to self-repairing concrete.
  • the present invention employs polyvinyl alcohol (PVA) as an emulsifier.
  • PVA polyvinyl alcohol
  • the polyvinyl alcohol does not react with the epoxy resin of the core material, and the dispersion property does not change greatly with the change of temperature and pH value, so that the coating efficiency and effect are better.
  • PVA has a relatively low emulsifying ability, and its emulsification is relatively stable under heating conditions and a low pH liquid environment.
  • PVA is a nonionic surfactant, which has good hydrophilicity and poor lipophilicity.
  • PVA can be stably adsorbed on the surface of epoxy emulsion droplets, does not desorb due to changes in temperature and pH, and can induce cross-linking polymerization of melamine resin at the water/oil interface to form a capsule wall.
  • FIG. 1 is a schematic view of an electron microscope of an epoxy resin microcapsule provided by a first embodiment of the present technical solution.
  • FIG. 2 is a schematic view of an electron microscope of an epoxy resin microcapsule provided by a second embodiment of the present technical solution.
  • Fig. 3 is a schematic view showing an electron microscope of a microcapsule provided by a comparative example of the present invention.
  • a method for preparing an epoxy microcapsule comprises the steps of:
  • an epoxy resin is added to an aqueous solution of an emulsifier to obtain an epoxy emulsion, and the emulsifier includes polyvinyl alcohol;
  • the pH of the epoxy emulsion is adjusted to 4.5 to 5.5, and then the melamine resin prepolymer is added dropwise to obtain an epoxy microcapsule obtained by in-situ polymerization using a melamine resin as a wall material.
  • the melamine, formaldehyde, and water having a molar ratio of 1:2 to 3:20 to 35 are mixed according to a mass ratio of about 1:0.47 to 0.71:2.8 to 5.0, and the pH is adjusted to 8 to 9.
  • triethanolamine can be used to adjust the pH.
  • the temperature is raised to 60-80 ° C, the reaction is carried out for 30-120 minutes, and the stirring rate is 200-500 rpm to obtain a melamine resin prepolymer.
  • the epoxy resin is added to the aqueous solution of the emulsifier, and the mixture is emulsified at a high speed for 10 to 30 minutes, and the stirring rate is greater than 500 rpm.
  • the emulsifier includes polyvinyl alcohol (PVA).
  • PVA polyvinyl alcohol
  • the emulsifier is a mixture of polyvinyl alcohol and a monomolecular sulfonate type anionic surfactant, wherein the mass ratio of the polyvinyl alcohol to the sulfonate type monomolecular anionic surfactant is 1:0 to 50.
  • the polyvinyl alcohol has a degree of alcoholysis of 80 to 92% and a degree of polymerization of 400 to 2,200.
  • the monomolecular sulfonate type anionic surfactant preferably sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulfonate (SDS), sodium petroleum sulfonate, sodium succinate sulfonate, wood Sodium sulfonate.
  • SDBS sodium dodecyl benzene sulfonate
  • SDS sodium dodecyl sulfonate
  • sodium petroleum sulfonate sodium succinate sulfonate
  • wood Sodium sulfonate preferably sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulfonate (SDS), sodium petroleum sulfonate, sodium succinate sulfonate, wood Sodium sulfonate.
  • the concentration of the emulsifier is 1 to 7 wt%, and the balance is water.
  • a pH adjuster is added to the epoxy emulsion, the pH is adjusted to 4.5 to 5.5, and the melamine resin prepolymer obtained in the first step is added dropwise, and the temperature is raised to 60-80. °C, in-situ polymerization for 30 ⁇ 120 minutes, decanting, rinsing and filtering to obtain microcapsule products.
  • the pH adjuster is preferably a 1 to 10% by weight aqueous solution of citric acid. During the reaction, the pH of the reaction solution was kept constant, and the fluctuation was less than or equal to plus or minus 0.1.
  • a melamine resin prepolymer is prepared.
  • an epoxy resin is added to an aqueous solution of an emulsifier to obtain an epoxy emulsion.
  • the pH of the epoxy emulsion is adjusted to 4.5 to 5.5, and then the melamine resin prepolymer is added dropwise, and an epoxy microcapsule using a melamine resin as a wall material is obtained by in-situ polymerization.
