Plant molecule to make our roads greener

Use of a plant molecule in asphalt and sealant mixtures could make roads environmentally friendly and help roofs hold up better under different weather conditions, contends a study.

The plant molecule called lignin could one day replace bitumen, a by-product of crude oil production which is currently used as the main sticky ingredient in asphalt and roof sealants, noted the study presented at the 249th National Meeting & Exposition of the American Chemical Society (ACS) in Denver.

As oil is a non-renewable resource and fluctuations in the oil market have made it more difficult to get high-quality bitumen, manufacturers have been forced to look for alternatives, said Ted Slaghek, senior scientist at TNO, a non-profit organisation in the Netherlands.

"In the long term, we have to move to renewable products that we can harvest every year," pointed out Slaghek.

Lignin is a renewable resource that makes up as much as a third of the dry material in trees, where it keeps out water and binds together other components of plant biomatter, like cellulose, the researchers noted.

Lignin is also plentiful -- and therefore, inexpensive, the researchers noted.

To use it as an additive, the researchers said, lignin must be integrated into the bitumen on the molecular level, not just mixed into it. By integrating the lignin, it is possible to reduce the amount of bitumen needed by as much as half, Slaghek said.

As with other additives, lignin makes sealants perform even better -- but those polymer additives come from petroleum sources, making them just as problematic as bitumen.

Slaghek's team developed a number of lignin-bitumen mixtures that make the asphalt harder in warm weather, preventing rutting and adding several years to a road's lifespan.

"We have also developed lignin-bitumen mixtures that keep the bitumen more tacky, so at lower temperatures it is still a good road," Slaghek added.