Water absorption by polymers

Fedors, J., Osmotic effects. 1. Water absorption by polymers,... 

Let s consider the reasons for decreases in the stress-strain parameters of furfurol-acetone polymer concrete in a wet environment. The process of water absorption by polymer concrete occurs in two ways by diffusion and absorption. The latter is associated with the presence of free benzene sulfonic acid, which is highly hygroscopic and absorbs moisture from the environment and thus increases... 

R. F. Fedors, Osmotic Effects 1. Water Absorption by Polymers, Polymer, 21 207 (1980). 

Fedors, R.F. (1980) Osmotic effects in water absorption by polymers. Polymer, 21, 207. 

The physical effect of water can be seen after water absorption by polymers in the accompanying plasticizing effect and swelling, in changes in crystallinity, or in the... 

Rigid PVC is an amorphous polymer with low shrinkage, a fair coefficient of thermal expansion for a polymer, limited creep at room temperature, and low water absorption by moisture exposure. 

The dielectric constant of polyimide films in the wet condition (50% RH atmosphere) is higher than in the dry condition. This is attributed to water absorption by the polyimides. Figure 15.5 also shows the water absorption of die polyimides, which is due to the presence of imide groups in the polymer and decreases widi increasing fluorine content because of the hydrophobic effect of fluorine atoms. The water absorption is related to the stability of the dielectric constant. The dielectric constant variability between the dry and wet conditions of highly fluorinated polyimides, P3FDA/TFDB and P6FDA/TFDB, is smaller than... 

Almost none of the cited papers dealing with water absorption by syntactic foams deals with the mechanism by which water or other small molecules penetrate into these materials. Filyanov et al.148,149) undertook one of the first attempts using the ED-20 epoxy oligomer—glass microsphere system. Water absorption by a filled polymer is known to depend on the sorptive properties of the binder, the stability of... 

Most of these aspects of water-sorption equilibrium correspond to the equality of chemical potentials of water in the medium and in the polymer. The consequences of this principle are illustrated by the experiment of Fig. 14.2, where an interface is created between water and a nonmiscible liquid (oil, hydrocarbon, etc.), and a polymer sample is immersed into the organic liquid. It can be observed that, despite the hydrophobic character of the surrounding medium, the sample reaches the same level of water saturation as in direct water immersion or in a saturated atmosphere. What controls the water concentration in the polymer is the ratio C/Cs of water concentrations in the organic phase, where Cs is the equilibrium concentration, which can be very low but not zero. In other words, hydrophobic surface treatments can delay the time to reach sorption equilibrium but they cannot avoid the water absorption by the substrate. 

The decrease in the water absorption by an addition of neutral salts is because of the decrease in the osmotic pressure between inner and outer sides of the polymer hydrogels in their aqueous solution. 

Polysulfone. Polysulfone homo- (19) and copolymers have been formed into hollow fiber membranes for hemofiltration by solution extrusion, followed by coagulation and washing. Equilibrium water absorption by these membranes varies between 0.85 and 2.1 percent. The water-equilibrated polymers are glassy at room temperature. Sieving properties of copolymer hemofilters prepared with a 2-phenyl-2-phenoxy propane segment have been characterized (2). The hydrophobicity of this polymer is reflected in a significantly altered rejection spectrum in the presence of protein when compared to saline solutions. 

A noted phenomenon is caused by water absorption of polymer concrete (Figure 1.8). The penetration of water into polymer concrete leads to a softening of its structure and consequently to loss of strength and an almost threefold increase in the deformability of the material. 

Water penetration of the test samples occurs in several ways. Samples that are placed in mediums with humidity of 50%-60% and 85%-95% swell gradually and are not stabilized in weight within one year. The samples stored in water are saturated with it in half a year and their subsequent storage in these conditions does not lead to increase in weight. By this time, the stress-strain parameters in compression are stabilized. Note that these parameters continue to decrease for the samples in 50%-60% and 85%-95% humidity because water absorption of polymer concrete continues. 

The difference in water uptake between S-PEEK and S-PPBP can be attributed to flexibihty of the phenoxybenzoyl group in the side chain of S-PPBP, which favours water permeation into the polymer and water absorption by the terminal sulfonic acid group. Water uptake of S-PPBP is comparable to that of Nation membranes. 

In devices in which wetting is hy immersion, the sample is immersed in water while the surface is exposed to light. Since water absorption hy polymers from a humid atmosphere or hy direct wetness is a diffusion-controlled process, the frequency and duration of the exposure to moisture is often a critical parameter. Weathering processes can he accelerated by more frequent swelling and contraction than occius in practice. The length of the required wet period depends on the water diffusion coefficient and water absorption capacity of the material as well as on its thickness. Rain, humidity periods, or both ranging up to hours may be required for some pol5uneric types. 

Wuttisela K, Panijpan B, Triampo W, Triampo D. Optimization of the water absorption by crosslinked Agar-g-Poly(acrylic acid). Polymer (Korea) 2008 32 537-543. 

Silica NPs have been reported to improve mechanical and barrier properties of several polymer matrices. Addition of silica NPs to starch polymer matrix not only increases the tensile properties but also increases elongation (Azeredo, 2009). Moreover, silica NPs addition decreased water absorption by starch (Xiong et al., 2008). 

The influence of polymer matrix on the behavior nanocomposite system was the drastic increase of composite conductivity caused by absorption of water vapors by polymer matrix. The value of such a change has the sharp extremum corresponding to the range where hopping conduction dominates the system electroconductivity> It was assumed that the influence is primarily realized through the dependence of hopping conductivity (see Eq. (25)) on dielectric constant of polymer matrix, which is drastically changed when absorption of such polar molecules as HjO takes place. The simple theoretical model has been developed (mean field approximation) ... 

In a manner similar to the method described in the water uptake information four types of superabsorbent polymers were used as common samples and eight organizations determined the rate of water absorption by varying conditions that included particle size, the amount of sample, the method of sample addition to the solution, stirring condition, method to identify the end point, two types of solution, the amount of solution, measurement temperature, and the number of measurements. Based on the results and their analysis, the method for measuring the rate of water absorption for superabsorbent polymers is proposed as follows. 

Although both starch components behave similarly with regard to water absorption, in the case of high ambient moisture levels amylose absorbs greater amount of water than amylopectin because the crystallization reduces water absorption by the hydrophilic polymers [17, 44, 53, 54]. 

Hemicellulose is a hydrophihc polymer it therefore largely determines the water absorption by vegetable fibers [6]. 

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