THE USE OF RE-DISPERSIBLE POLYMER___________________
Re-dispersible polymer powder is obtained by spray-drying a polymer emulsion normally with a PVA as protective colloid.
When added f.i. in a cement or cement mortar when mixed with water It is dispersed to form an emulsion again.
Addition of a polymer in either emulsion or as re-dispersible latex to a dry-mix mortar is to improve its properties.
HOW IT WORKS __________________________________________
When cement is brought in contact with water hydration starts and calcium hydroxide is released immediately and quickly reaches saturation and precipitates crystalline phases in form of ettringite and hydrated calcium silicate gel.
Polymer particles are deposited on the gel formed as well as on un-hydrated cement particles.
As this process continues and the amount of hydrates increase, fine polymer particles gradually fill the pore structure and form a dense layer within the matrix.
This film enrobes the fine cement grains preserving moisture in the pore structure enabling complete and full hydration.
Formation of ettringite and calcium hydroxide crystals may be effected by formation of a layer on the interface of cement grains and polymer, leading to retardation of cement hydration.
On the other hand active groups in polymer molecules will be cross-linking with phases of these cement hydrates.
As the water content is further reduced by hydration and evaporation, polymer particles condense closely forming a flexible film improving the adhesion of cement and fillers.
This bond of cement hydrates and polymer improves the physical structure of hardened cement; internal stress is relieved and micro-cracking reduced.
In further hydration of cement water is consumed from the capillary pore structure and replaced by viscous polymer particles adhering on to un-hydrated cement and fillers.
After drying in most cases the continuous film formed by the construction of a polymer network is insoluble in water.
