Alkali-treatment

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 

The effectiveness of the treatment, of course, depends on the alkali treatment condition adopted. Uses of excessive alkali concentration, extended time, and high temperature can accelerate the extent of treatment but may depolymerize the cellulose component and damage the pristine natural fibers, resulting in the deterioration of the fiber strength [4j. 

The following scheme represents the established chemical reaction scheme of NaOH with hydroxyl groups in natural fibers. 

The alkah treatment may increase the degree of crystallinity by the removal of cementing substances. 

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Several cortisone derivatives with glucocorticoid effects are most active, if they contain fluorine in the 9or-position together with an Il(9-OH group. Both substituents are introduced by the cleavage of a 9,11 -epoxide with hydrogen fluoride. The regio- and stereoselective formation of the -epoxide is achieved by bromohydrination of a 9,11-double bond and subsequent alkali treatment (J. Fried, 1954). 

Cationic polymerization of coal-tar fractions has been commercially achieved through the use of strong protic acids, as well as various Lewis acids. Sulfuric acid was the first polymerization catalyst (11). More recent technology has focused on the Friedel-Crafts polymerization of coal fractions to yield resins with higher softening points and better color. Typical Lewis acid catalysts used in these processes are aluminum chloride, boron trifluoride, and various boron trifluoride complexes (12). Cmde feedstocks typically contain 25—75% reactive components and may be refined prior to polymerization (eg, acid or alkali treatment) to remove sulfur and other undesired components. Table 1 illustrates the typical components found in coal-tar fractions and their corresponding properties. 

Alkali Treatment. Caustic washing is the treatment of materials, usually products from petroleum refining, with solutions of caustic soda. The process consists of mixing a water solution of lye (sodium hydroxide or caustic soda) with a petroleum fraction. The treatment is carried out as soon as possible after the petroleum fraction is distilled, since contact with air forms free sulfur, which is corrosive and difficult to remove. The lye reacts either with any hydrogen sulfide present to form sodium sulfide, which is soluble in water, or with mercaptans, foUowed by oxidation, to form the less nocuous disulfides. 

Removal of Free Fatf Fields. Alkali treatment of the oil is accompHshed by the use of caustic soda solutions to neutralize the excess free fatty acids. Because castor oil readily forms emulsions with water and/or alkaline solutions, special techniques have been developed to neutralize the acids. A continuous counter-current process was developed using a stationary contact reactor (15). Treatment in the presence of a solvent is also utilized (16). 

The 4,5,6,7-tetrahydro-2,1-benzisoxazole group is the most reported category. The action of hydroxylamine on )3-diketones produced a mixture of 2,1- and 1,2-benzisoxazoles (Scheme 186). Ring opening gave )3-ketoacids which, under subsequent alkali treatment, degraded to diacids (67AHC(8)277). 

A similar mixture results from the reduction of quininone, and an analogous mixture of cinchonine and cinchonidine, each accompanied by its epimeride, results from alkali treatment of cinchonine or cinchonidine or from the reduction of cinchoninone. The characters of the whole series... 

Early efforts to partially synthesize 20-keto and 17a-hydroxy-20-keto steroids led to ring D-expanded products isomeric with the desired compounds. Darzens condensation of 3/5-hydroxyandrost-5-en-17-one acetate (75) with ethyl a,a-dichloropropionate, followed by alkali treatment and decarboxylation, gives both the expected 3j5-hydroxypregn-5-en-20-one (78) and an isomer now known to be 17a-methyl-D-homo-17-ketone (79).36,37a alternative route for the introduction of the two carbon side chain, Ruzicka... 

Auwers and others soon discovered that the transformation 3 —> 6 did not consistently give flavonols such as 2. For example, alcoholic alkali treatment of dibromide 11 produced 2-benzoyl-benzofuran-3-one 12 instead of the corresponding flavonol. The same observation was made by Robert Robinson in a failed attempt to make datiscetin in 19257 It has reported that when there is a meta (to the coumarone ring oxygen) substituent such as methyl or methoxy, flavonol formation is hindered, whereas methyl, methoxy, and chlorine substituents at the ortho and para positions are conducive to flavonol formation. ... 

The structure of only one 1,2,4-thiadiazole salt has been determined. Unambiguous synthesis of the imino compound obtained on alkali treatment of the salt formed by the reactions of methyl iodide with 5-amino-1,2,4-thiadiazole established that the salt possesses structure 7 136 pjjjg quatemization exactly parallels the reaction occurring in... 

