Cellulose nanofibril core–shell silica coatings and their conversion into thermally stable nanotube aerogels

Abstract

A facile water-based one-pot reaction protocol for obtaining 20 nm thick uniform silica coatings on cellulose nanofibrils (CNFs) are herein presented for the first time. The fully covering silica shells result in a thermal stability of the CNFs improved by ca. 70 °C and 50 °C under nitrogen and oxygen atmosphere, respectively. Heating of the core-shell hybrid fibres to 400 °C results in complete degradation/removal of the CNF cores, and demonstrates an inexpensive route to large-scale preparation of silica nanotubes with the CNFs used as templates. The key to a uniform condensation of the silica (from tetraethyl orthosilicate) to the cellulose is a reaction medium that permits in-situ nucleation and growth of the silica phase on the fibrils, while simultaneously matching the quantity of the condensed silica with specific surface area of the CNFs. Most coatings were applied to bundles of 2-3 associated CNFs, which could be discerned from their negative imprint that remained inside the silica nanotubes. Finally, it is demonstrated how the coated nanofibrils can be freeze-dried into highly porous associated silica/cellulose aerogels with a density of 0.005 g/cm 3 and how these hybrid aerogels preserve their shape when extensively exposed to 400 °C under air (>6 h). The resulting material is the first reported silica nanotube aerogel obtained by using cellulose nanofibrils as templates.

In situ fabrication of cellulose nanocrystal‐silica hybrids and its application in UHMWPE: Rheological, thermal, and wear resistance properties

“…The thermal stability of the CNC was significantly improved after hybrids with inorganic nano‐particles. The T 10% and T max increased by 6.48% and 11.70% when CNC was hybrid with silica, respectively, which was attributed to the strong organic–inorganic phase interactions, i.e., the covalent bonding and hydrogen bonding . The improvement of CNC thermal stability could broaden the processing temperature and then enlarge its application.…”

“…As a common inorganic filler, nano‐silica (SiO 2 ) possesses small size effect, surface and boundary effect, quantum size effect, and so on, which give it high strength, toughness, and thermal stability . Nano‐silica is expected to hybrid with CNC to develop a novel CNC‐SiO 2 nanohybrids with better properties, especially thermal stability . The sol–gel method is a commonly used method for the in situ formation of the nano‐silica.…”

“…Previous research indicated that adopting tetraethyl orthosilicate to in situ generate nano‐silica on cellulose nanofibrils (CNFs) could coat the CNFs with the silica coating of 20 nm thick. The fully covered silica shells greatly improved the thermal stability of the CNFs under either nitrogen or oxygen atmospheres .…”

Optimizing 3D printing performance of acrylonitrile‐butadiene‐styrene composites with cellulose nanocrystals/silica nanohybrids

“…At present, some breakthroughs have been made in the research on CNC nanohybrid materials, and the inorganic materials used are related to graphene oxide, quantum dots, calcium carbonate, silica (SiO 2 ) etc. Among them, nano‐silica (nano‐SiO 2 ) has a small size effect, a large specific surface area and a quantum size effect, imparting high strength and thermal stability . The novel CNC‐SiO 2 nanohybrid materials have been proved by our group to have excellent properties and have achieved satisfactory results in terms of the wear resistance of ultrahigh molecular weight polyethylene .…”

“…Among them, nano‐silica (nano‐SiO 2 ) has a small size effect, a large specific surface area and a quantum size effect, imparting high strength and thermal stability . The novel CNC‐SiO 2 nanohybrid materials have been proved by our group to have excellent properties and have achieved satisfactory results in terms of the wear resistance of ultrahigh molecular weight polyethylene . Unfortunately, research on the use of novel organic–inorganic nanohybrid materials with excellent properties to improve the performance of FDM filaments and printed products has not been reported.…”