Films de PLA y PLA-PHB plastificados para su aplicación en envases de alimentos. Caracterización y análisis de los procesos de degradación

Laburpena

Plasticized PLA-PHB films for food packaging applications. Characterization and analysis of degradation processes The main objective of this thesis was the development and characterization of biodegradable films based on poly(lactic acid) (PLA) with improved properties for their application in food packaging. To modulate PLA properties and to improve its functionality the incorporation of different additives was studied through melt blend process, such as plasticizers (D-limonene, poly(ethylene glycol) (PEG) and acetyl(tributyl citrate) (ATBC)), another biopolymer (poly(hydoxybutyrate) (PHB)), nanocomponents (cellulose nanocrystals (CNC)) and one antioxidant ((+)-catechin). PLA plasticization was evaluated through the addition of two different concentrations of D-limonene and the structural, thermal, mechanical and oxygen barrier properties of these materials were evaluated. Flexible materials were obtained due to the reduction of the glass transition temperature. The increase in PLA chain mobility generated an increase of oxygen permeability and material showed reduced thermal stability. The addition of 25wt% of PHB increased the crystallinity and as a consequence the oxygen permeability decreased and the surface humidity of PLA. The plasticization of PLA-PHB blends improved the interaction between the polymers, increased the ductility and speeded up the degradation process in compost, but the thermal stability was not improved. The best results were obtained with ATBC. To improve the thermal stability of materials cellulose nanocrystals (CNC) were synthesized from microcrystalline cellulose (MCC). The incorporation of 5 wt% of cellulose nanocrystals resulted in a significant improvement in thermal stability by increasing the process window. In the subsequent step, cellulose nanocrystal surface was modified by means of a surfactant to avoid nanocrystals agglomeration. The functionalization of nanocrystals (CNC-s) resulted in a homogeneous dispersion of them in the PLA-PHB matrix and the obtained materials showed improved mechanical and barrier properties. Likewise, CNC-s produced a decrease of the UV light transmission and also speeded up the degradation in composting of materials. Finally, the addition of (+)-catechin as the active agent provided effective protection of biopolymers against their oxidative degradation while releasing into fatty food simulant showed significant antioxidant activity. The materials retained their structural and mechanical properties during exposure to food simulant.