Scientists from Japan have produced nanocomposite sheets containing powdered chitin from fully transparent crab shell that could offer a range of applications in devices requiring high light transmittance, such as flat panel displays.
The researchers at Kyoto University led by Hiroyuki Yano, whose work was published in the journal Soft Materials [Shams et al. Soft Matter (2011) DOI: 10.1039/c1sm06785k], used hydrochloric acid, sodium hydroxide and ethanol to eliminate all minerals, proteins, lipids and pigments from the crab shells, leaving only critin, before immersing the nanofibrous structure in an acrylic resin monomer. Upon polymerization, they were left with an optically transparent shell with an intact original shape and substantial morphological detail. The researchers then treated the crab shell powder with the same process to obtain nanoscale chitin powder particles, and compressed the particles into paper sheets impregnating them in the same acrylic monomer as previously to give optically transparent nanocomposite sheets.
A big advantage was that the optical transmittance of the composite was shown to be stable over a wide range of temperatures, with the sheets now presenting virtually no decrease in light transmittance at temperatures as high as 80°C, in comparison to typical nanocomposite technologies – such as glass-fiber epoxy composites – which show a decrease in transmittance of up to 65% when the temperature is pushed up to around 100°C.
With the team previously managing to develop optically transparent nanocomposites that were reinforced with cellulose nanofibers and chitin nanofibers, they realized that when natural nanofibers are dispersed widely enough throughout a transparent polymer matrix, they can strengthen the polymer, with the resulting nanocomposite material retaining its transparency. Given the difficulty of extracting nanofibers from plant fibers or marine bio-resources, the researchers were keen to identify an easy method of fabricating optically transparent composites. The comparatively straightforward nature of a crab or shrimp shell’s microstructure and the nature of chitin led them to this breakthrough.
A crucial finding was that heterogeneous micro-scale crab shell chitin particles could successfully process transparent nanocomposites. The composites reinforced by the chitin powder retained the transparency of the resin and also helped the effectiveness of its mechanical properties and thermal stability. This could lead to a number of important commercial applications, and is a significant move towards the sustainable utilization of biomass resources. As the chitin powder composites do not expand when heated, it is hoped they could be used in developing flat or bendable type displays for next-generation optoelectronic devices or in solar cells.