Sustainable Polymers from Recycled Waste Plastics and Their Virgin Counterparts as Bitumen Modifiers: A Comprehensive Review

Abstract

The failure of bituminous pavements takes place due to heavy traffic loads and weather-related conditions, such as moisture, temperature, and UV radiation. To overcome or minimize such failures, a great effort has been put in recent years to enhance the material properties of bitumen, ultimately improving field performance and increasing the pavement service life. Polymer modification is considered one of the most suitable and by far the most popular approach. Elastomers, chemically functionalised thermoplastics and plastomers * (* Note: notwithstanding the fact that in Polymer Science the word ‘plastomer’ indicates a polymer with the simultaneous behaviour of an elastomer and plastics (thermoplastics), this paper uses the term ‘plastomer’ to indicate a thermoplastic polymer as it is more commonly found in Civil and Pavement Engineering.) are the most commonly used polymers for bitumen modification. Plastomers provide several advantages and are commonly acknowledged to improve high-temperature stiffness, although some of them are more prone to phase separation and consequent storage instability. Nowadays, due to the recent push for recycling, many road authorities are looking at the use of recycled plastics in roads. Hence, some of the available plastomers—in pellet, flakes, or powder form—are coming from materials recycling facilities rather than chemical companies. This review article describes the details of using plastomers as bitumen modifiers—with a specific focus on recycled plastics—and how these can potentially be used to enhance bitumen performance and the road durability. Chemical modifiers for improving the compatibility between plastomers and bitumen are also addressed in this review. Plastomers, either individual or in combination of two or three polymers, are found to offer great stiffness at high temperature. Different polymers including HDPE, LDPE, LLDPE, MDPE, PP, PS, PET, EMA, and EVA have been successfully employed for bitumen modification. However, each of them has its own merit and demerit as thoroughly discussed in the paper. The recent push in using recycled materials in roads has brought new light to the use of virgin and recycled plastomers for bitumen modification as a low-cost and somehow environmental beneficial solution for roads and pavements.

Using Plastic Waste in a Circular Economy Approach to Improve the Properties of Bituminous Binders

“…In the case of PMB + wax, because of the introduction of the functional additives already mentioned, it was not the case that the penetration grade was higher (and the softening point was lower) than for PMB. This disposition was in line with what is suggested by several authors, such as those mentioned in [3], who recommended that additives to modify bitumen must have, among other attributes, the ability to reduce its thermal susceptibility.…”

“…In this sense, as explained by Russo et al [1] when referring to the road infrastructure pavement sector, an appropriate contribution to the fulfilment of this goal can be given by the incorporation of different materials (including waste) that improve the performance of bituminous mixtures. These materials comprise not only a variety of polymers [2] (such as styrene-butadiene-styrene (SBS), poly(ethylene terephthalate) (PET), high-density polyethylene (HDPE), low-density polyethylene (LDPE), polystyrene (PS), polyurethane (PU), polypropylene (PP), crosslinked polyethylene (XLPE or PEX), acrylonitrile butadiene styrene (ABS), ethylene-vinyl acetate (EVA), styrene-isoprene-styrene (SIS), and others), Sulphur, mineral acids, and sustainable polymers from recycled waste plastics [3] but also different types of waxes (natural or synthetic).…”

Recent advances in the construction of sustainable asphalt roads with recycled plastic

“…24 Wet method Low-melting-point plastics such as PE (T m = 100-140 °C) and PP (T m = 150-170 °C) are commonly used as bitumen modifiers and incorporated via the 'wet method' where the plastics are melted with hot bitumen at 160-180 °C before the blend is added to hot aggregates. 14 It is crucial not to find any residues of high-melting-point plastics, such as PET and polystyrene (T m > 200 °C), or impurities, such as paper or metal, in the recycled plastic sources to ensure that all the plastics are evenly melted in bitumen. Such residues are commonly found in PC recycled plastics (Fig.…”

“…8,12,13 Although virgin thermoplastics have successfully been used in bituminous materials, 10 the overall sustainability, feasibility and environmental impact of using recycled plastic waste in asphalt pavements are still under debate among the scientific community. 10,14 Economic benefits are indeed limited by the low cost of virgin materials and the amount of plastic that can be incorporated in roads due to asphalt production and road performance constraints. The potential leaching of hazardous contaminants present in plastic and the release of microplastics (MPs) in the environment must also be controlled to ensure that the sustainability of using recycled plastic in roads is maintained.…”

Performance Optimization Approach of Polymer Modified Asphalt Mixtures with PET and PE Wastes: A Safety Study for Utilizing Eco-Friendly Circular Economy-Based SDGs Concepts

“…The performance parameters and ultimate stability of asphalt pavements are heavily reliant on the binder's functionality. The degradation of the bitumen binder causes a wide range of road pavement failures such as cracking failures, rutting, and fatigue cracking [1,2]. Moreover, the increasing cost of bitumen has significant effects on the overall project cost.…”