Subsequent Wetting Research Articles

Effect of Fiber Swelling on the Structure of Lyocell Fabrics

The effect of liquid swelling on the structural rearrangement of lyocell twill fabrics is studied using a variety of techniques, including optical microscopy, dimensional measurements, and water and hexadecane retention. Lyocell fibers swell predominately laterally in water by about 30% over the dry diameter. Fiber lateral swelling in NaOH solutions is greater than in water, with diameters increasing by over 200% at optimum concentrations. The lateral expansion in the fibers leads to fabric shrinkage (reduced planar dimensions and increased fabric thickness), which explains most of the irreversible constructional changes that occur during tensioned preparation from the loomstate. Fabric structural changes during subsequent wetting and drying are also explained using swelling-shrinkage and hygral expansion-contraction models. Irreversible swelling-shrinkage in NaOH is exaggerated, and subsequent rewetting leads to reversible fabric growth rather than the reversible shrinkage experienced by fabrics prepared in water. NaOH treated fabrics also have lower wet state rigidity than fabrics prepared in water. Tensioned NaOH treatment allow fabrics to be stabilized at larger dimensions and a permanent, flatter fabric construction with lower amplitude reversible behavior.

Stochastic model for posttillage soil pore space evolution

Tillage operations disrupt surface layers of agricultural soils, creating a loosened structure with a substantial proportion of interaggregate porosity that enhances liquid and gaseous exchange properties favorable for plant growth. Unfortunately, such desirable soil tilth is structurally unstable and is susceptible to change by subsequent wetting and drying processes and other mechanical stresses that reduce total porosity and modify pore size distribution (PSD). Ability to model posttillage dynamics of soil pore space and concurrent changes in hydraulic properties is important for realistic predictions of transport processes through this surface layer. We propose a stochastic modeling framework that couples the probabilistic nature of pore space distributions with physically based soil deformation models using the Fokker‐Planck equation (FPE) formalism. Three important features of soil pore space evolution are addressed: (1) reduction of the total porosity, (2) reduction of mean pore radius, and (3) changes in the variance of the PSD. The proposed framework may be used to provide input to hydrological models concerning temporal variations in near‐surface soil hydraulic properties. In a preliminary investigation of this approach we link a previously proposed mechanistic model of soil aggregate coalescence to the stochastic FPE framework to determine the FPE coefficients. An illustrative example is presented which describes changes in interaggregate pore size due to wetting‐drying cycles and the resulting effects on dynamics of the soil water characteristic curve and hydraulic conductivity functions.

Yielding characteristics of unsaturated compacted soils

The elasto-plastic constitutive model for unsaturated soils postulates the existence of a loading collapse yield locus (LC) and a suction increase yield locus (SI) in the p:s stress plane. The characteristics of the LC yield locus have been reasonably well established in recent years but there is a much greater degree of uncertainty in relation to the SI yield locus. In the work reported in this paper a number of stress path tests in the p:s plane were conducted on samples of unsaturated compacted kaolin in a modified triaxial apparatus. Two series of tests were conducted on samples compacted to an identical initial condition so as to ensure a uniform soil structure prior to testing. Samples tested in Series 1 were taken through three stages: wetting at constant mean net stress, drying at constant mean net stress and a combination of isotropic compression and wetting. Samples tested in Series 2 were taken to pre-selected values of suction prior to isotropic compression. Data obtained from these tests indicate a possible form of single yield locus for unsaturated compacted soil. The data also indicate that the position of the yield locus, initially imposed by the compaction process will be influenced by the subsequent wetting process. Copyright © 2000 John Wiley & Sons, Ltd.

Regolith behaviour and physical weathering of clayey mudrock as dependent on seasonal weather conditions in a badland area at Vallcebre, Eastern Pyrenees

Studies on badland areas in the Vallcebre basin (Pyrenees) suggest that erosion rates are controlled by the weathering rate of mudrocks. To obtain the temporal pattern of physical weathering and its control on the erosive processes, monitoring of regolith temperatures at different aspect, depth and lithology, and periodical determination of regolith moisture and bulk density were carried out. Changes in surface regolith have also been monitored by means of photographic techniques, using an especially designed tripod. Finally, the hydrological and erosive response of the regolith trough the seasons were studied using rainfall simulations. The results obtained support and confirm previous knowledge on the role of frost action in mudrock weathering and the role of subsequent regolith development and wetness status on infiltration and runoff generation. These seasonal changes of behaviour are so important that they raise serious questions about the validity of observations or experiments carried out in only one season. This work confirms that erosion processes are controlled by regolith formation during winter and regolith depletion by storm rainfall erosion during summer, spring and early autumn. It also raises important points about annual trends of infiltration and erodibility, that should be used as guidelines for modelling runoff and sediment production.

