Understanding hemicellulose-cellulose interactions in cellulose nanofibril-based composites
JOURNAL OF COLLOID AND INTERFACE SCIENCE
Authors: Lucenius, Jessica; Valle-Delgado, Juan Jose; Parikka, Kirsti; Osterberg, Monika
Abstract
Plant-based polysaccharides (cellulose and hemicellulose) are a very interesting option for the preparation of sustainable composite materials to replace fossil plastics, but the optimum bonding mechanism between the hard and soft components is still not well known. In this work, composite films made of cellulose nanofibrils (CNF) and various modified and unmodified polysaccharides (galactoglucomannan, GGM: hydrolyzed and oxidized guar gum, GGhydHox: and guar gum grafted with polyethylene glycol, GG-g-PEG) were characterized from the nano- to macroscopic level to better understand how the interactions between the composite components at nanoimicroscale affect macroscopic mechanical properties, like toughness and strength. All the polysaccharides studied adsorbed well on CNF, although with different adsorption rates, as measured by quartz crystal microbalance with dissipation monitoring (QCM-D). Direct surface and friction force experiments using the colloidal probe technique revealed that the adsorbed polysaccharides provided repulsive forces-well described by a polyelectrolyte brush model - and a moderate reduction in friction between cellulose surfaces, which may prevent CNF aggregates during composite formation and, consequently, enhance the strength of dry films. High affinity for cellulose and moderate hydration were found to be important requirements for polysaccharides to improve the mechanical properties of CNF-based composites in wet conditions. The results of this work provide fundamental information on hemicellulose-cellulose interactions and can support the development of polysaccharide-based materials for different packaging and medical applications. (C) 2019 The Authors. Published by Elsevier Inc.
HST/FGS Trigonometric Parallaxes of M-dwarf Eclipsing Binaries
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC
Authors: van Belle, Gerard T.; Schaefer, Gail H.; von Braun, Kaspar; Nelan, Edmund P.; Hartman, Zachary; Boyajian, Tabetha S.; Lopez-Morales, Mercedes; Ciardi, David R.
Abstract
Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) trigonometric parallax observations were obtained to directly determine distances to five nearby M-dwarf/M-dwarf eclipsing binary systems. These systems are intrinsically interesting as benchmark systems for establishing basic physical parameters for low-mass stars, such as luminosity L, and radius R. HST/FGS distances are also one of the few direct checks on Gaia trigonometric parallaxes, given the comparable sensitivity in both magnitude limit and determination of parallactic angles. A spectral energy distribution (SED) fit of each system's blended flux output was carried out, allowing for estimation of the bolometric flux from the primary and secondary components of each system. From the stellar M, L, and R values, the low-mass star relationships between L and M, and R and M, are compared against idealized expectations for such stars. An examination on the inclusion of these close M-dwarf/M-dwarf pairs in higher-order common proper motion (CPM) pairs is analyzed; each of the 5 systems has indications of being part of a CPM system. Unexpected distances on interesting objects found within the grid of parallactic reference stars are also presented, including a nearby M dwarf and a white dwarf.