Citric acid crosslinking of poly(vinyl alcohol)/starch/graphene nanocomposites for superior properties

Abstract

Polyvinyl(alcohol)/starch/graphene nanocomposites with enhanced properties were prepared by solution mixing and casting process with the aid of glycerol as plasticizer and citric acid (CA) as crosslinker. The dispersion of graphene in water was made by sonication prior to mixing it with PVA/starch solution. The effect of varying the concentration of CA crosslinker in PVA/starch nanocomposite with 0.5 wt% of graphene was studied in detail. The structural changes, properties and morphologies were characterized by different techniques. The FTIR results revealed that the crosslinking reaction enhanced the interaction between the hydroxyl groups in PVA and/or starch and the oxygen-containing groups present on the graphene sheets. The mechanical properties were also improved by the crosslinking reaction and reinforcing with graphene. The formation of PVA crystal from solution was interrupted to a large extent by the interface at the amorphous zone of polymers and also the crosslinks between the PVA and starch polymer chains. The total crystallinity of the system was found to decrease with increase in degree of crosslinking. There was a marked increase in the thermal stability as the blend system was crosslinked with CA. CA crosslinking produced compact bulk morphology and improved the homogeneity between PVA and starch. The results of this study illustrate that citric acid can be an effective crosslinker and/or compatibilizer in PVA/starch/graphene nanocomposites for improving properties, and for this reason it is a candidate to replace non-biodegradable plastic films in food packaging sector.