An overview of the effect of recycling processes on the mechanical and thermal properties of natural fiber composites

The escalating environmental challenges posed by plastic pollution and agricultural waste have accelerated interest in sustainable composite materials that support circular economy frameworks. This review critically evaluates the recyclability of natural fiber composites, focusing on tensile strength, elastic modulus, degradation temperature (TGA), and melting behavior (DSC). The findings indicate that flax/PP-g-MA composites retain up to 85% of tensile strength after five cycles, while PLA-based systems degrade more rapidly. These insights highlight the industrial potential of recycled biocomposites in packaging, automotive interiors, and construction. Drawing from a wide range of studies involving fibers such as rice husk, flax, hemp, bagasse, and wood flour in matrices like recycled polypropylene (RPP), polylactic acid (PLA), and polyethylene (PE), the analysis highlights key degradation mechanisms including fiber attrition, polymer chain scission, and reduced interfacial bonding. Mechanical testing consistently shows that tensile strength and elastic modulus are retained during early recycling stages but gradually decline with repeated processing. Thermal assessments, including thermogravimetric and differential scanning calorimetry analyses, reveal a 5–10 °C reduction in onset degradation temperature after 3–5 cycles, while melting points confirms remain stable within ± 2 °C. Despite performance losses, many composites maintain acceptable properties for low to moderate load-bearing applications such as packaging, automotive interiors, and consumer products. The findings underscore the potential of natural fiber composites to be reused effectively over multiple cycles, offering a viable pathway for sustainable material development and waste valorization in Malaysia and globally.