Influence of storage conditions on starch/PVA films containing cellulose nanofibers

Abstract

Cellulose nanofibers (CN) with high aspect ratio were obtained and their transverse modulus (Et) was determined for the first time by peak force (PF) QNM (quantitative nanomechanical mapping). The PF QNM value of Et (18.8GPa) was comparable with that of cellulose determined by other methods. CN were used as reinforcements in starch/poly(vinyl alcohol) (S/PVA) cross-linked films and the influence of storage conditions on the properties of these films was investigated in this paper. It was found that over 4wt%, CN form a real network and hinder starch recrystallization. CN determined a significant increase of strength and stiffness of S/PVA depending on storage conditions. Two fold increase of modulus was observed in thermal treated samples compared to fresh ones and the increase of both strength and modulus in samples exposed to humid atmosphere. PF QNM successfully explains the influence of moisture on the properties of the films exposed to humid atmosphere, emphasizing new well organized sub-micron amorphous formations on their surface. Starch films with 7wt% CN showed strength and stiffness close to that of polyolefines (19.5MPa and 1199MPa, respectively), and can be seen as a low cost “green” substitute for application in food packaging and conservation.