High Barrier Layer Though Dielectric Barrier Discharge (DBD) Plasma Assisted Atomic Layer Deposition Alumina at Atmospheric Pressure on Polylactic Acid Web

Abstract

Owing to increased impact of environmental protection issues, a greater effort has been made in developing degradable biological materials without any environmental pollution to replace oil-based traditional plastics. Among numerous kinds of degradable polymers, polylactic acid (PLA), an aliphatic polyester and biocompatible thermoplastic, is currently a most promising and popular material with the brightest development prospect. However, the poor barrier properties at a relative high humidity due to absorption of water and swelling of polymer block this plastic application. Therefore, in order to enhance the applications, the Al2O3 thin film has been deposited on the 40μm PLA surface through atomic layer deposition (ALD) technique. As comparison polyethylene terephthalate (PET) web, 125μm in thickness, is also used as substrates. The highlight in this work is that we employ a dielectric barrier discharge plasma, working at an ambient pressure, plasma assisted ALD to grow Al2O3 coating. We use trimethylaluminum (TMA) and Ar/O2 plasma as precursor and oxidant at temperatures of 65°C and 80°C, respectively, to study the influence of the deposition temperature effect. After measurement of barrier properties, we result that ALD Al2O3 coating can greatly decrease the water vapor transmission rate (WVTR) but depending on the coating thickness. When the thickness of ALD Al2O3 is over 80 nm, the role of thickness on the barrier properties is negligible, whereas the pinholes are the main path for the water permeation. The minimum WVTR values of ALD Al2O3 coating PLA and PET reach 200 mg/m2/day and 2 mg/m2/day, compared to the pristine value of 80040 mg/m2/day and 3170 mg/m2/day respectively. Additionally, the chemical composition and surface morphology of Al2O3 coating are characterized by spectroscopic ellipsometer, x-ray diffraction, x-ray photoelectric spectroscopy, atomic force microscopy and scanning electron microscopy, respectively, for analysis of the high barrier properties.