Effect on Water Absorption

Coupling agents often improve density of WPC. For example, with an increase in the amount of Fusabond WPC-576D in an HDPE-based composite, containing 60% of wood flour w/w, from 0 to 3% w/w, density of the composite increases from 70.4 Ib/fC (1.13 g/cm ) to 74.7 Ib/fC (1.20 g/cm ), respectively [4]. This in turn leads to decrease of water absorption by the composite materials, which is almost invariably observed at the introduction of coupling agents (Table 5.14). 

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Hagenmaier (10) demonstrated that pH had little effect on water absorption of oilseed protein products, but solubility was pH dependent. He suggested that the differing degree of dependence on pH indicates that water absorption and protein solubility are not correlated. Contrastingly, Wolf and Cowan (28) reported the pH-water retention curve of soy proteins to follow the pH-solubility curve. Both solubility and water retention were minimal at the isoelectric point (4.5) and increased as the pH diverged from this point. Hutton and Campbell (20) reported that the effects of pH and temperature on water absorption of soy products paralleled those of solubility for the most part. 

The effects of pH on water absorption of a soy isolate and soy concentrate are represented in Table VII. Water absorption of a soy isolate increased as pH increased from 5.0 to 7.0. This increase was evident at all temperatures studied (4 0, ambient, and 90°G). For soy concentrate samples, the effect of pH was similar in direction to the effect on water absorption of the isolate but was of smaller magnitude (23). 

Hermansson reported that heating of a soy isolate enhanced swelling. Huffman et al. (11) reported that temperature had no noticeable effect on water absorption of sunflower products. 

Sucrose Elgedaily and Campbell (24] found sucrose, within the concentration range used, to have no significant effect on water absorption of three soy protein isolates. 

Block copolymer, 67 Blowing agent, 90, 91 Board density, effect on water absorption, 403, 407... 

Ability to absorb oil, 124 Ability to absorb water, 124 Aspect ratio, 124 Chemical composition, 124 effect on flammability, 467 effect on water absorption, 385 chemical composition, 124 color, optical properties, 125 cost of, 123 density, 124... 

The decrease in bulk density of a soil produced by the addition of peat, plus the ability to hold much larger amounts of water, are factors that can have a marked effect on water absorption under field or garden conditions. Even the hardest rains can usually penetrate the peat—soil mixtures, where in the absence of the peat a heavy runoff would be expected. There is one possible exception to this statement. Thoroughly dry peats are sometimes difficult to wet quickly, but as they gradually take up moisture they tend to act like a sponge. This slow wetting is in evidence when the peat is used as a mulch, but when mixed with soil in the usual proportions the peat is rarely so dry as to lose its ability to take up water readily. 

When dimensional accuracy is required in a specific application the effect of water absorption should also be considered. Manufacturers commonly supply data on their products showing how the dimensions change with the ambient humidity. 

Weathering. This generally occurs as a result of the combined effect of water absorption and exposure to ultra-violet radiation (u-v). Absorption of water can have a plasticizing action on plastics which increases flexibility but ultimately (on elimination of the water) results in embrittlement, while u-v causes breakdown of the bonds in the polymer chain. The result is general deterioration of physical properties. A loss of colour or clarity (or both) may also occur. Absorption of water reduces dimensional stability of moulded articles. Most thermoplastics, in particular cellulose derivatives, are affected, and also polyethylene, PVC, and nylons. 

Wang, D. 1994. Effect of Broken and Pericarp Damaged Com on Water Absorption and Steepwater Characteristics. M.S. thesis, University of Illinois, Urbana, IL. 

An interesting point arises from this method. The particles of material are exposed to water vapour at a set humidity and hence the results equate to that humidity. The measured equilibrium absorption is substantially the same as the equilibrium absorption that would be obtained by immersion in an aqueous solution which would maintain the test humidity. As this implies, the equilibrium water absorption is reduced if the water is not pure. Hence, exposure to aqueous solutions should be made at the concentration of interest. As the humidity approaches 100% even small amounts of a salt have a significant effect on equilibrium absorption. 

Fleming et al. (18) did not examine the effect of pH on water absorption, but these researchers examined the effect of "pH activation" on water absorption of sunflower and soy products. For pH activation, 1.25 N NaOH was added to slurries to achieve pH 12.2 and then 6.0 N HGl was added to return to pH 6.0 in 10 min. The pH activation process improved the water absorption properties for most products but did not increase water absorption of the soy flour. Processes similar to pH activation may be encountered in the processing of vegetable protein additives. 

Hutton and Gampbell (20) reported that the overall effect of temperature, disregarding pH, was increased water absorption for a soy isolate and a trend in that direction for a concentrate. The effect of temperature on water absorption of the soy isolate... 

Hermansson ( 2) examined the effect of ionic strength on swelling-of soy isolate, caseinate, and WPG products. The effect of NaCI on water absorption was not consistent among the products. Generally, as ionic strength increased from 0.0 to 1.0 M NaCI, water absorption increased for the soy isolate and caseinate. 

Effects of Substitution on Spectra Solvent Effects. Solvent effects on the absorption spectra can be summarized as follows if the compound is soluble in water, alcohols, and polar, protic solvents such as DMSO, DME, and DMF, the /.max is most red shifted in polar, nonprotic solvents. Compounds that are soluble in nonpolar solvents such as CH2C12 are generally not soluble in water, and their absorption lies at about the same place in both alcohols and methylene chloride, but is shifted to the red in polar, nonprotic solvents. The value of Amax also reflects the hydrogen bonding ability of the... 

FOS and oligofuctose are fructose oligomers that are either produced by enzymic conversion of sugar or extracted from chicory, as inulin, and then hydrolysed. These products behave as soluble fibres and prebiotics. In acid conditions, they can hydrolyse, but are usually sufficiently stable for short-shelf-life juices, near-water products with low acid levels or powdered soft drinks. Prebiotic activity varies with preparation and required daily dose can be as low as 2.5-5.0 g/day for shorter chain FOS preparations (DP 2 1). Some positive effects on magnesium absorption and calcium absorption (in some populations) have also been shown (Beghin Meiji, 2001). 

According to the results shown for this polymer, it is possible to confirm the hypothesis of Riggs et al. [129] concerning the existence of two mechanisms of water absorption. On the other hand it is interesting to note that the dielectric analysis of these polymers allow to know the importance of water sorption in this kind of polymers what is very important from technological an medical point of view. Therefore dielectric measurements on these kind of polymers result in a powerfull tool to analyze the effect of water absorption on the polymeric matrix and then to applications of these materials. 

Moisture has, in itself, usually not much effect on polymer properties, though the amount of moisture which can be absorbed by polymers varies within wide limits (between zero and a few %). Logically, the electric properties such as resistivity and dielectric losses are the most sensitive to water. As to mechanical properties, nylons show the strongest dependence on water absorption. PA-6 is able to take up a... 

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