Study on the minimum film forming temperature of RDP

As a key modified material for dry-mixed mortar, the minimum film forming temperature (MFT) of redispersible latex powder directly affects the application performance of the material in the fields of tile adhesives, exterior wall insulation, etc. This article systematically analyzes the core characteristics of this parameter from a technical perspective.

Basic definition

The minimum film forming temperature refers to the critical temperature threshold for a polymer to form a continuous film without the aid of a film-forming agent. When the ambient temperature is lower than the MFT, the latex particles cannot be effectively fused, resulting in discontinuous film formation, which in turn affects the key performance indicators of the material such as bonding strength, flexibility and weather resistance.

Material composition correlation

The MFT of RDP essentially depends on the glass transition temperature (Tg) of the polymer matrix. Among the mainstream products:

The MFT range of vinyl acetate-ethylene copolymer (VAE) is 0-5℃

Acrylic products can break through the 0℃ threshold

Styrene-butadiene copolymer (SBR) has a higher MFT (10-15℃)

By adjusting the copolymer monomer ratio, introducing flexible segments or adding film-forming aids (such as polyols), the MFT can be effectively adjusted to meet different application requirements.

Key influencing factors

In addition to the intrinsic properties of the polymer, the actual MFT performance is restricted by multiple factors:

① Ambient temperature and humidity conditions

② Water absorption rate of the substrate

③ Auxiliary agent compatibility system

④ Construction process parameters

Especially under low temperature (<5℃), high humidity (RH>80%) or rapid water loss conditions, delayed film formation or film formation defects may occur.

Engineering application guidelines

It is recommended that the construction environment temperature be at least 3-5℃ higher than the MFT. For winter construction or cold areas, acrylic products with MFT≤0℃ are preferred, and film-forming promoters can be used in combination if necessary. Special attention should be paid to the pretreatment of the base layer, and the water absorption rate should be controlled within the range of 1.0-2.0 kg/(m²·h) to ensure effective film formation.

Test method

The standard MFT determination adopts the temperature gradient plate method: the redispersible emulsion is applied to the surface of the metal plate with a continuous temperature gradient, and the critical temperature value is determined by visually observing the milky-transparent transition point. This method complies with international standards such as DIN 53787.

Conclusion: Reasonable selection of the MFT value that matches the construction conditions is the core prerequisite for the redispersible latex powder to exert its modification effect. It is recommended to consider environmental adaptability from the material formula design stage, and verify the film-forming behavior under different temperature and humidity conditions through systematic testing to ensure the durability and reliability of the final product.