Pyrolysis of polyolefin plastic waste and potential applications in asphalt road construction: A technical review

Pressures on the current plastic waste management infrastructure has made the growth of new sustainable recycling capacities crucial. Pyrolysis is an emerging thermochemical technology that may be utilised at a large scale to aid in reaching the EU 2030 targets for plastic waste. Plastic valorisation via this process could gain increased competitiveness with conventional methods through the use of concepts such as ‘Design for Recycling’, identifying further marketable applications for pyrolysis end co-products. This paper presents a review on the pyrolysis of the most abundant plastic waste polyolefins, low-density polyethylene (LDPE), high-density polyethylene (HDPE) and polypropylene (PP), with a focus on the heavy wax products. A sizeable research gap in its known applications outside of the petrochemical and chemical feedstock industries was identified. Furthermore, its potential use in the hot mix asphalt (HMA) layers of flexible roads as an alternative binder material and aggregate is discussed. A plastic-derived bitumen modifier could be a viable solution to the current limitations associated with plastic bitumen modifiers (PMB), while producing asphalt with enhanced rheological properties and failure resistances. Consequently, future trends in research may include obtaining a full understanding of the capacity for pyrolysis products from waste polyolefins in bitumen modification. The key relationships between pyrolysis process parameters and the subsequent product properties, modification mechanisms and binder performance may also be explored. This application pairing process for pyrolysis products from plastic wastes may also be more extensively adopted in sustainable infrastructure, as well as other industries.