Polymer Powder Treatment in Atmospheric Pressure Plasma Circulating Fluidized Bed Reactor

Abstract

The surface activation of high‐density polyethylene powder using a remote plasma process at atmospheric pressure is investigated. The developed circulating fluidized bed plasma reactor enables to carry fine‐grained powder particles repetitively through the afterglow of 64 dielectric barrier discharges of argon with O2 and CO2 admixtures. The evolution of particle size distribution during conveying in the reactor is monitored by laser diffraction and reveals that only a small particle fraction is lost during the process. The contact angle of activated powder samples steadily decreases with increasing treatment time. The surface activation is most effective for O2 admixtures of 0.25 vol% and CO2 admixtures of above approximately 1 vol%, respectively.

Plasma treatment of polymer powders – from laboratory research to industrial application

“…In practice, the weight of liquid penetration into a packed polymer powder column is measured over time ( m 2 / t ), which leads to the modified Washburn equation: where η L [Pa s −1 ], ρ L [kg m −3 ], and σ L [mN m −1 ] correspond to the viscosity, density, and total surface tension of the testing liquid. The term C is a geometric factor [m 5 ], which is determined from measurements with a nonpolar liquid that perfectly wets the polymer powder (i.e., hexane, heptane, or octane) for which the contact angle against the powder is assumed to be 0° (cos 0° = 1). The C values are measured independently for each type of polymer powder packing (untreated and plasma‐treated powders) and their accurate determination is essential for a correct application of Washburn's equation.…”

“…Patra et al compacted LDPE powder for about 1 min by mechanical vibration under a dead load of 2 kg. After powder packing, the cylindrical measurement tube is attached to an electronic balance of a tensiometer (e.g., K12 or K100 from Krüss GmbH, Germany), which is linked to a control unit and a computer.…”

“…Also, arrangements with shell type (C) or parallel electrodes (D) are applied, as well as external bar electrodes, which rotate a dielectric tube (E) . A unique configuration are multichannel DBDs providing a central afterglow treatment zone (F) . Some configurations apply water‐cooled electrodes to prevent high gas temperatures, which may provoke powder melting.…”

“…(E) Rotating dielectric tube with external electrode bars . (F) Multichannel configuration with plasma afterglow directed toward a center treatment zone…”

Contact Angle Decay Model to Study Plasma Afterglow Activation of Polymers

“…[15] As the feasibility of activating fine-grained high-density polyethylene (HDPE) powder was previously shown, we now focus on improving the efficiency of the developed afterglow process. [16] Herein we investigate the influence of geometrical properties of single discharge channels on their polymer surface activation capability. Due to time-consuming construction of several MCDs of different channel geometries and complex subsequent powder analysis, we examined the functionalization of plane HDPE substrates in the afterglow of single discharge channels.…”