How Much Do You Know About VAE Redispersible Powders?

The main markets for VAE RDP are the building and construction industry, where they are used to formulate dry mix products. The global market for these products is expected to grow by more than 7%. Technological developments in the field of thin layer tile adhesives are one of the drivers of growth.

What is VAE/RDP?

Vinyl acetate-co-polyethylene copolymer (VAE) in powder form is a white, free-flowing, dry powder that can be easily redispersed into water to re-form a stable emulsion. Sometimes referred to as "solid latex", VAE redispersible powders (RDP) are easier to transport, store (excellent storage stability), handle and dry blend than VAE in emulsion form. VAE represents the majority of the global market for redispersible polymer powders.

The advantages of adding VAE-RDP to dry blend formulations include improved workability and water retention, plasticity, dispersibility and freeze stability. Due to the relatively high ethylene content, VAE resins are soft and flexible. As a modifier, VAE-RDP improves flexural strength, crack resistance, adhesion, abrasion and impact resistance, and water resistance.

VAE/RDP

The manufacturing process of VAE-RDP

Vinyl acetate and ethylene are copolymerised in an emulsion process to produce a VAE composition with an ethylene content of 10% to 40% in the copolymer in the first instance. Ethylene is a soft, hydrophobic monomeric unit in the copolymer that acts as the internal "plasticising" part.

In the copolymer, ethylene effectively lowers the glass transition temperature (Tg) of the hard, polar vinyl acetate monomer to 30 °C. As a result, we can achieve copolymers with a Tg range of +15 °C to -15 °C, while converting the base emulsion resin used in VAE production into a redispersible powder. By using ethylene monomers to regulate Tg, the formulator does not need any external plasticisers.

We describe the manufacturing process for redispersible powders below. Starting with a VAE emulsion produced using a colloidal stabiliser such as polyvinyl alcohol, the emulsion is mixed with a fine mineral anti-caking agent and then spray dried. This provides a stable, free-flowing powder that can be redispersed when mixed with water. the minimum solids content of RDP is 98%; the anti-caking agent content is up to 8-12% of the total weight. These VAEs have a very low volatile organic compound (VOC) content and low odour levels.

VAE/RDP

Applications of VAE-RDP

Applications for VAE-RDP include the formulation of building materials such as tile adhesives, grouting, finishing plasters, smoothing compounds, thin mortars and sealing pastes. The amount of VAE-RDP added to cement and mortar is approximately 2-10%, depending on the desired increase in strength, impact resistance, adhesion and water resistance of the compound.

For wall tile adhesive applications, VAE-RDP improves slump, water retention and workability. This allows tiles to be laid from top to bottom without tile slippage or the need for shims, VAE-RDP also improves the levelling properties of tile adhesives and other cementitious materials.

Demand for VAE-RDP has also grown into surface coating compounds where VAE helps to improve wall adhesion and crack bridging properties.

For Self-leveling Mortar

In oil and gas well cementing operations, polymer powder/cement combinations exhibit improved rheological properties and durability, while also causing water loss in cement slurries and oilfield fluids. The powder enhanced gas migration control of the cement slurry with minimal effect on extending the slurry setting time.

By improving particle-to-particle bonding, hardened cement/polymer compositions exhibit improved flexibility and strength properties, as well as higher adhesion and durability. For on-site operations, VAE dispersible powders offer advantages in handling, storage and on-site mixing, while improving water retention, workability and mechanical strength properties, as well as reducing the permeability of the cementitious material.

VAE/RDP

VAE-RDP grades and general applications can be distinguished by their glass transition temperature (Tg), which for amorphous polymers such as VAE is the critical temperature at which the material changes from a glassy solid to a rubbery material. When the ambient temperature is above Tg, the polymer becomes rubber. When the ambient temperature is below Tg, the polymer becomes a glassy material.

In the VAE-RDP range, the grades range from low Tg soft materials (DA 1400 series) to medium Tg flexible materials (DA-1200 series) to high Tg hard materials (DA 1100 series).

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