TECHNICAL NOTES

Technote 7: Polymer Modified Emulsions

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Polymer modified emulsion may be prepared several ways and contain several different polymer types. The method of preparation and the polymer chosen will affect the performance of the cured binder.

Types:

Basic polymer types in used for emulsions are:

1. Anionic styrene butadiene high solids latex (SBR) Roadchem™ 615,616
2. Cationic styrene butadiene high solids latex (SBR). Roadchem™ 600
3. High solid natural latex (flipped for cationic, straight for anionic) - Roadchem™ 604
4. Synthetic latex of various types- polyurethane, acrylic)
5. Styrene Butadiene Block copolymer- radial. Roadchem™ 108
6. Styrene Butadiene Block copolymer- linear Roadchem™ 105
7. SEBS
8. EVA –Roadchem™ 106
9. EMA -Roadchem™ 503
10. Crumb Rubber, Roadchem ™ 110

Addition:

Polymer may be added to the emulsion in several ways:

1. Via latex added either into the emulsion, soap solution or directly injected into the colloid mill (a-d).
2. Via pre-blending with binder before emulsification (e-j).

Which is chosen will depend on the final application and the binder properties needed. For almost all road applications latex is satisfactory. SBS, EVA and EMA modified emulsions are used for some sealing and industrial applications and for this pre-blended polymer bitumen is needed.

Latex is best added by comilling this will give the best dispersion of latex in the emulsion and in the final polymer bitumen film.

What Polymers Can Do?

Polymers are much larger molecules than bitumen so they can have a dramatic effect on bitumen film properties. Polymers will:

• Increase the softening point: - the flow point is higher and so susceptibility to bleeding is decreased
• Increase the binder viscosity:- the resistance to flow is higher at any given temperature so film thickness can be higher with subsequent improved aging resistance.
• Decrease the thermal susceptibility:- the binder has higher stiffness at high temperature and lower stiffness at low temperature, that is its properties are much more uniform with temperature.
• Increase the elastomer properties: The ability to absorb energy and elongate with stress and recover after stress is removed. Leads to improved deformation and crack resistance.
• Increase cohesion: Improved strength to resist fracture
• Increase low temperature tensile strength and flexibility: Leads to better low temperature crack resistance and less likelihood of brittle fracture at low temperatures

The polymer type and method are chosen according to the final binder properties needed. VSS is pleased to assist. VSS can formulate any polymer emulsion for any application.