Grantee Research Project Results

2005 Progress Report: Cellulosic Carbon Fiber Precursors from Ionic Liquid Solutions

EPA Grant Number: R831658
Title: Cellulosic Carbon Fiber Precursors from Ionic Liquid Solutions
Investigators: Collier, John R. , Rials, Timothy G. , Petrovan, Simioan
Institution: University of Tennessee
EPA Project Officer: Aja, Hayley
Project Period: June 1, 2004 through May 31, 2007 (Extended to May 31, 2008)
Project Period Covered by this Report: June 1, 2005 through May 31, 2006
Project Amount: $350,000
RFA: Technology for a Sustainable Environment (2003) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , Sustainable and Healthy Communities

Objective:

In this report part of the data on the following two objectives are presented:

Preparation of ionic liquid (IL) cellulose solutions from dissolving pulps of different degrees of polymerization (DP).
Preparation of cellulose solutions by using a laboratory internal mixer and comparison with the solutions prepared by manually mixing.

Progress Summary:

Experimental Part

Materials and Equipment. Three dissolving pulps of DP 670, 1720, and 3900 were used, all from Buckeye Technologies, Inc., Memphis, TN.

Rheological measurements were done on an ARES (Advanced Rheometric Expansion System, TA Instruments) rheometer, using parallel plate geometry. Dynamic frequency sweep mode of operation was used to measure and plot complex viscosity and dynamic moduli (storage (G’) and loss (G”) modulus, respectively) versus angular velocity at different temperatures. The linear viscoelastic region was tested by performing a dynamic strain sweep test. Solutions of different concentrations of cellulose were prepared by using an internal mixer type C. W. Brabender Type-6 mixer (C. W. Brabender Instruments, Inc.).

Technique. Dissolving pulp sheets were cut in small pieces, shredded into a fine powder, and then dried at 105°C to constant weight. IL solid powder was melted in the mixer chamber and then dissolving pulp and propyl gallate were added. The mixer was run at 60 RPM until a clear yellow solution was obtained. All solutions were stored in glass jars until used for rheological measurements.

Dynamic rheological measurements were performed on the ARES instrument using the parallel plate geometry (d = 20 mm at a gap of 1 mm). In order to avoid water uptake by the sample while running the experiment, the edge of the specimen between the plates was covered with a thin layer of viscosity standard silicon oil (29.1 Pa s at 25oC).

Results

Effect of the Degree of Polymerization. As the DP increased, the solution viscosity also increased (Figures 1, 2). The torque was below the lower limit of the equipment for the DP 670 solution at 100°C. The effect of temperature is seen by comparing the curves from Figures 1 and 2.

Figure 1. Complex Viscosity of 3 wt% Cellulose/IL Solutions Manually Prepared Using Different DPs at 80[C]
Figure 1. Complex Viscosity of 3 wt% Cellulose/IL Solutions Manually Prepared Using Different DPs at 80°C

Figure 2. Complex Viscosity of 3 wt% Cellulose/IL Solutions Manually Prepared with Different DPs at 90[C]
Figure 2. Complex Viscosity of 3 wt% Cellulose/IL Solutions Manually Prepared with Different DPs at 90°C

The viscoelastic properties of the IL/cellulose solutions varied with the DP. The lower the DP, the more the solution behaved like a viscous liquid instead of a viscoelastic liquid. This can be seen from Figure 3 for a solution of 3% DP 1720 dissolving pulp, where the loss or viscous modulus is higher than the elastic modulus on the whole range of angular velocities tested. For a DP 3900 dissolving pulp solution, Figure 4, there is a cross-over point, where the moduli are equal. This point separates the curves into two regions—one dominantly viscous, where loss modulus is higher, and one elastic domain, where the storage or elastic modulus is higher.

