Adhesion of the oral bacterium Streptococcus sanguis was investigated on two series of surfaces, one solid, non-porous and one porous with a pore diameter centered around 0.2 µm. Each series consisted of four substrates with varying surface free energies: pure aluminum oxide, PEG modified aluminum oxide, and two types of silanized aluminum oxide. The surface composition was analyzed by ESCA and the surface free energy and acid-base character were determined by contact angle measurement using water, formamide and diiodomethane according to Van Oss and Good. Contact angle measurements were conducted on non-porous substrates which had been subjected to the same silanization procedure as the porous ones. Untreated aluminum oxide and PEG modified aluminum oxide were both hydrophilic and gave water contact angles of less than 10°. One silanization procedure gave a surface of intermediate hydrophobicity, with a y-tot of 47.5 mN/m; the other gave a strongly hydrophobic surface of y-tot = 27.4 mN/m. Adhesion of S. sanguis was measured by using radiolabelled bacteria. It was demonstrated that more bacteria adhered to the porous than to the non_x001F_porous substrate and that the PEG treatment, as well as the two sil aniz ation pro cedures, resulted in a decreas e in bacterial adhesion, b oth to the controls treated with aqueous buffer and to surfaces treated with fresh saliva.

The effect of oxygen plasma treatment of fiber on the adhesion between regenerated cellulose fiber and polyethylene (PE) was investigated using the single-fiber fragmentation test. In addition to allowing the calculation of the interfacial shear strength, the fragmentation test gave extensive information on shear transfer and failure mechanisms in the systems. It was found that oxygen plasma treatment enhanced the interfacial adhesion considerably, as established both by the calculated shear strength values and the birefringence patterns observed. The influence of treatment time on the adhesion was studied and fond to be a most important parameter. The role of surface chemistry and surface energetics of fiber in the interaction balance was investigated using electron spectroscopy for chemical analysis (ESCA) and contact angle measurements. It was seen that the changes in surface energetics owing to treatment had no positive effect on adhesion. Instead, the improved adhesion was ascribed to the presence of hydroperoxides, as detected by ESCA, on treated fibers. Decomposition of these peroxides is believed to occur at the production of single fiber specimens, and covalent bonds are formed between fiber and matrix.

Poly(ethylene glycol) (PEG) has been grafted to polystyrene using branched poly(ethylene imine) (PEI) as an anchoring polymer. A dense grafting of PEG chains is obtained if a PEG-PEI adduct is first prepared by treatment of PEI with PEG epoxide and the adduct subsequently adsorbed on an oxidized polystyrene surface. Prepared in this way the PEG-PEI adduct is irreversibly attached to the surface with the PEG chains oriented towards the aqueous phase, as shown by ESCA and ellipsometry. This dense PEG coating is highly effective in preventing adsorption of fibrinogen and IgG, as well as adhesion of the oral bacterium Streptococcus mutans. Somewhat surprisingly, the degree of PEG branching, as well as the PEG molecular weight, did not markedly influence protein rejecting properties. The water contact angle on polystyrene decreased in the order: untreated polystyrene > oxidized > PEI treated > PEG-PEI treated. Block copolymers of poly(ethylene glycol)/poly(propylene glycol) type attached to polystyrene showed temperature dependent protein rejecting properties. At temperatures well below the cloud point of the polymer in water the surface is protein repellant whereas around and above the cloud point protein adsorption occurs to a considerable extent. The block copolymer layer expands and contracts with temperature variations, as can be monitored by ellipsometry.

This paper reports on a special pilot coating and industrial printing trial designed to gain fundamental knowledge on ink adhesion failure on coated papers. We found that ink adhesion failure resulted in white spots without ink on the paper, referred to as uncovered areas and these spots gave print mottle problems. The white spots were due to two fundamentally different types of ink adhesion failure. One is the well-known ink rejection, which simply means that ink is not transferred to the surface. The other is a new type of ink adhesion failure, confirming a previous hypothesis suggested from laboratory observations. We refer to this as ink-lift-off adhesion failure, meaning that ink initially deposited on the paper surface becomes lifted off from the surface in a subsequent print unit. Adhesion failure by this mechanism was seen to occur more frequently than failure due to the well-known ink rejection.

The influence of surface treatments including pigment coating, surface sizing and calendering on the mechanical strength of hotmelt adhesive joints in pilot made cartonboards was studied. The mechanical strength of the joints was investigated using the Y-peel test device at 23C and 50% relative humidity. Some of the samples were investigated with respect to the failure mode by scanning electron microscopy. The surfaces were characterized in terms of surface roughness, surface chemical composition, and adhesion behaviour. A strong adhesive bond displayed fibre tear. In addition to fibre tear, interfacial failure, i.e., failure between the cartonboard and the adhesive, was the main reason for fracture in the bonded assembly. The most important factor controlling the integrity of adhesive joints seemed to be the real contact area. The adhesive joints showed significantly higher strength when the hotmelt adhesive was first applied onto the rougher cartonboard of the assembly and then the smoother cartonboard was pressed on the adhesive than vice versa. The surface roughness of cartonboards mainly depended on whether the surface was pigment coated or not. Calendering displayed only a minor effect. No clear influence of surface chemical composition of the cartonboards on the adhesive joint strength was found due to the fact that changes in surface chemistry in this study also led to changes in surface roughness. The strongest adhesive joint was created between two medium-rough and surface-sized cartonboards.