  • the epoxy resin microcapsules prepared in this example were observed by an optical microscope, and the particle diameter was 500 to 2000 ⁇ m.
  • a melamine resin prepolymer is prepared.
  • an epoxy resin is added to an aqueous solution of an emulsifier to obtain an epoxy emulsion.
  • the pH of the epoxy emulsion is adjusted to 4.5 to 5.5, and then the melamine resin prepolymer is added dropwise, and the melamine resin obtained by in-situ polymerization is used as the epoxy microcapsule of the wall material.
  • the epoxy resin microcapsules prepared in this example were observed by an optical microscope, and the particle diameter was 500 to 1500 ⁇ m.
  • SDS sodium dodecyl sulfate
  • a melamine resin precursor Take 6.7 g of melamine, 10 g of 37% aqueous formaldehyde solution, 15 g of deionized water, mix, pour into a three-necked flask, adjust the pH to 8.5 with triethanolamine, heat in a water bath at 70 ° C, and stir the reaction at 350 rpm for 20 minutes. , a melamine resin precursor.
  • the epoxy resin microcapsules prepared by the comparative example were observed by an optical microscope, and the particle size was about 5 ⁇ m, and the particles adhered to each other, indicating that the epoxy was not wrapped, and the particles were mixed with many dense particles.
  • the invention provides a method for preparing epoxy microcapsules with a larger particle size melamine as a wall material by in-situ polymerization, and the obtained microcapsules can be applied to self-repairing concrete.
  • the present invention employs polyvinyl alcohol (PVA) as an emulsifier.
  • PVA polyvinyl alcohol
  • the polyvinyl alcohol does not react with the epoxy resin of the core material, and the dispersion property does not change greatly with the change of temperature and pH value, so that the coating efficiency and effect are better.
  • PVA is a nonionic surfactant, and its emulsifying ability is not as strong as some ionic surfactants, but its emulsification is relatively stable under heating conditions and in a low pH liquid environment.
  • PVA has good hydrophilicity and poor lipophilicity, which can greatly reduce the surface tension of water.
  • emulsified viscous epoxy at room temperature it is easy to obtain a larger size of epoxy emulsion droplets, and thus a larger particle size.
  • An epoxy microcapsule using a melamine resin as a wall material As a good emulsion stabilizer, PVA can be stably adsorbed on the surface of epoxy emulsion droplets, not desorbed by temperature and pH changes, and can induce melamine resin cross-linking polymerization deposition at the water/oil interface. Wall of the capsule.
  • an emulsifier having a strong emulsifying epoxy property can be used to obtain melamine/epoxy microcapsules, but the particle size is small, such as the most commonly used epoxy emulsifier styrene-Malay.
  • An acid anhydride block copolymer (SMA) the obtained melamine/epoxy microcapsules have an average particle diameter of less than 10 ⁇ m. If only monolayer sulfonate anionic surfactants such as sodium dodecyl sulfonate (SDS) and sodium dodecyl benzene sulfonate (SDBS) are used, their HLB values vary with temperature and pH.
  • Another feature of the present technical solution is the higher acidification end point (i.e., the pH at the time of in situ polymerization).
  • the purpose of acidification is to promote cross-linking polymerization of the melamine resin precursor, and the lower the pH, the faster the crosslinking reaction. Too fast reaction rate will lead to nucleation of melamine resin at the non-water/oil interface, reducing the coating rate; when the pH is high, the wall formation time is long, in the early stage of microcapsule formation, due to the thin wall of the capsule, very It is easy to break due to the stirring of the solution, which also reduces the coverage.

