Short-time plasma surface modification of polymer powders in a down flowing tube reactor

A novel down flow reactor is being developed and tested for the functionalization, here the change of contact angle, of temperature sensitive polymer particles (high density polyethylene (HDPE) and co-polyamide (Co–PA) powders) in a low-pressure plasma treatment with O2 / Ar glow discharge. The effects on wettability and chemical composition of processed material at exposure times to the plasma of less than 0.13 s have been determined. X-ray photoelectron spectroscopy (XPS) was used to characterize the powder surfaces. HDPE and Co–PA powder reached a water contact angle reduction down to 65° and 76°. Ageing effects are being observed with HDPE. Contact angles on co-polyamide do not change over time. XPS analysis of the treated HDPE powders indicates the formation of oxygen containing groups, e.g. diethyl ether (C–O–C), carbonyl (C=O) and carboxyl (O–C=O) groups even after short-time treatment. A correlation between the O2-content in the plasma process gas and the oxygen to carbon (O / C) ratio is found. The O / C-ratio increased from 0.0 (no oxygen on the non-treated powder) up to 0.15 in the short-time plasma treated HDPE powder surface.