Figure 3. Storage and Loss Moduli of 3 wt% DP 1720 Cellulose/IL Solution at 90[C]
Figure 3. Storage and Loss Moduli of 3 wt% DP 1720 Cellulose/IL Solution at 90°C

Figure 4. Storage and Loss Moduli of 3 wt% DP 3900 Cellulose/IL Solution Manually Prepared at 90[C]
Figure 4. Storage and Loss Moduli of 3 wt% DP 3900 Cellulose/IL Solution Manually Prepared at 90°C

The cross-over points for the three DPs solutions and at different temperatures are presented in Table 1. It is seen that DP 670 solution behaves as a viscous fluid at all temperatures. The intermediate DP dissolving pulp solution (DP 1720) shows a viscoelastic behavior at low temperature and the high DP solution shows this character at all temperatures, due to the longer macromolecular cellulosic chains.

Table 1. Cross-over Points of Solutions with Various DPs

Degree of Polymerization	Cross-over Point		Temperature, °C
Degree of Polymerization	ω	G’(=G”)	Temperature, °C
670	NA	NA	80
670	NA	NA	90
670	NA	NA	100
1720	2.897	256.3	80
1720	NA	NA	90
1720	NA	NA	100
3900	0.6058	204.4	80
3900	2.014	234.2	90
3900	11.08	329.5	100

As the temperature increases, the cross-over point is usually shifted to higher angular velocities, decreasing the viscoelastic domain. The reciprocal of the cross-over point angular velocity has units of time and is an indication of the relaxation time of the macromolecular chains from the solution, which is an important parameter of the fiber forming process.

Shifting of the viscosity curves was done, and a typical master curve is presented in Figure 5, for a DP 3900 dissolving pulp solution. Activation energy for shear flow is determined from the Arrhenius plot, presented in Figure 6. Also, the effect of DP on the activation energy is shown in Table 2.

Figure 5. Master Curve for 3 wt% DP 3900 Cellulose/IL Solution Manually Prepared
Figure 5. Master Curve for 3 wt% DP 3900 Cellulose/IL Solution Manually Prepared

Figure 6. Arrhenius Plot for 3 wt% DP 3900 Cellulose/IL Solution Manually Prepared
Figure 6. Arrhenius Plot for 3 wt% DP 3900 Cellulose/IL Solution Manually Prepared

Table 2. Activation Energy of Flow for IL/Cellulose Solutions Manually Prepared with Various DPs.

Degree of Polymerization	ΔE_a, (Kcal/mol)	R²
670	NA	NA
1720	44.56	0.9576
3900	25.71	0.9997

Effect of Preparation Technique. The viscosity curves for 3 wt% DP 3900 cellulose solutions that were prepared by manual and mechanical mixing are shown in Figure 7. The manually mixed solution had a higher viscosity. For the 10 wt% DP 670 solution, the mechanically mixed solution had a higher viscosity (Figure 8). From these results, it can be concluded that the effect of preparation method on viscosity was dependent on the DP of the cellulose dissolving pulp.

Figure 7. Complex Viscosity of 3 wt% DP 3900 Cellulose/IL Solution Manually and Mechanically Prepared
Figure 7. Complex Viscosity of 3 wt% DP 3900 Cellulose/IL Solution Manually and Mechanically Prepared

Figure 8. Complex Viscosity of 10 wt% DP670 Cellulose/IL Solution Manually and Mechanically Prepared
Figure 8. Complex Viscosity of 10 wt% DP670 Cellulose/IL Solution Manually and Mechanically Prepared

The viscoelastic properties of the IL solutions at 90°C are displayed in Figures 9 and 10. Both preparation method and DP are important parameters for a solution’s viscoelasticity, as seen also in Table 3. Three percent solutions prepared with DP 3900 cellulose exhibited a cross-over point regardless of the preparation method. The 10wt% solution prepared with DP 670 cellulose was dependent on preparation method. The mechanically prepared solution had a cross-over point, but the manually prepared solution did not have a cross-over point at 90o and 100oC. It behaved as a viscous liquid at these temperatures because the loss modulus was higher than the storage modulus.

