Modeling of negative Poisson’s ratio (auxetic) crystalline cellulose Iβ

Energy minimizations for unstretched and stretched cellulose models using an all-atom empirical force field (Molecular Mechanics) have been performed to investigate the mechanism for auxetic (negative Poisson’s ratio) response in crystalline cellulose Iβ from kraft cooked Norway spruce. An initial investigation to identify an appropriate force field led to a study of the structure and elastic constants from models employing the CVFF force field. Negative values of on-axis Poisson’s ratios nu31 and nu13 in the x1-x3 plane containing the chain direction (x3) were realized in energy minimizations employing a stress perpendicular to the hydrogen-bonded cellobiose sheets to simulate swelling in this direction due to the kraft cooking process. Energy minimizations of structural evolution due to stretching along the x3 chain direction of the ‘swollen’ (kraft cooked) model identified chain rotation about the chain axis combined with inextensible secondary bonds as the most likely mechanism for auxetic response

Thermal characterization of chicken feather/PLA biocomposites

In this work, thermal properties of composites from chicken feather fiber (CFF) and polylactic acid (PLA) were investigated. CFF/PLA green composites were manufactured by extrusion and injection molding. Short and long fibers (3 and 20 mm) were used at different contents (2, 5 and 10 mass%). The effects of fiber concentration and fiber length on thermal properties of CFF/PLA composites were studied. Thermal properties of CFF/PLA composites were examined through differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and dynamic mechanical analysis (DMA). From the experiments, it was found that addition of CFF was effective to improve the thermal properties of PLA. The DSC results showed that heat flow increased with the increase in CFF content on the glass transition, on the crystallization temperature and on melting temperature. The TG results revealed that addition of CFF to PLA had positive effect on the thermal stability. In addition, the results of DMA experiments showed that the tan δ decreased with the increasing CFF content, indicating less damping and more elastic behavior in the composites. The results obtained from this study provide important information on the temperature-dependent properties of CFF/PLA and lead to new product development based on natural resources. © 2017, Akadémiai Kiadó, Budapest, Hungary