The influence of the amount of cellulose ether, relative molecular mass and modification method on the water-absorbing and whitening phenomenon of real stone paint is discussed, and the cellulose ether with the best water-whitening resistance of real stone paint is screened out, and the comprehensive performance of real stone paint is evaluated detection.
Key words: real stone paint; water whitening resistance; cellulose ether
0、Preface
Real stone varnish is a synthetic resin emulsion sand wall architectural coating made of natural granite, crushed stone and stone powder as aggregate, synthetic resin emulsion as base material and supplemented with various additives. It has the texture and decorative effect of natural stone. In the exterior decoration project of high-rise buildings, it is favored by the majority of owners and builders. However, in rainy days, water absorption and whitening have become a major disadvantage of real stone paint. Although there is a big reason for the emulsion, the addition of a large number of hydrophilic substances such as cellulose ether greatly increases the water absorption of the real stone paint film. In this study, from the hands of cellulose ether, the influence of the amount of cellulose ether, relative molecular weight and modification type on the water-absorbing and whitening phenomenon of real stone paint was analyzed.
1. The mechanism of water absorption and whitening of real stone paint
After the real stone paint coating is dried, it is prone to whitening when it meets water, especially in the early stage of drying (12h). In rainy weather, the coating will become soft and white after being washed by rain for a long time. The first reason is that the emulsion absorbs water, and the second is caused by hydrophilic substances such as cellulose ether. Cellulose ether has the functions of thickening and water retention. Due to the entanglement of macromolecules, the flow of the solution is different from that of Newtonian fluid, but shows a behavior that changes with the change of shear force, that is, it has high thixotropy. Improve the construction performance of real stone paint. Cellulose is composed of D-glucopyranosyl (anhydroglucose), and its simple molecular formula is (C6H10O5)n. Cellulose ether is produced by cellulose alcohol hydroxyl group and alkyl halide or other etherification agent under alkaline conditions. Hydroxyethyl cellulose ether structure, the average number of hydroxyl groups substituted by reagents per anhydroglucose unit on the cellulose molecular chain is called the degree of substitution, the 2, 3, and 6 hydroxyl groups are all substituted, and the maximum degree of substitution is 3. The free hydroxyl groups on the molecular chain of cellulose ether can interact to form hydrogen bonds, and can also interact with water to form hydrogen bonds. The water absorption and water retention of cellulose ether has a direct impact on the water absorption and whitening of real stone paint. The water absorption and water retention performance of cellulose ether depends on the degree of substitution of cellulose, substituents and the degree of polymerization of cellulose ether itself.
2. Experimental part
2.1 Experimental instruments and equipment
JFS-550 multi-function machine for steady stirring, high-speed dispersion and sand milling: Shanghai Saijie Chemical Equipment Co., Ltd.; JJ2000B electronic balance: Changshu Shuangjie Testing Instrument Factory; CMT-4200 electronic universal testing machine: Shenzhen Sansi Experimental Equipment Co., Ltd. company.
2.2 Experimental formula
2.3 Experimental process
Add water, defoamer, bactericide, antifreeze, film-forming aid, cellulose, pH regulator and emulsion to the disperser according to the formula to disperse evenly, then add colored sand and stir well, and then use an appropriate amount of thickener Adjust the viscosity, disperse evenly, and get real stone paint.
Make the board with real stone paint, and do the water whitening test after curing for 12 hours (immersion in water for 4 hours).
2.4 Performance testing
According to JG/T 24-2000 “Synthetic Resin Emulsion Sand Wall Paint”, the performance test is carried out, focusing on the water whitening resistance of different hydroxyethyl cellulose ether real stone paints, and other technical indicators must meet the requirements.
3. Results and discussion
According to the performance characteristics of hydroxyethyl cellulose ether, the effects of the amount of hydroxyethyl cellulose ether, relative molecular weight and modification method on the water-whitening resistance of real stone paint were emphatically studied.
3.1 The effect of dosage
With the increase of the amount of hydroxyethyl cellulose ether, the water whitening resistance of real stone paint gradually deteriorates. The greater the amount of cellulose ether, the more the number of free hydroxyl groups, the more water will form hydrogen bonds with it, the water absorption rate of the real stone paint film will increase, and the water resistance will decrease. The more water in the paint film, the easier it is to whiten the surface, so the water whitening resistance is worse.
3.2 Effect of relative molecular mass
When the amount of hydroxyethyl cellulose ethers with different relative molecular masses is the same. The larger the relative molecular mass, the worse the water whitening resistance of real stone paint, which shows that the relative molecular weight of hydroxyethyl cellulose ether has an impact on the water whitening resistance of real stone paint. This is because chemical bonds > hydrogen bonds > van der Waals force, the greater the relative molecular mass of cellulose ether, that is, the greater the degree of polymerization, the more chemical bonds formed by the combination of glucose units, and the greater the interaction force of the entire system after forming hydrogen bonds with water , the stronger the water absorption and water retention capacity, the worse the water whitening resistance of the real stone paint.
3.3 Influence of modification method
The test results show that the nonionic hydrophobic modification is better than the original, and the anionic modification is the worst. Non-ionic hydrophobically modified cellulose ether, by grafting hydrophobic groups on the molecular chain of cellulose ether. At the same time, the thickening of the water phase is achieved through hydrogen bonding of water and molecular chain entanglement. The hydrophobic performance of the system is reduced, so that the hydrophobic performance of the real stone paint is improved, and the water whitening resistance is improved. Anionically modified cellulose ether is modified by cellulose and polyhydroxysilicate, which improves the thickening efficiency, anti-sag performance and anti-splash performance of cellulose ether, but its ionicity is strong, and the water absorption and retention capacity is improved , The water whitening resistance of real stone paint becomes worse.
4. Conclusion
The water absorption and whitening of real stone paint are affected by many factors such as the amount of cellulose ether and the modification method of relative molecular mass. Water absorption and whitening of real stone paint.