Figure 9. Dynamic Moduli for 3 wt% DP 3900 Cellulose/IL Solution at 90[C] Mechanically and Manually Prepared
Figure 9. Dynamic Moduli for 3 wt% DP 3900 Cellulose/IL Solution at 90°C Mechanically and Manually Prepared

Figure 10. Dynamic Moduli for 10 wt% DP 670 Cellulose/IL Solution at 90[C] Mechanically and Manually Prepared
Figure 10. Dynamic Moduli for 10 wt% DP 670 Cellulose/IL Solution at 90°C Mechanically and Manually Prepared

Table 3. Cross-over Points for Different Preparation Methods and DPs Various Solutions

Concentration of Cellulose	Preparation Method	Degree of Polymerization	Cross-over Point		Temperature °C
Concentration of Cellulose	Preparation Method	Degree of Polymerization	ω	G’(=G”)	Temperature °C
10	Mechanical	670	27.49	2751	80
10	Mechanical	670	52.00	2900	90
10	Mechanical	670	84.84	3128	100
3	Manual	3900	0.6058	204.4	80
3	Manual	3900	2.014	234.2	90
3	Manual	3900	11.08	329.5	100
3	Mechanical	3900	12.67	413.5	80
3	Mechanical	3900	25.24	423.7	90
3	Mechanical	3900	46.33	466.2	100
10	Manual	670	66.38	2786	80
10	Manual	670	NA	NA	90
10	Manual	670	NA	NA	100

Differences between the preparation methods are shown in Table 4, where the activation energies are presented.

Table 4. Activation Energies for Flow of IL Solutions with Different Mixing Methods

Concentration of IL Solution, %	Degree of Polymerization	Method of Preparation	Activation Energy for Shear Flow, Kcal/mol	Coefficient of Determination for Arrhenius Plot
3	3900	Manual	25.71	0.9997
3	3900	Mechanical	12.17	0.9999
10	670	Manual	21.99	0.9943
10	670	Mechanical	10.53	0.9410

Conclusions

IL/cellulosic solutions of DP 670, 1720, and 3900 were prepared and tested for their rheological characteristics. The complex viscosity and dynamic moduli were determined at different temperatures. The 3 wt% DP 670 solution behaves as a viscous liquid at all temperatures tested. The DP 1720 solution displayed a viscoelastic character at low temperatures and behaved as a viscous liquid at high temperatures. The DP 3900 solution showed viscoelastic characteristics on the whole range of temperatures tested.

Manually prepared IL/cellulose solutions were compared to those mixed mechanically. The solutions were then tested for their rheological properties. The 10 wt% DP 670 solution prepared mechanically had a higher viscosity than the 10 wt% DP 670 solution manually prepared. For the 3 wt% DP 3900 solution, the manually prepared solution had a higher viscosity than the mechanically prepared solution. Both mechanically prepared solutions displayed viscoelastic properties. The manually prepared 3 wt% DP 3900 also displayed viscoelastic properties, though the cross-over point was at a lower angular velocity than both of the mechanically prepared solutions. The manually prepared 10 wt% DP 670 solution displayed properties of a viscous liquid. The 3 wt% DP3900 showed no interaction between the mixing method and the temperature. Some interaction between mixing method and temperature for 10 wt% DP 670 was recorded.

Journal Articles:

No journal articles submitted with this report: View all 4 publications for this project

Supplemental Keywords:

Sustainable Industry/Business, RFA, Scientific Discipline, TREATMENT/CONTROL, INTERNATIONAL COOPERATION, Technology for Sustainable Environment, Chemical Engineering, pollution prevention, Sustainable Environment, Environmental Chemistry, Chemistry and Materials Science, cleaner production/pollution prevention, Environmental Engineering, Technology, catalysts, cellulose, automotive components, pyrolysis molecular beam spectroscopy, ionic liquids, automotive industry, clean manufacturing, clean technologies, cleaner production, elongational flow spinning process

Progress and Final Reports:

Original Abstract

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.