Acetyl content

Table 1. Relationship of Cellulose Acetate DS to Acetyl Content and Combined Acetic Acid...

Starting cellulose, prepared by deacetylation of commercial, medium viscosity cellulose acetate (40.4% acetyl content). 

The common commercial products are the primary (triacetate) and the secondary (acetone-soluble, ca 39.5% acetyl, 2.45 DS) acetates they are odorless, tasteless, and nontoxic. Their properties depend on the combined acetic acid content (acetyl, see Table 1 and Figure 4) and molecular weight. Solubihty characteristics of cellulose acetates with various acetyl contents are given in Table 4. 

Cellulose triacetate [9012-09-3] has the highest melting point (ca 300°C) of the triesters melting points generally decrease to a minimum of ca 230°C as the acetyl content decreases to 38—39% (secondary acetate). 

Moisture sensitivity and vapor-permeabiUty rate of cellulose acetate increase with decreasing acetyl (increasing hydroxyl) content. Thermoplastic characteristics are gready improved as the acetyl content is increased from ca 20% (DS(acetyl) = 1) to ca 39% (DS(acetyl) = 2.4) (9). 

The acetyl content of cellulose acetate may be calculated by difference from the hydroxyl content, which is usually determined by carbanilation of the ester hydroxy groups in pyridine solvent with phenyl isocyanate [103-71-9J, followed by measurement of uv absorption of the combined carbanilate. Methods for determining cellulose ester hydroxyl content by near-infrared spectroscopy (111) and acid content by nmr spectroscopy (112) and pyrolysis gas chromatography (113) have been reported. 

Cellulosic Membranes The first commercial UF membranes were made from cellulose acetate (CA), with an acetyl content of about 37 percent. They are prized for their low level of interaction with proteins and are still used in other applications where long life is not critical. 

Degree of substitution Acetyl content (%—COCH3) Acetic acid yield (%) Solubility Uses... 

Wood pulp and cotton linters were partially acetylated to different acetyl contents ranging from approximately 6%-13% (0.23-0.54 degree of substitution [D.S.]). The increase of the DS of partially actylated cotton linters from 0.26 to 0.56 causes the percent graft of partially acetylated cotton linters to decrease slightly from 0.93% to 0.6%. In the case of wood pulp, the effect is somewhat different—the percent graft increases with an increasing DS until about 0.48, then the percent graft decreases. 

Acetylated polysaccharides form part of the structure of wood, the acetyl radical constituting some 2-5Vo by weight of the dry wood. Hydrolysis to free acetic acid occurs in the presence of moisture at a rate varying from one species to another a wood of lower acetyl content can liberate acetic acid much faster under given conditions than another wood of higher content Small quantities of formic, propionic and butyric acids are also formed but their effects can be neglected in comparison with those of acetic acid. There is a broad, but only a broad, correlation between the corrosivity of a wood and its acidity. The chemistry of acetyl linkage in wood and of its hydrolysis has been examined in some detail. ... 

Substrate Acetyl content (w/w) Activity (mU/mg) Release (% of total)... 

Uronic acid was estimated by the rw-hydroxyphenyl method [4], O-Acetyl contents by the method of Hestrin [5], carbohydrate by the phenol-sulfuric acid method [6] and protein by the Hartree method [7]. 

Acetylated m-cresol novolac copolymers were prepared by acetylation of m-cresol novolac with acetic anhydride in the presence of sodium hydroxide. The following acetylation procedure is typical. 3.2g of sodium hydroxide (50 mmol) was added to 4.8g of cresol novolac (40mmol) in 10 ml. of water. The reaction mixture was stirred for 10 mins, until all polymer went into solution. The required amount of acetic anhydride was then added, the reaction mixture was stirred for 10 more mins, and poured in 150 ml. of iced water. The polymer was filtered and purified by reprecipitation from a chloroform/benzene (5 2 v/v) solution by the addition of hexane. The acetylation content was determined by H and 13C NMR. 

Acetyl values from fully acetylated xylan preparations indicate a D. P. of about 100 or greater. The theoretical acetyl value for a fully acetylated xylan molecule of infinite size is 39.8%. As the molecule decreases in length, its acetyl content increases because of the increasing proportion of triacetyl-bearing end units. Assuming an accuracy of 0.1% for the acetyl determination, a noticeable deviation from theory would be apparent in acetylated xylan of less than D. P. 100. 