An analysis of the fragmentation of remolded soils, with regard to self-mulching behavior

A power-law relation was used to analyse the (mass-derived) number-size distributions of fragments generated by wetting and drying remoulded soils. Various soils from Europe and Australia produced a range of values for the two fragmentation coefficients, d and k, generated by the power-law function. Both coefficients had physical significance with respect to self-mulching behaviour. Likened to a fractal dimension, the d coefficient varied directly with the tendency of the remoulded soil to fragment during wetting and drying. Assessment of the number of generated fragments >1 cm was made with the k coefficient. Consideration of both coefficients together in a plot of k v. d enabled similar soils to be grouped and falsely large values of d to be identified; k values were small for limited fragmentations even if the size distribution of the fragments that were produced gave large values of d. Most strongly self-mulching soils produced d values >1 . 5 after three wet/dry cycles, and k values that increased sharply after one cycle and declined with subsequent wetting and drying. Other soils with lesser abilities to self-mulch generally produced smaller d values and more variable k values. Reasonable correlations were found between these two coefficients and other measurements of self-mulching behaviour, particularly after three cycles of wetting/drying. Examination of the aggregate size distributions produced from remoulded soils in this way offers the potential to understand more clearly the dynamics of structure regeneration in soils exhibiting various degrees of self-mulching behaviour.

Heat affected zone cracking in cast inconel 718

Electron beam welding parameters have been shown to influence heat-affected zone (HAZ) microfissuring behavior in cast Inconel 718 (Inconel is a trademark of INCO Alloys). Travel speed was shown to be the most significant factor in influencing HAZ cracking behavior by modifying the thermal gradient(s) and subsequently the stress state in the HAZ. This has been shown previously to be related to a change in weld pool geometry and to the effect of speed on heat flow in the weld zone. Microfissuring in the HAZ was observed to occur intergranularly in areas containing Laves phase. Liquation of the Laves phase and subsequent wetting of the grain boundary is believed to be but one element of the complex interactions occuring in the HAZ during the weld thermal cycle.

Modification of kaolinite by surface polymerization

AbstractKaolinite filler surfaces were modified by both surface adsorption and surface reaction. Their subsequent wetting and adhesion properties were determined by measurement of the contact angle of the powders by the Washburn technique using three probe liquids that spanned molecular polarity. Surface modification by adsorption utilized the kaolinite surface acidity to polymerize styrene. Surface reaction involved reaction of kaolinite hydroxyl groups with aryl diisocyanates and subsequent termination with a series of alcohols of increasing complexity.It was shown that kaolinite surfaces could be modified to produce surfaces of controlled hydrophobicity that could exceed that of conventionally silanated kaolinite. The ability of phases to spread and wet these filler surfaces was analysed in terms of the thermodynamic functions—spreading coefficient S12 and spreading pressure πe.

Secretion of Mucoid Material by Lymphokine-Activated Killer Cells: Study by Light and Electron Microscopy

