# Using Plastic Waste in a Circular Economy Approach to Improve the Properties of Bituminous Binders
## 1 Introduction
As a curiosity, these last authors also used an orthogonal array (fractional factorial design) of the Taguchi method to optimize the wax production in their reactional system. In the same direction, other recent reviews [9; 10] showed that transforming waste plastic into other products is a procedure with great potential and meets several of the mentioned U.N. Sustainable Development Goals (SDG). According to the estimates cited in [10], this conversion, through chemical recycling (where pyrolysis is included), could represent a saving of 3.5 billion barrels of oil per year. The Circular Plastics Alliance, created under a European Strategy for Plastics initiative ([[https://ec.europa.eu/growth/industry/strategy/industrial-alliances/circular-plastics-alliance_en](https://ec.europa.eu/growth/industry/strategy/industrial-alliances/circular-plastics-alliance_en)]([https://ec.europa.eu/growth/industry/strategy/industrial-alliances/circular-plastics-alliance_en](https://ec.europa.eu/growth/industry/strategy/industrial-alliances/circular-plastics-alliance_en)), accessed on 23 February 2022), is already pushing for this processing, having committed to boosting \"_the EU market for recycled plastics to 10 million tonnes by 2025_\". Indeed, one of the most sustainable and efficient processes for obtaining waxes (>C21) is pyrolysis, which happens in the absence of oxygen (usually at a temperature between 350 \({}^{\circ}\)C and 900 \({}^{\circ}\)C). Another exciting advantage of the pyrolysis of plastic waste, particularly polyolefins (PO) (that constitute about % of the overall plastic waste), is that it can be carried out in small units close to collection sites, thus avoiding their high transport costs [5]. However, [PERSON] et al. [11] mentioned that the tertiary methods (chemical) of waste plastic recycling (which also include pyrolysis) usually have high costs. In [12] can be found a very recent review of three pyrolysis processes of various plastic wastes (with the respective average production by a fraction): slow pyrolysis (usually performed at temperatures ranging from 350 \({}^{\circ}\)C to 550 \({}^{\circ}\)C and heating rates from 1 to 10 \({}^{\circ}\)C/min \(\rightarrow\) produces more wax than oil), fast pyrolysis (generally at temperatures between 500 \({}^{\circ}\)C and 700 \({}^{\circ}\)C with heating rates above 1000 \({}^{\circ}\)C/min \(\rightarrow\) yields more liquid hydrocarbons), and flash pyrolysis (commonly above 700 \({}^{\circ}\)C \(\rightarrow\) releases more gas than liquids and more oil than in fast pyrolysis). As pointed out by [PERSON] et al. [13], pyrolysis offers valuable products that are rich in hydrocarbons (liquid and wax--predominantly composed of alkanes and alkenes), and it is interesting for waste management and treatment activities [14]. It is also suitable to reprocess polymers that are difficult to recycle or even non-recyclable, including polypropylene (PP), polystyrene (PS) mixtures, and others. Consequently, different waxes that can be mixed with bituminous binders are available, namely those produced from waste plastic bags [15], PEX waste [6; 16; 17], PE waste [18], HDPE or low-density polyethylene (LDPE) [19], as well as Fischer-Tropsch wax (FTW) [20] (currently with some limitations because this process is essentially carried out using coal). Some authors [9] also highlighted the need to reduce biodiesel' percentage of waxes to avoid the filters' clog. Therefore, this removal can lead to its greater availability. The processing of plastic waste through pyrolysis is also economically viable on an industrial scale, taking into account the value of its calorific potential, as confirmed by [PERSON] et al. [21]. In the profitability analysis of the pyrolysis suggested by those authors, a rate of return on investment (ROI) of 54% was achieved (assuming a feed rate of 40 tons/day and that the plastic waste would be collected, transported, and delivered to the processing site free of charge).