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 grapheneoxide) in a high amorphous vinyl alcohol (HAVOH) polymer has been investigated. Nanocomposite films havebeen obtained by dissolving in water the HAVOH polymer and suitable fillers, thus leading to the formation of avery 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 andXPS results clearly show that the presence of mercapto silane has a twofold effect. Mercapto groups have thecapability to reduce chemically the graphene oxide (GO) filler to reduced graphene oxide (rGO) during thepreparation of the HAVOH-based composites and to crosslink the HAVOH structure. Tensile tests show that theeffect of siloxane crosslinking leads to an embrittlement of the HAVOH matrix, which is avoided when rGO ecellulose nanocrystals (CNC) are dispersed in the composites. The permeability results show that all the compositesexhibit better barrier properties than pristine HAVOH. Particularly, the highest water permeabilityreduction of about 45% is observed for the sample containing 1% wt/wt GO and 1% wt/wt CNC. This significantdrop in permeability is likely related to three concurrent effects, a) the crosslinking of HAVOH matrix, b) thebinding of water molecules due to CNC presence and c) the more hydrophobic behaviour associated to a highamount of rGO.