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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:
There has been considerable interest over the last decade in the use of super critical (sc) and high pressure (hp) carbon dioxide for replacing highly toxic organic solvents and plasticizers used in the synthesis and processing of polymeric materials. CO2 is non-toxic, non-flammable, chemically inert, completely recoverable, and inexpensive. It has solubilization characteristics similar to organic solvents like CFCs and is known to plasticize amorphous and some semi-crystalline (with low degrees of crystallinity) polymers. To date hp- and sc-CO2 have been used primarily as solvents and non-solvents for polymerization, to generate micro-cellular plastics, to impregnate polymers with various additives and to extract impurities and low molecular weight polymers from a polymer. This work is concerned with the use of carbon dioxide as a processing aid to render polymers, which must ordinarily be processed in the presence of environmentally unfriendly solvents, melt processable.The first goal of this research is to develop a general procedure for melt spinning polymers using the exemplary acrylic copolymer system plasticized with carbon dioxide in such a way that foaming is eliminated or at least minimized. The second goal of the work is to devise a technique for rapidly saturating the acrylic copolymers with CO2 and to optimize the copolymer structure to accelerate the saturation.
Approach:An exemplary system chosen here is the commercially prevalent (about 6 billion pounds are produced annually) acrylic copolymers consisting of acrylonitrile (AN) and methylacrylate (MA) which are solution spun using highly toxic solvents to form fibers for use in textiles and as precursors to carbon fibers. Solution spinning is necessary as these materials with levels of AN greater than 85 to 90 mole % crosslink and cyclize (degrade) rapidly at temperatures where they might be melt processable (e.g. 220 oC). Initial studies in our laboratory have revealed that low levels of absorbed CO2 (<12 wt %) significantly reduce the glass transition temperature of AN/MA copolymers and thereby allow them to be extruded at temperatures low enough that significant degradation can be avoided. However, capitalizing on this effect to produce melt spun fibers and films is extremely difficult as foaming of the polymer occurs immediately as the melt exits the die (i.e. spinneret hole or film die). A chamber will be designed for controlling the pressure and temperature of the environment into which the fibers exit in order to control the release of CO2 in such a way as to avoid flashing and yet allow continuous passage of the fibers from the controlled environment to ambient conditions. Numerical simulation techniques will be used to select appropriate processing conditions, i.e. temperature and pressure, to control the release of the CO2 according to spinning speed, melt temperature, and fiber diameter. Saturating the copolymers with CO2 at rates which are commercially acceptable will also present a challenge. Two approaches will be investigated: one a batch process involving high pressure saturation; the other a continuous process using scCO2 injected into the polymer in the screw extruder. Although we will concentrate on the spinning of AN/MA copolymers, the knowledge gained here is expected to be translated to other polymer systems. Expected Results:
The successful spinning of AN/MA copolymers in the presence of CO2 will play a significant role in reducing environmental pollution and costs associated with solvent processing of these commercially important high volume materials. The toxic solvents presently used must be recovered, but some amounts escape into ground water and rivers. CO2 is extracted from the air and released back to the air with no net addition of CO2. Publications and Presentations:
Publications have been submitted on this project: View all 20 publications for this project
Journal Articles:Journal Articles have been submitted on this project: View all 6 journal articles for this project
Supplemental Keywords: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
Progress and Final Reports:
2002 Progress Report
2003 Progress Report
Final Report