Study On Preparation Of The Amphiphilic Acrylic Copolymers And Its Applications In Water-sensitive Breathable Coatings

With the development of science and technology and improvement of people's living standard, the roles of coatings are gradually developing from pure protective and decorative functions to special and intelligent functions. The preparation methods of the smart coatings mainly depend on polymers, pigments and functional fillers, and special technology. Especially, the design of polymers with stimulus / response functions and depending on the external environment is the most important. The relative humidity of the arid regions represented by the northwest China is lower, heating for residential buildings will also result in humidity decreasing sharply. Therefore, water-sensitive breathable coatings are made in order to relieve the phenomenon. The water-sensitive breathable coatings can absorb and release humidity by itself to regulate interior humidity of rooms with the change of the environment humidity, which don't consume artificial energy. The traditional view of truth, which regards truth as poor water resistance due to better water absorption of coating, was challenged. The total of hydrophilic groups was greatly increased in order to improve water absorption function of coatings under the important precondition which ensure the basic performance of coatings. The water-sensitive breathable coating has the performance keeping the environment humidity and is a kind of the coatings with environmental-friendly coating.After reviewing the types, properties, preparation methods, advantages and disadvantages of smart coatings, humidity materials and humidity coatings at home and abroad, the studies were carried out. At first, the four kinds of amphiphilic acrylic copolymer used in the water-sensitive breathable coatings were prepared. They are water-dispersed polymer, emulsion, emulsifier-free emulsion and emulsifier-free core-shell emulsion. The important parameters influencing conversion and stability polymerization, such as the content of monomers, emulsifiers, initiator and regulator, temperature, dropping time, et al, were studied. Then, polymers, cross-linking agent, porous functional pigments and fillers were mixed together to make the two-component room temperature curable water-sensitive breathable coatings. Effect of the ratio between pigment and binder on performances of coatings was researched, such as water absorption, water resistance, humidity-control performance, et al. The compositions, morphologies, particle sizes, potentials and thermal stability of coatings were respectively characterized by infrared spectrum (FTIR), transmission electron microscope (TEM), scanning electron microscope (SEM), Zetasizer diameter tester (DLS) and thermogravimetry (TG). The components, specific surface area, porous volume and pore size distribution of fillers and water-sensitive breathable coatings were respectively characterized by X-ray diffraction (XRD) and nitrogen adsorption-desorption investigations (BET-BJH). According to the analysis results, the mechanisms of water absorption, water resistance and humidity control of coatings were described in detail in the paper. The main conclusions were following.1. The water-dispersed amphiphilic acrylic copolymer and its water-sensitive breathable coating have been prepared. The rule of water-dispersed polymer dissolving in water was studied in detail. There was not water dilution peak during the course of polymer dissolved in water while polarity of polymer was very high, which was different from common acrylic resin. The reason is that the higher polarity of polymer is, the better aqueous solubility of polymer is, the more clear its aqueous solution is, and the higher viscosity is on the condition of same solid content. A lot of factors influencing the polymerization and the properties of polymer and coating were researched, for example, the properties of polymer and coating were the best while temperature was 85℃, dropping hour was 3-4 hours, the pigment-binder ratio was 10:4-6. Thermal stability of polymer was improved from 300-390℃to 330-420℃after adding ADH.2. The amphiphilic acrylic copolymer emulsion containing high keto-carbonyl groups and its water-sensitive breathable coating have been prepared. The optimum dosage of emulsifiers, DAAM, MAA and NaHCO₃ in the amphiphilic acrylic copolymer emulsion and the reaction temperature were defined by tests, and the thermal decomposition temperature of resin was 370-450℃.3. The amphiphilic acrylic copolymer emulsifier-free emulsion containing high keto-carbonyl groups and its water-sensitive breathable coating have been prepared. After comparing emulsifier-free emulsion polymerization with conventional emulsion polymerization, we thought that emulsifier-free emulsion polymerization method was more suitable for polymer containing a large of hydrophilic groups. The amounts of carboxylic acid monomer and technological parameters of polymerization, such as neutralization degree, reaction temperature, stir speed and the pigment-binder ratio were defined by tests.4. The amphiphilic acrylic copolymer emulsifier-free core-shell emulsion containing high keto-carbonyl groups and its water-sensitive breathable coating have been prepared. The amphiphilic acrylic copolymer emulsifier-free core-shell emulsion and the amphiphilic acrylic copolymer emulsifier-free core-shell emulsion containing nano-SiO₂ have been firstly studied in detail. The composition of core and shell monomers, the optimum amount of acrylic acid, nano-silicon sol and initiator, and optimum reaction temperature and dropping hour were defined. Effect of the coating formulation design and the pigment-binder ratio on water absorption, water resistance and humidity control of coatings was studied.The emulsifier-free core-shell emulsion polymerization is colligated the advantages of emulsifier-free emulsion polymerization and core-shell emulsion polymerization. The particle sizes of latex produced in this way were small, narrow distribution and mono-disperse. The latex has good general performance because of no emulsifier. Adding a large of hydrophilic monomers was benefit for good water absorption. It is the most important that the emulsions with hard core and soft shell can form smooth, bright, clear film at lower room temperature (<5°C) on the absence of film forming agent and exhibit high strength. Moreover, the emulsifier-free core-shell emulsion containing nano-silicon sol will exhibit the more excellent performances than the emulsifier-free core-shell emulsion, because of nano-silicon sol containing a large of silicate and about 30% nano-SiO₂.The basic performances of the four water-sensitive breathable coatings using the corresponding the four amphiphilic acrylic copolymer all reached to Chinese standard about interior wall coating, that is GB/T 9756-2001 the latex coating standard, and had largely exceeded in water absorption, water resistance and humidity control. The morphologies, components, specific surface area and porosity of the porous fillers and the water-sensitive breathable coatings were respectively characterized by SEM, XRD, BET and BJH. Their water absorptions were tested by absorption and release humidity (or water) tests. Therefore, the porthole effect and surface effect of mineral materials and coatings were confirmed. Meanwhile, the finer porous fillers are, and the lower temperature is, the higher water absorption is, the more obvious porthole effect is. The mechanism of water absorption was hereby described in detail. The cross-linked amphiphilic acrylic copolymers can cure at room temperature and have more excellent performances than ordinary thermoplastic acrylic resin because they contain the higher keto-carbonyl group, carboxyl group, hydroxyl, amide group and cross-linking agent. The water-sensitivity of coating is more superior because of adding a large of porous functional fillers. While water is sprinkled on the coating, it can be transiently inhaled. Because water absorbent resins and porous functional fillers were added to coating, the coating could combine with wall to form a permeable coating, which the water absorption, water resistance, humidity control, breathability and moisture permeability of the coating are more excellent. The water-sensitive breathable coatings have features of safety, environmental protection and energy saving, the raw materials and devices are obtained easily, preparation technology and finishing manner are simple so that the coatings have low cost and will be easy to popularize and apply.