WANG Ying，GAO Luming
（Shanghai Greenchem Trading Co. Ltd.，Shanghai 200003，China）
Abstract：The effect of 5 kinds of starch ether on the properties of cement-based ceramic tile adhesive was investigated. The results show that the starch ether ExcelCon T500 can prolong the open time of ceramic tile adhesive，starch ether has no obvious advantages in improving the tensile adhesion strength of ceramic tile adhesive，but ExcelCon T500 has almost the same effect on tensile adhesion strength as cellulose ether when the ceramic tile adhesive is kept for 10 min. The starch ether ExcelCon A850 can significantly improve the anti-slip property of ceramic tile adhesive.
Cement-based tile adhesives, as a type of widely used dry powder mortar, have always been the focus of attention. In general, after mixing the tile adhesive with water, it is best to adjust the construction within a certain period of time. This requires that the tile adhesive cannot be quickly set and has a long opening time. After the tile is pasted, the ideal situation is that the adhesion is firm and will not fall off, which in turn requires the tensile adhesive strength and anti-sliding of the tile adhesive. Adding appropriate additives can change some properties of tile adhesives, and different types and proportions of additives have different effects on performance. Redispersible latex powder can make the tile adhesive uniform in strength, cohesiveness, cohesiveness and flexibility. Cellulose ether generally plays a role in water retention and thickening of the tile adhesive. Lignocellulose can increase the tile adhesive. Yield stress, calcium formate can increase the early strength of tile adhesive. Starch ether is the reaction product of starch molecules and active substances, with a certain number of functional substituents, which can improve the rheology and workability of dry powder mortar. Starch ether used in mortar is generally modified from natural starches such as potato, corn, and cassava. It is a renewable resource and a new type of green and environmentally friendly building material additive. This paper explores the effects of five commercially available starch ethers on the open time, tensile bond strength, and slip resistance of cement-based tile adhesives, and provides some references for the further application of starch ethers in tile adhesives.
1.1 Raw material
cement: 42.5 grade white portland cement, Jiangxi Yinshan White Cement Co., Ltd .; graded sand: machine sand, 40 ~ 70 mesh, 70 ~ 140 mesh, Zhoushan Shengsi County Huangsha Village machine sand factory; heavy Calcium: 300 mesh, China Resources Mineral Powder Processing Plant, Lingshou County, Shijiazhuang; Calcium formate: 98% purity, LANXESS, Germany; Lignocellulose: ZZC 500, JRS, Germany; Redispersible powder: VINNAPASS R5010N , WACKER CHEMICAL (CHINA) CO., LTD .; Cellulose ether: M4025, Brinell viscosity 40 000 mPa · s, Hercules Temp Chemical Co., Ltd .; Starch ether: ExcelCon T500, ExcelCon A850 Tapioca starch ether, Siam, Thailand Siam Modified Starch Co., Ltd. (SMS), there are three other commercially available starch ethers SA, SB, SC; water: tap water.
1.2 Basic formula of tile adhesive (see Table 1)
1.3 Test method
(1) Opening time: Carry out the test of the test piece according to the method specified in EN 1346.
(2) Tensile bond strength: According to JC / T 547-2005 “Ceramic Wall and Floor Tile Adhesive”, the original tensile bond strength is tested.
(3) Anti-slip property. Refer to JC / T 547-2005 and make improvements. The tile glue mixed with water was allowed to stand for 5 minutes, and then applied to the PVC board. A toothed spatula with a 6 mm × 6mm notch and a center distance of 6 mm was also combed at a 60 ° angle with the board surface. The back-dried vitrified tiles (108 mm × 108 mm) were affixed to the tile adhesive, and a 5 kg weight (100% coverage of the tile area) was pressed for 30 s. Remove the heavy objects and carefully make the PVC board vertical to avoid vibration. Measure the slip distance of the tile after 2 minutes of vertical. If no slip is seen, add an anti-slip test device (as shown in Figure 1), and gradually add weights, and wait 2 minutes after each weight increase. If the tiles begin to slip, the test is over and the total weight is noted.
2 Results and discussion
According to the formula in Table 1, different starch ethers were used in the test. The substitution rate of starch ether to cellulose ether was [1.2 / (2.8 + 1.2)] × 100% = 30%. In all blank tests, all starch ethers were replaced with cellulose ethers, that is, 0.4% cellulose ether was added and no starch ether was added as a control.
2.1 The effect of starch ether on the open time of tile adhesive (see Figure 2)
Figure 2 shows that after adding starch ethers SA, SB, and SC, the opening time of the tile adhesive is relatively short, only 15 minutes; adding ExcelCon A850 or cellulose ether can extend the opening time to 20 minutes. Adding ExcelCon T500 works best with an open time of up to 25 minutes. The opening time of tile adhesive is closely related to its water retention. Starch ether itself does not have much effect on water retention, but starch ether often shows a synergistic effect with cellulose ether, thereby extending the opening time of tile adhesive. Adding ExcelCon T500 tile adhesive has adjustability for a long time after mixing, indicating that the synergy between ExcelCon T500 and cellulose ether is ideal. ExcelCon A850 is equivalent to the extension effect of cellulose ether under the experimental proportion (30% substitution rate for cellulose ether). Considering the improvement of other properties of tile adhesive by starch ether, ExcelCon A850 is also a promising tile adhesive additive.
2.2 The influence of starch ether on the tensile bond strength of tile adhesive
In actual construction, tile adhesive is often left to stand for a certain period of time after preparation. It is of great significance to examine the performance of tile adhesive under a certain time. Table 2 compares the tensile adhesive strength of tile adhesives with different starch ethers before and after 10 minutes.
From Table 2, it can be seen that:
(1) The tensile adhesive strength of all starch adhesives added to tile adhesives is less than that of blank samples, whether unopened or for 10 minutes, indicating the contribution of cellulose ether to the adhesiveness of tile adhesives. To be slightly larger.
(2) No matter what kind of additives are used, the tensile adhesive strength of the tile adhesive has decreased after being left to stand for 10 minutes, and most of them have dropped below 80% when not being left to stand. Only the tile adhesive with ExcelCon T500 is added to stretch the adhesive. The knot strength still reached 98.2% when unopened, as high as 1.66 MPa, which was very close to 1.70 MPa when the blank sample was left unopened for 10 minutes, showing the advantages of ExcelCon T500 over other starch ethers.
2.3 Effect of starch ethers on the anti-slip properties of tile adhesives (see Figure 3)
It can be seen from Figure 3 that all the starch ethers tested have improved the slip resistance of tile adhesives better than cellulose ethers. Among them, ExcelCon A850 and SB and SC only slip when the weight exceeds 770 g, which is better than ExcelCon T500. The corresponding data (<500 g) with SA is increased by more than 50%. In general, the more branched structures in the polysaccharide molecule, the more complicated the network structure formed after being dispersed in water, the more obvious bridging effect on the cement particles, the greater the yield stress given to the mortar, and the resistance to sagging or sliding The better the shift effect is . Cellulose ether has fewer branched structures, which makes it difficult to improve the slip resistance of tile adhesives. It may be an ideal choice to produce special starch ether for tile glue using natural starch with high amylopectin content (such as tapioca starch) as raw material.
Different types of starch ethers have different effects on tile adhesive opening time and tensile bond strength. Starch ether can improve the sliding resistance of tile adhesive, but the degree of improvement is also related to its type. Taken together, ExcelCon T500 can extend the opening time of tile adhesive and improve its tensile bond strength. ExcelCon A850 can significantly improve the anti-slip property while extending the open time. These two new types of tapioca starch ethers are expected to be used in tile adhesive. Get further promotion and application.