Plasma-Induced Reactive Compatibilization of Polypropylene/Polyamide 6 Blends

The immiscible nature of most polymers causes challenges while formulating blends due to their interfacial tension and uncontrolled phase separation. Reactive compatibilization addresses this issue by introducing interconnecting groups, thereby reducing interfacial tension and stabilizing the morphology. This study investigated the use of a nonequilibrium atmospheric pressure air plasma jet (APPJ) during the extrusion process as a reactive compatibilization method for polypropylene (PP) and polyamide 6 (PA6) blends. As a proof of concept, we first evaluated the effect of plasma on the chemical structure and mechanical properties of PP and PA6. Attenuated total reflectance Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy analysis of the plasma-treated PP (pPP) revealed distinct peaks corresponding to hydroxyl and carbonyl stretching vibrations, confirming the presence of polar functional groups. Blends of PP/PA6 with 20/80, 50/50, and 80/20 weight ratios, with and without polypropylene grafted maleic anhydride (PP-g-MAH) as a compatibilizer, were compared to pretreated (PTIP) and in situ treated (PTB) blends. The PTIP blends demonstrated a significant increase in tensile strength and modulus compared with the untreated blends. Scanning electron microscopy of plasma-treated PP/PA6 blends revealed an excellent morphology akin to PP-g-MAH blends. Unlike PTB and untreated blends, the PTIP blends exhibited a continuous phase morphology. Compared to PTB blends, the plasma pretreatment in PTIP blends ensured comprehensive generation of reactive functional groups, resulting in significantly improved interfacial interactions and enhanced stress transfer during subsequent blending. FTIR spectroscopy at the Australian Synchrotron indicated that plasma-treated and PP-g-MAH compatibilized blends exhibited comparable molecular orientations at the interfaces. These findings demonstrate the effectiveness of plasma treatment in the reactive compatibilization of PP/PA6 blends, offering a sustainable method to enhance blend compatibility in polymer recycling processes.