Highly tough and transparent layered composites of nanocellulose and synthetic silicate

Abstract

A highly tough and transparent film material was prepared from synthetic saponite (SPN) nanoplatelets of low aspect ratios and nanofibrillar cellulose. The nanofibrillar cellulose was chemically modified by topological surface oxidation using 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) as a catalyst. Both synthetic SPN nanoplatelets and TEMPO-oxidized cellulose nanofibrils (TOCNs) have abundant negative charges in high densities on their surfaces and are dispersed in water at the individual nanoelement level. Layered nanocomposite structures of the SPN nanoplatelets and TOCNs were formed through a simple cast-drying process of the mixed aqueous dispersions. The TOCN/SPN composites with 0-50% w/w SPN content were optically transparent. Mechanical properties of the TOCN/SPN composites varied depending on the SPN content. The composite with 10% w/w SPN content (5.6% volume fraction) exhibited characteristic mechanical properties: Young's modulus of 14 GPa, tensile strength of 420 MPa, and strain-to-failure of 10%. The work of fracture of the composites increased from 4 to 30 MJ m(-3)- or by more than 700%--as the SPN content was increased from 0 to 10% w/w. This surprising improvement in toughness was interpreted based on a model for fracture of polymer composites reinforced with low-aspect-ratio platelets.

Mechanism of TEMPO-oxidized cellulose nanofibril film reinforcement with poly(acrylamide)

“…A similar explanation is used for the nano-reinforcement effect of nanoclay/TOCN composite films (Wu et al 2012(Wu et al , 2014, and therefore these effects are characteristic of TOCNs, which form self-aligned and nematic-ordered domain structures in aqueous dispersions. A schematic diagram of the mechanism of the improvement of the tensile properties of PAM/ TOCN = 25/75 composite films is shown in Fig.…”

“…If TOCNs can be replaced by an inexpensive conventional polymer, while giving mechanical, optical, oxygen-barrier, and thermal properties similar to those of 100 % TOCNs, less expensive materials for use in various high-tech fields could be produced. Because TOCN is nanodispersible in water, it is advantageous for TOCNs to contain water-soluble polymers or water-nanodispersible nanoclays to achieve homogeneous distribution of TOCN elements in matrix polymers or inorganic nanoparticles (Henriksson et al 2008;Johnson et al 2009;Sehaqui et al 2010Sehaqui et al , 2011Liu et al 2011;Endo et al 2013;Wu et al 2012Wu et al , 2014.…”

Transparent and Flexible Nacre‐Like Hybrid Films of Aminoclays and Carboxylated Cellulose Nanofibrils

“…Hybrid films of MTM or saponite and carboxylated cellulose nanofibril displayed, e.g., a tensile stress of around 400 MPa but only a 4.3% strain to failure at a 50 wt% nanoclay content. [11a] CNF does not absorb light in the visible range and CNF‐based hybrid films with a high transparency have been obtained by using 50 nm saponite particles …”

Nanocellulose Film Properties Tunable by Controlling Degree of Fibrillation of TEMPO-Oxidized Cellulose

“…where the true density of 1.6 g/cm 3 was used for wood TOCNs (Daicho et al, 2018). The surface roughness values of the films were measured for the film/air interface side, which formed during the film preparation process, from the atomic force microscopy (AFM) images (Wu et al, 2014). The light transmittance values of the sheet and films were measured with the V-670 UV-vis spectrophotometer and normalized to 50 µm thickness according to the Lambert-Beer law.…”