Copper number, cellulose

The term hydrocellulose has been assigned to the hydrolytic products intermediate between cellulose and n-glucose. When cellulose is subjected to the action of acid for even brief periods, there is a change in its tensile strength, copper number and viscosity. 

As shown experimentally by Piest [75], cotton which was subjected to various operations, e.g. bleaching, treatment with alkalis or acids, strong heating prior to nitration furnishes nitrocellulose solutions of low viscosity. At the same time an increase in the solubility of the nitrocotton was also observed. This is evidence that the cellulose molecules are shortened and their content of terminal group is increased. A certain proportion of hydrocellulose and oxycellulose may result. The total effect is to bring about an increase in the reductive properties of the cellulose, i.e. an increase of the copper number. 

No. Material for nitrating Cellulose content % Copper number Pentosans content % Lignin content % Fats, waxes content 0/ /o Ash content %... 

Copper Value (Copper Index or Copper Number) of Cellulose It represents the amt of Cu reduced from the cupric to cuprous state in alkaline sola by lOOg of cellulose (such as cotton). In case of cotton, it gives an indication as to whether any appreciable changes have taken place during purification proceduresjin case of woodpulp, it indicates the degree of purity. Accdg to Doree (Ref 4 pp 26 32-3)>normal cotton cellulose has copper values below 0.2 while sulfite pulp has value>2. The alpha-cellulose obtd from sulfite pulp had a value of 0,8... 

The so-called copper number is still the method of choice in the pulp and paper industry in process control, but sometimes also in the research lab. The reducing power of cellulose is measured by reaction with an alkaline Cun-salt under defined conditions, the formed Cu1 ions can be titrated after re-oxidation [82]. The underlying reaction mechanisms are still not entirely understood, neither are the types of oxidized structures recorded. However, even though the copper number is only a sum-parameter, the data of which cannot be directly linked to the quantity of a specific oxidized function, it remains a valuable parameter for control in a number of industrially relevant processes. 

When cotton is treated with very dilute solutions of hydrogen chloride in an aprotic solvent such as benzene it suffers severe degradation. This is because the small amount of hydrogen chloride in the solvent is redistributed in the water adsorbed on the cotton, forming a very concentrated aqueous solution of hydrochloric acid [454]. At low moisture contents, the sites of the consequent hydrolysis are near the ends of the cellulose chains. The relation between DP and copper number therefore differs from that for normal aqueous hydrolysis. However, as the moisture content of the cotton increases, the type of hydrocellulose produced approaches that found with aqueous systems. 

Cotton is frequently treated with hot alkali in the processes preparatory to dyeing, as well as in the preparation of pure cellulose for research purposes. In the now nearly obsolete process of kier boiling as much as 4% of its cellulose content might be lost as soluble products. The observations that the loss in weight of hydrocelluloses in alkali boiling is directly proportional to the copper number led to the suggestion that short-chain materials were detached from the reducing ends of the hydrocellulose chain molecules and passed into the solution [455]. This was later fully confirmed and the mechanism of the process elucidated [456 64]. 

JCP Specifications. The U.S. Congressional JCP has published six government paper-specification standards for permanent-record paper (32). These specifications were written in the tradition of cotton or linen fiber, high folding endurance, and high cellulose purity as indicated by high a-cellulose content and low copper number. 

The damages that occur during various pre-treatment processes of cellulosic fibres can be detected by various chemical tests like fluidity, copper number. Methylene Blue absorption and silver nitrate staining etc. 

Methylene blue does not react with aldehyde groups which are characteristic of hydrocellulose or oxidation of cellulose under acid conditions. Thus a sample with a high copper number and low methylene blue affinity indicates either hydrocellulose or acid oxidation. Hydrocellulose is usually accompanied by residual traces of acid. If there is a reduction in the methylene blue absorption brought about by boiling in dilute sodium hydroxide, it indicates the presence of acid, because this treatment has no effect upon the number of carbosyl groups. The latter will only be converted into sodium carbosylate which will revert to sodium chloride and carboxylic acid groups with the hydrogen chloride in the methylene blue hydrochloride. 

Copper number, a method of determination of reducing end groups in cellulose, was measured using a standard method described by Earland and Raven (16). 

Changes in degree of polymerization and copper number of cotton cellulose during cutting with a Wiley mill. 

Figure 2. Changes in degree of polymerization and copper number of cotton cellulose during milling with a Norton ball mill. Key Y, milled fiber V, O,...

Oxidation in neutral or acidic solutions give oxidized celluloses of the reducing type, that is, they have high copper numbers. After oxidation in alkaline solutions, the products have high eontents of acid groups (as shown by absorption of the basic dye. Methylene Blue) but have low copper numbers. 

The formation of cuprous oxide fiom reaction of cellulose with Fehling s solution provide a number known as the copper number. The test is well- standardized and gives a quantitative measure of the reducing ability of a cellulose sample (10). 

Explain why oxidation of cellulose results in cellulose with a high copper number but alkaline oxidation gives cellulose with high acid group content but low copper numbers. 

Oxidation in neutral or acidic solutions oxidizes the hemiacetal group to an aldehyde or reducing end group which can reduce copper from cupric to cuprous. That is, the oxidized cellulose has a high so-called copper number. 

The number of these ends, and thus the extent of degradation, is determined by reacting a fiber sample with Fehling s solution to produce copper(I) oxide. The result is known as the copper number . Cellulosic fibers degraded in this manner are known as hydrocelluloses. 

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