Abstract
This work established an energy-saving and straightforward treatment of cellulosic pulp to obtain functional cellulose nanofibers equipping them at the same time with catalytic activity and flame-retardant properties. For this purpose, dried cellulose pulp was mixed with a recyclable swelling agent, ZnCl2 hydrate, at room temperature. The mild treatment affected the crystal structure through a partial amorphization, yielding a mix of native cellulose I and regenerated cellulose II. This treatment tremendously facilitated the fibrillation into a cellulose nanofiber (CNF) network. In comparison to fibrillated cellulose from nontreated pulp, the ZnCl2-treated counterpart featured higher viscosity, film transparency, better mechanical properties, and higher heat stability. Films produced from these nanofibers showed flame-retardant properties without any further modification. The ZnCl2–CNF showed also high reactivity in fiber surface acetylation and allowed a fast and efficient reaction while using very mild conditions. All in all, we propose a simple and resource-efficient cellulose treatment to obtain a nanostructured cellulose. These nanofibrils are decorated with ZnCl2 which imposes flame-retardant properties and confined catalytic activity at the fibril surface.
Highlights
Cellulose is the most abundant renewable polymer and bioproduct on Earth, which is found in plants and in some animals and bacteria.[1]
One type of cellulose that has gained huge attention as a research subject is nanostructured cellulose, which is a term for cellulosic materials with at least one dimension being in the nanometer range,[4] nanocrystalline and nanofibrillar cellulose being the two most prominent subforms, which are referred to as cellulose nanocrystals and cellulose nanofibers (CNF), respectively
One group of solvents used for cellulose pretreatment are molten salt hydrates which are nonderivatizing per se, though they can be used as media for chemical derivatization.[8−10] ZnCl2 hydrate is the inorganic molten salt hydrate[10] most widely used for dissolution of cellulose and as a medium for hydrolysis and derivatization.[11]
Summary
Cellulose is the most abundant renewable polymer and bioproduct on Earth, which is found in plants and in some animals and bacteria.[1]. ZnCl2 hydrate melts are used to obtain vulcanized fibers This process works by swelling and subsequent gelation of the cellulose fiber exterior, which increases interfibrillar adhesion, preserving the native cellulose I structure.[15] The presence of. In our search for environmentally friendly, energy-saving methods for the production of functionalized cellulose nanofibers, the utilization of ZnCl2 hydrate melt as a physical and mild pretreatment met all our prerequisites, offering established recovery procedures, chemical innocuousness, and the plus of simultaneously introducing new advantageous properties. The swelling of the cellulose fibrils by the salt hydrate melt reduces the amount of energy necessary for homogenization of the fibrils to nanocellulose This letter demonstrates these advantages and studies the functionalization of these nanocelluloses with regard to their increased thermal stability and catalytic activity
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