FORMATION OF POLY(1,1,2,2-TETRAHYDROPERFLUORODECYL ACRYLATE) SUBMICRON FIBERS AND PARTICLES FROM SUPERCRITICAL CARBON-DIOXIDE SOLUTIONS

Rapid expansion from supercritical solution (RESS) of a crystalline fl uoropolymer, poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) or poly(T A-N), in carbon dioxide produces submicron to several micron sized par ticles and fibers. The understanding of the RESS mechanism has been cl arified by careful design of experimental variables and procedures. Th e concentration of the poly(TA-N)/CO2 solution was held constant (at 0 .5 and 2.0 wt %), the solution cloud point curves were obtained, the p re-expansion temperature was varied above and below the cloud point, a nd the length to diameter (L/D) ratio of the nozzle was varied from 8. 5 to 508. The morphology is explained in terms of the location of phas e separation within the expansion nozzle. The. L/D is the most influen tial variable for achieving a transition from particles or fibers. In most cases, manipulation of the solution concentration and the pre-exp ansion temperature did not produce this transition but did have a larg e effect on the sizes of the particles and fibers. These results are a n important step in demonstrating CO2-based spray processes which do n ot require any volatile organic solvents.