Spruce pre-hydrolyzed sulfate method for the preparation of Lyocell fiber dissolving pulp
In order to solve the problem of low quality and unstable source of dissolving pulp for domestic lyocell fiber,Russian spruce was used as raw material and high-quality dissolving pulp was prepared for lyocell fiber by pre-hydrolyzed sulfate cooking process.The effects of pre-hydrolysis,sulfate cooking,chlorine dioxide-hydrogen peroxide bleaching and acid treatment on the key technical indexes of dissolved pulp,such as α-cellulose content,polymerization,whiteness,ash content and metal ion content,were investigated.The experimental results show that the holding time of 90 min,the temperature of 150℃and the solid-liquid ratio of 1∶4 were the optimal prehydrolysis conditions,and the alkali content of 24%,the degree of vulcanization of 30%and the holding time of 180 min were the optimal cooking conditions.The slurry prepared under the optimal prehydrolysis and cooking conditions was treated with 1.5%chlorine dioxide bleaching,12%cold alkali extraction,5%hydrogen peroxide bleaching and 6%acetic acid,and the resulting pulp had a α-cellulose content,a whiteness of 85%,a polymerization degree of 647,an ash content of 0.06%,an iron ion content of 6 mg/kg,and a copper ion content of 3 mg/kg.Polarizing microscopy showed that the slurry could be completely dissolved in NMMO(moisture content of 13.3%)at 90℃for 30 s.
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