Comparison of refining response of Soda AQ and Organosolv Wheat Straw pulps with traditional wood pulps

Concerns about long term fiber supply and more stringent environmental restrictions have increased the interest in non-wood fiber raw material for paper manufacture. This paper presents the comparative assessment of refining response and physical properties of bleached chemical wheat straw fiber with hardwood and softwood pulps. Two different pulping processes were used to produce the wheat straw pulps, the traditional soda AQ process followed by DED bleaching and organosolv pulping followed by one oxygen bleaching stage and several hydrogen peroxide stages. As expected the two unbeaten wheat straw pulps showed different characteristics. The soda AQ pulp had a considerable higher tensile strength but a higher fines content and a lower freeness. Both types of straw pulp showed only moderate response to beating in a PFI mill. Nevertheless, if compared at given freeness levels the organosolv pulps show the same tensile strength as hardwood pulps, while the soda AQ pulps are comparable to softwood pulps. As expected both wheat straw pulps had considerably lower tear strength than the wood fibers. No external fibrillation after beating could be observed for both beaten straw samples. It was concluded that bleached chemical straw fibers do not benefit greatly from beating/refining.