Abstract

一种环氧微胶囊的制备方法，包括：制备密胺树脂预聚体；将环氧树脂加入到乳化剂的水溶液中得到环氧乳液，所述乳化剂包括聚乙烯醇；调整所述环氧乳液的pH值至4.5-5.5，然后滴加所述密胺树脂预聚体，进行原位聚合反应得到以密胺树脂作为壁材的环氧微胶囊。该方法能够制备粒径较大的密胺树脂壁材环氧微胶囊，可用作自修复混凝土中微胶囊修复剂。

Description

环氧微胶囊的制备方法 技术领域
本发明涉及自修复混凝土领域，具体地说，涉及到微胶囊型自修复混凝土中微胶囊修复剂的制备方法。
 背景技术
自修复混凝土是将修复剂预埋在混凝土中，当混凝土内部出现裂纹时，修复剂被释放，自主修补裂纹。一种较好的在混凝土中包埋修复剂的方法是将其微胶囊化，在水泥制浆时与粗细骨料一起加入，浇注后微胶囊就被埋在混凝土构件中，成为一种潜伏型修复剂。
环氧树脂因与混凝土有很好的粘接性能，且固化时收缩率低, 性能稳定, 贮存期长，成了最常选用的混凝土有机修复剂。但是，将环氧树脂微胶囊化却不容易，这主要是因为环氧树脂相对黏稠，分子的极性大、反应活性高，不易乳化，在微胶囊形成过程中易与壁材的前驱体反应，导致破乳和较低的包覆效率。因此，虽然微胶囊在食品、医药、化妆品、纺织、饲料、电子墨水、相变贮能等许多领域也获得了广泛应用，技术成熟，制备方法众多，但成熟的制备环氧树脂微胶囊的方法却不多。对于自修复混凝土，现有技术中，通常采用以脲醛树脂为壁材的环氧微胶囊，一般采用原位聚合法制备。然而脲醛树脂的原位聚合反应机理复杂，使脲醛/环氧微胶囊的形态不易控制，迄今还未商业化应用。
密胺树脂与脲醛树脂一样，也属于氨基树脂，但密胺树脂更容易形成壁材。事实上，在制备脲醛/环氧微胶囊时，常会加入适量的三聚氰胺对脲醛进行改性，得到脲醛-密胺复合壁材的微胶囊，大大提高了包覆效率。这是因为三聚氰胺比尿素更易与甲醛反应，形成体结构的聚合物，加快聚合物在O/W界面上的沉积而形成囊壁。在工业上，以纯密胺树脂为壁材的微胶囊在压敏型复写纸方面（芯材为染料）已获得大规模应用，用密胺树脂包覆的红磷微胶囊也常用作阻燃剂。
混凝土自身是一个多孔结构，过小的微胶囊修复剂承载量低，囊壁不易破裂，修复效率低。通常希望用于自修复混凝土的微胶囊粒径在50微米以上。，以纯密胺树脂为壁材的微胶囊通常粒径较小，约5微米左右，这不适合用于自修复混凝土。
 技术问题
本发明旨在提供一种能够制备具有较大粒径的密胺树脂作为壁材的环氧微胶囊的制备方法，解决现有技术中以密胺树脂为壁材的微胶囊通常粒径较小的技术问题。
技术解决方案
本发明是这样实现的，通过原位聚合法制备较大粒径以密胺树脂作为壁材的环氧微胶囊的方法，所述的环氧微胶囊的制备方法包括步骤:
制备密胺树脂预聚体；
将环氧树脂加入到乳化剂的水溶液中得到环氧乳液，所述乳化剂包括聚乙烯醇；以及
调整所述环氧乳液的pH值至4.5~5.5，然后滴加所述密胺树脂预聚体，进行原位聚合反应得到的密胺树脂作为壁材的环氧微胶囊。
 有益效果
本发明提供的通过原位聚合法制备较大粒径以密胺树脂作为壁材的环氧微胶囊的方法，所得微胶囊可适用于自修复混凝土。本发明采用聚乙烯醇（PVA）作为乳化剂。在微胶囊制备过程中，聚乙烯醇不与芯材的环氧树脂反应，其分散性能亦不随温度和pH值的变化而有较大的改变，所以有较好的包覆效率和效果。并且PVA相对较低的乳化能力，其乳化作用在加热条件下和低pH值的液体环境中比较稳定的特性， PVA为非离子表面活性剂，亲水性好亲油性差，在室温乳化黏稠的环氧时，容易获得较大尺寸的环氧乳滴，制得的以密胺树脂作为壁材的环氧微胶囊粒径较大。PVA能稳定地吸附在环氧乳滴的表面，不因温度和pH值的变化而解吸，且能诱导密胺树脂在水/油界面上交联聚合沉积，形成囊壁。
