Effects of degradation of 3D- printed recycled glass fiber- reinforced polypropylene on mechanical behavior

Abstract

The growing need to reuse plastic waste has increased interest in recycled polymers for structural and semi- structural applications. Recycled polypropylene (rPP), when combined with glass fiber reinforcement and processed via 3D printing, presents a promising route for reducing plastic waste while enabling the fabrication of load-bearing components. However, the long-term durability and environmental resistance of 3D-printed rPP reinforced with glass fibers (rPP-G) remain insufficiently understood. This study investigates the degradation behavior of 3D-printed rPP-G under combined ultraviolet (UV) radiation, elevated temperature (60 and 80 °C), and high humidity (up to 95% Relative Humidity).
Results show that under moderate aging (60 °C), rPP-G retains relatively stable tensile properties with only minor reductions in strength and stiffness. In contrast, more severe aging at 80 °C and 95% RH results in notable deterioration, including approximately a 6% decrease in ultimate tensile strength, a 2% reduction in Young’s modulus, and a 30% decline in storage modulus compared to unaged material. Additionally, a shift in glass transition temperature toward lower values suggests increased molecular mobility and reduced stiffness. Creep performance is significantly affected under severe conditions, with a substantial reduction in time to failure (up to 522.58% reduction compared to the unaged specimen), indicating compromised long-term load-bearing capability.
SEM analysis reveals increased fiber pull-out and interfacial debonding, while ATR-FTIR confirms oxidative degradation. Humidity is identified as the dominant degradation factor, with temperature acting as a key accelerator. These findings highlight both the potential and limitations of rPP-G for outdoor structural applications.