MODIFICATION OF POLY[(3-HYDROXYBUTYRIC ACID)-CO-(3-HYDROXYVALERIC ACID)] FILM SURFACES IN AN OXYGEN LOW-PRESSURE PLASMA

Poly[(3-hydroxybutyric acid)-co-(3-hydroxyvaleric acid)] (91:9 mass-%) (P(HB-co-9% HV)) film surfaces were modified by an oxygen plasma trea tment (75 W, 50 Pa, 5 min). The number of oxygen atoms increases about 12-13% and the polar component of the surface energy increases from 6 .3 to 21 mN . m(-1). However, the wettability is stable only after 60 days. Untreated and treated him surfaces are studied by means of X-ray photoelectron spectroscopy with two different depth analyses. With st orage time, the oxygen contents of the modified film is constant at a take-off angle of 20 degrees but decreases to the initial value at a t ake-off angle of 70 degrees. The superficial layer of the polymer film between the top of the film to a depth of 10 nm is divided into three superimposing zones. The interpretation is supported by motions of mo dified macromolecular chains and buried polar groups, chain cleavage a nd the formation of low-molecular-weight molecules which leads to a de crease of the glass transition temperature (plasticizer effect) and mi gration of short chains from the lowest modified zone toward the surfa ce.