Nanofibril reinforced unsaturated polyester nanocomposites: Morphology, mechanical and barrier properties, viscoelastic behavior and polymer chain confinement

•Higher aspect ratio of the nanofibrils led to improved network and good mechanical properties.•From viscoelastic properties, the amount of polyester chains confined at the nanofibrils were quantified.•To understand the role of the constrained region, a constrained polymer model is proposed.•With respect to the neat, the percentage increase in tensile strength was 57%.•The presence of INF increases the Tg of polyester matrix by 10°C. Isora nanofibrils (INFs) were extracted from Helicteres isora plant by steam explosion process and the resulting fibers were analyzed by transmission electron microscopy (TEM). It is observed that nanofibrils showed network like structure with a length of 300nm, width of 20nm and an aspect ratio of 15. Then these nanofibrils were incorporated into unsaturated polyester (UPR) by conventional mechanical mixing process. Higher aspect ratio of the prepared nanofibrils led to improved network in the polyester matrix and this resulted in good mechanical properties of the prepared composites. With respect to the neat polyester, the percentage increase in tensile strength of 0.5wt% INF filled nanocomposites was 57%. From the data of viscoelastic properties obtained, the amount of polyester chains confined at the cellulose nanofibrils were estimated and quantified. The volume fraction of the constrained region is highest for 0.5wt% INF. To understand the role of the constrained region in enhancing the mechanical properties of the nanocomposite, a constrained polymer model is proposed. The presence of INF increases the Tg of polyester matrix by 10°C. Spectroscopic studies revealed the presence of strong hydrogen bonding interaction between nanofibril surface and polyester matirx. Composites showed 73% decrease in water absorption indicating superior barrier properties of nanocelluose in the polyester matrix due to the network formation of the nanofibrils in the polyester matrix.