Ultrasonically sprayed poly(vinylidene chloride) coating on polyurea as moisture barrier

As an emerging protective coating material, elastomeric polyurea (PU) coatings have found a variety of applications in impact resistance and anti-corrosion. However, its moisture barrier performance is not very ideal，which limits its further applications for waterproofing and anti-corrosion purposes. Improving PU's moisture barrier property is decisive in further realizing its full potential as a protective coating material. Here we provide a facile, precise, and straightforward process to improve the moisture barrier property of the PU film. The process involves coating PU film with a thin layer of poly(vinylidene chloride) (PVDC) by using ultrasonic spray coating technique. The quality of PVDC coatings was optimized through tuning of flow rate and solid content of PVDC emulsion. It was found that the thickness of PVDC coating was proportional to the number of spraying scans. Water vapor transmission rate of PVDC coated PU film was reduced by 85.11%, compared with that of pristine PU film, indicating substantial improvement of the moisture barrier property. Strong adhesion of PVDC coating on PU films was verified through cross-cut test. Aging tests of PVDC coated PU films in acid, base, salt, and heat environments verified the durability of the film, with only minor loss in the moisture barrier property and mechanical performance after aging.