Structural Changes of Cellulose Crystallites Induced by Mercerisation in Different Solvent Systems; Determined by Powder X-ray Diffraction Method

The completeness of mercerisation can be evaluated by investigating the changes in the crystalline regions of cellulose from cellulose I (C-I) to cellulose II (C-II) by the X-ray powder diffraction method. Mercerisation experiments in four different solution systems: ethanol/water, acetone, DMSO and xylene, are reported. Also the effect of some additives, external pressure, treatment time and alkalisation temperature were studied. In two-phase solvent systems, structural changes of cellulose crystallites depended primarily on the distribution and solubility of sodium hydroxide in the solvent phases. The sodium hydroxide concentration in the hydrophilic phase must exceed 7–8 w/w-% before complete crystal change from C-I to C-II can occur. The precipitation of sodium hydroxide due to high concentration prevents the successful use of one-phase ethanol/water system in slurry process. On the contrary, the 2-propanol/water/sodium hydroxide system separates into two layers; to the water-rich lower layer and the 2-propanol-rich upper layer, where the sodium hydroxide remains mainly in the water-rich lower layer. This prevents the precipitation of sodium hydroxide and promotes the alkalisation of cellulose. Ammonium chloride and ammonium hydroxide clearly had a positive effect by promoting the crystal changes, however, the urea concentration used in this study was obviously too small. In the advantageous two-phase 2-propanol/water systems, the alkalisation time was only 15 min when the treatment temperature was kept between 0 and 10 °C. Reduced external pressure was found to have a small but still detectable positive effect on cellulose alkalisation while over-pressure prevented crystal changes.     

A new ionic liquid dimethyldinonylammonium bromide as a flow modifier for the simultaneous determination of eight carboxylates by capillary electrophoresis

Two new methods of capillary zone electrophoresis based on aqueous phosphate running buffers with UV spectrophotometric detection were developed and optimized for the determination of eight carboxylates as copper complexes. Metalcomplexes are negatively charged, so measurements were made as anion analyses with flow reversal in the capillary. Two flow modifiers were used: a common tetradecyltrimethylammonium bromide (TTAB) and a new ionic liquid dimethyldinonylammonium bromide (DMDNAB). The methods were compared to each other. Better separation was achieved with DMDNAB as the flow modifier. Method development was done using a fused silica capillary (61 cm x 50 microm i.d.).Optimization was done using 95 mmol L(-1) phosphate buffer with TTAB or DMDNAB in the concentration 0.5 mmol L(-1) at pH 7.1. A -20 kV voltage and direct UV detection at 254 nm was used in measurements. In both CE methods all the peaks in the electropherograms were properly separated, the calibration plots gave good correlation coefficients and all eight carboxylates were detected in less than 7.5 min. The two methods were tested with natural water samples and a paper mill sample, and proved to be feasible.