Mitigating UV‑C Degradation in Polypropylene Using Hybrid TiO₂/Few-Layer Graphene/Photostabilizer Systems

Polypropylene (PP) is a versatile thermoplastic widely used in industrial fields. In medical devices, PP is preferred for applications that involve storing or coming into contact with biological fluids. However, when exposed to UV-C, commonly used as a cleansing tool in hospitals, PP undergoes a photodegradation process, resulting in chain scissions and branching reactions that impact the material properties and lifespan. Different photostabilizers can be used to enhance polymer resistance against UV, such as UV screeners like titanium dioxide rutile (TiO₂), radical scavengers like Irganox B215, a commercial H-donor and peroxide scavenger, and, more recently, graphene and its derivatives like few-layer graphene (FLG). Graphene has gained attention as an alternative photostabilizer in polymers for having different types of UV photoprotection mechanisms, such as UV absorbers/screeners and radical scavengers. In this context, this study aimed to evaluate the effectiveness of FLG and Irganox B215 as radical scavengers in combination with TiO₂ to minimize the effect of parallel radical formation (ROS) from TiO₂ electron-hole reactions and from the PP photodegradation autocatalytic cycle. A Design of Experiments (DoE) approach was employed to identify the optimal UV-C photostabilization mixture. Infrared spectroscopy and rheological measurements were used to assess the effects of UV-C photodegradation on PP. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to analyze the stabilizer distribution and dispersion, and electron paramagnetic resonance evaluate the effectiveness of FLG and Irganox B215 as radical scavengers. EPR results showed that mixing radical scavengers with TiO₂ reduced OH formation by ∼30% for the FLG and ∼25% for the B215 mixture. Although the stabilizers exhibited poor dispersion but good distribution, the addition of FLG had a synergistic effect with TiO₂. At the highest level (+1), i.e., TiO₂ 3% and FLG 2% m/m, PP UV-C photoprotection was enhanced by diminishing chain scission and scavenging ROS from TiO₂.