Effect of Redispersible Latex Powder Dosage on Mortar
Release Time:
2021-06-21
Source:
Redispersible Latex Powder
As the final polymer film forms, a framework system composed of inorganic and organic binders is established within the cured mortar: the hydraulic material provides a brittle, rigid skeleton, while the redispersible latex powder forms a flexible interfacial layer in the pores and on solid surfaces, creating a ductile bond. This bonding can be visualized as numerous tiny springs connecting to the rigid skeleton; because the tensile strength of the polymer resin film formed by the latex powder typically exceeds that of the hydraulic material by more than an order of magnitude, the overall strength of the mortar—i.e., its cohesive strength—is enhanced. Moreover, since polymers exhibit far greater flexibility and deformability than the rigid structures formed by materials such as cement, the mortar’s deformability is improved, stress dispersion is significantly enhanced, and consequently the mortar’s crack resistance is increased.
As the dosage of redispersible latex powder increases, the entire system shifts toward a more plastic behavior. At high latex-powder contents, the polymer phase in the cured mortar gradually surpasses the inorganic hydration products, leading to a fundamental transformation: the mortar becomes an elastomer, while the cement hydration products assume the role of a “filler.” The film formed by the redispersible latex powder after it is dispersed at the interface further plays another critical role—enhancing adhesion to the substrates it contacts. This is particularly important for surfaces that are difficult to bond, such as those with extremely low or no water absorption (e.g., smooth concrete and cementitious surfaces, steel plates, homogeneous tiles, and vitrified tile surfaces) as well as organic substrates (e.g., EPS boards and plastics). Inorganic binders rely on mechanical interlocking for adhesion: the hydraulic paste penetrates the pores of the substrate, gradually hardens, and ultimately locks onto the surface like a key in a lock. However, for the aforementioned difficult-to-bond surfaces, because the binder cannot effectively penetrate the substrate to establish robust mechanical interlocking, mortars based solely on inorganic binders fail to achieve adequate adhesion. By contrast, polymers adhere through intermolecular forces rather than depending on the porosity of the substrate surface; of course, a rough surface with increased contact area will enhance the bonding strength.
