Brewers' spent grain for organic thin-film transistor application.

Brewer's spent grain (BSG) represents the main by-product of the brewing industry, accounting for ~ 85 % of the total by-products. The annual global production of BSG is massive, that is ~ 40 million tons. In the European Union, the production is ~ 3,4 million tons/year [1]. Currently, BSG is mainly sold to farmers (~ 30 % in EU) as animal feed, with a low market value of ~ 35 Euro/ton or landfilled. Finding alternatives, higher value uses for BSG is therefore particularly attractive from the point of view of brewery economics [1]. Besides, disposable electronics applications such as in smart food and beverage packaging require environmentally safe devices with low cost and large volume processability. Therefore, switching from nonrenewable manufacturing to sustainable processes is a major challenge for next generation electronics, and organic materials offer a unique opportunity to drive the electronic industry in an environmentally safe direction [2]. Among various organic electronic devices, thin film transistors (OTFTs) are fundamentals. They are multilayered-structured devices that comprises conducting electrodes, dielectrics and semiconductors. We investigated for the first time the use of two no starch polysaccharides components of BSG, β-glucans and arabinoxylans, as green dielectric materials for OTFTs. Since such components possess rich polar functional groups, they can be in principle effectively employed as dielectric layers for OTFTs due to their good polarization under electric field, which would lead to high capacitance and, ultimately, to promising possibilities and applications for green devices. The thin films were prepared by spin coating technique and, indeed, encouraging capacitance values of ~1820 nFcm^-2 at 1 kHz were obtained for both components. β-Glucans revealed to be particularly promising when implemented in OTFTs, enabling devices giving good response, i.e. a charge mobility of 1.5 cm²/ Vs with average current on/off ratio of ~ 10⁴ and a threshold voltage of -1 V. The Ph-BTBT-C10 benchmark semiconductor was employed as active layer. Further developments along this line are currently in progress and will include the use of the devices as platform to realize smart food and beverage package demonstrators.