Capillary water absorption

In buildings, water absorption in the facade area is described by the water absorption coefficient (w value). This returns the capillary water absorption of building materials as a function of time and is defined in DIN 52617 as w [kg/m h ]. 

A detailed description of specimen production and Marshall testing is provided in Annex 6.B, and a detailed description of the soaking test-capillary water absorption test is provided in Annex 6.C both annexes are found at the end of this chapter. 

ANNEX 6.C SOAKING TEST - CAPILLARY WATER ABSORPTION TEST... 

The SEM technology was also used to demonstrate that the redispersible powders continue to fulfil their functionality over an extended period of time. This is also shown by experiments to determine physical factors such as water absorption and water vapor permeability on defined test specimen after long-term exposure to outdoor weathering conditions. Figure 13-11 shows the capillary water absorption of test specimen after up to 6 years outdoor exposure at different polymer levels. 

Capillary water absorption of mineral topcoat - long term exposure... 

Swelling method. Measurement of swelling is a second method used to estimate water absorption of a sample. A swelling apparatus was devised and described by Hermansson (, 13). In this method, a small amount of sample is dusted on a wet filter paper fastened on a glass filter. The filter is fitted on top of a thermostated funnel filled with water and connected to a horizontally located capillary. The uptake of fluid is followed in the capillary evaporative losses are prevented by a glass lid... 

Evaluation of the absorptive features of different powders these were quantified according to Enslin as previously described.8,9 Briefly, a thermostated glass cylinder with a porous membrane on one end was filled with water and connected to a graduated capillary tube at the other end. The membrane was covered with the powder. Water absorption through the membrane was measured by the variation in the liquid level in the capillary tube. 

The hygroscopicity of a drug and pharmaceutical substances is a potential parameter to be considered in tablet formulation. The moisture uptake rate is quite variable depending on the type of drug and excipients as well as the environmental conditions. So, a concise definition of hygroscopicity is not possible. Powders can absorb moisture by both capillary imbibition and swelling. The instantaneous water absorption prosperties of pharmaceutical excipients correlate with total surface area while the total absorption capacity correlates with powder porosity [22],... 

Although the maximum pore radius distribution in conventional gypsum microstructures usually lies within the range of capillary suction action (100 nm to 1 mm) [44, 52], the roughly 50% water absorption that occurs in untreated gypsum is often reduced to less than 5 wt% [44, 45] at standard market application rates of just 0.3 - 0.5 wt% H-siloxane. The optimum amount to use depends upon the gypsum raw material, the fineness of the grain in the plaster of Paris, its specific sur ce area, and the reaction temperature. 

It is known that papers, cotton, and cellulose are natural hydrophilic polymers, which can absorb water, but are insoluble in water. Therefore, they have been used as disposable diapers, feminine napkins, etc. They absorb water by capillary action. Therefore, they absorb only a small amount of water and the water absorbed is easily removed by applying low pressure. Synthetic crosslinked poly(vinyl alcohol) and crosslinked poly(oxyethylene) are also hydrophilic polymers and they have almost the same water-absorption capacity of about 1-20 g water per gram of polymer as natural polymers. Those natural polymers and synthetic polymers do not essentially have ionic groups. 

The water-absorption rate of superabsorbent polymers is affected by 1) the specific surface area of the polymers 2) the capillary action and 3) the formation of fish-eyes in the polymer hydrogels. 

The water-absorption rate of the polymers can be increased by use of capillary action. It is reported that fibrous carboxymethyl celluloses, which were crosslinked with epichlorohydrin and had the carboxymethylation degree of 0.2-0.4, had high water-absorption rate of 20-40 ml/ g-polymer/min. 

In wood, as in all of the above model compounds, the formaldehyde absorption and subsequent reaction depends on the presence of an aqueous phase. This phase may be a monomolecular layer of water on the cell surface, or water on the cured UF-resin film, but the largest reservoir of water is within the wood cell. As indicated, wood may contain two types of water (a) free or capillary water, and... 

Water absorption by porous solids depends on the water-solid contact angle and on the liquid surface tension. The spreading of water in fabrics is the result of wetting the fiber surface, penetration into the fibers, and capillary pressure [20], The wetting of yarns depends on their surface energy and the interfiber space. 

W. Lei, K. Fujiwara, K. Fuwa, Determination of phosphorus in natural waters by long-capillary-cell absorption spectrometry, Anal. Chem. 55 (1983) 951. 

Water Uptake Measurements. The water absorption capability of films was determined by measurements of water rising by capillary action. The experimental device, also called Baumann apparatus is shown in Figure 1. The samples were cut in order to expose their inner structure to water rising. They were then coated on each of their faces (except the contact surface) with epoxide resin to prevent their swelling and put on fritted glass in contact with distilled water. The absorbed water volume versus time data is then recorded as water penetrates into the sample. 

Metabolic production of water, diffusion of water within the substrate particle, exchange of water between the particle and the interparticle spaces, the effect of solute production and consumption on water activity, and the binding of water by capillary or absorptive forces... 

As shown in Table 6.1, the water absorption of methyl cellulose-modified systems increases with rising polymer-cement ratio. By contrast, the water permeation decreases with an increase in the polymer-cement ratio, as represented in Fig. 6.2.f l Methyl cellulose causes a considerable swelling due to water absorption, and seals capillary cavities in the modified systems, and hence decreases permeability. 

The passage of viral-sized particles through ostensibly intact NR latex films has been directly observed in the laboratory (Carey et ah, 1992 Kiernan, 1996), and indirectly observed in the field (The New York Times, 1994). Evidence for such flaws in NR comes from microscopic observations (Arnold et al., 1988), as well as water absorption measurements, wherein the initial rapid uptake suggests the existence of capillary channels (Gazeley et al., 1988). 

In another study, Martinola et al. (2002) evaluated the water permeability of cracked and uncracked HPFRCC by water absorption test. In their study, the amount of water taken up by capillary suction was determined on cubes cut out from the middle section of the beams, which were subjected to a four-point bending test. Maximum crack width in the cracked HPFRCC specimens was found to be about 0.10 mm. Both cracked and uncracked HPFRCC exhibited very low water absorption coefficient in their study. 

In other words, the water absorption coefficient is a measure of the capillary absorption behavior of a building material and returns the value for absorption expressed in terms of square meters after an hour s exposure. A w value of 0.5 therefore means that the building material can absorb roughly half a liter of water per square meter in one hour. 

The plasma treatment also reduced the water absorption of the composite by a factor of 3 and converted it from capillary (wicking along the fiber-matrix interface) to Pick s law absorption through the body of the matrix. The rate of water absorption in the composite was less than it was in a block of neat epoxy the same size as the composite. The difference in absorption rate was the same as the volume fraction of epo in the composite. This change in absorption mechanism would predict that there should be a great improvement in the hydrothermal stability of plasma treated composites. 

---