When beer is brewed, the wort is processed from the mash and the spent grains often become animal feed or end up on the compost heap. Researchers at Empa have been working on a further utilisation for the spent malt and have produced nanicellulose, which can also be used for packaging.
Researchers from Empa's «Cellulose and Wood Materials» laboratory, headed by Gustav Nyström, believe there is more to it. They have now developed a process to produce high-quality nanocellulose from brewery waste - a versatile, biodegradable raw material that can be used, for example, to Packaging or fibre-reinforced plastics can be processed. The researchers have now published their findings in the journal «ACS Sustainable Chemistry & Engineering».
The first author of the study, Nadia Ahmadi Heidari, is a doctoral student at Isfahan Technical University. She came to Empa for a year as part of a Swiss Government Excellence Scholarship. She was particularly interested in the Production of biodegradable packaging materials from waste products - one of the focal points of the «Cellulose and Wood Materials» laboratory. „We are very interested in developing new sources of valuable raw materials such as cellulose fibres and lignin,“ says Gustav Nyström.
Micro- and nanofibrillated cellulose products are currently made from wood pulp. However, wood can be utilised more effectively elsewhere. „Wood binds CO2 from the atmosphere very well, but only grows slowly,“ explains Nyström. „It is therefore much better suited for long-lasting applications, such as in construction or for making furniture.“
The much faster-growing annual plants can supply raw materials just as well, but are still hardly used for this purpose.
„With our process, we can extract high-quality materials from a waste product that is available very cheaply and in large quantities and is largely wasted today. This also benefits small companies, which can get the most out of the raw materials they already use.“
Gilberto Siqueira, Empa researcher and co-author of the paper
The spent grains that the researchers used for their experiment also came from one such small company, the Pentabier brewery in Dübendorf. From this they extracted the nanocellulose fibres and processed them into an aerogel by freeze-drying. This «airy» material contains a large number of pores, which gives it excellent thermal insulation properties. Aerogels can be made from different materials - silicate aerogels, which are used in construction, are particularly well known. Nanocellulose-based aerogels have additional advantages: they come from renewable sources and are biodegradable. The aim is to use them for packaging, especially for temperature-sensitive foods such as meat.
In order to explore the potential of nanocellulose from spent grains in more detail, the researchers varied the individual pre-treatment and production steps and tested their effects on the end product. For example, the quality of the nanocellulose fibres obtained is improved by bleaching and oxidising the starting material. Different freezing processes can be used to control the size and orientation of the pores in the aerogel, which in turn improves its insulating and mechanical properties.
„We endeavoured to keep the entire process as simple as possible,“ says Siqueira. After all, to find application in the real world, not only does the end product have to be convincing - it should also be as simple and cheap to produce as possible. This is another reason why the researchers are interested in Extracting raw materials from waste products. „Compared to residues from the agricultural industry, wood is a costly source of cellulose, and it already has so many other applications,“ explains Siqueira. In further research projects, the scientists are therefore investigating other waste products from the food industry and forestry. And although Nadia Ahmadi Heidari has already returned to Isfahan Technical University, the Empa researchers are planning another publication together with the young researcher, in which they will describe the aerogels made from spent grains in more detail.
Source: Empa
