打浆过程预添加CMC对杨木APMP浆悬浮液屈服应力的影响

摘要

为考察打浆过程中添加羧甲基纤维素钠(CMC-Na)对杨木碱性过氧化氢化学机械浆(APMP浆)悬浮液屈服应力的影响,在分析杨木APMP浆打浆度与屈服应力关系的基础上,先添加一定量的CMC-Na对杨木APMP浆进行预处理10 min后,再分别用瓦利打浆机和PFI磨打浆处理,分析不同打浆方式以及添加CMC-Na预处理后对杨木APMP浆的打浆度和屈服应力的影响.结果表明:对于相同打浆度的杨木APMP浆,屈服应力(τy)随着浆料质量分数(Cm)的增加而迅速增加,且符合指数方程τy=aCbm,其中a与b值与打浆方式和打浆度的大小密切相关;经低浓度游离状的瓦利打浆机处理的浆料,其屈服应力随着打浆度的增加而减小,而中高浓度黏状的PFI磨打浆处理结果则相反.打浆过程预添加CMC-Na时,浆料打浆度随CMC-Na添加量(以绝干浆质量计)的增加先升高后降低;当CMC-Na添加量为2%并预处理 10 min 时,经瓦利打浆机处理的浆料打浆度可由45°SR提高到48°SR,而经PFI磨处理的浆料打浆度可由40°SR提高到50°SR,并且浆料悬浮液的屈服应力均达到最低值,分别为16.4和22.8 Pa(浆料质量分数为3%).%In order to study the influence of the addition of CMC-Na before refining on the yield stress of refined poplar APMP pulp fiber suspension, a certain amounts of CMC-Na were added to the APMP and the APMP were pretreated for 10 min before individually refining by Valley beater and PFI mill.The influences of the refining and CMC-Na pretreatment on the beating degree and yield stress (τy) of poplar APMP fiber suspension were analyzed respectively.It was found that the yield stress of the poplar APMP fiber suspensionwith a similar beating degree increased rapidly with the rising of CMC-Na concentration, and the yield stress was accordance with the concentration (Cm)via a power relationship of τy=aCbm(the values of a and b were closely related with the beating ways and beating degree).After refining under a low concentration by free beating device (e.g.Valley beater), the yield stress of the poplar APMP fibers suspension decreased with the increased beating degree, while reverse results were observed under the medium concentration refining by shiny beating device (e.g.PFI mill).After 2% CMC-Na (based on the dry pulp weight) was added the pulp and pretreated for 10 min, the beating degree of poplar APMP was increased to 48°SR from 45 °SR with valley beater refining and ascended to 50°SR from 40°SR with PFI refining.Meanwhile, the yield stresses of the poplar APMP fibers suspension were reached to the minimum value with the same beating conditions, the minimum values of the yield stresses were 16.4 Pa and 22.8 Pa (PFS mass fraction was 3%), respectively.