Oxygen diffusion barrier properties of plasma deposited SiO_x films on low density polyethylene

Polyethylene is a promising material for packaging applications due to its good mechanical and sealing properties. Also it is a low cost material. Oxygen diffusion barrier property of polyethylene is not sufficiently good to be used alone as a packaging material. This means the material allows large number of oxygen molecules to pass through which reacts with the packed product and degrades the same. Because of this reason multi-layer (3 - 9 layers) packaging structures are being used for flexible packaging. To address this problem, in the present work we have deposited nano-scale SiO_x films on Low Density Polyethylene (LDPE) surface by radio frequency (13.56 MHz) capacitively coupled Oxygen/HMDSO plasma at low pressure. Film properties such as surface chemistry, morphology and oxygen diffusion rate are studied by Fourier Transform Infrared Spectroscopy (FT-IR), High Resolution Scanning Electron Microscopy (HR-SEM) and Gas Transmission Rate Testing machine respectively. Film thickness and surface roughness is determined by contact mode stylus profileometry. Experimental results reveal that oxygen transmission rate reduces from 3300 cc/ m²/day (OTR Value of untreated polyethylene) to 350±100 cc / m²/ day with increase in oxygen concentration in Oxygen / HMDSO gas mixture. Organic-inorganic double layer SiO_x film gives better barrier properties compared to single layer film. (author)