24—STOICHIOMETRIC ANALYSIS OF THE WOOL-WATER ISOTHERM

Determination of the amount of absorbed water attributable to the various types of side-chain polar groups in wool keratin at humidities of up to 80% r.h. enables a stoichiometric analysis of the wool-water isotherm to be made. The amount absorbed by the aromatic (tyrosine) hydroxyl and aliphatic (serine and threonine) hydroxyl groups was estimated from the change in the water-absorption isotherm after separate chemical modification of these groups. The reduction in water content was much less than that for either amino-group or carboxyl-group modification, the data for these having been reported previously for wool from the same source examined under identical conditions.

The difference between the sum of the water attributable to the side-chain basic, carboxyl, and hydroxyl groups, and the water content of unmodified wool has been designated as water attached to peptide and amide groups. The water-sorbing power of these groups is in good agreement with experimental data for peptide groups in polyglycine. It thus appears that all peptide groups are accessible to water vapour. A change in properties of the wool-water system at 75–80% r.h. is attributed to the formation of a hydrogen-bonded network. The water involved is termed ‘network’ water.     

Influence of Welding Parameters and Wood Properties on the Water Absorption in Scots Pine Joints Induced by Linear Welding

Wood welding is an environmentally-friendly and very quick technique to yield wood joints in just a few minutes and without using any adhesives. The only limitation of welded wood is that the joint is suitable only for interior use. Exterior use, or use in an environment with varying humidity requires water resistance of the welded joints. An investigation was performed to determine the effects of welding parameters and wood properties on water absorption in the weldline and how to reduce it through controlling the production parameters. The influences of welding pressure, welding time, and heartwood/sapwood on water absorption in the weldline of Scots pine (Pinus sylvestris) joints were investigated. Specimens composed of two pieces of heartwood or sapwood, each of dimensions 200 mm × 20 mm × 20 mm, were welded together to form specimens of dimensions 200 mm × 20 mm × 40 mm. The specimens were allowed to stand in 5-mm-deep tap water and then they were taken out of the water one at a time and scanned in 10-min intervals until the first crack appeared in the weldline. An X-ray Computerized Tomography scanner was employed to monitor water movement and density change in weldlines during water absorption–desorption. All three evaluated parameters showed significant effect on water absorption. Samples of heartwood welded by 1.3 MPa welding pressure and 1.5 s welding time showed the lowest water absorption.     

Effects of Adding Unsaturated Polyester to the PVAC Adhesive on the Dimensional Stability of Laminated Veneer Lumber

Many properties of wood are affected by changes in moisture content below the fiber saturation point of wood. In this study, the dimensional stability of laminated veneer lumber (LVL), according to TSI EN 4084 and EN 4086, was evaluated. For this purpose Scots pine (Pinus sylvestris L.) and Oriental beech (Fagus orientalis L.) LVL panels were used. Panels of LVL were manufactured from cut veneers, and poly-vinyl acetate (PVAc), unsaturated polyester (uPE) and mixtures of them, as adhesives. Laminated veneer lumber panels with 4 plies and 5 mm in thickness were produced for each group. Depending on the adhesive type, the swelling and water absorption of the samples were measured by determining the weight increase in the two conditions of oven dried and being above the fiber saturation point. The lowest volumetric swelling of the Scots pine was measured as 10.4% bonded with 100% PVAc (control) and the highest volumetric swelling was measured as 13.8% bonded with 90% PVAc and 10% unsaturated polyester. The lowest volumetric swelling of the Oriental beech was measured as 17.2% bonded with 100% PVAc (control) and the highest volumetric swelling was found to be 21.8% bonded with 90% PVAc and 10% unsaturated polyester. Statistical analysis results show that adding unsaturated polyester to the PVAc increased the volumetric swelling and water absorption levels of both the Scots pine and Oriental beech LVL panels.     

Units and Conversions

A review of SI units of relevance to the metal finisher is presented. Interconversion between multiples and submultiples of derived units is explained. Tables facilitating conversion between SI and the British foot-pound-second system are included.     

