木质素化学改性抑制杨木碱性过氧化氢机械浆返色的研究

中试系统制备了杨木碱性过氧化氢机械浆。分别在水相 /有机溶剂相 /气相等条件下 ,使用乙酐处理杨木化机浆 (原浆及硼氢化钠还原后纸浆 ) ,分别抄造成 60g/m2 纸片 ,测定了不同时间紫外线照射后试样白度。运用返色值 (PCno .)和白度稳定效果 (BSE)等指标评价处理后浆料的光学稳定性。研究结果表明 ,有机溶剂相和气相乙酰化后的纸浆 ,光学稳定性的提高程度取决于乙酐用量和反应时间即乙酰化程度。通过乙酰化 ,可以获取光学完全稳定的杨木化机浆。紫外漫射反射光谱表明 ,杨木APMP机械浆光诱导返色的主要原因是纸浆木质素中羰基和酚羟基团吸收紫外光后变化形成发色结构所致。还原配合纸浆乙酰化处理 ,可能成为防止高得率纸浆返色的工业应用方法

CHEMICAL MODIFICATION OF LIGNIN IN POPLAR APMP PULPS TO PREVENT LIGHT INDUCED YELLOWING

Different brightness levels of poplar APMP pulps were prepared in a pilot scale system by alkaline peroxide mechanical pulping process, Un treated and reduced pulps(borohydride reduction)were modified by acetic anhydride under different conditions, such as in aqueous, organic solvents and gaseous phases.The brightness of pulps before and after UV light exposure for different periods were measured on handsheets, post colour number and BSE (brightness stabilizing effect)were used to evaluate the photo stability of the treated pulps. The results show that, both gaseous and organic phase acetylations improve pulps brightness stability more or less depending on amount of acetic anhydride applied and reaction time i. e. degree of acetylation. Completely stabilized pulps were obtained by thorough acetylation.Form UV diffuse reflectance spectra, it seems that carbonyl and phenolic groups mainly contribute to the light induced yellowing of poplar APMP. Sodium borohydride/sodium bisulfite mixture treatment of pulps followed by gaseous phase acetylation on paper sheet was proposed to be one of the practical process for yellowing inhibition of bleached APMP pulps.