Plasma surface treatments of melt-extruded sheets of poly(L-lactic acid)

Poly(L-lactic acid) sheets, prepared by melt extrusion, were treated with O-2-, He-, and N-2-plasmas generated in radio frequency (RF) at 13.56 MHz. Atmospheric pressure discharge at 20 kHz in helium was also applied to the modification of the sheets. The surface of the PLLA sheets was etched to form the characteristic morphology, and the patterns were different depending on the type of plasma. Polar groups composed of -COOH and -OH were incorporated by plasma treatment, and the surface became wettable. Surface modification became effective after a short treatment period, e.g., 30 seconds. Receding contact angles (theta(r)) changed remark ably, and the surface properties were closely related to the increase in the surface energy of the polar contribution (gamma(s)(p)). Biodegradation of the poly(L-lactic acid) sheets was not enhanced practically, even though the surface became hydrophilic after plasma treatment.