(b) Compression of nanoparticle-coated paperboard by calendering with hard metal and soft polymer roll

calender. The compressibility of TiO2 nanoparticle-coated paperboard surfaces was investigated by calendering in which the paperboard is compressed between two rolls as shown in Figure 1b. Calendering is a well-known surface finishing technique widely used in papermaking. In our case, we use a soft roll/hard roll calender (DT Laboratory Calender, DT Paper Science Oy, Turku, Finland) with a selleck lineload of 104 kN/m and a temperature of 60°C. The samples were treated with the same parameters in successive calendering nips with the nanoparticle-coated this website surface always facing the steel roll to prevent nanoparticle adhesion to the polymer roll. A schematic illustration of the calender is presented in Figure 1b. Surface chemistry was studied with water contact angle measurements performed using the commercial contact angle goniometer KSV CAM 200 (KSV Instruments Ltd., Helsinki, Finland) with an automatic dispenser and motorized stage. The images of the droplets were captured by a digital CCD camera with a 55-mm-zoom microscope lens with a blue LED light source and analyzed with the KSV CAM software. The standard deviation of the contact angle (CA) measurements was approximately ±3°. Contact angles of the Milli-Q (Millipore, Billerica, MA, USA, resistivity

18.2 MΩ) purified water was measured in air in ambient conditions (room temperature 23°C ± 1°C and relative humidity 30% ± 5%) after MK1775 2 s of the droplet application. The volume of the droplets was approximately 2.0 μL, and the reported CA values are mean Sinomenine values of three individual measurements. The TiO2 nanoparticle-coated paperboard surface was exposed to UVA light (Bluepoint 4 ecocure, Hönle UV Technology, Gräfelfing, Germany) with a central wavelength of 365 nm using a filter for 320 to 390 nm. A constant intensity of 50 mW/cm2 was applied for 30 min that converted the initially superhydrophobic

surface to a highly hydrophilic one. The scanning electron microscopy (SEM) imaging of the samples was performed using a field emission scanning electron microscope (FE-SEM; SU 6600, Hitachi, Chiyoda-ku, Tokyo, Japan) with an in-lens detector. All samples were carbon-coated to obtain conductivity. The secondary electron (SE) imaging mode was used for topographical imaging with a magnification of ×50,000 and ×5,000 with an accelerating voltage of 2.70 kV and a working distance of 4 to 5 mm. Cross sections of the TiO2 nanoparticle-coated samples were prepared using an Ilion+ Advantage-Precision Cross-Section System (Model 693, Gatan Inc., Pleasanton, CA, USA). One cross section was milled for each calendered sample with an argon broad ion beam using an accelerating voltage of 5 kV for 150 min. The paper samples were platinum-coated before the cutting to improve heat exchange and to reduce heat damage at the cutting area.