20. Recycling Polymer Blends

Starting with the second half of the 1970s, polymer recycling was extensively adopted to reuse plastics otherwise destined for landfills with the goal to avoid the consequent net loss of money and energy. The simple idea to reintroduce scraps or post-consumer plastics in the processing lines actually revealed complications because even adding the recycled polymer to the same virgin material often led to secondary materials due to differences in the molecular weight, branching, and difference of density. The situation appeared more complicated in the recycling of commingled plastics. In this case, the chemical nature and structures of the different components produce secondary materials with poor properties, thus inhibiting any possible practical application. Nevertheless, enforcement of the law about mandatory collection of post-consumer plastic and the repeated economic crises pushed toward the implementation of recycling of polymer blends in industrial processes, especially if the same processing equipments/methods used for virgin materials can be adopted. In this chapter a review of the recycling technologies of plastic blends is presented. In particular, the mechanical recycling of single polymers in the same virgin materials (the so-called “homopolymer” blends), typical in the on-site reuse of industrial scraps, and, in another section, the strategies that can be pursued to recycle directly a stream of commingled post-consumer plastics to obtain secondary materials with properties suitable for practical applications are analyzed.