Answer Happy

Using the conclusion information below, prepare a power point presentation. Conclusion This review has outlined methods for the molecular weight determination of cellulose and has taken older methods and historical approaches into account. Some of the older methods will remain more or less of historical interest or are only used now in very specific cases such as obtaining detailed information on the structure in solution. However, the main limitation of all methods is the solubility of the polymer. New solvents, like the ionic liquids that were introduced recently in cellulose chemistry, are also of interest in the analytical field but have not yet reached the level of application in SEC. There is clearly a lack of analytical methods for low-molecular mass cellulose. There is also a lack of knowledge on the viscosity of solutions containing high amounts of degraded cellulose fragments. The Mark-Houwiak parameters are known to be susceptible to change with small molecules, leading to errors in viscosity measurements, and it is not yet clear when these parameters begin to change. The same is true for the refractive increment, which is only a constant for polymers. Comparative studies of different methods for determining molecular weight are still rare, mainly because an evaluation of methods in this field demands dramatic complexity involving a significant number of different parameters. The neglected oligomeric part of (hemi-)cellulose is an issue for several reasons, including the fact that side streams, as found in pulping and paper processing, can be a valuable source for small (hemi)cellulose fragments. Before processing such small molecules, however, a proper analytic is a minimum requirement. The influence of oligomeric compounds on a polymer product and its properties is still not clearly understood. Therefore, new methods are needed which will allow the clarification of the low molecular weight portion of the cellulose molecule. In the future, only powerful solvents compatible with advanced analytical systems will enable a real step forward. For the solvents, this requires a rather low viscosity, no interference with absolute detection systems (no fluorescence, no absorption, etc.), and chemical compatibility with all elements of system hardware. The currently used salt-containing solvents cause manifold problems in that respect. The application of alternative separation methods like field flow fractionation (FFF) techniques would be beneficial in avoiding expensive sets of separation columns but are not yet compatible with cellulose solvents.