Cellulose is the most abundant natural polymer which has been used mostly in the form of fibers in a wide range of products and materials. Acid hydrolysis of cellulose fibers yield rod-like crystalline by-products known as Cellulose nanocrystals (CNC). CNC has numerous applications in nanotechnology and nanomedicine, including nanocomposites, enzyme immobilization, antimicrobial and medical materials, green catalysis, bio-sensing, and drug delivery. CNC dimensions, such as length and width, may vary depending on the origin of cellulose fibers and the acid hydrolysis conditions. CNC exhibits a relatively broad distribution in length and width. The average length can vary from tens of nanometers to several micrometers, while width ranges from 3 nm to 50 nm. The morphology of the CNCs has been traditionally studied by bulk characterization techniques such as electron microscopy, atomic force microscopy, light scattering techniques including small angle neutron scattering (SANS) and dynamic light scattering (DLS). However, important size-dependent information can be overlooked in such measurements. Using a separation technique allows for more detailed investigation of distributed properties such as morphology and aspect ratio. Field-flow fractionation (FFF) is an elution-based separation technique which is capable of rapid and high resolution separation of macromolecules, colloids and particles. The separation in FFF takes place inside an open channel where an external physical field is applied. Different types of separation fields can be implemented in FFF which result in realization of different FFF sub-techniques. The most prominent ones are Centrifugal (or sedimentation) FFF, Flow FFF, Thermal gradient FFF (Thermal FFF), Electrical FFF and Magnetic FFF. Each sub-technique separates sample species based on their specific properties, such as mass or density, hydrodynamic size, composition, charge and magnetization. In this presentation FFF separation principles and theory will be discussed. Advantages and limitations of different FFF sub-techniques in characterization of natural and synthetic polymers will be demonstrated. Data will be presented for the analysis of a CNC sample by Asymmetric Flow FFF interfaced with a multi angle light scattering detector. It will be demonstrated that in a run time of 30 minutes, valuable information on length, width and aspect ratio of the nanocrystals as function of hydrodynamic size can be obtained.

Determination of thickness, aspect ratio and size distribution of cellulose nanocrystals using asymmetric flow FFF and MALS

253rd National Meeting (2017)

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