Halloysite nanotubes and thymol as photo protectors of biobased polyamide 11

The formulation of cost-effectiveness sustainable materials is extensively growing and becoming an attractive approach for both industrial and academic fields. In this context, the bio-based aliphatic polyamide 11 (PA11) has acquired significant interest as environmentally friendly thermoplastic option. In addition, its formulation with selected natural antioxidant and/or reinforced compounds through green processing methods, might improve physical and mechanical properties without sacrificing the intrinsic bio-based nature of the matrix. In this work, we have investigated and compared the photo-oxidative degradation processes occurring on PA11 composites based on thymol and halloysite nanotubes prepared by using ball-milling method. In particular, halloysite nanotubes were used as green nano-container of a natural antioxidant molecule, and reinforced nano-filler as well. Molecular and structural information of photo-exposed samples were obtained by using size exclusion chromatography (SEC) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Thermal and mechanical properties were also tested as well as thymol release. Data collected confirmed that PA11 filled with HNTs-Thymol nano-hybrid showed superior durability performance if compared to both pure PA11 and PA11 blend realized by simply adding thymol and HNTs to polymer matrix. Furthermore, we found that HNTs and thymol combined in the nano-hydrid form exhibited an active and synergic role to achieve a major photo stabilization of PA11 biocomposite, without sacrificing its mechanical properties.