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Final Report: Benign Processing of Polymers Plasticized with Absorbed Carbon Dioxide
EPA Grant Number: R829555Title: Benign Processing of Polymers Plasticized with Absorbed Carbon Dioxide
Investigators: Baird, Donald G.
Institution: Virginia Polytechnic Institute and State University
EPA Project Officer: Richards, April
Project Period: January 1, 2002 through December 31, 2004 (Extended to July 31, 2005)
Project Amount: $325,000
RFA: Technology for a Sustainable Environment (2001)
Research Category: Pollution Prevention/Sustainable Development
Description:
Objective:The objectives of this research project were to: (1) develop a melt spinning process for acrylic polymers that ordinarily would have to be solution spun using toxic organic solvents and supercritical CO2 as a plasticizer (i.e., replace the toxic organic solvents with benign CO2); (2) develop a technique that will allow the rapid saturation of acrylic copolymers with CO2; (3) optimize the copolymer structure to accelerate the saturation process; and (4) design a chamber that prevents foaming of the extruded filaments.
Summary/Accomplishments (Outputs/Outcomes):It has been discovered that CO2 can be adsorbed into acrylonitrile (AN) copolymers and serve to plasticize them, leading to a reduction in glass transition temperature, Tg. Plasticization leads to the reduction of viscosity of the acrylic copolymers at a given temperature. Currently, acrylic copolymers used in the manufacture of textile fibers and as precursors for carbon fibers must be solution spun in toxic solvents such as N,N-dimethylformamide or dimethylacetamide to prevent them from crosslinking and cyclizing. When introduced at elevated temperatures and pressures, the gas can absorb and diffuse into the investigated copolymers, resulting in a reduction of the glass transition temperature Tg. Copolymers of AN and methyl acrylate (MA), which are solutions traditionally processed to produce acrylic fibers or carbon fiber precursors, have been adsorbed with CO2 and tested via thermal analyses. AN copolymers containing between 65 and 88 mole percent AN all have been shown to adsorb CO2. Although the diffusivity of CO2 in polyacrylonitrile copolymers is very low, the solubility is relatively high.
A Tg reduction of 31°C (measured using differential scanning calorimetry) and a CO2 uptake of 6.7 weight percent (measured using thermogravimetric analysis) were observed in the 65 mole percent AN copolymer by using a batch method to saturate the copolymer in a 17.237 MPa (2,500 psi) CO2 environment at 120°C for 6 hours. Pressurized capillary rheometry shows a viscosity reduction of 25 to 60 percent over the range of shear rates tested, increasing with the weight percent of CO2. Weight percent uptake of CO2 was found to depend on the saturation conditions; however, pressure was limited to 17.237 MPa (2,500 psi) for batch testing because of equipment limitations. Even with this limitation, it has been found that a 6.7 weight percent uptake of CO2 yields a processing temperature reduction of roughly 30°C.
It is desired to melt process high AN content copolymers (85% and greater); therefore, determining the viscosity and process temperature in a continuous process is required to verify further the feasibility of this goal. A high-pressure liquid pump was used to inject CO2 into a single-screw extruder with a two-stage screw. Viscosity reduction of the 65 mole percent copolymer was measured using slit die rheometry, with 5-10 weight percent CO2 uptake measured using a Coriolis mass flow meter. A viscosity reduction of up to 50 percent was obtained over the range of shear rates tested. Stability tests were performed on the 65 percent and 85 percent AN content copolymers to determine the ideal melt processing temperature range that would allow the 85 percent AN copolymer to remain sufficiently stable while in the extruder. Results showed that the 85 percent polymer is stable enough to melt process at temperatures up to 200°C and should be lower for long processing (residence) times. Viscosity must be sufficiently low, however, for melt processing, especially for melt-spinning fibers. The pure 85 percent AN copolymer has a zero-shear viscosity on the order of 104 Pa-s at 180°C, about 2,500 Pa-s at 200°C, and about 1,000 Pa-s at 180°C. Pressurized capillary rheometry with 5.6 weight percent CO2 uptake showed an average viscosity reduction of 60 percent at 200°C. Combining the stability and viscosity reduction data indicates that melt processing the 85 percent AN copolymer at 190-200°C with CO2 should allow the polymer to remain sufficiently stable at a suitable viscosity.
