Size characterisation of modified celluloses in various solvents using flow FFF-MALS and MB-MALS

The size characterisation of modified celluloses is a necessary, but also complex, task that often requires use of different methods. In this paper, two different size characterisation methods were used to obtain molar mass and size information of three hydroxypropylmethyl cellulose (HPMC) samples in four different solvents. The two methods employed were the combination of flow field-flow fractionation and multiangle light scattering (MALS) as well as sole utilisation of the MALS instrument itself performed in the so-called micro-batch mode (MB-MALS). The influence of the different solvents, on the obtained molar mass and size for the HPMC-samples was found to be pronounced. For example, the molar mass obtained for the high molar mass HPMC 10000 increased from 310,000 up to 650,000 g/mol when the solvent was shifted from a 50% methanol¯salt mixture into 1 mM NaCl. Also the radius of gyration was clearly affected by the change in solvent. Theses changes were compared with values of the second virial coefficient, A2, obtained from MB-MALS. Furthermore, both techniques were able to identify clear differences in solution behaviour between the HPMC-samples, which were delivered by two different manufacturers. It was concluded that the two methods gave comparable results and complement each other well in the size analysis of these complex polymers.