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

Abstract

Abstract 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\u202fat. %) 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\u202f°C. Techniques such as Fourier-transform 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\u202fg/m2-day for the 3D ABS uncoated samples as compared with 28.8\u202fg/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.