When lymph node cells from nude mice were grown on embryonic fibroblast monolayers together with rat interleukin-2, only one type of colonies developed. These colonies were composed of cytotoxic cells termed "granular/lymphokine-activated killer/mucus-secreting cells" (LAK-GM). An extensive differentiation course, in which all the cellular components were involved, ended with a population of short-lived, mature, nondividing large cells that apparently synthesized and deposited a flowing mucoid material (FMM) that stained distinctly blue with periodic acid-Schiff/alcian blue (PAS-Ab) at pH 1 and distinctly red by the naphthol AS-D-chloracetate method for specific esterase. So far, the best monolayers to trigger the FMM synthesis were those prepared from 16- to 18-day-old whole embryos. These cells were compared with LAK cells that developed on monolayers (such as embryonic skin or adult kidney) that did not trigger FMM synthesis. They were also compared with other cell types that differentiated in colonies on the fibroblast monolayers: histiocytes (fixed macrophages), mixed granulocytes/monocytes, mucosal mast cells; and with populations of mature rat T-killer cells developed on same mouse monolayers. Features distinctive to the secreting LAK-GM cells were presence of masses of membrane-limited vesicles that were strictly confined to the surface of the cells in FMM-containing colonies. All transitional forms of budding activity could be seen on the cell surface facing the masses. Within the same cells, many granules displayed varying degrees of degradation, the granular material being transformed into flocculent material that formed small pools facing each degraded surface. Other characteristics of the LAK-GM lineage were the accumulation of glycogen prior to the appearance of the FMM, the presence of several structures of a ribosome-lamella complex in the LAK-GM in colonies that did not accumulate FMM, and filopodia commonly emerging from the pole proximal to the nucleus. Of various fixation methods tried, only after treatment with absolute alcohol and subsequent drying was the FMM stained with PAS-Ab. By subsequent wetting, the capacity to be stained was irreversibly lost. After incubation of the living cultures with the enzymes hyaluronidase or chondroitinases AC or ABC, the FMM disappeared. These observations suggest a triggering mechanism by the embryonic mesenchymal fibroblastoid cells for synthesis and secretion of mucous material that is a proteoglycan of the chondroitin sulfate group.

Possible identification of poorly crystalline inorganic matter present in Athabasca oil sands

In Athabasca oil sands there is a fraction of poorly crystalline minerals tightly bound to humic matter. This fraction resists subsequent wetting by water and introduces serious problems in bitumen recovery when using water-based processes. In this study 29Si solid state magic angle spinning (MAS) NMR, infrared spectroscopy and transmission electron microscopy were applied to characterize these minerals isolated from Athabasca oil sands of estuarine and marine origin. It was demonstrated that poorly crystalline inorganic matter present in Athabasca oil sands is comprised of aluminosilicates, most probably allophane-like minerals. Humic matter could interact with this type of material through incorporation of an organic anion as a ligand to a metal ion, coulombic and van der Waals forces and hydrogen bonding.

Dynamic modulus of Portland cement paste and mortar as affected by ambient relative humidity

Results are given of an investigation into the influence of drying and wetting on changes in weight and dynamic modulus of paste and mortar specimens dried at different relative humidities at room temperature. Drying causes a significant drop in the dynamic modulus probably due to moisture stress gradients and removal of interlayer water which is recovered from subsequent wetting of the specimens. This suggests that drying-induced microcracking is unlikely to occur. The percentage reduction in dynamic modulus of prisms (2·5 mm × 10 mm × 75 mm) increases with increasing aggregate concentration and decreases with increasing water/cement ratio.

Effects of solvent and temperature on the coupling agent/epoxy resin interface

Increased wetting of the coupling agent/epoxy resin interface was observed when γ-glycidoxypropyltrimethoxysilane, polyfunctional aminosilane and γ-aminopropyltriethoxysilane were applied respectively from methyllethylketone, dimethylformamide and water on woven glass cloths which had been cleaned at 300°C. However, when factory-applied coupling agents were burnt off the woven cloths and fresh coupling agents re-applied, it was found that the nature of the factory-applied coupling agent influenced subsequent wetting. Thinner glass fibres showed a greater improvement in wetting rate than thicker fibres in those solvents identified to be good for improved wettability, irrespective of the heat-cleaning temperature.

Changes in Cross-Sectional Dimensions of Cotton Fibers on Crosslinking and on Subsequent Wetting

Changes in cross-sectional dimensions of cotton fibers resulting from crosslinking treatments were studied. One variety of cotton, Sujata, was subjected to crosslinking in dimethyloldihydroxyethyleneurea and in formaldehyde to different add-on levels. The changes in cross-sectional area and perimeter due to crosslinking, as well as the changes in these dimensions resulting from subsequent wetting, were measured. The results were discussed in the light of available information on fiber morphology and the nature of crosslinking reactions.

Effects of experimentally induced fleece-rot on the structure of the skin of Merino sheep.

