A-cellulose content

At first glance, the HRC scheme appears simple the polymer is activated, dissolved, and then submitted to derivatization. hi a few cases, polymer activation and dissolution is achieved in a single step. This simplicity, however, is deceptive as can be deduced from the following experimental observations In many cases, provided that the ratio of derivatizing agent/AGU employed is stoichiometric, the targeted DS is not achieved the reaction conditions required (especially reaction temperature and time) depend on the structural characteristics of cellulose, especially its DP, purity (in terms of a-cellulose content), and Ic. Therefore, it is relevant to discuss the above-mentioned steps separately in order to understand their relative importance to ester formation, as well as the reasons for dependence of reaction conditions on cellulose structural features. 

Recently it received a certain physico-chemical justification as the resv.lt of Rlnby s [46] work (p. 224). In any case it serves a useful purpose in practice. This method of classifying being widely used, as for example in order to estimate the value of a sample of chemical wood pulp for nitrating, when certain quantitative requirements concerning the minimum a-cellulose content are imposed. 

Finishing wood cellulose. The finishing process is made to obtain a higher a-cellulose content and to endow the wood pulp with a shape conducive to easy nitration. This is the last operation prior to nitration. It consists in removing hemicelluloses, pentosans, and hexosans, which are undesirable ingredients of wood pulp. An insufficiently purified wood pulp may contain 5-6% of pentosans, straw cellulose even as much as 20%, whereas cotton does not contain more than 0.5-0.6%. 

Experiments with wood fiber pulps by the National Bureau of Standards have shown that the purer the pulp (higher the a-cellulose content) the more permanent it is. Moreover, as the a-cellulose content in these pulps approaches that of the a-cellulose content of rag fibers, the permanence of these fibers likewise approaches that of rag fiber. Therefore, paper made from sulfite pulps which have a high a-cellulose content would have better permanency properties than sulfate pulps provided that they are carefully made. 

Methyl-and ethylcelluloses are prepared by reacting purified woodpulp or cotton linters having a high a-cellulose content with aqueous sodium hydroxide and then with methyl chloride or ethyl chloride according to the following scheme ... 

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. 

Thermal Degradation. Whatman No. 42 ashless filter paper has a basis weight of 92 g/cm2, an a-cellulose content of 98%, and a solubility in hot 1%... 

Qualification of different cellulose sources for the various end use applications is determined on the basis of purity, molecular size, and a-cellulose content, a-cellulose refers to the portion of cellulose insoluble in 18% aqueous sodium hydroxide. Whereas the content of noncellulosic polysaccharides has proven to be a hindrance to the clarity of cellulose esters (determined as haze in otherwise clear films), a-cellulose content is important for the spinnability of cellulose solutions into regenerated fibers, and for viscosity characteristics of cellulose ethers. Molecular weights play an important role in various cellulose ethers. 

The two primary categories of cellulose derivatives, cellulose esters and cellulose ethers, which dominate the markets for cellulose derivatives (O Table 8), have somewhat different raw material requirements. Whereas both types of modification technologies prefer to start with chemical cellulose of high a-cellulose content, ethers give preference to molecular weight considerations while esters are sensitive to impurities. This is a consequence of the predom-... 

Cuprammonium rayon is made from scoured and bleached cotton linters or purified wood pulp with a high a cellulose content. The cellulose is washed and then pressed until it contains about 50 per cent of water. In this state, it is placed in a mechanical mixer together with cuprammonium solution and agitated until completely dissolved, whilst the temperature is maintained at 5° C (41 °F). The solution is then diluted to about 10 per cent concentration. After filtration and exposure to vacuum to remove air bubbles and dissolved gases, the solution is allowed to ripen in enclosed vessels until it is the desired viscosity. In modem practice copper carbonate is mixed intimately with the cellulose in a shredding machine and the resultant mass is then broken up and stirred for some hours with aqueous ammonia and caustic soda, when it passes into solution. 

The principal commercial sources of chemical cellulose are purified cotton linters of about 99 per cent a-cellulose content and purified wood pulp of about 96 per cent cellulose content. Cellulose occurs in these materials as a fairly highly crystalline, high-molecular-weight polymer. It is in a fibrous form, which is insoluble in common reagents. Cellulose wUl not react to any significant d ee with acetic acid and will react with acetic anhydride without a catalyst only at very high temperatures, at which the cellulose is degraded. 

Clark and Wolff carried out the first studies on the changes in the chemical composition of kenaf as a function of the growing season [22]. They also studied the chemical differences along the stem and between leaves and stem. This data showed that the pentosans, lignin, and a-cellulose content increases with age, while the protein and hot water extractives content decreases with age. Data taken from the top part of the plant shows similar trends however, the top part has less cellulose, pentosans, and lignin, but higher hot water extractives and protein than the bottom part of the plant (Table 7.4). 

In the early days, viscose composition was around 7.0% cellulose, 6.0% NaOH, and 34% CS2 (based on cellulose), with a viscosity of about 50 P. Wood pulp of about 88% a-cellulose content was the typical cellulose source for ordinary rayon, although purified cotton linters were used for higher-strength rayons. With commercialization of the zinc-based process. 

Cellulose from Af (gmol ) a-Cellulose content (%) /o(%) AGU Acetic anhydride ... 

The production of high-quality cellulose esters requires that special attention be paid to the selection of the starting materials. The cellulose bases generally consist of highly purified cotton linters with a cellulose content of over 99% and celluloses from wood pulp that contain between 90 and 97% cellulose. 

Reacted with nitric acid, acetic add, etc. a-cellulose yields the cellulosic plastics. It is also a filler for urea and melamine resins, and paper with high a-cellulose content is used in the manufacture of vulcanized fiber. 

In addition to several empirical methods involving the evaluation of the a-cellulose content or the copper number of cellulose, there are methods such as the determination of furfural, mentioned in Chapter VI. Interest was also paid to the determination of sulphur in viscose rayon. 

Eco-fiiendly extraction of MCCs from EFB at low concentration of (10% v/v) and formic acid (20% v/v) with ultrasound and heat assistance have been developed. Ultrasonie extraction carried out with at 40 kHz and room temperature, yields 49% MCC with a-cellulose content of 91.3%, and erystallinity of 68.7%. Autoelave extraction with a mixture of H202 and formie acid at 120°C and further bleaehing with H2O2 at 80°C, yields 64% of MCC with a-eellulose content of 93.7% and crystallinity of 70% (Nazir, 2013 Nazir etal., 2013). 

Oven-dried cotton contains about 90% cellulose whilst cotton linters contain 80-85%. In the preparation of chemical cellulose, cotton linters are processed in the following manner. Firstly, the linters are heated at 130-180°C under pressure with 2-5% aqueous sodium hydroxide for 2-6 hours this treatment solubilizes particles of seed-hull and other contaminants present in the linters. The liquor is drained off. The residual linters are washed with water, bleached with gaseous chlorine or calcium hypochlorite, re-washed and dried at about 70°C. The final product has a cellulose content of about 99%. 

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