An Efficient Method for Recycling Polypropylene with the Antioxidant Additive Propyl Gallate

In this study, a new approach to stabilizing polypropylene (PP) melts using the bio-based antioxidant propyl gallate (PG) is considered. Since PG is extensively used in the food and cosmetics fields and its low doses do not cause reactions in humans, producing PP melts with PG is an interesting approach. Furthermore, PG is already actively used in the processing of natural polymers, for example, in the NMMO process. It is shown that introducing up to 0.2 wt.% PG into the system is sufficient to significantly reduce the decrease in melt viscosity during repeated PP processing. After five processing cycles, the viscosity of systems with PG decreases by less than an order of magnitude, while for melts without the antioxidant the viscosity drops by almost three orders of magnitude to 10 Pa s. For melts with antioxidant additives, the crossover point position in the frequency dependences remains virtually unchanged, indicating the preservation of the system’s elastic properties. Macrofibers were spun from the resulting melts, which can then be used for concrete reinforcement. For the spun fibers with PG, the strength decreased to 68.1 MPa after five passes, whereas for the PP fibers, the values did not exceed 31 MPa. The structure and properties of the fibers were studied using X-ray diffraction and IR spectroscopy, and contact angles were determined.