Development and characterisation of acid free mushroom dervied multilayer chitosan coating for grease resistant paper packaging

Paper-based packaging systems could be considered as potential substitutes to current plastic ones, thus reducing plastic waste and environmental impact. However, paper implementation in food packaging, and more specifically in case of fatty foods is constrained by its porous structure which limits barrier properties, and enhances the quick migration of oil and grease. This thesis assesses an acid-free chitosan coating made from mushrooms as a completely bio-based surface treatment, to enhance the functional performance of Avana kraft white paper for fatty foods packaging. Acid-free chitosan solution was prepared according to an innovative procedure by exploiting water carbonation. Plasticized and non-plasticized chitosan solution was deposited by rod coating with a different number of layers (1-8). The obtained packaging system was characterized from physical, chemical and barrier properties perspectives. At low coating layers, the chitosan solution primarily penetrated and filled the paper pores. A continuous surface film only formed after pore saturation, which led to a non-linear increase in coating accumulation with layer number. FTIR spectroscopy confirmed chitosan deposition and its progressive surface enrichment with increasing layers; multivariate assessment and semi-quantitative band-ratio analysis confirmed a shift toward saturation following the intermediate build-up phase. Tensile experiments showed that the coating architecture and glycerol addition significantly change the coated papers' toughness, elongation at break, Young's modulus, and ultimate tensile strength when compared to the uncoated substrate. Even with increasing coating mass and thickness, water vapor transmission measurements revealed that the naturally hydrophilic cellulose–chitosan system did not provide a significant moisture barrier, resulting in WVTR values that are comparable to the reference paper. However, testing of grease penetration at 40°C and 60°C revealed a discernible, layer-dependent delay in oil permeability. The best protection was provided by multilayer structures, suggesting that coating architecture is an important design lever for fatty food packing performance. Overall, the work finds multilayer chitosan coatings as a scalable, sustainable method to improve grease resistance while preserving a recyclable, fiber-based packaging idea and demonstrates structure–property connections for acid-free chitosan-coated paper.

I sistemi di imballaggio a base carta rappresentano una possibile alternativa ai materiali plastici tradizionali, contribuendo alla riduzione dell’impatto ambientale. Tuttavia, nel packaging di alimenti grassi, la carta presenta limiti legati alla sua struttura porosa, che facilita la migrazione di oli e compromette le proprietà barriera. In questo lavoro è stato studiato un rivestimento di chitosano acid-free di origine fungina come trattamento superficiale completamente bio-based per carta Avana kraft bianca. La soluzione è stata ottenuta tramite una procedura basata sulla carbonatazione dell’acqua e applicata mediante rod coating con 1, 4 e 8 strati, in formulazioni plasticizzate e non plasticizzate. I risultati mostrano che ai bassi numeri di strati il chitosano tende principalmente a penetrare nei pori del substrato; solo con l’aumento della deposizione si osserva la formazione di un film più continuo, con un incremento non lineare dello spessore. L’analisi FTIR ha confermato la progressiva presenza del rivestimento sulla superficie. Dal punto di vista meccanico, numero di strati e contenuto di glicerolo influenzano in modo significativo le proprietà del materiale. Le prove di trasmissione del vapore acqueo non hanno evidenziato miglioramenti rilevanti nella barriera all’umidità, mentre i test di penetrazione dei grassi hanno mostrato un netto aumento della resistenza con l’incremento degli strati. Nel complesso, lo studio evidenzia come l’architettura del rivestimento sia determinante per ottimizzare le prestazioni di packaging fibrosi sostenibili.