Modulation of surface properties of cellulose substrates by adsorption of Passerini-modified polysaccharide derivatives: Towards advanced paper packaging – Moderato

The Moderato interdisciplinary project involves two academic partners (IMP, CERMAV) who are experts in polysaccharide modifications and characterizations, and the Technical Center of Paper (CTP), a French Technical Institute dedicated to the pulp, paper and board industries. It aims at designing novel families of chemically modified polysaccharides, to be used as bio-based functional coatings in order to impart paper materials with barrier properties, which will be enhanced and maintained upon changes of relative humidity and temperature, for end-uses in the flexible food packaging field. The cornerstone of the Moderato project is to exploit the appealing Passerini-three component reaction (P-3CR), and to apply it to both polysaccharide chains (carboxymethyl cellulose, alginic acid) and cellulose particles (oxidized cellulose microfibrils, MFCs) to graft onto the biopolymer backbone and at the surface of MFCs judiciously chosen hydrophobic and/or thermosensitive derivatives. P-3CR, a reaction at low environmental impact, is particularly attractive since this catalyst-free atom-economy route based on the reaction of three precursors (carboxylic acid-isocyanide-aldehyde) is efficient in mild aqueous conditions, and allows for designing dually functionalized derivatives in a one-pot manner through the formation of an acyloxycarboxamide ligation. After two intensive tasks of synthesis and detailed characterization, the P-3CR modified biosourced polymer chains and particles will be coated onto cellulosic/paper substrates by using well-managed physical deposition processes. The adsorption and film-forming mechanisms as well as the (topo)chemical, physico-chemical, and morphological features of the coatings will be investigated in-depth in a third task, while a final fourth task will be focused on the barrier properties against liquids (H2O, grease), and gazes (water vapor, O2), the recyclability ability, the harmlessness and the economic viability of the coated cellulosic substrates. The ternary relationship between the chemical structure, characteristics of the coatings and barrier properties will be established in order to optimize the design of the modified polysaccharides and their film-forming ability towards the best barrier properties and industrially-compatible products. The twofold hydrophobization (triggered or not by a T° increase) of the polysaccharides, never described for this aim, is targeted to lead to a permeability decrease by conferring an enhanced water-repellent character to the coating (“umbrella” effect), and by restricting the chains mobility by the formation of hydrophobic interactions able to generate a highly packed coating in its entire depth. The use of MFC with high ratio aspect constitutes an additional asset to lead to a hierarchized percolating coating, presenting a peculiar tortuosity efficiently impeding the permeation of small species. Moreover, the employment of degradable polymers functionalized by a hydrolysable ligation and the use of physically adsorbed coatings are factors expected to facilitate a good recyclability of the coated cellulose substrates (eco-conception). In addition to the development of biobased products fulfilling the needs to exhibit good barrier properties maintained upon relative humidity and temperature changes, the Moderato project strategy will provide pivotal knowledge in the understanding of the mechanisms governing the permeability phenomena.