**1. Introduction**

The goal of realizing the conditions for achieving a truly circular economy is one of the main challenges in which scientists are involved to solve the problems concerning both global warming and the end of mineral resources. Over the last twenty years, the number of companies involved in environmental issues is continuously increasing and now almost all companies are, even in a different way, involved to solve this problem. These resources also represent a strong driving force for the development of sustainable industrial processes.

The world plastic production in 2019 was 368.0x106 tons with an increase of 2.5% concerning for 2018 [1] while in the same year the European production was 57.9x106 tons among thermoplastic and thermosetting polymers.

Among them, polyolefins are the most produced and employed materials for applications in everyday life for industrial, domestic, and technological applications [1]. They are thermoplastic polymers and are mainly used for packaging, whose life cycle is very short which means they may be disposed of in a short time after their production. A less important part of them is employed to realize furniture, insulating materials, automotive parts, and so on and their life cycle is considerably longer (ten years or more).

Polymeric materials are easily recycled through mechanical processes, as reported in **Figure 1**, for the production of renewed objects prolonging the life of these plastic materials, avoiding their disposal through landfilling or combustion, and reducing

the use of raw materials. This is a very friendly and economic process, however, it may be applied only when a single plastic material is available or when the material is not contaminated or strongly deteriorated. In these cases, other routes such as thermochemical processes may be followed as an environmentally friendly procedure avoiding to send these materials to combustion or landfilling, so giving a contribution to realizing a circular economy and reducing the emission of greenhouse gases (GHG).

Thermochemical processes may supply fuels and chemicals using recycled or renewable feedstock as alternatives to oil-based raw materials [2]. These led to the development of new technologies able to carry out the optimal use of such resources minimizing the environmental impact and producing a limited amount of secondary waste. It means that waste disposal or contaminated plastic materials may be transformed into useful products. Among these processes, the microwaves technologies have taken large attention due to their high efficiency to supply the energy required for a plethora of industrial processes. The main performances on the use of microwave as correlated to a classical heating system are resumed in **Table 1**.

### **Figure 1.**

*Pathway to recycle thermoplastic materials.*


### **Table 1.**

*Correlation between microwave and conventional heating.*

This chapter aims to offer a comprehensive description of new results reported to provide an updated description to the specialist and open this knowledge to a greater audience. So our intent is to contribute to extend the application of this technology to many other fields.
