Active bi-layer cellulose-based films: development and characterization

This work aims at the development and characterisation of bio-based active bi-layer films by solvent casting and electrospinning in order to be used for setting up active packaging solutions. Ethyl cellulose was used as the main material for the production of a layer on microfibrillated cellulose (MFC) films. This layer was formed with and without the incorporation of cinnamaldehyde (CNMA) which was used as antimicrobial compound. The MFC structures were obtained with a combination of different fibre dimensions and degree of fibrillation resulting in 16 different structures with porosities varying from 33 to 63%. A computational 3D simulation study of the porous structures was performed providing information about thickness, porosity and pore size uniformity and based on that a Picea abies-based MFC structure was selected. Structure characterization was evaluated using scanning electron microscopy, and pore dimensions were quantified using an image analysis tool. The bi-layer films chemical properties were studied using Fourier transform infrared spectroscopy and X-ray diffraction. Regarding barrier properties the bi-layer films produced by solvent casting were the ones showing a better barrier capacity. Both solvent casting and electrospinning processing showed to be useful to obtain a more hydrophobic surface (evaluated through contact angle measurements), being the higher values obtained for bi-layer films produced by electrospinning. Regarding colour parameters, the bi-layer films showed to be highly influenced by the production method and by the incorporation of CNMA. Regarding the antimicrobial activity, the bi-layer films with the incorporation of CNMA showed high antimicrobial activity against Listeria monocytogenes and Salmonella Typhimurium when the solvent casting method was used. Overall results showed that MFC-based films can be functionalised through the casting or electrospinning of ethyl cellulose solutions, aiming an antimicrobial and hydrophobic bi-layer film based on cellulose.