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

Abstract

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.