To prevent the polymer from excessively foaming upon exit of the extrusion die, a pressurized step-down chamber has been designed and built to cool the polymer while under pressure to a temperature below its Tg. Once cooled, the polymer may enter atmospheric conditions as a solid fiber, where it can be processed later into textile fiber or carbon fiber. The specifications for a cooling water pump, as well as a method for incorporating it, have been developed to allow this process to run continuously.
Conclusions:A method and an apparatus have been developed for continuously melt processing AN-MA copolymers with CO2. It has been shown that CO2 can be used to reduce the viscosity of these polymers by 60 percent on average under typical processing conditions, which facilitates the melt processing of polymers of at least 85 percent AN content with suitable viscosity and stability. A pressurized step-down chamber has been designed and shown to suppress foaming within the extrudate to allow for production of sufficiently void-free materials.
Journal Articles on this Report : 6 Displayed | Download in RIS Format
| Other project views: | All 20 publications | 6 publications in selected types | All 6 journal articles |
| Type | Citation | ||
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Bortner MJ, Baird DG. Rheology and extrusion of CO2 plasticized acrylic copolymers. Society of Plastics Engineers 2002;60(1):1024-1028. |
R829555 (Final) |
not available |
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Bortner MJ, Wilding MD, Baird DG. Melt processing of thermally unstable polymers plasticized with CO2. Society of Plastics Engineers 2003;61(3):2811-2815. |
R829555 (Final) |
not available |
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Bortner MJ, Baird DG. Absorption of CO2 and subsequent viscosity reduction of an acrylonitrile copolymer. Polymer 2004;45(10):3399-3412. |
R829555 (2003) R829555 (Final) |
not available |
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Bortner MJ, Bhanu VA, McGrath JE, Baird DG. Absorption of CO2 in high acrylonitrile content copolymers: dependence on acrylonitrile content. Polymer 2004;45(10):3413-3422 |
R829555 (Final) |
not available |
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Bortner MJ, Bhanu VA, McGrath JE, Baird DG. Shear rheological properties of acrylic copolymers and terpolymers suitable for potentially melt processable carbon fiber precursors. Journal of Applied Polymer Science 2004;93(6):2856-2865. |
R829555 (2003) R829555 (Final) |
not available |
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Wilding MD, Nguyen QT, Bortner MJ, Baird DG. Melt processing of traditionally solution-processed polymers with CO2. Society of Plastics Engineers 2004;62(3):3776-3780. |
R829555 (Final) |
not available |
green chemistry, environmentally conscious manufacturing, engineering, acrylic copolymers, carbon dioxide, CO2, plasticizer, toxic organic solvents, polymers, copolymers, carbon fiber,
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Air, Sustainable Industry/Business, Scientific Discipline, RFA, Technology for Sustainable Environment, Sustainable Environment, Chemical Engineering, air toxics, cleaner production/pollution prevention, Chemistry and Materials Science, New/Innovative technologies, Engineering, supercritical carbon dioxide, solvent replacements, high pressure (hp) carbon dioxide, carbon dioxide, environmentally-friendly chemical synthesis, clean technologies, recovery, solvents, alternative solvents, environmentally benign solvents, plastics, polymer design, stratospheric ozone, polymers, polymerization chemistry, organic solvents, supercritical carbon dioxide (SCCO2) technology, pollution prevention, plastic, environmentally benign alternative, alternatives to CFCs
Relevant Websites:
Progress and Final Reports:
2002 Progress Report
2003 Progress Report
Original Abstract