Hydroxyl-rich surfaces have been obtained through the plasma polymerization of allyl alcohol on various polyolefin-based substrates. The influence of plasma parameters (deposition time and power), the type of substrate, and water washing on the chemical structure of the formed plasma polymers was investigated. The characterization involved contact angle measurements, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) analyses. To increase the sensitivity of XPS towards hydroxyl groups, derivatization with trifluoroacetic anhydride was performed. In addition, the adhesion between plasma-polymerized layers and a two-component polyurethane lacquer was evaluated by a 90° peel test. It was shown that power had a pronounced influence on both water wettability and hydroxyl group retention, while deposition time mainly influenced the film thickness. A relationship between the extent of hydroxyl functionality and the loss of material during the washing procedure was also found. Fur thermore, it was shown that the chemical structure of the plasma polymers was not seriously affected by the choice of substrate. On the contrary, the adhesion properties of the substrates with plasma-polymerized layers were found to be highly dependent on the substrate used. For one of the substrates, the adhesion tests revealed an excellent lacquer adhesion when appropriate process parameters during the plasma deposition were used. The other substrate showed considerably lower peel forces. The difference in adhesion properties between the substrates may be explained as an effect of vacuum-ultraviolet (VUV) emission present during the plasma deposition. The VUV emission is able to create radicals in the near-surface region of the substrate and thereby cause chain scission reactions, lowering the cohesive strength of the substrate. Finally, this study showed that reflection absorption spectroscopy (RAS) is a suitable FTIR technique for obtaining structural information about plasma-polymerized layers thinner than 50 nm.

Hydrophobic plasma coatings were deposited on pigment-coated paper with the purpose of reducing dampening water absorption and create uniform surface chemistry. The influence of plasma coatings on sheet-fed offset printabil ity was also studied. Three plasma chemistries, fluorocarbon, organosilicon and hydrocarbon, were used to adjust the hydrophobicity of paper surface. The plasma coatings reduced, and in some cases prevented, the dampening water absorption into pigment-coated paper in both laboratory and pilot scale trials. Ink transfer, mottle and ink setting were altered due to the presence of the plasma coatings, whereas porosity and surface strength of the pigment-coated papers were not affected. These results suggest that the preferred way to improve the print quality with both mineral and linseed oil-based inks is to use plasma chemistry that modifies the paper surface to be both hydrophobic and oleophilic. Hydrophobic and oleophobic surfaces were found to cause ink repellence. Uniformity of the plasma coatings was crucial for obtaining an even print appearance.

Interfacial properties of bulk polymer samples have been characterized by direct measurements of long-range and adhesion forces using a non-interferometric bimorph surface forces apparatus. For this purpose we developed a method where bulk polystyrene was melted and formed into drop-shaped surfaces with a cylindrical shaft. In the case of very smooth polystyrene samples the adhesion in air and water was very strong and when brought into contact a cold welding of the polymers sometimes took place. Upon separation, it was found that a cohesive failure occurred and the surfaces were locally damaged. In the case of less flat polystyrene surfaces, the adhesion increased with the applied (external) load to a saturation value. We attribute this to a local flattening of nanometer sized protrusions. The long-range interaction in water is dominated by a weak electrostatic double-layer force. At separations below about 10 nm, an attractive force component predominates the interaction. The adhesion in aqueous solutions decreased dramatically in the presence of a nonionic surfactant, n-octyl b-D-glucopyranoside. The surfactant adsorbs onto hydrophobic surfaces, such as the polystyrene surface used here, and close to the critical micellar concentration it forms an oriented monolayer where the polar sugar units are directed towards the solution. The range of the short-range repulsion between polystyrene surfaces coated with a monolayer of n-octyl b-D-glucopyranoside is about 2-3 nm, slightly larger than observed previously for such surfactant layers adsorbed onto very flat hydrophobized mica surfaces. Further, a considerably stronger attractive force is observed upon separation of the surfactant coated surfaces in case of polystyrene compared to when hydrophobized mica is used. The influence of the substrate surface on the interaction can be rationalized by their differences in surface roughness.

Wettability and ESCA studies have been carried out using unextracted and extracted kraft pulps with different amounts of lignin. The effect of oxygen plasma treatment was investigated. The wettability was studied by placing a drop of water on a sheet made from the pulp and following the decrease in drop volume and apparent contact angle with time. The first reading is taken after approx. 0.1 s. Extrapolation to zero time gives the initial contact angle. The initial absorption rate was also determined. Good correlation between the initial contact angle and the oxygen to carbon atomic ratio was found for the pulps without extractives. Pulps containing extractives are very hydrophobic, but an oxygen plasma treatment renders these pulps as hydrophilic as the purest pulps. It is concluded that the oxygen plasma treatment oxidizes the lignin and the extractives but reduces the pure cellulose surface. The oxidized extractives appear to act as wetting agents. The initial absorption rate is strongly dependent on the amount of extractives in the pulp. An oxygen plasma treatment improves the absorption rate, especially if the pulp contains high amounts of extractives.

The forces acting between cellulose surfaces have been studied using the interferometric surface force apparatus. The cellulose surfaces were prepared by Langmuir-Blodgett deposition of trimethylsilyl cellulose (TMSC) onto hydrophobised mica. Prior to measurements the surfaces were desilylated to obtain pure cellulose. The degree of silylation and the molecular weight of the TMSC both affect the structure of the deposited layer. This was observed from the surface pressure/area isotherm, force versus distance curves and atomic force microscopy images. The forces between the cellulose surfaces were found to depend on the pH of the solution. In dilute electrolyte solutions the cellulose film was uncharged and rather compact when the pH of the solution was 6.0. However, when the pH was increased to 7.3 the cellulose film swelled considerably and a long-range steric force was measured. The swelling of the film is interpreted as being due to dissociation of a few carboxylic acid groups present along the cellulose chain. The forces measured were, however, dominated by steric interactions. The repulsion does not increase substantially when the pH is increased from 7.3 to 9.5. Our results suggest that the pKa of the acid groups present within the cellulose film is larger than it would be in bulk aqueous solution.