Progress 08/15/00 to 08/31/04
Outputs
Cellulose from different sources was dissolved in N-methyl morpholine oxide/water (NMMO)/H2O to form lyocell solutions. Fibers regenerated from lyocell solutions are referred to as lyocell fibers. Commercial fibers are made using blends of two dissolving pulp grades, and marketed under the tradenames Tencel and Lyocell. Alternative cellulose sources considered in this research were recycled hardwood and softwood, recycled newsprint, thermomechanical pulp, sugarcane bagasse, cotton linters, and kudzu. All except bagasse, cotton linters and kudzu were studied as bleached and unbleached sources. Rheological properties of the solutions were determined and compared to those of lyocell solutions made with commercial dissolving pulps with two different degrees of polymerization (DP). Shear rheology of cotton linters with a DP of 1305 was nearly identical to a DP 1720 dissolving pulp. Bleached and unbleached hardwood and softwood pulps had a lower shear viscosity than a DP 670
dissolving pulp, with the other source solutions lying between the 670 and 1720 DP dissolving pulps at the same cellulose concentrations. With proper blending ratios these alternative sources could be considered as replacements for blends of the two dissolving pulps for lyocell fibers. Matching of rheology could be considered since the rheology of the lyocell solutions is sensitive to cellulose concentration. Selected post-treatments were applied to the regenerated fibers from the recycled wood and dissolving pulps to enhance fibrillation and produce microfibers. The most effective treatment was 17.5% NaOH for 5 minutes, followed by application of pressure to the treated fibers. This separated the fibers into fibrils of a diameter of few microns along the fiber axis. Microfibers were also produced by melt blowing lyocell solutions to form nonwoven webs. Initially microfiber webs were formed by preparing 14% lyocell solutions from dissolving pulp and processing them in a laboratory
scale 6-inch melt blowing line. Web collection was followed by washing with water to remove the solvent and precipitate the fibers. A further processing enhancement was direct mixing of the dissolving pulp with NMMO/H2O in a twin-screw extruder connected to the melt blowing apparatus. With a 14% cellulose solution, it was possible to melt blow nonwoven webs with different basis weights (27, 79, and 141 g/m2) and thicknesses (0.3-0.9 mm). The mean fiber diameter was 2.3 microns. Lyocell concentrations below 14% had poor spinnability. A method for determining the molecular weight average and distribution of cellulose using lyocell solution shearing rheology was developed and demonstrated on two dissolving pulp samples and controlled blends of the two. This group also developed a computational technique for determining the material parameters that are needed for the type of software available on most research rotational shear rheometers to calibrate the rheological results for the
specific polymer systems studied.
Impacts
This work demonstrated use of wood pulps and lignocellulosic agricultural by-products as raw materials for regenerated cellulosic fibers. Bleached and unbleached hardwood and softwood pulps had rheological properties similar to those of dissolving pulps used in commercial fiber processing. Proper blending ratios of these and other alternative cellulose sources could be considered as replacements for blends of dissolving pulps commonly used in industrial processes. Fibers produced from these materials, using the lyocell process, can be treated to induce fibrillation and separation into microfibers. Products of cellulosic microfibers combine the drape and softness of microfibers with the absorbency of cellulosic materials. A further demonstration of this work was use of a twin screw extruder for mixing and preparation of lyocell solutions, providing a continuous extrusion process for nonwoven webs of lyocell microfibers. A method for determining molecular weight average
and distribution of cellulose using lyocell solution shearing rheology was developed and demonstrated.
Publications
- Wei, X., J.R. Collier, and S. Petrovan, Shearing Rheology of Dissolving Pulp Cellulose Solutions to Calculate Molecular Weight, Submitted to Journal of Applied Polymer Science (2004).
- Collier, B.J., J.R. Collier, S. Petrovan, M. Dever, Z. Li, and Z. Ling Wei, Rheology of Lyocell Solutions from Different Cellulose Sources, Polymer fibres 2002, July 10-12, 2002, Manchester UK.
- Collier, B.J., M. Dever, S. Petrovan, J.R. Collier, Z. Li, and X Wei, Rheology of Lyocell Solutions from Different Cellulose Sources, Journal of Polymers and the Environment, 8(3), 151-154 (2000).
- Dever, M., B.J. Collier, S. Petrovan, and J.R. Collier, Lyocell Solutions from Alternative Cellulose Sources, Clothing and Textiles Research Journal, 21(4), 167-173 (2003).
