Bio-based chitosan supramolecular shell enabling synergistic flame retardancy and anti-aging in polypropylene

Commercial intumescent flame retardants (IFRs) effectively reduce the flammability of polypropylene (PP) but significantly deteriorate its weather resistance. Although hindered amine light stabilizers (HALS) can improve UV-aging resistance, their intrinsic acid-base antagonism with IFRs limits their combined application. In this study, a bio-based supramolecular approach is proposed by employing chitosan (CS) as a functional shell to encapsulate HALS116, forming a core-shell structured light stabilizer (CS@HALS116). The resulting PP/IFR/CS@HALS116 composites exhibit excellent flame retardancy, achieving a limiting oxygen index (LOI) of 30.0% and a UL-94 V-0 rating. Thermal analysis shows that the chitosan shell broadens the effective thermal action range of HALS116 to above 600 °C, preventing its premature degradation from interfering with char formation while enabling gas-phase radical scavenging. Meanwhile, the composites demonstrate outstanding UV-aging resistance, retaining 95.1% of tensile strength after 120 h of UV exposure and maintaining the V-0 rating. The carbonyl index (CI) is reduced to 0.37, much lower than that of neat PP (0.72). Mechanistic analysis reveals a dual anti-UV effect: the chitosan shell physically shields the NOR structure from acidic attack, while the hydrogen-bond network facilitates proton transfer and enhances nitroxide radical (NO·) regeneration. This work highlights a bio-based supramolecular design strategy for overcoming incompatibility in multifunctional polymer systems, offering a promising route toward durable and sustainable polyolefin materials.