Preparation, characterization and barrier properties of silver/montmorillonite/starch nanocomposite films

The present work reports a strategy involving the preparation of nanocomposite films based on a natural biodegradable matrix. The polymer was a natural potato starch and the nanofillers were silver nanoparticles (AgNPs) and a natural montmorillonite (MMT). The AgNPs were prepared by an ex situ or an in situ method. The influence of the preparation method of AgNPs and the presence of MMT were investigated on the structure, morphology, water sorption and oxygen barrier properties of the nanocomposite films. Two distinct AgNPs populations in size were highlighted from the ex situ method, whereas one population was highlighted from the in situ method. Crystalline AgNPs were obtained only from the in situ method. The addition of MMT did not modify drastically the average size and size distribution of AgNPs despite the presence of some clusters of AgNPs in the vicinity of lamellar layers of MMT. The in situ formed AgNPs had a predominant role on the oxygen barrier properties with a 90% improvement independently of the presence of MMT for water activity (aw) equal to 0.45. This significant improvement was mainly related to the crystalline structure of the AgNPs and the cohesive interface between the AgNPs and the starch polymer matrix. Synergism effect of the AgNPs and MMT leading to 65% improvement for aw=0.45, was observed when AgNPs were prepared by the ex situ method and was related to the intercalation of AgNPs between the lamellar layers of MMT which led to improve the dispersion of MMT within the polymer matrix.