Nanocellulose Hydrogels Research Articles

Influence of radiolysis on the yield of nanocellulose from plant biomass

Radiolysis of plant biomass with doses of 200–300 kGy prior to dispersing by chemimechanical methods increases the yield of nanocellulose from cellulosic feedstock by more than a factor of two. Another advantage of radiation pretreatment of initial samples is the effect of radiation sterilization of isolated nanocellulose hydrogels, whereas the hydrogel obtained without preliminary irradiation rapidly suffers from the attack of molds during storage in the laboratory. Photolysis of plant raw material at a wavelength of 253.7 nm has almost no effect on the yield of nanocellulose. The molecular and supramolecular structure of nanoparticles with a size of 200–300 nm remains unchanged on passing to the nanoscale and corresponds to the macromolecular structure of cellulose. Industrial testing of the hydrogel as an additive (2.5%) for an adhesive composite used in the manufacture of wood laminates (plywood) showed an enhancement of the strength characteristics of the products by 15–20%. The increase in strength is mainly due to an increase in the contact area of cohesive bonding through small coiled molecular entities composed of 10–16 Kuhn segments including up to 28 monomer units each.

Inorganic Hollow Nanotube Aerogels by Atomic Layer Deposition onto Native Nanocellulose Templates

Hollow nano-objects have raised interest in applications such as sensing, encapsulation, and drug-release. Here we report on a new class of porous materials, namely inorganic nanotube aerogels that, unlike other aerogels, have a framework consisting of inorganic hollow nanotubes. First we show a preparation method for titanium dioxide, zinc oxide, and aluminum oxide nanotube aerogels based on atomic layer deposition (ALD) on biological nanofibrillar aerogel templates, that is, nanofibrillated cellulose (NFC), also called microfibrillated cellulose (MFC) or nanocellulose. The aerogel templates are prepared from nanocellulose hydrogels either by freeze-drying in liquid nitrogen or liquid propane or by supercritical drying, and they consist of a highly porous percolating network of cellulose nanofibrils. They can be prepared as films on substrates or as freestanding objects. We show that, in contrast to freeze-drying, supercritical drying produces nanocellulose aerogels without major interfibrillar aggregation even in thick films. Uniform oxide layers are readily deposited by ALD onto the fibrils leading to organic-inorganic core-shell nanofibers. We further demonstrate that calcination at 450 °C removes the organic core leading to purely inorganic self-supporting aerogels consisting of hollow nanotubular networks. They can also be dispersed by grinding, for example, in ethanol to create a slurry of inorganic hollow nanotubes, which in turn can be deposited to form a porous film. Finally we demonstrate the use of a titanium dioxide nanotube network as a resistive humidity sensor with a fast response.

Mechanical Properties of Bacterially Synthesized Nanocellulose Hydrogels

AbstractThe mechanical characteristics of bacterially synthesized nano‐cellulose (BNC) were studied with uniaxial compression and tensile tests. Compressive loads result in a release of water and the deformation of the water‐saturated network corresponds approximately to the volume of released water. The BNC hydrogel exhibits a mainly viscous response under compression. The strain response under tensile loads has an elastic and a viscous component. This can be described with a Maxwell model, where the viscosity is strain rate‐dependent. When the aqueous phase of the BNC hydrogel is stabilized with an additional alginate hydrogel matrix, the system exhibits an elastic response under compressive loads. The analysis of the ‘alginated’ BNC network with the Maxwell model shows that the alginate matrix increases the viscosity of the composite system. The results of the mechanical tests show that the water absorbed in the BNC hydrogel strongly influences its mechanical behavior.