Joakim Järnström

H2S modified atomic layer deposition process for photocatalytic TiO2 thin films

H2S modified TiO2 films were grown by atomic layer deposition (ALD) using TiCl4, H2S and water as precursors. The films were characterized by XRD, XPS, TOF-SIMS, SEM and UV-VIS spectrometry. Photocatalytic activities of the films under UV and visible light were determined by the degradation of a thin layer of stearic acid. Light induced superhydrophilicity of the films was also studied. Although the sulfur content of the films was very low, substantial modification of the film properties occurred. All the films prepared at 400 and 500 °C with H2S were photocatalytically active under visible light. Photocatalytic activity under UV irradiation of the H2S modified films was also drastically improved when proper deposition parameters were applied.

The Effect of Base Paper and Coating Method on the Surface Roughness of Pigment Coatings

Ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC) was applied on base paper with various coating amounts and two different coating methods. The surface topographical images were captured by atomic force microscopy and confocal optical microscopy. The surface roughness of pigment coatings was analyzed by using a two-point correlation method where both the amplitude and lateral spacing of surface heights are considered. Isotropy and periodicity of roughness were studied by using the angular distribution of the correlation length (T) and the autocorrelation function (ACF). All the studied pigment coatings gave a random distribution of surface heights. Both PCC and GCC considerably smoothed the base paper surface. However, the differences in roughness of PCC and GCC were quite small for similar coating parameters (e.g., amount, method). The increase of coating amount decreased the surface roughness. Rod coating yielded a somewhat more isotropic coating than blade coating. The best coating surface was achieved by using rod coating and GCC with coat weight of 23 g/m2. PCC coatings yielded about 10 units higher gloss (Ga) compared to GCC coatings with similar coating parameters. Ga was further found to correlate with σ/T, even if the correlation was not purely linear.

Influence of surface structure on wetting of coated offset papers

Abstract To obtain more knowledge of the properties affecting print quality and adhesion characteristics in the printing process, attention has been directed to the nature of surface energy. The aim was to compare different surface-energy calculation models and to investigate the influence of surface roughness on wetting of coated offset papers. The wetting process was studied by static contact angle measurements using a series of reference liquids. Topographical characterization was carried out using atomic force microscopy. Surface energy components were determined using different calculation models. The determination can be considerably simplified using a mono-monopolar model, which has been proven in previous studies. The surface energy components were derived from both apparent and topography-corrected contact angles. The surface topography had a significant effect on wetting of the samples studied.

Modification of pine pulp during oxygen delignification by xylan self-assembly

Self-assembly is a technique of preparing functional materials based on targeted intermolecular interactions involving different macromolecules. In this work, hardwood xylan was disassembled from wood and birch bleached kraft pulp using pressurized hot water extraction (HWX) and cold alkali extraction (CAX), respectively. The extracted biopolymers were characterized using gas chromatography (GC), size exclusion chromatography (SEC) and Fourier transform infrared spectroscopy (FTIR), and subsequently added into an oxygen delignification reactor containing pine kraft pulp. The assembly of xylan-pulp fiber was characterized using advanced time-of-flight secondary ion mass spectrometry (ToF-SIMS) and imaging. The xylan-pine pulp assembly was not significantly removed during the whole elemental chlorine free bleaching sequence or during low consistency refining. Modified fibers had superior mechanical properties compared to the reference pulp. Our concept can be easily applied in the pulp and paper industry, and it opens new possibilities for the utilization of fully bio-based fibers in new materials.

Dynamic Spreading of Polar Liquids on Offset Papers

The aim of this study was to investigate the spreading of sessile drops of polar probe liquids (water and ethylene glycol) on pigment coated offset papers. Furthermore, existing theoretical models for spreading were applied to evaluate the experimental results. The hydrodynamic model gave a better fit to the results at lower spreading rates, while the molecular-kinetic theory gave a good fit over a larger velocity range. Factors introduced to correct for the exponential dependency on time of the drop base radius and its contact angle can be interpreted as coupled processes. Differences in the spreading between the papers were found to correlate with the acid and base components of the surface energy, rather than with differences in surface roughness.

Acid–base properties of polymer-coated paper

The wetting behavior of a series of polymer-coated papers has been studied. Different ways of determining the acid–base properties of the polymers are presented. The well-known van Oss–Chaudhury–Good (vOCG) bi–bi polar model is compared with more simplified mono–bi polar and mono–mono polar models. The effect of surface roughness on the wetting was also studied with atomic force microscopy. The overall wetting of each probe liquid was evaluated by calculating the work of adhesion to the polymer surfaces. It is shown that ethylene glycol and water may be considered as mono polar liquids, which simplifies the original vOCG-model. It is also shown that in most cases the surface energy values are in the same range when using both the complex bi–bi polar approach and the simpler mono–mono polar approach. The different polymers used are found to be of a predominating basic character.