As the main adhesive of putty, the amount of redispersible latex powder has an effect on the bonding strength of putty.Figure 1 shows the relationship between the amount of redispersible latex powder and the bond strength.As can be seen from Figure 1, with the increase of the amount of re-dispersible latex powder, the bond strength gradually increased. When the amount of latex powder is small, the bonding strength increases with the increase of the amount of latex powder. If the dosage of emulsion powder is 2% , the bond strength reaches 0182MPA, which meets the national standard of 0160MPA. The reason is that the hydrophilic latex powder and the liquid phase of the cement suspension permeate into the pores and capillary of the matrix, the latex powder forms film in pores and capillaries and is firmly adsorbed on the surface of the matrix, thus ensuring a good bonding strength between the cementing material and the matrix [4] . When the putty is removed from the test plate, it can be found that the increase of the amount of latex powder increases the adhesion of putty to the substrate. However, when the amount of latex powder was over 4% , the increase of bonding strength was slowed down. Not only redispersible latex powder, but also inorganic materials such as cement and heavy calcium carbonate contribute to the bonding strength of putty.
The water resistance and alkali resistance of putty is an important test index to judge whether putty can be used as water resistance of interior wall or exterior wall putty. Fig. 2 investigated the effect of the amount of re-dispersible latex powder on the water resistance of putty
As can be seen from Figure 2, when the amount of latex powder is less than 4% , with the increase of the amount of latex powder, the water absorption rate shows a downward trend. When the dosage was more than 4% , the water absorption rate decreased slowly. The reason is that cement is the binding material in putty, when no redispersible latex powder is added, there is a large amount of voids in the system, when redispersible latex powder is added, the emulsion polymer formed after re-dispersion can condense into a film in the putty voids, seal up the voids in the putty system, and make the putty coating and scraping to form a denser film on the surface after drying, thus effectively preventing water infiltration, reduce the amount of water absorption, so that its enhanced water resistance. When the dosage of latex powder reaches 4% , the redispersible latex powder and the redispersible polymer emulsion can basically fill the voids in the putty system completely and form a complete and dense film, thus, the tendency of the decrease of the water absorption of putty becomes smooth with the increase of the amount of latex powder.
By comparing the SEM images of putty made by adding redispersible latex powder or not, it can be seen that in Fig. 3(a) , the inorganic materials are not fully bonded, there are many voids, and the voids are not evenly distributed, therefore, its bond strength is not ideal. A large number of voids in the system make the water easy to infiltrate, so the water absorption rate is higher. In Fig. 3(b) , the emulsion polymer after re-dispersing can basically fill the voids in the putty system and form a complete film, so that the inorganic material in the whole putty system can be bonded more completely, and basically does not have the gap, therefore can reduce the putty water absorption. Considering the influence of latex powder on bonding strength and water resistance of putty, and considering the price of latex powder, 3% ~ 4% of latex powder is suitable.Conclusion redispersible latex powder can improve the bonding strength of putty. When its dosage is 3% ~ 4% , putty has high bonding strength and good water resistance
Post time: Jul-19-2023