Various polymers can be used for bitumen modification, including caoutchouc. The key property of caoutchouc is stretching 2-10 times with application of a stretching force and return to initial state afterwards.
This is due to the structure of caoutchouc. Macromolecules of this substance are coiled, therefore, interaction between them is much weaker than intermolecular bonds. Also, macromolecules are only connected in certain locations.
Due to the large size of caoutchouc macromolecules the material solves in organic solvents poorly. The situation can be improved by:
- intensive stirring;
- milling at elevated temperature;
- thermomechanical destruction of molecules.
Consider the types of caoutchouc which can be used in modification of road bitumens.
Butadiene-styrol caoutchouc includes 21-25% styrol and methyl styrol. These substances have a molecular weight of 150 to 400 thousand and a density of 930 kg/m3. Butadiene-styrol caoutchouc is produced by polymerization of divinyl with styrol.
Butyl caoutchouc is produced by copolymerization of isobutylene with 1-5% isoprene. With 910-920 kg/m3 density, the molecular weight of this caoutchouc is 300-700 thousand. Composition and structure of butyl caoutchouc is similar to those of natural caoutchouc. This substance is resistant to cold and acids, flexible, gas tight and stable to oxidation.
Butyl caoutchouc is widely used in construction industry as a base material for production of sealants, adhesive mastics and modification of bitumen. Caoutchouc comes in the form of liquid, water dispersion and solid elastic product.
Ethylene propylene caoutchouc is a copolymer of ethylene, propylene and diene hydrocarbon. Due to its structure, this material is resistant to weather, water and cold. The same properties are assumed by bitumen-caoutchouc binders.