Study on the Sorting Process on the Basis of the Effect of Shrinkage and Melting of Plastics and Its Impact on Further Processing of the Materials

Abstract

In the era of high generation of waste, it is necessary to improve the sorting processes in order to obtain clean, homogeneous secondary raw materials suitable for recycling. The article presents the results of experimental studies aimed at finding the optimal separation method for two-component waste, in which one of them is plastic, and the previously known methods are ineffective or are not economically justified. Two methods have been proposed based on the use of two specific properties of plastics: precisely defined melting point and temperature shrinkage. As a result, the two technologies of separation were developed. Both involve heating the waste until the expected changes in the waste material are achieved. Determined experimentally the optimal melting point parameters for the tested polystyrene and polypropylene waste were 150ºC and 180ºC, respectively, with a 7-second contact time with a metal surface. The optimal shrinkage for PS occurred at 160°C with a 2-minute heating time, and for the tested PP, the optimal shrinkage temperature was 170°C, applied for 4 minutes. Both proposals were tested in laboratory and technical conditions, giving satisfactory results, and then successfully used in the industry. In order to extend the research, it is planned to expand the range of plastics and their mixtures with other wastes, as well as to develop a comparative test of the adhesion strength of melted plastics to various surfaces. At the suggested temperatures of thermal sorting, there is no depolymerization of materials. Thus, the proposed method of shrinkage and melting in the sorting process can serve as a step of separating the PP or PS material from the waste mixture without its negative impact on further processing processes in thermal, chemical or mechanical recycling.