附图说明
图1 为本技术方案第一实施例提供的环氧树脂微胶囊的电子显微镜的示意图。
图2为本技术方案第二实施例提供的环氧树脂微胶囊的电子显微镜的示意图。
图3为本技术方案对比例提供的微胶囊的电子显微镜的示意图。
 本发明的实施方式
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。
一种环氧微胶囊的制备方法包括步骤:
第一步，制备密胺树脂预聚体；
第二步，将环氧树脂加入到乳化剂的水溶液中得到环氧乳液，所述乳化剂包括聚乙烯醇；以及
第三步，调整所述环氧乳液的pH值至4.5~5.5，然后滴加所述密胺树脂预聚体，进行原位聚合反应得到的以密胺树脂作为壁材的环氧微胶囊。
第一步中，将摩尔比为1:2~3:20~35的三聚氰胺、甲醛、水按（质量比约为1:0.47~0.71:2.8~5.0）混合，调节pH值至8~9，具体的，可以采用三乙醇胺调节pH值。升温至60~80℃，反应30~120分钟，搅拌速率200~500rpm，得到密胺树脂预聚体。
第二步中，将环氧树脂加入到乳化剂的水溶液中，高速搅拌乳化10~30分钟，搅拌速率大于500rpm。所述乳化剂包括聚乙烯醇（PVA）。具体的，所述乳化剂为聚乙烯醇与单分子磺酸盐型阴离子表面活性剂的混合物，其中聚乙烯醇与磺酸盐型单分子阴离子表面活性剂的质量比为1:0~50。所述聚乙烯醇的醇解度为80~92%，聚合度为400~2200。所述单分子磺酸盐型阴离子表面活性剂，优选十二烷基苯磺酸钠（SDBS）、十二烷基磺酸钠（SDS）、石油磺酸钠、琥珀酸酯磺酸钠、木质素磺酸钠。所述乳化剂的浓度为1~7wt%，余量为水。所述聚乙烯醇（干重）与环氧树脂的质量比为1:50~100。所述环氧树脂包括环氧树脂本身以及环氧稀释剂。
在第三步中，向所述环氧乳液中加入pH值调节剂，调整pH值至4.5~5.5，滴加第一步中制得的所述密胺树脂预聚体，升温至60~80℃，原位聚合反应30~120分钟，倾析、冲洗、过滤得到微胶囊产品。pH值调节剂优选1~10wt%的柠檬酸水溶液。反应过程中保持反应液的pH值恒定，波动小于等于正负0.1。
下面，具体用实施例说明本技术方案提供的环氧树脂微胶囊的制备方法。
实施例1
第一步，制备密胺树脂预聚体。
取三聚氰胺4g，37%甲醛水溶液6g，去离子水12g，混合后倒入三口烧瓶，用三乙醇胺调节pH值至8~9，置于70℃的水浴锅中加热，以350rpm的速率搅拌反应50分钟，得密胺树脂预聚体。
第二步，将环氧树脂加入到乳化剂的水溶液中得到环氧乳液。
取环氧E-51树脂8g，加入1g正丁基缩水甘油醚（BGE），搅拌稀释10分钟，加入100毫升0.1wt%浓度的聚乙烯醇（PVA-1788）水溶液，以1000rpm的速率搅拌乳化20分钟，得环氧乳液。
第三步，调整所述环氧乳液的pH值至4.5~5.5，然后滴加所述密胺树脂预聚体，通过原位聚合反应得到以密胺树脂作为壁材的环氧微胶囊。
向环氧乳液中缓慢滴加5wt%柠檬酸水溶液，调节pH值至5.2，置于水浴锅中加热至70℃，以350rpm的速率开始搅拌，缓慢加入密胺树脂前驱体，继续滴加5wt%柠檬酸水溶液，以保持pH值恒定在5.2。密胺树脂前驱体加入完毕后，继续保温搅拌反应2小时。反应完成后，反应液经过倾析、水冲洗、过滤，得到微胶囊成品。
