Progress 07/01/02 to 06/30/07
Outputs
OUTPUTS: Aging studies were conducted to confirm that the EDA/KSCN solvent system does not degrade cellulose. 5 weight percent of cellulose of low molecular weight (Degree of Polymerization (DP) less than 200) was dissolved in 74/26 EDA/KSCN (w/w) and aged in a conditioning room. Additionally, 5 weight percent of the same type of cellulose was dissolved in the solvent with different salt concentrations. Those cellulose samples were then precipitated out from solutions with distilled/deionized water, followed by being washed thoroughly with distilled/deionized water until the pH of the residual water was constant, which indicated no residual EDA. The absence of salt (KSCN) in the recovered cellulose was confirmed by the absence of the strong peak (2047 inverse cm) associated with the SCN bond in FTIR spectra. All the recovered cellulose samples were dried in a vacuum oven at 60 degrees C before characterization. The average degree of polymerization (DP) of the recovered cellulose
samples was determined by re-dissolving the samples in 0.5 M cupriethylene diamine solution (ASTM D 4243-99) and measuring the viscosity of the solutions. A Cannon-Fenske capillary viscometer was used in the measurements. The rheological properties of cellulose solutions were measured on a controlled-stress rheometer (TA instruments, AR-2000). Dynamic or oscillatory shear measurements of cellulose solutions were carried out using a parallel-plate geometry with the upper plate diameter of 60 mm. The experimental frequencies ranged from 0.1 to 100 rad/s at 25 degrees C. The range of temperatures explored in time-temperature superposition (TTS) method was 5-30 degrees C. An oscillatory stress sweep was conducted before each dynamic measurement to ensure the sample was in the linear viscoelastic region. Steady state shear measurements were performed at 25 degrees C by varying the shear rate from 0.01 to 100 inverse seconds. A solvent trap was employed during the rheological measurements
to minimize solvent evaporation by creating a saturated solvent atmosphere in the air next to the sample.
PARTICIPANTS: Margaret W. Frey Min Xiao
Impacts
Ethylene diamine (EDA)/salt solvent systems can dissolve cellulose without any pretreatment and/or derivatization. Measurement of the cellulose molecular weight (as degree of polymerization - DP) confirmed that the solvent does not degrade cellulose even after storage times of up to 1 month and regardless of salt concentration. Solutions exhibit shear thinning behavior and viscosity of the system continually decreases over time. This decrease in viscosity, without an accompanying decrease in polymer molecular weight, is attributed to constantly evolving interactions between cellulose and the solvent.
Publications
- Xiao, M. and Frey, M. W. 2007. The Role of Salt on Cellulose Dissolution in Ethylene Diamine/Salt Solvent Systems, Cellulose, 14:225-234.
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Progress 01/01/06 to 12/31/06
Outputs
Ethylene diamine (EDA)/KSCN solvent can dissolve high molecular weight cellulose without any pretreatment and/or derivatization. 39K and 14N NMR experiments conducted at 70C showed that the K+ ion interacts with the cellobiose more than the SCN- ion does. Regenerated cellulose was studied by infrared spectroscopy (FTIR) and wide angle X-ray diffraction (WAXD). Changes in the FTIR absorption bands were associated with a change in the conformation of the C-6 CH2OH group and to the breaking of hydrogen bonds in cellulose. Cellulose regenerated by precipitating cellulose solutions with water, transformed from cellulose I to cellulose II crystalline structure.
Impacts
New solvents for cellulose will provide processing routes for rapidly renewable, biodegradable engineering materials.
Publications
- Frey, M.W., Li, L., Xiao, M. and Gould, T. 2006. Dissolution of cellulose in ethylene diamine/salt solvent systems, Cellulose, 13(2):147-155.
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Progress 01/01/05 to 12/31/05
Outputs
Biotin has been successfully incorporated into polylactic acid (PLA) nanofibers through electrospinning to prepare membrane substrates for biosensors based on biotin-streptavidin specific binding. Biotin incorporated PLA nanofiber membranes were characterized with scanning electron microscopy (SEM), electron microprobe analysis (EMPA) and confocal microscopy. Under optimized conditions, small fiber size and uniform morphology were achieved for PLA nanofibers with and without biotin incorporation. Sulfur mapping indicated a non-uniform distribution of biotin on the membranes, presumably due to aggregation of biotin during the electrospinning process. Pre-blocking the membranes effectively eliminated non-specific binding between streptavidin and PLA. Preliminary biosensor assays confirmed that streptavidin immobilized on the membrane surface could capture a biotinylated DNA probe. Nylon-6 nanofibers, electrospun from a multiple-nozzle set-up, were coated on air filter
media to improve the filtration efficiency. The average diameters of electrospun nylon fibers increased from 120 nm to 700 nm as solution concentration increased from 20 to 30 percent. Adhesion between nylon fibers and air filter fibers was observed. The filtration efficiency of the air filter media was found to increase with increasing coverage level of nylon-6 fibers. At the same coverage level, the filtration efficiency decreased with increasing nylon-6 fiber size. The results also showed that nylon fibers were very durable on the air filter media at the coverage level of 0.1 g/square meter. (Frey, M.W., A.J. Baeumner and D. Li. 2005. D-3680 Electrospun Nanofiber-based Biosensor Assembles, Provisional patent filed, May 2005.)
