Application of HPMC in Self-compacting Concrete
November 27th 2024
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.
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