请参阅图1，通过光学显微镜观察本实施例制得的环氧树脂微胶囊，粒径为500~2000微米。
实施例2
第一步，制备密胺树脂预聚体。
取三聚氰胺4g，37%甲醛水溶液7g，去离子水12g，混合后倒入三口烧瓶，用三乙醇胺调节pH值至8~9，置于70℃的水浴锅中加热，以350rpm的速率搅拌反应50分钟，得密胺树脂预聚体。
第二步，将环氧树脂加入到乳化剂的水溶液中得到环氧乳液。
取0.1wt%浓度的聚乙烯醇PVA-0588水溶液100毫升，加入1g十二烷基苯磺酸钠（SDBS），制成混合乳化液。加入9g环氧树脂E-44，以1000rpm的速率搅拌乳化20分钟，然后加一滴消泡剂（正丁醇），得所述环氧乳液。
第三步，调整所述环氧乳液的pH值至4.5~5.5，然后滴加所述密胺树脂预聚体，进行原位聚合反应得到的密胺树脂作为壁材的环氧微胶囊。
向环氧乳液中缓慢滴加5wt%柠檬酸水溶液，调节pH值至4.7，置于水浴锅中加热至70℃，以350rpm的速率开始搅拌，缓慢加入密胺树脂前驱体，继续滴加5wt%柠檬酸水溶液，以保持pH值恒定在4.7。密胺树脂前驱体加入完毕后，继续保温搅拌反应50分钟。反应完成后，反应液经过倾析、水冲洗、过滤，得到微胶囊成品。
请参阅图2，通过光学显微镜观察本实施例制得的环氧树脂微胶囊，粒径为500~1500微米。
对比例 1
为了进一步说明本技术方案的中乳化剂和酸化终点pH值重要性，以十二烷基磺酸钠（SDS）作乳化剂，酸化终点设定在pH=3.5，做了对比例试验。制备密胺/环氧微胶囊的具体步骤如下：
取三聚氰胺6.7g，37%甲醛水溶液10g，去离子水15g，混合后倒入三口烧瓶，用三乙醇胺调节pH值至8.5，置于70℃的水浴锅中加热，以350rpm的速率搅拌反应20分钟，得密胺树脂前驱体。
取100毫升去离子水，加入SDS 0.2g，环氧E-51 10g，以1200rpm的速率搅拌乳化20分钟，然后加一滴消泡剂（正丁醇），得环氧乳液。
向环氧乳液中缓慢滴加5wt%柠檬酸水溶液，调节pH值至3.5，置于水浴锅中加热至70℃，以350rpm的速率开始搅拌，缓慢加入密胺树脂前驱体，继续滴加5wt%柠檬酸水溶液，以保持pH值恒定在3.5。密胺树脂前驱体加入完毕后，继续保温搅拌反应50分钟。反应完成后，反应液经过倾析、水冲洗、离心沉淀。
请参阅图3，通过光学显微镜观察本对比例制得的环氧树脂微胶囊，粒径约为5微米左右，且颗粒间相互粘连，表明有环氧没有被包裹，颗粒间还混有很多密胺树脂絮状沉淀物。表明酸化终点过低，或者乳化剂SDS不能有效地诱导密胺树脂在水/有界面处交联沉积。
本发明提供的通过原位聚合法制备较大粒径密胺作为壁材的环氧微胶囊的方法，所得微胶囊可适用于自修复混凝土。本发明采用聚乙烯醇（PVA）作为乳化剂。在微胶囊制备过程中，聚乙烯醇不与芯材的环氧树脂反应，其分散性能亦不随温度和pH值的变化而有较大的改变，所以有较好的包覆效率和效果。PVA为非离子表面活性剂，乳化能力没有某些离子型表面活性剂强，但其乳化作用在加热条件下和低pH值的液体环境中比较稳定。PVA有很好的亲水性和差的亲油性，能大幅度降低水的表面张力，在室温乳化黏稠的环氧时，容易获得较大尺寸的环氧乳滴，进而制得粒径较大的以密胺树脂作为壁材的环氧微胶囊。作为很好的乳化稳定剂，PVA能稳定地吸附在环氧乳滴的表面，不因温度和pH值的变化而解吸，且能诱导密胺树脂在水/油界面上交联聚合沉积，形成囊壁。
