Photo initiated chemical vapour deposition to increase polymer hydrophobicity

Apple growers face new challenges to produce organic apples and now many cover orchards with
high-density polyethylene (HDPE) nets to exclude insects, rather than spraying insecticides.
However, rainwater- associated wetness favours the development of apple scabs, Venturia inaequalis,
whose lesions accumulate on the leaves and fruit causing unsightly spots. Treating the nets with a
superhydrophobic coating should reduce the amount of water that passes through the net. Here we
treat HDPE and polyethylene terephthalate using photo-initiated chemical vapour deposition (PICVD).
We placed polymer samples in a quartz tube and passed a mixture of H2 and CO through it while a UVC
lamp (254 nm) illuminated the surface. After the treatment, the contact angle between water droplets
and the surface increased by an average of 20°. The contact angle of samples placed 70 cm from the
entrance of the tube was higher than those at 45 cm and 20 cm. The PICVD-treated HDPE achieved a
contact angle of 124°. Nets spray coated with a solvent-based commercial product achieved 180° but
water ingress was, surprisingly, higher than that for nets with a lower contact angle.