Polymers come in many types and have many different physical forms. This gives a very wide range of properties that can be created.

There are two main types of polymer used in the road industry

Elastomeric
Plastomeric
Elastomeric:

Elastomeric polymers are ones, which have a high level of elastic recovery. Unlike true elastic materials elastomeric materials absorb energy by extending or straining. They have a structure then which will allow them to recover.

This is a time dependent function that is although there may be some instant recovery- real elastic behavior- most of the recovery will be over time. For this reason such materials are usually better on deflecting pavements or in crack treatments.

See figure This shows the stages of strain as the sample is stressed then released. The recovery is part elastic part elastomeric and part irrecoverable.

Examples are SBS, SBR, Crumb rubber, SEBS.

Plastomeric:

Plastomeric materials are ones that have a high stiffness and can resist deformation. They are called Plastomeric because they exhibit plastic flow, or irreversible deformation when certain yield strength is exceeded. Such materials will exhibit some elastomeric properties and have some recovery below this yield strength. For this reason such materials are better for deformation resistance and high temperatures applications where the base bitumen may be soft.
Figure shows the different behavior of materials. Plastomeric is like behavior A, B and C. Elastomeric like D.
Examples are EVA, EMA, Urethanes, Polyesters, Polyethylene

Figure shows load elongation curves for polymers that give

Brittle fracture
Ductile fracture
Plastic flow
Elastomeric behavior
In most countries elastomeric materials are chosen as they give elastic recovery, so better crack resistance and deformation resistance and they have high softening points and low Fraas points so they cover hot and cold weather.

Compatibility:

Compatibility between bitumen and polymer is a key issue to performance. Low compatibility results in poor use of polymer and inferior properties.

Compatibility requires a design and optimization of the formulation. This must be done in the laboratory and with respect to the needed field properties.

The compatibility can also be observed by the rate of separation of the polymer from the bitumen.

Bitumen may be made compatible with polymer by the use of additives.

Manufacture:

Manufacture of polymer-modified binders requires correct formulation and the right polymers, additives and bitumen.

A colloid mill is usually required or other system that allows high shearing of the polymer into the bitumen. The polymer is usually pre-wetted with the modified bitumen before milling.

VSS can supply the state of the art colloid mill blend systems.