Moisture absorption and wet-adhesion properties of resin transfer molded (RTM) composites containing elastomer-coated glass fibers

Transient water sorption studies were carried out at constant temperature (45 °C) to assess the hydrolytic stability and wet-adhesion properties of glass fiber/epoxy composites having different sizings. Lower effective diffusivity values correlated with improved overall mechanical performance in relation to the control (unsized) samples, and revealed the importance of changing the surface energy characteristics of glass fibers by using distinctively hydrophobic pure polymers. Admicellar polystyrene and styrene-isoprene coatings formed over the inorganic reinforcement appear to create an interface with much higher resistance to moisture attack than the organosilane/matrix interface in composites with commercial sizing. This fact was corroborated by comparing their effectiveness in property retention, which showed the mechanical property (e.g. ultimate tensile strength, stiffness and interlaminar shear strength) increased with respect to the uncoated composites in the dry state as well as after water saturation. Poor wet-adhesion properties of commercial sizings in humid conditions could perhaps be attributed to higher contents of inert material present in these coatings. Fractography analysis was consistent with the previous observations regarding catastrophic failure in composites without coating, and suggested that interfacial debonding, extensive fiber pullout and matrix crazing were the major contributors to the overall failure mechanism. Failed surfaces of both commercial and elastomer-coated composites also showed areas with fiber pullout, but in this case, matrix residues remained on the fiber surfaces, yielding a much rougher appearance. Good fiber-matrix adhesion, particularly in admicellar-coated composites, was also revealed by the presence of hackles and more tortuous failure paths.     

Investigation of coating failure on the surface of a water ballast tank of an oil tanker

The current crude oil tanker is constructed as a double-hull structure which consists of an oil tank and a water ballast tank whose surface is coated with epoxy paint to prevent corrosion. Since the cracks that developed in the epoxy coating have caused corrosion of the interface of the water ballast tank, the identification of the parameters for crack development is important. In addition, the moisture absorption by the epoxy coating can cause deterioration of bond strength, which results in delamination of the coating and accelerates the corrosion at the interface. In this study, after the mechanical and thermo-mechanical properties of epoxy paints were measured, the residual stresses induced by the temperature change and cure shrinkage were calculated by the finite element analysis, which were compared with the experimental results. Also, the pull-off tests were performed to investigate the deterioration of the bond strength of epoxy coatings due to moisture absorption. It was found that the thermo-mechanical properties such as the coefficient of thermal expansion and glass transition temperature of the coating materials had dominant effects on the crack resistance rather than the cure shrinkage; the moisture penetration to the bonding interface caused interfacial failure and a significant deterioration of bond strength.     

Gas absorption in grey cast iron during mould filling

Abstract

The effect of mould filling on the hydrogen and nitrogen concentration in grey cast iron has been investigated. A special mould was designed and the influence of several process and mould parameters, such as degree of turbulence, permeability, core binder and coatings, were studied. The hydrogen concentration increased during mould filling and the absorption was favoured by turbulent filling, low permeability and larger gas evolution from the mould and cores. In some cases, the hydrogen concentration in the iron after mould filling almost reached the solubility limit, which increases the risk that gas precipitates during solidification.

Exact values of the influence of mould filling on the nitrogen concentration could not be obtained, but some observations could still be conducted. The absorption of nitrogen seemed to be favoured by the same parameters as hydrogen.     

Static and Dynamic Aspects of Liquid Capillary Flow in Thermally Bonded Polyester Nonwoven Fabrics

The weight gain method is employed to study the vertical capillary flow of wetting liquids in polyester nonwoven fabrics with different basis weights. The quantity of liquid absorbed by capillarity in the nonwoven is recorded as a function of time, until saturation. The liquid retention capacity of the nonwovens has been studied from their “saturation level”, i.e. the fraction of pore volume effectively filled with liquid. It is found that this saturation level varies greatly with the type of nonwoven, and generally decreases with nonwoven thickness. Moreover, the expected 100% value is rarely attained even when the sample height is smaller than the Jurin equilibrium height. These observations are attributed to the more heterogeneous pore sizes in very thin nonwovens, where the interconnection of large and small pores inhibits the continued capillary rise of liquid front. The other part of the study concerns the kinetics of liquid capillary flow which has been analyzed by taking into account the contribution of the meniscus in filling the pores. By subtracting this contribution from the mass of liquid absorbed, the new absorption mass is found to vary linearly with the square root of time, in agreement with the Washburn theory. For the thinnest nonwovens, the very small and unrealistic values of Washburn radii deduced from the experimental results do not correspond to the real physical pore sizes, but reflect slow capillary kinetics. This phenomenon is, however, less important when the thickness of the sample increases.