Wheat Straw Cellulose Pulp: Production of dissolving-grade pulp using a combined organosolv–soda process for textile applications

Abstract

The demand for sustainable textile fibers has increased the interest in alternative cellulose sources instead of traditional wood-based pulp. This thesis studies the production and characterization of dissolving-grade cellulose pulp from wheat straw using a combined organosolv–soda pulping process. The aim was to evaluate if the produced pulp could be suitable for textile fiber production. This work was conducted in collaboration with TreeToTextile, reflecting an industrial interest in developing alternative cellulose feedstocks for fiber production. Wheat straw was pretreated with ethanol/water mixtures containing 50% or 65% ethanol, with and without the addition of acid. After pretreatment, soda pulping was carried out using different effective alkali (EA) levels. Some samples also received an additional cold caustic extraction treatment. Grass was included as a second raw material to examine whether the process could be used for other annual plants. The produced pulps were analyzed based on chemical composition, intrinsic viscosity (IV), water retention value (WRV), color, and dissolution behavior in cold alkali (NaOH/ZnO). The results showed that effective alkali was the dominant factor on cellulose chain length and dissolution behavior. Higher EA levels gave lower IV values and improved dissolution. Higher ethanol concentration and acid addition also improved lignin and hemicellulose removal. The highest cellulose purity was obtained with 65% ethanol at EA 0.72, while the highest glucose yield compared to the initial biomass was obtained with 65% ethanol at EA 0.48. For the samples with EA 0.48, IV had the strongest effect on dissolution, although cellulose purity and WRV also seemed to influence the results. The grass sample produced a cellulose-rich pulp with low lignin content under the same conditions as wheat straw. This shows that the process may also work for other annual plant materials. Overall, the results showed that a mild organosolv–soda process can produce pulp with properties close to those needed for dissolving-grade applications from annual plant feedstocks