相反，如对比例1所示，使用乳化环氧能力强的乳化剂，虽能获得密胺/环氧微胶囊，但粒径很小，如使用最常用的环氧乳化剂苯乙烯-马来酸酐嵌段共聚物（SMA），获得的密胺/环氧微胶囊平均粒径不到10微米。如果只使用像十二烷基磺酸钠（SDS）和十二烷基苯磺酸钠（SDBS）这类单分子磺酸盐类阴离子表面活性剂，由于其HLB值随温度和pH值而变，在原位聚合阶段极易破乳，导致很低的包覆效率。本技术方案的另一个特点是较高的酸化终点（即原位聚合时的pH值）。酸化的目的是为了促进密胺树脂前驱体的交联聚合，pH值越低，交联反应越快。过快的反应速率会导致密胺树脂在非水/油界面处形核沉积，降低包覆率；当pH值高时，囊壁形成时间长，在微胶囊形成初期，由于囊壁薄，很容易因为溶液搅拌而破裂，同样会降低包覆率。通过原位聚合法制备以密胺树脂为壁材的微胶囊时，传统方法的酸化终点一般设定在pH=3左右，本技术方案设定在pH=5左右，这一值是根据使用PVA作主乳化剂这一情况而确定的。
以上所述仅为本发明的较佳实施例而已，并不用以限制本发明，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。

Claims (10)

  1. 一种环氧微胶囊的制备方法，包括步骤:
    第一步，制备密胺树脂预聚体；
    第二步，将环氧树脂加入到乳化剂的水溶液中得到环氧乳液，所述乳化剂包括聚乙烯醇；以及
    第三步，调整所述环氧乳液的pH值至4.5~5.5，然后滴加所述密胺树脂预聚体，进行原位聚合反应得到的密胺树脂作为壁材的环氧微胶囊。
  2. 如权利要求1所述的环氧微胶囊的制备方法，其特征在于，所述第一步中，将摩尔比为1: 2 ~ 3: 20 ~ 35的三聚氰胺、甲醛、水混合，调节pH值至8~9，升温至60 ~ 80℃，反应30~120分钟，搅拌速率200~500 rpm，得到密胺树脂预聚体。
  3. 如权利要求2所述的环氧微胶囊的制备方法，其特征在于，采用三乙醇胺调节pH值至8 ~9。
  4. 如权利要求1所述的环氧微胶囊的制备方法，其特征在于，在所述第二步中，将环氧树脂加入到乳化剂的水溶液中，高速搅拌乳化10 ~ 30分钟，搅拌速率大于500 rpm，得到所述环氧乳液。
  5. 如权利要求1所述的环氧微胶囊的制备方法，其特征在于，所述乳化剂为聚乙烯醇与单分子磺酸盐型阴离子表面活性剂的混合物。
  6. 如权利要求5所述的环氧微胶囊的制备方法，其特征在于，所述聚乙烯醇与单分子磺酸盐型阴离子表面活性剂的质量比为1:0~50。
  7. 如权利要求5所述的环氧微胶囊的制备方法，其特征在于，所述聚乙烯醇的醇解度为80 ~ 92 %，聚合度为400~2200，所述单分子磺酸盐型阴离子表面活性剂为十二烷基苯磺酸钠、十二烷基磺酸钠、石油磺酸钠、琥珀酸酯磺酸钠或木质素磺酸钠。
  8. 如权利要求5所述的环氧微胶囊的制备方法，其特征在于，所述乳化剂的浓度为1~7 wt%，余量为水，所述聚乙烯醇与环氧树脂的质量比为1:50~100。
  9. 如权利要求1所述的环氧微胶囊的制备方法，其特征在于，在所述第三步中，滴加所述密胺树脂预聚体之后，升温至60 ~ 80℃，原位聚合反应30 ~120分钟，倾析、冲洗、过滤得到所述环氧微胶囊。
  10. 如权利要求1所述的环氧微胶囊的制备方法，其特征在于，在第三步中，采用1~10 wt%的柠檬酸水溶液调节pH值，并且反应过程中保持反应液的pH值恒定。
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