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crystalline cellulose

02.07.2015

Everyone talks about cellulose fibers, pulp, but what is crystalline cellulose? The fiber consists of nanofibrils, nanofibrils - of polymer filaments, and in some areas long cellulose molecules are firmly connected by hydrogen bonds and highly ordered, while in others they have an amorphous structure.

Cellulose, purified from lignin and hemicellulose, is soft and fibrous. But if it is treated, for example, with a strong acid or an enzyme that destroys the disordered sections of the polymer, then miniature needles of nanometer diameter will remain, consisting of tightly packed fragments of glucose chains. These needles - crystalline nanocellulose (CNC) - are stronger than Kevlar and carbon fiber, and cost ten times less. Their output is about 30% of the pulp mass, they hope to bring the price in mass production to several dollars per kilogram. In addition, cellulose nanocrystals are transparent, and nanocrystalline cellulose films have interesting optical properties.

Cellulose fibers, or nanofibrils, of nanometer diameter and a few micrometers long, are also useful materials; they can be used to make nanocomposites, films for various filters, and solutions of cellulose nanofibers have unusual physical properties. Unlike many other nanoparticles, nanocellulose is completely biocompatible and does not inspire fear in the most ardent environmentalists. These materials have an important disadvantage - high hygroscopicity: even small particles of wood tend to bind water. But here the cards are already in the hands of chemists and technologists.

Hydrophobic, plastic and transparent nanocellulose films have recently been obtained by a group of Japanese researchers who have been working for many years with cellulose nanofibers oxidized with NaClO in the presence of (2,2,6,6-tetramethylpiperidin-1-yl)-oxyl (TEMPO or TO for short) and bromide. sodium. During oxidation, free surface -CH2OH groups are converted into carboxyl -COO-; the researchers called such nanofibers TOCN. In this work, the Japanese obtained films by drying an aqueous TOCN dispersion with quaternary alkylamines, molecules in which four alkyl chains are attached to one positively charged nitrogen atom. Alkylamines became counterions for carboxylate surface groups and imparted plasticity to the film - alkyl chains cover its surface and occupy the space between nanofibers.

In addition, the nanocellulose film became water-repellent: if tetra(n-butyl)-ammonium is used, then the contact angle with water reaches 100°. Such nanofibrils can be a filler in hydrophobic polymer matrices.

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The Sunswift 7 electric car weighs only 500 kg. That's about a quarter of the weight of a typical Tesla car. To invest in such a small weight limit, engineers had to abandon the air conditioning system, ABS brakes, airbags, wipers and other features familiar to production cars. Instead, engineers focused on aerodynamic efficiency and rolling resistance. If the Tesla Model S has a drag coefficient of 0,208, then the Sunswift 7 has a drag coefficient of only 0,095.

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