ZHANG Yan-fa, LI Shi-xiong, CHEN Xiao-bo, QIN Jiang-ding, LIU Yan
(BATF Industrial Co., Ltd., Foshan 528322, Guangdong, China)
Abstract: Vinyl acetate/acrylic copolymer emulsion has advantages such as low raw material prices, environmental non-toxicity and excellent compatibility, but its shortcomings such as poor water resistance, alkali resistance and stability greatly limit its application in JS waterproof coatings. By adjusting the emulsification system and adding functional monomers, a vinyl acetate/ acrylic emulsion suitable for waterproof coatings is prepared.
0 PrefaceOrdinary cement concrete has defects such as tensile resistance, low bending strength, easy cracking, and long curing time. Polymer waterproof coating (JS) is a type of architectural waterproof coating composed of high molecular polymer emulsion and inorganic cement as main components, and adding a small amount of auxiliary agent. The polymer waterproof coating has the advantages of hydraulicity and high impact resistance of cement, and also has the characteristics of flexibility, high elasticity and water resistance of the polymer coating film. Currently, JS waterproof coatings on the market are mainly based on acrylate and ethylene-vinyl acetate (EVA) systems. As the market price of raw materials continues to rise, the cost of acrylic esters is higher, and although the cost of EVA is lower, it also has disadvantages such as poor film formation at low temperatures and poor water resistance.Vinyl acetate-acrylic acid copolymer (vinyl acrylate) emulsion has the advantages of low raw material price, environmental protection, non-toxicity, excellent compatibility, etc., but has the disadvantages of water and alkali resistance, poor stability, etc., greatly limiting its use in JS Application in waterproof coatings. In this paper, by adjusting the emulsification system and adding functional monomers, a vinegar-acrylic emulsion suitable for waterproof coatings is prepared.
1 Experimental part
1.1 Reagents and instruments
Vinyl acetate (VAC), butyl acrylate (BA), vinyl tert-carbonate (VV10), vinyltrimethoxysilane (A-171), acrylamide (AM), ethylene glycol dimethacrylate (EGDMA ), Anionic emulsifier, non-ionic emulsifier, reactive emulsifier, sodium persulfate, and caustic soda are all commercially available industrial products; cement P.O42.5, Conch; snowflake white, 80 to 120 mesh; 400 mesh weight Calcium, domestic; ASE60.1.2 Experimental equipment5 000 mL four-necked flask; condensing tube; thermometer; water bath, triangle; temperature controller, domestic; peristaltic pump, domestic; disperser, domestic; rotary viscometer, domestic; hose; several beakers of different capacities; 1 000 μm, 2 000 μm filmmakers.1.3 Preparation methodIn order to ensure the stability and reproducibility of the polymerization system, a semi-continuous polymerization process of pre-emulsified seeds was selected in this experiment. Its polymerization principle is radical polymerization. The specific reaction mechanism is as follows:
1.3.1 emulsion preparation process
The emulsion preparation process is shown in Figure 1, and the basic formula of the emulsion polymerization is shown in Table 1.
18.104.22.168 Preparation of pre-emulsions
Dissolve part of the anionic emulsifier, nonionic emulsifier and reactive emulsifier in a 1000 mL beaker with an appropriate amount of deionized water, and then use a disperser to stir and disperse. After all the emulsifiers have been dissolved, milk vinyl acetate, butyl acrylate, ethylene terephthalate, and an appropriate amount of crosslinking monomer and persulfate are added in order, and dispersed for 10-15 minutes.22.214.171.124 Preparation of seed emulsionAdd an appropriate amount of deionized water, the remaining anionic emulsifier, nonionic emulsifier, and reactive emulsifier into the flask, and stir to dissolve while heating up. When the temperature reaches 70 ～ 80 ℃, take 5% pre-emulsion and an appropriate amount of sodium persulfate aqueous solution to add, and keep for 30 minutes.126.96.36.199 Semi-continuous dropping process and specific experimental stepsThe remaining pre-emulsion was added dropwise within 3 to 4 hours, and the temperature was maintained for 1 hour. The temperature was lowered to below 50 ° C, and the pH value was adjusted to 6 to 7, 350 mesh filter cloth to filter out the material.1.3.2 Preparation of waterproof coatingsSee Table 2 for compatible formulations of waterproof coatings.
