Progress 10/01/04 to 09/30/05
Outputs
This report refers to the following two tasks: 1. Dissolution kinetics by using FTIR technique. The technique is based on the fact that the concentration of cellulose in the NMMO/water system can be approximated by the projected area of the fiber embedded in a film on a hot stage. The FTIR spectra (using ZnSe windows) and images were taken and the ImageJ software allowed the area of the fibers in the collected images to be measured. By measuring the area at different times, it was possible to plot the curves for the variation of cellulose concentration in time at different temperatures. From these curves the initial dissolution rates were determined. Then the reaction order (n) and rate constants (k) could be determined. Also, pre-exponential factor (A) and activation energy (E) were determined from the Arrhenius plot. It was found that the reaction order was n = 1.6871 and activation energy ratio E/R = 5146 K. From the temperature coefficient aT = 1.5 and activation
energy it is to be concluded that the dissolution process is diffusion controlled. This means that NMMO should diffuse through the cellulose structure and reach the hydrogen bonding sites before breaking these and forming another complex that allows dissolution to occur. 2. Lyocell solution blowing and characterization of produced nonwovens. Solution blowing of lyocells was tested on the 6 in melt blowing line from TANDEC to which a Leistritz twin-screw extruder was attached to drive the processing line. A 14% lyocell solution (prepared from NMMO monohydrate and DP 670 dissolving pulp) was used and cellulosic nonwoven webs of different basis weights, were prepared by coagulating the blown web in water, washing, and drying. Extrusion temperature and die to collector distance were chosen as independent parameters. The nonwoven samples obtained were tested for tensile strength, fiber diameter, absorbency, bubble point and web structure. SEM images were taken, which showed that the fiber
diameter varied from 0.8 to 6.23 microns, with an average of approximately 2.27 micron. Twin-screw extruder driven solution blowing line was also used to carry out both lyocell solution preparation from 50/50 (NMMO/water) solution and cellulosic fibers and blowing of the homogenized lyocell solution in one process. This run proved the feasibility of manufacturing cellulosic nonwovens in one extrusion process, by removing the excess water (up to the monohydrate composition) through one of the venting ports on the extruder barrel, dissolution of cellulosic fibers in NMMO monohydrate, solution homogenization, blowing, coagulation, washing, and drying. The solvent (NMMO) can be recovered and recycled to the extruder feeding port by collecting the coagulating and washing streams and concentration to 50/50 by weight. Experimental results presented above are part of two students graduating works [1,2] and two papers submitted and published. References: 1. Tierney, John William, MS Thesis,
Chemical Engineering Department, The University of Tennessee, Knoxville, 2005. 2. Dahiya, Atul, Dissertation, Chemical Engineering Department, The University of Tennessee, Knoxville, 2005.
Impacts
Studying the fundamentals of cellulose dissolution in NMMO/water solvent will help in better understanding the process of using this new, environmentally friendly, solvent. A thorough rheological characterization of lyocell solutions is very important for finding the best procedures for processing these solutions and manufacturing high value-added products from cellulosic fibers sources. Cellulosic nonwovens obtained by solution blowing will find a broad range of applications, such as industrial, personal care, and different medical fields. Developing new and environmentally friendly techniques for processing lower value renewable and biodegradable cellulosic sources will have a great impact by offering new opportunities to US agriculture and rural communities.
Publications
- X. Wei, J. R. Collier, and S. Petrovan,(2005) Determination of cellulose molecular weight from dissolving pulp solutions via rheology measurements, Submitted to Cell. Chem. Technol.
- J. Collier, S. Petrovan, P. Patil, and B. Collier, (2005) Elongational rheology of fiber forming polymers, Journal of Materials Science, 40, 5133-5137.
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