In this article, shear rheology of solutions of different concentrations obtained by dissolution of cellulose in the ionic liquid (IL) solvent 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) was studied by measuring the complex viscosity and dynamic moduli at different temperatures. The obtained viscosity curves were compared with those of lyocell solutions and melt blowing grade polypropylene melts of different melt flow rates (MFR). Master curves were generated for complex viscosity and dynamic moduli by using Carreau and Cross viscosity models to fit experimental data. From the Arrhenius plots of the shift factors with respect to temperature, the activation energies for shear flow were determined. These varied between 18.99 and 24.09 kCal/mol, and were compared with values for lyocell solutions and different polymeric melts, such as polyolefins, polystyrene, and polycarbonate.

Elongational rheological properties of polymer melts and solutions may be measured using nonlubricated flow characteristics through a semihyperbolic converging die. The effects of body forces related to developing orientation in the fluid during converging extensional flow are so strong that the shearing contribution become negligible in comparison, eliminating the need for lubrication to achieve an essentially pure elongational flow. The effective elongational viscosities of polypropylene melts and lyocell solutions correlated with shear-flow determinations were used to estimate the enthalpy and entropy changes as function of processing conditions. The flow of lyocell solutions through a converging die had, as a result, not only phase separation and cellulose crystallization, but also microfibers formation and high orientation.

Molecular dynamics simulations of poly(ethylene terephthalate) (PET) oligomers are performed in the isobaric-isothermal (NpT) ensemble at a state point typical of a finishing reactor. The oligomer size ranges from 1 to 10 repeat units. We report thermodynamic properties (density, potential energy, enthalpy, heat capacity, isothermal compressibility, and thermal expansivity), transport properties (self-diffusivity, zero-shear-rate viscosity, thermal conductivity), and structural properties (pair correlation functions, hydrogen bonding network, chain radius of gyration, chain end-to-end distance) as a function of oligomer size. We compare the results with existing molecular-level theories and experimental data. Scaling exponents as a function of degree of polymerization are extracted. The distribution of the end-to-end distance is bimodal for the dimer and gradually shifts to a single peak as the degree of polymerization increases. The scaling exponents for the average chain radius of gyration and end-to-end distance are 0.594 and 0.571, respectively. The values of the heat capacity, isothermal compressibility, and thermal expansivity agree well with the available experimental data, which are of much longer PET chains. The scaling exponents for the self-diffusivity and zero-shear-rate viscosity are, respectively, -2.01 and 0.96, with the latter one being close to the theoretical prediction 1.0 for short-chain polymers.

The focus of this article of a three part series is the effects of preparation and composition on the shear rheology of cellulose in the ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl). Included are the effects of three different degrees of polymerization, (i.e., average molecular weight), manual versus high shear mixing, a range of cellulose concentrations, and the effects of controlled amounts of lignin and a hemicellulose. The rheology implies that a gel phase develops at higher degrees of polymerization, higher concentration, and at lower temperatures. The first article focused primarily on shear rheology of cellulose in [Bmim]Cl with a high shear preparation technique, one degree of polymerization, a narrow range of cellulose concentrations, and temperature. The third article focuses on elongational rheology of cellulose in [Bmim]Cl.