Cellulose drawbacks

The first successhil attempt to make textile fibers from plant cellulose can be traced to George Audemars (1). In 1855 he dissolved the nitrated form of cellulose in ether and alcohol and discovered that fibers were formed as the dope was drawn into the air. These soft strong nitrocellulose fibers could be woven into fabrics but had a serious drawback they were explosive, nitrated cellulose being the basis of gun-cotton (see Cellulose esters, inorganic esters). 

Cellulose was the first type of solid support introduced for SPPS [91 ] however, the scope of its use is limited by low loading capacity ( 0.1 mmol/g) and chemical stability. In spite of these drawbacks, microwave-assisted synthesis was successfully performed on cellulose membranes [92-94] and beads [95]. 

Recent years have seen considerable research into the modification of cellulose and reactive dyes, specifically to overcome some of the drawbacks of this dye-fibre system, including the limited degree of fixation in full depths, the need for alkali and relatively high concentrations of electrolyte. This research, which is driven by environmental considerations, was discussed in sections 7.10 and 10.9.1. Thus it need not be considered further here. 

Larger Scale Testing. The standard card gap test (2) is test No. 1 of a series of larger scale tests designed to determine the sensitivity of liquid propellants to hydrodynamic shock. In this test, relative sensitivities of various propellants are determined in terms of the number of 0.01-inch thick cellulose acetate cards required to attenuate a standard shock sufficiently just to prevent initiation in the test sample. When performed according to the exacting conditions of apparatus and procedure, the results are very reproducible from one laboratory to another. However, small variations in the apparatus or procedure can cause major variations in the resulting data, and therefore the test can be considered only relative. A major drawback of the standard test is that it cannot accommodate materials that are volatile under the test condition. At TCC-RMD some special equipment has been developed that allows tests to be made on confined samples at elevated temperature and pressure. 

From the observation that N-(mcLhylcnc)morpholinium cations (17) induced the autocatalytic decomposition of tertiary amine W-oxides in combination with the proof that these intermediates were actually present in Lyocell dopes, the question arose why Lyocell solutions were stable at all. The answer is found in the fact that carbenium-iminium ions generated are immediately consumed by reaction with water and carbohydrate structures as the most abundant and most reactive nucleophiles present. Only when the local concentration of 17 increases to such a high level that the consumption by reaction with water or cellulose cannot compensate for its production, does the reaction with NMMO become uncontrollable and lead to an exothermic event. The pulp used in the Lyocell process acts as a quasi-stabilizer for the solvent NMMO, albeit with the drawback of increased chromophore generation. 

Due to the potential regression in supply and use of disazo directs and vats as well as more strenuous wet fastness requirements, textile firms dyeing cotton-containing fabrics are projected to switch production to reactive dyes in increasing numbers. Reactive dyes are unique in that the dye with the cellulose in cotton or rayon. In the process the material is impregnated with the reactive dye, base is added to the bath to effect the dye/fiber chemical reaction, and the fabric is then carried through an afterscour. Reactive dyes have several severe drawbacks ... 

For years, conservators have been concerned about the water used for washing paper artifacts. Although deionized water and distilled water are employed extensively in washing paper artifacts, tap waters have found wide application as well. Unfortunately, very purified water, such as distilled or deionized waters, have been found to shorten the life of some papers (2), probably through removal of calcium ion. Tap water also has certain drawbacks. It usually contains chlorine, which acts to oxidize cellulose, and traces of iron and copper compounds, which may act as oxidation catalysts for paper stored under humid conditions. Tang and Jones (2) concluded that water used for washing paper artifacts should be free from chlorine and iron and copper compounds, all of... 

Usually, a gradient of ethanol is superimposed on the aforementioned salt gradient, to lessen the affinity of trityl-containing compounds for the cellulose derivative, but a drawback with this procedure is that flow rates then tend to decrease. Relevant fractions... 

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