Currently, the world is facing the problems of the gradual depletion of nonrenewable fossil resources and the severe harm of non-degradable plastic waste to the land and marine ecological environment. Because of the rapid increase in the demand for fiber materials, the development of high-performance biomass-based fibers has emerged as an important research topic to reduce the reliance on petroleum-based synthetic fibers. In this study, a novel green wet-spinning strategy is used for the fabrication of super-strong and super-stiff chitosan filaments from an aqueous KOH/urea solution using a two-step drawing process. The highly ordered hierarchical structure of the resulting filaments contributes to their excellent mechanical properties. The tensile strength and Young's modulus of the chitosan filaments are 878 ± 123 MPa and 44.7 ± 12.3 GPa, respectively, and these values are comparable to those of spider silk and bacterial cellulose. The chitosan filaments prepared in this study are superior to low-density steel in terms of the specific strength and modulus. The green and scalable strategy proposed in this study will broaden the application range of chitosan filaments in flexible bioelectronics, biomaterials, and textiles.
The rapid dissolution of β-chitin and hierarchical self-assembly of chitin chains have long attracted research from the perspectives of both the fundamental sustainable chemistry and potential applications in materials chemistry....
We report the design and fabrication of double-network polyurethane (PU)/nanoporous cellulose gel (NCG) nanocomposites with excellent mechanical properties, multistimuli-responsive shape-memory effects, and solvent resistance using NCG as a 3D reinforcement nanofiller for the PU network. The interconnected nanofibrillar cellulose networks of the NCG are finely distributed and preserved well in the PU network after polymerization. The modified percolation model agrees well with the mechanical properties of the PU/NCG nanocomposites. The remarkable reinforcement effect on the PU network is most probably due to the incorporation of the permanent, rigid, three-dimensional percolating network of the NCG that successfully transfers mechanical stresses through the covalent cross-linking, hydrogen bonds, and chain entanglements between the NCG and PU networks. The PU/NCG nanocomposites have excellent shape-memory properties with good thermal-and water-stimuli responsiveness, good dimensional stability, excellent solvent resistance, and outstanding mechanical properties in organic solvents, and they have considerable potential applications in switchable devices, sensors, biomaterials, and many other fields.
Nanocellulose has
attracted significant attention due to its fascinating
properties and great potential in the preparation of high-performance
functional materials for specific end-use applications. Most cellulose
nanocrystals and cellulose nanofibrils are in the cellulose I crystal
structure; however, attempts to fabricate cellulose nanofibrils with
the cellulose II crystal structure by self-assembly from cellulose
solutions are rarely reported. Here, we demonstrate a new approach
to the fabrication of carboxymethylated cellulose nanofibrils (CMCNFs)
by homogeneous carboxymethylation and the self-assembly of cellulose
chains from cellulose solutions using sequential “top-down”
and “bottom-up” strategies. Furthermore, CMCNFs were
used as reinforcing nanofillers to enhance the properties of water-borne
polyurethane (WPU) and were evenly distributed in the WPU matrix.
Dynamic thermomechanical analysis on the WPU/CMCNF nanocomposites
demonstrated a significant reinforcement effect based on the tensile
storage modulus above the glass transition temperature of the soft
segments of the WPU, and the results were well-fit by the percolation
model. The sequential top-down and bottom-up strategies developed
here produce CMCNFs and should contribute to the reinforcement of
polymer matrices, improving the practical exploitation of CMCNFs.
Polysaccharide-based
materials, which have the advantages of abundant
reserves and excellent biocompatibility and biodegradability, have
attracted growing interest due to public awareness of sustainable
development. Herein, we demonstrate the formation of high-strength
and high-toughness double-cross-linked (DC) cellulose films. For the
first time, stress whitening of DC cellulose films is reported, which
has never been observed in cellulose-based films or other polysaccharide-based
materials. The epichlorohydrin-to-anhydroglucose unit of cellulose
(ECH-to-AGU) molar ratio, ethanol concentration, and relative humidity
are critical parameters that influence the microstructure and stress
whitening of DC cellulose films. Moreover, the incorporation of chemically
and physically cross-linked heterogeneous structures, strong hydrogen
bonding, and irreversible chemical covalent interactions among cellulose
chains endows DC cellulose films with excellent mechanical properties
and superior toughness. The drawing orientation can produce extremely
high-strength and high-toughness DC cellulose films with tensile strength,
Young’s modulus, and work of fracture values of 234 MPa, 9.3
GPa, and 28.2 MJ·m–3, respectively. The developed
DC cellulose films also exhibited excellent thermomechanical properties,
moderate thermal stability, and extremely low oxygen permeability
and should contribute to potential applications in food and drug packaging,
battery separators, and biodegradable flexible electronics.
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