Isolation of cellulose fibres from agricultural waste. Production of dissolving-grade pulp from oat husk and wheat straw

Examensarbete för masterexamen
Sjöstedt, Niclas
Recent decades have seen an increase in environmental awareness about the impact of everyday products. Cellulose is the most abundant natural polymer in the world and has long been used for production of films and textiles. The cellulose has traditionally been isolated from wood as a dissolving-grade pulp and then further processed into the desired product. Dissolving-grade pulps have narrow molecular weight distribution and contain high levels of cellulose, low hemicellulose and low amounts of lignin and ash and can be turned into a wide range of products. However, due to a future expected shortage of fibres, finding new raw materials is a must. One alternative source of cellulose could be to isolate cellulose from agricultural waste. This project has been evaluating the suitability of using oat husk and wheat straw as alternative raw materials for the production of dissolving-grade pulp. These raw materials were chosen because of their abundance in Sweden, their low value and relatively high cellulose content. The process chosen was the prehydrolysis-soda pulping process, where a prehydrolysis step is used to remove hemicelluloses and facilitate delignification, and soda pulping is used as the main delignifying step. An acid prehydrolysis-soda pulping process followed by a total chlorine-free (TCF) bleaching sequence was proven to be suitable for oat husk. The produced pulps had uniform molecular weights, high cellulose content, low hemicellulose content and little to no lignin content. The acid prehydrolysis was efficient in removing hemicelluloses and facilitating delignification in the soda pulping step. With a higher liquid to solid ratio in the acid pretreatment and higher concentrations of NaOH during cooking, wheat straw exhibited similar properties regarding molecular weight distribution, cellulose and hemicellulose contents. However, ash and lignin removal was difficult. When the leaves were removed from the wheat straw, nearly all requirements for use as dissolving-grade pulp were met but the lignin levels. Both of the raw materials assessed in this project show great potential to be used as raw materials for dissolving-grade pulps while also requiring milder process conditions than wood. Even though more research is needed to fully assess the suitability of the raw materials for dissolving-grade pulp production, the door of possibilities is wide open.
Dissolving-grade pulp, cellulose fibres, soda pulping, acid pretreatment, utohydrolysis, hot water extraction, wheat straw, oat husk, agricultural waste, spruce
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