Effects of flow-rates and sample concentration on the molar mass characterisation of modified celluloses using asymmetrical flow field-flow fractionation-multi-angle light scattering

Modified celluloses are an important group of polymers used in many applications, such as in the food and drug industry. Thus, their physicochemical properties are of considerable interest and need to be characterised carefully. In this study, asymmetrical flow field-flow fractionation (asymmetrical flow FFF) connected on-line to a multi-angle light scattering (MALS) detector was used to study the molar mass and molar mass distribution of three different hydroxypropylmethylcelluloses (HPMCs). The influence of the flow-rates and the sample concentration on the results obtained was found to be significant, emphasising the importance of optimising the experimental conditions so as to obtain reliable information about the polymer system. With the use of appropriate conditions, flow FFF-MALS was found to be a suitable method for the characterisation of these complex samples. The weight-average molar mass ranged from 132 000 g/mol to 309 000 g/mol. The z-average radius of gyration was found to be high relative to the molar mass, ranging from 58 nm to 73 nm, suggesting an expanded structure. This was also confirmed by double logarithmic plots of the molar mass versus the radius of gyration, the slope being approximately 0.7 for the two high molar mass samples. (C) 1997 Elsevier Science B.V.