10 May 2012
What is Atactic Polypropylene
Polypropylene is a, fatigue resistant, thermoplastic, used in a wide variety of applications. It is not a rubber. The addition of approximately 30% of APP modifier can increase the flexibility of the bitumen binder to such an extent that it may stretch up to fifty percent of its original length before fracturing.
When added to the bitumen binder in the production of bituminous roofing membranes it extends fatigue resistance and by definition life span. As a general rule the greater the amount of polymer added the greater the performance of the modified bitumen However the improvement only takes place up to a certain percentage of the mix after which the addition of the polymers makes no difference to performance. Bitumen becomes hard and brittle when it freezes and liquid as the temperature increases. The addition of polymers greatly increases the flexibility of bitumen at very low temperatures and stability as the temperature increases.
Atactic polypropylene is polymerized polypropylene. The link between the structure of polypropylene and its properties, the relative orientation of each methyl group relative to the methyl groups in neighboring monomers, is tacticity. When the methyl groups in a polypropylene chain exhibit no preferred orientation, the polymers are called atactic. Atactic polypropylene is an amorphous thermoplastic material with very high adhesive properties and when added to bitumen the bitumen assumes some of the qualities of the Actactic Polypropylene.
APP membranes are often assumed to more resistant to UV light radiation than SBS membranes and are often left exposed. This is a mistake. APP membranes should be protected by a coating of mineral granules or alternative solar protection.
The use of atactic polypropylene in bitumen membranes greatly increases the cost of the membrane. Membranes vary greatly in price and as a general rule the less expensive the price the less polymer additive in the bitumen binder; the lower the performance characteristics of the membrane.