Plasma afterglow treatment of polymer powders: Process parameters, wettability improvement, and aging effects

Abstract

Polyethylene powder is treated in an atmospheric pressure circulating fluidized bed plasma reactor, in which powder particles pass the afterglow of 64 discharge channels multiple times. Contact angle drops with increasing treatment time and powder gradually becomes wettable with liquids of higher surface tensions. X‐ray photoelectron spectroscopy is used to prove particle surface functionalization induced by the afterglow process. Two different channel arrangements and geometries are studied and the influence of applied voltage and frequency on activation efficiency is investigated. Minimal surface aging is observed when samples are stored in air. However, when dispersed in water, particles maintain the engineered wettability.

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…”

“…The majority of published studies discusses plasma treatment of PE powder for wettability improvement by Ar/O 2 , Ar/CO 2 , He/O 2 , He/Ar/O 2 , air, or N 2 /CO 2 plasmas . Other studies report about the fluorination of PS particles with He/CF 4 to be applied as antifoaming powders .…”