Technological Considerations Regarding the Mechanical Recycling of Waste from Polyethylene and Polypropylene Packaging

Plastic materials have found applications in almost all fields as a result of their properties and low price. More than 30% of the production of plastics is intended for obtaining packaging. Since they are non-biodegradable and represent a hazard to the environment, strategies and directives have been adopted at national, European, and global level, regarding the recycling of packaging waste. The main ecological method of recycling them is mechanical recycling. The paper presents the main stages of an industrial mechanical recycling process, namely: collection, sorting, grinding, washing, drying, (purification), granulation, packaging, storage and marketing. This underlines the fact that in order to obtain high-performance PE or PP raw materials from recyclable polymer waste from packaging, the recycling process requires advanced sorting to separate them into polymer classes, because the mixtures of the polymers involved are incompatible in their melted state. This incompatibility leads to the lower processability and physical-mechanical performance of the products manufactured from these types of recycled polymer waste. In addition to the sorting methods currently used in the industry, new advanced methods of selective sorting of waste according to the type of polymer were also presented, such as: spectroscopic method, selective dissolution of polymers, thermal adhesion method, froth flotation method, electrostatic separation methods. It was emphasized that by using state-of-the-art technologies such as electron beam treatment followed by the electrostatic separation of waste mixtures from packaging, it is possible to obtain recycled polymers with high purity (90-97%) at advantageous production costs.