This report is the result of a three-year research program. It describes the chemical character of cellulose ethers as a general class of polymers and establishes an approximate ranking of the relative stability of each generic chemical subclass. Ranking the thermal stability of the polymers with respect to color change and loss in degree of polymerization led to the conclusion that as generic chemical classes, methylcellulose and carboxymethylcellulose appear to be the most stable of the cellulose ethers. Water-soluble ethylhydroxyethylcellulose apparently also possesses good stability. Of questionable long-term stability are hydroxyethylcellulose and hydroxy- propylcellulose. Ethylcellulose and organic-soluble ethylhydroxyethylcellulose proved to be of poor stability, potentially undergoing marked changes in twenty years or less under normal museum conditions.
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An important additional conclusion reached here, as well as in an earlier investigation, is that considerable variations in stability can occur within a generic chemical class from differences in the basic raw material, a natural product from plants, which is not a uniform, manufactured, chemical substance. Further variations can exist due to different manufacturing processes or commercial sources. Hence, commercial products must be evaluated individually to determine the most stable of a given generic type. Nonetheless, the authors believe the conclusions expressed here to be valid with regard to the relative stability of the generic chemical classes of cellulose ethers.
How to Cite this Work
Feller, Robert L., and M. Wilt. . Evaluation of Cellulose Ethers for Conservation. Research in Conservation 3. Marina del Rey, CA: Getty Conservation Institute. http://hdl.handle.net//gci_pubs/cellulose_ethers
Cellulose ether is a major additive in the dry-mix mortar. Although the addition amount is very low, it can significantly improve the performance of mortar. It can improve the consistency, working performance, bonding properties and water retention properties of mortar, and plays a very important role in the field of dry-mix mortar. Its main features are as follows:
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Water retention is one of the important indicators to measure the quality of the cellulose ether and becomes even more important especially in the thin layer construction. Improving the water retention of mortar can effectively prevent the drying cased by too fast water loss, and the phenomena of strength decrease and cracking resulting from insufficient cement hydration. The factors affecting the water retention of mortar include the dosage, viscosity, fineness and use environment of cellulose ether. In general, the higher the viscosity is; the finer the fineness is; and the greater the dosage is, the better the water retention will be. The water retention of cellulose ether is related to the degree of etherification. When the content of methoxy group is the highest, the water retention is the best.
Cellulose ether has a very good thickening effect. Adding cellulose ether into dry-mix mortar can make the viscosity increase by several thousand times, the mortar have better adhesion and pasted tiles have better sag resistance. The viscosity degree of cellulose ether can affect the bond strength, fluidity, structural stability and constructability of mortar.
Generally speaking, the higher the viscosity is, the better the water retention effects will be. But the higher the viscosity is, the higher the molecular weight of cellulose ether will be. Its dissolution performance will be reduced accordingly, which has a negative effect on the strength and construction performance of mortar. The higher the viscosity is, the stickier the wet mortar will be. It is easy to stick the scraper, of little help to increase the structural strength of wet mortar itself, and not obvious in improving anti-sagging effects.
Since the surface particle of cellulose ether is specially processed, it is very good in the solubility whether in cement mortar, plaster or coatings system, not easy to agglomerate, and fast in the dissolution speed.
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