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Progress 01/01/02 to 12/31/02
Outputs
The primary goal of the project is to develop manufactured cellulosic microfibers from wood pulps and lignocellulosic agricultural by-products. Objectives include preparation and rheological characterization of lyocell solutions, extrusion behavior studies of the lyocell solutions, and production of absorbent cellulosic microfibers. The specific aims for the second year were: (a) preparation of lyocell solutions in a vented twin screw extruder as well as with a Helicone mixer to provide better solutions for extrusion and melt blowing, (b) to producing lyocell microfibers through direct extrusion in a Rheometric Advanced Capillary Extrusion Rheometer (ACER) with hyperbolic converging dies to induce elongational flow, phase separation and development of a microfibrillar structure, (c) melt blowing approach to produce microfibers and (d) microfiber characterization. A vented twin screw extruder was demonstrated to be able to prepare lyocell solutions successfully. The
NMMO monohydrate and finely ground cellulose powder (DP670) were mixed homogeneously and placed in the hopper of the twin screw extruder at 90 degrees C. With this method, homogenous lyocell solutions prepared were: DP670 wood pulp, 8% and14%; and sugarcane bagasse, 8%. Single fibers were spun from these solutions in the ACER using a hyperbolic die with a Hencky strain of 7. Optical and scanning electron microscopy was used to characterize the morphology of the fibers. The high strain rate and rapid phase separation did not induce the desired fibrillar structure in the fibers, so other methods for developing fibrillation were investigated. Fibrillar phenomena were observed in fibers treated with 18% NaOH and subjected to pressure.
Impacts
This work demonstrated use of wood pulps and lignocellulosic agricultural by-products as raw materials for regenerated cellulosic fibers. Fibers produced from these materials, using the lyocell process, can be treated to induced fibrillation and separation into microfibers. Commercially available microfibers are made from synthetic materials and are not absorbent. Products of cellulosic microfibers would combine the drape and softness of microfibers with the absorbency of cellulosic materials. A further demonstration of this work is use of a twin screw extruder for mixing and preparation of lyocell solutions from different cellulosic sources. This can provide a continuous extrusion process for lyocell fibers.
Publications
- Collier, B. J.; Dever, M.; Petrovan, S.; Collier, J. R.; Li, Z. & Wei, X. Rheology of lyocell solutions from different cellulose sources. Journal of Polymers and the Environment (2000), 8(3), 151-154.
- Collier, B.J., Collier J.R., Petrovan, S., Dever, M., Li, Z., & Wei, X. Rheology of lyocell solutions from different cellulose sources. Proceedings of Polymer Fiber, 2002, July 10-12, 2002, Manchester, UK.
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Progress 01/01/01 to 12/31/01
Outputs
The primary goal of the project is to develop manufactured cellulosic microfibers from wood pulps, as well as from lignocellulosic agricultural by-products. Objectives are to: produce lyocell solutions [cellulose in N-methyl-morpholine-N-oxide(NMMO)]; investigate the rheological and extrusion behavior of the lyocell solutions; and produce absorbent cellulose microfibers. The specific aims for the first year, (a) developing the method to prepare NMMO monohydrate from aqueous solutions, (b) setting up standard methods to prepare lyocell solutions of different concentrations from different cellulose sources, and (c) characterizing rheological properties of lyocell solutions have been achieved.
Impacts
NMMO monohydrate was distilled using a rotary vapor vacuum evaporator. NMMO aqueous solutions (51.90wt%) provided by Huntsman Corporation were used. The NMMO aqueous solutions were distilled under continuous mixing and vacuum in a water-bath. Lyocell solutions were prepared in the mixing chamber of a Brabender extruder. Cellulose sources included: bleached softwood, unbleached softwood, bleached hardwood, unbleached hardwood, bleached recycled newsprint, unbleached recycled newsprint, bleached TMP (thermal mechanical pulp), unbleached TMP, kudzu, sugarcane bagasse, and commercial dissolving pulps of different degrees of polymerization (DP). Lyocell solutions of different concentrations were prepared and it was determined that time for complete dissolution of the cellulose was dependent on the target concentration: 4% (1 hr), 6% (1.5 hrs), 8% (3 hrs), and 14% (4 hrs). The temperature was set at 90EC at a mixing speed of 80 RPM.. A filter device was designed to filter
the lyocell solutions immediately after the preparation. Rheological properties of all lyocell solutions were characterized at 90EC between parallel plates in a dynamic mode in a rotational Advanced Rheometric Expansion System (ARES) by Rheometric Scientific. The higher the concentration and DP, the more elastic and viscous the lyocell solutions were. Material properties to calculate molecular weight and molecular weight distribution of dissolving pulps by a rheological method were determined. A melt blowing trial was run using solutions prepared with dissolving pulp. Initial processing conditions were explored.
Publications
- Collier, B.J., M. Dever, S. Petrovan, J.R. Collier, Z. Li, and X Wei, 2001. Rheology of Lyocell Solutions from Different Cellulose Sources, Journal of Polymers and the Environment.
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Progress 01/01/00 to 12/31/00
Outputs
We have begun by preparing lyocell solutions from different cellulosic sources: purified dissolving pulp (as the standard), softwood pulp, sugar cane bagasse, kenaf fibers, and recycled cotton. Rheological measurements were made to characterize the behavior of the solutions and predict their spinnability and the effect of impurities such as lignin on the processing. Both shearing and elongational viscosities were determined. The dominance of viscous behavior over elastic behavior is affected by cellulose concentration and molecular weight. At lower concentrations and degrees of polymerization (DP), solutions show viscous, inelastic behavior at the same strain rate. Higher concentration and DP solutions are more elastic at typical processing strain rates. Solutions prepared with kenaf and sugar cane fibers show similar properties to those using pure disolving pulp, and comparisons can indicate the molecular weight and/or the presence of other substances such as lignin
in the cellulose from these alternative sources.
Impacts
(N/A)
Publications
- No publications reported this period
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