Rowell and Rowell (1989) acetylated Scandinavian spruce Picea abies) wood chips, then subsequently reduced these to fibres in a laboratory disc refiner, fibre production did not result in loss of acetyl content, but it was found that new water sorption sites were produced as a consequence of the refining process. In addition, these workers modified a variety of lignocellulosic materials and found that all of the materials studied exhibited the same reduction in EMC at comparable WPGs. 

Hardwoods are less thermally stable than softwoods and this is attributable to differences in the hemicellulosic content and composition. Pentosans (which are found in higher proportions in hardwood hemicelluloses) are more susceptible to thermal degradation than hexosans (Fengel and Wegener, 1989). Additionally, hardwoods, in general, have a higher proportion of hemicellulose, and the hemicelluloses of hardwoods also have a higher acetyl content compared to softwoods. 

Larsson Brelid, P. (2002). The influence of post-treatments on acetyl content for removal of chemicals after acetylation. Holz als Roh- and Werkstoff, 60(2), 92-95. 

With acetyl chloride, the carboxyl groups were acetjdated as well as the phenols (45). The resulting acetyl contents were equivalent to the NaOH neutralization. 

Carbohydrate/O-acetyl content of P. deltoides LCCs appears in Table III. All purified LCCs were 0-acetylated moieties containing varying amounts of glucose, mannose, xylose, and uronic acids. Relative to xylose, the highest levels of uronic acid and 0-acetyl content were encountered in LCCs 1 and 2. LCC 1 was the sole moiety to contain galactose. Xylose was the most abundant sugar found in both LCCs 3 and 4, both of which also contained nearly equimolar amounts of glucose and mannose. 

Figure 10 shows the IR spectrum of a normal cellulose acetate membrane. Figure 11 shows the spectrum of the hydrolyzed membrane. The decrease of absorption around 1,720 cm, and the increase of absorption around 3,200 to 3,500 cm are shown. The first peak correspond to the C = 0 double bond, and the second to the 0 - H single bond. These spectra show the decrease of the acetyl content in the membrane. 

Analysis of Chemical and Structural Change. Membranes of separation between 90% to 30 % were examined in their chemical and structural change. All samples of membranes were dissolved into acetone completely and any trace of undlssolved matter could not seen. This means acetyl content of any deteriorated membranes is still over 32.6%. 

Membrane deterioration may be merely caused by decrease of acetyl content(C ) in the active surface layer as a result of hydrolysis or oxidation, not by structure change. Analysis was carried out based on solution-diffusion model proposed by Lonsdale etal( ), using their measured values of solute diffusivity and partition coefficient in homogeneous membrnaes of various degree of acetyl content and also using those values of asymmetric membranes heat treated at various temperatures measured by Glueckauf(x) ... 

Model of Deterioration Mechanisum, As acetyl content decreases due to hydrolysis or oxidation of ester bonding, solute permeability increases. Then concentration of solute( in this case sodium hypochlorite) in the membrane increases and the hydrolysis or oxidation rate increases and so on. It will be more reasonable to assume that hydrolysis or oxidation rate of cellulose acetate in the active surface layer may be accelerated by the action of the nascent oxygen generated from sodium hypochlorite. 

Then the decrease rate of acetyl content may be expressed as the second order reaction of the solute concentration in the membrane. 

Substituting equation (5) into equation (U) and integrating the equation (1 ), we can obtain equation (T)> where fi(C ) and fa( Cj) are function of acetyl content and is a function of temper-... 

Symbol in equation (lO) means for homogeneous membrane of acetyl content C, and (Ca) without for asymmetric membrane. Rj(Ca) for IJaOCl in membrane of any degree of acetyl content are obtained and shown on Table 5> assuming that relation of solute permeabilities in homogeneous membrane for IJaCl and NaOCl may be expressed as follows... 

Procedure of Analysis. Rate constant can be calculated as a slope of the line plotted right hand side of equation ( ) against time elasped. At first acetyl content is estimated from the ratio of sodium chloride permeability of the deteriorated membrane and the initial by Fig.12. Using the estimated acetyl content, and f2(CA) can be obtained from Fig. 12. Using these values and f ... 

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