Surface modification of fine powders with low and atmospheric pressure plasmas in a circulating fluidized bed reactor

Abstract

The surface modifications characteristics of polymeric powders with the low-pressure plasma have been determined in a circulating fluidized bed reactor. The performance of surface modification has been evaluated and compared between a circulating fluidized bed and a bubbling fluidized bed reactors as a plasma reactor. Also, a non-thermal plasma source, capable of operating at atmospheric pressure, was developed for the surface modification of inorganic powders. The CFB reactor is composed of a riser $(10 mm-i.d. × 850 mm-high, Pyrex glass)$, a cyclone, downcomer (22 mm-i.d., Pyrex glass) and a loop-seal (10 mm-i.d.). An inductively coupled electrode (4.8 mm-o.d. copper tube, 12 turns) was placed at the upper region of the riser and plasma was generated by coupling with a radio frequency (rf) of 13.56 MHz. Particles in the CFB were entrained by gas flow, collected by cyclone and pass through the reaction zone repeatedly. There is no distinguishable dense bed and plasma is generated in dilute phase of solids in the riser. The difference in static head in the reactor governs the driving force for solids circulation, and the hydrodynamics in the CFB under low-pressure exhibits similar fluidizing behavior to that of atmospheric pressure. To modify the surface properties of fine powders, HDPE powders $(d_p=231 ㎛, \rho_s = 956 kg/㎥)$ have been oxidized and fluorinated by the active species in a glow discharge. The optimum reaction conditions for oxidation and fluorination of polymer powders in a CFB have been determined under the several different plasma conditions. The chemistry of the oxygen and fluorine reactions with polymer powders in the plasma is also elucidated. The chemical and physical properties of the modified surfaces have been determined by using electron spectroscopy for chemical analysis (ESCA), Fourier transform infrared spectroscopy (FTIR), the contact angle measurements, and scanning electron microscopy (SEM). The high voltage electrodes, capabl...