Highly hydrophilic poly(ethylene terephthalate) films prepared by combined hot embossing and plasma treatment techniques

Abstract

Combined hot embossing and low pressure RF plasma treatment techniques were used with the aim to enhance surface wettability of biaxially oriented semicrystalline poly(ethylene terephthalate) (PET) films. Produced by industrial stretch-blow molding PET film of the 300μm thickness was chosen for the experiments. Hot embossing of the prepatterned Ni stamp led to additional crystallization and the increment in effective surface area of the polymer. One set of the embossed samples was treated by CF4 plasma, while the other was successively treated by O2 and CF4 plasma. Changes in the dimensions of the embossed bumps were observable after the plasma treatment due to the release of frozen internal stresses. Nanoroughening of the surface associated with the plasma treatment was more significant for the O2 and CF4 plasma treated PET. Surfaces of both sample sets were hydrophobic immediately after the plasma treatment due to the large amount of incorporated fluorine. However, wetting tended to increase rapidly during the first days of ageing. After 10 days of storing, average water contact angle was about 20° for the hot embossed and CF4 plasma treated PET films, and it was about 11° for the hot embossed and successively O2 and CF4 plasma treated films. Further ageing up to 60 days have not revealed noticeable changes in the surface wetting. So, combined hot embossing and plasma treatment techniques were found to be beneficial for the enhancement of the surface wetting compared to plasma treatment alone.