Cellulose ether (hydroxypropyl methylcellulose, HPMC for short) is a common admixture for building interior wall putty and plays an important role in putty. HPMC with different viscosities has a great influence on the performance of putty. This paper systematically studies the effects and laws of different viscosities of HPMC and its dosage on the performance of putty, and determines the optimum viscosity and dosage of HPMC in putty.
Key words: cellulose ether, viscosity, putty, performance
0.Preface
With the development of society, people are more and more eager to live in a good indoor environment. In the process of decoration, large areas of walls need to be scraped and leveled with putty to fill holes. Putty is a very important supporting decoration material. Poor base putty treatment will cause problems such as cracking and peeling of the paint coating. Using industrial waste and porous minerals with air-purifying properties to study new building environmental protection putty has become a hot topic. Hydroxypropyl methyl cellulose (Hydroxypropyl methyl cellulose, English abbreviation is HPMC) is a water-soluble polymer material p, as the most commonly used admixture for construction putty, it has good water retention performance, prolongs working time and improves construction performance , Improve work efficiency. Based on the previous experimental research, this paper prepared a kind of interior wall environmental protection putty with diatomite as the main functional filler, and systematically studied the effects of different viscosity HPMC and the amount of putty on the putty’s water resistance, bonding strength, initial drying crack resistance, grinding Influence of workability, workability and surface dry time.
1. Experimental part
1.1 Test raw materials and instruments
1.1.1 Raw materials
The 4 W—HPMC, 10 W—HPMC, and 20 W—HPMC cellulose ether and polyvinyl alcohol rubber powder used in the test were provided by Kima Chemical Co.,Ltd ; diatomite was provided by Jilin Diatomite Company; heavy calcium and talcum powder Provided by Shenyang SF Industrial Group; 32.5 R white Portland cement was provided by Yatai Cement Company.
1.1.2 Test equipment
Cement fluidity tester NLD-3; initial drying anti-cracking tester BGD 597; intelligent bond strength tester HC-6000 C; mixing and sanding dispersing multi-purpose machine BGD 750.
1.2 Experimental method
The basic formula of the test, that is, the content of cement, heavy calcium, diatomite, talcum powder and polyvinyl alcohol is 40%, 20%, 30%, 6% and 4% of the total mass of the putty powder, respectively. The dosages of HPMC with three different viscosities are 1‰, 2‰, 3‰, 4‰ and 5‰ respectively. For the convenience of comparison, the thickness of putty single-pass construction is controlled at 2 mm, and the expansion degree is controlled at 170 mm to 180 mm. The detection indicators are initial drying crack resistance, bond strength, water resistance, sanding property, workability and surface dry time.
2. Test results and discussion
2.1 Effects of different viscosities of HPMC and its dosage on the bond strength of putty
From the test results and bond strength curves of different viscosities of HPMC and its content on the putty’s bond strength, it can be seen that the putty’s bond strength increases first and then decreases with the increase of HPMC content. The bond strength of putty has the greatest influence, which increases from 0.39 MPa when the content is 1‰ to 0.48 MPa when the content is 3‰. This is because when HPMC is dispersed into water, the cellulose ether in the water swells rapidly and fuses with the rubber powder, interlaced with each other, and the cement hydration product is surrounded by this polymer film to form a composite matrix phase, which makes the putty bond The strength increases, but when the amount of HPMC is too large or the viscosity is too high or too low, the polymer film formed between HPMC and cement particles has a sealing effect, which reduces the bond strength of the putty.
2.2 Effects of different viscosities of HPMC and its content on the dry time of putty
It can be seen from the test results of different viscosities of HPMC and its dosage on the surface-drying time of putty and the surface-drying time curve. The greater the viscosity of HPMC and the greater the dosage, the longer the surface-drying time of the putty. /T298—2010), the surface dry time of the interior wall putty shall not exceed 120 min, and when the content of 10 W—HPMC exceeds 4‰, and the content of 20 W—HPMC exceeds 3‰, the surface dry time of the putty exceeds the specification requirements. This is because HPMC has a good water retention effect. When HPMC is mixed into the putty, the water molecules and the hydrophilic groups on the molecular structure of HPMC can combine with each other to introduce tiny bubbles. These bubbles have a “roller” effect, which is beneficial to the putty batching After the putty is hardened, some air bubbles still exist to form independent pores, which prevents the water from evaporating too quickly and prolongs the surface drying time of the putty. And when HPMC is mixed into the putty, the hydration products such as calcium hydroxide and C-S-H gel in the cement are adsorbed with HPMC molecules, which increases the viscosity of the pore solution, reduces the movement of ions in the pore solution, and further delays the cement hydration process.
2.3 Effects of different viscosities of HPMC and its dosage on other properties of putty
It can be seen from the test results of the influence of different viscosities of HPMC and the amount of the putty on other properties of the putty. The addition of HPMC with different viscosities makes the initial drying crack resistance, water resistance and sanding performance of the putty all normal, but with the increase of the amount of HPMC , poor construction performance. Due to the thickening effect of HPMC, too much content will increase the consistency of the putty, which will make it difficult to scrape the putty and deteriorate the construction performance.
3. Conclusion
(1) The cohesive strength of putty increases first and then decreases with the increase of HPMC content, and the cohesive strength of putty is most affected when the content of 10 W-HPMC is 3‰.
(2) The greater the viscosity of HPMC and the more the content, the longer the surface drying time of the putty. When the content of 10 W-HPMC exceeds 4‰, and the content of 20 W-HPMC exceeds 3‰, the surface-drying time of the putty is too long and does not meet the standard. Require.
(3) Adding different viscosities of HPMC makes the initial drying crack resistance, water resistance and sanding performance of the putty normal, but with the increase of its content, the construction performance becomes worse. Considering comprehensively, the performance of the putty mixed with 3‰10 W-HPMC is the best.