Novel end products from grass fibres

Legislation

Nathalie Devriendt from ProNatura opened the session presenting the impact of the end-of-waste criteria on possible applications of grass fibers.

Embedded in the revised Waste Framework Directive, the end of waste criteria specify when certain waste ceases to be waste and becomes a product, or a secondary raw material, that could be freely traded. Therefore, specific conditions and requirements should be met by a product derived from waste in order to determine that its use is not detrimental for human health and environment.

In Flanders, roadside grass clippings are still regarded as waste and thus also grass fibers. Therefore their transport and use are strictly regulated. In order to allow the use of grass fibers in novel end-products, ProNatura applied for the Grondstof verklaring, which is part of the Material Decree in the Region. Nathalie explained their practical experience with the procedure, stressing how the current lack of flexibility at legislative level risks to have a negative impact on local value chains in circular economy.

After discussing the legislative hurdles hindering the use of grass fibers for end-applications, speakers showcased the possibilities and feasibility of producing different building materials and landscape infrastructures from grass fibers.

Picnic set

Harm Jan Thiewes from Millvision discussed the development of thermoplastic biocomposite compounds using grass fibers for landscape infrastructures. Within Grassification, Millvision prototyped a 1.5 meters picnic set. Harm described the entire process, explaining that grass clippings were firstly transformed into grass pellets to be used as half-finished product for bio-composite production. This resulted in an increased grass storability, which ensured a higher availability and reduced transport costs. After testing different type of roadside clippings, a bio-based composite compound recipe with good mechanical properties was profiled. The recipe was compounded on a pilot scale at a Millvision’s partner and it has been processed via extrusion technique in a 10x10cm profile. The functionality and the design of the picnic set were assessed and the picnic set was built and placed at Millvision’s premises to be tested under weather conditions.

Construction materials

Following up on that, Dries Vansteenkiste showcased 4 different prototypes developed by HoGent. Stressing the potential of the use of roadside grass clippings as wood substitution for biocomposites materials and products, Dries detailed the three stages of the prototyping process, which consisted in collecting different type of roadside clippings, preprocessing the grass and developing the prototypes. Small grass clippings fiberboards, mineral building blocks and beams, needles punch mats and permeable roof or floor tile were developed. Currently prototypes are integrated in a demo construction and they are now at a technological readiness level (TRL) from 4 to 6.

Then, Willem Bottger from Avans presented the development of a 100% bio-based material that can be used outdoors to replace tropical hardwood and aluminum. This material will be demonstrated in façade cladding and a nature patch (knuppelpad) plank.

Avans produced a prototype samples, whose mechanical properties were tested. Accelerated weathering tests demonstrated a good life time expectance of the material. Currently, Avans is redesigning the planks looking into two potential techniques, the pre-pregging and bulk moulding compound (BMC) and optimizing the use of the material. The end-result can be use for a 100% biobased demonstration nature path.

Circular matters

Lastly, Hanne Schatteman from Circular Matters presented their high-quality rigid materials from plant derived sources as alternative to synthetic resins and plastics. In their process, two side streams, one acting as a bio-based binder and the other one acting as a natural fiber, are mixed and pressed together in a 2D or 3D shapes. After discussing the process leading to their end-products, Hanne showed some of the materials from Circular Matters already used in stores and focused on the encountered challenges, like grass contamination, the size of the fiber, bulk density as well as seasonality and logistics.

During the interactive part of the webinar, Jappe de Best, who moderated the event, engaged the audience in the debate. Participants agreed that the biggest challenge to make re-use of grass fibers is the legislation, together with the quality of grass and the market. Cooperation among the key stakeholders of the entire value chain seems to be the key aspect to ensure the uptake of grass fibers for novel end-products.