Water absorption and permeability

Water Permeation and Solute Separation through the Membrane. The measurements of water permeability of the 67 membranes prepared under different conditions were carried out by using an Amicon Diaflo Cell (effective membrane area, 13.9 cm2) under a pressure of 3 kg/cm2 at 25 °C. Some results are listed in Table 1067. It is apparent that much higher water absorption and permeability than the cellulosic membrane are characteristic of the 67 membranes prepared by both the casting polymerization and conventional casting. 

PP/PA maleic, fumaric. low water absorption and permeability Nishio et at., 1990... 

Ashton 117, 118) reported on studies for predicting the durability of clear finishes for wood from the basic properties of the finishes. He reviewed the relationships between composition, water absorption, water vapor permeability, tensile strength, and elongation. Single and multiple regressions were used to establish the relative importance of the different properties in determining the durability of the finishes on wood exposed outdoors. The durability of clear phenolics and alkyds could be predicted from water absorption and permeability properties. Tensile strength and mechanical properties were of less importance. 

Weathering also changes the physical properties such that the stone becomes more susceptible to atmospheric attack. These properties relate to mechanical strength, water absorption, and permeability of the stone. Design of conservation treatment should include regeneration of these properties so that the stone performs as though it had been established anew in the existing environment. 

The physical properties relate to the mechanical strength, water absorption, and permeability of the stone. The mechanical strength of the stone becomes highly reduced in the zone of weathering, while the water absorption greatly increases the permeability is reduced in crusted stone, but it increases in naturally-cleaned surfaces. 

Polypropylene is a relatively low cost material available in different grades for different applications and is claimed to be a thermoplastic with a well-balanced relationship between toughness, stiffness and hardness with the additional benefits of high heat resistance, excellent resistance to chemicals, low water absorption and permeability to water vapour, easy and flexible to process and of low density. These qualities enable PP to be used for a wide variety of electrical and electronic applications including battery containers, cable retention clips, screws, nuts and washers. 

Significant piopeities of insulation (Table 1) include tliermal conductivity, fite resistance, and ntiniinal production of toxic gases primarily during combustion. Other criteria include water-vapor permeability, resistance to water absorption, and dimensional stability over prolonged periods of submission to extreme environments. 

Polyisobutylene has a similar chemical backbone to butyl rubber, but does not contain double carbon-carbon bonds (only terminal unsaturation). Many of its characteristics are similar to butyl rubber (ageing and chemical resistance, low water absorption, low permeability). The polymers of the isobutylene family have very little tendency to crystallize. Their strength is reached by cross-linking instead of crystallization. The amorphous structure of these polymers is responsible for their flexibility, permanent tack and resistance to shock. Because the glass transition temperature is low (about —60°C), flexibility is maintained even at temperatures well below ambient temperature. 

Fluorinated poly(arylene edier)s are of special interest because of their low surface energy, remarkably low water absorption, and low dielectric constants. The bulk—CF3 group also serves to increase the free volume of the polymer, thereby improving various properties of polymers, including gas permeabilities and electrical insulating properties. The 6F group in the polymer backbone enhances polymer solubility (commonly referred to as the fluorine effect ) without forfeiture of die thermal stability. It also increases die glass transition temperature with concomitant decrease of crystallinity. 

The genesis of in silico oral bioavailability predictions can be traced back to Lip-inski s Rule of Five and others qualitative attempts to describe drug-like molecules [13-15]. These processes are useful primarily as a qualitative tool in the early stage library design and in the candidate selection. Despite its large number of falsepositive results, Lipinski s Rule of Five has come into wide use as a qualitative tool to help the chemist design bioavailable compounds. It was concluded that compounds are most likely to have poor absorption when the molecular weight is >500, the calculated octan-l-ol/water partition coefficient (c log P) is >5, the number of H-bond donors is >5, and the number of H-bond acceptors is >10. Computation of these properties is now available as an ADME (absorption, distribution, metabolism, excretion) screen in commercial software such as Tsar (from Accelrys). The rule-of-5 should be seen as a qualitative, rather than quantitative, predictor of absorption and permeability [16, 17]. 

Because of their low refractive index (less than 1.43), low permeability of water and weather vapor, very low water absorption, and good adhesion to glass and optical polymers, fluoropolyurethanes are suitable for cladding of optical fibers. A variety of specialty resins are used for this purpose, which are most frequently photocurable. 

In suppositories cetyl alcohol is used to raise the melting point of the base, and in modified-release dosage forms it may be used to form a permeable barrier coating. In lotions, creams, and ointments cetyl alcohol is used because of its emollient, water-absorptive, and emulsifying properties. It enhances stability, improves texture, and increases consistency. The emollient properties are due to absorption and retention of cetyl alcohol in the epidermis, where it lubricates and softens the skin while imparting a characteristic velvety texture. 

Cell Structure and Permeability. Table 33 shows the values of water absorption and water-vapor transmission (1). 

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 absorption characteristics indirectly represent the porosity through an understanding of the permeable pore volume and its connectivity. In order to investigate the effect of nano-Si02 particles on cement mortar permeability, a water absorption test was carried out on various mixtures A-1 (plain cement mortar), A-5 (cement mortar with 7% nano-SiO ), A-7 (cement mortar with 20% RHA replacement) A9 (cement mortar with 20% RHA replacement and 3% nano-SiO ). The final absorption of these mixtures are shown in Table 5.4. It can be seen that mixture A-5 (cement mortar with 7% nano-SiO ) showed the lowest absorption of all the mixtures which shows that nano-SiO is more effective in reducing the permeability than RHA. Integrating nano-SiO into RHA mortar reduced the water absorption from 5.42% to 4.45%. Results showed that the presence of nano-SiO particles in cement mortar could decrease the water absorption and the likely permeability of cement mortar. This impermeability increase can be attributed to two concomitant phenomena ... 

Table 7.16 Change percentages of strength properties, water absorption and air permeability of paper samples...

BS EN 1062-3 (1997). Paints and Varnishes - Coating Materials and Coating Systems for Exterior Masonry and Concrete. Part 3 Capillary Absorption and Permeability to water, British Standards Institute, London. 

Of all these properties, let us now consider two in particular, namely water absorption and water vapor permeability. These are two physical properties that have an incisive effect on water balance in buildings. 

LCP characteristics, such as high mechanical properties (strength, modulus), ease of processibility, excellent thermal resistance, low water absorption, and low gas permeability, make LCPs attractive for a wide range of applications. The applications of main-chain LCPs can be divided into several areas extrudates (fibers, rods, sheets) used in the chemical and materials industry, and moldings (chip carriers, connectors, switches) used in microelectronics [6]. 

Embankment soils need to develop high shear strength, low permeability and low water absorption, and undergo minimal settlement. This is achieved by compaction. The degree of compaction achieved is reflected by the dry density of the soil. The relationship between dry density and moisture content of a soil for a particular compactive effort is assessed by a compaction test. 

---