Wool pellets from unutilized wool on Gotland – a development project with focus on the pelleting process

A large proportion of the wool produced in Sweden is discarded as it cannot be used by the textile industry. Before the wool can be used it must be collected and washed. However, a large quantity of low-quality wool is mixed in with the high-quality wool and thus enter the processing industry when the wool is collected. As it is not usable by the industry, this low-quality wool simply takes up space and lowers the processing speed as it must be separated from the high-quality wool and be discarded, lowering the economic output of the wool processing industry. However, unutilized wool has the potential to be used as a slow-acting fertilizer, soil amendment, or mulch for cultivation purposes. Pelleting is an attractive method of processing biomass into a product that is efficient and easy to handle, transport and use. Pellet presses are commercially available from small farm-scale to large-scale facilities. The aim of the project was to develop and adapt the pelleting technology to work with Swedish wool that cannot be used to produce yarns or other textiles. The goal was to develop methods and technology for pre-treating or disintegrate the wool, adapt the input and pelleting part of the pelleting process to work with low-quality wool and try to optimize the quality of the pellets. Furthermore, the goal was to analyze the plant nutrient value and strength of the pellets produced and create a packaging prototype. During the project, additional goals were added: to automate the process from pre-treatment to packaging as much as possible, and to use literature to determine if the pelletizing process is likely to be sufficient enough to hygenize the wool from weed seeds. An automated production line from wool to finished pellets has been built at Ullkontoret (Sweden’s only full-scale wool washing facility). Coarse and fine shredding, feeding and regulation of feed capacity function well, while the pelleting pressing does not work sufficiently well. Wool pelleting of only low-quality wool proved technologically challenging and neither the modified pellet presses nor the imported wool pellet press worked, despite modifications. In other European countries, this problem is solved by mixing in higher quality wool. Further technological development of wool pelleting is needed to obtain a system that can handle all types of low-quality Swedish wool. Literature studies and nutritional analyses confirm that wool pellets work well as a slow-acting fertilizer (often in mixture due to a very low phosphorus content), but the potential of wool as a soil amendment, mulch and snail repellent requires more studies. Pelleting is probably not enough to hygenize the wool from weed seeds. It is a challenge to produce a packaging that both meets the quality requirements of the product (e.g., maintain the right humidity, preventing odors) and at the same time meets the demands of the type of environmentally conscious consumer who is the main target group for a nature-based product.