Water barrier performance of additively manufactured polymers coated with diamond-like carbon films

Whilst additive manufactured polymers have unique and useful properties, the deficiency of water barrier performance limits their shelf-life and functionality as a diffusion barrier for long life product durability. In this work, the induced modification of diamond-like carbon (DLC) coatings using nitrogen (N) (up to 2.02 at. %) to improve water barrier performance has been studied. DLC thin films were deposited onto additively manufactured polymers: acrylonitrile butadiene styrene (3D ABS) and Verogray polymers using microwave-plasma enhanced chemical vapour deposition (MW-PECVD) technique. Test results are described for two N-doped DLC films (a-C:N:H): DLC-1 and DLC-2 deposited at temperatures below 40 degrees C. Techniques such as Fouriertransform infrared spectroscopy (FTIR), atomic force microscopy (AFM), Raman spectroscopy, mercury injection capillary pressure (MICP) measurement and nanoindentation were utilised to study both material and film properties. A good correlation between film thickness and water barrier function for 3D ABS was found. However, for the Verogray samples, film thickness played a limited role in reducing the WVTR. Distinguishable microstructural pit-like defects present on the 3D ABS substrate were seen to promote a higher WVTR of 73.31 g/ m2-day for the 3D ABS uncoated samples as compared with 28.8 g/m2-day for Verogray. The result from this test show strong evidence that DLC coatings could serve as a good water vapour barrier in additively manufactured polymer systems where polymer-water vapour contact may be required, especially in the packaging and food industry where modified atmospheric packaging may be required.