An older method of cellulose fiber modification is mercerization [22,33-36], which has been widely used on cotton textiles. Mercerization is an alkali treatment of cellulose fibers. It depends on the type and concentration of the alkalic solution, its temperature, time of treatment, tension of the material, and the additives used [33,36]. At present there is a tendency to use mercerization for natural fibers as well. Optimal conditions of mercerization ensure the improvement of the tensile properties [33-35,37] and absorption characteristics [33-35], which are important in the composing process. 

Predpitation of amino adds with salts, like ammonium and caldum salts, and with metals like zinc are also commonly used. This is followed by add (or alkali) treatment to obtain the free or acid form of tire amino acid. 

NOTE NVAT = Non-volatile alkali treatment, AVT = all-volatile treatment, ND = not detectable, NR = not recommended. 

Fischer s base, a typical starting material, is commercially available and is also obtained in situ from the corresponding quaternary salt, substituted indolines 4 can be prepared by TV-alkylation of 2,3,3-trimethyl-3//-indole followed by alkali treatment, or by exhaustive alkylation of 2,3-dimethylindole (N- and C-alkylation) followed by alkali treatment (Scheme 3). Further, methylation of indoline 5 with methyl iodide leads to C-methylation on the methylene group or the Plancher rearrange-... 

The acid and alkali wastes are pumped from the acid-alkali wastewater sump [T-30] into the acid-alkali treatment module [T-31], Metering pumps controlled by pH instruments feed either acid or caustic to the module as required to maintain an acceptable alkalinity for the formation of metal hydroxides prior to discharge to the precipitator consisting of a mixing tank [T-98], a surge tank [T-99], and a sedimentation clarifier [T-101], The pH is adjusted to a value of 8.5 for optimum metal hydroxide formation and removal. 

An ultrasonic transducer is installed on the pH probe mount in the acid-alkali treatment module [T-31], This prevents fouling of the electrodes and provides a more closely controlled pH in the effluent discharged to the precipitator. 

Other aquatic weeds such as reed mat, mangrove (leaves), and water lily (Nymphaceae family plants) have been found to be promising biosorbents for chromium removal. The highest Cr(III) adsorption capacity was exhibited by reed mat (7.18 mg/g), whereas for Cr(VI), mangrove leaves showed maximum removal capacity (8.87 mg/g) followed by water lily (8.44 mg/g). It is interesting to mention that Cr(VI) was reduced to Cr(III), with the help of tannin, phenolic compounds, and other functional groups on the biosorbent, and subsequently adsorbed. Unlike the results discussed previously for the use of acidic treatments, in this case, such treatments significantly increased the Cr(VI) removal capacity of the biosorbents, whereas the alkali treatment reduced it.118... 

It is not safe to store quantities of THF which have been freed of the phenolic inhibitor (e.g. by alkali treatment) since dangerous quantities of peroxides may build up in prolonged storage. Peroxidised materials should not be dried with sodium hydroxide or potassium hydroxide, as explosions may occur [1,2],... 

The reaction of potassium 3-amino-4-oxo-3,4-dihydroquinazoline-2-thiolate 62 with a-bromophenylacetic acid 63 resulted in the formation of (3-amino-4-oxo-3,4-dihydroquinazolin-2-ylsulfanyl)-phenyl-acetic acid methyl ester 64 which on alkali treatment and subsequent acidification resulted in the synthesis of 2-phenyl- 1-thia-4,4a,9-triaza-anthracene-3,10-dione 65 <1999JCR(S)86>. Similarly, the reaction of potassium 3-amino-5,6-dimethyl-4-oxo-3,4,4a,7a-tetrahydrothieno[2,3- pyrimidine-2-thiolate 66 with a-bromo-ester 67 resulted in the formation of 2-(3-amino-5,6-dimethyl-4-oxo-3,4,4a,7a-tetrahydrothieno[2,3- / pyrimidin-2-ylsulfanyl)-propionic acid ethyl ester 68. Subsequent treatment with alkali followed by acidification resulted in the formation of 2,3,7-trimethyl-3a,9a-dihydro-l,8-dithia-4a,5,9-triazacyclopenta[ ]naphthalene-4,6-dione 69 <2000JHC1161>... 

Effect of Alkali Treatment on Maize Amylose Sub-fractions147... 

The effect of alkali treatment on molecular weight (compare with the case of the starch components) has been studied treating a 5% solution of rabbit-liver glycogen in 2 N sodium hydroxide, for 90 minutes at 100°, decreased the sedimentation constant (Sits X 1013) from 86 to 57 (that is, by 34%).237... 

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