First add the emulsion and water to the disposable cup, then add the 400 mesh heavy calcium and cement that have been mixed evenly, and stir with a spatula. Add quantitative water, emulsion, defoamer, thickener to the dispersion tank, and disperse for 3 minutes at an appropriate stirring speed. Add the pre-mixed uniform cement, 400 mesh heavy calcium and snow white, and adjust the appropriate stirring speed. Disperse for 5 minutes, and defoam for 20 minutes. The basic formula of the mechanical properties of the waterproof coating is shown in Table 3.
1.4 Testing methods for JS waterproof coating performance
The vinegar-acrylic JS waterproof coating obtained in this study needs to be tested for its mechanical properties, mechanical stability, storage stability, compatibility and open time.1.4.1 Testing of mechanical propertiesAccording to the basic formula of mechanical properties of waterproof coatings in Table 2, according to the national standard GB / T 23445—2009 “Polymer Cement Waterproof Coatings”, test samples were prepared and tested.1.4.2 Compatibility and Open Hour TestingAccording to the compatibility formula of the waterproof coating in Table 1, and use the initial stirring resistance as the dispersibility criterion, it is rated 5-4 when it is easy to disperse the powder uniformly, and 3-2 when it needs a certain amount of stirring to be uniformly dispersed. Score 1-0 when larger stirring intensity and longer stirring time are required; use the stirring resistance of 10 min, 30 min, and 2 h as the standard for the opening time. When the resistance is small, the score is 5-4, and when the resistance is normal, the score is 3-. 2. Score 1-0 when resistance is high.1.4.3 Mechanical stabilityThe emulsion sample is filtered with a 300-mesh filter cloth, and then dispersed in a small high-speed disperser at a high speed of 4 000 r / min for 10 minutes, and then filtered with a 300-mesh filter cloth. If it can be filtered, and the gel content is less than 0.01 g , The mechanical stability of the emulsion is considered to pass.1.4.4 Storage stabilityTake 200 g of a 300 mesh filtered emulsion sample and seal it in a sample cup, and store it in a blast oven at 50 ℃ for 7 d, 14 d, and 1 month. When there is no precipitation at the bottom or delamination on the liquid surface, then Storage is considered stable.1.4.5 Gelation rateThe synthesized emulsion sample was filtered with 300 meshes, and the aggregates on the filter residue, the stirring paddle, and the reactor wall were dried at 120 ° C. to a constant mass Wc, and the gel amount was calculated as shown in formula (1).
In the formula: Wc is the mass of agglomerates, and Wt is the actual amount of reactive monomer in the polymer emulsion.
2 Results and discussion
2.1 Effect of monomer system on emulsion performance
The monomer is the basic composition of the polymer. When selecting the monomer, the appropriate monomer type should be selected according to the requirements of the film-forming properties of the emulsion and the characteristics of each monomer. Glass transition temperature is an important characteristic of the copolymer, which has a decisive effect on the mechanical properties of the polymer. Considering the stability of polymerization, n-butyl acrylate and isooctyl acrylate were selected as soft monomers, and vinyl acetate was selected as hard monomer. According to the basic formula of emulsion polymerization in Table 1, different systems are designed according to Table 4, Table 5. Tg experiment.
By trying different systems with different Tg emulsions, we mainly tested their mechanical properties and compatibility. From the results in Tables 6 and 7, it can be known that, under the condition that Tg is unchanged, the emulsion synthesized by the BA-VAC system has better mechanical properties and compatibility with the powder after preparing the sample, and Formula 2 -EHA-VAC is slightly worse. In the BA-VAC system, the mechanical properties of Formula C are better, followed by Formulas B and C, and Formulas A and E are worse. Therefore, when the Tg is designed at -25 ℃, the softness and hardness of the emulsion is more suitable. The sample has good mechanical properties.
