Increased moisture absorption

Mercerized celluloses absorb more water, have higher regains and more easily wet out than unmercerized fibres. Due to caustic soda penetration, many hydrogen 

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The last group of non-durable antistats is composed of non-ionic compounds such as ethoxylated fatty esters, alcohols and alkylamines (Fig. 10.3). Mixtures of cationic and non-ionic surfactants demonstrate synergistic antistatic properties. The non-ionic materials provide increased moisture absorption and the cationic products provide the mobile counterions. 

Inhibition of events resulting from increased molecular mobility due to increased moisture absorption and a subsequent reduction in Tg can be accomplished by formulating such materials with amorphous substances of higher Tg. The net effect is to increase molecular interaction and raise the system Tg to a level where molecular mobility is again sufficiently low (high viscosity) such that the undesired property changes do not occur.f ... 

Data in Table 4.6 show that both calcium carbonate and talc increase flexural modulus by about 40-60%, decrease impact resistance and energy to break by about 30-40%, and slightly increase moisture absorption. All these effects are generally known in the composite research and development, and slightly vary quantitatively by changing the particle size of minerals, a type of plastic, a type of cellulose (wood) fiber, density (specific gravity) of the matrix, and so on. 

These uncross-linked functionalities are undesirable as they depress Tg, increase moisture absorption, increase the dielectric constant, etc. 

Addition of increased amounts of glycerin increases moisture absorption (Figure 11.78). The equilibrium moisture depends on both the plasticizer concentration and the relative humidity of surrounding atmosphere. " It is also noticeable that starch without plasticizer behaves differently (lower rate of moisture increase at differerrt relative humidities). This indicates that glycerin controls moisture absorption in plasticized samples. The presence of glycerin seems more important than its concentratioa... 

Effect of fiber size The dielectric constant of alkali-treated fiber composites changed slightly with fiber size, however untreated fiber composites did not show variation with fiber size [39]. The effective dielectric constant decreases with increasing filler size due to increased interface volume when filler of less particle size was used for a given volume fraction of filler [31]. Also at a given volume fraction of filler, the smaller particle size has more polarization in the interface surface as a result of increased moisture absorption for small size fillers due to increased surface area [78]. Water has unfavorable dielectric properties, which increases the dielectric constant. 

Plant fibers are bundles of elongated dead plant cells with thick walls. The individual fibers look like microscopic tubes of a cell wall surrounding the lumen. The presence of lumen increases moisture absorption. The cell wall is composed of several concentric layers. Whereas the primary (P) cell wall is formed first during cell growth, the secondary cell wall (S) has three layers S, S, and S. The porous outer cell wall, forming the surface of the fiber, includes the most of the non-cellulosic components, and is considered as the cause of poor absorbency and poor wettability [56]. Table 11.3 compares the physical properties of agrowaste fibers with conventional plant fibers and E-glass fibers. 

The hygroscopic and humectant properties of com symps are of great importance in many apphcations. Depending on the type of symp and on the specific conditions of temperature and humidity, the products may either resist or facihtate moisture loss or moisture absorption. The abihty to attract moisture or retard its loss increases with increasing DE value. Prevention of moisture pickup is more characteristic of symps having low DE values. 

Carbon Blacks. The high electrical conductivity of carbon black is utili2ed where its color is not objectionable and its reinforcing action is used (see Fillers Composites). Carbon black increases the electrical conductance of the polymer to which it is added, and therefore its effectiveness does not depend on moisture absorption (see Carbon, carbon black). 

Another major drawback of polysaccharides is their hydrophilic nature leading to low degrees of adhesion between fiber and matrix [11]. Moisture absorption takes place by three types of mechanisms namely diffusion, capillarity, and transport via micro cracks [2]. Among the three, diffusion is considered to be the major mechanism. Water absorption largely depends on the water-soluble or hygroscopic components embedded in the matrix, which acts as a semipermeable membrane. While, fiber/matrix adhesion and fiber architecture also affect the moisture absorption. The results of the water sorption experiment showed an interesting trend. The extent of water uptake was not very significant and also did not increase linearly with amount of filler (Table-2). 

Interest in cyclic olefin (co)polymers has increased dramatically over the past decade. This is because this class of polymers displays many attractive properties such as high thermal stability, high optical transparency, low dielectric constants, and low moisture absorption. Thus, these polymers can potentially be utilized in many electronic and optical applications. Although cyclic olefin (co)polymers typically include ring-opening metathesis polymers, vinyl-addition homopolymers, and vinyl-addition co-polymers with acyclic co-monomers such as ethylene, we will mainly deal with vinyl-addition homo- and co-polymers in this section. 

It is determined by exposing the formulation (2g) at 52%, 63%, 75% and 84% RH for a period of six hours. Moisture absorption is calculated from the increase in the mass which is due to moisture absorption. 

Mercer et al. have studied the effect of moisture in fluorinated polyimides extensively. Beuhler et al. have also studied moisture absorption in fluorinated polyimides and have shown that moisture absorption decreases with fluorine incorporation, even as free volume increases (see Table 13.6). 

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