VAE Redispersible Powders (RDPs) in Building & ...

Vinyl acetate-co-ethylene copolymers (VAE), available from Gantrade Corporation and Dairen Chemical Corp. in powder form, are white, free-flowing, dry powders that are readily redispersed into water to re-form a stable emulsion.  Sometimes called &#;solid latex,&#; VAE redispersable powders (RDPs) are easy to ship, store (excellent storage stability), handle, and dry-mix versus VAEs in an emulsion form. VAEs account for the majority of the global market for redispersible polymer powders. 

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Dry mixing with other powders such as cement, sand, or light aggregate at a field site or manufacturing location can facilitate consistency and reliable performance.  VAE-RDPs are used as cement and plaster modifiers or as a binder resin for inorganic materials such as gypsum and hydrated lime. Formulators also use VAE-RDPs as the sole binder resin for construction adhesives.

The advantages of incorporating VAE-RDPs in dry-mix formulations include improvements in workability and water retention, plasticity, dispersion, and freeze stability.  The VAE resins are soft and flexible because of their relatively high ethylene contents. As a modifier, VAE-RDPs improve flex strength, crack resistance, adhesion, abrasion and impact resistance, and water repellency. 

Applications for VAE-RDPs include the formulation of construction materials such as tile adhesives, grouts, finishing plasters, troweling compounds, thin set mortars, and sealing slurries..  The amount of VAE-RDPs added to cements and plaster is about 2-10 percent, depending on the improvement of strength, impact resistance, adhesion, and water resistance required of the compound.

VAE-RDP: Manufacturing Process

Vinyl acetate and ethylene are copolymerized in an emulsion process to first produce VAE compositions containing between 10 and 40 percent ethylene in the copolymer.  Ethylene is a soft, hydrophobic monomer unit in the copolymers, functioning as an internal &#;plasticizing&#; moiety. In copolymers, ethylene effectively reduces the glass transition temperature (Tg) of the hard, polar vinyl acetate monomer, which has a Tg of 30 °C.  Thus, we can achieve copolymers with Tgs ranging from +15 °C to minus 15 °C while converting the base emulsion resins used in the production of the VAE into redispersible powders. By using ethylene monomer to adjust the Tg, the formulator does not require any external plasticizers.

We&#;ve depicted the manufacturing process for redispersible powders below.  Starting with a VAE emulsion produced using a colloid stabilizer like polyvinyl alcohol, the emulsion is mixed with a fine mineral anti-caking agent and then spray-dried.  This affords a stable, free-flowing powder which can be redispersed when mixed with water. The RDP&#;s minimum solid&#;s content is 98 percent; the level of anti-caking agent content is up to 8-12 percent of the total weight.  These VAE&#;s have very low amounts of volatile organic compounds (VOCs) and low odor levels.

The picture below shows the free-flowing nature of the VAE-RDP.  The SEM micrograph shows a VAE solid particle. The anti-caking agent or partitioning agent also appears in the SEM.  The graph on the right shows the particle size dimensions (um) and number average distribution of the original VAE emulsion (red line) and the powder when redispersed into water (blue line).  Noteworthy is the retention of the dimensions of the original VAE emulsion particle, after redispersing the powder. The blue hump in the graph is associated with the anti-caking agent.

VAE-RDP Grades, Properties and Applications

We can segregate the grades and general applications of the VAE-RDPs by glass transition temperature (Tg).  The Tg of an amorphous polymer like VAE is the critical temperature at which the material changes its behavior from being a glassy solid to a rubber material.  When the ambient temperature is above the Tg, the polymer becomes a rubber. When the ambient temperature is less than the Tg, the polymer becomes a glassy material.

In the series of VAE-RDPs, the grades range from low Tg soft materials (DA series) to medium Tg flexible materials (DA- series) to high Tg harder materials (DA series).

Special Grade

The dominant market for VAE RDPs is in the building and construction industry, where they are used to formulate dry-mix products.  The global market for these types of products is projected to grow at more than seven percent. Technological developments in the field of thin-bed tile adhesives is one driver of growth. For wall tile adhesive applications, VAE-RDPs improve slump property, water retention, and workability. This allows tiles to be laid from the top to the bottom without experiencing tile slippage or the need to use spacers. VAE-RDPs also improve the leveling properties of tile adhesives and other cementitious materials. 

Demand for VAE-RDPs has also grown into the area of skim-coat compounds, where VAE contributes increased wall adhesion and crack-bridging properties.

We have provided the recommended grades of Dairen&#;s VAE redispersible powders for various building and construction application applications in the chart below.

Selection Guide for VAE-RDP Grade in Construction Products Applications

Grades

Tile Adhesives

Sealing Slurry

Repair Mortars

Troweling Compounds

Self-Leveling Compounds

Thermal Insulating System

Mineral Plasters

Gypsum-based Compounds

Cementitious Wood Adhesives

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In oil & gas well cementing operations, polymer powder/cement compositions present improved rheological properties and durability, while also imparting fluid-loss to cement slurries and oil field fluids.  The powders enhanced gas migration control to the cement slurries with only a small effect on extending slurry set times. By improving particle-to-particle bonding, the hardened cements/polymer compositions exhibit better flexibility and strength properties, as well as higher adhesion and durability.  For field operations, VAE redispersible powders have advantages in handling, storage, and field mixing, while enhancing water retention, workability, and mechanical strength properties, as well as decreasing permeability of the cementitious materials.

Sales Specifications

We have delineated the  sales specifications for various  grades of VAE-RDPs available from Gantrade and Dairen Chemical below.

Grade

Protective Colloid

Solid Content* wt%

Ash Content* wt%

Bulk Density g/ml

Average Particle Size um

50% Redispersion

Viscosity
cP 25 °C
10rpm

pH

Tg*
(Onset, °C)

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The redispersible powders are available from Gantrade Corporation in 25 kilogram multi-layer paper bags with an inner plastic bag.  We have packaged the 25 kg bags in 450 kg. carton boxes containing 18 units. Flexible jumbo bags are also available in both 550 Kg. and 600 kg sizes within a carton box.  VAE RDPs absorb moisture and should be stored under dry and cool conditions to prevent caking.

We designed this article to help those looking to select the right VAE-RDP for enhancing your specific adhesive, construction compounds, or cementitious products.  Gantrade&#;s professional staff is ready to assist with your selection, ensuring that you match the right VAE-RDP to the performance requirements of your application. Get in touch today!