2.2 Effect of emulsification system on the stability of vinyl acetate emulsion
Emulsifier is one of the main components of emulsion polymerization. Generally speaking, it does not participate in chemical reactions, but it plays a pivotal role in the emulsion polymerization process. The dispersion and compatibility play an important role. Table 8 adjusts the emulsifier portion of the emulsion polymerization formulation.
The reactive emulsifier is fixed on the surface of the latex particles by combining with the polymer molecular chain. Compared with the non-reactive emulsifier, the latex particles can be better protected during vigorous movement, but it is not easy. Condensation and even demulsification occurred. Analyze the test data in Table 9 and compare the formulas F, G, and H. The increase of the reactive emulsifier can improve the stability of the polymerization system, and the addition amount of 0.3% is optimal. Non-ionic emulsifiers make the latex particles have a thicker protective layer. By comparing formulas H, I, and J, the improvement of non-ionic emulsifiers is beneficial to storage stability, and 1.5% is appropriate.
The introduction of emulsifier can improve the hydrophilicity of the emulsion, which is beneficial to the dispersion and wetting of the powder. Comparing formulas H and J, with the addition of non-ionic emulsifier to 1.5%, the highest score in 2 hours of open time, the smallest stirring resistance, slower drying rate, which will reduce the construction efficiency, so formula H is the best.
2.3 Effect of ethylene tert-carbonate on emulsion performance
Ethylene tert-carbonate is a kind of multi-branched monovalent saturated carboxylic acid vinyl ester. The steric hindrance formed by the abundant alkyl group on the carbon atom and the non-polarity of the alkyl group have good copolymerization characteristics with vinyl acetate. It has a certain protective effect on the ester group, thereby improving the water and alkali resistance of the coating film. Table 10 adjust the amount of VV-10 added to see its effect on mechanical properties. Table 11 shows the test results.
The addition amount of VV-10 in formulas K to O increased from 1% to 30%. From Table 9, it can be seen that with the increase of VV-10, the elongation and strength of untreated did not change much, but after water treatment and alkali treatment, The elongation and strength of the compound increased significantly, reaching the optimum in the formula N, while the addition of the formula O decreased by 30%. Considering the problem of cost, it is suitable to adjust based on the formula M and the addition amount of VV-10 is 10%.2.4 Effect of cross-linking monomer on emulsionIn order to improve the mechanical properties of the coating film after water and alkali treatment, an attempt was made to introduce cross-linking monomers to improve the compactness, water resistance and alkali resistance of the film formation, thereby improving the mechanical properties after treatment. Tables 12 and 13 attempt to introduce different crosslinking monomers.
This article uses different types of cross-linking monomers. The addition amounts are all 0.1%. The results in Table 14 show that after the introduction of the silicone-based monomer A-171, the results of water treatment and alkali treatment are better, while TMPTMA used in Formula R It is a trifunctional cross-linking monomer. After the introduction, the degree of cross-linking is large, which has a large impact on the hardness of the coating film, resulting in a higher tensile strength and a lower elongation. EGDMA and AM were used in formulations Q and S, and the effects were not obvious.
The introduction of silicone-based monomers into the polymer chain can improve the water resistance of the molecular chain . Table 13 adjusts the amount of addition. It can be seen from Table 15 that the addition amount of A-171 in the formulas T to Z gradually increases, and the mechanical properties after water treatment and alkali treatment first increase slightly. Adding 0.3% to the formula T is the optimal value. With the increase of the amount, there is a large decline in performance. Combined with the test results of gel amount, storage stability and compatibility, the excessive introduction of silicone-based crosslinking monomers makes the degree of crosslinking of the polymer chain too large, and the gel As the amount increases, the compatibility deteriorates and the mechanical properties deteriorate. Therefore, formula T is more suitable.
By adjusting the monomer system, the type of emulsifier, the glass transition temperature, and the comprehensive adjustment of the crosslinking monomer, it was finally confirmed that a Tg was 248.15K, the amount of non-ionic emulsifier was 1.5%, and the amount of reactive emulsifier was 0.3%. VV-10 is added with 10%, A-171 is added with 0.3% of n-butyl acrylate / vinyl acetate system emulsion, which has excellent performance in JS waterproof coating.