One-layer water vapor Poly(olefin) barriers compete metal sputtering onto flexible substrates

Abstract The effect of one-layer polymeric barrier coatings onto flexible and thin polyethylene terephthalate (PET) film is herein examined towards the blockage of water vapor. It is observed that well-known semi-crystalline polymers such as poly(ethylene) (PE), partially chlorinated PE (47% Cl-PE), poly(propylene) (PP), and poly(vinylidene fluoride) (PVDF) completely fail (0–4%) to reduce PET's water vapor transmission rate (WVTR). A similar trend is also shown for amorphous hydrophobic polymers such as poly(dimethyl siloxane) (PDMS) and commercial poly(silazanes). Poly(vinylidene chloride) (PVDC) containing halogen groups blocks water vapor, but its high viscosity and film inhomogeneity at higher thickness restricts it's WVTR reduction up to 40% onto PET. On the other hand, alkylated poly(olefins) of controlled molecular weight and low dispersity, prepared by living cationic polymerization, act as highly effective transparent polymeric barrier coatings. Reduction in PET's WVTR up to 62% is shown for one-layer barrier, and 69% for a two layer coating, values highly comparable with the costly Al sputtering (74% reduction; completely metallic coating). The incorporation of nanomaterials into high polymeric barriers is also discussed. Lastly, mechanical tests on elongation of PET/barrier coatings reveal the necessity to examine polymeric barriers in a broader spectrum, covering WVTR reduction, transparency, and coating-induced resistance towards cracking/deformation.