Size-exclusion chromatography with on-line viscometry of various celluloses with branched and linear structures

Abstract

We analyzed softwood and hardwood bleached kraft pulps (SBKP and HBKP, respectively), and Japanese cedar (Cryptomeria japonica) celluloses prepared from wood powders using delignification, hemicellulose removal, and dilute acid hydrolysis. For sample preparation, each sample was dissolved in 8% (w/w) lithium chloride/N,N-dimethylacetamide (LiCl/DMAc), after the sample was soaked in ethylenediamine (EDA) and the EDA was exchanged with DMAc through methanol. These solutions were diluted to 1% (w/v) LiCl/DMAc and subjected to size-exclusion chromatography (SEC) combined with multiangle laser light scattering and viscometry analyses. SEC/multiangle laser light scattering and SEC/viscometry use different principles to determine the molecular structures of polymers dissolved in LiCl/DMAc. Both methods showed that SBKP celluloses with high molar masses had branched structures, whereas HBKP celluloses had linear structures as like cotton, bacterial, tunicate, and algal celluloses. Conventionally, viscosity-average molar masses or viscosity-average degrees of polymerization of SBKP and HBKP are obtained by capillary viscometry using a 0.5 M copper ethylenediamine hydroxide (cuen) solution. Because SBKP and HBKP have different cellulose structures (branched and linear molecules, respectively), their viscosity-average molar masses and viscosity-average degrees of polymerization should not be calculated using the same Mark–Houwink–Sakurada equation.