Rheology-morphology relationships of new polymer-modified bitumen based on thermoplastic polyurethanes (TPU)

Abstract

The present study reports a new type of polymer-modified bitumen (PMB) which considers the use of a thermoplastic polyurethane (TPU) as an alternative to conventional thermoplastic elastomers such as poly(styrene-b-butadiene-b-styrene) block copolymers. As for other block copolymers, the structure of the TPU, made of two types of segments which can microphase-separate, leads to its selective swelling by the oily fractions of bitumen. The poor compatibility of hard segments (HS) with bitumen is responsible for this partial swelling of the TPU by the maltene fractions. By varying the TPU content in the bitumen-TPU blend a dramatic change in viscoelastic properties for a TPU content close to 11 wt% is shown, with the appearance at high temperatures of an elastic response due to the percolation of the TPU-rich phase. This percolation phenomenon is highlighted by multiscale morphology characterizations and well described by a conventional mechanical percolation model. Different TPU architectures, i.e. different hard to soft segments ratios, are studied. The best compromise is found for a blend containing TPU with 13 wt% of HS as it displays a favorable swelling of percolated TPU rich phase while maintaining its viscoelastic behavior.