Impacts
Improved air filtration efficiency has been demonstrated based on addition of fibers with diameters less than 500 nanometers to existing air filter media. Biotin can be incorporated into electrospun poly lactic acid (PLA) fibers to form attachment sites for an array of biohazard sensor molecules.
Publications
- Whang, H.S., N. Aminuddin, M. Frey, S. M. Hudson, and J. A. Cuculo. 2005. Specialty Biodegradable Fibers, In Biodegradable and Sustainable Fibers, R.S. Blackburn, Ed. Woodhead Publishing, London, 2005.
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Progress 01/01/04 to 12/31/04
Outputs
Investigation of the cellulose dissolution process by infrared spectroscopy (FTIR) and thermal analysis (DSC) indicated that changes to the solvent during freeze thaw cycling of mixtures was consistent with increased interaction between cellulose and solvent. Thermal transitions in the system, however, occurred at temperatures outside the range used in thermal cycling to promote dissolution. Further exploration of the dissolution and mixing process indicated that mixing was the limiting step in solution formation. A new dissolution process with no freeze thaw cycling requirement is presented.
Impacts
Several corporations have expressed interest in materials and methods under development in our laboratory. Potential commercial applications range from pulp and paper to filtration and even aerospace components.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
The ability of a new Cellulose solvent system to dissolve Cellulose from a variety of sources in under investigation. The solvents are solutions of Ethylene Diamine and various salts. Solubility limits of salts in ethylene diamine have been determined. Initial experiments on the optimum salt concentration have been conducted. Rheology of cellulose solutions in ethylene diamine/KSCN solvent has been determined as a function of shear rate, cellulose concentration and salt concentration. Films have been formed in a variety of coagulants and the physical properties of the resulting films measured as a function of the initial solution composition and the coagulant type. Research is ongoing into the optimum solution composition for wet spinning and electrospinning cellulose fibers. A flexible electrospinning apparatus has been built in the Frey laboratory with capability of independently spinning two different polymers simultaneously. Fibers are currently being electrospun
from a variety of other polymers. Various bioactive compounds are being included in the spinning dopes and their activity in the spun fibers is under investigation.
Impacts
Several corporations have expressed interest in materials and methods under development in our laboratory. Potential commercial applications range from pulp and paper to filtration and even aerospace components.
Publications
- No publications reported this period
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Progress 01/01/02 to 12/31/02
Outputs
The ability of a new Cellulose solvent system to dissolve Cellulose from a variety of sources is under investigation. The solvents are solutions of Ethylene Diamine and thiocyanate (SCN-) salts. Solubility limits of three thiocyanate salts, NH4SCN, KSCN and NaSCN in ethylene diamine have been determined. Initial experiments on the optimum SCN- salt concentration have been conducted. For Ethylene Diamine/KSCN and Ethylene Diamine/NaSCN solutions a salt concentration in the range between 50 and 75 percent of the saturation point appears to be optimum for cellulose dissolution. Ethylene Diamine/NH4SCN solutions did not dissolve cellulose. Initial experiments in electrospinning nano scale fibers from Cellulose solutions have been conducted. Solutions of Cellulose in ammonia/ammoniumthiocyanate (NH3/NH4SCN) solvent could not be electrospun. Ammonia evaporated too rapidly leaving a bead of solid Cellulose/NH4SCN at the spinneret (syringe) tip. Fibers were formed via
electrospinning Cellulose from Ethylene Diamine saturated with NaSCN. These fibers were thicker than nano scale (i.e. Greater than 100 nm diameter). Further experiments are planned to determine the optimum solution conditions for spinning nanoscale fibers from Cellulose. A fiber wet spinning line has been installed in the fiber formation laboratory. The line is designed to be flexible and capable of spinning fibers from small amounts of polymer solution (less than 200ml). Initial experiments are planned to investigate fiber formation from cellulose solutions in ethylene diamine/thiocyanate salt solvents and cellulose solutions in ionic liquids.
Impacts
Cellulose is an abundantly available renewable resource polymer. Many properties that are valued in high performance polymers such as high molecular weight and polymer chain rigidity are available in cellulose. All solvents investigated for cellulose solution processing to date have serious drawbacks including toxicity, instability, cellulose degradation or volatility which limit their usefulness. The ethylene diamine/thiocyanate salt solvent systems and/or ionic liquids are expected to overcome many if not all of these draw backs.
Publications
- No publications reported this period
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