Four medium- and six strong-wool Merino sheep were exposed to continuous simulated rain (4 x 5 mm/h) for periods ranging from 3 to 9 days. In response, the sheep developed characteristics typical of fleece-rot lesions such as exudative encrustation and bacterial discoloration of the fleece. Skin samples were taken periodically for histological examination from the trunk region of the sheep prior to, during, and after wetting. An inflammatory response to wetting occurred in the upper layers of the dermis and this caused the release of cells which began invading the epidermis after only 6 h of wetting. An associated increased in vascular permeability was observed macroscopically following intravenous injection of Pontamine Blue dye. The incidence and extent of the inflammation increased during subsequent wetting while epidermal acanthosis and hyperkeratosis became increasingly evident. Epidermal thickness returned to pretreatment levels by 13 days after cessation of wetting when inflammatory regions were absent from most of the sheep. Cellular lysis occurred in the suprabulbar and keratogenous regions of a small proportion of follicles (1-13%) during wetting, resulting in the interruption of fibre growth and keratinization in these follicles and the occlusion of follicle hair canals with inner root sheath material ('plugs') which persisted after wetting ceased. These morphological changes in the epidermis, follicles and fleece are considered to occur as a consequence of the initial rapid inflammatory response to wetting during the developing of fleece-rot lesions.

On-site glue/nail joints in farm structures

In a series of experiments on joints between birch plywood and softwood made with glue, the joints were stronger than the timber at any practical level of moisture content and even after soaking in water for 7 hours. Considerable differences in moisture content between timber and plywood, uneven moisture distribution, or subsequent wetting and drying cycles did not prevent the making of satisfactory joints. It was concluded that glued joints made on site, using a few nails to apply pressure until the glue had set, was a suitable technique for timber farm structures of which two examples are given.

Water movement in unsaturated soils as influenced by gypsum

Three soils varying in texture and exchangeable sodium were treated either with distilled water or with a gypsum solution of 10 or 30 m-equiv./l. concentration and their water-flow properties, diffusivity (D), capillary conductivity (K), and weighted mean diffusivity (D) determined. Invariably the treatment of soils with gypsum resulted in increased D and K, the increases being more pronounced near saturation and declining with desaturation. The soil with the highest clay content and exchangeable sodium percentage (ESP) responded most. For the three soils, at the end of the third wetting and draining cycle the highest increase in D and K varied from about 3 to 15 times while D increased by a factor of 2 to 7.5. Wetting and draining cycles resulted in decreased D for all soils when distilled water was used, but only for two soils when 10 or 30 m-equiv. solutions were used. In the soil most responding to gypsum D was slightly increased with increasing number of wetting and draining cycles when gypsum solutions were used. This was due probably to rebuilding of structure by cation exchange, which was lost by slaking and dispersion during the first wetting and draining cycle. The electrolyte concentration of flowing solution did not significantly affect the water flow properties provided that the slaking and dispersion were reduced by a solution of high concentration during the process of cation exchange. At the end of the third wetting and draining cycle, 30 m-equiv. solution gave about 1.7 times higher D compared to 10 m-equiv. for the high clay, high exchangeable sodium soil. This was probably because initial structural loss caused by the first wetting and draining with 10 m-equiv. was not fully regained during subsequent wetting and draining.

Gel‐Like Films that May Form at the Air‐Water Interfaces in Soils

AbstractWhen dry soil material is moistened stepwise and then slowly submerged, a film appears on the water surface where it may remain floating for several days as a coherent patch. The film consists of a gel‐like matrix that contains particles ranging upward to sand size. The evidence to date indicates that the film matrix differs little from the < 0.2 µ cay. It is thought that material disaggregated from the surface of the soil material by the disruption of drying and subsequent wetting becomes caught at the air‐water interface and is there spread out by surface tension forces. The possible role of the films in translocation of solids and other aspects of soil development is discussed.

Clay Dune Formation Near Corpus Christi, Texas

ABSTRACT Desiccation of saline mud flats produces a mud-cracked surface layer of clay impregnated with saline evaporite crystals and covered with a thin film of algae. The action of the wind against the upturned edges and lower surfaces of the mud-cracked polygons frees pellets or aggregates of clay which are swept across the tidal flat or saline basin to accumulate along the lee shore in long, transverse ridges. Subsequent wetting causes the clay to regain its plasticity, the freshly deposited material becomes stabilized and the clay dune results.