2.2. Preparation of Copolymers Samples with Varying Concentrations of Sorbitol

To create copolymers samples with sorbitol, the following procedure was conducted: individual weights of 0.0, 0.5, 1, 1.4, 1.8, 2, 2.5, 3.75, and 4 g of sorbitol were measured. Each amount of sorbitol was mixed with 1 kg of virgin copolymer resin. Subsequently, each mixture was pre-blended at 800 rpm for 7 min using a standard Prodex Henschel 115JSS mixer. Following this, each sample was extruded in a Welex-200 24 extruder. This extruder operates with five temperature zones along the entire extrusion process, maintaining temperatures of 190, 195, 200, 210, and 220 °C. This ensures a uniform mixture. At the end of the extruder, a molten PP-Sorbitol blend is obtained. For each type of molten blend, 30 g of molten material was fed into a CARVER 3895 hot press. In this CARVER machine, the samples were compressed to create films with a diameter of 300 mm and a thickness of approximately 100 µm. The films obtained in the experiment were identified as PP/PE1 (0 ppm sorbitol), PP/PE2 (500 ppm sorbitol), PP/PE3 (1000 ppm sorbitol), PP/PE4 (1400 ppm sorbitol), PP/PE5 (1800 ppm sorbitol), PP/PE6 (2000 ppm sorbitol), PP/PE7 (2500 ppm sorbitol), PP/PE8 (3750 ppm sorbitol), and PP/PE9 (4000 ppm sorbitol).

Samples of copolymer in different forms (films, pellets, and ground material) to which sorbitol was added were obtained. Cyclohexane was used as the extraction solvent, and the ultrasonication technique was employed (in a conventional laboratory ultrasonic bath). For the ultrasonic bath, 5 g of PP was added to a 30 mL vial, and then 20.0 mL of the internal standard solution was added using a 5.0 mL micropipette. The sonication process was carried out for three hours in the ultrasonic bath, maintaining the temperature under control, with a maximum of 50 °C. After the sonication process was completed, the vials were removed from the ultrasonic bath and left to stand for 10 min. Disposable PTFE syringe filters were used to filter the extracted sorbitol sample solutions. In the case of crushed, pelleted, and films, the extraction took place for 60 min in the ultrasonic bath, with the solution being agitated for at least 25 s every 10 min.