Effect of mercapto-silanes on the functional properties of highly amorphous vinyl alcohol composites with reduced graphene oxide and cellulose nanocrystals

The reinforcing and synergistic effect of a 1D filler (cellulose nanocrystals) and of a 2D filler (reduced graphene oxide) in a high amorphous vinyl alcohol (HAVOH) polymer has been investigated. Nanocomposite films have been obtained by dissolving in water the HAVOH polymer and suitable fillers, thus leading to the formation of a very promising material for eco-friendly food packaging applications. In addition, the effect of (3-Mercaptopropyl) trimethoxysilane as crosslinking agents for the vinylalchol-based polymer has been studied. FTIR and XPS results clearly show that the presence of mercapto silane has a twofold effect. Mercapto groups have the capability to reduce chemically the graphene oxide (GO) filler to reduced graphene oxide (rGO) during the preparation of the HAVOH-based composites and to crosslink the HAVOH structure. Tensile tests show that the effect of siloxane crosslinking leads to an embrittlement of the HAVOH matrix, which is avoided when rGO e cellulose nanocrystals (CNC) are dispersed in the composites. The permeability results show that all the composites exhibit better barrier properties than pristine HAVOH. Particularly, the highest water permeability reduction of about 45% is observed for the sample containing 1% wt/wt GO and 1% wt/wt CNC. This significant drop in permeability is likely related to three concurrent effects, a) the crosslinking of HAVOH matrix, b) the binding of water molecules due to CNC presence and c) the more hydrophobic behaviour associated to a high amount of rGO.