Simioan Petrovan

Elongational rheology of polymer melts and solutions

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.

Rheology of cellulosic N-methylmorpholine oxide monohydrate solutions of different degrees of polymerization

Preparation and shear and elongational rheology of cellulose solutions of different degrees of polymerization (DP) in N-methylmorpholine oxide monohydrate (lyocell) were investigated. The dissolution process takes place in two stages, depending on the content of low and high DP fractions from the dissolving pulp blends. The influence of the DP of cellulosic chains on elongational and shear viscosity is greater at low deformation rates. Low DP solutions behave more like viscous fluids and the increase of the chain length brings about an increase of the elastic component. Orientation induced by the convergence flow is enhanced by the higher DP cellulosic chains.

Rheology of cellulosic N‐methylmorpholine oxide monohydrate solutions

Shear dynamic and elongational rheology of concentrated solutions of cellulose in N-methylmorpholine oxide monohydrate (lyocell) were investigated at different temperatures and for two Hencky strains. Shear thinning and strain thinning behavior is characteristic for dynamic viscosity and effective elongational viscosity of lyocell solutions. Body forces, enthalpy, and entropy of orientation are high at low temperature and high deformation rates, showing a strong orientation effect.

Rheology of Lyocell Solutions from Different Cellulose Sources

Rheological measurements were used to characterize the behavior of lyocell solutions, i.e., cellulose dissolved in N-methymorpholine-N-oxide. Cellulose sources included dissolving pulp, kraft pulp, sugar cane fibers, and kenaf fibers. The dominance of viscous behavior, G′ values, over elastic behavior, G″ values, is affected by cellulose concentration and molecular weight. At lower concentrations and degrees of polymerization (DP), dissolving pulp solutions show viscous, inelastic behavior at low frequencies. At higher concentration and DP, dissolving pulp solutions are more elastic at higher frequencies. Solutions prepared with kenaf and sugar cane fibers show similar properties to those using pure dissolving pulp, and comparisons suggest the molecular weight and/or the presence of other substances such as lignin in the cellulose from these alternative sources affect the rheology.

Lyocell Solutions from Alternative Cellulose Sources

Lyocell fibers, a generic subclass of rayon fibers, are produced from cellulose dissolved in N-methylmorpholine oxide (NMMO). The lyocell solutions typically consist of blends of cellulose from similar low and high degree of polymerization (DP) dissolving pulps to achieve desired spinnability and fiber properties. The objective of this research was to determine if alternative lower value cellulose sources could be used as raw materials for lyocell by characterizing solutions made from these sources. Shear viscosity, which strongly affects spinning of fibers, of ten cellulose sources at four concentrations was compared to that of five industrial dissolving pulp standards with DPs from 670 to 1720. Bleaching, concentration, cellulose source, and their interactions had significant effects on shear viscosity. Kudzu, sugarcane bagasse, recycled, and thermomechanical cellulose pulps had higher viscosities than did the more highly processed hardwood and softwood. Bagasse was similar to the lowest DP dissolving pulp standard. Recycled and thermomechanical pulps were similar to the higher DP standard and bleaching affected the shearing behavior of these less pure pulps. Shear viscosity measurements were effective in determining differences among the pulps.