Sodium hydroxide concentration, effect properties

Wang et al. [54] studied the effect of WG on the degumming process of jute fiber in order to improve the fiber properties. It was found that the WG concentration, sodium hydroxide concentration, and treatment time were the three most important parameters for the degumming process. The authors concluded that the degumming process was an effective method for ranoving hemicellulose, lignin, pectin, and certain other noncellulose materials. WG or alkali treatments depend on several variables such as the concentration of the alkaline solution, temperature, and the duration of the treatment. These variables directly affect the adhesion between the fiber and the matrix, and consequently, they also affect the mechanical and thermal properties of the fiber-reinforced composites. 

Figure 16 shows relationships between the number of introduced side chains and relaxation rigidity (G,) at 900 s for carboxymethylated wood binding various metal ions [341. Wood specimens were prepared from Japanese linden Tilia japonica Smik.). Carboxymethylation and the introduction of metal ions was the same procedure as mentioned in the previous section [32,33]. Stress relaxation measurements were carried out in an aqueous solution at 30°C. The relaxational property of carboxymethylated wood without metal ions is first discussed. For carboxymethylated wood (a broken line in Fig. 16), Gf (900) decreases with an increase in the number of introduced side chain. This rapid decrease appears to be caused by two factors. One is the effect of sodium hydroxide (NaOH). Young s modulus of wood treated with an aqueous solution of NaOH decreases remarkably under wet conditions, especially at concentrations above 10% NaOH [35]. The other factor is the electrostatic repulsion of ionized carboxymethyl groups in carboxymethylated wood, as mentioned in the above section [291. For example, conformation of polypeptide is influenced by the ionization of the side chains, and the structural change of the helix-coil transition has been interpreted as a reversible transformation. Theoretical treatment of the transformation has been reported to explain the mechanism [23-25, 36-43]. The conformation of component molecules in wood, however, cannot change markedly by ionization in comparison with soluble polyelectrolytes in water, because carboxymethylated wood is not dissolved in water. Only space among the main chains is expanded by the electrostatic repulsion due to negatively charged side chains. For these reasons, G (900) of carboxymethylated wood decreases with an increase in the number of introduced side chains.

Identification of Phenols.—The reactions of phenols which are of particular value in their identification, are those that take place with alkalies, ferric chloride, and bromine water. Most phenols react with an aqueous solution of sodium hydroxide to form soluble salts, but are insoluble in a solution of sodium carbonate. The behavior of phenols with these two reagents shows their weakly acidic properties, and serves to distinguish them from acids. Phenols which contain strongly negative substituents decompose carbonates, and show all the properties of acids. It is difficult, therefore, to identify as a phenol substances which contain such substituents. Ferric chloride produces marked colorations in aqueous solutions of most phenols. The reagent produces a similar effect with certain other compounds, and the formation of a color with ferric chloride can be taken, therefore, only as an indication of the presence of a phenol. With bromine water most phenols yield a precipitate of a brominated phenol. Other compounds, amines for example, are also converted into insoluble substitution-products by bromine water. Notwithstanding this fact the test is of value. Many phenols form colored products when heated with phthalic anhydride and concentrated sulphuric acid. The reaction will be described under phenolphthalein (558, 639). 

Cheng and Rodriguez [195] demonstrated that the addition of boric add (H3BO3) to poly(vinyl alcohol) solutions has hardly any effect on the gelation properties. Addition of sodium hydroxide, by which NaB(OH)4 fe formal, results in gel formation. The maximum effect is observed for [Na ]/[B] = 1 addition of more sodium hydroxide has no effect Results are shown in Fig. 52, where logG is plotted vs added sodium hydroxide logG rises linrarly with added sodium hydroxide up to the point where the sodium/borate ratio is 1. From then on, the modulus is constant This confirms the Shibayama model [193], where Na is needed to form a crosslink. From the work of Kurokawa et al. [196] it became clear that the phase behaviour of the aqueous ix>ly(vinyl alcohol)/borate system not only depends on concentration of polymer and borate, but also on the addition of alkali hydroxide and of indifferent electrolytes like sodium chloride. 

Alkali treatment of natural fibers, also referred to as mercerization, is an old and most widely used method for modifying ceUulose-based natural fibers [30-36]. The most favorable alkali solution for mercerization is sodium hydroxide (NaOH) aqueous solution. The effect of alkali treatment on the properties of the composite as well as on the natural fibers strongly depends on alkali solution type, alkali concentration, treatment time, treatment temperature, and treatment tool. Alkali treatment may cause fibrillation of pristine natural fibers, resulting in the breakdown of individual fibers with smaller fiber diameter. This phenomenon can not only increase the aspect ratio of reinforcing natural fibers but also roughen the fiber surfaces. As a result, the fiber-matrix interfacial adhesion may be enhanced and the... 

Residual sodium from the use of the hydroxide or carbonate for preparations by DP (Section 4.2.3) may also affect catalytic properties, and therefore be a cause of irreproducibility. However, the literature is not agreed on whether sodium acts as a poison15,22 or as a promoter 8,20 this may depend on its concentration and on the support used. Nitrate ion may also have a promotional effect depending on the concentration23 (see Section 4.2.2 for the use of nitrate salts as precursors for preparations by COPPT). 

The effect of a reducing sodium borohydride treatment followed by a mildly alkaline wash on the physical properties and stability of paper was studied. Test papers were characterized by measuring their initial pH value, brightness, and folding endurance. Then they were subjected to borohydride treatment and washed with dilute calcium hydroxide solution or deionized water. The concentrations of sodium borohydride... 

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