微晶纤维素制备过程中纤维素结构与形态特征的变化

纤维素的超分子结构是由分子链排列整齐、有规则的结晶区和分子链排列松散、无规则的无定形区交错结合组成的。通过研究HCl在不同反应时间阶段(20~120 min)降解纤维素的特性,在HCl浓度2.5 mol/L,反应温度80℃,固液比1∶15,搅拌器转速120 r/min的条件下,纤维素选择性酸水解的最佳反应时间为60 min,此条件下水解纤维素的得率达96.04%,纤维素的聚合度、结晶度由661、58.92%变为99、76.01%。此外,长纤维和细小纤维平均长度分别为288、59μm,细小纤维含量达90.31%。     

Pierre-gilles de gennes nobel laureate in physics 1991

Grafting of acrylonitrile on to hydrocellulose derived from the hydrolysis of wood pulp has been studied using cerie ammonium nitrate as initiator. The graft yield, the grafting efficiency and the total conversion were found to be highly affected by the various parameters studied including the initiator and monomer concentrations, the polymerization time and temperature. Moreover, the effect of the extent of grafting on the moisture regain property of the hydrolysed wood pulp has been also investigated.     

Effect of the agitation rate on the generation of low-crystallinity cellulose from phosphoric acid

Changes in the basic powder properties of low-crystallinity powder cellulose (LCPC) as a function of the agitation rate used during its generation from phosphoric acid were investigated. We reacted cotton linter with phosphoric acid (85% w/v) at room temperature for an hour and then at 50°C for 3 h to produce the LCPC solution. The latter was slowly added to water (ca. 10 times the volume of phosphoric acid used) at a constant agitation rate of 700, 2000, or 4000 rpm. LCPC powder thus formed was collected by filtration, washed with water and acetone, and dried at 30°C. Scanning electron micrographs showed the three products to be highly aggregated in structure. The crystallinities of LCPC prepared at 700, 2000, and 4000 rpm were 39, 31, and 24%, respectively. The crystalline component of LCPC produced at 700 and 2000 rpm contained both cellulose II (major component) and cellulose I (minor component), whereas LCPC generated at 4000 rpm belonged to the cellulose II crystal lattice. The porosity and true, bulk, and tap densities of LCPC made at 4000 rpm were 88.55% and 1.435, 0.138, and 0.164 g/cc, respectively. The corresponding values for LCPC made at 700 and 2000 rpm were 60.30% and 1.452, 0.541, and 0.576 g/cc and 54.49% and 1.465, 0.583, and 0.667 g/cc, respectively. Avicel® PH-101, in contrast, had a degree of crystallinity of 89% and a true density value of 1.577 g/cc. The porosity, bulk density, and tap density values were intermediate to those of LCPC made at 4000 rpm and 700 or 2000 rpm. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2624–2628, 2001     

水化纤维素膜的褪色及强度降低的原因

聚乙烯-丙烯酸接枝膜上的抗氧化剂和丙烯酸残留量较大时,在湿度较大的环境内隔膜吸收水分;抗氧化剂会破坏水化纤维素膜的大分子结构,使其抗拉强度降低,使锌银蓄电池的使用寿命缩短.