Plasma modification of powder has recently attracted much interest because of new prospects of the interfacial properties supervision. There was mostly used the low-pressure plasma modification in fluidized bed, but for industrial-scale application the employment of mechanical stirring also appears to be very promising at the moment. It was shown that application of plasma modification methods led to substantial process time reduction. In case of the polyethylene, parts sintered from the plasma-modified polyethylene powder were characterized with high surface tension, which allowed e.g. direct painting or adhesive bonding without any additional pre-treatment. Plasma modification also significantly enhanced the adhesion of the polymer to the substrate. Adhesion and wettability measurements were carried out to reveal surface modification of plasma treatment of HDPE powders. This paper describes results of the polyethylene powder plasma treatment in microwave low-pressure plasma and discusses possibilities of its application.

The surface modification of polyethylene powder using a plasma reactor based on a dielectric barrier discharge in air at atmospheric pressure and ambient temperature is investigated. The process is inexpensive, and the necessity of any vacuum equipment and technical gases is alleviated. The efficiency of the modification process was successfully demonstrated by ESCA measurements that proved formation of new functional groups at the modified powder surface. The modification effect was also evaluated by means of dynamic capillarity rising measurements. Powder capillarity tests proved significant powder capillarity changes. The reduction of the modification effect was also limited (max. reduction of about 20% during 1 100 d after the modification date).magnified image

Problems of the powder particles plasma modification are practically the same as in the case of solid films. Troubles of the powder treatment are related with its threedimensional character, small size of particles, treated large area and problems with powder manipulation, that also must not be neglected. For modification of polymer powder surface properties like wettability and adhesion without changing powder bulk properties there have been mostly applied methods employing low temperature (cold) plasma treatment at low pressures. Presented contribution describes design and investigation of a novel plasma reactor exploiting the dielectric barrier discharge burning in air at atmospheric pressure by ambient temperature and its usability tests. For tests HDPE powder Borealis CB 9155-01 was used. This plasma reactor is of a very simple construction in comparison with other in literature described apparatuses used for this purpose and needs no vacuum equipment. Powder capillarity tests had proved significant powder capillarity changes induced by DBD plasma modification. Modification effect reduction (aging) is remarkably small (max. reduction about 20 % in one year after the modification date), hence modification effect is very time stable.

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